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Exergy for Sustainability

2008;():1-12. doi:10.1115/ES2008-54033.

This study deals with types of micro cogeneration (or micro combined heat and power, MCHP) systems and reviews energetic and exergetic analysis of MCHP systems, which are also called building cogeneration systems. These are classified as micro and macro cogeneration systems and figured within subgroups. Previously conducted studies on exergy and energy analyses of internal combustion engines (micro turbines), external combustion engines (Ericsson engines), fuel cells (solid oxide fuel cells) and thermophotovoltaic systems are treated in this paper. The main objectives of this study are to classify MCHP systems used in building cogeneration systems, to introduce types of MCHP systems and to better define micro cogeneration systems in the light of previously conducted studies. In this regard, energetic and exergetic efficiencies of various MCHP systems are graphically obtained. Under grouping presented MCHP systems, internal combustion engines based MCHP systems are defined to be the best choice with energetic and exergetic efficiency values of 86.0% and 40.31%, respectively. Micro gas turbines and Ericson engine based micro cogeneration systems are also obtained as valuable systems with the energetic values of 75.99% and 65.97% and exergetic values of 35.8% and 38.5%, respectively. However, in this building cogeneration group, energetic and exergetic efficiencies of the thermophotovoltaic systems have 65.0% and 15.0%, respectively. It may be concluded that system choice depends on the type of the system, energy flow of the system, system parts and developments, while building, system capacity, comfort and maintenance are the other factors to be considered.

Commentary by Dr. Valentin Fuster
2008;():13-17. doi:10.1115/ES2008-54063.

Piezoelectric materials can be used to convert oscillatory mechanical energy into electrical energy. This technology, together with innovative mechanical coupling designs, can form the basis for an energy harvesting solution for military and commercial systems. The US Army-CERDEC at Ft. Belvoir, VA and Continuum Photonics, Inc. in Billerica, MA completed a three year Science & Technology Objective (STO) research effort that focused on harvesting energy from physical exertion. The effort was aimed at investigating the concept of Piezoelectric Energy Harvesting for supplying supplemental power for dismounted soldiers. This STO effort resulted in the development of four proof-of-concept Heel Strike Units where each unit is essentially a small electric generator that utilizes piezoelectric elements to convert mechanical motion into electrical power in the form factor of the heel of a soldier’s combat boot. The Power Technology Branch has tested and evaluated the Heel Strike units. The results of the testing and evaluation and the performance of this small electric generator are presented. The generator’s piezoelectric conversion of mechanical motion into electrical power, its efficiency, the processes it goes through to produce useable power and commercial applications of the Heel Strike electric generator are discussed.

Commentary by Dr. Valentin Fuster
2008;():19-27. doi:10.1115/ES2008-54089.

Thermo-volumes allow the design engineer to expediently understand the thermal resistance of a given cooling solution (an indicator of performance) along with its flow resistance (an indicator of the pumping power, or energy consumption, which will be required by the fluid handler). In the present work, we expand upon thermo-volumes by including the lifetime exergy cost (in units of Joules of availability destroyed) as a means to enable the consideration of resource consumption (and thus the environmental sustainability) of the cooling solution. To achieve these exergo-thermo-volumes, we reinterpret previous definitions of thermo-volumes in terms of the entropy generated during heat transfer and fluid flow. The Guoy-Stodola theorem is used to convert this entropy generation into an ‘operational’ exergy loss. Next, based on the material choice and assembly processes used in creating the product, an embedded exergy consumption that accounts for the amount of exergy destroyed during extraction, transportation and disposal of the material is attached to the operational exergy loss. Thus, the total ‘cradle-to-cradle’ exergy loss of the solution is devised. In this framework, the optimal solution will be that which destroys the minimal amount of exergy. Correspondingly, instead of relying upon the COP (which is focused on operational consumption), we propose evaluation of cooling solutions in terms of the heat removal capacity per unit lifetime exergy consumption. The paper concludes by illustrating applicability of the method to the design of an enterprise server. It should be noted that although the paper is focused on electronics cooling solutions, the methodology is designed to be sufficiently general for use in any thermal management application.

Commentary by Dr. Valentin Fuster
2008;():29-33. doi:10.1115/ES2008-54104.

The Integrated Energy Strategy (IES) is a systemic approach to pursue several goals by applying technologies that have not been integrated before. The concept was to maximize the use of proven technologies that reduce the risk while focusing on the key enabling developments that leverage the benefits of a systems approach. Each of the component operations illustrated in the paper will be part of the US energy infrastructure in the future. Additional economies of scale and advantages of earlier availability result from the APS-NETL approach. The future of America’s energy infrastructure must support utilities becoming leaders in transitions rather than just forced customers of risky solutions.

Commentary by Dr. Valentin Fuster
2008;():35-42. doi:10.1115/ES2008-54181.

As the use of information technology becomes more ubiquitous, the need for data processing and storage capabilities increases. This results in the construction and operation of large data centers—facilities that house thousands of servers and serve as the backbone for all types of computational processes. Unfortunately, as processing power and storage capacity increases, so does the corresponding power and cooling requirements of the data centers. Several studies have examined the efficiency of data centers by focusing on server and cooling power inputs, but this fails to capture the data center’s entire impact. To accomplish this, the use of a lifetime exergy (available energy) analysis is proposed. This study first details the development of a lifetime exergy consumption model designed specifically for data center analysis. To create a database of computer components, a disassembly analysis was performed, and the results are detailed. By combining the disassembly analysis of a server with the aggregation of energy and material data, a more rigorous and useful assessment of the server’s overall impact is demonstrated. The operation of the lifetime exergy consumption model is demonstrated by case studies examining the effects of variance in transportation and cooling strategies. The importance of transportation modes and material mass, which are greatly affected by supply chain parameters, is shown. The impact of static and dynamic cooling within data centers is also demonstrated.

Commentary by Dr. Valentin Fuster
2008;():43-50. doi:10.1115/ES2008-54241.

This paper compares the Eco-Footprint of three (3) sustainable on-site CHP system alternatives vs. a representative 30% thermally efficient conventionally designed remote electric utility/merchant power generation station (EPGS) serving a 3.5 MW gas turbine installation proposed for a central California university campus. It has been demonstrated (ASHRAE Transactions # DA-07-009) that sustainable on-site cooling-heating-power (CHP) systems for large multi-building projects employing a simplified design approach from that of a conventionally designed mini-utility-type CHP systems employing large volume/footprint, costly, high thermal mass heat-recovery steam-generators (HRSG’s), and 24/7 stationary engineers, can result in lower annual owning and operating costs. The above peer-reviewed 2007 paper illustrated the use of prefabricated, skid-mounted hybrid steam generators with internal headers, fully integrated with a low-pressure drop heat extraction coil (in lieu of a HRSG) located in the combustion gas turbine (CGT) exhaust. Subject CGT extraction coil utilized environmentally benign heat transfer fluid to redistribute extracted CGT exhaust waste to serve campus multi-building annual space cooling, heating, and domestic hot water loads with system thermal balance facilitated via maintenance of a high year-round log-mean-temperature-differential at the CGT extraction coil, also resulting in a lower CGT back-pressure, and significant life-cycle cost savings. This paper also takes an alternative look at the above referenced CHP plant designs for greater operating economies along with a third CHP alternative employing a direct CGT exhaust gas fired 2-stage absorption chiller, and then compare the Eco Footprint and life cycle cost for each of the three CHP options with the above referenced EPGS supplying comparable annual electric power requirements. Finally, using the Eco Footprint of the EPGS as a baseline, the most promising CHP alternative of the above three will also be explored as a potential “cap and trade” candidate to further reduce its first cost and therefore enhance its sustainability from both an energy with greenhouse gas emissions standpoint.

Commentary by Dr. Valentin Fuster
2008;():51-56. doi:10.1115/ES2008-54346.

A natural gas fired combined cycle power plant with indirectly-fired heating for additional work output is investigated in the current work. The mass flow rate of coal for the indirect firing mode in circulating fluidized bed combustor is estimated based on fixed natural gas input to the topping combustor. The effects of pressure ratio, gas turbine inlet temperature, inlet temperature to the topping combustor on the exergetic performance of the combined cycle configuration are analysed. The use of coal in indirect-firing mode reduces with increase in turbine inlet temperature due to increase in the use of natural gas. The exergetic efficiency increases with pressure ratio up to the optimum pressure and it also increase with gas turbine inlet temperature. The exergy destruction is highest for the circulating fluidized bed combustor (CFBC) followed by the topping combustor. The analyses show that the indirectly fired mode of the combined cycle offers better performance but with higher exergy destruction and the opportunity for additional net work output by using solid fuels (coal in this case) in existing natural gas based power plant is realized.

Commentary by Dr. Valentin Fuster

Emerging Energy Policy Issues

2008;():57-67. doi:10.1115/ES2008-54120.

This paper presents energy end-use model of the U.S. Chemical Industry. The model allocates combustible fuel and renewable energy inputs among generic end-uses including intermediate conversions through onsite power and steam generation. Results of this model provide the basis to scale energy process-step models. Two federal databases used to construct energy end-use models are Manufacturing Energy Consumption Survey of the U.S. Energy Information Administration, and the Energy Information Administration’s “EIA-860B: Annual Electric Generator Report”. These databases provide information on energy consumption for each end-use, electricity generation, and recovered waste heat at the prime mover level of detail for each industry on a national scale. Results of the model show that the majority of the fuel input is used directly for the end-uses. Although the rest of the fuel is used to generate steam and power, most of this energy contributes to the end-uses as steam. Therefore, the purpose of fuel consumption at non-utility plants is to run their end-uses. During the course of this study, the most recent U.S. federal energy database available was for the year 1998. Currently, the most recent available U.S. federal energy database is given for the year 2002 based on the data collected from 15,500 establishments.

Topics: Heat , Waste heat
Commentary by Dr. Valentin Fuster
2008;():69-77. doi:10.1115/ES2008-54136.

The U.S. military conducts a full spectrum of contingency operations in which it provides humanitarian assistance, logistical support, peacekeeping stability functions, and reconstruction activities. It is becoming increasingly important to incorporate the concept of “sustainability” into these operations. Making contingency operations more sustainable will provide force multiplier aspects that increase operational efficiencies and reduce logistical burdens and costs. The military requires enormous energy resources to maintain its mission readiness, which contributes greatly to logistical burdens and costs. A wide range of sustainability considerations relate to the cross-functional use of energy in contingency operations, from the interface with a host nation’s infrastructure; temporary construction practices; fuel convoys; cascading material use; the handling and treatment of waste, water, and hazardous materials; logistics footprint, etc. This paper describes military issues that will affect deployed base mission requirements and future investment policies. It also describes the ongoing process to develop an Army vision for sustainable contingency operations. This vision will consider the integration of cross-functional energy uses and establish sustainable operational requirements and investment policies. These insights are also applicable to many international humanitarian situations.

Commentary by Dr. Valentin Fuster
2008;():79-88. doi:10.1115/ES2008-54147.

Worldwide demand for petroleum grows steadily every year due to increasing demand in the United States as well as countries with fast-growing economies such as China and India, where the populations are striving to attain higher standards of living and lifestyle. Concern over this increased demand for petroleum in light of worries about reliable supply and global climate change has resulted in the US government passing new Corporate Average Fuel Economy (CAFE) standards and a Renewable Fuels Standard (RFS). The existing mandate in the US to blend ethanol into gasoline (approximately 15 billion gallons annually by 2015) had effectively committed 860 billion gallons of irrigation water in 2005 (approximately 2.4% of U.S. 2005 freshwater consumption) for producing fuel for the light duty vehicle (LDV) transportation sector. It is estimated that by 2030, nearly 2,700 billion gallons of water per year will be consumed and 4,700–6,400 billion gallons withdrawn to produce fuels used in LDVs. Irrigation for biofuels dominates the projected water usage for fuels production, but other alternatives to petroleum gasoline (coal to liquids, oil shale, and electricity via plug-in hybrid vehicles) will also contribute appreciably to future water consumption and withdrawal, especially on a regional level.

Commentary by Dr. Valentin Fuster
2008;():89-96. doi:10.1115/ES2008-54148.

This paper presents the first-ever comprehensive assessment of the installed solar capacity in Texas. While the power generated from grid-tied solar photovoltaic installations can be tracked, an inventory including the capacity of these and other types of solar installations has never been performed. In contrast, installed wind capacity in Texas is closely tracked and widely publicized. Because of this discrepancy, decision-makers have lacked critical information to gauge the appropriateness of solar versus wind power for future installations, complicating their ability to prioritize which renewable power sources to incentivize. The work presented in this paper fills this knowledge gap by providing the methodology and results from a bottoms-up survey of major solar installers, large solar customers, and relevant government agencies (for example government agencies that are responsible for issuing rebates, or those that are major solar customers themselves). Over thirty entities were systematically contacted to obtain proprietary data that were then aggregated to determine the total installed solar capacity in Texas. Both power generation and heating applications are considered, including the following: photovoltaic (on- and off-grid), concentrating solar power (CSP), solar pond, and solar water heating (SWH). Other heating forms such as room and pool heating are not considered. An aggregate figure is presented and then benchmarked against installed wind capacity. Findings reveal that after 30 years and roughly $56 million in installation costs (at approximately $8300/kW), Texas possesses about 6.7 megawatts (MW) of installed solar electric capacity. Comparatively, in over 6 years and an estimated $6.9 billion in installation costs (at approximately $1600/kW), installed wind capacity in Texas approaches 5000 MW, which is more than any other state in the United States. Notably, at least another 8000 MW of new wind projects are in various stages of development, whereas few significant solar projects have been announced. This solar assessment exposes a stark difference in pace, cost and total size of installation for these two power sources, which is the likely experience for many other states. While these differences do not negate solar as a future power option, they raise further questions about the technical, social, and economic barriers each renewable technology faces, as well as the feasibility and design of incentives to further market penetration. Understanding this mixed history for these two power sources offers instructive guidance and useful insights to policymakers nationwide.

Topics: Solar energy , Wind
Commentary by Dr. Valentin Fuster
2008;():97-104. doi:10.1115/ES2008-54155.

Microgrids are systems of linked distributed energy (DE) generation sources that provide power for a relatively small number of users. In this work, we show how microgrids can be used to reduce emissions and deliver power with an annual amortized cost that is competitive with grid power. To perform the analysis, average hourly electrical load profiles for residential customers in Washington, DC were obtained from the utility company (Pepco). Hot water and heating fuel consumption is modeled computationally using prototype building characteristics. The energy consumption data is then used with a computer-based model to analyze grid-tied microgrids. The DE sources examined in this work are photovoltaic arrays and combined heat and power (CHP). The cost and CO2 emissions for the microgrid are compared to the case where power is drawn solely from the grid. We show that when DE capacity is optimally utilized, the microgrid is cost competitive, and the cost to reduce emissions is lowered.

Commentary by Dr. Valentin Fuster
2008;():105-116. doi:10.1115/ES2008-54169.

This paper is based on a research study which was carried out, to empirically assess the impact of power sector reforms, comprising privatization, competition and regulatory reforms in 29 African countries, for the period 1988–2005. The list of countries in the research sample is shown in Appendix 1. The main findings for the generation sector is that, in Africa, though energy sector regulation backed by sector law can bring about favorable outcomes, better results are likely to be achieved if the regulatory agency has been in existence for at least 3 years, and it co-exists with either competition ‘for’ the market or private sector participation. On private sector participation, the presence of Independent Power Producers, management contracts and private shareholding in generation assets, can enhance generation sector performance. The results on the transmission system seem to indicate that though the establishment of a regulatory agency can reduce transmission system loss level, this outcome is likely to be achieved if the regulatory agency has been existence for at least 3 years. On distribution system loss, it emerged that the sole existence of a regulatory agency may not be enough to influence a downward trend in distribution system loss level, unless the market, permits the co-existence of competition ‘for’ the market, with a regulatory agency.

Topics: Performance
Commentary by Dr. Valentin Fuster
2008;():117-126. doi:10.1115/ES2008-54247.

For the majority of commercial and industrial facilities in the United States, electrical power represents a significant portion of their total operating costs and a cost over which they have little or no control. The cost of electrical power has risen dramatically during the past three years, and is projected to continue to increase due to uncertainties in global fuel supply, production investments necessary to meet increasing demand, increased maintenance and repair costs of aging production and transmission infrastructure, the decommissioning and remediation of life-expired generating facilities, and the implementation of increasingly stringent pollution control measures. These trends and influences are seen, to a greater or lesser extent, across the entire nation, but their impact upon the northeast and mid-Atlantic states of Connecticut, Maryland, New Jersey and Delaware has been particularly significant. While solar photovoltaic systems can provide an excellent on-site power source for many commercial and industrial facilities, and would reduce the burden on the existing, over-stretched and aging national power transmission infrastructure, the high capital cost of solar photovoltaic systems represents a significant barrier to the wide-scale commercial adoption of this technology. In an attempt to overcome this barrier, individual states are implementing a variety of rebate and incentive programs designed to promote the installation and use of solar power systems. However a unifying Federal Renewable Portfolio Standard does not presently exist and the complex administration demand of state programs represents a further barrier to adoption for many companies. Further, while a Federal Investment Tax Credit is available, certain organizations for whom solar photovoltaic power would otherwise be an attractive cost-saving opportunity, notably municipalities and non-profits, are generally unable to take advantage of this benefit. In response to this unsatisfactory situation, Soltage, Inc. designs, installs, operates, maintains, and retains ownership of commercial-scale solar photovoltaic power stations at client sites, providing solar-generated power directly to the client. Our customers incur no capital, maintenance or operating costs, and have no administrative burden beyond purchasing solar-generated power at rates that are below their existing utility rate and which are stabilized and guaranteed into the future. For our clients, this is their most effective means of controlling and stabilizing energy expenses in the immediate and long terms. For our nation, this is the key to rapidly implementing the adoption and scale-up of solar photovoltaic power, with all of its inherent benefits.

Topics: Solar energy
Commentary by Dr. Valentin Fuster
2008;():127-136. doi:10.1115/ES2008-54296.

Coal consumption accounted for 36% of America’s CO2 emissions in 2005, yet because coal is a relatively inexpensive, widely available, and politically secure fuel, its use is projected to grow in the coming decades [1]. In order for coal to contribute to the U.S. energy mix without detriment to an environmentally acceptable future, implementation of carbon capture and sequestration (CCS) technology is critical. Techno-economic studies of CCS have demonstrated its large expense due to substantial energy requirements and capital costs. However, such analyses typically calculate cost indicators using static plant performance parameters that are assumed to be constant over plant lifetime. That is, CO2 capture systems are generally assumed to capture a constant percentage of CO2 from power plant flue gas and consume a particular amount of plant gross generation capacity. Such studies do not consider dynamic plant operation that may result from diurnal and seasonal variations in electricity supply and demand, nor do they capture the economic desire to minimize CO2 emissions costs while maximizing profits by selling electricity at high price times. In this study, CO2 capture systems are analyzed in a grid level dynamic framework by considering the possibility of turning capture systems off during peak system load to regain generation capacity lost to the energy requirement of CO2 capture. This practice eliminates the costs of building additional generation capacity to make up for CO2 capture energy requirements, and it allows plant operators to benefit from selling more electricity during high price time periods. Dynamic CO2 capture operation is particularly suited to post-combustion (PC) CO2 absorption, a leading capture technology that, unlike other capture methods, offers the ability for flexible or on/off operation. This paper presents a case study on the Electric Reliability Council of Texas (ERCOT) electric grid of baseline cost and CO2 emissions estimates associated with different strategies of using on/off CO2 capture operation to satisfy peak electricity demand. It compares base cases of no CO2 capture and “always on” capture with scenarios where capture is turned off during: 1) peak load hours every day of the year, 2) days of the year of system peak load, and 3) system peak load hours only on seasonal peak load days. The study considers the implications of installing PC CO2 capture on all coal-fired plants in the ERCOT grid to better understand if on/off operation is desirable and which operational strategy may be the most economically viable under a policy of constrained CO2 emissions.

Commentary by Dr. Valentin Fuster
2008;():137-145. doi:10.1115/ES2008-54306.

The increasing interest in recent years in energy efficiency and sustainability has generated a wealth of new innovations. Whether it is improved systems for generating energy from wind or water, new biofuels, or methods for increasing energy production from conventional fossil fuels, such innovations require expenditure of considerable research and development money. Failure to take measures to protect those innovations leave a company’s treasures open for others to use. While some feel that no protection should be granted on methods and devices that are designed to heal our Earth, the law was developed to encourage companies to invest in research. As it is, a large number of companies have already sought Intellectual Property protection for the advances they have conceived. Automotive companies have been protecting hybrid and hydrogen developments for many years. Other fields, such as solar power and wind generation, have seen a recent increase in patent applications on new developments. Navigating through these developments is becoming more and more complex as companies seek not only to protect devices that they have brought to market, but also improved concepts and advanced stages of research. Many companies blindly spend vast sums of money researching advances in a particular field, only to find out that another company has placed an Intellectual Property obstacle that inhibits bringing the advanced technology to market. Recent cases, including those from the Supreme Court have significant impact on how and whether new technology can be protected. This paper explains why patenting of green technology is beneficial to our society and some important things that companies involved in sustainability and energy advances need to know to protect themselves in this new green tinted world.

Commentary by Dr. Valentin Fuster
2008;():147-153. doi:10.1115/ES2008-54361.

The world’s energy supplies will continue to be pressured as population grows and the standard of living rises in the developing world. A move by the rest of the world towards energy consumption rates on par with the United States is most probably unsustainable. An examination of population trends, current energy utilization rates, and estimated reserves shows that a major worldwide transition to renewable resources is necessary in the next one hundred years. This paper examines one possible scenario of how energy usage and renewable power generation must evolve in this time period. As the global standard of living increases, energy consumption in developing nations will begin to approach those of the developed world. A combination of energy conservation and efficiency improvements in developed nations will be needed to push the worldwide energy consumption to 200 million BTU per person per year. Fossil fuel resources will be exhausted or become prohibitively expensive, necessitating the development of renewable energy resources. At this projected steady state population and energy consumption, the required contribution of each type of renewable resource can be calculated. Comparing these numbers to the current renewable capacities illustrate the enormous effort that must be made in the next century.

Commentary by Dr. Valentin Fuster

Life-Cycle Costing of Energy Systems

2008;():155-165. doi:10.1115/ES2008-54130.

The Chilean Energy Policy calls for 15 percent of new power generation capacity to come from renewable energy sources from 2006 to 2010, and then a 5% of electric energy generated from renewable energy sources with gradual increases in order to reach 10% by 2024. Neither the government nor the power generation sector plans mention solar energy to be part of the renewable energy initiative. Part of this apparent lack of interest in solar energy might be due to the absence of a valid solar energy database, adequate for energy system planning activities. Monthly means of solar radiation are used in order to estimate the solar fraction for a 100 MW plant for four given locations. Our analysis considers two cases: operation during sunlight hours, and continuous operation during 24 hours a day. A net energy analysis for concentrated solar power (CSP) plants in Chile is then performed, considering the energy costs of manufacturing, transport, installation, operation and decommissioning. The results indicate that the CSP plants are a net energy source in three of the four locations, when operating in sunlight-only mode. This is due to the lower radiation levels available at that location, which implies a high fossil fuel back-up fraction. In the continuous operation mode, the CSP plants become fossil fuel plants with solar assistance, and therefore all locations display negative net energy. Based on this result, the back-up fraction required for the plants to be net energy sources is estimated from the EROEI as function of the back-up fraction. It is estimated that the net energy analysis is a useful tool for determining under which conditions a CSP plant becomes a net energy source, and thus can be utilized in order to define geographical locations and operation conditions where they can be considered renewable energy sources.

Commentary by Dr. Valentin Fuster
2008;():167-171. doi:10.1115/ES2008-54203.

“Spark spread” refers to the difference between the cost of electricity and the cost of fuel on a per-MMBTU basis. This metric is often considered when recommending equipment retrofits that require fuel switching. A spark spread of at least $12 per MMBTU is considered the threshold for economic viability of Combined Heat and Power (CHP) systems. However, this study shows that an increase in the electric utility rate has an impact on the spark spread required to maintain the economic viability of a CHP project. This challenges the paradigm that a single value for spark spread can be used as a “rule of thumb” for determining the economic viability of CHP projects. As utility rates increase, so does the importance of understanding the relationship between spark spread and the economic viability of projects.

Commentary by Dr. Valentin Fuster
2008;():173-182. doi:10.1115/ES2008-54245.

On the basis of experimental results obtained during performance evaluation of five types of solar stills, kept in outdoor conditions on a single plate form, the cost of distilled water produced have been calculated by using a uniform cost analysis method. The experiments were performed at I.I.T. Delhi, India during year 2001–2002 under summer and winter, both the climatic conditions. It can be concluded that the cost of distilled water produced from a multiwick double slope solar still is lesser than other solar stills due to higher yield/hour. However for small scale purposes, multiwick single slope solar still is better option.

Topics: Solar stills
Commentary by Dr. Valentin Fuster
2008;():183-189. doi:10.1115/ES2008-54313.

The heating of water for domestic purposes presently accounts for 24 percent of Canadian residential energy consumption (Natural Resources Canada, 2006). This energy demand is primarily met by conventional sources such as electricity, natural gas and oil. Recent changes in fuel availability and price as well as environmental concerns lead consumers to give further consideration to the use of solar energy for heating water. The objective of this paper is to simulate the different domestic hot water (DHW) systems to examine their fuel consumption, greenhouse gases (GHG) emissions, life cycle costs and pay back periods. In this case study, seventeen different DHW systems were simulated using TRNSYS as simulation engine. These include solar-based models (with electric and natural gas backup tanks), electric and natural gas tank models (with and without gray water heat recovery), on-demand and combo-boiler systems. This paper will discuss three solar-based systems in detail, however their result comparison with other systems will be discussed. Three different solar-based systems are: I) Solar pre-heat with .56 efficiency natural gas back up tank; II) Solar pre-heat with .94 efficiency electric back up tank; III) Timers (off during peak times 7am till 10 pm) with solar pre-heat and electric (.94 efficiency) secondary. Results indicate that solar alternative having timers with solar pre-heat and electric secondary gives best results in terms of annual fuel consumption ($93) and GHG emissions (266 kg). However on demand modulating gas combo boiler (0.78 efficiency) with gray water heat recovery (0.6 efficiency) has best 30-year life cycle cost ($12332).

Commentary by Dr. Valentin Fuster
2008;():191-198. doi:10.1115/ES2008-54329.

A life cycle assessment (LCA) of nuclear-based hydrogen production using thermochemical water splitting is conducted. The copper-chlorine thermochemical cycle is considered, and the environmental impacts of the nuclear and thermochemical plants are assessed. Environmental impacts are investigated using CML-2001 impact categories. The nuclear plant and the construction of the hydrogen plant contribute significantly to the total environmental impacts. The environmental impacts of operating the hydrogen production plant contribute much less. Changes in the inventory of materials or chemicals needed in the thermochemical plant do not affect significantly the total impacts. Improvement analysis suggests the development of more sustainable processes, particularly in the nuclear plant and construction of the hydrogen production plant.

Commentary by Dr. Valentin Fuster

Emissions, Energy and Environment

2008;():199-204. doi:10.1115/ES2008-54105.

In recent years, greenhouse gas (GHG) emissions and their potential effects on the global climate change have been a worldwide concern. Based on International Energy Agency (IEA), power generation contributes half of the increase in global GHG emissions in 2030. In the Middle East, Power generation is expected to make the largest contribution to the growth in carbon-dioxide emissions. The share of the power sector in the region’s total CO2 emissions will increase from 34% in 2003 to 36% in 2030. Therefore, it is very important to reduce GHG emissions in this industry. The purpose of this paper is to examine greenhouse gas emissions reduction potentials in the Iranian electricity generation sector through fuel switching and adoption of advanced power generation systems and to compare these potentials with Canadian electricity generation sector. These two countries are selected because of raw data availability and their unique characteristics in electricity generation sector. To achieve this purpose two different scenarios have been introduced: Scenario #1: Switching existing power stations fuel to natural gas. Scenario #2: Replacing existing power plants by natural gas combined-cycle (NGCC) power stations (The efficiency of NGCC is considered to be 49%). The results shows that the GHG reduction potential for Iranian steam power plants, gas turbines and combined cycle power plants in first scenario are 9.9%, 5.6%, and 2.6%, respectively with the average of 7.6%. For the second scenario the overall reduction of 31.9%, is expected. The average reduction potential for Canadian power plants for scenario number 1 and 2 are 33% and 59%, respectively. As it can be seen, in Canada there are much higher potentials to reduce GHG emissions. The reason is that in Canada majority of power plants use coal as the primary fuel. In fact almost 73% of electricity in thermal power stations is generated by coal. Whereas in Iran almost all power plants (with some exceptions) are dual fuels and 77% of energy consumed in Iran’s thermal power plants come from natural gas. Also, 21% of total electricity generated in Iran is produced by combined-cycle power plants.

Commentary by Dr. Valentin Fuster
2008;():205-211. doi:10.1115/ES2008-54218.

Catalytic combustion is useful to avoid emission of carbon monoxide and nitrogen oxides into the environment. The widespread use of the catalytic converter was the response of the automotive industry to the legislation of the countries which sets limits on pollutant emissions. The catalytic combustion of CO + NO and air mixtures in a planar stagnation-point flow over a platinum foil is studied numerically in this paper. In order to optimize the operation of the platinum converter, chemical kinetic knowledge is necessary, therefore a kinetic model is proposed, based on elementary reaction steps, that allows to describe the experiments quantitatively. The heterogeneous reaction mechanism is modeled with the dissociative adsorption of the molecular oxygen and the nondissociative adsorption of CO, together with a surface reaction of the Langmiur-Hinshelwood type and the desorption reaction of the adsorbed products, CO(s) and NO(s). The resulting governing equations based on the boundary layer theory have been numerically integrated by using Runge-Kutta method and the response curve has been obtained as a function of the initial mixture concentration. The reduction of NO and oxidation of CO in absence and presence of O2 has been investigated, and the optimal oxygen feeding into the initial mixture concentration for the maximum reduction of CO and NO was found and corresponds to the reported experimental results.

Commentary by Dr. Valentin Fuster
2008;():213-220. doi:10.1115/ES2008-54225.

Energy efficiency and emission control has traditionally been a priority area in refining and petrochemical industries. In the last 15–20 years these issues has increasingly been focused in the upstream oil and gas industry. Emission taxes and commitment from the industry has led to significant improvements. Energy consumption and emission to air, especially CO2 and NOx has been reduced by typically between 10 to 30% by relatively simple and cost-effective methods. In parallel, change in design practise for new plants has contributed to similar reductions. This paper outlines the analysis and methods used and the results achieved.

Commentary by Dr. Valentin Fuster
2008;():221-228. doi:10.1115/ES2008-54355.

Biomass is currently used as an alternative energy source in some industries. Due to problems with disposal of wastes, using biomass as an energy source is economically and environmentally attractive. In this work seven wastes from textile and food industry were characterized and their gaseous emissions resulting from their combustion in a pilot unit were measured. The aim of this paper is to evaluate the usage of industrial wastes as an energy source taking into account their composition and gaseous emissions when submitted to combustion tests. Gaseous emissions were compared to limits imposed by Brazilian and international current legislations. Volatile organic compounds (VOC) were analyzed by GC-MS and their content values were expressed as total organic carbon (TOC). Four combustion tests were carried out in a cyclone combustor and all TOC emissions were below regulations limits. CO, CO2 , NOx , Cx Hy and SO2 were also measured. Chemical properties showed that the volatile matter values of all biomass were high what indicate that the solids burn rapidly and some biomass presented high levels of sulphur and consequently high levels of emission of SO2 when burned. The lower heating values ranged from 14.22 to 22.93 MJ.kg−1 . Moisture content and particulate matter (PM) were measured during the combustion tests and showed effective combustion conditions. Thermogravimetric analysis of the biomasses showed ignition temperatures and maximum burning rate which were compared to other papers data. The usage of these biomasses as an energy source is possible however gas treatment would be required specially if the solid presents high levels of sulphur and chlorine.

Commentary by Dr. Valentin Fuster

Alternatives to Carbon-Based Energy Technologies

2008;():229-232. doi:10.1115/ES2008-54007.

The element and mineral composition and the physical characteristics of fly ash from circulating fluidized bed boiler, are different to the other kinds of boilers. The aim of the study was to discuss the distinctive feature between the fly ash from CFB and the fly ash from pulverized coal fire boiler. The experiments show that the change of element composition from CFB and PC boiler has the some rule with the change of granularity. The carbon content of residua from CFB is higher than the content from PC boiler obviously. The SiO2 dioxide content decreases with the granularity of residua fining, while the content of Al2 O3 , CaO, MgO has the reverse rule in despite of CFB or PC boiler. The content of TFeO of residua increases in CFB while the content decreases in PC boiler with the granularity of residua fining. And the component form of TFeO in CFB is mainly Fe2 O3 while the component in PC boiler is mainly Fe3 O4 . The higher the content of carbon was, the lower the special resistance was.

Topics: Fly ash
Commentary by Dr. Valentin Fuster
2008;():233-244. doi:10.1115/ES2008-54177.

Rapid depletion of conventional sources of energy and the growing environmental concern of their use warrant urgent attention to look for suitable energy alternatives. In this regard the seeds of Jatropha curcas, constituting 40–50% bio-crude oil are considered as one of the most promising alternatives for the production of bio-diesel. It is estimated that about 1.5 tons de-oiled cake is produced from seeds obtained from one hectare of plantation, utilized for bio-diesel extraction process. Being non-edible due to its toxic contents, cost effective safe disposal of this by-product can only be possible if there is a meaningful utilization. India’s tobacco industry is the second largest in the world after China, having vast area under tobacco cultivation. The wastes from tobacco industry lead to significant environmental pollution that has severe impacts on both flora and fauna. A few studies on this aspect have revealed that Jatropha and tobacco bio-wastes have potential to be used as organic fertilizers. The present study aims at developing appropriate bio-processes and formulation that utilize Jatropha seed cake and waste of tobacco industry as organic fertilizer for improving the growth of Chrysanthemum, a flower variety valued for its beauty and fragrance and having wide applications in cosmetic and perfumery products. Pot experiments were carried out by adding specific proportions of Jatropha de-oiled cake and tobacco waste to normal garden soil. The growth and morphological parameters of Chrysanthemum plants grown in pots prepared by the treated soil were monitored for 4–5 months and the results were recorded. The results have been encouraging as the treatments lead to a significant enhancement in flower growth as well as yield. 11.5% increase in number of buds per plant was recorded for treated soil as compared to the control soil. The number of flowers per plant also recorded an increase of 16% to 24% due to the effect of formulation applied to the soil. Similar trends were observed for other parameters like flower size, flower head size, flower weight and ray floret number. Through experimentation new composted organic fertilizer formulations, tailored to specific commercial crop has been developed. The research findings would enable these bio-wastes to be used as a viable alternative to the energy intensive chemical fertilizers for floriculture, thus contributing to the mitigation of global climate change. This addition in the value chain would improve the financial viability of bio-diesel extraction process. This new synergistic organic fertilizer formulation when used as an alternative to nitrogenous chemical fertilizers would also provide an opportunity to earn carbon credits which is estimated to be € 67904 millions/year.

Topics: Fertilizers , Diesel
Commentary by Dr. Valentin Fuster
2008;():245-249. doi:10.1115/ES2008-54239.

Although this is not a new idea, it certainly seems to be a forgotten idea; use lunar materials to construct solar power stations at a geosynchronous orbit to beam energy via microwave to the earth’s surface at a safe 225 watts per square meter. In the 1970’s Gerard O’Neill, physics professor at Princeton and founder of Space Studies Institute, proposed this idea (1). Significant research on the establishment of lunar based mining stations, lunar launch mechanisms, low earth orbit manufacturing stations, and geosynchronous power stations was conducted. Without developing new physics principles and with less capital than was being invested in the fusion technology, a clean solar based energy generation and delivery system was possible for any point in the world. The obvious benefit would be the elimination of carbon-based fuel consumption and associated pollution, and the not-so-obvious benefit of the elimination of the 2nd law thermal pollution from any earth based energy conversion to electricity. Heat rejection from all current electricity generating facilities: coal, gas, nuclear, geothermal, even solar, reject at least two thirds of the energy converted as waste heat. By moving the heat rejection process to the extra-terrestrial environs, the useful energy available for humanity for a given temperature rise in the atmosphere, triples at least. Thus, the life style of all of humanity can practically be increased without harm to the environment. This paper will give an overview of that technology, its history from the mid 1970’s till now, and why it has not been considered in the modern context of the new “hydrogen” based energy system.

Commentary by Dr. Valentin Fuster

Sustainable Energy Figures of Merit

2008;():251-254. doi:10.1115/ES2008-54004.

This paper discusses the major obstacles in harvesting the energy of sea waves. These natural phenomena offer a huge source of pollution-free energy. The energy from this source might be capable of replacing all the energy presently supplied by the existing fossil burning plants. This means, that the harvest from this source of energy is capable of drastically reducing the amount of polluting gases which are presently being emitted into the atmosphere. In addition to the above, this source does not pose such colossal potential dangers to humans, as the use of nuclear energy. Nor does it cause the often so unpleasant noise pollution generated by wind farms. However, to the best of the author’s knowledge, this source of energy still remains unexploited. This paper discusses five of the major obstacles which, till now, have prevented this objective from becoming a reality. These are: a. The random nature of the variations in the occurrence and the intensity of the sea waves, makes the supply of energy from that source very irregular and unreliable. b. The corrosive activity of the sea water and of secretions from certain forms of sea life, creates a need of frequent replacements of the wetted parts, respectively the need to make them of exotic and often very expensive materials. c. The blocking, clogging and jamming of the equipment by seaweeds and other matter which is being carried by the waves, may cause frequent interruptions in the operations of the power plant and extra expenses on cleaning the affected parts of the equipment. d. The destructive nature of the sea waves, like the abrasion of parts by particles of sand which are carried by the waves, or the impact of floating logs of fallen trees etc. may require frequent shutdowns of the plant and costly repairs. e. The economic aspects of such a power plant. The cost of constructing and of running such a plant has to be adequately low. To allow an affordable supply of power. This paper present the outline of a design, which is capable of reducing the severity of all the obstacles listed above, to tolerable limits.

Topics: Waves , Seas
Commentary by Dr. Valentin Fuster
2008;():255-259. doi:10.1115/ES2008-54062.

We have investigated the power generation characteristics of thermoelectric devices made from high Figure of Merit p-type Bi2 Te3 /Sb2 Te3 and n-type Bi2 Te3 /Bi2 Te2.7 Se0.3 superlattice materials. The Figure of Merit, ZT (where Z is a measure of the material’s thermoelectric properties and T is the absolute temperature) of the p-type and n-type superlattices were each measured at 300K and found to be 2.4 and 1.2 respectively [1]. Sixteen p-n couples were developed using these superlattice materials and they were configured into a 4×4 thermoelectric module. The electrical measurements (Current, Voltage, and Power) of the 4×4 superlattice thermoelectric modules under various resistive loads and temperature differentials in a standard pressure environment are presented and from these, we have determined the peak power and internal resistance of the module. We also discuss other opportunities to further investigate this device as well as its suitability for power applications.

Commentary by Dr. Valentin Fuster
2008;():261-266. doi:10.1115/ES2008-54111.

So far the energy saving potentials in refrigeration and air conditioning systems are the focuses of researchers all over the world. The all cold air distribution systems are being widely used due to the advantages of saving building space, less energy consumption in some given conditions and less initial cost, mostly in the residential or office buildings. The stratified air conditioning technology is adopted mainly for large space buildings to reduce the system energy consumption, normally at conventional supply air temperature. In this paper, with an example of large space building, the energy consumptions of four all outdoor air systems are calculated and compared from the view of the total annual primary energy consumption. The detailed analysis shows that comparing the conventional all outdoor air system for the whole indoor space or that with stratified air conditioning technology, the all cold outdoor air system with stratified air conditioning has the energy saving potentials. It will be promoted in the future application of HVAC systems in large space buildings.

Commentary by Dr. Valentin Fuster
2008;():267-274. doi:10.1115/ES2008-54112.

At present all cold air distribution systems are being used widely due to their advantages of smaller ductwork, shorter floor-to-floor height and less energy consumption etc. They are mostly used in VAV (Variable Air Volume) systems or with the radiant panel systems in the office and residential buildings at the supply air dew point temperature of 6∼10°C, rarely used in large space buildings. The technology of stratified air conditioning is one of the energy saving technologies to large space buildings, which has been popularly used in the conventional air supply systems with the supply air dew point temperature of 11∼16°C. In this paper, the cold air distribution system and the stratified air conditioning technology in a large space building are combined to study. With the method of CFD, the indoor thermal environment of a large space workshop is simulated. The velocity and the temperature as well as the relative humidity fields under different air flow modes are presented, analyzed and compared. With the help of numerical simulation results, the optimal airflow mode is proposed, which show that the all cold air distribution with the stratified air conditioning is a good option for large space buildings. All these above will be good references to the application of cold air distribution system and the selection of the airflow mode in large space buildings.

Commentary by Dr. Valentin Fuster

Energy Systems Technologies, Analysis and Design

2008;():275-282. doi:10.1115/ES2008-54040.

Coalbed methane (CBM) is a kind of important energy resources in the world. Liquefaction is a good option for recovery of CBM. Generally, CBM consists of a lot of nitrogen besides methane, which is usually required to be separated by adsorption before liquefaction, or by distillation after liquefaction. For the CBM adsorption-liquefaction processes, two novel processes are proposed, which integrate the two parts of adsorption and liquefaction together by utilizing the residue pressure of the waste nitrogen: the released nitrogen expanded directly to precool CBM, or further compressed and then expanded to liquefy CBM. Taking the unit product liquefaction power consumption as the major index and nitrogen content of CBM feed gas together with residue pressure of waste nitrogen as variables, the system performance of these two integrated processes is studied and compared with that of the nitrogen expansion liquefaction process without integration. By simulation and calculation with HYSYS, it is confirmed that system power consumption can be reduced by both methods to utilize the residue pressure, and for CBM with high nitrogen content, the energy conservation effect is considerable, furthermore, it is better to use waste nitrogen to precool CBM than to liquefy it.

Commentary by Dr. Valentin Fuster
2008;():283-290. doi:10.1115/ES2008-54041.

The introduction of sustainable energy systems is strongly associated to what choices real estate owners make among different energy supply system options. This paper reviews briefly the evaluation criteria and methods of energy supply system, from technical, economical, environmental and social aspects. A new methodology for the integrated evaluation of the energy supply system’s feasibility is presented, which adopts the grey relational analysis method. As an example, three energy supply systems to provide cooling, heating and power to users are synthetically evaluated and compared in multi-criteria. The weights, used in multi-criteria evaluation, is discussed and suggested. The results prove that the grey relational analysis is an effective tool for decision making compared to single criteria evaluation.

Commentary by Dr. Valentin Fuster
2008;():291-302. doi:10.1115/ES2008-54047.

Efficient energy use is critical for the success of any industrial facility since reduced energy consumption through energy conservation/saving programs can benefit not only consumers and utilities, but society in general as well. In particular, reduced energy consumption generally leads to reduced emissions of greenhouse gases and other air pollutants into the environment. It also helps reduce the operational costs in the facility. There is a strong need to take some energy saving measures in every plant/ facility. Although these may be quite diverse, some of these measures include thermal insulation, use of more efficient equipment, heat recovery systems, high efficiency lighting, changing the fuel, reducing the cost of compressed air, and enhancing productivity. In this study, some certain energy conservation measures are considered for assessing a packaging film manufacturing facility in Gaziantep, Turkey. Taking advantage of dry and hot climates of the city, cooling compressor inlet air by evaporative cooling technique is also assessed. Our investigation shows that there is a huge room for energy conservation measures. The total savings potential are expected to be 869,350 YTL (about $725,000) representing about 16% of the total energy consumption. The payback periods for the identified measures are justified. We believe that the results are typical rather than exceptional for the industrial sector in Turkey.

Commentary by Dr. Valentin Fuster
2008;():303-319. doi:10.1115/ES2008-54103.

The global problems of energy supply and demand, climatic change due to artificial global warming, and providing economical and clean human comfortable condition are a complex issue. These problems have become globally political, economical and technological in the center stage of global arena. Utilization of alternative energy resources which are clean and green, hand in hand with the development of alternative clean and green technologies can indeed reduce the global and environmental problems. This paper invasions the idea of harnessing the power of clean energy resources and of developing clean technology for the production of clean environmental conditions. Synergization of clean energy resources, clean technologies and production of clean environment is implemented through the thermally activated desiccant cooling system. The experimental facility is constructed which consists of thermal energy system, desiccant cooling system and the artificially controlled environmental conditions for experimental evaluation purposes. Preliminary experimental investigation is being undertaken to evaluate the performance of the thermal energy system and of the desiccant cooling system. Based on the results, thermal energy system is functioning to its expectations. However, the desiccant cooling system still needs improvement to optimize its cooling capacity. With this study, practical combination of clean energy utilization and of clean technology development for the production of clean environment is possible through proper design and implementation.

Commentary by Dr. Valentin Fuster
2008;():321-330. doi:10.1115/ES2008-54106.

Interests in coal-to-liquid (CTL) and other fuels have grown greatly in the last couple of years with steadily increasing oil prices. National energy security concerns related to liquid transportation fuels also have revived interests in alternative liquid fuel sources. Coal-to-fuel technologies feature high efficiency energy conversion and environmental advantages. While a number of factors are driving coal-to-fuel projects forward, there are several barriers to wide commercialization, such as financial, construction, operation, and technical risks. The purpose of this study is to investigate the performance features of CTL and other coal-to-fuel systems based on different gasification technologies. The target products are Fischer-Tropsch (F-T) crude and synthesis natural gas (SNG). Two types of entrained-flow gasifier based coal-to-fuel systems are simulated and their performance features are discussed. One is single-stage water quench (WQ) cooling entrained-flow gasifier, and another is two-stage syngas cooling (SC) entrained-flow gasifier. The conservation of energy (first law of thermodynamics) and the quality of energy (second law of thermodynamics) for the systems are both investigated. The results of exergy analysis provide insights about the potential targets for technology improvement. The features of different gasifier-based coal-to-fuel systems are discussed. The results provide information about the research and development priorities in future.

Topics: Fuels , Coal , Exergy analysis
Commentary by Dr. Valentin Fuster
2008;():331-338. doi:10.1115/ES2008-54121.

This paper gives a representative energy process-step model of hydrogen production in the U.S. Chemical Industry based on federal data. There have been prior efforts to create energy process-step models for other industries. However, among all manufacturing industries, creating energy flow models for the U.S. Chemical Industry is the most challenging one due to the complexity of this industry. This paper gives concise comparison of earlier studies and provides thorough description of the methodology to develop energy process-step model for hydrogen production in the U.S. Chemical Industry. Results of the energy process-step model of hydrogen production in the U.S. Chemical Industry show that steam allocations among the end-uses are: 68% to process cooling (steam injection to product combustion gases), 25% to process heating, and 7% to other process use (CO2 converter). The model also shows that the major energy consuming step in hydrogen production is the reformer, which consumes approximately 16 PJ fuel. During the course of this study, the most recent U.S. federal energy database available was for the year 1998. Currently, the most recent available U.S. federal energy database is given for the year 2002 based on the data collected from 15,500 establishments.

Commentary by Dr. Valentin Fuster
2008;():339-349. doi:10.1115/ES2008-54191.

Small-scale motion energy harvesting has garnered significant interest in recent years, especially given advances in piezoelectric materials, but with limited commercial application. Most harvesting methods to date, including those employing magnetic induction, have focused on coupled resonance. Such harvesters are tuned to resonate with their excitation source and have shown promise in capturing moderately high-frequency (>10Hz), low-displacement motion that is steady. However, coupled harvesters lose efficiency significantly when a source deviates slightly in frequency. They also require large masses and/or buoyant volumes to efficiently capture low frequency (<10Hz) motion. We have been developing a novel technology that combines electromagnetic induction with a proprietary catch-and-release mechanism that absorbs an input motion and then releases it at a much higher frequency to improve conversion efficiency. The energy harvester is simple, compact, and insensitive to excitation frequency. Initial prototypes have demonstrated power densities and specific powers many multiples greater than the best-performing, commercial vibration harvester. We have also developed a validated computer model of the system that indicates that performance could be improved 2–4 times over initial prototypes.

Commentary by Dr. Valentin Fuster
2008;():351-360. doi:10.1115/ES2008-54196.

As concerns over the rapid depletion of our natural resources, air quality, and the environment continue to grow, so do the technologies being developed to address those issues. Thus it’s essential that government agencies and educational institutions alike become leaders in the promotion of “green” technologies and “green” design as they are becoming more than ever before concrete solutions to our environmental concerns. This report describes the project undertaken by a multi-disciplinary group of Engineering and Technology students at California State University, Los Angeles. This project looked into a sustainable approach to reduce the overall campus energy use and its environmental impact. Over the course of the project, a detailed investigation of the campus energy demand was conducted and solutions to improve the aging campus energy infrastructure were drafted. Some of thee short term solutions included Energy Conservation Measures (ECM) that focused on the operation and management of our energy with respect to lighting, air conditioning, and building envelope. Some mid-range solutions included the increase in capacity of the TES and an overall design of a hydrogen generation station was developed for future consideration.

Commentary by Dr. Valentin Fuster
2008;():361-370. doi:10.1115/ES2008-54220.

Thermodynamic and thermoeconometric aspects of a 12.5kW residential solar-thermal power generating system are presented in this paper. The design of a meso-scale power system greatly differs from centralized power generation and as a result, this system is limited to maximum pressure of 4 MPa and maximum temperature below 500°C. The cycles under consideration are the Rankine cycle, the Organic Rankine cycle (ORC) with toluene, R123, and ethylbenzene as working fluids, and the Kalina cycle. Cycle comparisons are based off of a steady-state first law analysis of the systems under consideration. These systems are characterized to determine the system with the highest efficiency and minimum collection area. The solution that best fits a solar-thermal power system limited to 2 MPa is an ethylbenzene ORC. If the pressure is limited to 4 MPa, then the toluene ORC shows good potential.

Commentary by Dr. Valentin Fuster
2008;():371-375. doi:10.1115/ES2008-54221.

It’s important to deal with building energy-saving in one city level and plan the energy system from one building to one city level. It’s suggested strongly to conduct urban building energy planning in urban planning system in China. There are two main characteristics of urban building energy system. That is, firstly, the terminal building energy demand is dynamic timely, such as the heating, cooling, gas and electricity load of 8760 hours a year with peak and valley load. Secondly, the energy demand, energy sources supply, energy equipments and networks of heating, cooling, gas and electricity are distributed in urban space. It’s meaningful to conduct an innovative urban energy planning with space distribution and time dynamic simulation. In this paper, the energy planning method with space and time characteristics is presented and analyzed briefly. In the meanwhile, to meet the same energy demand in buildings, such as heating, air conditioning, gas and electricity, different energy equipments such as boiler, CHP, CCHP and heat pump based on different energy sources such as coal, gas and electricity can be planned and should be alternative among those energy sources and equipments. Thus, a well alternative urban energy system with high energy efficiency and low environmental emission should be simulated. Therefore, an urban building energy planning (UBEP) simulation tool developed by our research group is introduced. And finally, a case of energy planning in Beijing City in 2010 for heating and air conditioning system is simulated dynamically and analyzed.

Topics: Simulation , Cities
Commentary by Dr. Valentin Fuster
2008;():377-385. doi:10.1115/ES2008-54272.

This paper describes the development of a program in Innovative and Sustainable Design that focuses on transportation and building systems. Transportation and buildings consume approximately 75% of the energy used in the US and significantly contribute to the technical issues related to sustainable energy sources and the environment. The program will be organized into four areas that revolve around the nucleus of innovation, sustainability, and design processes: namely, research, educational, outreach, and collaborative arms. Research teams will design highly efficient buildings, vehicles, and mobility systems for the future. Students will learn design approaches to address the needs for energy-neutral building technologies and an efficient, environmentally friendly transportation system fueled by sustainable energy sources. Outreach efforts will recruit secondary school and community college students into engineering programs and expand visibility for the program. Collaborative projects will provide students and faculty with opportunities to work with engineers, designers, and scientists from other universities, government institutions, and industry on timely and technically important projects.

Topics: Green design
Commentary by Dr. Valentin Fuster
2008;():387-392. doi:10.1115/ES2008-54312.

Heating and cooling energy consumption measurements are critical for operations, controls, and fault detection and diagnosis of heating, ventilation and air conditioning (HVAC) systems. Generally water flow has to be measured in order to determine energy consumption in either chilled water systems or hot water systems. Economical and accurate water flow measurements are essential to develop energy meters. Since pump performance relates actual pump water flow to pump head and power, theoretically water flow through a pump can be determined by other pump performance characteristics, such as pump head and motor power. This paper presents the theoretical model of pump flow stations based on pump head and motor power, and the experiments and results of a cooling energy meter using a pump flow station developed on the chilled water system at a facility.

Commentary by Dr. Valentin Fuster

Performance Results of Renewable Energy Systems

2008;():393-398. doi:10.1115/ES2008-54030.

The work presented in this paper essentially consists of modeling and analysis of energy and exergy efficiency of a community solar cooker, installed at Holistic Health and Food Centre, I.I.T. Delhi India in March 1998. The cooker is meant for community cooking, which consists of a linear parabolic concentrator with concentration ratio of 20. The experiments, on this cooker, were performed in summer and winter, both the climatic conditions. The measurements were done by using microprocessor based on line data acquisition system using class I solar pyranometer and Pt. 100 temperature sensors. Based on the experimental data obtained by testing and performance evaluation of this concentrating type of solar cooker, the energy and exergy efficiencies are calculated. From an analysis of the experimental values the average efficiency of this cooker is measured as 14% only. The different losses contributes to low efficiency are optical losses (16%), geometrical losses (30%) and thermal losses (35%) accounts for more than, 80% energy waste from the radiation coming to the reflector. The rest of the losses are due to edge losses etc. the maximum temperature of water was recorded 98°C during water heating tests.

Commentary by Dr. Valentin Fuster
2008;():399-404. doi:10.1115/ES2008-54262.

An assessment of the University of South Carolina’s (USC) biomass gasification plant, which produces steam and electricity, is made using the five “Guiding Principles” found in the April 2007 update of the Union of Concerned Scientists’ (UCS) Principles for Bioenergy Development document [1]. The UCS’s guiding principles are to... “help guide bioenergy development in a manner that maximizes opportunities and helps address the challenges associated with this renewable resource.” The USC biomass plant is the first commercial biomass gasification plant producing steam and electricity in the USA. It uses bark chips from the pulp wood industry as its fuel source. Gasification of the bark produces syngas which is then oxidized and used as the heat source to generate 60,000 lb/hour (maximum) of steam at 600 psig and 740 F. The steam first passes through a turbine-generator producing 1.5 MW (maximum) of electricity and then is circulated via the campus system at 115 psig and 325 F for heating and hot water use. The plant’s construction, operational conditions, and environmental and economic impacts are examined versus the five UCS guiding principles.

Commentary by Dr. Valentin Fuster
2008;():405-412. doi:10.1115/ES2008-54284.

Thermodynamic analysis of a combined cycle producing power and refrigeration (cooling) effect simultaneously using solar energy has been analyzed. The working substance of the cycle is a binary mixture of ammonia and water. The effect of variation of absorber pressure, boiler pressure, boiler temperature and superheater temperature on the turbine work, refrigeration (cooling) effect and net output has been investigated. For different conditions of the above variables, the first law efficiency, the second law efficiency and the exergy efficiency of the cycle have been investigated. Since the ammonia water mixture boils at varying temperatures, Lorenz cycle instead of Carnot cycle is considered as the ideal cycle for this analysis. It is observed that the first law and the second law efficiencies are maximum under the same working conditions, but the exergy efficiency is maximum at some other working conditions. The maximum values of the first law, the second law and the exergy efficiencies are found to be 21.72%, 27.30% and 62.53% respectively.

Commentary by Dr. Valentin Fuster
2008;():413-418. doi:10.1115/ES2008-54335.

The southwestern US is an ideal location for solar power plants due to its abundant solar resource, while there is a difficulty in implementing wet cooling systems due to the shortage of water in this region. Dry cooling could be an excellent solution for this, if it could achieve a high efficiency and low cost as wet cooling. Some dry cooling systems are currently in operation, and investigations of their performance have been reported in the literature. This paper looks into the limits to the power production implicit in dry cooling, assuming that improvements might be made to the system components. Use of higher performance heat transfer surfaces is one such possible improvement. We have developed a model of a fairly typical, but simplified, solar trough plant, and simulated thermodynamic performance of this with the software Gatecycle. We have examined the power generation and cycle efficiency of the plant for the Las Vegas vicinity with conventional wet cooling and conventional dry cooling cases considered separately using this software. TMY2 data are used for this location for this purpose. Similarly, the same studies are carried out for “ideal” cooling systems as a comparison. We assumed that in the ideal dry cooling system, the condensing temperature is the ambient dry bulb temperature, and in the ideal wet cooling system, it is the ambient wet bulb temperature. It turned out that the ideal dry cooling system would significantly outperform the conventional wet cooling system, indicating the possibility of the dry cooling system being able to achieve increased performance levels with component improvements.

Commentary by Dr. Valentin Fuster

Advances in Transportation Fuels and Systems for the 21st Century

2008;():419-438. doi:10.1115/ES2008-54025.

Continuously Variable Transmissions (CVTs) can be used to optimize the energy utilization of systems by allowing the prime mover to operate at speeds of peak efficiency while allowing the driven components to move at desired speeds. A CVT saves energy by reducing the off-peak efficiency of a system. The basic design principles of a Continuously Variable Transmission composed of a sequence of 4-bar cranks are discussed. The vector solution for 4-bar cranks is iteratively solved for a crank sequence to illustrate how different output speeds can be obtained from the same input speed. This is accomplished by varying the length of the connecting link on each 4-bar crank in the sequence. Solutions are plotted. Each 4-bar crank is located on the same drive shaft and the same driven shaft. Each crank has the same drive link length and the same driven crank length. A one way clutch located on each driven link transmits motion to the driven shaft. The cranks are positioned so that they are out of phase with each other so that only the fastest crank transmits motion, over-running all the other cranks. For a given length of the connecting link, the motion of the driven shaft is not uniform. This is due to the 4-bar crank transmission of peak speed. As one 4-bar crank moves, at some point the angular speed of the driven link will overtake the speed of the driven link on the other crank sets. It will then peak and then slow to be overtaken by another crank-set. The more evenly distributed crank-sets used the more uniform the motion will be. In this sense, a given length of connecting link for the sequence of cranks will generate an average drive shaft speed. If the length of the connecting link in a 4-bar crank is changed, a change in motion of the driven shaft will occur. By changing the length of the connecting link on the 4-bar cranks, the average speed of the driven shaft can be changed. A CVT is made by infinitesimally changing the length of the connecting link. This infinitesimal change is easily accomplished via standard components such as pneumatic or hydraulic cylinders or various other means.

Topics: Design
Commentary by Dr. Valentin Fuster
2008;():439-443. doi:10.1115/ES2008-54076.

The Power Synthesizer of Parallel Hybrid Electric Vehicle (PHEV) has been the research object. It is composed of the differential gear train, in which its power distribution and sensitivity has been analyzed as main problems. The transmission ratio, torque and power distribution have been analyzed about the gear train. Whatever its structure is, if only the value of structure parameter K is same, then the corresponding relative kinematics relation and mechanics relation of the basic components are same absolutely. The calculation of power distribution among basic components has been introduced. The sensitivity has direct influence to the mobile performance of vehicle, so the angular speed response for output components to input components has been analyzed, and the connecting mode between engine or motor and differential gear train has been bought forward. The analytical results can be helpful for the parameters’ design of kinematics and dynamics of the vehicle, and for the vehicle’s control.

Commentary by Dr. Valentin Fuster
2008;():445-452. doi:10.1115/ES2008-54189.

Kettering University has developed a cleaner and quieter snowmobile using technologies and innovative methods which can be applied to existing snowmobile designs with a minimal increase in cost. Specifically, a commercially available snowmobile using a two cylinder, four-stroke engine has been modified to run on high-blend ethanol (E-85) fuel. Further, a new exhaust system which features a catalytic converter and mufflers to minimize engine noise and exhaust emissions was developed. A number of additional improvements have been made to the track to reduce friction and diminish noise. This paper provides details of the snowmobile development to make best use of E-85, documenting the results of these efforts on performance and emissions.

Topics: Ethanol
Commentary by Dr. Valentin Fuster
2008;():453-462. doi:10.1115/ES2008-54215.

Because of converging concerns about global climate change and depletion of conventional petroleum resources, many nations are looking for ways to create transportation fuels that are not derived from fossil fuels. Biofuels and hydrogen (H2 ) have the potential to meet this goal. Biofuels are attractive because they can be domestically produced and consume carbon dioxide (CO2 ) during the feedstock growth cycle. Hydrogen is appealing because its use emits no CO2 , and because hydrogen fuel cells can be very efficient. Today most hydrogen is derived from syngas, a mixture of hydrogen, carbon monoxide (CO) and carbon dioxide, which is produced through catalytic steam reforming of methane (CH4 ). Although effective, this process still produces CO2 . Another method used to generate hydrogen is water electrolysis, but this process is extremely energy intensive. Thus, finding an energy-efficient approach to producing hydrogen from biofeedstock is appealing. Though there are many biofuels, ethanol (C2 H5 OH) is a popular choice for replacing fossil fuels. However, many have questioned its value as a renewable fuel since it requires a significant amount of energy to produce, especially from corn. Producing pure ethanol requires substantial energy for distillation and dehydration to yield an appropriate “dry” fuel for traditional combustion engines. Wet ethanol, or ethanol that has not been fully distilled and dehydrated, requires significantly less energy to create than pure ethanol. In this paper, we present a non-catalytic pathway to produce hydrogenrich syngas from wet ethanol. The presence of water in the reactant fuel can increase the hydrogen mole fraction and decrease the carbon monoxide mole fraction of the product syngas, both of which are desired effects. Also, because there are no catalytic surfaces, the problems of coking and poisoning that typically plague biomass-to-hydrogen reforming systems are eliminated. The non-catalytic fuel reforming process presented herein is termed filtration combustion. In this process, a fuel-rich mixture of air and fuel is reacted in an inert porous matrix to produce syngas. Some of the ethanol and air mixtures under study lie outside the conventional rich flammability limits. These mixtures react because high local temperatures are created as the reaction front propagates into a region where the solid matrix has been heated by exhaust gases. These high temperatures effectively broaden the flammability limits, allowing the mixture to react and break down the fuel into syngas. The conversion of pure and wet ethanol is a novel application of this process. Exhaust composition measurements were taken for a range of water fractions and equivalence ratios (Φ) and were compared to equilibrium values. The water fraction is the volumetric fraction of the inlet fuel and water mixture that is water. Equivalence ratio is the ratio of the fuel to oxidizer ratio of the reactant mixture to the fuel to oxidizer ratio of a stoichiometric mixture. A stoichiometric mixture is defined as a mixture with proportions of fuel and oxidizer that would react to produce only water and carbon dioxide. The stoichiometric mixture (Φ = 1) of ethanol and oxygen (O2 ) is 1 mole of ethanol for every 3 moles of oxygen:

C2H5OH+3O2 ↔ 2CO2+3H2O
Hydrogen mole fraction of the exhaust gas increased with increasing equivalence ratio and remained nearly constant for increasing water-in-fuel concentration. Carbon monoxide mole fraction was also measured because it may be used as a fuel for certain fuel cells while it can poison others [1]. Species and energy conversion efficiencies were calculated, showing that significant energy savings could be made by reforming wet ethanol rather than pure ethanol into syngas. Also, it is shown that the hydrogen to carbon monoxide ratio increases with addition of water to the fuel, making this method attractive for the production of pure hydrogen.

Topics: Syngas , Ethanol , Hydrogen
Commentary by Dr. Valentin Fuster
2008;():463-470. doi:10.1115/ES2008-54227.

An experiment was performed to analyze the effects of biodiesel-ethanol blended fuel spray on the combustion and exhaust emission characteristics of a single-cylinder common-rail diesel engine. To analyze the macroscopic and microscopic characteristics of biodiesel blended fuel spray, measurements of the injection rate, droplet diameter, and spray tip penetration were taken using an injection rate meter, spray visualization and a droplet measuring system. The combustion, exhaust emission characteristics and size distributions of particulate matter were determined for various engine operating conditions using biodiesel-ethanol blends, and the results were compared to those of conventional diesel fuel. In this investigation, the measured results of biodiesel-ethanol blended fuels show that the Sauter mean diameter (SMD) decreased with an increase of relative velocity between the injected fuel and ambient gas. Comparing the combustion characteristics of diesel fuel and biodiesel-ethanol blended fuels, both diesel and blended fuel showed similar trends in combustion pressure and the rate of heat release. However, the combustion of biodiesel-ethanol blends had lower combustion characteristics such as combustion pressures and heat release rates than those of diesel fuel because of their lower heating values. In the case of exhaust gas recirculation (EGR), the indicated specific NOx (ISNOx ), and soot concentrations were lower than those of conventional diesel fuel.

Commentary by Dr. Valentin Fuster
2008;():471-476. doi:10.1115/ES2008-54238.

Per British thermal unit (BTU), in the United States, gasoline currently costs about 7.6 times as much as coal. Due to the prevalence of coal fired electricity generating stations in the country, electrically powered vehicles may provide a fuel cost savings over similar gasoline powered vehicles. Fuel costs for electric vehicles have been reported to cost about $0.045 per mile to operate. Higher efficiency, gasoline operated automobiles such as the Toyota Corolla have reported fuel costs of about $0.093 per mile. This paper provides a first glance examination of electrically powered and gasoline powered vehicles in the United States. While gasoline costs continue to rise, a cheap, environmentally safe transportation alternative is needed to maintain the flexible lifestyle currently enjoyed by Americans. The cycle energy efficiency of coal produced electricity for personal transportation is much lower than the energy efficiency of gasoline, but the large cost differences between these two forms of fossil fuels may provide a temporary fix to a looming transportation crisis in the United States. The long-term environmental effects of an electrically powered, private transportation fleet could prove catastrophic due to increased use of coal and accompanying combustion product air pollution, but clean, renewable, electricity producing technologies may support more prolific long-term use of electrically powered transportation modes.

Topics: Fuels , Vehicles , Gasoline
Commentary by Dr. Valentin Fuster
2008;():477-487. doi:10.1115/ES2008-54283.

Fast depletion of the conventional petroleum-based fossil fuel reserves and the detrimental effects of the pollutant emissions associated with the combustion of these fuels in internal combustion (IC) engines propelled the exploration and development of alternative fuels for internal combustion engines. Biodiesel has been identified as one of the most promising alternative fuels for IC engines. This paper discusses about the advantages and disadvantages of biodiesel vis-a-vis the conventional petro-diesel and presents the energetic performances and emission characteristics of CI engine using biodiesel and biodiesel-petrodiesel blends as fuels. An overview of the current research works carried out by several researchers has been presented in brief. A review of the performance analysis suggests that biodiesel and its blends with conventional diesel have comparable brake thermal efficiencies. The energy balance studies show that biodiesel returns more than 3 units of energy for each unit used in its production. However, the brake specific fuel consumption increases by about 9–14% compared to diesel fuel. But, considerable improvement in environmental performance is obtained using biodiesel. There is significant reduction in the emissions of unburned hydrocarbons, polyaromatic hydrocarbons (PAHs), soot, particulates, carbon monoxide, carbon dioxide and sulphur dioxide with biodiesel. But the NOx emission is more with biodiesel compared to diesel. A case study with Jatropha biodiesel as fuel and the current development status, both global and Indian, of biodiesel as a CI engine fuel have been included in the paper.

Commentary by Dr. Valentin Fuster
2008;():489-496. doi:10.1115/ES2008-54286.

The amount of Diesel (DI) that can be replaced by Natural Gas (NG) in turbocharged Diesel vehicles converted to dual operation and under urban traffic conditions is determined by the rapid changes of engine loads, which also limits the thermodynamic performance of turbochargers. Turbochargers control the air flow that enters to the engine at every single moment of its operation, and therefore supplies the Oxygen (O2 ) required for burning the fuels involved in the combustion process. This investigation models the energy consumption of a diesel engine operating in dual fuel mode in urban traffic conditions of Barranquilla, Colombia. This model is based on experimental studies of transient states of Turbocharged Diesel Engines and on recent research relating to the conversion of diesel engines to dual mode. Due to the absence of a standard test cycle for the city, this investigation uses a common driving behavior profile registered in 2006 with an urban bus Chevrolet B-70 with a Caterpillar 3126 Engine. It was determined that the greater replacement percentage was about 85% at maximum load and at cruising speeds, due to the air flow supplied by the compressor. The opposite effect was found at transient states; the absence of air is because of the turbocharger performance when the vehicle is leaving the stand-by condition.

Commentary by Dr. Valentin Fuster
2008;():497-505. doi:10.1115/ES2008-54326.

In order to decrease the use of petroleum and release of greenhouse gases such as carbon dioxide, the efficiency of transportation vehicles must be increased. One way to increase vehicle efficiency is by extending the electric-only operation of hybrid electric vehicles through the addition of batteries that can be charged using grid electricity. These plug-in hybrid electric vehicles (PHEVs) are currently being developed for introduction into the U.S. market. As with any consumer good, cost is an important design metric. This study optimizes a PHEV design for a mid-size, gasoline-powered passenger vehicle in terms of cost. Three types of batteries, Pb-acid, NiMH, and Li-ion, and three all-electric ranges of 10, 20, and 40 miles (16.1, 32.2, and 64.4 km) were examined. System modeling was performed using Powertrain Systems Analysis Toolkit (PSAT), an Argonne National Laboratory-developed tool. Performance constraints such as acceleration, sustained grade ability, and top speed were met by all systems. The societal impact of the least cost optimum system was quantified in terms of reduced carbon emissions and gasoline consumption. All of the cost optimal designs (one for each combination of all-electric distance and battery type) demonstrated more than a 60% reduction in gasoline consumption and 45% reduction in CO2 emissions, including the emissions generated from producing the electricity used to charge the battery pack, as compared with an average car in the current U.S. fleet. The least cost design for each all-electric range consisted of a Pb-acid design, including a necessary battery replacement of the battery pack twice during the 15 year assumed life. Due to the cost of the battery packs, the 10-mile all-electric range proved to be the least costly. Also, this system saved the most carbon dioxide emissions, a 53% reduction. The most fuel savings came from the PHEV40 system, yielding an 80% reduction in gasoline consumption.

Commentary by Dr. Valentin Fuster
2008;():507-515. doi:10.1115/ES2008-54328.

In this paper, the potential benefits and technical advantages of using ammonia as a green fuel for transportation are analyzed based on performance indicators including the system effectiveness, the driving range, fuel tank compactness, and the cost of driving per km. Similar to hydrogen, ammonia is a synthetic product that can be obtained thermally, physically, chemically or biologically either from fossil fuels, biomass, or other renewable sources and can be used as a clean fuel. The refrigeration effect of ammonia is another advantage of it and is included in the efficiency calculations. The cooling power represents about 7–10% from the engine power, being thus a valuable side benefit of ammonia’s presence on-board. If the cooling effect is taken into consideration, the system’s effectiveness can be improved by about 20%. It is shown that if a medium size hydrogen car converted to NH3 , it becomes more cost effective per driving range as low as CN$3.2/100 km.

Commentary by Dr. Valentin Fuster

Advances in Fuel Cells and Hydrogen Energy Technologies

2008;():517-524. doi:10.1115/ES2008-54031.

The aim of this work is to reduce the refueling time of a metal hydride storage tank by improving its design, taking in account the total volumetric and mass capacity of the tank. A heat and mass transfer model is proposed and solved to obtain the charging curve for 1 kg hydrogen in a LaNi5 reference storage tank. Compared to gas transport and reaction kinetics, heat transfer is found to limit the hydrogen charging dynamics of the storage tank. To improve the refueling time, it is found to be necessary to increase first of all the heat transfer inside the metal hydride bed, and subsequently the heat transfer from the metal hydride bed to the cooling fluid. Technical solutions such as the implementation of aluminum foam and/or internal heat exchanger tubes are investigated. By combining both solutions, the refueling time can be reduced from 400 minutes (reference tank) to 15 minutes. The tank volume still meets the DOE targets, but its mass remains a problem. Therefore, new materials with improved gravimetric capacity have to be developed. With this work it is now possible to improve the tank design for newly developed storage materials and to evaluate their potential for technical applications.

Commentary by Dr. Valentin Fuster
2008;():525-535. doi:10.1115/ES2008-54171.

Process conditions for the direct solar decomposition of sulfur trioxide have been investigated and optimised by using a receiver-reactor in a solar furnace. This decomposition reaction is a key step to couple concentrated solar radiation or solar high temperature heat into promising sulfur based thermochemical cycles for solar production of hydrogen from water. After proof-of-principle a modified design of the reactor was applied. A separated chamber for the evaporation of the sulfuric acid, which is the precursor of sulfur trioxide in the mentioned thermochemical cycles, a higher mass flow of reactants, an independent control and optimisation of the decomposition reactor were possible. Higher mass flows of the reactants improve the reactor efficiency because energy losses are almost independent of the mass flow due to the predominant contribution of re-radiation losses. The influence of absorber temperature, mass flow, reactant initial concentration, acid concentration, and residence time on sulfur trioxide conversion and reactor efficiency have been investigated systematically. The experimental investigations was accompanied by energy balancing of the reactor for typical operational points. The absorber temperature turned out to be most important parameter with respect to both conversion and efficiency. When the reactor was applied for solar sulfur trioxide decomposition only, reactor efficiencies of up to 40% were achieved at average absorber temperature well below 1000 °C. High conversions almost up to the maximum achievable conversion determined by thermodynamic equilibrium were achieved. As the reradiation of the absorber is the main contribution to energy losses of the reactor a cavity design is predicted to be the preferable way to further raise the efficiency.

Topics: Solar energy , Sulfur
Commentary by Dr. Valentin Fuster
2008;():537-547. doi:10.1115/ES2008-54197.

The present work presents a three-dimensional, non-isothermal computational model of PEMFC, implemented in the CFD code Fluent. The model accounts for all major transport phenomena, including: water and proton transport through the membrane; electrochemical reaction; transport of electrons; transport and phase change of water in the gas diffusion electrodes; diffusion of multi-component gas mixtures in the electrodes; and mass transport in the gas flow channels. First, the polarization behavior or steady state performance of the PEMFC has been simulated and then the transient response subjected to a variable load has been studied. In the steady state analysis, the polarization curves, obtained by single phase and two-phase numerical simulations, have been compared with the experimental data given in literature. A good agreement is evident for the curve given by the two-phase simulations, while the single-phase model is unable to reproduce the experimental data at the high current densities. A parametric study has been done to validate the model and the predicted polarization curves have been compared with experiments. Finally unsteady simulations have been performed. The effect of the rate of change in cell voltage on cell performance for three different rates have been shown. The transient results demonstrate that current density overshoots the stabilized state value when cell voltage is abruptly decreased.

Commentary by Dr. Valentin Fuster
2008;():549-558. doi:10.1115/ES2008-54206.

A reference design for a commercial-scale high-temperature electrolysis (HTE) plant for hydrogen production was developed to provide a basis for comparing the HTE concept with other hydrogen production concepts. The reference plant design is driven by a high-temperature helium-cooled nuclear reactor coupled to a direct Brayton power cycle. The reference design reactor power is 600 MWt , with a primary system pressure of 7.0 MPa, and reactor inlet and outlet fluid temperatures of 540°C and 900°C, respectively. The electrolysis unit used to produce hydrogen includes 4,009,177 cells with a per-cell active area of 225 cm2 . The optimized design for the reference hydrogen production plant operates at a system pressure of 5.0 MPa, and utilizes an air-sweep system to remove the excess oxygen that is evolved on the anode (oxygen) side of the electrolyzer. The inlet air for the air-sweep system is compressed to the system operating pressure of 5.0 MPa in a four-stage compressor with intercooling. The alternating-current (AC) to direct-current (DC) conversion efficiency is 96%. The overall system thermal-to-hydrogen production efficiency (based on the lower heating value of the produced hydrogen) is 47.1% at a hydrogen production rate of 2.356 kg/s. An economic analysis of this plant was performed using the standardized H2A Analysis Methodology developed by the Department of Energy (DOE) Hydrogen Program, and using realistic financial and cost estimating assumptions. The results of the economic analysis demonstrated that the HTE hydrogen production plant driven by a high-temperature helium-cooled nuclear power plant can deliver hydrogen at a competitive cost. A cost of $3.23/kg of hydrogen was calculated assuming an internal rate of return of 10%.

Commentary by Dr. Valentin Fuster
2008;():559-567. doi:10.1115/ES2008-54207.

We have conducted optimization for a flow process consisting typical direct internal reforming Solid Oxide Fuel Cell (SOFC) utilizing syngas with anode off gas recycling. The mass and energy balance analysis for the whole system has been carried out. Mass balance (or molar balance) analysis includes optimization for minimum fuel and oxygen consumption rates corresponding to the temperatures of pre-reformer and SOFC, the steam to carbon ratio inside the pre-reformer, recirculation ratio, and rate of CO2 capture. Studies on the reforming chemical reactions and chemical equilibria are presented. The results include CO2 adsorption in the adsorbent bed as well as recirculation. For the molar balance study, we provided methane consumption rate and overall molar balance. With the energy balance analysis, the temperature distributions in the system are calculated. We have also investigated the total system efficiency based on the first law of thermodynamics. The overall efficiency is defined as the total net power output divided by the lower heating value rate of fuel input. We also provided optimal case design parameters. Thermodynamic efficiency is mainly affected by CO2 adsorption percentage under low steam to carbon ratio region, while efficiency is mainly affected by recirculation rate under high temperature operation. In accordance with our simulation, it is recommended high SOFC temperature, moderate SC ratio, moderate CO2 adsorption and high recirculation operation.

Commentary by Dr. Valentin Fuster
2008;():569-576. doi:10.1115/ES2008-54303.

In this paper fluid dynamic behaviors of cathode gas flow in an external gas manifold of a planar solid oxide fuel cell (SOFC) stack are simulated to investigate the overall pressure variation and flow distribution. External manifold models are built in three dimensions for a 60-cell planar SOFC stack. Cell units of the stack are treated as porous media with appropriate resistances, which were determined by the previous results of cell modeling. In order to simplify this model, electrochemical reactions, heat and mass transport phenomena are ignored inside cells. The flows of cathode gas in the external manifolds of stack are modeled by means of computational fluid dynamics (CFD) methods. A commercial CFD package “Fluent” was used for geometry creation, grids generation of flow volume interiors, solving mass, momentum equations, plotting computational results. The detailed results of pressure variation and flow distribution of gases in the stack were achieved. The effects of different designs and parameters such as a gas distributor inside the external manifold, the permeability of porous media in cells and cathode gas feeding rate on gas distribution and pressure variation are studied. Comparison of different cases is carried out by the modeling results. Modeling results show for the proposed stack design in this paper the additional gas distributor located in the center of the inlet manifold and a rise of resistance in cells can respectively enhance the uniformity of flow distribution over 60 cells.

Commentary by Dr. Valentin Fuster

Heat Pump Systems and Technologies

2008;():577-588. doi:10.1115/ES2008-54002.

Research has been ongoing during the last several years on developing robust automated fault detecting and diagnosing (FDD) methods applicable for process faults in chillers used in commercial buildings. These FDD methods involve using sensor data from available thermal, pressure and electrical measurements from commercial chillers to compute characteristic features (CF) which allow more robust and sensitive fault detection than using the basic sensor data itself. One of the proposed methods is based on the analytical redundancy approach using polynomial black-box multiple linear regression models for each CF that are identified from fault-free data in conjunction with a diagnosis table. The second method is based on a classification approach involving linear discriminant analysis to identify the classification models whereby both the detection and diagnosis can be done simultaneously. This paper describes the mathematical basis of both methods, illustrates how they are to be tuned using the same fault-free data set in conjunction with limited faulty data, and then compares their performance when applied to different fault severity levels. The relative advantages and disadvantages of each method are highlighted and future development needs are pointed out.

Commentary by Dr. Valentin Fuster
2008;():589-599. doi:10.1115/ES2008-54027.

From the last two decades, the development of robust automated fault detection and diagnosis (FDD) methods applicable to HVAC&R equipment has been an area of active research, and several papers have been written on this issue. However, the use of these systems is not prevalent in the industry as yet, and some reasons for this status are presented in this paper. This paper also provides a description of the various functions and capabilities of an automated FDD system and summarizes pertinent lessons learnt from previous research studies. It is not meant to be a bibliographic review but a clear description and succinct assessment of the various issues which impact this topical area.

Commentary by Dr. Valentin Fuster
2008;():601-608. doi:10.1115/ES2008-54039.

A thermodynamic model is developed to predict trends in limiting COP of an adsorption cooling cycle with thermal regeneration between n beds, where n is any even number and each bed is spatially isothermal. The results of the model indicate the optimum distribution of beds throughout the cycle to maximize thermal regeneration. Simulations were run for silica gel-water and zeolite-water adsorbent-refrigerant pairs as the maximum bed temperature and the bed’s sensible load were varied. For the silica gel-water pair, the exothermic adsorption process occurs at lower temperatures than the endothermic desorption process, which prevents the latent loads from being thermally regenerated. This inability to regenerate latent loads results in a relatively small opportunity to increase COP through thermal regeneration, and this opportunity decreases rapidly with increasing number of beds. Conversely, for the zeolite-water pair much of the exothermic adsorption process occurs over the same temperature range as the endothermic desorption process, which allows a significant portion of the latent loads to be thermally regenerated. This ability to regenerate latent loads results in a much larger opportunity to increase COP through thermal regeneration, and this opportunity decreases much more gradually with increasing number of beds.

Topics: Cooling , Cycles
Commentary by Dr. Valentin Fuster
2008;():609-617. doi:10.1115/ES2008-54110.

Improved air-conditioning technology has the greatest potential impact on the electric industry compared to any other technology that uses electricity particularly during summer peak electric demand. Gas engine-driven units can provide overall peak load reduction and electric grid relief for summer peak demand. Peak-load conditions can lead to high electricity prices, power quality problems, and grid system inefficiencies, and even failures. Improved air-conditioning technology thus has the greatest potential impact on the electric grid compared to other technologies that use electricity. Thermally-activated systems, such as natural gas engine-driven heat pumps, can provide overall peak load reduction and electric grid relief for summer peak demand. This paper describes the development of an innovative 10 refrigeration ton (RT) natural gas engine-driven heat pump (GHP) for commercial application. The unit was tested at various Air Conditioning and Refrigeration Institute (ARI) heating and cooling conditions in a psychrometric chamber at Oak Ridge National Laboratory. The gas COP at 47°F rating condition exceeded the goal of 1.6 at both high and intermediate engine speeds. The gas COP in cooling mode also exceeded the goal of 1.2 at 95°F rating condition. In this study, principles of operation, unit performance and benefits are discussed.

Topics: Engines , Design , Heat pumps
Commentary by Dr. Valentin Fuster
2008;():619-627. doi:10.1115/ES2008-54125.

Absorption of ammonia vapor bubbles into a constrained thin film of ammonia-water solution is presented in the context of potential reduction in size of a heat-actuated heat pump component. A large-aspect-ratio channel with a depth of 600 μm restricts the thickness of the weak solution film, while ammonia vapor bubbles are injected from a porous wall. Experiments are performed at a nominal system pressure of 6.2 bar absolute and at an inlet weak solution temperature of 75 °C. A counter flowing coolant at a fixed inlet temperature of 58 °C removes the generated heat of absorption. The mass flow rate of the weak solution, vapor flow rate, and mass flow rate of the coolant solution are varied. Results indicate that a desirable operating condition for the absorber considering both heat and mass transfer attributes is obtained for a flow rate of 1.5 g/min of vapor and 35 g/min of weak solution. Variation of the coolant flow rate does not significantly affect the overall heat transfer coefficient at a low vapor flow rate of 1 g/min. Under these operating conditions, preliminary geometric scaling estimates indicate that a 11.3 kW heat load absorber would require a heat exchange surface area of 0.88 m2 . The excess pressure drop penalty on the vapor side across the porous plate for this absorber needs to be considered in terms of the overall absorption cycle performance.

Commentary by Dr. Valentin Fuster
2008;():629-635. doi:10.1115/ES2008-54186.

This study presents the concept, functionality, and economics of a solar-fired, single-effect, absorption air conditioning system. The goal of this project was to develop a mathematical model to determine efficiencies and capacities, which are then compared with a traditional 28 kW (8 ton) packaged vapor compression system. This comparison is then used to determine economic conclusions. The thermal system being examined is part of a proposed research and development project located in Phoenix, Arizona. This specific system will contain a six-module, single-axis, concentrating solar collector, a 119 gallon (450 L) storage tank, and a 35kW chiller. Using MatLab with Typical Meteorological Year 2 (TMY2) weather data [1], a model was created from readily available manufacturer specifications. After completing the model it was determined that the annual savings can range from $3,448 to $1,737 with simple payback periods of 18 to 36 years depending on collector efficiencies and current electrical rates. The model also proved that the proposed cooling system can supply over 20 kW of continuous cooling for 8 hours on a typical summer day.

Commentary by Dr. Valentin Fuster
2008;():637-649. doi:10.1115/ES2008-54209.

A 16 kW (4.6 refrigerant tons) steam driven, double effect, parallel flow absorption chiller has been designed, manufactured, and installed in the Intelligent Workplace (IW) of Carnegie Mellon University (CMU). This chiller is driven by 6 bar saturated steam and uses a 57% LiBr-H2 O sorbent. It is the smallest absorption chiller available in the existing market. The absorption chiller consists of five major and four minor heat transfer components. The manufacturer of the chiller has provided information on detailed configuration and dimensions of these components to support the calculation of their heat transfer areas, A’s, and the estimation of overall heat transfer coefficients, U’s. A steady state computational performance model for the chiller has been developed based on the applicable scientific and engineering principles. The model has been used to calculate all chiller internal working conditions and to analyze the experimental data over a wide range of operating conditions. Heat transfer coefficients inside and outside of the tubes making up the chiller’s heat transfer components have been estimated by published empirical correlations. The product of the overall heat transfer coefficient and the surface contact area, UA’s, for the 5 major heat transfer components have been estimated using the chiller model and measured performance data. Significant variations, 30%, in this parameter are observed under partial load, reduced flow conditions. Deviations between the experimental measurements and the model solutions have been analyzed to evaluate the model accuracy. At design operating conditions, the overall deviation is about 6%.

Commentary by Dr. Valentin Fuster
2008;():651-658. doi:10.1115/ES2008-54223.

Typically there is a great deal of waste heat available in drainage system of large-scale public bathhouses, such as public bathhouses in schools, barracks and natatoriums. The paper advances a heat pump system used in bathhouses for exhaust heat recovery. The system consists of solar energy collection system, drainage collection system and heat pump system for exhaust heat recovery. In the system, tap water is heated by energy from solar energy collection system, and is used as hot water for bathing at the beginning. At the same time, drainage collection system collects sewage from bathhouses, and then electric heat pump starts up and recovers the exhaust heat in sewage and heats the tap water. In this way, heat is recycled. Practical operation of the system was introduced, and drainage temperature as well as equipment capacity was optimized based on a practical example. Compared with gas-fired (oil-fired, coal-fired, electric) boilers, the system has advantages of lower energy consumption, less pollution and lower operating cost. Therefore, the system has great superiority in energy conservation and has a good application prospect.

Commentary by Dr. Valentin Fuster
2008;():659-668. doi:10.1115/ES2008-54232.

In this paper, computational fluid dynamics (CFD) is utilized to investigate thermal comfort and energy efficiency of an office in the Intelligent Workplace (IW) of Carnegie Mellon University. First, a comprehensive geometric grid model is constructed to represent the office including the walls, floor, roof, windows, doors, fan coil units, and furnishings. Then the air flow and accompanying heat exchange with the bounding surfaces of the office are calculated based on indoor and outdoor ambient conditions, the operating conditions of the fan coil units and windows, and the occupancy of the space. The computational results of the air flow provide the means to measure whether comfort conditions have been established based on the outside conditions and on the operation of the fan coil units. The operating conditions of the fan coil units, fan speed, and chilled/heated water flow, determine their effectiveness in cooling/heating and their operating costs. This CFD air flow simulation, therefore, when generalized, provides a design support system for architects and engineers. The numerical solutions of office space are calibrated and validated by empirical operational data from the fan coil units. The design support system will enable the evaluation of the annual performance and operating cost of given fan coil units in a given building space.

Topics: Air flow , Computation
Commentary by Dr. Valentin Fuster
2008;():669-682. doi:10.1115/ES2008-54274.

Increasing the coefficient of performance of a vapor compression refrigeration system may be realized by utilizing work recovering expansion devices that lower the enthalpy of the refrigerant at the inlet of the evaporator. Depending on the operational and geometrical parameters of the expander, laminar and viscous two-phase leakage flow within the expander may be present. Single-phase leakage models available in the literature must then be modified or re-derived accordingly. A dynamic frictional model for the expander must also be developed for ideal operation (i.e. no internal leakage) and modified to account for internal leakage accordingly. This paper presents a comprehensive component-level model of inherent friction and internal leakage losses in a two-phase circular rotary-vane expander used in a vapor compression refrigeration system. The model establishes the performance of the expander as a function of geometric and fluid parameters. Accurate modeling and prediction of frictional and internal leakage losses is vital to being able to accurately estimate the efficiency, rotational speed, torque and power of/produced by the expander. Directions for future work are also discussed.

Topics: Leakage
Commentary by Dr. Valentin Fuster
2008;():683-690. doi:10.1115/ES2008-54345.

In Chinese market, many homes use heat pump systems for heating and cooling. Domestic hot water is usually provided by a domestic water heater making use of electricity, natural gas or solar energy, which is known for its great energy costs. These systems consume much energy and increase the total cost of the required domestic energy. A new system combining heat pump with water heater is proposed in this paper, and it is named domestic energy system. The system can realize the provision of space heating, cooling and domestic hot water throughout the year. Based on the different types of heat pumps and water heaters, domestic energy consumption patterns are divided into five categories: heat pump and gas-fired water heater system, heat pump and solar water heater system, heat pump and electricity water heater system, heat pump and heat pump water heater system, and domestic energy system. This study describes and compares all of the above-mentioned systems including energy and exergy analysis. Results showed that the domestic energy system can save energy and provide good economy.

Commentary by Dr. Valentin Fuster

Distributed and Combined Cooling, Heating and Power Technologies (CHP, CCHP)

2008;():691-697. doi:10.1115/ES2008-54017.

This paper describes a study starting from an analysis of typical energy demand profiles in a hospital setting followed by the feasibility study of a cogeneration system (CGS). The concept is a future autonomous system for the combined generation of electrical, heating and cooling energy in the hospital. The driving cogeneration units are two high-efficiency gas engines; this is used to produce the electrical and heat energy. Gas engine is used as a driving unit because of high needs for electrical and heating energy. The natural gas-fuelled reciprocating engine is used to generate 735kW of power. In our case electrical energy will be used only in the Hospital. A deficit in electricity can be also purchased from the public network. The generated steam will be used to drive three steam-fired absorption chillers and delivered to individual consumers of heat. This system is capable of doing simultaneous heating and cooling. No obstacles were recognized for the technical feasibility of CGS. The average ratio between electric and thermal load in the Hospital is suitable to make CGS system operate. A feasibility analysis performed for a non-optimized CGS system predicted a large potential for primary energy saving.

Commentary by Dr. Valentin Fuster
2008;():699-706. doi:10.1115/ES2008-54042.

Distributed natural gas-driven combined cooling, heating and power (CCHP) systems, including various technologies, provide an alternative for the world to meet and solve energy-related problems, such as energy shortages, energy supply security, emission control, the economy and conservation of energy, etc. This paper analyzes the energy consumption structure in China at first; then the characteristics of natural gas-driven CCHP technologies, especially technical performances, are presented, as well as the status of utilization and development. The status of distributed CCHP development in China is briefly introduced by dividing China into four main sections: Beijing, Shanghai, Guangdong and other areas. Several problems regarding further distribution of natural gas-driven CCHP applications for buildings in China are discussed. It is concluded that, within decades, promising CCHP technologies can flourish with the cooperative efforts of government, energy-related enterprises and professional associations.

Commentary by Dr. Valentin Fuster
2008;():707-720. doi:10.1115/ES2008-54071.

A general approach, the HLRP technique, for determining the performance of a hybrid turbine-fuel cell cogeneration system with a renewable energy sources is presented for a domestic residence. The hybrid-cogeneration system provides the electric power as well as satisfying heating loads. In this paper a system level analysis that includes practical values of heat exchangers, pumps, and storage equipment is presented. The use of the ratio of the thermal load to required power parameter (HLRP), which has been used by the authors to scale energy systems, allows the performance to be quickly determined and preliminary carbon dioxide production rates and cost effects to be estimated. The present paper includes solar energy systems as renewable energy to illustrate the development of this technique and its integration with the hybrid fuel cell cogeneration system. Practical values of solar collector efficiency and storage tank and battery storage efficiency are included. The analysis focused on matching the transient characteristics of the power and thermal loads with those of the renewable energy system. The results demonstrate that for a typical winter day in the location studied there are not large variations in the energy utilization factors for the four different systems investigated. There is a 23% reduction in the carbon dioxide produced using the solar thermal or combined system as compared to the no renewable energy or photovoltaic systems. The information provided by the performance graphs is used to estimate costs for each system and to easily determine which system is the most efficient for satisfying energy requirements and reducing green house gas emissions. The results provide site planners and physical plant operators with initial information that can be used to design new facilities or effectively integrate large plant expansion that include renewable energy systems in a manner that will minimize energy requirements and reduce pollution effects.

Commentary by Dr. Valentin Fuster
2008;():721-727. doi:10.1115/ES2008-54080.

In China, the overall economical performances of heating systems are not very high, there are still some problems of high energy consumption, high gas emission and low heat utilization. The energy conversation and emission reduction are two most important things. The option of the heating system schemes is the key to improve such situation. An optimal heating scheme will be a good beginning to the whole heating system. In this paper, the GRA (Grey Relation Analysis) method is introduced and used, and with the example of a heating district, the most used and upcoming used heating schemes are listed, calculated and compared by using the method of GRA. The option of a heating system scheme is a typical multi-objective decision-making problem. The schemes are the district boiler heating system (including gas-fired, oil-fired, and coal-fired boilers), solar energy heat pump system and combined heating and power system etc. In the process of optimization calculation, the aspects of energy saving, economics benefit, environment benefit and social benefit are concerned about, and the initial cost, operating cost, employment life, environment influence and system reliability are taken into account. According to the calculation results, combined heating and power system is proposed to be optimal heating system scheme.

Topics: Optimization , Heating
Commentary by Dr. Valentin Fuster
2008;():729-733. doi:10.1115/ES2008-54087.

Distributed generation (DG) is becoming the indispensable supplement to the centralized generation. Micro-turbine is paid more and more attention in scientific research and commercial application due to its unique advantages and gradually becomes the core of distributed generation. It is essential to make a synthetic and scientific evaluation on the performance of micro-turbine in order to promote the progress of the distributed generation technology using micro-turbine. This article gives the synthetic performance evaluation of micro-turbine. Some performance characters (rated capacity, generating efficiency, rotation speed, pressure ratio, fuel consumption, multi-fuel, intake temperature, exhaust temperature, NOx emission level, noises and life time) were chosen as evaluating indicators and some common micro-turbines were taken as evaluating objects in this paper. Considering the difficulty of fuzzy synthetic evaluation method in calculation of the multiple factors and the ignorance of the relationship among evaluating objects, a new weight evaluation process using entropy method was introduced. The entropy method is an objective way for weight determination. The improved method for weight determination of the evaluating indicators was applied in performance assessment of the micro-turbines. The evaluation result of the example showed that this method was favorable for fuzzy synthetic evaluation when there was more than one evaluating objects and the entropy method for determination of weight was a very effective method for evaluating indicators. The method predigested the fuzzy synthetic evaluation process greatly and the evaluation results are more reasonable.

Topics: Entropy , Turbines
Commentary by Dr. Valentin Fuster
2008;():735-746. doi:10.1115/ES2008-54095.

The Power, Water Extraction, and Refrigeration (PoWER) engine has been investigated for several years as a distributed energy (DE) system among other applications for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semi-closed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, low emissions, lower air and exhaust flows (which decrease filtration and duct size) and condensation of fresh water. The present paper describes the preliminary design and its modeling of a modified version of this system as applied to DE system, especially useful in regions which are prone to major grid interruptions due to hurricanes, under-capacity, or terrorism. In such cases, the DE system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is contained in magnitude and scope. The paper describes the rather straightforward system modifications necessary for ice production. However, the primary focus of the paper is on dynamic modeling of the ice making capacity to achieve significant load-leveling during the summer utility peak, hence reducing the electrical capacity requirements for the grid.

Commentary by Dr. Valentin Fuster
2008;():747-754. doi:10.1115/ES2008-54096.

The Combined Cooling, Heating, and Power (CCHP) systems have been widely recognized as a key alternative for thermal and electric energy generation because of the outstanding energy efficiency, reduced environmental emissions, and relative independence from centralized power grids. Nevertheless, the total energy cost of CCHP systems can be highly dependent on the operation of individual components and load balancing. The latter refers to the process of fulfilling the thermal and electrical demand by partitioning or “balancing” the energy requirement between the available sources of energy supply. The energy cost can be optimized through an energy dispatch algorithm which provides operational/control signals for the optimal operation of the equipment. The algorithm provides optimal solutions on decisions regarding generating power locally or buying power from the grid. This paper presents an initial study on developing an optimal energy dispatch algorithm that minimizes the cost of energy (i.e., cost of electricity from the grid and cost of natural gas into the engine and boiler) based on energy efficiency constrains for each component. A deterministic network flow model of a typical CCHP system is developed as part of the algorithm. The advantage of using a network flow model is that the power flows and efficiency constraints throughout the CCHP components can be readily visualized to facilitate the interpretation of the results. A linear programming formulation of the network flow model is presented. In the algorithm, the inputs include the cost of the electricity and fuel and the constraints include the cooling, heating, and electric load demands and the efficiencies of the CCHP components. This algorithm has been used in simulations of several case studies on the operation of an existing micro-CHP system. Several scenarios with different operational conditions are presented in the paper to demonstrate the economical advantages resulting from optimal operation.

Topics: Algorithms
Commentary by Dr. Valentin Fuster
2008;():755-761. doi:10.1115/ES2008-54113.

With the rapid economic development, the energy demand is rising and energy-related greenhouses gas emissions are growing rapidly in China. The usage percent of renewable energy in use is still low while the energy consumption is still increasing. Due to the expanding pressure from energy demand, environment concerns and society issues, distributed energy systems (DESs), especially combined heat and power (CHP), are encouraged and expected to play a greater role by the government. This paper mainly seeks to explore and answer some of questions. Firstly, the different technologies of various DES options are briefly reviewed. Then the question of why distributed energy systems should be developed in China is considered. Recent trends and current patterns of energy supply and use in China are also discussed. Some typical distributed energy systems used in China are introduced. This article also discusses what barriers need be overcome if China wishes to move towards a sustainable energy future. Finally, several suggestions are proposed to favor the wide application of DES in China. It is concluded that DES is a good option with respect to China’s sustainable development that has institutional, market and regulatory support.

Commentary by Dr. Valentin Fuster
2008;():763-768. doi:10.1115/ES2008-54131.

Carnegie Mellon University’s departments of Architecture and Mechanical Engineering have teamed with Milwaukee School of Engineering’s Mechanical Engineering department to design and install a biodiesel fueled engine-generator with heat recovery equipment to supply electric and thermal power to an office building on campus, the Intelligent Workplace (IW). The installation was completed in early September 2007, and is currently being commissioned. Full scale testing will begin in early 2008. The turbocharged diesel engine-generator set is operated in parallel with the local electric utility and the campus steam grid. The system is capable of generating 25 kW of electric power while providing 18 kW of thermal power in the form of steam from an exhaust gas boiler. The steam is delivered to a double-effect Li-Br absorption chiller, which supplies chilled water to the IW for space cooling in the summer or hot water for space heating in the winter. Furthermore, the steam can be delivered to the campus steam grid during the fall and spring when neither heating nor cooling is required in the IW. Additionally, thermal energy will be recovered from the coolant to provide hot water for space heating in the winter, and for regenerating a solid desiccant dehumidification ventilation system in summer. All relevant temperatures, pressures, and flows for these systems are monitored via a building automation system. Pressure versus time measurements can be recorded in each cylinder of the engine. Emissions of nitric oxide (NO), nitrous oxide (NO2 ), Particulate Matter (PM), and carbon dioxide (CO2 ) are also monitored. Upon completion of this installation and the system performance testing, the operation of the engine generator with its heat recovery components will be integrated with the other HVAC components of the IW including a parabolic trough solar thermal driven LiBr absorption chiller, a solid desiccant dehumidification ventilation system, and multiple types of fan coils and radiant heating and cooling devices. This energy supply system is expected to reduce the IW’s primary energy consumption by half in addition to the 75% energy savings already realized as compared to the average US office space.

Commentary by Dr. Valentin Fuster
2008;():769-776. doi:10.1115/ES2008-54157.

It is well known that combined heating and power (CHP) generation permits the energy of the fuel to be more efficiently than electric and thermal separate generation. The paper deals with natural gas CHP system with a 70kWe gas-powered internal combustion engine (ICE), which has been set up at the Tsinghua University energy-saving building, in Beijing, China. The system is composed of an ICE, a flue gas heat exchanger and other heat exchangers. The conventional system’s characteristics is that the gas engine generates power on-site, and the exhaust of the gas engine is recovered by a high temperature flue gas-water heat exchanger, and the jacket water heat is recovered by a water-water heat exchanger to supply heat for district heating system. In order to improve the system’s performance, an innovative system with absorption heat pump is adopted. The exhaust of the gas engine drives an absorption heat pump to recover the flue gas sensible heat and further recover the latent heat, so the outlet temperature of the exhaust could be lowered to 50°C. In this paper, the electrical and thermal performance of the innovative system were tested and compared with conventional cogeneration systems. The test and comparison results show that the innovative CHP system could increase the heat utilization efficiency 10% in winter. All the results provide important insight into CHP performance characteristics and could be valuable references for CHP system’s improvements.

Commentary by Dr. Valentin Fuster
2008;():777-785. doi:10.1115/ES2008-54160.

In the last decade, technological innovation and changes in the economic and regulatory environment have resulted in increased attention to distributed energy systems (DES). Combined heating and power (CHP) systems based on the gas-powered internal combustion engine (ICE) are increasingly used as small-scale distribution co-generators. This paper describes an innovative ICE-CHP system with an exhaust-gas-driven absorption heat pump (AHP) that has been set up at the energy-saving building in Beijing, China. The system is composed of an ICE, an exhaust-gas-driven AHP, and a flue gas condensation heat exchanger (CHE), which could recover both the sensible and latent heat of the flue gas. The steady performance and dynamic response of the innovative CHP system with different operation modes were tested. The results show that the system’s overall efficiency could reach above 90% based on lower heating value (LHV) of natural gas; that is, the innovative CHP system could increase the heat utilization efficiency 10% compared to conventional CHP systems, and the thermally activated components of the system have much more thermal inertia than the electricity generation component. The detailed test results provide important insight into CHP performance characteristics and could be valuable references for the control of CHP systems. The novel CHP system could take on a very important role in the CHP market.

Commentary by Dr. Valentin Fuster
2008;():787-792. doi:10.1115/ES2008-54190.

A solid desiccant based ventilation system has been installed to provide ventilation, and cooling/heating as needed, to the Intelligent Workplace (IW) of Carnegie Mellon University, as part of the IW Energy Supply System (IWESS). Since its installation, extensive testing data have been collected and analyzed to characterize the operating performance and cost of each major component, namely the enthalpy recovery module, the active desiccant module, the heat pump module, and the overall system. It has been determined that the active desiccant wheel is expensive to operate due to the high price of natural gas in the current fuel market. In order to improve the energy efficiency and reduce the operating cost of the overall system, it has been proposed to regenerate the active desiccant wheel using the rejected heat from a bio diesel engine generator. Given the temperature and quantity of the rejected heat available, performance maps that relate the supply air temperature and humidity with various system operating variables have been constructed for the proposed integrated system, based on the predictions from an equation-based performance model of the active desiccant wheel. Using the IWESS project as a specific example, a procedure has been outlined for developing operating strategies for the active desiccant wheel integrated Combined Heating and Power (CHP) system.

Commentary by Dr. Valentin Fuster
2008;():793-800. doi:10.1115/ES2008-54252.

In this study, the retrofit project describes the conversion of the air-conditioning system at No.4 College Building in Donghua University in Shanghai China, to a building cooling heating and power (BCHP) system. This includes the optimal retrofit design models of the BCHP system, of which the exergetic efficiency and annual costs (AC) of the system are the separate objective functions. The retrofit scheme is planned to insert gas engines as prime movers into the original system, which have adopted gas-fired absorption chillers. The solutions of the optimization problems show that such retrofit can result in a remarkable rise in exergetic efficiency but is not currently viable with current fuel prices. The contradictory solutions reveal a gap between the current energy prices system of the country and the present energy situation. It is really an urgent task to reform the energy prices system in China. Further investigation gives the critical lines of which each divides the coordinate plane of natural gas-electric prices into 2 parts, viz., of benefit and deficit. It is found if the electric price rises to a certain extent, say a rise of USD0.0238, the retrofit will reach both a positive benefit and a remarkable increase in exergetic efficiency. Discussion and conclusions have been given and may be helpful for other similar retrofit projects that aim to both energy saving and benefits.

Topics: Absorption , Design
Commentary by Dr. Valentin Fuster
2008;():801-808. doi:10.1115/ES2008-54256.

A bioDiesel fueled engine generator with heat recovery from the exhaust as steam and from the coolant as hot water has been installed in the Intelligent Workplace, the IW, of Carnegie Mellon’s School of Architecture. The steam and hot water are to be used for cooling, heating, and ventilation air dehumidification in the IW. This cogeneration equipment is a primary component of an energy supply system that will halve the consumption of primary energy required to operate the IW. This component was installed in September 2007, and commissioning is now underway. In parallel, a systems performance model of the engine generator, its heat recovery exchangers, a steam driven absorption chiller, a ventilation unit, fan coil cooling/heating units has been programmed making use of TRNSYS transient simulation software. This model has now been used to estimate the energy recoverable by the system operating in the IW for different characteristic periods, throughout a typical year in Pittsburgh, PA. In the initial stages of this modeling, the engine parameters have been set at its design load, 27 kW, delivering up to 17 kW of steam and 22 kW of hot water according to calculation. The steam is used in the absorption chiller during the summer and in hot water production during the winter. Hot water is used in desiccant regeneration for air dehumidification during the summer, in IW heating during the winter, and in domestic hot water product year around. Systems controls in the TRNSYS simulation direct the steam and hot water produced in the operation of the engine generator system to meet the IW’s hourly loads throughout seasons.

Commentary by Dr. Valentin Fuster
2008;():809-820. doi:10.1115/ES2008-54314.

A 240 kWe integrated microturbine chiller/heater power system was installed on the campus of the University of Toronto at Mississauga (UTM) in 2005 to provide heating or cooling in combination with electric power generation. The system consists of four 60 kWe microturbines fueled by natural gas and a 110 refrigeration ton (389 kW) lithium bromide absorption chiller that utilizes waste heat from the microturbines. The chiller can be operated in cooling mode to supply chilled water in summer for cooling, or in heating mode to supply hot water (140°F or 60°C) in winter for heating. Campus requirements for electrical power, heating and cooling are presented. Results from operating experience over a two year period 2005–2006 are presented. Recommendations are provided to guide future installations to make full use of the equipment’s potential.

Commentary by Dr. Valentin Fuster

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