An overview of the results of 61 in-situ thermal response tests in the UK

The results of 61 in-situ UK thermal response tests, derived from three commercial test-rigs, have been analysed. Derived values of thermal conductivity yield a median of 2.25 W m K-1, with 25% and 75%-iles of 1.86 and 3.0 W m K-1. The lowest individual values are derived from Northern Irish basalt (1.1 W m K-1) and from Mesozoic / Tertiary argillites (often in the range 1.43 to 2 W m K-1), while the highest (>5 W m K-1) are from Sherwood Sandstone and Coal Measures strata where advective heat transport with groundwater flow may have led to an elevated apparent conductivity. Borehole thermal resistance exhibits 25%-ile, median and 75%-ile values of 0.09, 0.11 and 0.14 K m W-1 and correlates with borehole heat exchanger diameter and configuration. Undisturbed ground temperature exhibits 25%-ile, median and 75%-ile values of 11.7, 12.3 and 13.2°C and exhibits a latitude-dependence