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Avoid the Heat Pump Villain: Why Low-Loss Headers and Buffers Can Sabotage Your Heat Pump's Efficiency

 
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Air Source Heat Pumps (ASHPs)
Last Post by SUNandAIR 10 hours ago
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 Heatgeek
(@heatgeek)
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Joined: 5 months ago
Posts: 111
03/05/2025 10:06 am  

Posted by: @jamespa
↑

Presumably mixing of return water with flow water to the emitters (and thus a reduction of ft to emitters) will however still occur if the primary pump throughput is less than the secondary,

This could be mitigated by putting a one way check valve on the top input so that flow is only downwards. Can't think of any detrimental effects.

Private individual. No affiliation with commercial "Heat Geeks" of same coincidental name.


   
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 JamesPa
(@jamespa)
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Joined: 2 years ago
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03/05/2025 1:08 pm  

Posted by: @heatgeek
↑

This could be mitigated by putting a one way check valve on the top input so that flow is only downwards. Can't think of any detrimental effects 

Or of course not having a buffer at all! 

Would an installer that wants to fit a buffer unnecessarily because 'thats what we do' or because of warranty reasons be prepared to fit a three way buffer with a one way check valve.  I suspect this would be a tiny minority!

It's ab interesting thought experiment though.

This post was modified 12 hours 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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SUNandAIR
 SUNandAIR
(@sunandair)
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Joined: 2 years ago
Posts: 487
03/05/2025 2:41 pm  

Posted by: @heatgeek
↑

 

 

3 Port Buffer Tank

@heatgeek I kind of get it… but aren’t you still in the same situation of having excess flow temp water at the bypass entering the buffer at circa 23 LPM.

In so doing, raising the return temp and narrowing the DT… ergo prompting a raising of the flow temp and inducing the cycling.?

Only now there are 2 pumps?

(It isn’t like it’s just trickling into the buffer, is it? And the return pump will want to maintain the flow rate, for sure!)

Also on 4 port systems I’m not convinced that PWM pumps can cope with matching actual water flow rates, at variable speeds on either side of the hydronic circuits - since there is already believed to be a compromise or resistance to flow on the emitter side. Yet that’s possibly the very reason why buffers are being proposed. 

Is there a proper definition as to why buffer tanks are being specified and what exact problem is expected to be overcome?

 

 

 

This post was modified 10 hours ago 2 times by SUNandAIR

   
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