Heat pump one year stats

Theo · 2022-12-11T11:06:40+00:00

Just over a year ago we had a 13kW Grant air source heat pump installed. It's in a 1960s chalet bungalow with a very leaky loft conversion, 1990scavity wall insulation, 100mm loft insulation, 2021 EPC D (the 2011 EPC wasE with nothing changed since then).The ASHP is doing all heating and hot water. It's separately metered, andthe readings on the 1 year anniversary were:ASHP 2867.5 kWhImmersion boost for legionella 46.56kWh [1]Total 2914 kWhThe ASHP doesn't have a heat meter, but in previous years we'd have usedabout 1200 litres of oil:10.35kWh per litre => 1200*10.35 = 12420 kWhAssume oil boiler 85% efficient, 10557 kWh of heatEffective SCOP: 10557/2914 = 3.62I'm pretty happy with that.Elec tariff: 35.06p/kWh Gas tariff: 10.31p/kWh (we aren't on mains gas)Annual cost of elec at current rates: £1021Hypothetical cost of gas boiler at 93% efficiency:10557/0.93*10.31 = £1170Oil:At ~80p/litre (currently): 1200*0.8 = £960At 90p/litre (past months): £1080 So fairly competitive with both oil and mains gas, even on current tariffs.In the current temperatures (-3.5C outside) the smart meter says the houseis using about 45kWh per day. That includes a load of washing (hot waterdown the drain), tumble drying (in the garage) and 3D printing (garage) - ona summer's day like that we'd use 15kWh, so the net heating and hot waterload is about 30kWh. The house is perfectly warm - the heat pump ismanaging it quite happily.Theo[1] They've installed the most annoying timer for legionella cycles and forvarious reasons often they don't run. I'm in the process of rewiring this,but for the meantime we haven't been doing a full weekly 60C boost forsanitisation.

Theo 2 years ago

You may need to replace the radiators with ones with more panels or fins, eg we went from single-panel single-convector to double-panel, some single some double-convector. A couple of them got marginally larger. We opted to replace them all so they all matched (no old 1970s radiators remaining) but we didn't need to do that according to the heat loss calcs - some of the old radiators were in bad condition so it was better to start again.

No UFH, and with a concrete slab it would have been awkward to install that.

Theo

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Steve Jones 2 years ago

Thanks, I have a 1957 bungalow on a concrete slab, and am thinking of upgrading to a heat pump at some point

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Theo 2 years ago

Pretty similar here (1965 bungalow, loft conversion). Cavity wall insulation, ~100mm loft insulation, it works fine.

Theo

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Vir Campestris 2 years ago

Are you sure that's an upgrade?

Next time it's cold check the rad temperature, and that will give you an idea of whether a heat pump could cope.

If they're too hot to touch it won't.

Andy

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Theo 2 years ago

That's not correct. The boiler will output whatever temp it feels like - if it's not a condensing boiler then it can't lower the flow temp in relation to heat demand, or it may be set too high (often 60+C). Many boilers are massively oversized for the actual heating load so they cycle.

In most traditional boiler setups the boiler will heat the rads until the thermostat or TRV shuts them off. The rads go hot when the boiler runs and then cool off when the boiler doesn't run. Touching the rad when the boiler is or isn't running is no guide to how things will work with a lower flow temp.

Theo

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