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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 Potatoman 6 hours ago
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 Potatoman
(@potatoman)
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01/04/2025 10:01 pm  

@editor That's an interesting idea, I am not sure how they work, do you have any more details on them


   
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Mars
 Mars
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Topic starter 01/04/2025 10:20 pm  
buffer

@potatoman as you already know a four-port buffer can cause heat pump inefficiencies due to uncontrolled blending of hot and cooler water, which reduces the supply temperature and forces the heat pump to work harder.

3 pipe buffer

In contrast, a three-port buffer helps maintain stratification, reduces unnecessary mixing and ensures that the heat pump isn’t cycling. This improves efficiency and keeps return temperatures lower.

volumiser

A volumiser, while not technically a hydraulic separator, can also satisfy most manufacturers’ minimum volume requirements. Its primary role is to provide thermal mass to prevent short cycling, but because it’s integrated more seamlessly into the system than a four-port buffer, it avoids distortion issues.

Ultimately, both the three-port buffer and the volumiser offer better solutions than a standard four-port buffer by reducing mixing, maintaining flow rates and ensuring the heat pump operates within its optimal parameters.

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 JamesPa
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01/04/2025 10:57 pm  

Posted by: @potatoman
↑

@jamespa surely there must be a third way to improve efficiency, not just buffer or no buffer, but to balance a buffer, especially if you are using an open loop system.

Yes there is, provided the buffer is tall and well designed so there is stratification (forget 50l buffers so commonly fitted)

With one of these you have two temperature sensors and then you can detect where the thermocline (the division between cold water at the bottom and hot at the top) is.  This information can be used to switch the secondary pump on or off to ensure its always in the middle section.

Alternatively you can attempt to do it 'open loop' by adjusting the pumps either side to run at the same speed.  This only works fully with heat pumps that don't modulate the water pump speed to keep deltaT constant, unless they can modulate both water pumps, and with no valves that can switch on and off on the secondary side.  Effectively you are adjusting the pumps to operate as if the buffer tank weren't present at all (underlining the fact that it is unnecessary!).

You can also adjust the secondary pump to be slightly slower than the primary, ensuring the thermocline is at the bottom and thus the flow to the emitters is at the same temp as the flow from the HP.

Any of these are likely to be better than doing nothing.

 

Posted by: @judith
↑

they do allow a volumiser to be used, so the obvious question is could a 4 port buffer be configured as a volumiser and stay in warranty?

 

if that is the case then re-configuring it as a volumiser is the best thing to do.  The answer to the question 'can this be done?' is yes.  

 

This post was modified 1 day 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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 Potatoman
(@potatoman)
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02/04/2025 7:11 pm  

@editor Thank you for the information,do you have any information or a link of how to pipe up a 3 port buffer


   
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