Heat pump control, timed, 24/7, modulated or a combo?

I was curious how you ran your heat pumps, timed, 24/7, modulated or a combo?

I have my heat pump “on” 24/7, but with a setback temperature for nighttime.

Flow temperature is controlled by a combination of weather compensation and load compensation.

My Vaillant is running 24/7 on weather compensation
Target 20.5C indoor during the day
Night time setback of 19C

Heat pumps prefer to run low and slow.
Using weather comp you match the input from the rads/ufh to the heat loss of the rooms, so it just trickles the right amount of heat in to stay at target temp.

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Thanks, that is just what I wanted to know. How is the heat pump modulated?

It just adjusts demand (flow temp) based on outside temp. Although I do have “room influence” set on my Vaillant.

You can see the ebs and flows of outside temp versus flow temp by looking at the graphs.

Yes, but how does it vary the heat output? I understand the setpoint can be weather comensated. Does the compressor have a bypass or does its motor slow down, or does it just cycle on and off?

Heat pump modulates the compressor itself, between ~30% up to 100%, based on how much heat is needed to get up to the flow temperature.

Here’s an example of Mick’s heat pump modulating itself. At the start of the cycle, it puts in 2 kW of electricity (blue) to get up to the flow temperature (red) up to the target (40C), and then reduces back down to 1 kW to cruise along in at a steady temperature. Overall, this cycle is about an hour long.

Thanks. But how does it modulate?


It adjusts the speed of the compressor, which affects how much electricity it consumes and how much heat it outputs.

Cycling heatpumps on and off is generally avoided where possible.

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Bingo! Thanks. I wonder if other systems use something like a hot-gas bypass as variable-speed motors are quite expensive. I am reading the links posted by Zarch.

I think all modern heat pumps will use an “inverter drive unit” now, as explained by this article.

An inverter heat pump will continuously modulate its output in the background to provide the consistent temperature. It reacts to changes in heat demand to make sure the fluctuation in temperature is kept to a minimum. Whereas a fixed output heat pump will continuously cycle between maximum capacity and zero, finding the right balance to supply the temperature needed cycling more often.

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