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Heat pumps and hydro electricity: how to get your energy from a river

Posted by Tasha Kosviner on 12 March 2015 at 12:25 pm

When a river runs right past your house, as in Liz and Peter Downs’s case, it makes sense to use that water to heat and power your home.

The Downs bought Itteringham Mill, a 1778 Norfolk watermill in 2004 with the intention of turning it into a bed and breakfast with holiday cottages attached. The building is Georgian and was a working mill up until the 1920s, but was in need of updating.

“It was draughty and leaky and used far too much oil and electricity to run,” Peter says. “We knew we wanted to create an energy efficient, environmentally-sound home that was a showcase for renewable technologies, so we started to do our research.”

The house was to undergo a major remodelling to turn it into a B&B so it made sense at that time to improve the insulation and glazing at the same time, immediately making the house more energy efficient. But then the couple turned their attention to how to generate the energy they still needed to use.

“Prior to our various installations, we used about 17,000kWh annually for lighting, water heating and electrical equipment and appliances,” says Peter. “We also burned around 5800 litres of oil for heating.”

The solution to the energy drain was running right beneath the couple’s feet: the river that used to power the mill.

“We started off by installing a hydroelectric turbine,” Peter explains. “The system we chose uses a syphonic turbine with a flow rate of 450 litres per second on a head (the height the water falls) of 1.4 metres. At 80 per cent efficiency it has a potential output of just under 5kW.

“Following that, our hydro engineers suggested we get a water source heat pump because its makes more economic sense to use, rather than export, generated electricity. The pump extracts heat from the river (hence it is water source rather than air or ground source) by means of heat exchange coils buried in the silt. We use it for both heating and hot water.”

The heat pump had a rated output of around 27kW for which it required between just 5 and 8 kW of input – energy that could easily be provided by the micro hydro turbine (plus the occasional boost from an immersion heater in extreme cold).

To complement the pump, the couple then installed underfloor heating on the ground and first floors of the mill because a heat pump operates more effectively with this rather than radiators. The use of 12 independently controlled heating zones with wall mounted thermostats meant that each zone could be set to its own temperature and time, avoiding the need to be heating whole areas of the house – such as guest rooms – when they were not in use.

So how much did all this cost?

“The heat pump and all associated equipment cost around £23,000; the underfloor heating expenditure was around £9000 and the micro-hydro-turbine cost £30,000,” Peter explains. But the payback began immediately and gratified.

“We now no longer burn oil, and much of the electricity is self-generated from our hydro turbine,” says Peter. “We still have to import a little electricity but for the six bedroomed mill and the holiday cottages, our electricity payments are currently just £172 a month, or around £2064 a year.”

Plus, some exciting developments in government incentives, namely the feed in tariffs for electricity, and latterly the renewable heat incentive for the heat pump, mean the couple now get a very tidy income from their innovations.

“We receive around £1800 a year from the feed in tariff for our electricity generation,” says Peter. “And, since November 2014 we are in receipt of renewable heat incentive payments of £7743.24 a year. These payments will last for seven years meaning we will have paid off the cost of both the pump and the underfloor heating in just over four years and still have three years of payments left.”

So what would the couple have done differently?

“If you’re looking into a hydro turbine, make sure you’ve got your abstraction license from the Environment Agency (EA) in place,” says Peter. “We were poorly advised by the EA at the time and didn’t get one and getting one retrospectively is proving to be a bit of a headache, particularly since some of the conditions have now changed.”

Photos: SuperHomes

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