ASHP, UFH and solar thermal, or ASHP, UFH and MVHR????

[Dicky]

We are nearing determination date for our self build so I'm trying to get as much knowledge and information as possible so I know what route I'd like to take.

We are definitely going down the ASHP/UFH route as we have no mains gas coming up the road to our house. But after speaking to some people, I've had mixed comments on ASHP systems, mostly regarding hot water and not reaching a decent temperature for baths/showers etc...

 

What are other people's experiences with their ASHP systems and their hot water??

 

So with that this is the reason we may look at also installing a solar thermal system or a MVHR system.

 

Any help and advice will be much appreciated

 

Thanks

[ProDave]

Why make the choice between solar thermal OR MVHR.  they are both entirely different things for different purposes.

 

Many of us on here are using an ASHP to heat our DHW.  The two key things seem to be use an unvented hot water cyilinder, NOT a thermal store, and heat the DHW to about 48 degrees which is plenty hot enough and well within the capabilities of an ASHP.  You will probably want a larger HW tank because it is not at "gas boiler" temperature, 300L seems a popular choice.

 

MVHR is worthwhile in a well insulated well sealed house to reduce heating bills by reducing ventilation heat loss.  This is quite separate to the heating and HW system.

 

Solar Thermal is effective at heating your DHW in the summer but no so in the winter.  Many of us preferred instead solar PV which can be used for DHW heating as well as a whole host of other things.

 

Is budget limitation forcing you down the one or the other route?

[Bramco]

1 hour ago, ProDave said:

Solar Thermal is effective at heating your DHW in the summer but no so in the winter.  Many of us preferred instead solar PV which can be used for DHW heating as well as a whole host of other things

 

Agree wholeheartedly - we installed solar thermal when PV was too expensive - it's great in the summer for hot water but you need a few panels for it to be effective. In the winter it doesn't really do a lot, so no use for hot water, which in your question would mean an immersion heater if you didn't use the ASHP. If you use the ASHP for hot water as well as UFH then it should be up to a third cheaper than an immersion heater due to the COP of the ASHP.  MVHR will simply mean you don't lose a lot of heat through the air changes you need for air quality.

 

When PV came down in price we installed some PV - sadly we didn't remove the solar thermal and replace it with PV - wish we had!!  PV is much more versatile as you can divert any excess through an immersion heater into your hot water tank - and when that's had enough it will supplement the power needed for any other electrical devices and if they aren't using anything into a battery for later consumption, or your EV. 

 

And hopefully in a couple of years more vehicle manufacturers will get 'enlightened' and allow V2H or V2G - in which case you won't need a house battery as you'll have one on 4 wheels parked up outside. (Only the Leaf does this currently). Batteries are great for some of the new electricity tariffs like Octopus agile - if you can avoid the peak times, rates are cheap and last summer they were paying you to fill up your EV or battery storage overnight - yes a few p per kW to take electricity off their hands!!  Kerching!! 

 

Simon

 

PS We're also about to start a new build - ASHP (UFH and DHW), MVHR and a 4kW PV array (and when the SAAB convertible dies an EV...)

 

PPS I saw a table comparing prices of batteries on Naked Solar (was put on to this by a Mesh Energy presentation) Tesla come out as one of the cheapest in their comparison which wasn't what I expected -> https://nakedsolar.co.uk/storage/   scroll down a bit to see the comparison table.

Edited December 12, 2020 by Bramco

[Dicky]

3 hours ago, ProDave said:

Why make the choice between solar thermal OR MVHR.  they are both entirely different things for different purposes.

 

Many of us on here are using an ASHP to heat our DHW.  The two key things seem to be use an unvented hot water cyilinder, NOT a thermal store, and heat the DHW to about 48 degrees which is plenty hot enough and well within the capabilities of an ASHP.  You will probably want a larger HW tank because it is not at "gas boiler" temperature, 300L seems a popular choice.

 

MVHR is worthwhile in a well insulated well sealed house to reduce heating bills by reducing ventilation heat loss.  This is quite separate to the heating and HW system.

 

Solar Thermal is effective at heating your DHW in the summer but no so in the winter.  Many of us preferred instead solar PV which can be used for DHW heating as well as a whole host of other things.

 

Is budget limitation forcing you down the one or the other route?

@ProDave thanks for the reply and advice. No I wouldn't say budget is pushing us one way or the other, was just unsure of really what we should do. A company I contacted regarding ASHP, UNF and possibly solar thermal, basically said they would dump solar thermal in favour for MVHR. Which I have very little knowledge of.

Personally I'm not to fussed on MVHR system as I'm the kind of person that likes to have a window or 2 open so heat would be lost regardless.

Solar thermal I thought would help with hot water demand but obviously the winter I knew it wouldn't help so much.

If an ASHP can give us a decent hot water temperature and demand then I'd happily just stick with that and UNF.

Was mainly looking to see what people experiences with ASHP systems were for DHW supply.

 

2 hours ago, Bramco said:

 

Agree wholeheartedly - we installed solar thermal when PV was too expensive - it's great in the summer for hot water but you need a few panels for it to be effective. In the winter it doesn't really do a lot, so no use for hot water, which in your question would mean an immersion heater if you didn't use the ASHP. If you use the ASHP for hot water as well as UFH then it should be up to a third cheaper than an immersion heater due to the COP of the ASHP.  MVHR will simply mean you don't lose a lot of heat through the air changes you need for air quality.

 

When PV came down in price we installed some PV - sadly we didn't remove the solar thermal and replace it with PV - wish we had!!  PV is much more versatile as you can divert any excess through an immersion heater into your hot water tank - and when that's had enough it will supplement the power needed for any other electrical devices and if they aren't using anything into a battery for later consumption, or your EV. 

 

And hopefully in a couple of years more vehicle manufacturers will get 'enlightened' and allow V2H or V2G - in which case you won't need a house battery as you'll have one on 4 wheels parked up outside. (Only the Leaf does this currently). Batteries are great for some of the new electricity tariffs like Octopus agile - if you can avoid the peak times, rates are cheap and last summer they were paying you to fill up your EV or battery storage overnight - yes a few p per kW to take electricity off their hands!!  Kerching!! 

 

Simon

 

PS We're also about to start a new build - ASHP (UFH and DHW), MVHR and a 4kW PV array (and when the SAAB convertible dies an EV...)

 

PPS I saw a table comparing prices of batteries on Naked Solar (was put on to this by a Mesh Energy presentation) Tesla come out as one of the cheapest in their comparison which wasn't what I expected -> https://nakedsolar.co.uk/storage/   scroll down a bit to see the comparison table.

@Bramco we do have solar pv on the garage at the site currently. I have considered battery but we will install at a later date

[PeterW]

17 minutes ago, Dicky said:

Personally I'm not to fussed on MVHR system as I'm the kind of person that likes to have a window or 2 open so heat would be lost regardless.

Nothing with MVHR stops you opening Windows - it just ensures that where air is lost from the building in kitchens and bathrooms that it has 70-85% of its heat returned to the house. 

[Dicky]

@PeterW I understand it doesn't stop me from opening the windows, but That heat that can be recovered from kitchens and bathrooms and returned into the house, if a window or two are open (mainly during good weather) will still be lost.

 

Am I right in saying I will need a good air tightness to the house for a MVHR system.

[SteamyTea]

Why do you like to open windows?

 

And a new build should be as airtight as possible, regardless.

[joe90]

I am another with ASHP for UFH and DHW, like @ProDave I heat my water to 48’ with a larger tank, washing dishes you cannot keep your hand under the hot Tap when running!!!. And baths and showers are more than hot enough.

 

27 minutes ago, Dicky said:

Am I right in saying I will need a good air tightness to the house for a MVHR system.

generally yes, but when you get to good insulation levels the airtightness becomes more important and not expensive to do, just takes an eye to detail, lots of threads here about it.

 

27 minutes ago, Dicky said:

I understand it doesn't stop me from opening the windows, but That heat that can be recovered from kitchens and bathrooms and returned into the house, 

we tend to open windows in the summer so I switch the MVHR off!. In the winter the windows stay shut and waste heat is saved. A previous member here (@jeremy) his wife wanted windows open but by measuring air quality he proved to her that the MVHR was much more efficient in giving good air quality by a factor of 5 than opening windows.

 

27 minutes ago, Dicky said:

if a window or two are open (mainly during good weather) will still be lost.

you don’t need to save heat if the weather is good, most have a summer bypass anyway so heat is not returned to the house!!!

Edited December 12, 2020 by joe90

[Dicky]

16 minutes ago, SteamyTea said:

Why do you like to open windows?

 

And a new build should be as airtight as possible, regardless.

@SteamyTea Just to allow fresh air in and to let the house breath a little. Even these winter months there's always a window or 2 open 

Edited December 12, 2020 by Dicky

[PeterW]

5 minutes ago, Dicky said:

@SteamyTea Just to allow fresh air in and to let the house breath a little. Even these winter months there's always a window or 2 open 

Thats what MVHR does - takes stale warm air from the house and replaces it with filtered fresh air. Have you been inside a house with MVHR out of interest ..?

[Dicky]

4 minutes ago, joe90 said:

I am another with ASHP for UFH and DHW, like @ProDave I heat my water to 48’ with a larger tank, washing dishes you cannot keep your hand under the hot Tap when running!!!. And baths and showers are more than hot enough.

 

generally yes, but when you get to good insulation levels the airtightness becomes more important and not expensive to do, just takes an eye to detail, lots of threads here about it.

 

we tend to open windows in the summer so I switch the MVHR off!. In the winter the windows stay shut and waste heat is saved. A previous member here (@jeremy) his wife wanted windows open but by measuring air quality he proved to her that the MVHR was much more efficient in giving good air quality by a factor of 5.

 

you don’t need to save heat if the weather is good, most have a summer bypass anyway so heat is not returned to the house!!!

Thanks for the information @joe90. Was quite surprised with the MVHR stat about air quality.

 

so an ASHP alone should do us well for heating and DHW without looking at solar thermal. I understand MVHR has nothing to do with heating water but that was my main concern. Not really sure now why the company I spoke to tried to usher me down the MVHR route when the hot water supply was my main concern.

[Dicky]

@PeterW sadly I haven't been in a house with MVHR, im unsure if there are actually any around where I live.

I understand that's what an MVHR system does, just wondering if the price tag is worth it tho.

[SteamyTea]

16 minutes ago, Dicky said:

just wondering if the price tag is worth it tho

Once you go past a certain point of insulation, heat losses via ventilation start to dominate, MVHR recovers much of those losses, and gives you fresh air.

And in the summer you can turn it off, and in the shoulder months it can be set up to draw in colder air from outside, without any preheating if wanted.

[joe90]

30 minutes ago, Dicky said:

Not really sure now why the company I spoke to tried to usher me down the MVHR route when the hot water supply was my main concern.

Frankly he was talking bollocks!

 

 

Edited December 12, 2020 by joe90

[joe90]

30 minutes ago, Dicky said:

so an ASHP alone should do us well for heating and DHW without looking at solar thermal.

Yes but as long as it’s designed and installed properly, there are plenty of people dissatisfied with ASHP but only if it’s not designed and installed properly (I designed and installed my own, so not rocket science!).

[SteamyTea]

Energy in > Energy out

All you need to know really.