| Abstract |
This project was initiated by the Department of Energy in response to a request from the HVAC industry for consolidated information about alternative heating and cooling cycles and for objective comparisons of those cycles in space conditioning applications. Twenty-seven different heat pumping technologies are compared on energy use and operating costs using consistent operating conditions and assumptions about component efficiencies for all of them. This report provides a concise summary of the underlying principals of each technology, its advantages and disadvantages, obstacles to commercial development, and economic feasibility. Both positive and negative results in this study are valuable; the fact that many of the cycles investigated are not attractive for space conditioning avoids any additional investment of time or resources in evaluating them for this application. In other cases, negative results in terms of the cost of materials or in cycle efficiencies identify where significant progress needs to be made in order for a cycle to become commercially attractive. Specific conclusions are listed for many of the technologies being promoted as alternatives to electrically-driven vapor compression heat pumps using fluorocarbon refrigerants. Although reverse Rankine cycle heat pumps using hydrocarbons have similar energy use to conventional electric-driven heat pumps, there are no significant energy savings due to the minor differences in estimated steady-state performance; higher costs would be required to accommodate the use of a flammable refrigerant. Magnetic and compressor-driven metal hydride heat pumps may be able to achieve efficiencies comparable to reverse Rankine cycle heat pumps, but they are likely to have much higher life cycle costs because of high costs for materials and peripheral equipment. Both thermoacoustic and thermionic heat pumps could have lower life cycle costs than conventional electric heat pumps because of reduced equipment and maintenance costs although energy use would be higher. There are strong opportunities for gas-fired heat pumps to reduce both energy use and operating costs outside of the high cooling climates in the southeast, south central states, and the southwest. Diesel and IC (Otto) engine-driven heat pumps are commercially available and should be able to increase their market share relative to gas furnaces on a life cycle cost basis; the cost premiums associated with these products, however, make it difficult to achieve three or five year paybacks which adversely affects their use in the U.S. Stirling engine-driven and duplex Stirling heat pumps have been investigated in the past as potential gas-fired appliances that would have longer lives and lower maintenance costs than diesel and IC engine-driven heat pumps at slightly lower efficiencies. These potential advantages have not been demonstrated and there has been a low level of interest in Stirling engine-driven heat pumps since the late 1980s. GAX absorption heat pumps have high heating efficiencies relative to conventional gas furnaces and are viable alternatives to furnace/air conditioner combinations in all parts of the country outside of the southeast, south central states, and desert southwest. Adsorption heat pumps may be competitive with the GAX absorption system at a higher degree of mechanical complexity; insufficient information is available to be more precise in that assessment. |
