Domestic Solar Earth Charging: Modelling the Process for Augmentation of Heat Pump

This paper is a progress update on the solar thermal augmentation system for ground source heat pumps using solarium style panels to recharge the ground, previously reported at SET 2011. The system is running on a house in Nottingham, England. The house has a 4kW photovoltaic array and a ground source heat pump for heating and hot water, using twin 48 metre boreholes. Real-time, diurnial and inter-seasonal solar charging restores the energy level in the earth, thus preventing progressive chilling of the borehole zone. The first development in 2012 is that there is now sufficient real data collected to construct a computer simulation with that data, to see how it compares with the real pattern of behaviour. The modelling process attempts to identify the thermal elasticity of the borehole. The second development in 2012 has been the addition of an additional method of solar capture, vacuum tubes working to the same boreholes, with independent controls, pumping and metering. The solar collection systems provide a way of comparing the cost effectiveness, technical and visual impact of the technologies. Solar augmentation can improve the GSHP performance by a significant percentage, more than the 15% expected – it has been more like 40%, causing one to detect an accelerative effect with solar charging. The resulting economies have been sufficient to reduce the annual electrical consumption for heating and hot water to less than the annual power generated by the PV array on the roof, thus achieving net-zero carbon emission.