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Why Buffer Tanks & Low-Loss Headers Can Sabotage Your Heat Pump's Efficiency

 
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Air Source Heat Pumps (ASHPs)
Last Post by CH_18 3 months ago
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 Tim441
(@tim441)
Honorable Member Contributor
Joined: 4 years ago
Posts: 398
17/02/2025 3:07 pm  

@jamespa measuring with clamp-on heating pipe thermometer? I see ebay/amazon has them around £6 or £7 .. Good enough?


Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV


   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4799
17/02/2025 3:15 pm  

Posted by: @tim441
↑

@jamespa measuring with clamp-on heating pipe thermometer? I see ebay/amazon has them around £6 or £7 .. Good enough?

I believe so, we are looking for difference so as long as you can clamp consistently then it doesn't matter if the figure isn't perfect.

I stress there is absolutely no need to do this unless you want to.

 


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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 Tim441
(@tim441)
Honorable Member Contributor
Joined: 4 years ago
Posts: 398
20/02/2025 3:32 pm  

Borrowed a clamp on thermometer. 

Buffer tank:  PAW-BTANK50L-2 buffer tank
Only 48l
According to ashp controls
leaving temp 33deg
Return 31 deg

Arr from ashp BT 34.4flow
Leave BT 34.1 flow

Arr from house BT 33.2 return
Leave 33.8 BT return

I suspect not great test right now... as mild... so not working hard
Will be better to check on cold morning.. perhaps.

Will report again once more results


Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV


   
ReplyQuote



Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4549
Topic starter 20/02/2025 10:59 pm  

@tim441 the other thing to “check” is where the respective flow and returns are to see if your buffer has minimal distortion. Ideally, it’s plumbed like this:

buffer

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Subscribe and follow our YouTube channel!


   
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 Tim441
(@tim441)
Honorable Member Contributor
Joined: 4 years ago
Posts: 398
21/02/2025 9:32 am  

@editor 

Logically the electronic motorised valve.. I think... stops buffer being used when heating DHW/hot water tank. So will be on flow to BT?

With the pump on right on flow from BT?

Tap at bottom right ... return to BT?

So same as your diagram. but I'll try the thermometer a few times in different scenarios

20250220 135539

 


Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV


   
ReplyQuote
JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4799
21/02/2025 9:53 am  

Posted by: @tim441
↑

Logically the electronic motorised valve.. I think... stops buffer being used when heating DHW/hot water tank. So will be on flow to BT?

Is it a 2 way valve or a 3 way diverter valve.  Normally the (3 way) diverter valve is the only motorised valve needed.

As you say taking some temperature measurements when its working harder would be good, but your initial ones are encouraging.


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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 Tim441
(@tim441)
Honorable Member Contributor
Joined: 4 years ago
Posts: 398
21/02/2025 10:00 am  

@jamespa it's 3 way


Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV


   
ReplyQuote
JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4799
21/02/2025 10:02 am  

Posted by: @tim441
↑

@jamespa it's 3 way

I presume the diverter valve then, which would make sense.  As you say you would expect this to be on the inlet to the BT

 


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)
Trusted Member Member
Joined: 2 years ago
Posts: 57
29/03/2025 8:59 pm  

Hi, so if I wanted to make my system more efficient, It's open loop 28/22/15mm ,all rads,run via a Homely is it possible to remove the buffer tank but still comply with 7-year LG warranty requiring hydraulic separation. Thanks



   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4549
Topic starter 29/03/2025 11:32 pm  

@potatoman can you share LG's official documentation that explicitly requires hydraulic separation to maintain the 7-year warranty?

If you've got that document, it would be extremely valuable to see it.


Get a copy of The Ultimate Guide to Heat Pumps

Subscribe and follow our YouTube channel!


   
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 Potatoman
(@potatoman)
Trusted Member Member
Joined: 2 years ago
Posts: 57
30/03/2025 11:09 am  

@editor

487221638 10163211903663552 6665514382284125271 n

Regards



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4799
30/03/2025 2:14 pm  

To me that reads as 'Hydraulic separation optional but if present covered for 7 years if you take out the extended warranty', as opposed to 'Hydraulic separation mandatory'.  The very last line in the table (mag filter) would seem to confirm this.


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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