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Grant Aeona 3 R32 cycling with weather compensation.

Air Source Heat Pumps (ASHPs)

Last Post by JamesPa 7 hours ago

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GA3_USR

(@ga3_usr)

Active Member Member

Joined: 6 months ago

Posts: 6

Topic starter 13/05/2026 6:18 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;

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.

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.

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)

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 4858

13/05/2026 11:45 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 7 hours 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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