Mini split energy usage

[new2solar2]

I have a 36k mini split heating/cooling an off-grid cabin.

Solar setup includes a Solark 15k with 6 EG4 5.12 batteries, 20 400w panels.

I was wondering if anyone else with a similar setup had loads comparable to the cycling indicated in the attached graph? The only load I have right now is my mini split. Is it normal for it to cycle like this at night rather than being a flat line load?

I understand an ac unit will only kick in when needed, but it looks too consistent.

Thanks for any thoughts and input!

 

[sunshine_eggo]

I can only surmise that a 36K unit must have a threshold below which it can't maintain a low power steady state condition and must resort to cycling.

 

[dopeassjackson]

They do have a minimum btu output before they have to turn off.

 

[wpns]

They are supposed to modulate, but they frequently oscillate around an average.

 

[zanydroid]

Cooling load at night is way lower and most likely below the minimum. If the cycles are on the order of 30 min, that’s about as good as you’re going to get.

If you don’t like this, buy a system with 3 separate 12K heads and compressors. And it will most likely not need to oscillate (between the higher turndown on 12K systems, and the fact that you can turn off some heads and let the ones in the other parts of the house do the lifting). But you paid more.

 

[Zwy]

Not unusual behavior if room temp is close to setting. Unit will turn down and idle along, slowly the room temp can increase a few degrees, the thermostat signals to turn up. A unit oversized for the space will have less ability to turn down so it exaggerates the effect.

 

[1201]

I haven't seen that kind of oscillation but what I do frequently see is something like this. It runs at its minimum setting then goes high for a while and then settles back down to the minimum.

I've been told this is to circulate oil through the system.

 

[zanydroid]

OP's pattern looks pretty similar to my Mitsu 36K. The blower is 60W (runs even when the heat/cooling is off), and the minimum power is 1kW. So it cycles on and off between those levels.

 

[1201]

OP's pattern looks pretty similar to my Mitsu 36K. The blower is 60W (runs even when the heat/cooling is off), and the minimum power is 1kW. So it cycles on and off between those levels.

My midea used to run constantly too even when the system was "off". I found a way to set it to turn the blower off if there was no cooling or heating going on

 

[wpns]

Not all of them do it all the time, I’m sure they don’t have infinite control over all the controlled parameters (indoor and outdoor fan speeds, compressor speed, orifice size) nor are they doing a full PID control loop, and it’ll depend on indoor and outdoor temperatures and humidities, heating load, yaddah, yaddah, yaddah

 

[new2solar2]

I haven't seen that kind of oscillation but what I do frequently see is something like this. It runs at its minimum setting then goes high for a while and then settles back down to the minimum.

I've been told this is to circulate oil through the system.
View attachment 226381

I think this looks a lot like mine. Thanks for sharing.

 

[new2solar2]

OP's pattern looks pretty similar to my Mitsu 36K. The blower is 60W (runs even when the heat/cooling is off), and the minimum power is 1kW. So it cycles on and off between those levels.

Interesting. Mine pulls 100w when it's idle. Thanks for sharing.

 

[new2solar2]

Not all of them do it all the time, I’m sure they don’t have infinite control over all the controlled parameters (indoor and outdoor fan speeds, compressor speed, orifice size) nor are they doing a full PID control loop, and it’ll depend on indoor and outdoor temperatures and humidities, heating load, yaddah, yaddah, yaddah

View attachment 226384
View attachment 226383

Lower graph looks like 200w fluctuation through the night. Looks kinda like mine. Thanks for sharing. I'm thinking what I'm seeing is normal.

 

[teal95]

It keeps the fan running all the time because the thermostat is in the airstream before the heat exchanger. Without airflow it doesn't really know what the temperature is.

 

[Madcodger]

For those saying your Mitsubishi mini-splits are consuming 100W even when idle, that seems like a lot to me. We have three different mini-split brands across four different buildings. All have their power consumption monitored. I just checked the building with the Mitsubishi (three year old unit, 12K from memory). Tstat is set to 71, and building is at 69 (old, poorly insulated building and outside temp is 65). Fan set to auto. Unit is consuming only 13 watts, which is typical. Something seems off on your power consumption if it's just the fan running and it's set to auto. 100W seems way too high.