New concept of combined hydro-thermal response tests (H/TRTS) for ground heat exchangers

• Groundwater flow can affect the sizing of vertical ground heat exchangers.
• Standard tests only measure ground average thermal conductivity.
• A new test is introduced to estimate groundwater velocity and direction.
• Numerical simulations are performed to evaluate the potential of the test.
• Simulation shows that the test offers satisfactory estimates of ground properties.

Current thermal response tests, used to estimate the subsurface thermal conductivity in the geothermal domain, are not designed to take into account groundwater flows. To measure the flow parameters, a new concept has been developed. Heating cables are installed within a borehole in contact to the formation, with three temperature probes strategically located at the edge of the borehole. Study of the evolution of temperature for each probe during both a heat injection phase and a recovery period allows determining ground thermal conductivity, groundwater flow velocity and orientation. Numerical simulations have been used to validate the proposed concept and establish its limits.