地埋管群冷热负荷对岩土体温度及热泵效率的影响
Influence of Borehole Heat Exchanger (BHE) Array Cooling and Heating Load Ratio on the Ground Temperature Imbalance and the Heat Pump Efficiency
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摘要: 地埋管群(borehole heat exchangers,BHEs)是浅层地热资源有效利用的最常见形式。然而由于冷热负荷差异导致的埋管群周围岩土体温度不平衡现象是造成地源热泵(ground source heat pump,GSHP)效率(coefficient ofperformance,COP)逐年降低的重要因素。本文以加热为主工况下地埋管群周围岩土体温度与热泵效率为研究指标,采用经现场热响应试验(thermal response test,TRT)验证的有限元方法(finite element method,FEM),建立等进口温度运行模式的三维有限元模型。研究结果表明埋管群中心岩土体温度在无制冷负荷下,初始温度由16℃降低至5年后的5.3益,且冷热负荷比介于2/3~1时,有利于维持岩土体温度平衡。当负荷比由0提高到1时,热泵加热效率从3.8提升至4.5。相反,冷热负荷比的升高不利于制冷季节热泵效率的提升,当负荷比由0提高到1时,热泵制冷效率由7.2降至6.1。本文可为以加热为主工况的地埋管群冷热负荷合理制定与岩土体储能工程提供参考。Abstract: Borehole heat exchangers (BHEs) are the most common utilization of shallow geothermal resources. However, the ground temperature imbalance around the BHEs caused by the difference in cooling and heating loads is an important factor causing the low coefficient of performance (COP) of ground source heat pump (GSHP). In this paper, the ground temperature around the BHEs and the efficiency of the heat pump are taken as the research object, and the finite element method (FEM) verified by the thermal response test (TRT) is utilized to establish a 3D finite element model with the same inlet temperature. The research results show that the ground temperature in the center of the BHEs decreases from 16 ℃ to 5.3 ℃ after five years without cooling load, and when the cooling and heating load ratio is between 2/3 and 1, the ground temperature can maintain a considerable balance. When the load ratio increases from 0 to 1, the heating efficiency of the heat pump increases from 3.8 to 4.5. On the contrary, the increase of the cooling and heating load ratio is not beneficial to the improvement of the heat pump efficiency in the cooling season. When the load ratio increases from 0 to 1, the cooling efficiency of the heat pump decreases from 7.2 to 6.1. This paper can provide a reference for formulating the cooling and heating load of BHEs, as well as give guidance for the ground energy storage projects using BHEs.