Abstract

Commercially available heat pumps have traditionally relied upon fluorocarbon working fluids commonly known as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). These fluids are recognized as substances which destroy the earth’s ozone layer, and they are being phased out of production and use. Hydrofluorocarbons (HFCs) have been proposed as the next industry standard, but HFCs have extremely high global warming potential and, like their predecessors, are subject to regulation by the U.S. Environmental Protection Agency under provisions of the U.S. Clean Air Act. Similar restrictions exist internationally. HFCs are also costly and impose a handling and maintenance logistics burden, and in some cases pose performance limitations in high ambient temperatures. Consequently, they may represent only an interim solution for military air-conditioning and refrigeration needs.

On the other hand, carbon dioxide is inexpensive, safe, widely available, and fundamentally feasible. Operating at substantially higher working pressures, carbon dioxide (CO2) offers the potential of lighter, more compact systems, as well as providing environmental, performance, and logistics advantages that are attractive for military applications. With CO2, the Army sees the potential for smaller, lighter, systems with lower life-cycle costs. The U.S. Army Communications and Electronics Command’s Research, Engineering and Development Center has developed a first prototype packaged-unitary compact CO2 heat pump built within the physical constraints of existing Army ECUs (Environmental Control Units),. The performance of this unit has been further improved by the addition of an internal suction line heat exchanger. The unit is lighter in weight than the current military standard unit. When tested under a range of military operational conditions, it achieves a higher Coefficient of Performance (COP) but a lower capacity, than the military standard unit.

This paper will address the Army’s CO2 Development Program, with emphasis on fabrication and testing of the improved CO2 heat pump.

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