Has anyone used one of these? I believe they call it Mr Slim, but that may be just one incarnation. There’s a wall mounted air handler connected to an outside compressor via a 3 inch hole through the wall. It’s mostly promoted as an alternative to window units and as a one-room solution, but I’m designing a small guest house (1000 sq ft) and I’m wondering if this would work for the whole building, and whether it would be cost effective (initially and in use) compared to traditional ducted central air & heat.
Thanks in advance
Tom
Replies
These are called "mini-splits" and there are several mfgrs of them. They work well for conditioning rooms, but I doubt you'd be happy with one for a typical whole-house application, since there's no good way to move the conditioned air around.
Now, if you're in a loft condo, or an house without many walls and one floor, might work for ya.
Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.
Generally, I think window A/C is considered far less efficient than larger central systems. So compare the SEER to know for sure. Your 1,000 SF may be what 2 tons or more load? No idea where you are, though; you haven't filled in your profile. Not sure if the little unit will give you 2 tons+ cooling.
I don't know about using one to cool an entire house as another poster pointed out, but I can speak to the Mr Slim reliability. I have a 4 ton unit in my server room here at work that has been in continuous operation 24x7x365 for the past 5 years without a single problem. I'd avoid the cheap chinese units from fleabay as you can't get parts for them. At least in large metro areas, they're pretty common for commercial applications, so we have many dealers to choose from.
If you want to do an entire house, I know they make condenser units that can drive multiple indoor units (2-3 usually) so that you can 'zone' the house in a sense. The technology and efficiencies of good mini splits like the Mr Slim are usually a couple years ahead of ducted HVAC. You might want to look at ceiling cassette units if you've got the head space for it, they'll be more visually appealing since you'll not have a 4 ft long plastic tumor on your wall.
Z
Local Electric PUD has been promoting them like crazy.
You can get units that will support up to 4 handlers off the same compressor, so with a pair of units you can handle the average size house.
Here the only caveat they have is that you consider a back up heat source for our occasional below 32 deg. F. temps.
I wouldn't consider using them for heating applications, at least not where electricity costs are very high like here (Long Island NY). Maybe use in an area where you do not often need any heat at all. Just a few days in a years time.I do see many MANY of the air-conditioning-only versions used in Caribbean countries, both in hotels/resorts and in homes. Mini-splits are very quiet compared to window units. I believe mini-splits cost less and are easier to install than full ducted HVAC, in many cases. Especially where you do not have an easy access to run full ducts.Of course window units are much less expensive and very easy to install. Easiest to "zone" as well.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Why not use them for heating? A heat pump is a heat pump regardless of whether or not it's central. Maybe it's a regional bias due to electricity costs, but heat pumps are as common as water down here in the mid-atlantic.Z
Maybe it's a regional bias due to electricity costs
Re-read my first sentence. :-)
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Look up the Variable Refrigerant Flow (VRF) systems being promoted by Mitsubishi, Sanyo and Daiken (among others I'm sure). They are essentially outdoor compressors connected to several interior wall mounted units that either heat or cool the spaces where the units are located depending on demand. The variable part of the system is that one unit can heat while another cools, because of how the refrigerant is piped and utilized. They are quiet and efficient.
I'm not sure that the VRF I'm talking about is the same as the "mini-split" or others that have been described, but they can be ductless (don't HAVE to be, btw).
http://www.mehvac.com
EDIT: You don't just use ONE small interior "window unit," btw. You would have the system designed for the load, and connect all of the individual units (say one per room) to a manifold which directs and redirects the refrigerant through the line set piping (generally one long run between points and concealable through wall spaces, etc).
Edited 8/6/2009 1:57 pm ET by lindenboy
I have been using the to condition small spaces.....I use the for wine cellers.....
I have a 1.5 ton 13 SEER LG mini split for my tiny house, under 300 sq ft. It works hard to keep it cool in here during our South Georgia summers. If I turn off the A/C it will get up to 98 degrees on a sunny day. (House is sealed like an ice chest with refrigerator and freezer dumping a lot of heat, plus giant plate glass windows.) But the Power Cool feature can bring the house down to a comfortable level in under 10 minutes. I also have a ducted externally mounted Fantech exhaust fan and a filtered floor vent for air exchange. I don't turn the fan on much in the summer because the outside air is so humid.
The heating side of the situation is not as efficient. Only 10 SEER. I have electric radiant heat in the bathroom floor and only use the mini split to stir the air a bit. It has a radiant heater strip for really cold nights. My power bill is highest in February, oddly enough. I don't think that's because of the mini split though, I'm inclined to blame it on my electric instant water heater and fondness for a hot bath in cold weather.
Sometimes my LG unit spits out water. I clean the condensate drain from time to time, but with the high humidity down here the little pan gets overwhelmed when the unit runs a lot. I probably should adjust the mounting to tilt the wall unit towards the drain side more.
My mini split is very quiet. Comparable to the noise the refrigerator makes. Unfortunately I have to add an extra 10dB the sound level with a floor fan to keep the loft comfortable.
1.5 T for a 300sqft house?! Does it have any insulation?My 1200 sqft house needed only a 2T unit. DC has nasty summers, probably not as bad as yours, but still really nasty. Z
I know, 1.5 tons seems outrageous for a 12x18 house! But that's what the A/C man recommended and I listened to him! I have foamed in place icynene insulation. Literally like an ice chest. I was going for sound proofing, fire proofing, pest proofing, moisture proofing, and aesthetics. Limiting the temperature rise from radiant heat was down the list of priorities. I have a white metal roof with cathedral ceilings with only enough foam to achieve about R-17 worth of insulation up there, so that's non-ideal. I should have put fiberglass between the foam and the ceiling but I only have 2x8 rafters and the formaldehyde free ceiling stuff wouldn't fit. On the up side that metal roof cools off instantly the minute the sun sets. The main reason I need 1.5 tons of cooling is the 100 square feet of window surface (for 900 cubic feet of volume), although I do feel like the refrigerator and freezer really do dump a lot of heat in here too.
You need shades over those windows, from the outside to keep back the solar gain. Even reflective window film has to help.And you REALLY need better roof insulation. R17? It would be worth it to thicken the ceiling/roof so as to add more insulation.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
And/or an appropriate overhang, since I assume the windows face south for that much solar gain. 8" of spray foam is going to be better than 8" of FG batts, and I'd bet most of the gain is through the glazing. Beachton, what type of windows do you have in there? Z
My windows are reused 3' sliding glass doors from the mobile home factory, so pretty low quality. My loft puts my bed right up against that ceiling at the low end of the gable, so I really can't add anything there. I built this little paid-for house to be a little camphouse just used a few weeks a year. I just kinda got stranded here in the recession by unemployment. As it is my August power bill was only $60 with me here all day every day. A couple years of that is probably still cheaper than modifications would be, and won't add any uglification. I take a lot of photos out of here of deer and turkey and turtles and songbirds and squirrels and stuff (it's like I live in a blind) so I don't want to obstruct my view. Hopefully soon I'll get a job in a city and this house will be very comfortable for Christmas vacation.
Being from the land of passive solar design (Western Mass), I don't think that well engineered overhangs would be costly or block your view. Check out http://susdesign.com/tools.php for some tools to see how to use overhangs to reduce your summer solar gain.Sounds like a really neat house, btw. Got any pictures of it?Z
I studied the overhang calcs in my Ramsey and Sleeper Architectural Graphic Standards when I was designing it as just a utility building, but after I started building it I realized I was going to have to live here so I had to add a bathroom and a loft. I rotated the roof 90 degrees from my original plan to accommodate the loft, leaving the South window without an overhang.Pictures -- why didn't I think of that? I had the A/C contractor put my condenser unit under the house, which was certainly something they had never done before. (I didn't see why I should have to mow around it.) It has worked out great for me so far. The insulated tubing running on the North side of the house is pretty unattractive, but way less than a giant slide-in wall unit would've been. I meant to bend up some flashing to cover it but since I drive up to the house from the other side I don't have to look at it. If it doesn't bother me then why install a mouse habitat on the side of my house? You can put all that stuff inside the wall, but with my post and beam construction it wouldn't work. I'm growing mint in a brass bucket where the condensate drips.Those blue bins under my front steps hold my oven and a griddle. I don't have a range at all. I do most of my cooking on that table on the front porch to keep moisture and heat out of the house. In the winter I use the little oven indoors. I also have a microwave, rice cooker and an induction hot plate. Turns out that's all I need!
That house looks great. More power to you! My wife and I are going to be moving into our own small house sometime in the next few months. When we bought it, it was 650 square feet. I've since added on an additional 150. There's a six foot high basement under the house, so we've got plenty of room for storage. Our game plan is to pay the thing off quick and enjoy living within our means. Glad to see we're not the only ones!