竖直U型埋管地热换热器热短路现象的影响参数分析

通过引入换热器出口最高流体温度的概念,对地源热泵竖直U型埋管地热换热器的热短路现象进行了量化,基于竖直U型埋管周围的瞬时有限元模型,对影响热短路现象的主要参数(支管间距和回填料导热系数)进行了模拟分析,得出了量化结果。结果表明,增大支管间距可降低换热器出口最高流体温度,减小由热短路现象引起的热损失;回填料的导热系数对热短路现象的影响较大,当回填料导热系数小于周围土壤的导热系数时,增大回填料导热系数对减小热短路损失有较大作用,而当回填料导热系数大于土壤导热系数时则作用不大,推荐使用导热系数与周围土壤导热系数接近的回填材料。

PARAMETRIC ANALYSIS OF THERMAL INTERFERENCE IN VERTICAL U-TUBE HEAT EXCHANGERS FOR GCHP

The concept of maximum heat exchanger outflow temperature was introduced to quantify the thermal interference in vertical U-tube heat exchangers for ground-coupled heat pump(GCHP).A transient finite-element model of the heat transfer around a vertical U-tube heat exchanger was set up.Two main parameters(separation distance and backfill ther- mal conductivity)that affect the thermal interference were studied according to this model and quantified results were achieved.Results show that the maximum heat exchanger outflow temperature decreases with the increasing of separation distance and it is easily affected by thermal conductivity backfill.For backfills with lower thermal conductivity than sur- rounding soil,the maximum heat exchanger outflow temperature falls as backfill thermal conductivity increases,but for those with higher thermal conductivity than surrounding soil,increasing of backfill thermal conductivity has just a little effect.It is recommended to use backfill materials which have the same thermal conductivity as the surrounding soil.