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Personal experiences with Daikin Quaternity ductless heat pumps

I've read many times about the independent humidity control of Daikin's Quaternity models. I've even found myself jealous of them after installing a Mitsubishi and feeling muggy in my house on a mild spring day when there is little need for cooling, and the dry mode makes us feel too cold. There are illustrations and videos on the web showing how it works -- the indoor coil is split into two parts, one of which can be hot and one of which can be cold (at the same time), which allows for dehumidification without cooling. That's great, but in all my perusal I don't recall ever reading a single personal experience with how well this actually works in real life. Does it really maintain a stable humidity level year-round? How much is energy use increased by this additional dehumidification function? And why are these not hugely popular considering all the talk I've seen about latent loads being such an important issue in high performance homes?

Asked by Nick Welch
Posted Jun 10, 2014 3:29 PM ET


6 Answers

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try setting the fan speed manually to very low, and the temperature lower than the desired setpoint. I will act more like a dehumidifier

Answered by Keith Gustafson
Posted Jun 10, 2014 3:38 PM ET


Keith, isn't that what dry mode already does?

Answered by Nick Welch
Posted Jun 10, 2014 3:40 PM ET


I don't trust the machine to do what I want, it has a mind of its own.

Answered by Keith Gustafson
Posted Jun 10, 2014 3:57 PM ET
Edited Jun 10, 2014 3:57 PM ET.


Well, the main issue with dry mode is not that it doesn't dry, but that it has a slight cooling effect, which gets uncomfortable and causes us to turn it off. Running cooling mode on low would have the same problem.

Answered by Nick Welch
Posted Jun 10, 2014 4:03 PM ET


Umm, I guess you could assume that is true or do something radical like trying it............you can change both temp and fan settings to see if something works better than the stock setting

Answered by Keith Gustafson
Posted Jun 10, 2014 5:31 PM ET


From posts on other forums I'm led to believe that the Quaternity has a dehumidistat, but does not in fact (as implied) dehumidify without at least some sensible cooling, nor does it dehumidify in heating mode as I had previously been led to believe. There may have been a design revision, altering the operation function of their innovative split coil & valving in the indoor unit that allowed dehumidifying in heating mode , or completely without sensible cooling, or maybe there was confusion early on.

Beats me, but it does not dehumidify in heating mode, and there will always be some sensible cooling, though the latent/sensible cooling ratio will be different in DRY mode than in DRY COOLING mode, and it's not clear that it responds to the temperature setpoint in DRY mode.

In the engineering manual it implies that in DRY mode (as distinct from DRY COOLING mode) there is less sensible cooling as it approaches the humidity setpoint, but that's not the same as no sensible cooling. See the notes at the bottom of P49 (p50 in PDF pagination):


The coil & valving diagram on p.8 (p.9 in PDF) implies that the coil really is split, and operates differently in DRY mode.

If the internet-scuttlebutt about how well it works is true, the primary distinction between the way the Mitsubishi & Quaternity works in dry-mode may be that the Daikin's dry mode is under dehumidistat control, and stops when the RH hits it's setpoint, whereas the Mitsubishi keeps running until you put it in heating or cooling mode. But they allege there is at least some re-heat when in DRY mode.

Answered by Dana Dorsett
Posted Jun 10, 2014 5:59 PM ET

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