Harrow School, the world-famous boarding school established 400 years ago, has installed a state-of-the-art heat pump system to harness free energy from the ground. The hi-tech green technology is being used to heat a new building, Lyon’s House (named after the school’s founder, John Lyon), set on a hillside overlooking London.

The four-storey brick and tinted glass-clad building is the first new House to open at Harrow in over 100 years. It uses several sustainable technologies, including a rainwater-harvesting system and solar panels. Main contractor on the development was Osborne, M&E Contractor Norstead, and the heat pump system was designed and installed by Ecovision.

The ground-source heat pump is based on 6.6km of pipe buried in trenches in fields on the hillside surrounding the building. The 32mm diam MDPE pipe, carries glycol solution as a heat exchange medium.

The glycol solution circulating in the buried pipe absorbs heat from the surrounding earth. This is then transferred via a high efficiency brazed plate heat exchanger to a refrigerant circuit in the heat pumps, which upgrade the low grade heat to create a higher temperature for heating the building. For every 1KW of electrical power consumed, the heat pump delivers approx. 4kW of energy. This is used to heat pupils’ rooms, kitchens and communal areas in the new building via low temperature radiators and fan coil units.

Harnessing this free and sustainable source of energy cuts running costs by around 30 per cent a year compared with a conventional gas-powered heating system. The ground collector pipes are laid in an array of 66 trenches, each 50m long. These are arranged in groups of 11 loops, each with a flow and return pipe, and are brought together in six sub-headers. The sub-headers, concealed beneath the ground surface, feed into the main header which routes the primary flow and return pipes in 125mm diam HDPE pipe to the building’s plant room.

The system is based on three Si37TE Glen Dimplex heat pumps, each delivering up to 37kW. Kirsty Shanahan, communications manager for the school, said: “Harrow is steeped in tradition. However, we are also very forward-thinking as an institution, and keen to embrace the best new approaches and technology. “It is entirely fitting that Lyon’s House, named after the school’s visionary founder, makes use of state-of-the-art technology for harnessing sustainable energy and safeguarding the environment. It is something I am sure he would completely approve of!”

The new building is designed to provide high quality accommodation for 70 pupils, from 13 to 18 years of age. In addition to bedrooms, it includes a games room, assembly hall and library. Interest in the use of heat pumps is growing rapidly, according to Neil Otter: “There is no doubt that rising energy costs, combined with genuine concern over the environment, is stimulating demand for alternative and sustainable technology.”

He added, “We are now working on projects the length and breadth of the country, from stately homes through hospitals and schools to office developments.”

“The temperature of the ground is remarkably constant below the surface. In this area of the country, at a depth of 1.2 metres, it remains at a steady 10deg C throughout the year, even in the depths of winter. This may not sound very warm, but when conditions above the surface fall below this temperature – even by a few degrees – it provides a substantial amount of free energy that we are able to tap into and harness.”