I have read several good discussions on Mitsubishi mini split systems in this forum and others (reddit, etc), but I am still confused and hoping someone can help me understand just what is happening, and how to see good data, if what I have is not.
In a nutshell, I just installed a three zone Mitsubishi mini split. When all the heads are off and the indoor and outdoor temperature is in the mid-seventies (so no compressor heating, etc should be coming on) my Sense is telling me the Mitsubishi system is cycling consuming between 50 and 74 watts consumed. The system is on its own circuit, and I have the dedicated circuit monitoring clamps on it.
50 to 74 watts is too much and not to spec, it seems about 10x what I expected. I have read, but do not understand, some “power factor” component in the calculation of watts that might not be properly factored in. I am not sure if this is why I am seeing such high wattages while the system is in standby/off.
Is my Sense working properly? Does it take into account “power factor”? Could my Mit have an installation problem?
Here is what is installed:
208 V on a 40 amp circuit.
Mitsubishi MXZ-3C30NAHZ4-U1 outside unit
MSZ-FS18NA-U1 in living area, and
MSZ-FS09NA-U1 in each of two bedrooms.
So you have your mini-split on a 40A 208V circuit and are measuring via dedicated circuit monitoring (DCM) ? First a couple questions:
Why 208V ? Is your home wired for 3-phase as opposed to single phase split, like residences ? Sense is set up to measure real power, though if you have full 3-phase in your house (vs. 2 of 3 phases) things could be a little tricky.
Are you using a single CT with no neutral to measure via DCM or are you using both CTs ?
Are you sure that there is nothing else on that circuit ? BTW - Our mini-split controller powers a couple of thermostats so we pick up an extra 10W on top of the mini-split controller from those ?
My starting point of view is that the measurement is correct, especially with the cycling, and you’re just missing a load you hadn’t anticipated.
208V Because my home is a unit in a condo building. The building is three phase, but two come up to my unit, so inside the breaker box there is no main shutoff - it is in a common electric room- , but otherwise it looks just like a single family home, but the V is 208 rather than 240.
I have one CT (two clamps) on the incoming two wires, and the other “Flex” one on the two power lines coming out of the two pole 40A breaker, with DCM enabled.
There is nothing else on the circuit. The wire runs directly to the roof outside unit which powers each of the three heads.
Do you think the power factor is an issue? I read this discussed on another forum. According to the Mit specs 50-74 is much too high. As I recall, 5-8 is fine, unless it is cold out (<30°), then some power is used to keep the outside unit up to temperature. I am writing this last sentence from memory, so I might be a bit off.
Trying to understand your setup - there’s a chance that you are measuring the current twice with your setup if you don’t have a neutral wire. The way you set up your DCM also matters - there are 3 options if I remember correctly. A photo of the install would be handy.
Here are photos of my panel…
I am pretty sure the setup is correct, and the setting in the app are correct, but I look forward to learning otherwise.
I should have said that this setup predates the Mitsubishi 3 zone system. Previously I had a Panasonic 3 zone system. The Mitsubishi [supposed to be] is more capable.
I had this setup on the Panasonic system, of course on the same circuit. With all three heads off on the Mitsubishi I was a consumption of 32 watts, no cycling higher.
Notice I have the Mitsubishi breaker off. I’m in NH, it has been in the seventies most days lately. I have it off as I do not want to waste 50-75 W constantly. Being in a condo, my panel is easily accessible.
Quick question first - when you have the breaker switched off, does the usage via DCM go to zero ? What option did you use when you set up the DCM ? Both on 120V, one 120V and one 240V, or both on 240V ?
Of course, since I threw the breaker off it has shown 0 watts.
I do not recall what options I used when I setup the DCM, and it seems I can’t see those options in the app. I would expect I did both on 120V, but I seem to remember discussing this with someone in support due to the 120 and 120 being 208 rather than 240. As I recall, I was told it would account for that.
Do you know if there is a way I can see how to setup the DCM without having to reset it?
I only asked about the reading with the breaker off just to make sure there wasn’t any possible zero-calibration error. I don’t think there is a way to tell the option that you chose. I wish there was and I’m guessing support could tell you if you file a ticket. It sounds like you hot swapped the Mitsubishi for the Panasonic without doing a re-calibration ?
You might want to check in with support to double check, especially since you have the 2 of 3 phase thing going on. But pretty sure if you were to disable DCM under Settings > Connected Devices, then re-enable it would go through the option selection and calibration process again (turn off, then turn on AC step). You’ll need to figure out the correct option for your new setup, perhaps necessitating a support ticket like the last time. Based on my limited knowledge for split-phase systems, the right setup will depend on whether your mini-split uses a neutral wire - some do and some don’t.
I think this is one of the many things I read prior to posting.
I understand there’s power used to keep components effective in cold weather. But it’s in the 70s and 80s here in NH, so I didn’t expect to see that.
Did I miss something in the thread?
@USA_NH I would tend to agree however I don’t remember the paperwork saying it was a winter or cold only setting. It is selected on an internal board on the outside unit. Probably a good question for a Mitsubishi technician
The Texas weather is a little wild here and I can go from heat to cool several times depends on the day. I seem to remember seeing wattage usage like you described during those times when I was in “cool” mode but I could be mistaken.
The installers saw that most of the other units in our condo building, who have already replaced the original 3 zone mini splits used Mitsubishi with 18, 9 and 9 and a 30 roof unit. They said I could use 6 6 and 18. I asked about it. He said 18 9 9 was within Mit spec, but with all heads running, they would be to capacity.
I think maybe they did it that way because the bedrooms are on a colder side of the building, and the living area a warmer side. So they wanted to capacity for the bedrooms, while the living area was probably not working that hard. But I don’t know. After it was done, I was not sure why I didn’t ask about the cost difference in a 36k roof unit. Oh well. Next time.
In my prior house, I had 8-zone and 3-zone Mitsubishi hyperheat units on 2 separate DCMs. My 8-zone was consuming 15-25w in stand-by mode occasionally jumping to 50-70w but it had 2 branch boxes connected to it, 3-zone was always 50-75w and no one had idea why it was consuming so much… sold that house so now dealing with solar instead of minisplits
