Uses the moat for heat pump installation

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.

Ecovision are widely known for the 2010 BCI Award winning water source installation at Castle Howard in York, one of Britain’s finest stately homes, where the lake was used to provide the heating and hot water for this ancient building. The national newspaper coverage announcing Hon Simon Howard’s impressive savings encouraged owners of stately homes to turn to our design expertise, 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.

A combination of ground, water and air source heat pumps coupled with solar power are now collectively radically reducing energy bills and carbon emissions nationwide and providing users with valuable income.  With energy prices forecast to rise over 15% in the coming year, more and more homeowners are switching to renewables.

Over the years we have 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 not possible to drain the loop area prior to installation. An array of ground loops, were designed on a loop support frame, which we lowered into the water using buoys as floatation aids. After the loop array was launched into the moat, it was floated into position using ropes. 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.

“We have installed many closed loop water source systems using the same loop layout strategy. In the past we have had the luxury of a dry surface to construct them on. The challenge at Bishop’s Palace was to get the loop set in exactly the right position.  Calculations were made to ensure the loops, weighting blocks and frame would float and remain in position when filled and operational. It was a challenging part of the installation but with accurate planning it was plain sailing….”

Closed loop water source systems are becoming more and more popular.  They reduce the client’s capital outlay and almost eliminate the requirement for the alternative, which would be horizontal trenches or boreholes. In addition it 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. Ecovision is working on several other closed loop systems of varying sizes in large country houses and estates across the UK.

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 MDPE 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.

Reference:

Neil Otter, Operations Director, Ecovision Ltd