Air-source heat pump systems

Abstract

Applying heat pumps to space heating for residential buildings in cold regions will reduce the combustion of gas, oil, and other fossil fuels and the emissions of greenhouse gases. An air-source heat pump (ASHP), which uses the easily available air as heat source, is more easily deployed and applied than other types of heat pumps, such as geothermal heat pumps. In terms of an ASHP, however, it is hard to effectively maintain a high capacity all the time not only because of a variety of instantaneous loads and demands affecting efficiency curves but also due to the unstable outdoor air temperature and humidity during summer and winter seasons. These uncertainties will increase the difficulty to control, rate, and select ASHP units. Moreover, when an ASHP runs at low ambient temperatures, several problems restrict its applications, deteriorated heat output, high discharge temperature, and declining coefficient of performance (COP), due to an increase of the pressure ratio. The high discharge temperature may even result in an abnormal shutdown of the system. This chapter principally probes into discussions regarding ASHP systems, including the topics of system components, system performance ratings, defrosting methods, system design selections, unit(s) energy regulations, as well as installation considerations and technical measures. Additionally, this chapter also covers the most updated concepts to promote the performance of ASHP, including the subcooling cycle, the multistage cycle, the throttling losses recovery cycle, the multifunction cycle, the saturation cycle, and the frost-free system.