储热对中深层套管式地埋管供热系统能效提升的影响

Influence of heat storage on energy efficiency improvement of medium-deep coaxial borehole heating systems

针对中深层套管式地埋管供热系统长期运行存在地下岩土冷堆积、系统取热能力下降等问题,文章建立了中深层套管式地埋管换热器传热数值模型,基于有限差分法对控制方程进行离散,采用实验数据验证模型的准确性。分别研究了储热水温以及储热水质量流量对次年供暖季地埋管取热功率、系统能耗和系统能效的影响。研究结果表明:储热首先应确定储热水温的阈值,进口水温低于阈值将无法实现向岩土储热,该研究工况下的储热水温阈值为50℃,运行500 h后,当进口水温从50℃增加到80℃时,取热功率、系统能耗、能效分别提高54.41 kW,8.96 kW,0.17;当储热水质量流量从1 kg/s提高到7 kg/s时,取热功率、系统能耗、能效分别提高7.71%,6.34%,1.19%。因此,建议采用小流量高水温进行储热,能够提高储热效果并减少能耗。该研究为中深层地源热泵系统储热提供理论基础。

Aiming at the long-term operation of the medium-deep coaxial borehole heating system which has issues of cold accumulation in rock-soil and decrease in the heat extraction capacity of the system,in this research,a numerical heat transfer model for MDGSHPs was established,the governing equations were discretized based on the finite difference method,and the accuracy of the model was verified with experimental data.This research separately studied the effects of heat storage temperature(Tin) and flow rate of hot water injection(G) on BHE heat extraction rate(Q),system energy consumption(W) and the coefficient of system performance(CSP) in the next heating period.The results show that the first step to realize heat storage is to determine the threshold value for the temperature of heat storage water.Below the threshold,heat storage will not be achieved,and the threshold temperature for this study is 50 ℃.After operating for 500 hours,when the inlet water temperature increases from 50 ℃ to 80 ℃,Q,W and CSP increase by 54.41 kW,8.96 k W and 0.17.Furthermore,when the flow rate of hot water injection increases from 1 kg/s to 7kg/s,the growth rate of Q,W and CSP are 7.71%,6.34% and 1.19%.Therefore,a small flow rate with high temperature of heat storage water is recommended during the heat storage period which will improve heat storage effect and reduce energy consumption.This study provides a theoretical basis for heat storage in MDGSHPs.