Analysis of heat transfer performance of stepped phase change material energy pile

The effect of backfilled phase change material (PCM) on heat transfer performance of energy pile during heat storage and heat extraction was studied. A new phase change pile structure named the stepped phase change energy pile. The numerical heat transfer model was established by Comsol Multiphysics, and the heat transfer effect of single PCM, stepped PCM and gravel backfill energy pile were analyzed. The results show that: during the heat storage stage, the heat storage capacity of single PCM backfilled and stepped PCM backfilled energy pile is increased by 14.01 % and 18.98 %, compared to gravel backfilled, and the heat response radius is 0.28 times and 0.46 times that of gravel backfilled; in the heat extraction stage, the heat extraction of single PCM backfill and cascade PCM backfill energy pile is 13.32 % and 31.23 % higher than that of gravel backfill, and the heat response radius is 0.16 times and 0.44 times of gravel backfill.