Improve efficiency: Turn the heat pump off

The cloud is great until it goes away! e.g

However, I agree the cloud is very useful for some functions, but critical controls for heating and car charging must be local, or at least locally overridable.


I’m surprised at that. Would have thought it fitted nicely into the sort of things you have. You have the expertise in design and build.

We don’t have much free resource to take on another project atm! The redesign for all of our hardware is taking up all our deign and manufacturing resources. Maybe in a few months…

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:laughing: - I wasn’t suggesting doing it tomorrow!

I’ve noticed recently that our ecodan reports 120W power consumption repeatedly while cycling. It also occasionally reports 0 and 60W, but those are also reported while off (I suspect the 60W is the meters and control equipment), whereas 120W doesn’t seem to have ever appeared in another context.

So I’ve set a very simple rule in Domoticz to switch heating off if heating power consumption = 120W. It seems to work. One false trigger has occurred in two weeks, when the pump switched from hot water to heating and the pump was waiting for flow temperature to fall. It was cold enough then that the temperature logic kept the heating on anyway, so no harm done.


I’m doing something similar by monitoring HeatPumpFrequency from MELCloud; if that becomes zero while I expect the heating to be on, then I’ll drop the target flow temperature by 7 degrees. When the flow temperature drops to that new target, I restore it back up to what it should be which triggers the next heating cycle. This typically results in around 15 minutes of idle time between cycles, and possibly improve CoP a little too.

Power consumption remains about 120 or 180 W as the circulation pumps keep running.

John suggested doing the same in hardware: Someone needs to make a relay module

The electric meter is sending 1 pulse per Wh, and the FTC can only report whole numbers of energy consumption (not instantaneous power). 1Wh = 60W for 1 minute. As a result, you’ll see if flip between 0 and 60W when idle. For my system, this averages out to 20W.

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Tim, Sounds good. How about slowly ramping the temperature back up bit-by-bit. This might stop such a rev-up after start. I think this is what Trystan does. Not sure how the system will actually respond

Yep, I believe Tim is doing that. I think this is an example:

Here’s me walking mine gently up from 25 °C to 40 °C over about 90 minutes this morning. This is why I like have “desired” in my chart because I can see the heat pump rising up to it.

There’s a blip near the start for defrosting. There’s a spike in the middle where it decided it had done heating, spotted the hot water could do with some love, did that and then came back to find the space heating could do with another 15 minutes.

Ah, interesting. Now I’m getting HeatPumpFrequency again (every 2 minutes) I’ve re-introduced my code that says “if the heat pump thinks it’s time to stop bothering then simply switch off”. Then it goes into it’s “Let’s wait until the return pipe on the heat pump gets cold again” (as a proxy for the radiators getting cold and calling-for-heat).

For bonus points @TrystanLea we could have the app return an image when discourse was asking for a preview from a given URL with a time range :slight_smile:

Yes, I do this. I find that setting the target to be 7 degrees above return temperature seems to work pretty, though I’m open to other ideas. It’s a delicate balance between not letting HP get too excited, and failing to get the house warm enough. Tempted to try something based on runtime, like increasing by half-a-degree every minute.

Yep, my algorithm is based on finding that if it’s already pretty warm outside (e.g. over 9 °C) then the heat pump won’t walk up gently.

However, if it’s cold enough we can walk up gently.

Here is all it’s ugliness:

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I found that sometimes when I’d tell it to turn off (lower flow by 7 degrees) it had already decided to start a new cycle. Sending a “power off” message is more effective, but the compressor won’t like doing that too often. YMMV.

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Sorry to dig up an old part of the thread here, but I discovered something in my experimentation that it may be helpful for you to know. At least on our FTC6 unit, when you activate “Force DHW/Heat Now”, the system seems to ignore the “Eco” DHW setting, and instead heats in the more aggressive “Normal” mode.

My take-away from this is that it’s better to leave the DHW enabled at all times you might want it, and then to suppress it under software control by reducing the tank target temperature when you don’t want it to run. I haven’t actually implemented this yet, though!


Huh, that’s interesting - that would explain why I’m not seeing a difference after turning off Eco mode while forcing the hot water on at the same time every day. I’ll try it the other way, see how it performs.

(I had turned off Eco mode during the colder months in the hope that it would heat up the cylinder quickly and get back to heating the house sooner)


I was just about to dive into this, but I can see a hiccup.

In my case I’m regularly heating up the hot water in the middle of the night. Recently I had started turning on the heat pump around that time and a subtle bug meant it would end up doing space heating before considering switching to hot water. As a result I was spending a lot of money heating up the house during the night for no reason.

I like Paul’s suggestion but I believe the Ecodan will simply turn on and blunder off doing space heating even if the desired tank temp is set high. I may be wrong.

Good news on the low temp though, I was able to send an update which put the SetTankWaterTemperature down to 10 °C so that would be the “off” setting you are after.

I’ll probably wait until the warmer months before trying Eco mode again, when it won’t be competing with space heating, and I’ll be looking to minimise peak power usage while the sun is shining.

I’ll share this with you for kicks.

We went away for a few days so I blocked the heating. We got down to 15 °C inside and then it took about seven hours for things to come back up again fighting against what was fairly cold outside.

Now if only we could cope with living at 15 °C we could save loads of money on heating.

From this chart I’d say that I can see how the space heating would run for a long time, but it is pretty rare for me that it runs so much of the time that we couldn’t sneak some DHW in. I suspect I’ll come to the same conclusion as you that in Eco mode the DHW doesn’t get the job done quickly enough. However, maybe I can lean on my estimate of when the heating needs to come back on (based on the temp dropping) and pair the up with my “should the DHW be on” to decide if I can let Eco mode do the job. If it decides that Eco mode isn’t getting the job done then it could force the DHW.

I keep thinking up reasons this won’t work and then working around them. It may actually work.

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Another update from me breaking my system and it dropping back to default mode. It was running continuously from 14:00-18:00 so that’s four one-hour bars in the chart.

Here it is in MELCloud just for a change:

So when running continuously it used 2+1.6+1.8+1.7 = 7.1kWh and produced 6.3+5.6+5.8+5.5=23.2 for a CoP of 3.27.

Now, compare this with yesterday. The weather was practically identical and the house was set up the same.

So yesterday, (when my code was turning it on-and-off) it used 0.6+1.1+1.1+1.2=4kWh and produced 2.2+4+3.9+4.1=14.2kWh for a CoP of 3.55.

Yes, the CoP was better by turning it on-and-off, but that’s not the interesting part of the story. It only used 56% of the energy so turning on-and-off reduced the bill from 2.41GBP to 1.36GBP.

Of course, I got less heat out too, but it turns out the house was 20-21 °C yesterday and 21-22 °C today with constant-running. I could have held it back with TRVs, but we’ve all got them wide-open these days so that didn’t happen.

From where I’m currently sat, changing to constant-running would increase my power consumption from 4kWh to 7kWh which is a 77% increase.

Having it modulate down further would help, but I was surprised how easy it was to consume so much more power just by having this change. I can see how people are getting into trouble, even if their CoP seems good. They could still be consuming lots of energy that isn’t really making a difference to their lives.

(on the bright side we did work out the largest sphere you could host in a tetrahedron so the distraction was worth it :slight_smile: )


Thanks @pault

I think your useful observation is getting lost in the on/off discussion. Ironically I was looking for your post and even posted something else to this thread this evening :slight_smile:

I’ve taken the “force DHW” off over here so it’s got it’s own place to flourish.

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That is some statement!

I’m not entirely clear which chart is which situation. Is the lower chart (less consumption) where you are forcing it back to default mode?

This again demonstrates the highly complex nature of controlling HPs that the average Joe has little chance of understanding or manipulating to their benefit.