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How is water flow controlled in a heat pump system?

 
Air Source Heat Pumps (ASHPs)
Last Post by Gary 2 years ago
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 wvtienen1
(@wvtienen1)
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Topic starter 28/01/2025 8:30 am   [#2058]

Comming from a +20 years old heatpump installation where the flow of the water flow is fixed I am trying to understand how the water flow is controlled in modern modulation ASHP.

I am looking at the simple installation of floor heating, no thermostats in the house, floor heating always on, no water buffer....

When the heatpump modulates because heat demand drops because of higher outside temperature. 

- do HP keep the water flow constant (and this changing the delta temperature over the inflow-return)

- do HP change the flow so delta temperature over the inflow-return stays constant..

Or what do heatpump (of the circulation pump) control and how?  

And is there a best solution for efficiency?

Walter



   
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 Gary
(@gary)
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28/01/2025 9:18 am  

The short answer as always is it depends, different models do it differently.  Mitsubishi is constant flow rate so as the heat pump modulates down you will see changes in delta T.  Other manufacturers modulate the circulation pump flow rate and try to target dT5.

Is there an inherently better way to do it for efficiency, I don't believe so as just different sides of the mass flow equation in my opinion unless you want get into the watts a circulation pump uses.



   
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 wvtienen1
(@wvtienen1)
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Topic starter 28/01/2025 9:45 am  

Thanks for the feedback!

How does Mitsubishi control the flow rate? Is that the pump that does measure the rate or the Heatpump that measures and controls the pump power? And how is the pump power controlled? 

(Sorry for the questions; I have a hard time finding that info on the installation guides).

I indeed think my question goes back to how different manufacturers implement their controls and I guess it goes together how they manage the modulation of the heatpump.  

Thinking about it: Lowest water side temperature is best... So that would mean high water flow, meaning there would be no need to modulate the circulation pump down...

Maybe only when there is no heat demand from the house.

Opening the question how manufacturers would organize the modulation of the heatpump... 



   
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 Gary
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28/01/2025 10:02 am  

@wvtienen1

Posted by: @wvtienen1
↑

How does Mitsubishi control the flow rate? Is that the pump that does measure the rate or the Heatpump that measures and controls the pump power? And how is the pump power controlled? 

There is a flow meter that measures the flow rate and can be accessed on the heatpump controller, the pump speed/power can be set from the heat pump controller to an arbitrary value (1-5), you can then check the flow rate that each of these values achieves. 



   
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 wvtienen1
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Topic starter 28/01/2025 10:29 am  

@gary and how does Mitsubishi control the pump? Is there stearing signal going to the pump (pwm?) or ...?

Sorry fore the detailed question.  In think I need to read about circulation pump controls...



   
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 Gary
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28/01/2025 10:34 am  

@wvtienen1 Yes its controlled by a signal to the pump, if I change the value on the heatpump controller I can hear the pump speed up or slow down and I can see an increased or decreased flow rate on the controller.



   
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