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Drayton heating controls - an interesting function

Writer's picture: Stephen MonneryStephen Monnery
Drayton Wiser heating controls
Drayton Wiser heating controls

After some research, I decided to use the Drayton Wiser heating controls for our new heat pump installation at Artimus Towers.


Several years ago, we installed a PV system with a GivEnergy inverter and battery. This enables us to see how much electricity the house is using during the day. What jumped out is that the heat pump appeared to be cycling on a very regular basis.

Graph showing the electricity demand over 24 hours.
Graph showing the electricity demand over 24 hours.

I initially jumped to the conclusion that the heat pump was short cycling. Short cycling is where the heat pump is switching on and off over a period shorter than the manufacturer has designed, which can cause the heat pump to wear out prematurely. The heat pump switches off when it has reached the required water temperature.


Some of the reasons for short cycling are:

• Heat pump output exceeds demand

• Poor flow through the primary circuit, so the water circuit can't absorb and deliver the heat supplied

• Insufficient water volume in the primary circuit, so the water circuit can't store the heat delivered


After some thought, I checked the frequency of the peaks and troughs. Regardless of the outside air temperature, the frequency was about every 10 minutes. I thought the controller may be at fault and so slaved a new controller in, as I have a spare unit I use for setting up new systems. The frequency changed to every 20 minutes. The second controller was also a Drayton but a different model. I checked the documentation supplied but couldn't find any reference to the cycling.


Next I tried a smart control system from a different manufacturer; the cycling stopped.

Graph showing the demand profile for 12 hours without the cycling
Graph showing the demand profile for 12 hours without the cycling

The heat pump is working fairly constantly, meaning its output is meeting demand and so is in line with the system design. I’m obviously pleased about this as I designed the system! Secondly, the heat pump is working at lower power when compared to the cycling. This makes sense as the heat pump has modulated its output to meet demand. I love it when a system works as it should!


After more research, I found that some Drayton controls cycle the heating supply to try and ensure the energy inputted into the property meets demand. This is particularly relevant when the room temperature is close to the desired temperature and the system is trying to prevent the heating overshooting and so waste energy.


I plan to contact Drayton to see if they are willing to make the requirement to change the heat source setting more obvious in the setup documentation.


So, what are the key takeaways from this?

If you are using a Drayton control system with a heat pump, make sure the heating source is set to heat pump, otherwise the controller will cycle the heat pump more frequently than the manufacturer has designed, potentially wearing out the heat pump faster.


I need to see if the system is more efficient cycling 3 times an hour or working constantly but at a lower power. If I manage to pull together enough data for this, I’ll post the results.


Ultimately, I'm looking for the heat pump to work at its most efficient, thus lowering the cost and carbon footprint of my heating. I can then share this knowledge with clients and recommend the most cost effective solution to suit their premises.

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