Move the earth, take the heat
Duff Hart-Davis digs his own thermal heating system. But it didn’t quite go to plan...
Go green! Go geo-thermal! Get your heat from the ground beneath you, rather than from the Middle East! Stop pumping carbon into the atmosphere! Roused by such exhortations, 12 months ago my wife and I began to consider possibilities for our 17thcentury farmhouse. With an oil-fired Aga for cooking and a boiler for hot water and central heating, our fuel bill was nearly £3,000 a year – and rising. Besides, we were contributing substantially to global warming. So we took a few deep breaths and called in Ecovision Systems, a young company that has done extensive research into ground-source heating.
The principles are simple. The Earth acts as a giant heat-store, capturing the warmth of sun, wind and rain. At 1.5 metres below the surface of the ground in Britain, the temperature fluctuates between 4C in winter and 16C in summer. Pipes containing water and anti-freeze collect the latent heat and transfer it to a heat pump, or compressor, which boosts the temperature to provide hot water and central heating.
The system uses a small amount of electricity, produces no carbon and needs minimal maintenance. If – as is claimed – it reduces our fuel costs by between 50 and 70 per cent, it will pay off our outlay of £16,000 in less than 10 years. Besides, we shall qualify for a Government grant of £1,200. Monday D (for digging) Day. At 0800 three vehicles sweep into the farmyard, driven by Bob Cossins, boss of the digging team, Nick and Luke, who is on the dump truck.
Out in our middle paddock are five trenches, each 50m long, into which will go the slinkies – coiled pipes containing water and antifreeze – that will lead to a main collection point.
Moving fast and talking faster, Bob sprays a thin line of blue dye along the track of each trench. Old maps show that this sloping field was once a cider orchard but we’ve never known what lies beneath the surface. Old drains? Bones? Clay? Rock? Roman remains? 0920 Two diggers – Big Yellow and Little White – crawl up the field. Their buckets bite into the ancient turf. Up comes 8-10in of fine topsoil. The layer beneath is brashy – crumbly clay flecked with white grit. Below that is solid clay. 1430 A huge truck grinds up the lane with the first load of sand for lining the trenches. With a vast, deep hiss, 16 tons slides out. 1545 The first trench is finished, 2m deep and only 30cm wide. Sidling along it, I get an odd feeling thinking that no human feet can ever have walked on this level before. Tuesday 0800 Heavy rain in the night causes trench collapses, entailing much extra excavation. 1045 An orange van delivers the slinkies, each one 250m of tough 32mm black polyethylene pipe, tied in loops 1m in diameter. 1430 We lower the first slinky into its long home. The digger drivers pour sand on to the pipe so that it is snugly bedded. Once it’s covered, the rest of the trench can be back-filled with soil. 1545 Thunder crashes overhead. A downpour sets in. The diggers slide around, spreading greasy clay.
FIVE OF THE BEST
Wednesday 0930 Martin Allman, business manager of Ecovision Systems, arrives to check progress, along with Mark Witzenberger, his technical expert from Germany, where ground-heating systems have been in use for 25 years. Martin takes a radical decision: because of the weather and the clay, the other trenches will have to be wider and shallower, with the slinkies laid horizontally. So long as they are 1.2m beneath the surface, their efficiency will be unimpaired. Thursday Ross Verity, master plumber, tests the first slinky by filling it with water and pumping up the pressure to twice that of a car tyre. Friday Our equipment is delivered: heat pump – like a big upright fridge – hot-water tank and expansion tank. It’s all branded Dimplex, the Irish firm, but – because it’s made in Germany – it carries German labels. Monday A new digger-in-chief, Paul, has a velvet touch on the controls. As he back-fills the trenches, he clears earth and clay off the surviving turf with marvellous delicacy. Tuesday Chaos! Ross whacks into the plumbing. Out comes the old hot-water cylinder, so there’s no water in the house. In the field, the diggers’ buckets rattle and clank as they excavate a 2m-deep pit in which the slinkies will unite. In the hole, Bob starts building a surround of concrete blocks to house the manifold. Wednesday Fine and hot, but the chaos increases. A section of fence comes down to admit Little White into the garden. A turfcutter slices a path diagonally across the lawn – agony for the gardener (myself, naturally). Thursday Working on the pit. By evening, Ross has all the slinkies connected up. Friday In the garden, Little White digs a trench for the 63mm flow-and-return pipes connecting the manifold to the heat pump. Paul probes delicately to find the sewer. In spite of his care, his bucket cracks the old clay duct and a section has to be replaced with plastic. No flushing for the duration. Suddenly the digger is just 4ft from the front door. Up comes the concrete path, in jagged slabs. Great heaps of clay hem us in. We’re being attacked from all sides. “Trench warfare,” says Martin jovially.
Unannounced visitors arrive, eager to see the show. They’re appalled by the devastation. “Fear not,” I tell them. “It’s the new gardening.” But inwardly I feel that things can’t get any worse. Monday They do. We clear the utility room. Carpet, boots, coats, books, box-files, spin-drier – all out and into my study. When Ross cuts a channel through the floor tiles with a grinder, the dust is incredible. From outside, it looks as though the house is on fire: dense white clouds billow from the windows.
We feel like we’ve been dragged into running a marathon. The only saving grace is that our whole team is so lively, confident and cheerful. Tuesday Ross bores a tunnel under the house wall. By evening, the 63mm pipes, heavily insulated, are buried under a new screed. Wednesday He grapples with the maze of copper pipes, wheel-valves and sensors behind the heat pump. When asked how it’s going, he invariably replies, “Cool!” Thursday The house is alive with electricians – three of them, two called Roger, ranging through the rooms like ferrets. Friday Mark spends hours programming the heat pump’s electronics. The utility room is again under siege, with bright blue fluid coursing through coils of transparent pipe as Ross pumps glycol into the ground system. Monday Countdown! Final adjustments all morning. Then, at 1428, Mark switches on. The pump hums into life. Ten seconds later, with a death rattle, it shuts down. Curses! Have the Earth deities struck back at us for violating their abode? Not so. Ross divines the trouble and, at the second attempt, away the pump goes. “Cool!” he cries. But for once he’s wrong. Things aren’t cool: they’re hot. The incoming flow from the ground is at 16C: the flow up into the cylinder is at 55C. Magic! All over the house the radiators spring into life. The water in the taps is soon too hot to handle. Triumph! We’ve gone green – and our neighbours are green with envy.
Ecovision Systems, Dream House, Lampern Hill, Uley, Dursley, Glos (01453 861354; www.ecovision systems.co.uk). Econic, 9 Cotman Road, Norwich (01603 700999; www.econicltd.co.uk). Earth Energy, Falmouth Business Park, Bickland Water Road, Falmouth (01326 310650; www.earth energy. co.uk). Earthwise Scotland, Netherton Business Centre, Kemnay By Inverurie, Aberdeenshire (01467 641640, www.earthwisescotland.co.uk).
Warming up: Duff Hart-Davis (in striped shirt) and Martin Allman, of Ecovision Systems, prepare trenches for the water and anti-freeze filled heating pipes, which collect latent underground heat