Feasibility study on applications of an Earth-air Heat Exchanger (EAHE) for preheating fresh air in severe cold regions

Due to high power consumption and air pollution situation in China, insufficient indoor fresh air during heating season can be a noteworthy problem. Unlike previous researches, which mainly focused on cooling capacity of Earth-air Heat Exchanger (EAHE), feasibility of EAHE combined with Heat Recovery Unit (HRU) as an independent heat source to heat cold air in severe cold regions was firstly verified. U-shaped buried pipes were proposed to enhance heat transfer as well as save land-use. Thorough measurements of air and soil parameters and power consumption were conducted under several operation modes, performance indexes like heating capacity, heat transfer efficiency and COP were analyzed. Results showed average temperature rise of 14.0 °C provided by EAHE and further 12.1 °C promotion brought by HRU helped outdoor air reach to an acceptable level without auxiliary heating equipment. Heating capacity of EAHE increased with decreasing inlet temperature, when inlet temperature changed from −0.4 to −24.4 °C, heating capacity increased from 709 W (19.7 W/m) to 7718 W (214.4 W/m). Performance of HRU rarely reacted to climatic conditions because of the stable outlet temperature of EAHE. Maximum comprehensive COP was 16.3, which indicated the high efficiency of system. Results showed EAHE can be expanded to severe cold regions and achieve good efficiency.