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Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 31 minutes ago
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 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 2 years ago
Posts: 2468
22/05/2025 3:04 pm  

Posted by: @johnmo
↑

Posted by: @jamespa
↑

Almost but not quite a trv with remote sensor.  A trv with or without a remote sensor operates principally, so far as I know, as an on off device (albeit that there is an element of analogue control). 

No they are not on/off valves, they modulate flow. Exactly what you say you want, they do our the box. Modulate radiator flow based on room temperature. So as to keep room a a set temperature. Add weather compensation, they will continue to modulate flow as needed.

Simple description of a trv

https://www.traderadiators.com/blog/how-do-thermostatic-radiator-valves-work

Er - that description you posted says that the trv shuts off the flow when the room is at the set temperature, which is also what seems to happen in practice at least with my Drayton trvs.

 

 

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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 Johnmo
(@johnmo)
Noble Member Member
Joined: 2 years ago
Posts: 535
22/05/2025 3:56 pm  

Posted by: @jamespa
↑

Posted by: @johnmo
↑

Posted by: @jamespa
↑

Almost but not quite a trv with remote sensor.  A trv with or without a remote sensor operates principally, so far as I know, as an on off device (albeit that there is an element of analogue control). 

No they are not on/off valves, they modulate flow. Exactly what you say you want, they do our the box. Modulate radiator flow based on room temperature. So as to keep room a a set temperature. Add weather compensation, they will continue to modulate flow as needed.

Simple description of a trv

https://www.traderadiators.com/blog/how-do-thermostatic-radiator-valves-work

Er - that description you posted says that the trv shuts off the flow when the room is at the set temperature, which is also what seems to happen in practice at least with my Drayton trvs.

 

 

Think I attached the wrong link

https://www.draytoncontrols.co.uk/products/radiator-valves/auto-balancing-trvs/auto-balancing-rt414-trv-angled-15mm

 

Maxa i32V5 6kW ASHP (heat and cooling)
6.5kW PV
13.5kW GivEnergy AIO Battery.


   
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 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 2 years ago
Posts: 2468
22/05/2025 6:32 pm  

Posted by: @johnmo
↑

Think I attached the wrong link

https://www.draytoncontrols.co.uk/products/radiator-valves/auto-balancing-trvs/auto-balancing-rt414-trv-angled-15mm

 

Still not quite.  As I read this the body adjusts for fixed flow when on (based on an adjustment made by the installer according to a table that doesn't even include the dt5 condition with which heat pumps are commonly designed) and then the head works like any other head, turning the flow on or off.  We want something that adjusts the flow rate very slowly to achieve the required room temperature, as if adjusting a lsv manually.  It's really a commissioning device not a control device and once set it can stay set.

There is definitely a problem and thus an opportunity.  I've lost count how many times I have explained on this forum how to adjust WC, and then how to adjust lsvs to achieve equal room temps (or the desired different room temps) - in short how to set up an open loop WC based system.  Clearly therefore installers don't always do this which, given how long it takes (elapsed time not actual effort,), is unsurprising.

With a gas boiler installers simply whack up ft to max fit trvs and then let householders sort it out.  It needs to be as simple for an ashp.  There are two (somewhat interlinked) parts of this namely the WC curve set on the heat pump and the flow rates through each radiator.  Balancing for deltaT (which installers may do) is a start, but doesn't finish the job because radiators are inevitably not correctly sized.  Balancing for room temperature (as described also on the heat geek website) is what's needed, but takes time.

 

This post was modified 19 minutes ago by JamesPa
This post was modified 15 minutes ago 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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