Air cycle heat pumps

Abstract

Air cycle refrigeration and heat pump were one of the earliest forms of cooling or heating. In recent years, the development of air cycle refrigeration/heat pump system with moderate capacity of cooling has become unpromising in automotive or home use until the seriousness of ozone-depletion and global-warming potentials from CFC refrigerants was widely recognized. The heat pump operating with reversed Brayton cycle that employs air as the refrigerant, which is environmental friendly, seems to be necessarily reexaminated for domestic and other heating service, especially, due to the confluence of a number of technical advances, such as small physical size and reasonable efficiency of turbomachine, together with the development of air bearings and ceramic components. The prospect of using natural air appears to have been one of the driving forces behind this renewed interest in air cycle refrigeration/heat pump. In this chapter, the fundamental models regarding a fully open ideal air cycle heat pump with regenerative heat exchanger are derived and the COP of semiopen cycle air heat pump cycle hot water system for domestic heating is introduced considering thermodynamic losses from polytropic expansion and compression efficiencies as well as pressure loss factors. Moreover, a semi-open air cycle heat pump water heater system (ACHPWH) with each component (such as an expander, a compressor, heat exchangers, a water tank) by considering both design and off-design conditions is discussed. An air cycle heat pump with a turbocharger and a blower is evaluated.