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Posted By: davidfreeboroughIf you're using a heat pump to extract heat from the exhaust air then the only "new energy" the heat pump provides to the house is the electricity it consumes. In other words, you have a COP of around 3 for energy recycled within the house, but a COP of 1 for new energy introduced to the house.
Posted By: stonesReference the temp of exhaust air, the unit is currently extracting from the 'wet' rooms in the house at 18.1 c and expelling to the outside at -5.4 c. I have not yet seen the temperature of the expelled air rising above -1 c except when the defrost cycle is activated.
Posted By: stonesAssuming a conversion factor of 10.35 KwH to a litre of fuel oil, we have used the equivalent of just under 6 litres of oil to heat our home / DHW. That is the energy content in a litre of oil but you have to buy more than this as max boiler efficiency is 90%. So you actually get 9.35 kWhr/litre = 6.8 litres = £4.92Standard for COP calculation is BSEN 14511
Posted By: stonesGot the following figures taken at 0830 each morning over the past 2 days.
Posted By: DaveHempyardsThe total heat loss between the house and 470 is about 2 degrees; more alarmingly, the 470 produces return air at around 37 degrees, and much of this appears to be lost in the ducting. The furthest inlet to the house has had to be closed because in really cold weather it delivers air to the room below the general temperature of the house interior.The NIBE trained guy who commissioned the 470 said it was normal practice to run ducts in cavities, but it's not helped our system.
Posted By: DaveHempyardsI have built a house which surpasses building regs requirements. I feel cheated by a company whose sales literature is so poor that it is impossible to tell what you can expect - in particular, if they said that running consumption was anything like the figures quoted by Stones or myself, they wouldn't sell any of these machines.
Posted By: DaveHempyardsMy next investment was to have been £10-12K on solar PV. I'll get a better return by ditching the 470 and investing in a conventional air source heat pump and a heat recovery ventilation unit.
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