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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 3 weeks ago
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 Heatgeek
(@heatgeek)
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Joined: 5 months ago
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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 3 weeks 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: 495
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 3 weeks ago 2 times by SUNandAIR

   
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 Johnmo
(@johnmo)
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Posts: 545
04/05/2025 2:47 pm  

Posted by: @sunandair
↑

buffer tanks are being specified

A buffer is a legacy issue, they were never used on gas boiler systems, but generally specified when fixed output heat pump came along. So unlike today's heat pump which modulates they had a fixed kW output and generally a fixed flow temp. Add to this a UK liking for zones, the heat pump didn't stand a chance of running well without one.

Today people are still obsessed with zones - so it's the easy choice for manufacturers and installers to add one. Plus more product to install and sell, more profit.

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


   
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SUNandAIR
 SUNandAIR
(@sunandair)
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Posts: 495
05/05/2025 10:38 am  

@johnmo yes I can believe that. It seems to be human nature to keep dong what we did before.


   
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