Paper Conference

Proceedings of eSim 2012: 7th Conference of IBPSA-Canada


Simulations of a New Double U-tube Borehole Configuration with Solar Heat Injection and Ground Freezing

Parham Nejad, Michel Bernier

Abstract: Ground coupled heat pump (GCHP) systems are popular systems for space conditioning and hot water production. However, due to the high drilling costs of the ground loop portion, the initial investment is relatively high. In an attempt to reduce costs, a new borehole configuration has been recently proposed. It consists of a double U-tube borehole with two independent circuits and a saturated sand ring. One circuit is linked to a heat pump to extract heat from the ground and the other is connected to thermal solar collectors for solar heat injection. In effect, the borehole acts as a heat exchanger between the solar collectors and the heat pump. During peak building loads, usually at night when solar energy is unavailable, the heat pump extracts energy from the ground and in some cases the saturated sand freezes. This slows down the decrease in the return temperature to the heat pump and takes advantage of the relatively high energy content associated with the latent heat of fusion of water in the sand. When solar energy is available, solar heat is injected in the second U-Tube to melt the frozen saturated ring. The impact of this proposed system on borehole length is dependent on the building loads and the solar heat injection profiles. Preliminary simulation results show that the newly proposed configuration can reduce the borehole length by 18% for a well-insulated building located in Montréal with an annual space heating load of 11850 kWh. In this study, a parametric analysis is undertaken to study the impact of various building loads and solar energy profiles on borehole length requirements.
Pages: 257 - 268