Marianne Suhr: Installing a ground source heat pump

Old buildings expert Marianne Suhr drops in on 500-year-old Picketts Cottage where the owners, Alan and Sarah Tierney, are determined to reduce their carbon footprint by installing green technology - in the form of a ground source heat pump - to provide heating and water.

Alan and Sarah Tierney were keen to combine the repair of their historic home with their interest in sustainability. As a conservation consultant, Alan was also prepared to use his own house as a test bed to see just how compatible new green technologies are.

The main challenge was to heat an extremely draughty, timber-framed house with walls of just four inches thick. Alan needed an energy source that would be cheap and clean to produce as well as being sustainable. The ground source heat pump was his first port of call – a technology that is already widely used in Sweden.

Hidden heat
Ground source heat pumps rely on the fact that one metre below ground the earth remains at a temperature of between 7°C and 13°C. This heat is extracted by burying a pipe filled with water and glycol attached to a heat pump, which can then run underfloor heating systems or low temperature radiators. For every unit of electricity used to pump the heat, 3-4 units of heat are produced, making them economical.

After lots of investigation Alan discovered that it was possible to use compact heat collectors which would fit into his own back garden, just 12m wide by 15m long.

It would, of course, involve major excavation works, and so to keep the cost down to around the £6,500 mark, Alan decided to take a crash course in digger driving and move the 20 tonnes of earth himself. The only problem was that Picketts Cottage formed the central house within an ancient terrace and, with neighbours either side, the only access to his garden was through his dining room. Nobody believed that he would be able to drive a digger through his very low front door and across his ancient quarry tiled floor – but that’s exactly what he did.

Once the one metre deep trenches had been prepared, he laid the compact collectors with help from his wife, Sarah, and left the tubes out of the ground ready for connection by a specialist plumber. These were routed back to the heat pump located in a specially adapted outhouse.

ABOVE (left-right): Alan squeezes through his front door; Laying the compact collectors.

Warmth on tap
Warmth on tap With the infrastructure in place, Alan was able to utilise cheap hot water from the heat pump to heat his house. This was perfect for installing a wet underfloor heating system beneath the limestone flags in his new kitchen extension, and beneath oak boards on a suspended timber floor in his sitting room.

The floor in the dining room consisted of ancient quarry tiles, laid 400 years ago. Fitting an underfloor heating system would involve lifting the tiles, but Alan couldn’t bring himself to disturb them; he knew they would never look the same when they were relaid. Instead he ran a wall-mounted radiator off the ground source heat pump circuit to heat the room. This runs for longer periods at a lower temperature, and is topped up by a wood-burning stove whenever they use the room in winter.

When Alan fitted the ground source heat system, he decided to also fit a comfort cooling unit in the loft for an extra £1,000 – this sucks in hot air, removes the heat by feeding it back through the heat pump, and returns cool air to the house. At the time, with winter approaching and temperatures plummeting, he didn’t then envisage needing to use it. But during the summer heat and humidity, Alan and Sarah were amazed at just how efficient and useful this was – once fitted, it provided free air conditioning.

ABOVE (left-right): The compact collectors are connected to the heat pump and hot water tank; Marianne and Alan in the outhouse.

Rainwater harvesting

Alan also fitted a rainwater harvesting system to collect water from the roof. The gutters and downpipes channel all the rainwater into a sump, which was then pumped to a storage tank. This is connected to a garden watering system, set on a timer. This feeds soak hoses that allow water to slowly seep out across the vegetable beds.

ABOVE (left-right): The rainwater harvesting tank is lowered in place; Plants disguise the underground tank.

Marianne's checklist: Installing green technologies

• Always use a system that can be easily maintained and accessed; avoid burying pipe connections underground, and pressure test before backfilling. According to the Energy Saving Trust, expect to pay between £7,000-£13,000 and check whether there are any grants available.

• If you can’t fit a ground source heat pump, consider an air source heat pump.

• Photo-voltaic cells fitted to your roof can generate electricity to power electric appliances. If your old house isn’t suitable for fitting panels to the roof, consider siting them in your garden. Budget between £8,000 and £14,000 for a solar installation.

• Before starting work, check any planning regulations with your local authority first.

• Only use MCS-approved installers.

• Check whether your system will qualify for the Feed-in Tariff (FITs) scheme.

WORDS & PHOTOGRAPHS MARIANNE SUHR
Featured in the December 2010 issue of Period Living