Andrews supports solar water heating at County Hall, Bedford
Solar energy and Andrews oil-fired water heaters combine to reduce energy costs for generating domestic hot water at County Hall, Bedford by up to two-thirds in summer and a third in winter.
Demonstrating the potential of solar energy to substantially reduce the energy required to generate domestic hot water is a refurbishment project at County Hall, Bedford. It was in 2004 that consultants Mouchel Parkman advised that since 1965 when the building and its services were designed, the efficiency of technology for space heating and generating domestic hot water had advanced so much that significant savings in running costs could be achieved by replacing some of the 38-year-old plant. The recommendation was for space heating and domestic hot water to be decentralised and that the smallest of three boilers installed in 1966 solely to produce hot water be replaced by a solar-power system from Genersys, supported by Andrews independent oil-fired storage water heaters to raise the water to the required temperature. Peter Murphy of Mouchel Parkman explains, ‘In the basement plant room, two of the original oil boilers remain for space heating, together with one of the two previous hot-water cylinders. This now stores main-fed cold water before it is preheated by the solar panels and fed to the two Andrews direct-fired water heaters, each provided 2970 l/h output when raised through 44 K and regaining full capacity in under eight minutes.’ With the original plant, the mains water would have come in at anything below 10°C, and the boiler would have raised it to 60°C. Now the mains water is pre-heated by solar energy in winter to 25 to 26°C and in summer to up to 48°C before being raised to 60°C by the Andrews units. On the coldest day, energy costs are cut by a third and by up to two-thirds during summer. Since the solar-powered system was installed, the heating boilers have been shut down from 15 May to 15 September. In winter, the heating boilers are shut down at 1700 h, while the water heating may run on until 1900 h without wasting energy. The Genersys solar collector system is installed in a south-facing position on the roof. It comprises 40 m2 of solar panels with the capacity to heat 3000 l of water. There is room to add 10 m2 of panels. Highly insulated copper pipework connects the panels to the lower coil in a sealed circuit. The supporting water heater is connected to the upper coil. The payback for this installation is calculated at about 15 years at current energy prices. About a thousand people work in the building, and the annual cost of hot water exceeds that of space heating. As well as wash basins in the toilets, there is a commercial kitchen serving the canteen, which is open from 0800 to 1700 h — providing a steady demand for hot water throughout the day for food preparation, washing-up machines and washdown. The entire installation was carried out by Mellor Bromley of Leicester.