Numerical investigation on energy efficiency of horizontal heat pump systems in buildings heating and cooling: case study of Mostaganem (Algeria)

Geothermal energy in shallow depth is a locally generated, inexpensive, green renewable energy source. It has proven to be a desirable alternative to fossil fuels for building heating and cooling systems. Horizontal ground heat exchangers (HGHE) coupled to a ground source heat pump are among the shallow geothermal systems. The objective of this study is to investigate the thermal performance of a horizontal U-shaped geothermal heat exchanger for heating and cooling buildings in a region located in northwestern Algeria. Therefore, a three-dimensional transient numerical model based on the finite element method is established using COMSOL multiphysics software. The atmosphere-soil-HGHE interaction and moisture transfer in unsaturated soils are taken into account in this modeling. The effect of pipe length and fluid flow velocity on the performance of horizontal geothermal heat exchangers is also highlighted by this work. The study’s main findings indicate that the heat exchanger’s thermal capacity in summer is approximately 18.11% higher than in winter. This is due to a larger temperature difference between the inlet and outlet water in summer (2.31°C) compared to winter (1.72°C), improving the heat exchanger’s efficiency during summer. The long heat exchange tube is intended to enhance heat transfer. However, the effectiveness of the HGHE is adversely affected by the fact that as fluid velocity rises.