The underground heat store is an 1100m3 body of water that stores the heat generated by the PVT and solar thermal panels for use in the buildings during the colder months. The top of the store is insulated with a floating lid of 500mm expanded polystyrene. It is hinged around the perimeter to allow for the expansion and contraction of the water and the design also incorporates a suspension system to support the roof should the water level reduce. The sloping sides are uninsulated. As long as the ground around the store is kept dry, it will act as an insulator and additional thermal mass, increasing the capacity of the
store. The high specific heat capacity of water (4.2kJ/kg°C) makes it a good choice for storing heat.

During the summer there will be little or no demand for heat in the building, so the heat generated by the PVT array will stored in the heat store. In the autumn some of the solar heat generated will be used directly in the buildings and the excess will be added to the heat store. The temperature of the water in the store will gradually rise over the summer and early autumn. During the winter the solar heat generated will be less than the buildings heat load, and heat will be extracted from the heat store to heat the incoming air to the building. The temperature of the water in the store will drop as the heat is extracted. Some heat will also be lost to the surroundings. This is estimated to be about 50% of the total heat put into the store over the summer. The relatively low-grade heat from the store can be used to preheat the incoming air to the building, as the outside air will be at a lower temperature than the water.

Architectural Expression

No attempt was made to replicate the arts and crafts style of the original buildings in the new building works. The editions and replacements are expressed in a clean modern, albeit sympathetic, idiom reflecting the contemporary concerns of Renewable Energy Systems and the leading edge energy technologies deployed over the site and concealed within the buildings.

View from South West

PVT Array

Heat Store prior to lid being installed