Study on the effect of air–water flow rate ratio of heat source tower on the soil heat storage

Abstract

As direct contact heat exchanger, heat source tower (HST) can absorb the total heat of air by water, and then inject the heat into soil through ground heat exchanger (GHE) for soil heat storage in non-heating season. To achieve an optimal soil heat storage dynamic performance, the air–water flow rate ratio (AWFRR) of the HST and the operation strategy of the soil heat storage system should be optimized. Based on the proposed soil heat storage system and self-built module of the HST, the effects of AWFRR of the HST on soil heat storage characteristics were simulated and discussed in different operation modes with the TRNSYS software. In mode A, the values of AWFRR are the same during the whole non-heating season. While in mode B, the values of AWFRR are different during the transition season and cooling season. The results show that the soil heat storage capacity increases obviously with the increasing of AWFRR under specific water mass flow rate. About 64 % of the total soil heat storage capacity in the non-heating season comes from the soil heat storage capacity by HST in the cooling season. The coefficient of performance (COP) of the soil heat storage system first increases and then decreases with the increasing of AWFRR, and there is an optimal AWFRR under specific water mass flow rate to obtain the highest COP. The amounts of soil heat storage capacity, energy consumption and COP of mode A and mode B are similar, and mode A can be assumed to be the more suitable operating mode for its simple operation in engineering application. After optimization of mode A, not only the operating time of the system is reduced from 4440 h to 3264 h, but also more soil heat injection, less energy consumption and higher COP are achieved. To meet the needed soil heat storage of the proposed building in Changchun, the AWFRR and water mass flow rate in mode A should be 0.7 and 7.7 kg/s respectively.