Hot air solution
An air source heat pump has helped to cut carbon emissions by 65 per cent and halved the cost of heating and hot water during a retrofit trial of a 1960s
home. Carina Bailey reports
heat pump used 4,156kwh of electricity to supply all the heating and hot water, at a cost of £384, with the total cost of all the electricity consumed by the household being £810. This is down from a total electrical consumption of 15,563kwh a year – at a cost of £1,137 in bills. Subsequently, the household’s CO2 emissions have been reduced from nine tonnes a year to just 3.2 tonnes. Energy generation at the property is now also being supplemented with solar thermal energy, which Salter believes could generate up to 80 per cent of the tenants’ hot water in the height of summer. He says: ‘The project has generally gone very well, but there is quite a bit of education that you need to do with your tenants because of how the pump operates, it’s totally different to anything else. The radiators themselves don’t get very hot. The only “problem” we’ve had is that it takes two to three weeks to set the heat pump up to get the tenant comfortable.’
The Pearce family has seen their heating and hot water bills cut by 50 per cent since the air source heat pump was installed.
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“You could recover the money over the course of the RHI and end up in profit”
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CIBSE Journal June 2010
housing association’s efforts to retrofit a 1960s mid-terrace property has halved the cost of heating and hot water, and reduced the carbon footprint of the house by two
thirds. Cottsway Housing, the largest registered social landlord in west Oxfordshire, chose to install an air source heat pump on the three-bedroom mid-terraced house in Enstone, Oxfordshire, in August 2008. The 1960s traditional brick building had already undergone a series of insulation works – including filling the 50mm cavity wall with rock, placing 300mm insulation in the loft, and replacing the windows and doors with double glazing and new front and rear doors – some years before. The old heating systems – storage heaters in all rooms,
and a storage convector and solid fuel open fire in the lounge – were ripped out and replaced with an air source heat pump. Gary Salter, asset management surveyor at Cottsway, says the association has used geothermal and hydrothermal solutions in other retrofit projects, but on this occasion plumped for an air source heat pump because it was quick and easy to install compared with a ground source heat pump, and the family was considered to have an ‘average requirement’ for hot water (60 litres per day, per person). The property was also off the gas grid. During the year-long trial, the Mitsubishi Electric
Cost effective
Homes without gas usually rely on oil systems, but Salter says this leads to unknown costs for the tenant, with rising fuel prices, and makes it harder for the association to ensure it is complying with ever- changing legislation on standards. Salter says that Cottsway decided against simply connecting the house to the gas grid partly because of price – a gas connection to the grid can cost anything from £750 to £3,500. Add on the expense of a gas boiler, tanks, pumps, pipes and radiators and, he says, that could increase by another £4,000. In contrast, the air source heat pump with tank, radiators and so on, costs on average £5,300, with up to £3,300 funding from the Low Carbon Building programme currently available, making it a much more attractive option, explains Salter. Also, the pump is expected to deliver an average of £675 each year under the government’s Renewables Heat Initiative (RHI), a scheme designed to encourage better use of heat energy. It is expected to go live in April 2011. Solar thermal will also be eligible under the scheme. According to Salter, solar thermal heating and air
source heat pumps work well together, despite solar thermal adding £3,000 to the retrofit costs per project. ‘It’s not really just about cost. It’s really more about reducing the running costs for our tenants, the amount of energy used and the carbon footprint. It saves another tonne of CO2 a year.’ Salter also believes this combination will take off in the
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Cottsway HA
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