Horizontal Ground Heat Exchangers

Abstract

This study aims to present a comparison between temperature measurements relative to horizontal ground heat exchangers with predicted values using thermal response test. A scale 1 test facility of horizontal ground heat exchangers has been implemented in BRGM (Orleans -France) to test performances in real conditions. The heat exchanger is divided in four parts of 100 m² each with different characteristics:a sunny grass -a shaded grass -a sunny car-park -a shaded car-park These different configurations have been chosen to compare the performances of ground heat exchangers in different environments (surface state, boundary conditions). Furthermore, the temperature in the soil is measured continuously at 3 different levels (-0.5 m, -1 m, -1.5 m). To cartography the temperature field at these 3 depths, optical fibers are distributed in the underground and the use of a distributed temperature sensor (DTS) allows to accurately measure the temperature in the soil surrounding the ground heat exchanger.A thermal response is carried out on the horizontal ground heat exchanger. A monitored constant heating power is injected at a constant mass flow. The temperature measurements at the 3 different levels of a threedimensional numerical model of ground heat exchanger.The thermal response test gives in particular the noticeable differences between the 4 different conditions of each part of the ground heat exchanger. The conclusion will give indications on the consequences of uncertainty about soil thermal properties on sizing.