Experimental evaluation of an earth-to-air heat exchanger and air source heat pump hybrid indoor air conditioning system

Earth-to-air heat exchanger (EAHE) technology is promising for space heating/cooling. However, in most climates, EAHE alone cannot provide indoor thermal comfort. Hybrid systems combining an EAHE and an air-source heat pump (ASHP) can be used for indoor temperature regulation and energy conservation. We performed full-scale experiments to investigate the hybrid system performance for a building located in a typical hot-summer and cold-winter region of China. Variations in EAHE outlet/indoor air temperature, humidity, cooling/heating loads, energy consumption, and coefficient of performance (COP) were investigated. The results demonstrate a maximum reduction of 14.2 degrees C during summers and maximum gain of 8.2 degrees C during winters for the EAHE outlet air temperature, when the air-change rate per hour reaches 16.0. Moreover, the EAHE dehumidifies 1.95 g/kg moisture on average in summer, approximately accounting for 36.2 % of the dehumidification capacity of the hybrid system, with more dehumidification capability for high moisture contents. Compared with an independent ASHP for specific ambient air temperature and humidity ranges, the proposed system exhibits an average energy consumption reduction of 50.91 % and 16.78 %, increases COPASHP by 65.42 % and 11.21 %, and increases COPt by 145.37 % and 82.63 % during the summer and winter periods, respectively. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Earth-to-air heat exchanger (EAHE) technology shows promise for space heating/cooling but is usually not sufficient for indoor thermal comfort alone. Hybrid systems combining EAHE and an air-source heat pump (ASHP) can regulate indoor temperature and conserve energy. Full-scale experiments were conducted for a building in a typical hot-summer and cold-winter region in China, demonstrating the system's ability to cool and heat indoor air during summer and winter, respectively.