UK shallow ground temperatures for ground coupled heat exchangers

Abstract

Accurate estimations of shallow ground temperatures are required when sizing the horizontal closed loops and air supply culverts of ground coupled heating and cooling systems. These collector loops and culverts are within the zone affected by the seasonal swing in temperatures. Soil temperatures from 106 Met Office weather stations, located across the UK, have been analysed from which mean annual, seasonal minimum and maximum, and daily minimum and maximum temperatures have been calculated. Mean annual temperatures at 1 m depth, reduced to sea level, range from 12.7°C in southern England to 8.8°C in northern Scotland, with corresponding seasonal ranges in temperature of 10.3°C and 7.9°C respectively. An average urban heat island (UHI) effect at 1 m depth of 0.55°C has been observed at localities adjacent to urban green spaces, from which it can be assumed that the UHI effect will be greater in densely developed city and town centres. A linear relation has been derived for the mean annual temperature at any non-urban UK locality, at 1 m depth. The seasonal temperature cycle has been extrapolated accurately to several metres depth with site-specific thermal properties derived from the soil temperature measurements.