Use of energy piles in a residential building, and effects on ground temperature and heat pump efficiency

Piled foundations for residential buildings have predominantly been used in areas where conventional trench footing foundations have not been possible. The reasons for this have included loose and unstable overburden and contaminated ground, which result in the use of concrete piles as an economically technical solution. More recent methods have enabled concrete pile foundations to become an economic option for ground conditions that would be otherwise considered for trench-fill. It is also realised that the heat load of modern residential buildings has reduced significantly in recent years, and will fall further in forthcoming years. It is now considered that the residential energy piles can not only be economically installed, but can also provide the necessary heat requirement, which is sustainable over the life of the building. A test plot has been produced with 21 concrete piles, 10 m deep, with a single U-tube pipe in each. A heat rejection facility was devised to simulate the heat load of a two-storey, modern residential building with ground floor area 72 m². Testing of the energy piles has been conducted over the 2007–2008 heating season. The ground was monitored by thermocouples at depth along each pile, and also as an array at various depths and distances in the ground around the plot. The temperature variation of the ground and its effect upon the heat pump efficiency have been observed. Findings of the testing conducted over the 2007–2008 heating season are presented and analysed in this technical note.