Brand new Midea heatpump non-ducted multi-head not working as desired.
user-3954431
| Posted in Expert Exchange Q&A on
All units in Celsius.
Here are my Midea heatpump units (indoor and outdoor), Extreme Heat series:
1x MO6HX-H60B-2A Midea 5 ton multi outdoor
1x MSEHU-H24B-2A indoor air handler, 24K
1x MSEHU-H12B-2A indoor air handler, 12K
3x MSEHU-H06B2A indoor air handler, 6k
My house: Located in Northwest British Columbia, Autumn, daytime temperature around 8 degrees, night time temperature around 1-3 degrees. House size : 2600 square feet. 2 floors. The outside unit is a 5 ton 60k btu unit from Midea.
Basement: 1300 square feet: 2 bed rooms, one 6k unit in each bedroom (one is an office), 1 12k unit in the open basement space.
Upper: 1300 square feet: 1 master bedroom with one 6k unit and an open living/dining/kitchen area with a 24k unit.
My Problem: I usually run 4 or 5 out of the 5 indoor split units (heads) and set them at the desired temperatures, no other features activated just straight heat mode and fan speed set to automatic. My goal is to have a close to constant temperature in each of the rooms/areas. Instead, the units produce heat to reach the set temperature through full fan rpms, then they idle for 10-15 minutes while emitting below room temperature cooler air at minimum fan rpms and then the cycle repeats. It leaves the rooms constantly reaching set temperatures and then cooling down several degrees for 10-15 minutes which causes a constant up and down and temperature swings in each room and area.
I already tried reducing the fan speed to lower speed levels which did not help. I can’t get a hold of the installer who in the first place did not seem very knowledgable about heatpumps and other trades folks require months long wait periods as we are extremely underserved in terms of trades in the rurual northwest BC. Thats why I wanted to ask for more knowleadgable folks to chime in first. We went ahead with the install a few weeks ago anyway because we only had to pay $1,900 out of pocket, with the remainder covered by provincial grants. We were in a rush because we only qualify this year for grants and most installers do not install heatpumps after September where we live.
Any idea what to try?
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Replies
I can't help much with recommendations but I can sympathize. We also have a dearth of competent tradespeople here in VT, and my locally branded (The Granite Group) Medea heat pump also behaves poorly. I feel your frustration. It seems that these new-fangled fancy heat pumps are amazing machines, but if they don't work right out of the box, nobody knows how to fix them.
If your house is new construction and reasonably well built, your system is probably oversized. Even if your system is properly sized, it is running at only partial capacity in the current weather. Multi-head systems can do weird things under partial loading because the compressor can't throttle down low enough to satisfy the low loads from single heads without cycling.
You mention the 10-15 minutes of cooler air during "rest" phases. Have you actually measured the temperature to be significantly lower than the room temperature, or does it just "feel" cooler because it is moving air? The difference might help diagnosis.
You also mention trying to set the fan to a lower setting. Measuring the temperature of the room and supply air during both heating and rest phases with constant fan speed might also be helpful.
Hi Peter, thanks for chiming in. Our house is a 1976 build with ok insulation, not tops but doing ok, double glassed windows from the early 2000s, when the installer mentioned those and given he is licensed and regulated by the BC grant program I trusted his recommendations. I am pretty frustrated to now find out that our outside unit is probably not capable to provide lesser BTU without cycling down.
I will follow your recommendations and run a few additional tests. The temperature that is emitted at low fan rpm during those 10-15 minute phases is definitely cooler than room temperature, it does not just feel cooler. What makes me still have some hope is that even with all 5 heads running the rooms dont maintain set temps (intitially they do but then once the cycling begins they dont get back up to set temps) which might point to a different issue, not short cycling. Most of the heads frequently power down with still being 5F below set temperature, so later on the set temps are rarely if ever reached.
Your temperatures correspond to roughly 47°F daytime and mid-30s°F at night.
NW BC has a variety of design temperatures. Are you in a milder area or a colder area?
What's your house's age, insulation and airtightness? 5 tons is a lot for a reasonably well-performing 2600sf house.
My educated guess is that your outdoor unit simply can't ramp down far enough to provide a low level of continuous heat. Midea lists a minimum heating output of 20,000 Btu/h at 47°F for that outdoor unit.
Hi Michael,
Its an older 1976 built. Insulation has been moderately upgraded and the double glassed windows are early 2000s. Thats why the installer recommended the larger unit. My unit emits a minimum of 19k BTU before cycling down. Everything is said and done, had i known about all those nuances I would have done a lot more research myself and insisted on either a smaller capacity outdoor unit that can provide less btu at minimum or used several smaller outside units. I relied and trusted the installer as he is licensed and also part of the BC grant program which requires additional certification and training. Big mistake. Yes my outside heatpump is too large for our house but there is not much I can do at this point particularly about that short of selling it used and buying a brand new smaller unit and have it installed. Sigh....
Sounds like the system is hugely over sized for your present load. Being shoulder season, I would expect to only see small loads until it really gets cold. Like Michael said the minimum output from your single outdoor unit is much larger than the load your home is currently presenting.
I would expect the control system has some learning ability (PID). If you can reframe from changing the setting for a few day the unit may adjust its self and learn to stay closer to the set point. If you Google “how do PID temperature controller work” it might help you understand the math behind what is happening.
If you had asked earlier many of us would have tried to convince you to avoid the one large multi split system in favor of several mini split systems. The multi splits generally can slow to about 35% of the 60,000 BTU output or 21,000. If you had 2 or 3 24,000 BTU mini one unit would ramp down to about 10% or 2,400 BTUs. AT min speed the multi split is 8.75 times larger.
Walta
Here are links to webpages with links to the service manuals for the outdoor and one of the indoor units. Scroll down and click on the Documents tab/header:
MO6HX-H60B-2A https://www.famous-supply.com/Product/3634250
MSEHU-H06B2A https://www.famous-supply.com/Product/3634305?criteria=MSEHU-H06B2A
May not be relevant to this situation, but a quick scan of the manuals show:
- different line set sizes are required for the largest vs smallest indoor units
- settable indoor operating modes might allow you to change behavior
- 0-Off; 1-Cooling; 2-Heating; 3-Fan only; 4-Drying; 5- Auto; 7-defrosting; 12-Active clean
- indoor and outdoor units have displays that show error codes if any, as well as a connector for an attachable tech device to set advanced operating parameters
- the service manuals have brief descriptions of each possible error
My impression is that default settings tend to be cooling oriented, so there might be alternate settings that can shorten or eliminate the extended fan run time after the temperature set point has been reached.
Check if your unit has a demand control or quiet/night mode. This lets you set the max power of the unit which should help with the cycling. This is either set on the wired remote or through dip switches on the outdoor unit.
Unfortunately the setup you have, large multi split with many small heads, is problematic unless sized very accurately. Mitsubishi has a tech note specifically about this topic as it comes up very often.
Unless the installer is willing to cooperate and split the zones onto a couple of smaller multi splits, there isn't all that much you can do to make it work better.
You can try the follow me mode on the remote where it sense room temperature directly. This can sometimes help with comfort on these.
Multi splits flow refrigerant through all zones even when off. This reduces efficiency, so your best bet is to operate all zones (or at least on low heat) even if you don't need it.
I run my off-zones in fan only mode to use this heat (not all mini splits allows this) and control how much heat it puts into the off zone by adjusting the fan speed. Not ideal, but better than the efficiency hit.