Are there any minisplit heat pumps now available that control humidity as well or better than Daikin's Quaternity?
The nice thing about the Quaternity is that it can dehumidify even on days when there is no sensible cooling load. Only the Quaternity series will control to an RH setpoint independently settable from the temperature setpoint, and the only mini-split that can dehumidify without sensible cooling. This is due to a proprietary split coil and metering controls on the indoor head that gives it the capability to apply some re-heat to part of the coil at the same time that the other part of the coil is chilled to remove moisture.
That said, since only part of the coil is actively removing moisture, it won't remove moisture as quickly as a simpler mini-split operating in "DRY" or "DEHUMIDIFY" mode. Some mini-splits will still cool to the sensible cooling temp setpoint while in dehumidification mode, most will simply control the coil temp to maximize dehumidification, and will ignore the room temp, potentially overcooling the space. Whether either of those modes work for you depends on the particulars. Most people can deal with a dehumidification mode that still follows the sensible cooling setpoint, and it's almost impossible to over-dry the space with any mini-split.
No mini-split can truly keep up with an air-leaky house in a high dew-point climate (as fitter30 points out), and even with a tight house a Quaternity won't necessarily always keep up with the latent loads generated by the occupants on days when there is no sensible load. Wh0le house dehumidifiers are usually a bit like swatting flies with a sledgehammer in all but the MOST humid (as measured by outdoor dew point) climates, but running a portable room dehumidifier can keep up with reasonably tight houses, even though standalone room dehumidifiers convert that latent heat of vaporization into a sensible cooling load that the AC (mini-split/other) would have to handle.
Bottom line- the Quaternity works for most people, most of the time, but may still occasionally need supplemental dehumidification depending on your desired humidity setpoint, climate, and how leaky the house is. Other mini-splits with dehumidification mode may dry it out more quickly, but not without also cooling off the space.
Dana, thanks for your detailed reply. The spec sheet on the smallest Quaternity is really confusing. On the one hand, its SHR appears to be 99%. On the other, it removes 3.3 pints of water per hour. How is this possible?
1. Abandon the central system and replace with Daikin Quaternity. Pros are better humidity control and efficiency. Cons are initial cost and possible oversizing. The smallest available Quaternity is 3/4 ton, but each room only needs 1/2 ton, and the turn-down ratio is quite poor.
2. Abandon the central system and replace with 1/2 ton Mitsubishi minisplits plus supplementary dehumidification. Pros are super efficiency and a very flexible turn-down ratio. Cons are initial cost and the annoyance of dealing with dehumidifiers which are notoriously unreliable.
3. Replace with another central system. I am not sure this option is physically possible. SFAIK, R-410A coils are always larger the R-22 coils, and the existing R-22 coil is too big for the tiny closet in which it's installed. (The closet door is only 19" wide.) It once had a washable filter that ran into the door jamb when cleaning was attempted, so the filter was abandoned and a filter grille was installed at the beginning of the return plenum. If replacement with another central system is physically possible, the pro would be initial cost and the cons would be lower efficiency and continued excessive temperature variability among the different rooms.
If there are other options I should be considering, by all means let me know.
Why should 5, 1/2 ton Mitsubishis be considered insanely oversized? Sure, some rooms have a little less than 1/2 ton peak load, but those Mitsubishis have great turn down ratios.The "ductless head per room" approach almost always leads INSANE oversize factors.
I believe I noted that con in my previous post.The minimum modulated output of a 3/4 ton Quaternity could easily be 2x or more the actual design cooling/heating load.
Sealing of the house would definitely be part of a deep energy retrofit, but as I wrote previously, there is only some chance of that in the future. Is it basically impossible to choose a variable capacity system today that can accommodate today's loads and tomorrow's?Running an FH06 or FS06 in "DRY" mode should work without the supplemental dehumidification if you air seal the house/room reasonably.
I've not heard good things about the reliability of LG. Have you?There are some 3/4 ton LGs that can throttle back to ~1000BTU/hr at sorta reasonable efficiency (though not nearly as efficient at the Mitsubishis) as well as some that throttle back that low but are ridiculously inefficient at that low low speed.)
How is sweet spot range defined/determined? What is the sweet spot range for a 1/2 ton Mitsubishi? Is sweet spot range synonymous with your use of the term "Goldilocks Zone"?oversized mini-splits will still spend a lot of time cycling on/off, and only rarely modulate within the sweet spot range where it's efficiency (and comfort) maxes out.
And since you answered, let me again express my appreciation and gratitude for your thoughtful reply.OK, since you asked...
As I wrote above, the system runs continuously on the hottest afternoons, which I take as evidence that the system is correctly sized. I would not claim, however, that the room by room loads and duct sizes are correct, but if they aren't, I have no intention of modifying the duct system. The ducts are in the attic with no floor and only 4 feet of headroom. So it's either use the current duct system or abandon it in favor of mini or multisplits. I am open to the possibility of using the existing duct system for a central dehumidifier.Start by doing it at least "sorta right", beginning with a room by room Manual-J-ish load calculation.
Very interesting, thanks for bringing it to my attention.But for modulating heat pumps & mini-splits the go-too tool is the HVAC tool developed by the BetterBuiltNW utility consortium.
If you are going to group rooms together, why not just go with a multisplit?Clusters of low-load rooms that are reasonably close together are easily served at high efficiency with a "compact duct cassette"
Are the Chinese Midea/Carrier as reliable as the Japanese Mitsu/Fujitsu?A low-static 3/4 ton Midea (or Carrier) wouldn't be a bad choice
The ducts in your photo look really small, almost like high-velocity Unico. I'm pretty sure none of them would adequately serve the highest load upstairs bedroom. Regardless, I'm really reluctant to run new ducts and build soffits, because the ceilings are so low, I'm so tall, the house feels small and cramped, and I'd be worried that I couldn't find a contractor who would go to all this trouble.With the upflow configurations it's possible to build out a <10 square foot "utility cabinet" for ease of service, and run the ducts under ceiling level in soffits
If you had said Atlanta, I'd be impressed; Berkeley, not so much.This is a 1.5 ton Fujitsu that is heating & cooling an entire house in Berkeley CA:
As I wrote previously, the house does not have an open floor plan, so I see no chance at all of a single wall coil serving more than one room.For bigger rooms with bigger loads by all means, go with a less expensive and easier to install wall-coil type, setting it up to blow through any open archways/doorways/hallways if it's serving more than just one room.
Please explain why you would intentionally oversize anything, especially if you anticipate a deep energy retrofit.If possible, set up the modulating mini-splits with a 1.0-1.2x oversize factor
Why should 5, 1/2 ton Mitsubishis be considered insanely oversized? Sure, some rooms have a little less than 1/2 ton peak load, but those Mitsubishis have great turn down ratios.
Sealing of the house would definitely be part of a deep energy retrofit, but as I wrote previously, there is only some chance of that in the future. Is it basically impossible to choose a variable capacity system today that can accommodate today's loads and tomorrow's?
I've not heard good things about the reliability of LG. Have you?
How is sweet spot range defined/determined? What is the sweet spot range for a 1/2 ton Mitsubishi? Is sweet spot range synonymous with your use of the term "Goldilocks Zone"?
As I wrote above, the system runs continuously on the hottest afternoons, which I take as evidence that the system is correctly sized. I would not claim, however, that the room by room loads and duct sizes are correct, but if they aren't, I have no intention of modifying the duct system. The ducts are in the attic with no floor and only 4 feet of headroom. So it's either use the current duct system or abandon it in favor of mini or multisplits. I am open to the possibility of using the existing duct system for a central dehumidifier.
If you are going to group rooms together, why not just go with a multisplit?
Are the Chinese Midea/Carrier as reliable as the Japanese Mitsu/Fujitsu?
If you had said Atlanta, I'd be impressed; Berkeley, not so much.
Please explain why you would intentionally oversize anything, especially if you anticipate a deep energy retrofit.
I had such high hopes for VRF/inverter equipment, but now I'm feeling pretty disenchanted. It seems like they are only suitable for desert climates. Are the high-SEER VRF central systems from the traditional American brands just as problematic in humid climates?Despite the low modulation range, there isn't enough load to get it to do what you want it to do.
Why didn't Mitsubishi allow the blower to modulate lower?...since the blower's modulation range doesn't go very low.
Apologies, what does x represent?As long as you're careful to keep the equipment sizing relative to the "AFTER" picture <1.5x it will usually work just fine both now and into the future.
Off topic, but the battery in my electric car was made by LG in 2018. It is currently estimated to have a 1 in 2000 chance of spontaneously combusting while parked.A dozen years ago the quality control at LG wasn't as good as it is today...
I want to choose the equipment and the installer so well that the warranty is irrelevant.If you want better warranty support it might be safer to go with Carrier labled Mideas.
What are the other top tier manufacturers? Does Gree qualify?...they are at top tier manufacturer.
I had such high hopes for VRF/inverter equipment, but now I'm feeling pretty disenchanted. It seems like they are only suitable for desert climates. Are the high-SEER VRF central systems from the traditional American brands just as problematic in humid climates?
Why didn't Mitsubishi allow the blower to modulate lower?
Off topic, but the battery in my electric car was made by LG in 2018. It is currently estimated to have a 1 in 2000 chance of spontaneously combusting while parked.
I want to choose the equipment and the installer so well that the warranty is irrelevant.
What are the other top tier manufacturers? Does Gree qualify?
I've been thinking about the reasons that heating/cooling energy is wasted in houses. The obvious reasons everyone is familiar with are poorly insulated and sealed building envelopes, and inefficient HVAC systems. But another reason that nobody talks about is that much of the time, unoccupied rooms are being heated/cooled whenever the HVAC system operates. For example, in my house there are 3 people and 5 rooms, which implies that at least 2/5 of the heating/cooling energy is being wasted. Thus lower capacity minisplits are sorely needed. Do you concur?
Are you scolding me?(Simply counting on a high turn down ratio to quasi-right-size it for you when it's max capacity is ridiculously oversized isn't using it properly.)
I've heard of 2-stage. How many stages are possible?High SEER multi-stage (non VRF) equipment under US nameplates might be made by others, but it's a rapidly consolidating world market.
In shame I must confess that this is my idea, perhaps influenced by misleading media, not any contractor's.The "ductless head in every room" approach is really great for the contractor's ability to make their boat payments, but micro-zoning with ludicrously oversized equipment isn't doing the homeowner/occupants any favors.
Seattle? I thought it rained a lot there.dry, low summertime dew point climates such as Seattle or Las Vegas
Safety recalls? Because they might catch on fire?equipment recalls/updates
Mitsubishi headquarters is not far from Atlanta, but I don't think I'll have that many installers to choose from.I'm smack in the middle of Mitsubishi country, with the regional training center located 30 minutes from my door, and dozens of factory certified installers less than an hour away.
Do you think a small minisplit will ever rival the SHR of the best traditional system? Say, SHR = .68?I've read rumors of a Mitsubishi quarter-tonner under development, but haven't heard any details- it could simply be smoke.
Yes, but if a single coil and air handler continue to serve the entire house, will I not still be wasting 2/5 of my heating/cooling energy conditioning unoccupied rooms?But small mid-static slim-duct cassettes can usually be sized correctly even for fairly low load homes.
But generally not in the hot summer. When it's 60F outside and raining, the dew point is still at most 60F.Seattle? I thought it rained a lot there.
But generally not in the hot summer. When it's 60F outside and raining, the dew point is still at most 60F.
Cheers, Wayne
Are you scolding me?
I've heard of 2-stage. How many stages are possible?
Safety recalls? Because they might catch on fire?
Mitsubishi headquarters is not far from Atlanta, but I don't think I'll have that many installers to choose from.
Do you think a small minisplit will ever rival the SHR of the best traditional system? Say, SHR = .68?
Yes, but if a single coil and air handler continue to serve the entire house, will I not still be wasting 2/5 of my heating/cooling energy conditioning unoccupied rooms?
Are those numbers more stringent than given in the installation manuals?There are a LOT of hacks out there installing mini-splits who don't properly purge & pressure test with nitrogen (>500 psi for at least an hour- 24 hours would be better), followed by pumping it down to <500 microns and verifying that it will stay that low for an hour or more.
To make this work in my upstairs situation, I would need a duct to pass through a load-bearing wall framed 16" OC....run the ducts under ceiling level in soffits (even if you have to go with 3" x 30" or bigger for head clearance reasons), keeping it all fully inside of conditioned space.
How low does SHR go? What is the COP at that SHR?Yes- they pretty much all beat that when operating in "DRY" or "DEHUMIDIFY" mode.
Are those numbers more stringent than given in the installation manuals?
To make this work in my upstairs situation, I would need a duct to pass through a load-bearing wall framed 16" OC.
How low does SHR go? What is the COP at that SHR?
2 theoretical questions:
1. Is there a theoretical limit above which the laws of thermodynamics will not allow SEER or HSPF to rise?
2. We know that when you cool air without dehumidifying it, its relative humidity rises. How high does the SHR need to be to cause the relative humidity to rise?
This is awkward, but...
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