Comparison of a modelled and field tested piled ground heat exchanger system for a residential building

The ground source heat pump can reduce electrical energy requirements for the heating of buildings by up to 70% compared to electrical resistive heating; however, the cost of ground loop installation can be a disincentive to their use. Foundation structures, such as concrete piles are particularly applicable for loop incorporation and as such provide a cost effective solution for the installation of ground loops for new buildings. It is now considered that residential energy piles can not only be economically installed but also provide the necessary heat requirement, which is sustainable over the life of the building. A test plot of 72 m² (ground floor area) was produced with 16 perimeter 10m deep concrete piles, with a single U-tube in each. Over the heating season 2007/2008 a heat pump extracted heat from the pile loop circuit and the heat load was controlled as to simulate the heat demand of a modern detached 4 bedroom low energy residential dwelling. The ground physical and thermal properties were investigated by means of laboratory tests and an onsite thermal response test. These results were used within the borehole field software modelling program Earth Energy Designer (EED) as to computationally model the evolution of the mean circulating glycol temperature across the season. These results were compared against the measured results from the field test.