Comparison and analysis on air-to-air and air-to-water heat pump heating systems

In order to solve the problems of atmospheric pollution and haze caused by traditional coal-fired heating, the promotion and application of clean energy heating methods is urgently needed. The air-source heat pumps are applied in the residential buildings to replace traditional coal-fired heating in Beijing and Tianjin. Limited to the cost and economic conditions, air-source heat pumps are usually installed with the traditional steel radiator. The unreasonable selection and operation of equipment can lead to low energy efficiency of partial load operation. The importance of finding an economical and efficient alternative scheme, therefore, is beyond words. The experimental research and computational fluid dynamics simulation on the performance and air distribution of air-to-air heat pump and air-to-water heat pump under the same operating conditions are done in this paper. The results demonstrate that ATAHP has bigger heating capacity than ATWHP, the decrease of the actual operation COP of ATAHP is 28.30% which is smaller than that of ATWHP by 15.45% with the ambient temperature decreasing from 7 °C to −20 °C. Thus, ATAHP is better than ATWHP at low temperature operation conditions. The temperature and velocity distribution of indoor air with ATWHP is more uniform, but the high speed air with high temperature with ATAHP blows to the head and feet directly. Consequently, the air distribution with ATAHP is more in line with the requirements of thermal comfort. To conclude, ATAHP has better performance and thermal comfort, and ATAHP is more suitable than ATWHP to be applied and popularized in northern China.