How the system works
The system is designed to generate approx. 5,800 kWh per annum. It contains approx. 30 litres of water with an inhibitor, which also serves as an antifreeze down to -27 degrees C. Three sensors measure the temperature of the collectors (TC), the temperature of hot water near the top of the tank (T3), and the temperature near the bottom of the tank (T5) sensor. The pump starts when the temperature difference TC-T5 reaches 10 degrees C, and stops when TC-T5 falls to 5 degrees C. At temperatures lower than -5 degrees C, the pump 'kicks in' and moves the water around, to help prevent any freezing. This setting cannot be changed. It is worth noting that there is no water in the tubes on the panels – it flows across the top of each panel only!
Hot water is fed via a coil of copper pipe to a 274 litre hot water cylinder on the ground floor and then piped from the top of the tank to: three toilet hand basins; the staff kitchen sink; a washing machine (hot and cold fill); two Cafe hand wash sinks; and two Cafe washing-up sinks. The pressure is provided by a new cold water 'header' tank located high in the loft, approx. 30ft above the hot water tank.
Normal temperatures of 55-60 degrees C (top) and 15 degrees C (bottom) can be maintained all day, but, in order to comply with hygiene regulations, supplementary heating is in place to keep the Cafe's hot water supply at a minimum temperature of 50-60 degrees C. For the time being, the supplementary heating is provided by two immersion heaters, located near the top and bottom of the tank and on independent timers, and We have installed a kWh meter to measure the energy used by the immersion heaters. A second coil in the hot water tank is available for future use: if we improve our central heating, for example, this could easily be connected to provide the secondary heating.
The instant water heaters that we had been using until now are being removed. One will remain, relocated to the sink in the End Bay. This is too far away to make sending hot water for their low use efficient. A blocked-off spur exists, to change this situation if necessary.