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Fri 5th October 2012
Edgcote's lake and secret passage provide renewable energy

Edgcote House in Oxfordshire is one of most architecturally important country mansions in the UK. Unfortunately, the priorities of early 18th century architecture did not include a requirement for energy conservation and the present owners were finding the costs of their oil-fired heating excessive and the prospects of continuing increases in energy costs daunting.

As a result isonergy were approached to design a system that would provide more affordable central heating and hot water, not only for Edgcote House itself but also for the five cottages in the grounds nearby. Preliminary thoughts from the isoenergy design team were to use energy from the sun and stored in the huge grassed areas around the building. Ground sourcing has generally proved to be a very cost effective energy provider, but a first site visit showed the even greater attraction of the lake fed by the River Cherwell that provides a landscaping feature just 200 metres down from the house.

Water is an even more reliable and constant conserver of solar energy than earth, and isoenergy conceived a system involving 2700 metres of 40mm diameter plastic piping in loops across the lake and weighted to keep it at a depth below the surface.

Filled with a vegetable based, antifreeze solution that absorbs the heat permanently held in the lake water, the pipe pattern circulates the warmed liquid to shore where it passes through a manifold, from here it is transferred to the utility room of the House in a larger 90mm flow and return pipe through a 120mm conduit. It was at this stage period romance became wedded to renewable energy. Preliminary probes to establish the best position for the manifold disclosed the mouth of a forgotten secret passage, believed to link with a priest hole in Edgote House.

Investigations showed the passage to be in surprisingly good condition and isoenergy determined to use it to carry the pipe up to the house, saving considerable excavation work and disturbance to the well-trimmed lawns that complement the vista over the lake. It is here that the most modern of technology takes over to turn residual energy from the sun into heat suitable to provide spatial heat to the rooms and the energy required for hot water supply by means of heat pumps.

A ground source heat pump relies upon an efficient heat exchanger, which captures heat in the anti-freeze liquid passed through the ground. When compressed, the anti-freeze boils turning from a liquid to a gas, this produces heat, which is transferred through water into the hot water system. The antifreeze goes through another process of cooling and condenses back to a liquid, which is then transferred back to the lake to continue the cycle of energy transfer.

At Edgcote House, three of the new generation of super efficient Viessmann heat pumps, each with an output of 42kW, are employed for the purpose of providing heating and hot water.

The first operates to fulfil the hot water requirements of the house and the five cottages, delivering sufficient energy to supply water at a temperature of around 70 degrees Centigrade to a doubly insulated 1500 litre capacity hot water tank.

The other two pumps, in a master and slave configuration, are tasked with providing hot water to the radiators of the central heating systems and they feed into a 1,000 litre hot water tank linked to a 1,500 litres buffer tank which promotes efficiency of the system.

At times of non-peak demand the tank supplying the hot water system will also feed through to the 1,000 litre tank to boost input.

Since isoenergy’s lake-sourced heating works at an efficiency rating that delivers an output of well over four times the energy put into the system in the form of the electricity used to power the heat pumps, first indications are for an extremely substantial saving of around 70% in fuel costs against the original oil-fired fossil fuel boiler.

While expectations are that renewable energy systems are most effective in new-build situations isoenergy’s experience shows that savings in historic buildings and heritage sites can be even more impressive. Certainly the beautiful Edgcote House now has an ecologically sound heating system that delivers a warm ambience, plus an ample and reliable supply of hot water at a fraction of the original cost. Neither the fish in the lake or the ghosts of persecuted priests have even noticed the difference.