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(How) does your heat pump control its water pump?

 
Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 15 hours ago
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 JamesPa
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Topic starter 23/03/2025 9:36 am  

I'm in the process of writing up a piece highlighting the most common 'problems' that underlie the challenges people report with their ASHPs.  Hopefully I will also be able also to write up some solutions!

If the 'problem' is caused by a LLH, PHE or buffer tank, the 'solution' is affected by the control of the water pump.  I am thus interested in understand which models of heat pump control the speed of their water pump, and if so what the control attempts to achieve.  Im particularly interested in the answers for

  • Daikin
  • Midea
  • Panasonic
  • LG
  • Mitsubishi
  • Nibe
  • Samsung
  • Grant
  • Cool Energy

If you have one of these (or any other for that matter) and have worked out whether and how your heat pump controls its water pump(s) I would be most grateful if you could post answering the following (to the extent you know the answers).  If you prefer not to post feel free to DM me:

 

  1. Make and model of heat pump?
  2. Does your heat pump control the speed of the water pump?
  3. If so, do you know what it tries to achieve by doing so?
  4. Can your heat pump also control the speed of a secondary water pump (ie a water pump on the emitter side of a buffer tank, LLH, or PHE)?
  5. Does the heat pump also have the option to operate the water pump(s) at fixed speed? 

Many thanks for any info.

This topic was modified 2 days ago 2 times 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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bontwoody
 bontwoody
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23/03/2025 12:46 pm  

@jamespa 

Heat pump as per my footer, it has an option to use PWM via a cable to the pump. Below is todays graph.It only appears to change the pump speed when starting up and then it settles down to a steady flow. I was operating it at a fixed speed before I changed my pump to one that supported PWM.

{3376CBC5 F391 494D BBBF FA7CE932E5A8}

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 JamesPa
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Topic starter 24/03/2025 8:17 am  

Thanks.  To me it looks like pump speed follows compressor modulation (which makes some sense if it is trying to maintain roughly a fixed DT across emitters). 

As  matter of interest why did you change the pump to PWM and did it make a difference?

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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bontwoody
 bontwoody
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24/03/2025 8:37 am  

@jamespa I had a discussion with iancalderbank 

https://renewableheatinghub.co.uk/forums/thermostats-trvs-pumps-valves/pwm-pump-or-not#post-18612

Hard to tell what difference it has made as I was still in the throes of setting things up. 

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 Heatgeek
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24/03/2025 7:33 pm  

@jamespa

Hi. Information as requested.

1. Samsung Split Gen 4 with Grundfos UPM3 PWM pump integrated in the internal unit with PHE, running for 10 years.

2. Yes.

3. It MODULATES the flow according to heat load to maintain a steady dT of 5C, which I have given up trying to explain.

4. Yes.

5. No.

I have a UFH system for 200 sqm house with multiple loops, all in parallel. The HP connects directly to the manifold without mixer, and with one flow meter and thermometers for main F/R and all loops. Some secondary loops are kept open to meet minimum flow requirement. The rest, for principal rooms, are controlled by Heatmiser thermostats to deliver the precise amount of heat within the residual modulation range and gives flexibility of programming. As zones turn on and off randomly, the HP modulates its water flow to maintain 5C dT across loops, providing long running periods. The main issue is the Samsung mechanical 7 l/min flow switch which controls the flow alarm and is fitted to all models, even today it seems. This determines the minimum flow @2.5kW which restricts the range of smaller units which have the ability to modulate lower. A 5 l/min or less flow switch does not seem to be available on the market so other tricks have to be made. Samsung could be more intelligent by designing an electronically measured flow meter.

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


   
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 JamesPa
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Topic starter 24/03/2025 10:47 pm  

Thanks that's helpful.

 

Posted by: @heatgeek
↑

The main issue is the Samsung mechanical 7 l/min flow switch which controls the flow alarm and is fitted to all models, even today it seems. This determines the minimum flow @2.5kW which restricts the range of smaller units which have the ability to modulate lower.

So what do the smaller units do when the demand is <2.5 kW. If the compressor can and does go lower (which you imply it can) but the flow rate remains high, the DT will fall.  Is this what it does? 

Or does it stop the compressor modulating down (even though it could modulate down further), and thus cycle prematurely?

The latter seems bizarre but you seem to imply is the behaviour.

A separate question, but do the latest Samsung models still use hot gas bypass to extend the compressor output range?

This post was modified 15 hours ago 2 times 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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