Performance of a drainage trench employed as ground heat exchanger

Novel shapes of horizontal ground heat exchangers coupled with ground-source heat pumps represent a viable and efficient option for shallow geothermal plants. Here, the thermal performance of a drainage trench employed as a ground heat exchanger is studied. The 12 x 2 x 0.25 m trench is dug in shallow soil and filled with gravel; two tubes at the opposite ends of the trench act as inlet and outlet of the working fluid, flowing into the closed-loop of a system for heating/cooling of a residential building. Groundwater flow and heat transfer in the porous domain surrounding the trench are analysed via a 3D numerical model performing a 3-year simulation. The thermal impact of the exchanger is analysed considering different boundary conditions (1st/2nd kind), given as daily time series at the ground surface. The trench shows a good specific energy production and a significant capacity of smoothing thermal waves, and can be considered a convenient alternative to the flat-panel.