Field demonstration of a first thermal response test with a low power source

Thermal response tests conducted to assess the subsurface thermal conductivity for the design of ground-coupled heat pump systems require a power source of about 7–12kW to heat water circulating in a ground heat exchanger. This high power is commonly supplied with a fuel-fired generator, which is an important source of cost. An alternative method relying on a power source of less than 1kW was consequently developed and used for a first field demonstration. Heat was injected along ten short sections of heating cable standing in the water column filling the pipe of the exchanger. Recovery temperatures measured at the middle height of each heating section were analyzed with a linear heat source solution of finite length. The ten local measurements distributed over a depth of 139m and averaged according to the site stratigraphy revealed a subsurface thermal conductivity that is within an acceptable range of the bulk value determined with a conventional test. The new method has the potential to reduce the use of generators for thermal response tests since a low power source is common to construction sites.