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Hi-tech heat pumps hots up Harrow

Harrow School may be steeped in tradition, but it has designs on cutting edge heat technology

World-famous boarding school Harrow School has installed a high-efficiency ground source heat pump system 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, the M&E Contractor was Norstead, and the heat pump system was designed and installed by Ecovision.

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

Neil Otter, operations director of Ecovision, says: “The temperature of the ground is remarkably constant below the surface. In this area of the country, at a depth of 1.2m it remains at a steady 10 deg C throughout the year, even in the depths of winter.

“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.”

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 1 kW of electrical power consumed, the heat pump delivers approximately 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.

Tapping into the free energy cuts running costs by around 30 per cent a year compared with a conventional gas-powered heating system, says Ecovision.

The ground collector pipes are laid in an array of 66 trenches, each 50 m long. These are arranged in groups of 11 loops, each with a flow and return pipe, and 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 diameter HDPE pipe to the building’s plant room.

The system is based on three Si37TE Glen Dimplex heat pumps, each delivering up to 37 kW.

Kirsty Shanahan, communications manager for the school, says: “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. In all of these, we rely on the excellent backup and support provided by Pipe Center. They are a key partner and, wherever we work in the UK, help us ensure we deliver for our clients.”


Tech spec on Harrow project

·       Ground source heat pump system.

·       Employs 6.6 km of MDPE pipe buried in parallel trenches 1.2 m deep.

·       Ground pipe array in 66 runs, each 50 m long, set in surface of hillside.

·       Heat exchange medium: glycol solution.

·       Three Si37TE Glen Dimplex heat pumps, each rated at 37 kW.

·       System used to heat pupils’ rooms, kitchens and communal with low temperature radiators and fan coil units.

·       Estimated saving over gas heating – 30 per cent per annum.

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