I have an air to air minisplit as space heating in a Passivhaus standard retrofit (EnerPHit) on the West coast of Scotland. Generally it’s working very well, but there is one thing that I’d like to improve.
At low loads it cycles a lot (every five minutes). This suggests to me that there is not enough hysteresis in the system. If I set the target temperature at 20°C it will work fine until it gets to 20.5°C and then, if the heat required to keep at that temperature is less than the minimum the heat pump can deliver then it cycles. This is inefficient (it uses more energy than running steady at minimum output, and presumably delivers less heat), a bit annoying if you’re in the room and presumably decreases compressor life. What would be much better is if it got to 20.5°C and then turned the unit off until the room temperature dropped to 20.0°C, or something similar to that.
I’ve done a bit of looking in to products that can remotely control minisplit units (Sensibo, Boldr, Cielo), but I’m not sure they’ll do what is needed. Anyone got any experience of something similar to this, or any other ideas of how I might solve it?
Here’s the monitoring I’ve got on the unit (only electricity consumption monitoring unfortunately): Emoncms - app view
Click on January 31 to see an example of the cycling I mean, and January the 28th for an example of when it’s performing much better (with me turning it off manually to avoid the cycling episodes).
Hello Es! great to see you on here and congrats on your very nice house and air to air system! Anyone interested might like to listen to [Episode #217] – Passivhaus in Scotland | The Energy Transition Show. I guess there are no hysteresis settings available on the unit? is the room temperature sensor in the blower unit itself? If there was an option for a remote room sensor that might be a way of slowing the response?
Yeah the thermostat was in the unit, and the temperature control was previously really inaccurate as well as the cycling problem. I dug it out so it’s on a little wire sticking out the side of the unit.
No option to set the hysteresis. Yes, remote temperature sensing, especially with some hysteresis is what I was thinking would fix it.
Does the unit have a “follow me” or remote sense option? (where it uses a dedicated external sensor or a thermistor in the remote for temperature sensing?)
Embedding the air temperature sensor in a lump of something seems like a decent idea too!
Hi Marko. There isn’t a follow me or remote sensing mode I don’t think. There is only the thermistor that is inside the unit. I previously fished this out so that it is hanging outside the unit, which improved the temperature accuracy (previously the harder the unit was working the less accurate it was at hitting the requested indoor temp, presumably because the thermistor was right next to the heat source).
I tried this, taping a short bit of 3mm insulation wrap around the thermistor. It didn’t work though. On looking at some previous days I think it’s not quite as simple a problem as I initially described. It seems for a temperature setpoint of 20°C it will cycle whenever the room temp gets to around 20.5°C, but it’s not simply cycling to keep it at 20.5 (would be fixed with more hysteresis), it carries on cycling even if the room temperature goes considerably above this. See the plot for 30th Jan (Emoncms - app view), room temp goes up to 21.2°C but the unit keeps cycling. This was on a cold but very sunny day.
I had the same troubles you’re describing, with poor temperature regulation and tried Sensibo’s initially. They were easy to set up but hit and miss, for me, in that sometimes they’d send the on or off command but it wouldn’t be received by the indoor unit. I tracked some of the occurrences down to plasma TV interfering with the IR receiver but not all of them.
Next, I tried Switchbot temperature sensors and hubs. This offered better control but suffered from bugs and occasional internet/cloud outages.
I kept the Switchbot temperature sensors as they were reliable bluetooth devices, integrated them into a Pi running Home Assistant (which stored the IR commands and acted on the temp sensor readings) and used Broadlink RM3s as the new IR hubs. This removed all dependency on Internet services and provided 100% command transmission reliability.
It’s a bit more work to setup, but well worth it IMO.
So you have a Pi running Home Assistant, and that acts on information from the Switchbot temperature sensors and sends commands to your minisplit, have I understood that right? I already have OEM temperature and humidity sensors, so perhaps I could do it with them.
Never done anything with Pi or Home Assistant but this could be a way forward. Thanks.
Yes, I chose the Pi for it’s native bluetooth support and you can burn Home Assistant directly onto it. Apparently, it’s best to attach a USB2 disk for the database to help prevent running out of SD card write cycles. USB3 is bad for bluetooth reception.
I configured automations in HA to turn on and off the minisplits when they crossed temperature thresholds. I did it for heating and cooling but only use them for cooling now, since installing an ASHP. If you already have bluetooth sensors and the Pi can receive their signals, you can absolutely use them as the basis for automation triggers.
I’m not sure on that but you can integrate into HA broadlink rm3 minis (or similar) and locate it in the room(s) you need an ir blaster. I have the pi centrally located to pick up the Bluetooth signals from around the house and rm3s where the minisplits are.
Are you sensors WiFi? Home assistant mat have a way to integrate them.
I think the sensors are on the WiFi, they’re OEM ones. I’ll ask.
I think you’ve given me enough information that I can go away and do some learning by doing, thanks a lot Chris, really appreciate it. I’ll report back how it goes.