A short term heat store has been added to the passive solar energy capture system to retain heat captured during the afternoon. The store consists of two layers of Basalt blocks supported by a wooden frame within an insulated box located in the loft space of the house. There are 60 blocks each weighting approximately 400g giving a total mass of rock of 24 kg.
Air is extracted from the solar chimney and fed into the store. Initially the heat energy was transferred into the store by convection. However, more control was needed over the temperature at which air was fed into the store and it was decided to circulate the air around the top of the chimney and the store using an extractor fan and insulated ducting.
In the evening the fan between the chimney and the heat store is turned off and air is then circulated via ducting within the house. Air is drawn into the store through a vent in the ceiling of an upstairs room and then fed back down into a ground floor room.
There is also provision, on very cold days when heat storage is impractical, to circulate warm air through the chimney and the house without attempting to store it. In this case warn air is fed into the ground floor of the house and cold air is drawn out of the house into the out-house/conservatory through a vent.
The short term heat store proved effective in the autumn when it retained heat gathered while the sun was shining on the solar chimney, this air was then used to warm air circulating within the house for two hours after sunset. However it was found that the brick walls behind the ducting in the house were effective as a heat store and it seemed to make more sense to bring the heat into the house while the sun was shining and store it within the building’s infrastructure itself.
The ducting (see picture above) has a surface area of 1.4 square metres and its surface reaches a temperature of 27 degrees C. This provides additional heat for the upstairs bedroom and the hall. At a future date the upper section of the ducting will be insulated to prevent the over heating of the upstairs rooms.
The short-term heat store was also intended to double as heat exchanger to capture heat in the summer months for storage in clay surrounding the house. It is now intended to install a heat exchanger on the top of the solar chimney which as well as capturing heat will also cool the conservatory.