Two-stage air-source heat pump for residential heating and cooling applications in northern U.S. climates

Air-source heat pumps for residential heating are more widely used than geothermal heat pumps mainly due to their lower installation costs. Major disadvantages of air-source heat pumps are the decrease of heat output and coefficient of performance (COP), and increase in discharge temperature, towards low outdoor temperatures. In this paper an air-source two-stage heat pump using R410A as the refrigerant was simulated, designed, constructed, and tested at ambient temperatures as low as −30 °C and supply temperatures of up to 50 °C in air and water heating mode. In addition, the system is able to provide sufficient air conditioning in cooling mode (approximately 50–60% of the design heat transfer rate in heating mode). A short summary of an extended literature review is shown as well as a theoretical screening study of the three most promising cycles. Furthermore, the design and test results of a breadboard system and a comparison with commercially available heat pumps are presented. Second law efficiencies of up to 45% could be achieved, resulting in a coefficient of performance (COP) of 2.1 at −30 °C ambient temperature.