Experimental Evaluation of Return Air System Integrated with an Earth-to-Air Heat Exchanger in Winter

In order to mitigate the change of soil temperature near the buried pipe and to recover the relatively hot air in the room, this study proposed a combined model of earth-to-air heat exchanger and return air system, i.e., EAHE-RA system. The indoor air released from the door and window gaps was recovered by the return air system, mixed with fresh outdoor air in the mixing box and sent to the EAHE. We conducted a full-scale comparison experiment (traditional EAHE system and EAHE-RA system) in winter. The variation of EAHE inlet air temperature and humidity, outlet air temperature and humidity, indoor air temperature and humidity and EAHE heating capacity were researched. The results showed that the EAHE-RA system (Mode 2(I), Mode 2(II) and Mode 2(III)) increased the EAHE inlet average air temperatures by 6.8 °C, 5.9 °C and 4.7 °C, respectively, during the winter season. Compared to the traditional EAHE system (Mode 1), the average values of EAHE heating capacity were decreased by 588.7 W, 495.3 W, and 477.7 W, respectively, and the average values of return air heat recovery were 1223.4 W, 930.6 W, and 858 W, respectively.