Daikin highwall heat pump overheating room - how to make it stop heating at setpoint

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timmmay

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#302990 9-Jan-2023 10:20

I recently got a small Daikin Cora FTXM25UVMZ highwall heat pump for my office, which is about 4x2m with standard ceiling heights. It's mounted high up at one end of the office, pointed down the office. It has a thermostat inside it, and I have a temperature sensor on my desk.

Overall it works quite well, but it overheats the room. The screenshot below from the Daikin app is showing:

The heat pump is set to 21 degrees on heating
The inside temperature is 25 degrees
The outside temperature is 17 degrees
The temperature at my desk is 24.2 degrees

Even though the heat pump knows it's 25 degrees inside, the unit is on and actively heating. Once I turned it down to 20 degrees it turned off. If I set it to 23 degrees, which is about what I like, it reaches about 25 - 26 degrees.

The differential changes. If I set it to 20 degrees first thing in the morning the office will be heated to about 21 / 22 degrees. I can't just subtract say 3 degrees (set it to 20 degrees for target of 23 degrees) and set it to that temperature.

Does anyone know any way to have the Daikin heat to its setpoint then stop? I could do something in Home Assistant to tweak things, but I'd prefer not to. I could also call the installer, my electrician, I suspect they'd say "I don't know we just install them".

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#3018911 9-Jan-2023 11:00

I've found that using the heat or cool option usually pushes past by the set temperature but about a degree. I usually use auto unless I'm particular about wanting it to blow hot or cold. Have you tried auto?

From the manual: In AUTO operation, the system selects an appropriate operation mode (COOL or HEAT) based on the indoor temperature and starts the operation.

timmmay

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#3018912 9-Jan-2023 11:10

I don't use auto modes on heat pumps. Older models especially can cycle between heating and cooling. One degree over is fine, but this can be heating when it's already four degrees over the setpoint.

insane

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#3018920 9-Jan-2023 11:35

I think it's because of the units size. I have a 1.6kw unit in my office and a 2kw in my master bedroom.

I used to have a 3.5kw in the master bedroom and had similar experiences as it was overkill, so moved it to my granny flat living area where it's perfect.

Perhaps get a sensibo to override it's enthusiasm?

Otherwise try running it on the quiet/eco mode?

Having said that, surely there is way to recalibrate it?

timmmay

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#3018925 9-Jan-2023 11:54

I'm not sure the unit turns on when it's already up to temp because it's oversized. The unit seems properly sized - in the dead of winter I need the 3.5kw of heat at times, and now in summer being cold sometimes hot others it ticks along rather than cycling constantly.

I don't think it needs calibration, as it seems to know the temperature. It might just be a setting that needs to be adjusted. It might just be the way it works, and I have to get used to it.

neb

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#3018927 9-Jan-2023 11:59

There's something a bit odd about the Daikin Coras, we have one too and to get the temperature to (say) 22 degrees on a hot day need to set it to 23 or 24. Same with heating in winter, setting it to 21 gets the room a lot warmer than 21.

djtOtago

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#3018929 9-Jan-2023 12:00

timmmay:

I don't use auto modes on heat pumps. Older models especially can cycle between heating and cooling. One degree over is fine, but this can be heating when it's already four degrees over the setpoint.

Have you actually tried this unit on Auto?

The two Daikins in the office I use, work pretty good on Auto. They are floor units however.

kobiak

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#3018941 9-Jan-2023 12:18

I have similar "issue" with my AUX 3.5kw heat pump (only reason I got larger unit because price was cheap). also in the small bedroom (9sqm + 6sqm hallway on the ground floor) used for office. I set unit to 21C and have couple temp sensors. it was more around 25+C constantly heating... and I come up to this 19-20C set temp. AUTO speed. Gives me around 22C, which I'm happy. it goes quit, sometimes stops, usually when sun is out in the afternoon. When I do AUTO for heating/cooling - obviously it's blowing cold air right on my head when it hits the 23-24C internal temp :D so nope.

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timmmay

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#3018981 9-Jan-2023 13:18

djtOtago:

Have you actually tried this unit on Auto?

The two Daikins in the office I use, work pretty good on Auto. They are floor units however.

I've never run an air conditioner on auto.... until today. I'm giving it a go now. The room was 24 degrees, I set it to auto / 23 and it didn't do anything. Setting it to 22 and it's working. Interestingly when it's on cool the fan goes whether or not it's cooling or down to temp, with auto the fan stops when it's down to temp. Useful to know :) I'll experiment a bit , try auto for heating tomorrow morning, and use whichever works best.

timmmay

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#3018982 9-Jan-2023 13:19

kobiak:

I have similar "issue" with my AUX 3.5kw heat pump (only reason I got larger unit because price was cheap). also in the small bedroom (9sqm + 6sqm hallway on the ground floor) used for office. I set unit to 21C and have couple temp sensors. it was more around 25+C constantly heating... and I come up to this 19-20C set temp. AUTO speed. Gives me around 22C, which I'm happy. it goes quit, sometimes stops, usually when sun is out in the afternoon. When I do AUTO for heating/cooling - obviously it's blowing cold air right on my head when it hits the 23-24C internal temp :D so nope.

I think I'll probably just have to take your approach and set the temperature to what works, ignoring the number. The annoying part is it's different on each mode. I may automate the tweaking in Home Assistant.

Thanks all for your thoughts. If anyone has a solution to make the thermostat accurate, great, but I'm not sure it's a solvable problem.

neb

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#3018983 9-Jan-2023 13:22

timmmay:
I've never run an air conditioner on auto.... until today. I'm giving it a go now. The room was 24 degrees, I set it to auto / 23 and it didn't do anything. Setting it to 22 and it's working. Interestingly when it's on cool the fan goes whether or not it's cooling or down to temp, with auto the fan stops when it's down to temp. Useful to know :) I'll experiment a bit , try auto for heating tomorrow morning, and use whichever works best.

A problem with the "don't use auto mode" on heat pumps is that it dates from 15-20 years ago when they would mindlessly oscillate from heating to cooling mode to try and keep at the set point. Is this advice still relevant for today's systems?

timmmay

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#3018999 9-Jan-2023 13:34

neb: A problem with the "don't use auto mode" on heat pumps is that it dates from 15-20 years ago when they would mindlessly oscillate from heating to cooling mode to try and keep at the set point. Is this advice still relevant for today's systems?

Probably not. The current models have outdoor unit sensors so they can work things out more accurately.

I'm not sure if my Airtouch unit has access to the Daikin outdoor unit sensors. It doesn't expose that information to the user through the GUI or API. I don't use that one on auto anyway, we commonly have one room quite warm from the sun and the others cooler so I have to schedule things a bit carefully.

openmedia

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#3019004 9-Jan-2023 13:51

timmmay:

I recently got a small Daikin Cora FTXM25UVMZ highwall heat pump for my office, which is about 4x2m with standard ceiling heights. It's mounted high up at one end of the office, pointed down the office. It has a thermostat inside it, and I have a temperature sensor on my desk.

Overall it works quite well, but it overheats the room. The screenshot below from the Daikin app is showing:

The heat pump is set to 21 degrees on heating
The inside temperature is 25 degrees
The outside temperature is 17 degrees
The temperature at my desk is 24.2 degrees

I've had a similar issue with my Mitsubishi. The unit often thinks it is quite a different temperature to the room and I think it is because the temp sensor is close to the hole in the wall they use for the piping.

I generally don't set it to cool, I set it to dry which achieves the temperature balance I require.

Generally known online as OpenMedia, now working for Red Hat APAC as a Technology Evangelist and Portfolio Architect. Still playing with MythTV and digital media on the side.

richms

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#3019009 9-Jan-2023 13:59

neb:

A problem with the "don't use auto mode" on heat pumps is that it dates from 15-20 years ago when they would mindlessly oscillate from heating to cooling mode to try and keep at the set point. Is this advice still relevant for today's systems?

Its irrelevent now with them all being inverter ones. What the problem is caused by is that they try to be too smart based on the limited input they have from a sensor on the device itself which is clearly not the room temperature.

Why none of the aircons have a wireless temperature sensor for them is something I don't understand. Hell, they all still use a prehistoric IR remote protocol that makes it so you have to aim the remote like a 2000s dvd player.

Richard rich.ms

timmmay

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#3019010 9-Jan-2023 13:59

openmedia:

I've had a similar issue with my Mitsubishi. The unit often thinks it is quite a different temperature to the room and I think it is because the temp sensor is close to the hole in the wall they use for the piping.

I generally don't set it to cool, I set it to dry which achieves the temperature balance I require.

There is often a differential between the desk and heat pump temperature, but I can see what temperature it thinks the room is as well.

My understanding of how "dry" works is it cycles between hot and cold, so it's not very efficient. The cooling mode dehumidifies but also cools the room, so it switches to heating for a while to keep the temperature up. You might find your power bill goes down if you use one cycle and set the temperature to about where it needs to be.

richms

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#3019011 9-Jan-2023 14:02

timmmay:

There is often a differential between the desk and heat pump temperature, but I can see what temperature it thinks the room is as well.

My understanding of how "dry" works is it cycles between hot and cold, so it's not very efficient. The cooling mode dehumidifies but also cools the room, so it switches to heating for a while to keep the temperature up. You might find your power bill goes down if you use one cycle and set the temperature to about where it needs to be.

Not anymore, dry just runs it in cool but a slower fan speed so the air has time to condense out. In winter its useless to keep a room warm and dry and I run a normal dehumidifier.

Richard rich.ms

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