Found this (old) discussion very useful. I have a 6kw R32 Ecodan ASHP on oversized rads. Currently uses the auto-adaptive thermostat, but with the data logged to my EmonPi for flow/return, compressor, FSP (which I think is Flow Set Point - calculated dynamically). Screenshot from this evening - when it’s about freezing. The compressor (%) is plotted on the right axis.
Given my system is sized for -2C, I’m thinking it’s probably oversized. But wondering if I the patterns above look good/bad and whether I might want to try controlling the flow temp manually - which I can do over MQTT (but am not atm). Also wondered about changing the pump speed to influence the flow/return drop (currently 6-12C)
What makes you think it’s oversized?
What’s your actual heat loss at -2C?
Are all the valves open? Have the radiators been properly balanced?
Looks okay, though cycling sooner than I would expect and COP is less good on those subsequent cycles. There are some settings you can change to adjust the overshoot (but only when using Auto Adapt):
If oversized, it might be worth trying Quiet Mode (on FTC6), which reduces that maximum power output, raising flow temperature less quickly.
This is possible, but needs very close monitoring and control, and I found Auto Adapt to work way better (and more reliably) than anything I came up with.
The flow rate (plotted on new graph - same time period as before) hovers just under 10. Yes - it reports system power (it seems to round it to integers)
I think it’s oversized because the installer (and I) were a bit nervous about how cold it can be on my village (it’s 400m high), the heat loss was 5kw and the unit is 6kw. Also - (and this could be naive of me) - I see it overshoot and cycle more than I suspect is healthy.
Overshooting is a good way to describe my concern. If you see here, it sits idly and lets the room temperature drop to 20C before ramping the heatpump up to almost it’s maximum (6kw) output.
I’ve enabled quiet mode during peak tariff hours - will check it back out in a couple of days. That’s quite a nice hack! I’ll also check the dip switch, and maybe crank the max temp down (I’ve already reduced it to 40C but suspect I could drop it a bit more - though I wondered if that might worsen the cycling etc)?
All valves open and the system was balanced by the installer on service - I’ve no reason to doubt this will have been done well!
I thought manual flow control would be trickier - though I can easily use node-red (or similar) to send a temperature to the MQTT/CN12 device. I also noticed John Cantor’s installation has the same heatpump and is using some sort of manual flow control - though totally get it might be a bit aspirational of me to try and replicate his prowess/experience!
Can you set up the ‘My Heatpump’ app with feeds? I think you’ve got all the data it needs, and it will make it easier to analyse the behaviour.
The main reason to control flow temperature directly is to limit the power of the heatpump. This is more easily done with quiet mode. I have mine set permanently.
Limiting the maximum temperature will lead to more cycling, as the radiators aren’t able to keep up. It’s possible they were balanced too much, and the flow through them has been restricted. Or perhaps they’re not as oversized as you think (My Heatpump app can estimate the total size).
Delta between flow and return temperatures (dT) is quite big (7°), so there’s a big drop at the end of the cycle which triggers the next cycle right away.
Setting the diff.adjust Lower limit to -9 might help with that (default is -5). With this, the heatpump will wait longer before restarting.
Thanks Tim. That’s more really interesting and useful stuff to think about.
I know I should be able to get it into the My Heatpump app, I’ve been on the lookout for a decent set of instructions on how to do it. I did give it a try before Christmas, but I found that my EmonPi was only pushes new data when upload manually. It’s very much on my list and I totally appreciate it is might be a source of insight to others as well if I can get that to work!
After adding quiet mode this morning - it started up about 10:30 and has run without cycling at all, the compressor and FSP are also much more stable. The HeaterPower is rounded to the nearest KW - so I wouldn’t read too much into that - I summise it must be hovering around 3.5kw. I also think the flow/return gap has dropped a bit - I haven’t touched the diff.adjust yet, just waiting for it to cycle before I go onto the installer menu (which stops it running!)
Yup, looking much better. I’d guess dT to be about 5°, which given a flow of 10 l/min would mean heating power of 3.5 kW. This is a good place for the heatpump to be at, assuming your house is still warm enough. Will be interesting to see how it responds in warmer weather.
