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Grant Aeona 3 R32 cycling with weather compensation.

 
Air Source Heat Pumps (ASHPs)
Last Post by GrahamF 6 months ago
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 GA3_USR
(@ga3_usr)
Active Member Member
Joined: 11 months ago
Posts: 8
Topic starter 13/05/2026 5:18 pm   [#2992]

Our Heat pump has a low deltaT of 1 to 2degC. 

 

The way it appears to operate from being idle (no compressor, circulating pump runs 24hrs, room stat set at 24deg, WC enabled.)

 

The flow temperature drops to a certain value below the target flow temperature. The compressor starts at full pelt and flow temperature starts to rise.

When the flow temperature reaches the target the compressors throttles right back and micro adjusts itself so the flow temperature matches the target temperature during this time the flow temp may be a bit above or below the target.

 

Then one of the following seems to happen;

 

  1. The slug of initial hot water from the start of the cycle returns, and if this is hotter than the measured flow temperature the compressor stops until the flow and return are cool enough for the cycle to restart.

 

  1. The heat pump manages the compressor so flow temperature  matches target temperature, it doesn't get caught in the above loop and just runs steady for hours.

 

  1. The same as point 2, but at some point the outside temperature increases by 1degC, the target flow temp decreases by 1degC then the heat pump throttles back to lower the flow temperature and either the loop in point 1 begins, or it manages to continue as per point 2.

 

Given the resolution and precision of the data from the grant smart controller it's difficult to know if the above is the logic or just coincidence and I'm just seeing something which isn't there.

 

My thinking is if I could get the system to loose a little more heat through the radiators and have a larger delta T at the heat pump the system would ride out the small changes in outside temperature much better.

 

Any thoughts?

 

The images show what I would consider normal operation, and the cycling I'm trying to describe.

Compressor Hz,

Temperatures, Green:DHW, Blue:target flow temp, Yellow: flow temperature (at HP), Red: Return temperature (at HP) 

 

Screenshot 20260509 193606~2
Screenshot 20260509 142640~2

 

 

sd


   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 5602
13/05/2026 10:45 pm  

Posted by: @ga3_usr
↑

My thinking is if I could get the system to loose a little more heat through the radiators and have a larger delta T at the heat pump the system would ride out the small changes in outside temperature much better.

 

Any thoughts?

If the system loses more through the radiators the house will get warmer.  Is that what you want?  If you do want this then you will need to increase the flow temperature.

All heat pumps and boilers cycle if the house demand is less than the minimum output of which the device is capable.  This is bound to happen at moderate OATs and may happen even at low OAT if the heat pump/boiler is oversized.

What is it that you think is abnormal in your case?


This post was modified 6 months 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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 GA3_USR
(@ga3_usr)
Active Member Member
Joined: 11 months ago
Posts: 8
Topic starter 14/05/2026 5:40 am  

@jamespa 

What I would think of as abnormal would be the heat pump cycling on every small blip in another otherwise fairly consistent OAT, as opposed to cycling because the house is up to a temperature that it can't take any more heat from the radiators.

Of course without access to a detailed log I can only ever guess at what triggers what in the logic.

What I might do as an experiment is, if I catch a time when it looks like small OAT changes are causing cycling is turn off the WC, fix the flow temperature to that temperature and see how it behaves.  It might be Autumn for that though.

 

 

 



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 5602
14/05/2026 5:59 am  

Posted by: @ga3_usr
↑

What I would think of as abnormal would be the heat pump cycling on every small blip in another otherwise fairly consistent OAT, as opposed to cycling because the house is up to a temperature that it can't take any more heat from the radiators.

That would be abnormal but I cant see from your charts that its doing that.  The first chart looks like roughly hourly cycles, the second a single cycle and the third cycles every 2-3 hours.  The ups and downs of the compressor modulation seem to indicate a bit of hunting in the compressor modulation control loop, but I wouldn't worry about that personally, unless someone tells me otherwise.  Im concentrating mostly on the yellow (to understand what the FT control loop is doing) and ignoring the short term noise on this signal which could be due to almost anything including the effects you have mentioned (or it could literally be noise)

 


This post was modified 6 months 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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GrahamF
 GrahamF
(@grahamf)
Estimable Member Member
Joined: 2 years ago
Posts: 137
15/05/2026 7:12 am  

The hot water heating looks normal.  The heat transfer into the tank is so fast that the heat pump takes a long time to reach the target flow temperature.  When it does, or when the timer expires, it switches back to space heating.

The cycling is happening over a long period of time.  The heat pump is stopping for an hour and not just for a few minutes.  It is behaving as though the room thermostat has reached its target temperature and is no longer asking for heat, but that seems unlikely with a 24C target room temperature.

It would be interesting to plot the target and actual room temperature and outdoor temperature as well, if that is possible.

What are your weather compensation settings?

 


This post was modified 6 months ago by GrahamF

Grant Aerona 290 15.5kW, Grant Smart Controller, 2 x 200l cylinders, hot water plate heat exchanger, Single zone open loop system with TRVs for bedrooms & one sunny living room, Weather compensation with set back by room thermostat based load compensation


   
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