Where to Find a Modulating Multi-Zone Air-Source Heat Pump
I need to finalize the equipment selection for my current build. My engineer along with Mitsubishi spec’d a City Multi (VRF) PUMY outdoor unit with multiple indoor units. Unfortunately, this outdoor unit does not have hyper-heat, which means that in order to meet the 99% heating requirements, it will be grossly oversized for cooling. While the compressor can operate down to low-20% of rated capacity, that is still much higher than an MXZ minimum operation for the same sized unit. However, according to Dana, the MXZ will not operate at the lower capacity in multi-zone mode since it is not a true VRF unit and I will end up with a minimum operating capacity of the indoor units. This will not allow the system to modulate in low-loads and neither will the PUMY given its higher minimum operating capacity.
So I decided to look around to see if there is a better alternative and I think I may have found it. Daikin recently released a smaller version of its commercial VRV (they invented variable refrigerant and call it VRV) which is sized very similarly to Mitsubishi’s PUMY S-series. The Daikin system also has what they call variable refrigerant temperature (VRT) which varies the refrigerant temp based on load requirements which minimizes the energy requirements of the outdoor unit and allows the system to modulate in low-load conditions. They also have their own duct zoning system, which Mitsubishi does not. It also comes equipped with 3 standard operating modes, including a high sensible mode for greatest efficiency, standard mode for quickest reaction to load requirements and automatic mode which is a middle of the road mode.
This system appears to a great solution for those who require a 3, 4 or 5 ton, multi-zone system with higher static pressure. Am I getting over-sold by the marketing or does this really look someone finally addressing the multi-zone modulation dilemma? Below is a link to the product page. Thanks.
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I'm giving your question a bump by adding this comment. Perhaps our local minisplit expert, Dana Dorsett, will see your question and help you out.
Thank you Martin. I am hoping Dana will chime in.
I do have some additional information regarding the Daikin VRV unit in question. I spoke with their tech support yesterday and they confirmed that the btu output at my 99% design temp of 14F would still be 100% and even at -4F the 48k btu outdoor unit would provide 32k btu's. So similar to Hyperheat. Also, the condenser can run as low as 14% of rated capacity, again similar to the MXZ unit, but unlike the MXZ, the Daikin is not limited to the minimum capacity of any single indoor unit in a multi-zone setup.
I'm not sure I have anything of substance to add here.
Daikin is the world's largest vendor of variable refrigerant volume systems in commercial HVAC, and in your location you don't really need hyper-heating, but I've never taken a deep dive into their design manuals. The smallest model being a 3-tonner puts it on the "kinda-big" side for most high-R houses.
Daikin tends to be on the expensive side too, as I'm sure you'll find if you start soliciting quotes on real systems. But from a comfort and quality point of view their reputation is top-tier.
Mitsubishi's City Multi systems are pretty pricey (and likely oversized) too. (Haven't done the deep dive on those either.)
I know that Matt Risinger uses Positive Energy in Austin and they will design using the Multi city if you want. I'm just getting my plans together for a new build and trying to educate myself as much as possible.
Thanks for the response. Size wise, we are at a 4-ton unit at the design temp, (high R, but large footprint) and without the Hyperheat, Mitsubishi wants to have 2 - 48kbtu PUMY's to meet the load and have a buffer. That seems overkill to me, but I guess I should not be surprised as I recall from a previous thread Martin posted one of their marketing brochures showing an indoor unit in every bedroom. Daikin on the other hand seems to realize there are such things as low-load homes, shoulder seasons, mechanicals spending very little time operating at the design temp. Hence they have created their own ducted zoning system, low compressor operation capability, variable refrigerant temps, and an eco operation mode. I read through their engineering manual last night and even their eco mode has and eco mode.
The design was done by my engineer (who is also a Passive House Rater) along with Mitsubishi, but I have had a few others with knowledge look at it and they have the same concerns as I do. Unfortunately none of them are familiar with Daikin, so just hearing from Dana that they have a top-tier reputation make me more comfortable.
I have found some instances of residential installs of Daikin units in high-R homes, but those have been 1 to 1 setups. I hate to be the guinea pig as I can't find other multi-zone installs of Daikin in this kind of setup, but it does seem to be a good solution. We shall see.
Daikin does have a number of smaller models -- is there something essential that the VRV line does that they do not?
If I could do a 1 to 1 setup, any of the manufacturers systems would work well. The problem is this project has low loads, large footprint and high static pressure so it really needs a multi-zone system. Unfortunately, these systems are good at handling high static pressure and high loads for large footprints, but not so good when the loads are low. The new Daikin multi-zone system "seems" to be addressing the issue I have.
Let me put this out there probably insult the passive house forks.
If you add resistances heat, that will only run when it is below 10°. This would let you install a smaller heat pump that would better match you cooling loads and modulate more of the year.
I think this would be a much more comfortable system to live with. The last thing you want is an over sized AC system. Can you say cold and clammy?
Most years how many hours are you really below 10°?
That is something that I have contemplated before. In a heating climate, would it not be better to size a system for 75% of design load, whatever level maximizes modulation, and then use a back-up source for heat? I think i can be aggressive in the design because I will have a wood and a gas fireplace in the house that can play that back-up role. Both are sealed systems with their own outside combustion air, so the leakage penalty is minimized. The wood fireplace also has a duct kit that will blow the warm air into the 2nd floor. I have a similar wood fireplace in my current house and it is the only source of heat I need in my drafty house when it is running.
While this year was unusually cold, we don't spend much time below our design temp of 14F.
Why does the duct system have to be high static pressure?
Have you looked into using multiple 1-1 ducted splits?
We've done several large (up to 6,000sf), low-load houses using Fujitsu slim-duct single-splits. The 6,000sf job used 3 heat pumps (18k, 12k and 12k), each with extensive ductwork, MERV 16 filtration on 2 of the systems, MERV 13 on the third, and relatively low static pressure (measured total ESP was 0.26in.w.c. on the worst duct system).
" The problem is this project has low loads, large footprint and high static pressure so it really needs a multi-zone system." Sure, but Daikin also has the 8-zone MXS system: https://daikincomfort.com/products/heating-cooling/multi-zone/outdoor-units/8-zone-multi-split .
John - We did not want to go the wall mount route and we wanted individual room controls in certain rooms so a ducted zoning system seemed the way to go which will have higher static pressures given the layout of the house. Unfortunately with Mitsubishi, they don't have their own ducted system, so we would have to use a third party ducting system like AirZone or Honeywell. There are some integration issues there and Mitsubishi does not provide a lot of support on that end. Thankfully, Daikin has it own ducted zoning system so no integration issues there.
Irene - The Daikin S-series that I am looking at is similar to what you posted, except that its indoor line-up includes air handlers that I can add the ducted zoning system to and it has variable refrigerant temp.
Btw - we hit 91 degrees here today and my house is extremely uncomfortable at the moment because the AC is running and blowing 54 degree air out at a rocket like velocity. Ironically it was more comfortable in the attic in the job site which has 4" of exterior insulation and despite facing SE, the sheathing never exceeded 75 degrees.
Did you install the Daikin multi-zone ducted system? How is it working out?
Bumping this thread because my HVAC contractor prefers Daikin and I have similar questions about the variable refrigeration flow system. Is this type of multi zone more efficient than other manufacturers?
Matt In my opinion the multi head minis are not a good value. Yes, a multi head system will cost a little less and have few pieces of outdoor equipment but at the cost of efficiency and redundancy.
The multi head systems have a much smaller range of modulation what that means is if you need 4 tons of equipment the 4-ton multi will only be able to slow to about 33% so the min output is 16,000 BTUs. If you had four 1-ton systems that will slow to 10% you could turn 3 off and run 1 at 10% for 1,200 BTUs. What make minis so efficient is the fact they can run all day long without stopping and starting repeatedly the min output for the multi head unit is 13x higher it is likely to stop and start on all but the hottest of days making it less efficient.
The fact is sooner or later something will go wrong with every system when it does having 4 separate systems, means you still have 75% of you heat instead of zero%. You can make a relaxed call for service and have the best person come at their convenience, instead of begging to find any fool who will show up on that dark and stormy night.
When the system does break often the fault is a slow leak and slowly over time the systems performance will be reduced. When this happens to a multi head system you scratch your head and wounder if the system is working differently than it use to. When you have 4 identical systems you compare one to another and it is easy to decide if something is not 100% correct.
“Is Daikin’s multi zone more efficient than other manufacturers?”
I say the market is very completive and when I look at the ratings from the government required lab test systems no one manufacture stands out as better than any other in the mini’s.
I think the smart move is to pick the contractor you feel will do the best installation of his favorite brand of equipment. A poor installation of the finest equipment will never perform well and a good contractor will chouse something he can make work well.