PROGRAM AREA OVERVIEW

26. INNOVATIVE WASTE HEAT RECOVERY TECHNOLOGY AND NOVEL COOLING SYSTEMS

Many processes, especially in industrial applications, produce large amounts of excess heat – i.e., heat beyond what can be efficiently used in the process. Waste heat recovery methods attempt to extract some of the energy as work that otherwise would be wasted. Typical methods of recovering heat in industrial applications include direct heat recovery to the process itself, recuperators, regenerators, and waste heat boilers. In many applications – especially those with low-temperature waste heat streams, such as automotive applications – the economic benefits of waste heat recovery do not justify the cost of the recovery systems. Innovative, affordable methods that are highly efficient, applicable to low-temperature streams, and/or suitable for use with corrosive or “dirty” wastes could expand the number of viable applications of waste heat recovery, as well as improve the performance of existing applications. The focus of this topic is on the development of innovative waste heat recovery processes and techniques that are (1) more efficient than conventional methods, yet still cost-effective; and (2) applicable to waste streams from which heat cannot be recovered easily with conventional methods.

Turning to cooling, air conditioning systems consume approximately 10% of the energy used in U.S. buildings and are key contributors to peak demand. Consequently, improving the energy efficiency of air conditioning systems would substantially reduce overall energy consumption and enhance grid reliability. For example, compressors require cooling to dissipate the heat produced during compression and could benefit from improved surface heat transfer – innovative designs could increase the available heat-transfer area or materials enhancement could increase the heat flux between the hot and cool sides of a heat exchanger. Similarly, a reduction in the requirement for condenser cooling could provide significant energy savings if more-efficient, cost-effective technologies were developed. Grant applications are sought only in the following subtopics:

a. Novel Equipment and Materials for Industrial Waste Heat Recovery—The recovery of waste heat from exit gases can significantly increase the energy efficiency of industrial processes. Energy can be recovered from flue and stack gases, vent gases, and combustion gases at a variety of temperatures at large-scale industrial plants (chemical plants, petroleum refineries, biorefineries, pulp and paper mills, etc.). Grant applications are sought to develop novel equipment and materials for the recovery of this waste-heat energy. Areas of interest include: (1) waste heat boilers capable of recovering heat from corrosive streams, including the development of corrosion-resistant coatings for both low and high temperature applications; (2) improved heat transfer from new heat exchanger geometries and innovative fluids (used in closed-loop systems), for use in waste heat recovery applications; (3) thermally-activated refrigeration and heat pump systems driven by waste heat rather than direct gas firing; (4) development of advanced cycles and working fluids, which would increase temperature lift in absorption cycles and improve overall heating and cooling performance; and (5) cost-effective thermoelectric or thermoionic materials capable of producing electricity from heat, with at least 15% thermal efficiency.

b. Automotive Waste Heat Recovery—The growing demand for electric power in vehicles is currently being met with inefficient, pulley-driven mechanical generators that are driven off of the vehicle engine. Although improvements in generator efficiency have been on-going, it is the nature of such systems to rob the engine of shaft power, thereby decreasing overall system efficiency. In contrast, extracting electricity from the energy lost to engine exhaust or from the coolant loop would be, essentially, "free energy" and would improve overall system efficiency. As an example, in a spark-ignited automobile, 30% to 40% of the fuel energy is lost out the exhaust pipe, and an additional 30% is lost through the radiator. Recovering a portion of these heat losses as electricity could enable radical hybridization and allow spark-ignition technology to compete with diesel on an efficiency basis. Therefore, grant applications are sought to develop:

(1) Thermoelectric or thermionic energy conversion devices for the direct conversion of exhaust or coolant-rejected heat to electricity with conversion efficiencies greater than 15%. The devices should be able to provide power generation or heating/cooling for automotive applications within the cost criteria for commercial production.

(2) New approaches to recuperative or regenerative engine operating cycles, including modified compression/expansion ratio control. Such approaches would decrease the amount of energy expended, and consequently increase the proportion and amount of useful work produced, during the combustion process.

(3) Electric turbo-compounding systems that produce more electric power and provide higher overall engine efficiencies than current turbocharger systems. These electric turbo-compounding technologies should deliver over 1.5 kW of electric power for 2500 hours and increase overall engine efficiency by 10 percent or more.

Applications for technologies that merely reiterate currently-commercial technologies will not be considered.

c. Novel Cooling Systems for Buildings—Nearly all air conditioners sold in the U.S. are based on vapor compression technology, and the service, installation, and technical infrastructure to support this technology is well-established. Achieving air conditioner efficiency breakthroughs will require entirely new (non-vapor compression) approaches, revolutionary changes to traditional vapor compression systems, or new ways of operating conventional vapor compression systems. Therefore, grant applications are sought to design, develop, and demonstrate: (1) high efficiency non-vapor compression technologies, including but not limited to those listed above, that have the long term potential to achieve efficiencies much higher than conventional vapor compression systems, at modest cost premiums; (2) component technologies for vapor compression systems that can contribute to major improvements in system efficiency at modest cost—systems with reduced global warming potential are also desirable; or (3) technologies that facilitate new operational strategies for conventional vapor compression cooling, in order to substantially reduce energy consumption and possibly provide other non-energy benefits such as enhanced comfort, at modest cost. All grant applications must provide detailed estimates of the cost-effectiveness of the proposed technologies.

With respect to (1) above, numerous non-vapor compression cooling system approaches have been explored in the past, including thermally-activated absorption and adsorption, Stirling cycle, magnetic refrigeration, thermo-acoustic refrigeration, Malone refrigeration, and others. Aside from specialty applications where particular characteristics (e.g. very long life, ultra-high reliability) are necessary, few of these alternatives have gained significant commercial acceptance due to the high costs and low projected efficiencies. However, advances in materials, electronics, sensors and controls may provide new opportunities for improved efficiency at acceptable costs. In particular DOE’s Zero Energy Home (ZEH) project has called for the development of high efficiency systems with low cooling capacities (e.g. 1 ton) – improvements to some of the alternative approaches listed in this paragraph may be effective at these lower capacities.

With respect to (2) above, Direct Expansion (DX) systems like unitary central residential and commercial rooftop air conditioners, which are available in a variety of efficiency levels, account for the bulk of air conditioner energy consumption. Residential systems are available with Seasonal Energy Efficiency Ratio (SEER) levels from 10 (the minimum efficiency allowed by standards) to approximately 18, while rooftop units are available with Energy Efficiency Ratios (EERs) from approximately 9-12. However, the units with the highest efficiencies are too expensive to achieve any significant market acceptance, particularly in residential capacities. These high efficiencies are often achieved by adding large amounts of heat exchanger coil area and/or multiple compressors, leading to system sizes and costs that are unacceptable to consumers. Achieving dramatic increases in the efficiency of these vapor compression systems will require completely new designs for key components such as compressors, heat exchangers, fans, blowers, and motors. Examples might include variable capacity compressors that maintain high efficiency throughout their operating range, without the need for expensive inverters; new approaches for enhancing the heat transfer of heat exchanger coils using new materials or fabrication processes; or the application of advanced electronics and sensors.

With respect to (3) above, the energy consumption of conventional air conditioning systems could be reduced by adding features that allow the systems to operate more intelligently. Examples include: using adaptive/fuzzy logic controls to enhance comfort and indoor environmental quality while reducing energy consumption, providing real-time energy-use feedback to consumers in order to change their usage patterns, optimizing operations based on current or predicted outdoor and occupancy conditions, and improving zone control using approaches such as microenvironments or automated ductwork-damper systems with occupancy sensing.

d. Air-Cooled Condenser Enhancements—Air-cooled condensers, using banks of finned tubes with forced or inductive cooling airflow, are used in binary (organic Rankine cycle) geothermal power plants, in bottoming cycles for combined cycle power plants, and for waste heat recovery. A major challenge is to maximize the airside heat transfer at fixed or reduced airside pressure drop. Grant applications are sought to: (1) enhance the airside heat transfer coefficient via boundary layer renewal or flow control, using innovative devices such as small transverse fins (tabs) on the major fins, unique fin types such as pleated fins with flow through small holes in the fins, or vortex generators to direct flow into the wake region; (2) increase the effective temperature difference by using a water stream in contact with the incoming air to reduce the air temperature by evaporative cooling, or by dripping or flowing a limited amount of water over the fins and tubes (deluge cooling); or (3) decrease the parasitic power requirement by minimizing the pressure drop while maintaining constant heat transfer through an improved the airside flow path, or by innovative changes in the fan so that it moves more air with less energy.

References:

1. A Research Needs Assessment: Energy Efficient Alternatives to Chlorofluorocarbons (CFCs), prepared by Arthur D. Little, Inc. for U.S. DOE Office of Energy Research, June 1, 1993. (Report No. DOE/ER/30115-H1)(OSTI ID: 766411) (Full text available at: http://www.osti.gov/energycitations/search.easy.jsp. Under Identifier Numbers, search for 766411.)

2. Roth, K. W., et al., Energy Consumption Characteristics of Commercial Building HVAC Systems, Volume III: Energy Savings Potential, Technical Report, prepared by TIAX, LLC for U.S. DOE, July 2002. (NTIS Order No. PB2002-107657)*

3. Positioning for the Future: Strategic Planning for the HVACR Industry, prepared by J. M. Tooman, Inc. for the Air-Conditioning and Refrigeration Technology Institute, December 2001. (Available at: http://www.arti-21cr.org/21crstra/)

4. Fischer, S. K. and Labinov, S. D., Not-In-Kind Technologies for Residential and Commercial Unitary Equipment, Oak Ridge, TN: Oak Ridge National Laboratory, December 11, 2001. (Report No. ORNL/CON-477) (Available at: http://www.osti.gov/bridge/search.easy.jsp)

5. Hendricks, T. J. and Lustbader, J. A., “Advanced Thermoelectric Power System Investigations for Light-Duty and Heavy-Duty Vehicle Applications: Part I,” Proceedings of the 21^st International Conference on Thermoelectrics, Long Beach, CA, August 25-29, 2002, pp. 381-386, 2002. (ISBN: 0-7803-7683-8) (IEEE Catalogue No. TH8657)

6. Hendricks, T. J. and Lustbader, J. A., “Thermoelectric Energy Recovery Systems in Future Advanced Vehicles,” Proceedings of the 6^th ASME-JSME Thermal Engineering Joint Conference, Hawaii Island, Hawaii, March 16-20, 2003, Tokyo, Japan: Japan Society of Mechanical Engineers, 2003. (JSME Paper No. A4-334) (JSME Web site: http://www.jsme.or.jp/English/)

7. Crane, D. T. and Jackson, G. S., “Systems-Level Optimization of Low-Temperature Thermoelectric Waste Heat Recovery,” Proceedings of the 37^th Intersociety Energy Conversion Engineering Conference, Washington, DC, July 31, 2002, IEEE, August 2003. (ISBN: 0780372964) (IECEC Paper No. 20076)

8. Van Godbold, C., et al., “Thermal Analysis of High Power Modules”, IEEE Transactions on Power Electronics, 12(1):3-11, January 1997. (ISSN: 0885-8993)

9. Ross, P. E., “Beat the Heat”, IEEE Spectrum, 41(5):38-43, May 2004. (ISSN: 0018-9235)

10. FreedomCAR and Vehicle Technologies Multi-Year Program Plan, U.S. DOE, Office of FreedomCAR and Vehicle Technologies, undated. (Full text available at: http://www.eere.energy.gov/vehiclesandfuels/resources/fcvt_mypp.shtml)

11. Pellegrino, J., et al., Energy Loss Reduction and Recovery in Energy Systems Roadmap, Columbia, MD: Energetics, Inc. August 2004. (Available from Kevin Stork. Email: kevin.stork@hq.doe.gov. Please use 'Pellegrino SBIR references' as Subject of email.)

12. Pellegrino, J., Thekdi, A., et. al., Opportunities for Energy Loss Reduction and Recovery, Columbia, MD and North Potomac, MD: Energetics, Inc. and E3M, Inc., August 2004. (Available from Kevin Stork. Email: kevin.stork@hq.doe.gov. Please use 'Pellegrino SBIR references' as Subject of email.)

13. Kutscher, C. F.; and Gawlik, K. (Inventors) Heat Exchanger with Transpired, Highly Porous Fins. (U.S. Patent No. 6,378,605 B1of 4/30/2002) (Available at http://www.uspto.gov/patft/)

14. Sohal, M. S. and Mines, G. L. “Enhancement of Air Cooled Condenser Performance,” Proceedings of Geothermal Resources Council Annual Meeting, Morelia, Mexico, October 12-15, 2003, Davis, Ca: Geothermal Resources Council, 2003, 4 pages. (ISSN: 0193-5933) (Copy of 4-page paper available from Geothermal Resources Council at www.geothermal.org. In the red bar at the top of the page, click on “Search the GRC library”. At the center of the page click on “Order form” written in red. Follow the instructions on the order form, and include an attachment containing this citation.)

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