Mini Split questions

[kromkamp]

Hi, I just had a few questions about Mini Splits I'm hoping anyone might be able to answer.

1)All of these units seem to offer a 'dehumidify' mode, but from what I gather this mode is only a 'low fan speed' mode. Do any of these units offer a true dehumidify mode? (ie. heat the air back up to keep the temperature the same - I'm assuming a mini split with heating).

My main requirement is for modest cooling in a basement room that hovers around 65% RH, I'd like to maintain that at 40-50% if I could.

2)Is it possible to take a single zone outside unit and have two inside units installed on it? Of course they would have to be on the same zone and that fine. I just have two small rooms where even 9000BTU (the minimum mini split size) would be oversized for.

Thanks!

[Irascible]

I'm no mini-split expert. But at the same time I've never heard of unit with reheat. That would mess up their efficiency ratings. To buy such a thing would result in hired goons from the EPA flying to your house in black helicopters and breaking your shins. What you're talking about would more likely be in a commercial product and cost a fair amount more.

Mini-splits come in one, two and three zone varieties. I'm not aware of a unit that does more than three zones. Those would be cooling only systems that have one machine outside and one to three wall mounts inside. I'm not aware of a multi-zone heat pump mini-split. But I'm sure a mini-split expert will correct me if I'm wrong.

Be prepared for sticker shock. They're pretty expensive.

[johnsp]

True. The dehumidify option usually runs at low fan speed and will cycle the fan only when the compressor is on.
I don't think I've ever seen a mini-split eveporator less then 9K BTU. Sanyo and Mitsubishi have large multi-zone units but the individual evaps are never smaller then 9K.
I think Sanyo has an air handler that gets mounted up between the floor joists like a mini-air handler. It has 3 4" duct take offs that can be piped to individual rooms.

http://www.sanyo.com/industrial/HVAC/Concealed_Duct/Heat_Pumps/index.cfm?productID=1025

[Edited by johnsp on 06-10-2005 at 09:27 AM]

[pecmsg]

Sanyo or Samsung make a tri-zone 18 / 7 / 7. But if all you’re concerned with is humidity than just install 1 or 2 dehumidifier’s with a small window shaker. Basements that are primarily below grade need very little if any cooling.

[DeltaT]

Using any mini split for mainly dehumidification just won't work 98% of the time. It's better to just use a normal dehumidifier found at Sears or other places. Once the humidity is reasonable you probably will find the temperature confortable in a basement anyway and won't need mechanical cooling.

But if you insist on mechanical cooling I would find a small window unit to use and just let it run. That would dehumidify just as well and cool a little for 1/10 the cost of a mini-split

[kromkamp]

Thanks for all the feedback so far.

DeltaT, I do agree in some sense with what your saying. However, the fact that I require some cooling, dehumidification and supplimental heating (to augment the existing hot water heating) in this room in the winter makes a mini-split very compelling. (This room is an entertainment room and does require some cooling, but not a lot)

Also, I am unaware if there are any whisper-quiet, window dehumidifiers. Do you of any? floor space is at a premium in this room, and I dont want the racket of a traditional dehumidifier.

I agree that a multi-zone unit is not what I want, because each zone is sized at 9000BTW or higher (excepting those Sanyo/Samsung ones, thanks for that tip). I'm wondering if a single-zone compressor can be used to drive two inside evaporators.

Thanks!

[kromkamp]

Most of these mini-splits do offer 'seamless' heating and cooling (ie. they will switch between heating and cooling depending on the ambient temperature).

Could any of them cool (and dehumidify) to the point where the heating system is engaged in order to bring the room temperature back up? ie. ping-pong between cooling and heating.

[DeltaT]

Dehumidification is a side benefit of most any mechancial cooling system but not it's primary purpose. Mini-splits are prone to coil freezing that is why most of them have internal freeze controls. You can still use most any "window" unit either that is a heat pump or a small electric heater element to maintain temp. Fredrich (sp) makes some good ones.

Some of the mini splits will have a control for "auto" temp control which will switch between heating to cooling. Mini splits are also available in multi-evap cooling/heating heat pump using one condensor and a variable speed compressor; or with electric strip heaters as a form of heat.

They are expensive though but well worth me money.

[kromkamp]

DeltaT, the units with the "auto" temp control - do you know if these will work well in dehumidify mode as I mentioned? (ie. cool down below the heating threshold and then heat back up again to end up with a normal temp. but dryer room)

It seems like a lot of 'portable air conditioners' have a true dehumidify mode (ie. they blow warm air back into the room) - why dont mini splits offer this?

[DeltaT]

Any mechanical cooling system that advertises a dehumidification mode will only let the system get away with so much in dehumidification mode, say 2 to 3 degrees below the temperature set point to keep the system from going into self-destruct.

Mechanical cooling is not a primary dehumidifier unless the system is specifically built and set up for dehumidification, then it is not a "typical" mechanical cooling or A/C system.

Al the portable room A/C that I know about only blow the condensor air outside of the conditioned room and do not recirculate the hot condensor air back into the same room or what would be the purpose of having an A/C?

However, specifically build systems called dehumidifiers refrigerate the air and push the same air back through the hot condensor and back into the same room. But they are dehumidifiers, not air conditioners.

[Irascible]

Perhaps he's talking about the portable air conditioners that roll around on casters and have a hose that discharges the hot air to a cracked window. I suppose if he discharged all or part of the hot air back into the space, and if it was the type that collected the condensate in a container then he'd have his dehumidifier.

[kromkamp]

If you look at, for example:

http://www.sharpusa.com/products/ModelLanding/0,1058,1525,00.html

If you look at the manual online, pg21 it says "When operating dehumidification with container, the unit generates heat during dehumidification mode and the room temperature will rise".

Sounds like it does indeed redirect the vented hot air back into the room. There are Pinguino models that do the same thing. So it does exist for these portable units. But they are even bigger than just a dehumidifer :) I'd really prefer the identical features in a mini-split. Otherwise, I will just get a small dehumidifier (I've found a small, quiet one by a company called surround air).

Thanks!

[Irascible]

Right-O. And even if it wasn't in writing you could force the issue by leaving the discharge hose off (for some models). But for mini-splits it doesn't seem to be the case. Besides... Have you priced a mini-split? The price ain't so mini.

[DeltaT]

Thanks for the feedback. Never seen that unit before but it still would seem it would be in a selfdestruct mode. If you get one let us know how it works. I could not find the price anywhere so let us know too. Best of luck.

[kromkamp]

I have a quote for a cheap-o mini split (Soleus, which seems to be an OEM of Hitachi) installed for $1200 canadian (about $1000 US), which is not bad at all. A lot of mini-splits are expensive but there are a couple that are more reasonably priced.

But if it cant do what I want it to do then even $1 is too much :)

Right now, unfinished, the room is 20 degrees celcius when its 32 degrees outside. The RH in the room is 78%. Clearly the humidity is much more of an issue than the temperature.

Thanks guys!

[kromkamp]

In fact, I just had a closer look at the Sharp manual. The dehumidify mode *is* basically 'remove the exhaust hose'.

The manual also mentions not to run the unit in dehumidify mode for more than 8 hours/day, which leads me to suspect you are right about the 'self-destruct'.

Why is it that a dehumidifier can run all day and night, but running a unit like this in this mode continuously would cause damage to it?

[johnsp]

The portable AC will never cycle off if the hot exhaust is put back in the room. A dehumifier is more like a frig. compressor and the humistat will be satisfied regardless how warm the room gets. With the condensation tank, most expect to turn off after the bucket fills up. You realize that these will raise the temp, so you're not adressing the cooling needs. Your high humidity level is also coming from the unfinished portion of the basement. I bet a small window shaker in the unfinished portion will drop the overall humidity level without over cooling the theater space. Just get a cheap $100 unit, more undersize the better. Your audio/video components must be putting out some heat also, that needs to be addressed. For heating, your current hydronic system would be the best solution. A small zone of baseboard or a pannel rad is probably all you need.