The Influence of Atmospheric Air Temperature and Humidity on the Heat Pump COP

The use of energy-saving technologies for heat supply to buildings is relevant for Russia, since in most regions of the country, long winters result in significant costs for heating. Interest in the use of air heat pumps for these purposes is observed all over the world. However, in the majority of regions, the atmospheric air temperature during the heating season is in the region of negative values. Under such conditions, the air heat pump coefficient of performance (COP) is significantly poorer in comparison with that of heat pumps operating on other low-grade thermal energy sources. The simplest and most cost-effective process cycle circuit of heat pumps using low-grade atmospheric heat has limitations in application stemming from significant temperature variations not only during the heating season, but also during the day. Factors influencing the air heat pump COP are considered: atmospheric air temperature and relative humidity, and frost formation on the evaporator walls during operation in the range of negative temperatures. The evaporator defrosting cycles are calculated taking into account the atmospheric air thermal and humidity characteristics. A defrosting method involving the use of heating elements placed in between the heat transfer tubes has been chosen. The studies were conducted in the Chelyabinsk region (in the heating season 2022-2023). During the study period, the heat pump COP varied in the range from 3.78 to 2.18. In evaluating the heat pump COP, the energy consumed for the defrosting mode was taken into account; as a result, the pump COP was found to be in the range from 3.6 to 1.57, and the seasonal COP became by 9.26% lower. This circumstance should be taken into account in choosing the air heat pump capacity.