Heat Pump Water Heater

[AlexMc]

I was thinking about installing anASHP water heater like https://www.modernheat.co.uk/product/2484/ for all my hot water needs, and a mono block ASHP strictly for heating. I know it’s more expensive, but I suspect I will get better performance since my new build will be a highly insulated envelope and hopefully won’t need much, if any, heating for most of the year. Has anyone ever done this? Is it a good idea? I’d appreciate your comments and don’t mind being told it’s a bad idea (as long as you keep it respectful and tell me why). Thanks.

[SteamyTea]

I quite like the idea of separating space heating and DHW.

It should be possible to calculate how much extra ventilation is needed to supply the DHW with warmed house air.

I would exclude bathroom and kitchen ventilation as these are, generally, variable, and will not coincide very well with the slower heating up of water.

 

It may also be worth looking at A2AHPs for space heating and a Genex system for DHW that works off the MVHR.

[JohnMo]

I did toy with the idea also, but the maths makes little sense. They are a £1000 more than a direct immersion one - that's a lot of electricity. Plus you have a decent ASHP sitting ideal that can do the DHW easy enough on just as good CoP.

 

Some are coated steel with anodes to change so be careful, the Edel units are stainless.

 

 

[AlexMc]

10 hours ago, SteamyTea said:

I quite like the idea of separating space heating and DHW.

It should be possible to calculate how much extra ventilation is needed to supply the DHW with warmed house air.

I would exclude bathroom and kitchen ventilation as these are, generally, variable, and will not coincide very well with the slower heating up of water.

 

It may also be worth looking at A2AHPs for space heating and a Genex system for DHW that works off the MVHR.

I’m not familiar with the Genex system, but I’ll check it out. The DHW unit draws air from outside and could be located in the attached garage. There’s also a system from Nilan that looks promising. It’s essentially a MVHR that has a small heat pump and DHW storage. I did a quick heat loss, and I’m looking at around 3 to 3.5kW which is pretty good. Seems like everyone I talk too recommends a 8kW to 11kW heat pump. Not making sense to me, but I may be missing something.

[JohnMo]

5 hours ago, AlexMc said:

quick heat loss, and I’m looking at around 3 to 3.5kW which is pretty good. Seems like everyone I talk too recommends a 8kW to 11kW heat pump. Not making sense

8 to 11kW is way over sized. Our heat loss is the same as yours and we have a 6kW and it's big.

 

16 hours ago, AlexMc said:

won’t need much, if any, heating for most of the year

Don't underestimate what heating you will need, don't believe the hype that well insulated means no heating. 3kW over 24 hrs is still quite a bit of heating to do, 72 kWh a day, CoP of 3 that's still £6 a day. 7 deg day will be about half of that.

[AlexMc]

2 hours ago, JohnMo said:

Don't underestimate what heating you will need, don't believe the hype that well insulated means no heating. 3kW over 24 hrs is still quite a bit of heating to do, 72 kWh a day, CoP of 3 that's still £6 a day. 7 deg day will be about half of that.

I was assuming that the need for heat during the spring and summer wouldn't be much, but your point is well taken.

[JohnMo]

41 minutes ago, AlexMc said:

No need for heat during the spring and summer

That will be the case, our heating last year was off in April, this year in May, not back on again til late October. Once we go below an average of 10 degs (24 hr average) the house is starting to cool enough to prompt the heating going on.

 

But we have cooling on as required via UFH system mid May to mid September.

 

Our last couple of houses, the heating was never actually switched off, had known it to come on mid July on a colder than normal nights.