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Domestic Hot Water & Cylinders
Last Post by Toodles 7 months ago
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 asoksevil
(@asoksevil)
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07/08/2025 8:42 pm  

I am thinking on installing this as well given space constraints. 

Is it actually better to let the solar PV or the battery charge the sunamp

for hot water and use the ASHP entirely for heating? (Underfloor heating). Or would you go about this? 

 


This post was modified 7 months ago by Mars

   
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JamesPa
 JamesPa
(@jamespa)
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Posts: 4391
09/08/2025 7:58 am  

Posted by: @asoksevil
↑

I am thinking on installing this as well given space constraints. 

Is it actually better to let the solar PV or the battery charge the sunamp

for hot water and use the ASHP entirely for heating? (Underfloor heating). Or would you go about this? 

 

Depends on your electricity tariff and in particular your export tariff, also on time of year.

So for example my import tariff is 7p midnight-7am, 25p the rest of the time.  My export tariff is 16.5p.  So for me it makes sense to do DHW heating at night on the heat pump (and as a result export more), even though the heat pump will be less efficient than if I did it during the day.

If I didn't have an export tariff then self-consuming as much solar as possible makes sense.  In this case there is an argument for a solar diverter (which I guess but dont know you can use with a sunamp) precisely to match the load to the available excess, or alternatively play the numbers game by scheduling the ASHP to do the DHW/sunamp heating from noon-2pm or thereabouts, reckoning that, on average, this will work out better.

In winter all of your solar will be consumed by the ASHP anyway most days, so best just to use the ASHP to heat the sunamp at a COP of 2, rather than the resistance electric element at a COP of 1, whatever your export tarrif.

The other calculation that might be worth doing is payback time for the additional cost of the sunamp with the facility to be heated by the ASHP, relative to an electric-only one.  Its probably a long time!  An electric-only sunamp would invalidate the BUS grant, however, so may not be an option.

 


This post was modified 7 months ago 4 times by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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Toodles
 Toodles
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Topic starter 09/08/2025 8:12 am  

@jamespa Just for clarification, yes the Myenegi Eddi can be used to supply the Sunamp thermino. We have the Sunamp Thermino ePV210 version which is heated from solar or grid energy; by the way, we did get the £5000 BUS grant, perhaps that is because the solar energy may be used to heat the water. Our ASHP does not heat the DHW at any time - but we do have some space in our airing cupboard!😉 Regards, Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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JamesPa
 JamesPa
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09/08/2025 9:55 am  

Posted by: @toodles
↑

We have the Sunamp Thermino ePV210 version which is heated from solar or grid energy; by the way, we did get the £5000 BUS grant, perhaps that is because the solar energy may be used to heat the water. Our ASHP does not heat the DHW

Interesting, I must reread the BUS rules for this combo....

 

....Ok the relevant rules are below. I can't see how a heat pump with electric only sunamp meets condition (c) unless previously your dhw was heated on immersion only, which may be the case, but then it falls foul of (b).

Of course that's all a bit academic!

 

 A heat pump meets the suitability criteria in relation to the eligible property, or a property to which regulation 14(1)(b) applies, for which it is installed where—

(a)it provides heating—

(i)solely to that property, or to both that property and any related property, and

(ii)for the purpose of both space heating and hot water heating, using liquid as a medium for delivering that heat,

(b)it is capable of meeting the full space heating and hot water heating demands of that property, and

(c)it replaces the heat generating components of the original heating system installed in that property (where applicable), other than any—

(i)supplementary electric heater, including any immersion heater,

(ii)circulation pump, or

(iii)solar thermal collector.


This post was modified 7 months ago 3 times by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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Toodles
 Toodles
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Topic starter 09/08/2025 3:11 pm  

@jamespa A few days after the installation had been commissioned, I had a ‘phone call from someone within the hallowed temples (AKA MCS) to enquire if my system had been installed to my satisfaction and if everything was fully operational. The enquiry included a reference to my DHW and was everything working fully? I assured the gentlemen who rang from the hallowed temples that yes, all was working fine. His paperwork will (I suppose) have shown the details of the heat pump and the DHW arrangements; he made no further mention nor did he ask any more about the Sunamp system and my installer received the grant on my behalf. Regards, Toodles.


This post was modified 7 months ago by Toodles

Toodles, heats his home with cold draughts and cooks food with magnets.


   
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