Influences of seasonal changes of the ground temperature on the performance of ground heat exchangers embedded in diaphragm walls: A cold climate case from North China

Compared with ground heat exchangers (GHEs) in typical vertical boreholes with depth of 100–120 m, GHEs embedded in the diaphragm wall of buildings are more easily affected by periodic changes of the shallow ground temperature. Here we numerically solve the heat transfer model of the diaphragm wall with GHEs considering actual ground temperature boundary conditions in cold climate region, North China, and investigate the influences of seasonal variations of the ground temperature on heat transfer performance of GHEs. Results show that due to the above seasonal effect, the heat exchange performance of GHEs may decrease to different extent especially in relatively shallow diaphragm walls, thereby causing non-negligible design deviations. Under the present geometric and climate conditions, as the depth of GHEs increases, the maximum thermal influence distance from the diaphragm wall tends to increase during the cooling season and decrease during the heating season, respectively. The optimal spacing between GHE groups ranges from 0.5 to 0.9 m, and though a high construction cost, a smaller spacing is more favorable for improving the overall energy efficiency. The present work is expected to provide useful references for optimal design and performance prediction of GHEs embedded in diaphragm walls with similar climate conditions.