Improve efficiency: Hold down the flow temperature as long as possible

My heat pump has a habit of quickly ramping up the flow temperature up to the desired flow temperature.

Unfortunately that means:

  • It’s spending more time running at less efficient flow temps
  • It needs to de-frost itself

So I’ve taught it to behave more sensibly.

My control algorithm that turns the heat pump on chooses a low initial “desired” temperature. The heat pump ramps up to that and then I watch to see when it it starts to dip or if it’s been constant for quite a while. In that case I nudge up the desired temperature and the heat pump keeps chugging along rather than deciding it should give up.

In this graph you can see the desired temperature is slowly nudged up.

The initial desired temp is set based on the weather and the current flow temp. For example, we always make the initial desired temp higher than the recorded flow temp or else the heat pump decides it’s not worth doing anything.


Whilst I’m very aware that the “instantaneous CoP” is mostly nonsense, here’s a good example where I think it might be telling me something useful.

As I tinker with the target flow temperature I often find the return gets quite close and so it’s possibly not as efficient at that point.

I think this graph is showing the efficiency wobble up and down as the return gets too close to the flow.

It’s showing that each time I bump up the target flow temp the efficiency can improve.

Unfortunately, as it goes from left to right the peak efficiency drops because the flow is getting hotter and the delta with outside is getting bigger.

So we’re trying to balance the “difference between the return and flow” with the “rising flow temp”. It’s questionable that holding down the flow is improving things. That’s why I need data from my experiments.

Notably my control algorithm doesn’t even bother attempting this when the outside temp is over 10Celsius because the flow temp rises so quickly anyway that the default flow controller behaviour is fine.