After the addition of a thermostatically controlled pump linking the chimney with the heat store a short test was carried out to determine how the short term heat storage performed.
Detailed results are available in spreadsheet format.
The heat store reached a temperature of 60˚ C by 18:40 in the evening after rising by 2˚ every 15 minutes from 15:55 when the test began. Although the solar energy available was high – up to 950 watts/m² - being a vertical mounted structure the solar chimney was not exposed to the full amount of solar radiation during the afternoon. Hence the temperatures in the top of the chimney were only marginally higher than they were during later winter months.
The heat store was still at a temperature of 57˚ C at 20:15 and 42˚ C at 06:15 the next day.
The thermostat on the pump was set at 80˚ C and the pump started operating at 15:45 – just before the test began. A further test with the initial thermostat setting lower and a gradual increase during the afternoon with the final setting at 90˚ is planned. Eventually a programmable system will have to be developed to optimise heat transfer.
Heat loss from the store was too high and too much heat was lost into the loft itself. This is possibly due to the lack of valves in the 100mm pipes connecting the store to the chimney and to pump 2 causing heat to radiate from the pipe work and also for warm air to leak back into the chimney during the evening.
The arrangement of the blocks inside the heat-store also prevents efficient airflow and moving some these to the edge of the store may help insulate the unit and prevent so much heat escaping to the loft