Bishop's Palace turns to renewables

More than simply an historic house and garden, Bishop’s Palace is a splendid medieval Palace, which has been the home of the Bishops of Bath and Wells for 800 years. The Palace is surrounded by a stunning moat and it is from here that the renewable energy is sourced for the newly constructed visitor’s centre. For buildings located near a suitable body of water, a water source heat pump offers an attractive alternative to ground source systems. They are virtually silent, maintenance needs and costs are negligible and there are no visible external units.

In 2010 Ecovision won the BCI Award for the water source installation at Castle Howard in York, one of Britain’s finest stately homes. In this case the lake was used to provide the heating and hot water for this ancient building. The Hon Simon Howard made no secret of his impressive savings and thereby encouraged owners of stately homes to turn to Ecovision for advice on the alternatives, including Ascott House, Harrow School, Treago Castle and many more throughout the UK. These older buildings were designed to operate at consistent lower temperatures provided originally by fires, maintaining the thermal mass in the thick stone walls. Heat pumps do something similar, but at a much cheaper rate than an oil or gas fired system.

Julian Sowerbutts, Managing director of Ecovision commented: “A combination of ground, water and air source heat pumps coupled with solar power are radically reducing our energy bills and carbon emissions nationwide and providing users with valuable income. With energy prices forecast to rise over 15% in the coming year we urge people to consider the alternatives.”

Ecovision has designed and installed an increasing number of closed loop water source systems but Bishop’s Palace was a more complex challenge. Unlike the Castle Howard system it was impossible to drain the loop area prior to installation. An array of ground loops, were designed on a loop support frame and lowered into the water using buoys as floats. When the loop array was launched a system of ropes was used to guide it into position. A diver then guided the array into the final position before lowering it under the water. The array sits on the moat bed but is lifted by weighting blocks which keeps it in position and holds the bottom of the loops 200 mm off the moat bed.

Closed loop water source systems are becoming increasingly popular. The client’s capital outlay is reduced and it almost eliminates the requirement for horizontal trenches or boreholes. It also provides a solution for a building that does not have sufficient land space or for client’s who want as little disturbance to the grounds as possible.

Although often the ground space is available, the number of horizontal loops required for several of these projects would have been expensive and would have involved extensive digging through beautiful parts of the grounds.

At Castle Howard there was already a plan to drain and dredge the lake, which offered an opportunity to lay the 56 coils of pipe on the lake bed before it was re-filled. Each coil measured 100 metres in length and were filled with a diluted glycol, an environmentally friendly anti-freeze which will absorb the heat from the lake. All the pipes converge into a chamber on the lakeside and from there the warmed fluid is pumped in buried pipes to the heat pumps in the main house at a temperature of 10ºC. It ends up in one of two 100kW Dimplex heat pumps in the plantroom in the basement of the building.

Closed loop systems make GSHP installations more viable and depending on the water temperature and the flow rate, they also provide a more efficient heat source. The Bishop’s Palace closed loop water source system comprises 6 x 100 metre coils headed into one larger flow and return, which penetrates the moat wall adjacent to the plant room.

The heat pump is the Dimplex SIH 20TE, it’s output is 22kW and it can achieve a maximum flow temperature of 70º C which will supply all of the heating and the hot water for the building.

Ecovision estimates the average temperature of the moat during the heating season to be approximately 7ºC. The underfloor heating has been designed to operate effectively at the lowest possible flow temperatures. With this delta t across the system the average CoP will be approximately 5.2. This system will be approximately 20% more efficient over the year than an equivalent ground source heat pump system.

The return from the Renewable Heat Incentive will be in the region of £1,700 per annum. An alternative conventional oil system would have cost approximately £2,900 per annum to heat the building. The heat pump will cost approx £1,200 per year to run, giving an annual saving on heating costs of £1,700 and a combined annual financial benefit of £3,400. The project received funding from the heritage lottery fund and Church Commissioners for England.