24 June 2014

Insights from field experiments to conduct thermal respone tests with a low power source

The assessment of the subsurface thermal conductivity with a conventional
thermal response test is a costly procedure that has to be paid at the forefront of a geothermal heating and cooling project. Prohibitive cost, which is a drawback to geothermal
technologies, can be avoided by reducing the power needed to conduct such tests. The conventional test method with flow of heated water in the ground heat exchanger is however
not suited for low power. An alternative method using interchanging sections of heating cable to inject heat underground with a 120 V and 10 A power source is described in this study.
Preliminary field tests, conducted to understand heat transfer phenomena, showed that recovery temperatures can be analyzed with a heat conduction solution when disks are placed at the extremities of the heating sections to reduce free-convection in the standing
water column of the ground heat exchanger. The proposed method is expected to provide a subsurface thermal conductivity profile using less than 10 % of the energy required for a
conventional thermal response test.