Someone needs to make a relay module

I’ve been running with this relay for most of the winter season, and have found it works pretty well. The technique I used was wait for the compressor to disengage at the end of a cycle, and drop the target flow temperature by 6C. This would convince the heat pump to stay off for a few minutes before starting a new cycle.

However, I did eventually realise a couple minor issues with this approach:

  1. if the flow temp hadn’t yet reached the target temperature, then a 6 C dip below the target doesn’t quite have a big enough affect, and the next cycle starts up soon after. This could be seen as a feature, as it allows the heat pump to reach the target earlier, but this isn’t what I want for my oversized system.
  2. the circulation pumps keep on running while the compressor is off, which seems a little wasteful. It’s only about 120 W, but it’s still going to be dragging my COP down by a tiny fraction.

So, I’ve switched to something more like John’s original suggestion: when my program detects the compressor stopping at the end of the cycle, it turns off the power to the heat pump for 10 or 15 minutes to let the whole system cool down a bit. Then, when the heat pump is turned back on again it will begin a new cycle from a lower flow temp.

I need to put in some smarts to decide when the pause should be 10 minutes or 15 minutes. The shorter pause is better in the morning when trying to heat the house up, while longer pauses are better in the afternoon when we just need to maintain the temperature. I might just stick it on a simple timer for now.


Quite phenomenal though, that a bit of kit worth multiple £K needs to be forcibly switched off to be most efficient! :man_facepalming:

Indeed. Had it been correctly sized to begin with, and been installed with the right controls, I wouldn’t have had to do this. I may at some point fit better controls so that I can use the built-in “autoadapt” feature, which seems to work well on other systems I’ve seen it on. But for now, I can get better performance for “free” by using a software hack.

I think the EcoDan has it’s own “wait X minutes between cycles” feature, but I’ve not be able to find it on my system.

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Auto Adapt is something I have wanted to study using graphs, but I have never done it methodically enough… and given up. Interesting the observations that speed goes lower in auto-adapt. Not sure why that should be. Is it because it knows the room is warm. But if 3rd party stats are used, it assumes some rooms could be quite cold, hence the mild panic and rev-up?.. I don’t know
Anyhow, looking at the way Auto Adapt seems to look at the rate of rise in room temperature, it should be possible to trick the room sensor and ‘tame’ the system. It might take a while to fathom it out though

Morning All,
I’ve been running my system under Home Assistant for a few years now.
Before I got rid of my Grant UK unit, i was playing around with the reduce capacity switch of the heat pump.
This would be controlled Via a Shelly relay, under HA automations like, CO2 grid data, Octopus Tariff Data, House grid consumption etc.
My planwas to be able to reduce the output by 50% via ( a flick of a switch ) unfortunately the Grant Unit would only go down to 50%, so if it was running at 80%, the switch would take it to 50%, if the unit was running at 40% it would stay at 40%.

This would work in the colder days where the unit was working hard, but in the shoulder months, not much use to you at all.


Instead of trying to control the heat pump, why not install a throttled zone bypass valve across the primary flow and return, like a 240v Actuator TRV, this would increase the return temperature and then in turn the unit would shut down due to a tighter DT.