Split heat pump system cycling too much

[soldar]

I have a split heat pump inverter system for heating in my computer room.  Maybe I did not notice it before or maybe it is getting worse but it seems to cycle more than it used to and it is very annoying.

It used to be that, on an average day, it would reach equilibrium and work continuously at about 450W and the temperature was stable and comfortable. (I have thermometer and power meter all the time.)

Lately it seems like it will go full blast, 1000 - 1500 W, for a few minutes, making the air a bit too hot, and then shut off for a while continuously blowing the now colder air.  This makes it quite uncomfortable. And it is less efficient and uses more power.

Having studied PID control in my younger days, I figure I should set the setpoint just above the actual temperature so that the unit works at a minimum. If it is totally not working at all for a while then I raise the setpoint by one degree. And raising the set point very slowly. But it will still do that. It will start at full blast and then shut off for a while.

I wish I could have some degree of control, like set max power at 600 W but I just have a normal remote control and can only set the temperature setpoint. I have no access to the code in the control unit.

So I am trying to think if there is anything I could do to prevent this cycling.

Cycling, oscillation, is caused by too much feedback... right? I somewhat confused by this. Maybe if I place an air diffuser?

While I think about this, anyone have any ideas?

[Stray Electron]

I have a split heat pump inverter system for heating in my computer room.  Maybe I did not notice it before or maybe it is getting worse but it seems to cycle more than it used to and it is very annoying.

It used to be that, on an average day, it would reach equilibrium and work continuously at about 450W and the temperature was stable and comfortable. (I have thermometer and power meter all the time.)

Lately it seems like it will go full blast, 1000 - 1500 W, for a few minutes, making the air a bit too hot, and then shut off for a while continuously blowing the now colder air.  This makes it quite uncomfortable. And it is less efficient and uses more power.

Having studied PID control in my younger days, I figure I should set the setpoint just above the actual temperature so that the unit works at a minimum. If it is totally not working at all for a while then I raise the setpoint by one degree. And raising the set point very slowly. But it will still do that. It will start at full blast and then shut off for a while.

I wish I could have some degree of control, like set max power at 600 W but I just have a normal remote control and can only set the temperature setpoint. I have no access to the code in the control unit.

So I am trying to think if there is anything I could do to prevent this cycling.

Cycling, oscillation, is caused by too much feedback... right? I somewhat confused by this. Maybe if I place an air diffuser?

While I think about this, anyone have any ideas?

   I think that your basic problem is that you're setting the temperature too high and that's what is causing the room temperature to be too high.  Then when the room temp gets too high, the heat shuts off completely and the fan then blows cold air.  Also where is the cold air coming from? Is it bringing in outside air?  The air in the room should be warm so if it's recirculating room air then it shouldn't be blowing any cold air at that point.

   My Mitusbishi mini-split has a number of modes, if your's does too then you should set your temperature lower and try something like economy mode where the heater will heat up slower and without over shooting and then shutting down completely.

   My mini doesn't keep the room quite up to the temperature that it's set for (the room is usually about 2 degrees cooler) but it does keep the room at almost exactly the same temperature all of the time even when the outside temp drops 40+ degrees overnight.

[Stray Electron]

  FYI, I've also started using heat dishes in the winter.  In terms of pure heat output, they're not as efficient as the mini-splits but they put all of the heat (IR) right were you can feel it instead of trying to heat the entire room or the entire house.  So if I'm staying in one spot very long I can use a small ~ 300 W heat dish pointed at where I'm sitting and it will keep me completely conformable even when the room temperature is in the low 60F range. 

   Let me repeat, I don't try to heat the entire room with one of these, only the spot where I'm sitting.

   My small one is something like this but even smaller (~300 W running wife open) and mine doesn't oscillate or anything else.

  https://www.amazon.com/BLACK-DECKER-Portable-Oscillating-Protection/dp/B0B6VBXT5S/ref=sr_1_2?dib=eyJ2IjoiMSJ9.XYQEX_CJyehkq46sCvlk1Fv9NNax2FmwH32nynkvQ1dsEAj7zW1avfkRsRJWHdJDVs96NiJid179PD6VHJsGi2U5BJLIl7or8fhtMqi1jYZzlIOmwbi8l_tL8cQJFHke8lIH0BQPZdKcsR58h98Z4lPZKMzxLFdL3EH9wgDMfTZufxJndZE2NY8KvW-aukMslXxxnEPWQJ8VyZi7h3nGCdfptXjSYdfhqv6iAuV0XffArrANdnsjbe-paQxm9T5XYSLafR0WN5X-Lu69eFSNAgljeCMgynsPdzBnrQN84lo.yc8hcMXLAfG0NiM2ZdtIZr-Hd4slX-ODDPczAXnO6OE&dib_tag=se&keywords=heat+dish+heater&qid=1772982179&sr=8-2

[Marco]

Maybe it has an open/reverse-engineered protocol and you can use your own compressor speed control with home assistant?

[soldar]

   I think that your basic problem is that you're setting the temperature too high and that's what is causing the room temperature to be too high.  Then when the room temp gets too high, the heat shuts off completely and the fan then blows cold air.  Also where is the cold air coming from? Is it bringing in outside air?  The air in the room should be warm so if it's recirculating room air then it shouldn't be blowing any cold air at that point.

   My Mitusbishi mini-split has a number of modes, if your's does too then you should set your temperature lower and try something like economy mode where the heater will heat up slower and without over shooting and then shutting down completely.

   My mini doesn't keep the room quite up to the temperature that it's set for (the room is usually about 2 degrees cooler) but it does keep the room at almost exactly the same temperature all of the time even when the outside temp drops 40+ degrees overnight.

I already said I am setting the setpoint temperature at room temperature and raising it gradually very slowly so the problem is not that I am setting the temperature too high. The exact temperature in degrees is not relevant. I am just playing it by feel.

And the "cold air" blowing is the air in the room, no outside air.

[soldar]

  FYI, I've also started using heat dishes in the winter.  In terms of pure heat output, they're not as efficient as the mini-splits but they put all of the heat (IR) right were you can feel it instead of trying to heat the entire room or the entire house.  So if I'm staying in one spot very long I can use a small ~ 300 W heat dish pointed at where I'm sitting and it will keep me completely conformable even when the room temperature is in the low 60F range. 

   Let me repeat, I don't try to heat the entire room with one of these, only the spot where I'm sitting.

   My small one is something like this but even smaller (~300 W running wife open) and mine doesn't oscillate or anything else.

   https://www.amazon.com/BLACK-DECKER-Portable-Oscillating-Protection/dp/B0B6VBXT5S/ref=sr_1_2

Man, clean up those links before posting them!

I have space heaters of all types and sorts and do use them occasionally but in this room I already have this heat pump installed and it works really well. Using about 400W or a bit more it would heat the room very nicely so very preferable to a space heater. But lately it is doing this thing where it runs in bursts, like it has higher hysteresis and it overheats for a while and then stops for a while. This is uncomfortable and less efficient.

In another computer room I used to have an electric mat to heat my feet and that worked really well. There was not enough space for a space heater. 

[soldar]

Maybe it has an open/reverse-engineered protocol and you can use your own compressor speed control with home assistant?

This is a really cheap unit I got and installed quite some years ago. It does not have any kind of data interface that I know of. Just a remote control to set the basic settings.

Maybe I should try to search for the manual and see if there is anything there I could use.

[seanf]

Blowing out cold air, or just moving/recirculating the room air?

Any fault codes/lights on the controller or outdoor unit?

Anyway to check the temperature and pressure sensors are reading correctly and consistantly?

Are all the basic stuff ok? like indoor air filters clean, outdoor heat exchanger clean and free of frost/ice, outdoor fan running....

[Addicted2AnalogTek]

Check that your indoor temperature sensor is clean and the airflow around it is unobstructed.

Sounds like your compressor drive control board could be faulty or it could be low on refrigerant. Either way, the compressor drive does not seem to be varying the speed of the compressor effectively. Whether the cause is due to bad input from a sensor, low refrigerant, or faulty control board requires more information. If it is a control board fault, it'll likely be the capacitors in the bootstrap circuit for the IPM and possibly low voltage filtering capacitors. Conformal coating also tends to age poorly outdoors.

[soldar]

Blowing out cold air, or just moving/recirculating the room air?

Any fault codes/lights on the controller or outdoor unit?

Anyway to check the temperature and pressure sensors are reading correctly and consistantly?

Are all the basic stuff ok? like indoor air filters clean, outdoor heat exchanger clean and free of frost/ice, outdoor fan running....

Check that your indoor temperature sensor is clean and the airflow around it is unobstructed.

Sounds like your compressor drive control board could be faulty or it could be low on refrigerant. Either way, the compressor drive does not seem to be varying the speed of the compressor effectively. Whether the cause is due to bad input from a sensor, low refrigerant, or faulty control board requires more information. If it is a control board fault, it'll likely be the capacitors in the bootstrap circuit for the IPM and possibly low voltage filtering capacitors. Conformal coating also tends to age poorly outdoors.

Thanks to both. I feel silly not having thought of checking the filters and other basic things. I have a tendency to start looking for the most complicated explanations while ignoring the easy ones. I feel there is a very good chance that is where the issue lies. I will do that and see how it goes.