Solar energy and gas replace oil on site near Norwich
Viessmann’s largest solar thermal installation in the UK delivers nearly 56 MWh of energy a year at the site of Petans near Norwich to help heat a large indoor survival training pool and provide hot water for 26 showers. The total installation comprises 86 m2 of solar tubes and by reducing the consumption of LPG will save over 13 t of carbon-dioxide emissions a year, with a payback on embodied carbon dioxide of one to two years. Petans specialises in safety training for the offshore and other industries. One of its facilities is a 495 m3 pool where trainees are taught to escape from a simulated helicopter ditching. Instructors and their trainees spend several hours a day in the water, so it is heated to around 30°C. The required heat was previously provided by oil-fired boilers, but rising oil costs and a desire to reduce carbon-dioxide emissions prompted Petans management to consider renewable energy. EnergyWorx, a contractor specialising in renewable systems, worked with Viessmann and proposed a solar thermal system combined with condensing LPG boilers. The payback is estimated at five years, based on current oil prices. 80 m2 of Viessmann Vitosol 200 evacuated tubes were installed on the gently sloping roof of the pool building to provide 52.3 MWh of energy a year to the pool, which is expected to meet 88.4% of its annual requirement. A further 6 m2 of evacuated tubes are installed on a vertical facade to contribute to the requirement for domestic hot water. 3.6 MWh is delivered to hot water in a year, or 35.6% of requirement. The panels on the roof are connected to a Vitrotrans 200 heat exchanger, which transfers the heat to the pool. The supporting boiler plant comprised three Vitodens 300 LPG condensing boilers rated at 49 kW. They have Matrix burners and can modulate down to 11 kW — so thermal outputs from 11 to 147 kW are available. On a reasonably bright Spring day, the solar installation can deliver hot water at 37°C, so that only one boiler is required. EnergyWorx also recommended that the existing DHW cylinders were replaced because of their excessive thermal losses. They were replaced with a 500 litre Vitocell B300 stainless-steel twin-coil cylinder with a standing loss of just 1%. Installing the system posed challenges for EnergyWorx. They included working on an exposed, windy site next to Norwich Airport, so good safety measures on the roof were vital. The use of evacuated tubes helped, since they could be taken up to the roof one at a time. In addition, there was only a 24 hour window to make the change from the existing system to solar thermal as Petans cannot close the facility for longer.