Mitsubishi H2i Electrical Usage Question
Similar to this question https://www.greenbuildingadvisor.com/question/help-understanding-if-a-multi-minisplit-is-running-properly
Started monitoring my usage with iotawatt and seeing all sorts of things I didn’t expect around the house. Trying to figure out of my expectations were wrong or if I need to take action on something.
Recently had a minisplit installed. 2 head unit. Bonus room above, converted garage below. I realize that over-under rooms with dual heads aren’t great after reading some articles. Installer didn’t say anything about this and even if he had, I probably still would have gone with it to be honest.
It’s heating fine from a comfort perspective. Upstairs definitely gets warm and is rarely ever the ‘calling’ unit. Downstairs also stays a within an expected temp range and is comfortable.
I was just expecting to see a lower, more constant energy usage vs what looks like normal heat pump on/off cycles.
I still have some hopefully significant insulation improvements to do in the downstairs room. It’s waiting for paint so it’s currently empty (no thermal mass), has bare uninsulated concrete floor (installing a 1/4 foam board beneath new tile. May not have any real impact but hopefully better than nothing short of tearing up the slab), and exposed foundation edges (will install 1″ or 1.5″ foam installed this spring once I settle on how to protect it).
Outdoor temps were around 35F.
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What’s the outdoor unit model number? There’s only so small you can go on the multi-split Mitsubishis, so it’s not all that bad considering.
Thanks for taking a look Paul.
Outdoor unit is a 20k MXZ-2C20NAHZ3
Indoor units-
Downstairs: 12k Ceiling Cassette MLZ-KP12NA
Upstairs: 9k Floor Mounted Unit MFZ-KJ09NA-U1
Glad to hear it doesn't look like something is significantly wrong. I've just seen some graphs from others in the low watts that seem to just hover there, never spiking up to anywhere like the 2kW I am seeing. Those may have been apples to oranges though. The chart in the link I posted earlier looks more similar in the spike (aside from frequency) so maybe it is a Mitsubishi thing? Or else I don't understand the modulating thing or how it works with multi heads.
I think I've posted about these rooms before but they've been quite the undertaking and with the help of this site, are worlds different in terms of comfort from a year ago. R-13 cathedral ceilings left a loft to be desired... At that time, my winter frequency with the old ducted heat pump made my ecobee graph look like a solid line of Aux heat and it was still cold. Ugh.
I think there’s also a line of thinking that using wall mounted thermostats will lead to longer run times. I’m not up to date on that. I think generally you’re probably a good bit oversized, but that’s basically how it goes with multisplits.
The min output on the MXZ-2C20NAHZ3 is around 1.5kW to 2kW (~12000BTU). It is basically running fine but it is cycling since it is oversized for the place.
The non-hyper heat 2c20 with a base pan heater accessory might have been a better (and cheaper) fit for you assuming it can keep up with heat at the design temperature at your location.
Do you have the fan speed on low? I can see my power consumption jump several hundred watts when I raise the fan speed- so long as there is demand for heat.
My rough understanding is that the mini split will try to keep the indoor coil at a certain temp and the indoor unit fan speed, indoor air temp, set point, outdoor temp, etc. will have an effect on what level the compressor runs at. So with a higher fan speed your compressor will tend to run at a higher level, all else being equal- which I've seen in live power consumption. For me lower fan speed = less heat being moved into the room = longer run times.
For my Mitsubishi Mini Split external thermostats were a game changer, so I its worth looking into, though your mileage may vary.
Sounds like I just need to insult the living daylights out of these rooms so it never runs :)
Being oversized is interesting. I only say that because 2 of the 3 installers had 24k outdoor units with 12k indoor for both. Maybe those outdoor units could ramp down lower though (and may be why you said that about the non hyper heat version Akos?). I only had eyes for the appeal of the low temps and sounds like that worked against me some.
Mjhill - I have it set on auto. You have yours set strictly to low?
Do you mean those little cube remote thermostats that work with kumo cloud? If so, I got one for the downstairs ceiling unit a month ago and you are right - it made a huge difference at least in comfort around the room. I wasn't checking power usage at that time so not sure the impact there.
Using my graph as a starting point, could someone explain how a perfectly sized unit would look?
Here is a one day snapshot. Outdoor is around freezing, the constant up/down zaggle is the fridge. The big spike at around 7am is a defrost cycle. The occasionally spikes in power are for oil recovery, most units ramp to max occasionally to move the oil back to the compressor.
You can see the power dropping down during the day and ramping back up when the sun goes down. The unit never shuts down, the compressor is always running.
The MXZ-2C20NAHZ is good for almost 2 tons of heat, that is about the heat load for a small house at 5F (say 1200sqft, insulated 2x4 walls and budget double panes). For it to heat just two rooms, even if one is a leaky bonus room, is guaranteed to be oversized.
-Yep, I run mine on low pretty much all the time unless it dips below the 20s - then I will tend put it on auto.
- The little square thermostat is exactly the thermostat I was referring to. You might want to experiment with placement as I've found that to make a difference. I put mine on the side of my kitchen island where it is in the path of the airflow but protected by the cabinets from getting direct warm air. This was somewhat counterintuitive, but it's also where air from adjacent rooms (also heated by that wall head) mix in. I've recently tried the thermostat elsewhere and I saw short cycling again.
Attached is the recent hour by hour usage for my mini-split. Around 40 degrees (which it was today) is the sweet spot for my setup which lets it sit at 500-600 watts for hours. Overall I find the power usage of my unit to ramp between 500 watt increments (plus or minus 100 watts or so).
Jealous of both of your graphs.
Temps in the 20s today and the comfort level is still great in those rooms, it's definitely cycling more frequently now. *sigh*
I'll play around with moving the thermostat around some to see what impact it has. Thanks for that suggestion.