Mitsubishi 5 zone early impressions AND question
My Mitsubishi system has been up and running for 5 days in outdoor temperatures of 28-53F (07480)
This is a MXZ, SVZ, MLZ, MSZ system.
Initial impressions:
Kumo Cloud control: considering the many bad reviews I’m finding Kumo better than expected. Apparently the previous generation was awful, but this 2nd gen seems OK. I actually prefer Kumo over the Nest on my oil burner.
SVZ full Air Handler: Controlled by PAR-CT01 thermostat. This unit is ducted to three bedrooms that I was told are too small for individual wall units. The air handler is nearly silent and runs within 1 degree of thermostat setting. The PAR-CT01 thermostat might be overkill tech for this application but the MHK-1 looks too dated IMO, particularly compared to the Nest we just removed.
MSZ-FE wall unit: installed in basement. Love this unit but not the the I-see feature. Very quiet. Runs within 1-2 degrees of internal temperature sensor setting (using remote control).
MLZ ceiling cassettes x3 (kitchen, living room, basement): Not until the required 4’ by 14” ceiling holes were cut did I think of the energy sacrifice this gives up to the traditional wall units!
The MLZ in the living room and kitchen tend to overshoot temp settings by 3-5 degrees in the afternoons, even with PAC-USWHS003 wireless sensors. The basement MLZ is running perfectly within 1-2 degrees of setting.
I have read that residual refrigerant is always traveling around in multi-zone systems even when units are not calling…I think that’s what happening with my upstairs MLZ’s. I have also noticed virtually Zero heat comes out of the MLZ’s when you manually turn the fan off. I’m considering cutting the jumpers on the control board that allows the MLZ fan to stop when set temperature is reached. Anyone have thoughts on that?
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Replies
If you have remote temperature sensing, stopping the fan is a good idea.
>"I’m considering cutting the jumpers on the control board that allows the MLZ fan to stop when set temperature is reached. Anyone have thoughts on that."
Some people will go WAY out of their way to violate the warranty...
I don’t think it violates the warranty since it was the Mitsubishi tech line that offered up the instructions on which jumpers to cut to “activate” the “thermal-off” feature.
As crazy as it sounds this jumper cutting is apparently quite common with mitsu indoor units. For example, on page 8 and 9 of the MLZ service manual it shows which jumpers to cut for all sorts of other features.
http://meus1.mylinkdrive.com/files/MLZ-KP-NA_Service_OBH802_03-18.pdf
It would be nice if mitsu used pull out jumpers....
If it's a legitimate modification spelled out in the tech manual, go for it!
Thanks for this description of your experiences! I'm consider the 3-ton MXZ system (to run two air handlers, with duct systems), so very curious how the following month has gone as it warms up a bit. Have you been able to get a sense of the low-load performance of this system yet? I wonder if you can shed any light on the discussions that have occurred on these Q&A boards about whether the MXZ systems really turn down to load capacities in shoulder seasons, or if they end up cycling a bunch. Thanks!
> down to load capacities in shoulder seasons, or if they end up cycling a bunch.
Why is it important? Note that the latter can be more efficient.
See discussions at https://www.greenbuildingadvisor.com/question/mitsubishi-hyperheat-multi-splits-and-modulation and https://www.greenbuildingadvisor.com/question/mitsubishi-multi-zone-hyper-heat-models-true-minimum-output. If a 3-ton unit has a practical minimum heating capacity of 22,500 BTU/hr (which is what the NEEP sheets say for the 3 ton MXZ), vs. the Mitsubishi claimed 7,200 BTU/hr, that makes a big difference as to whether the system is cycling through just a few weeks of shoulder season, or cycling through most of the winter. My understanding is that a lot of the efficiency (and comfort) benefits of inverter-based heat pumps comes from their ability run consistently and just turn up or down a bit to match load, instead of cycling (and dealing with start-up losses each time they cycle).
If the original poster is seeing reasonable continuous operation with ambient temps in the 40s, then the system's minimum heating capacity must be closer to the Mitsubishi submittal's value (7,200 BTU/hr or what have you). If they are seeing lots of cycling, and continuous operation only as it approaches freezing, then these systems are likely not as efficient in practice.
Multi-head systems are specced as, and appear to actually perform, less efficiently than single-head systems. I'm trying to figure out how to get the best performance from a multi-head system (and also whether the City Multi system - more like real VRF) might be a better solution even though the only published data I've found on its minimum heating capacity (from the NEEP sheets) is about 12,500 BTU/hr (compared with the MXZ's 7,200 in submittal/22,500 on NEEP).
There is fair amount of cycling going on when its >40F. How it impacts efficiency I don’t know but there has been some controversy here on GBA regarding how much the cycling penalty is.
There is a very informative podcast/article about the cycling and multi-spilt efficiency from a few weeks ago here:
https://www.greenbuildingadvisor.com/article/multi-zone-heat-pump-issue
The Mitsubishi rep on that podcast was refreshingly upfront about the pros and cons of multi-splits. I found it interesting that he stated the multisplit turndown range is only 35% of max and commented that minisplits are best suited for higher demand houses with equivalent seasonal oil use of >700 gallon/yr oil. Here is a snippet:
Dana: Yeah, you can get pretty close to a COP of 3 (meaning one unit of energy in for three units of energy moved) in the highest performance, well-matched systems in Maine through our fun winters. With multi-zone systems, I think you could get a seasonal average of around 2.6 or 2.7 for your COP. It’s going to be a little bit less efficient, just because of the size of the system and the motors that are involved. But if you’re dramatically oversized, it might be lower – like 2! Which is still…
Phil: Or less.
Dana: Yeah.
.....
BTW: I cut the "fan-off" jumpers on my head-units about 4 weeks ago. I’m very happy with the results. The actual temperature now remain 1-2 degrees from the set temperature with no over-shoot. An external thermostat or temp sensor is a must for anyone wanting to do this. Without an external temperature sensor the wall unit will think the room is much hotter than actual due to residual hot refrigerant and no air movement across the internal temperature sensor.
Another discovery I made is that the temperature over-shoot potential of the MLZ cassettes seems greater than wall units because the MLZ cassette has only 3 fan speeds compared with MSZ-FE wall units 5 speeds. The wall units lowest speed is much lower than the cassettes lowest speed.
Mark
Which external thermostat/temp sensor did you end up going with? I'm seeing similar issues with overheating and overcooling (https://www.greenbuildingadvisor.com/question/is-my-mitsubishi-heat-pump-short-cycling).
FluxCapacitor,
I appreciate having the review. If you're still following the forum, I'd be curious about your impressions a year later since we are contemplating an MXZ, MFZ, SVZ system.