Well that was an interesting session to watch on a wet Saturday morning!
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Very relevant in this thread as well.
I went to visit a low carbon social housing scheme yesterday (semi detached 2/3/4 bed homes). They’re being built to Passive House Low Energy Building standards. No gas, heating provided by 2 electric panel heaters (in 2 bed house), ASHP for hot water and MVHR.
The hot water tank and what looked like a condenser(?) above it was in a cupboard in the middle of the ground floor (not next to an external wall). The MVHR kit was in a similar sized cupboard upstairs. When I asked to see the ASHP unit itself, I was eventually told that it was in the loft. There were 2 pairs of what looked like 2 air vents on the gable wall, and I got the impression that one pair was for the MVHR and the other for the ASHP. Is that usual?
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I looked seriously into an exhaust air heat pump taking air from my MVHR’s output. On the surface it seems to make sense. There must be more heat in the exhaust than in the atmosphere unless the heat exchanger is 100 efficient. The problem is that the airflow rate for the heat pump is far greater than the balanced MVHR could deliver, so two independent systems are installed, each with their own inlet and outlet vents.
It does also mean that if one system fails the other can continue to operate.
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I didn’t even think about the ASHP and MVHR being connected in any way Tim. Maybe they are? It’s just that I thought ASHPs were big white boxes fixed to the wall, I’ve never heard of them being sited within the building before!
There are various monoblock ASHP available. They are often used for properties without a ground floor or where the noise of the system would exceed permissible limits.
Yes as Tim says these (exhaust air hot water ASHP systems) are becoming increasingly common especially in apartment schemes where developers try to avoid gas heating altogether. What Tim says about the airflow associated with MVHR and the exhaust air ASHP systems also makes sense.
There are also 1 or 2 such systems which can handle space heating as well; but only typically suited to small properties although could potentially also work with PH where heat loss is very low. Small Home and Apartment Heat Pump | Ground Sun
Heat pumps seem to be quite versatile. Just the fact they can be installed into your radiator system impressed me when I first enquired via the Green Grant.
As an aside - do any of you know of any heat pump engineers who would service a Misubishi Ecodan ASHP in the South Manchester Area - a person on the Freecycle community made a random enquiry.
Thanks
Carla
Thanks all for the info. I was just on a visit to see what Housing Associations are building for their tenants, and how they arrived at decisions on the heating/hot water systems. Noone who was there on the day seemed to really understand how it all worked, and it looked ‘different’ from what I’ve seen elsewhere.
Our ASHP set up has been running for 11months now. The energy use / heat production statistics look like this so far.
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Peak daily cost would be interesting. Cop X demand X electrical price on variable tariff. Have you seen ways this has been presented well? I’ve been meaning to look into it.
I’m not sure what you mean by “peak daily cost” or why that might be a useful measure.
I will provide a full annual running cost breakdown when we have clocked up a full 12months with our ASHP, ie in about 4 weeks from now.
Here is a somewhat delayed reply containing a full break-down of our household electricity & gas use for the 12months before and 12months after we had our ASHP installed. As you will observe in very simple terms it effectively is a pretty much break-even result (actually saving 10p but hey).
NB these costs do not include revenue from PV exported (on a deemed export tariff) or revenue from the Renewable Heat Incentive which we also receive.
Oh and more importantly the ASHP has resulted in a 64.5% reduction in the carbon emissions associated with our heating and hot water relative to the 12months prior having the heat pump installed. Total CO2 emissions for heating + DHW before ASHP = 1520kgCO2e, with ASHP = 540kgCOe. Also assuming the electricity grid continues to decarbonise (more renewables) then this figure with the ASHP will continue to decrease year on year.
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Thanks for this Dom. Very interesting. Your low bills and emissions are terrific and most enviable from the perspective of a leaky 1950s as-yet-not-retrofitted house. In your third line, ‘House’ means ‘Non-heating use by household equipment’ I presume (all contributing 100% to heat in the house no doubt, albeit often in warm weather when none is needed). Was there a reason for not correcting your 777 kWh of ‘before ASHP’ resistive electrical heat?
Hi @Paul_Hadfield.
Yes, “House” here means general household appliances (including electric oven, TV, computers etc) and yes, the majority of the waste heat from these devices will be indirectly heating the house, ie providing passive thermal gains.
A lot of the “resistive heat” is for heating hot water so has been excluded from the degree.day correction. Either way (correcting it or not correcting) it would not make much difference to the results.
For those who would like to see live real time heat pump performance. If you already have a heat pump and have a monitoring set-up then do consider sharing your data if you are comfortable with that.
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My ASHP stats Nov-2022
Elec consump = 242Wh
Overall COP = 3.78
COP space heat = 4.11
COP hot water = 2.12
total heat delivered = 916 kWh
Average target flow temp = 30.6°C
Average flow temp = 32.1°C
Typical Power draw SH = 450W
Typical Power draw DHW = 1.4kW
kWh of electrical consumption versus kWhs of heat delivered looks great.
As we’re hitting colder weather, how are you finding the monthly running costs versus the cost of gas?
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Our overall bill for the month of November is shown below.
The ASHP consumed 43% of the electricity we used or probably a bit less once you factor in PV self-consumption. So let’s say 40% to keep it simple. Hence 40% of £175 is £70 (cost of the electricity to heat our house during November). December and January will probably be a little higher than this, say around £100-120 for each month in terms of heating cost. We keep our house at ~19.0-19.5C.
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