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Solar Thermal as a pre-heater for a heat-pump

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Mars
 Mars
(@editor)
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@chris-a, thanks for sharing and it’s all looking very positive. Keep us updated as temperatures start to drop. I’ll be great to get an update in December.

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(@derek-m)
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@chris-a

Thanks for the update, it is always very useful to get feedback, whether suggestions work or do not. Dependent upon the capabilities of your heat pump controller, it may be possible, during the Winter period, to set the DHW heating temperature to say 50C or 55C during the cheap overnight period and then drop it back to 45C during the rest of the day.

This would help keep the cost down, but would of course mean the heat pump would be working harder during the colder overnight period when it will be less efficient.

This is one of the problems with both water heating and home heating using ASHP's, in that weather conditions can vary quite considerably from day to day, so settings that work well one day are far from ideal the following day. I suppose it is a matter of finding the settings which give the most consistent results during the different periods of the year, so you may need Spring settings, Summer settings, Autumn settings and Winter settings.


   
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(@ken-bone)
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Have installed two systems like this for clients already. 

Heat pump installer


   
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(@derek-m)
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Posted by: @ken-bone

Have installed two systems like this for clients already. 

Two systems like what? Please clarify.

 


   
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(@ken-bone)
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Posted by: @derek-m

Posted by: @ken-bone

Have installed two systems like this for clients already. 

Two systems like what? Please clarify.

 

I have had the pleasure in working with clients who believed in my proposed setup, (which is not new).

So the system consisted of heat pump and system upgrade, new dual coil solar/heat pump hot water cylinder.

1/ ST array wall mounted facing South/East. 

2/ ST array facing South on pitched roof.

Another buffer the would be heating with low grade ST in the winter, once it hits a certain threshold it can be used to preheat the heat pump return.

 

 

 

Heat pump installer


   
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(@johnmo)
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Posted by: @transparent

configure it as a pre-heater to a heat-pump when one gets installed

 

I am currently doing a project where the ST is directly plumbed into the return piping to the ASHP via a close coupled tee. The ASHP does DHW and UFH, with UFH flow temps typically around 30, sometimes higher or lower depending on OAT. The aim is to add temperature to the return flow when solar is available, through a close coupled tee.

The solar system is a drain back with PHE. 

IMG 20230712 180310

Basically I will run the DHW via a thermostat and timer and the solar thermal has a legionella program, so will run at the same time as the DHW call for heat. This will increase the return to the heat pump up to 60 degs, the hope is the heat pump will stop adding heat but carry on circulation until thermostat is made.

UFH will be similar to the DHW, but will be limited to 35 degrees, via the normal setting within the controller.  A temperature probe downstream of the CCT will be linked into the ST controller.

 

Hoping the low temperature requirements will improve the yield from the panel. I have a heat meter installed to get an idea of efficiency and how much energy savings are available.

 


   
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