I know this is the wrong season for an air conditioning question but I am trying to plan my cabin. Building a 20x34 1 1/2 story over a full basement in Alabama so it must have A/C. My problem is dealing with the duct work. I would like to keep my basement walls to 9 foot but then there is not sufficient room to hid the duct work and maintain a 8 foot ceiling (losing 8" for gravel and slab). I will also lose part of closet upstairs for the return. I started looking for alternatives and saw the Ductless Mini-split systems. They are not as visually pleasing but may be an alternative to central air. Does anyone have any experience with a ductless system in the South?
LG makes a mini unit. Actaully a couple of different sizes. They are very good. I have been in shops and small houses with them and the people that had them said they were great with no problems. The area that these were used in was central Georgia as far as climate.
Split minis are very energy efficient. If there is more than one room look for a unit that can support several in-room air handlers off the one external unit. Each room or zone can have its own thermostat. Well worth looking into, IMO.
Split-minis (ductless) air conditioners get my nod. I first saw them years ago in Italy, and was disappointed they did not seem to be available in the States then. Today there are several available here. Good! But I wonder how accurate the SEER ratings really are? Has anyone seen any installation instructions on-line? I would like to know how close, in elevation, the inside and outside units have to be. ??
I don't know the actaul spec's but the one's I saw were mounted on platfroms right beside the location it was used in. Like a normal unit. The one in the shop I saw, the owner said the AC installer told him the inside unit/ handler had to be less than 25 foot from the outside unit. This was a small version though, probably the smallest one available.
Actually they are normally called mini-split or ductless units. Not trying to be a smart-a$$ or anything. I have installed many dozens of these units and for the most part they are great for their intended job. Which is cooling and or heating a given area, depending on size. Of the ones I've installed they cool WAY better than heat, at least the ones that are heat pump models. The units that use electric resistance heating elements heat much better and will perform better at colder temperatures. Some units like the Energy Night have a maximum line set length of around 55'. Some of the Fujitsu units can go around 100'. MOST not all can have the outdoor unit 20'-30' above the indoor unit. The other way around is no problem with line set length. To expand on the heat pump units not heating well, I need to explain that they usually heat fine down to around 30F to maybe 25F then some units shut off. They are not designed to be a primary heat source.
As with all heat pumps they loose efficiency as the outdoor temps fall, but most of these units actually have a temp sensor to shut down the unit.
Having said this it would be hard to find another unit that can provide excellent air conditioning in summer and provide mild season heating duties that is better suited for the smaller cabins designed by John and others on here. When I build I hope to afford a mini-split A/Cm a wood stove, and a few base-board electric heaters for times when I'm not home to load the stove.
Hope this helps.
Any suggestions on how to layout the indoor units? Basement has 2 bedrooms with individual baths. Main floor is very open with only a bath enclosed separately. There will be a small loft with the rest as a cathedral system. Basement will likely be ICF. I ran a Manual J using HVAC-Calc and there is only 10K BTUs of heat gain for the entire structure. 8K+ is the upstairs and very little in the basement. The smallest unit I have found so far is 9k up to four units (9k + 9K +9k + 9k). Putting a 9k in each bedroom sounds like major overkill but I also need to think about humidity control. 1 9k in the center hall for the basement but what about moving the cool air to both bedrooms/bath.
Maybe a 9k at both ends of the main floor??
The central air solution is simpler because you can put ducts in each room and control the flow with dampers.
If humidity is a factor, and it is there, the units have to be sized correctly. Too much cooling capacity means the unit does not run long enough to drop the humidity enough. That is where some expert advice is needed.
I believe the one disadvantage to a mini-split is they will cost more to buy than a central ducted system.
From what I've seen on the minis though, when sized right they are very good. Quiet.
I have little or no experience on ducted, accept for my time in the US
Ducted to me seem very lossy and need a lot of space for the ducts, insulation etc etc.
In lationo land and here in the middle east most modern buildings use split AC systems
I have 6 in this house..........50deg summers with 90% humidty
and the last in oman had 7 units
all the compressors and fans are on the roof and the two pipes are ducted down in a 4" plastic pipe to make repair and removal easier
Compared to noisy window units these are way quieter and work fine.
Usually 1 unit per room and 2 in the larger living areas
all are set up high and produce enough to cool the corridors and bathrooms as well
I wonder how the lubrication is managed when the compressor (outside) unit is higher in elevation than the evaporator (inside) units. Whereas the refrigerant changes phases, going from gas to liquid and back as it circulates around the system loop ... the lubricant always is liquid. I know on some very large systems, sometimes special provisions must be made to return the oil from "low points" back to the compressor inlet. Even dedicated oil pumps are sometimes required in large building units. In automobiles and window units not much is required because the entire system is all "level". But in split mini systems ....??
As far as ducted being lossy, that is true if ductwork is installed the old way with the ducts in unconditioned space. Now a good builder provides chases for the ductwork that are conditioned. Here in NM I've seen new solar powered homes built that way. Even the central A/C runs off what the PV panels produce. Grid tie system though.
I still like the idea of mini-splits best though.
There are in-ceiling mount air handlers available for mini-split systems. If you built your floor with joist trusses you could have a clear span in the basement and hide the air handler and all the ductwork between floors.
JRR....Most of the lubricant in any refrigeration system stays in the compressor crankcase. The small amount of oil that leaves the crankcase is slowly returned via the suction line (low pressure gas). All systems, but especially the mini-splits have maximum and minimum line set lengths, and charts on adjusting refrigerant levels per length. This also effects oil return to the compressor. Now if the outdoor unit is below the indoor unit the oil is gravity returned. If the outdoor unit is installed above the indoor unit the compressor has enough suction to lift the oil 20'. If you have to go more than that then P traps should be installed every 20' of vertical rise. That is for regular large split systems. Mini-splits usually don't allow for over 20' feet rise. That is why you see them mounted on the side and roofs of buildings so much.
Don...A properly sized duct system that is lined (insulated inside), sealed, and using quality supply, but more importantly return air grilles can be real quiet. Especially if the furnace or air handler is equipped with a variable D.C. motor. Another "trick" to make duct systems quieter is to size the supply runs to the boots one size bigger then reduce right at the boot. Also insulated return air boxes (called cans) at each return air grille, really helps quiet them down.
Don't rule out central air. You could order 20' floor trusses with an HVAC chase. The chase can be built into the truss at any part of the span. You could then vent to the ceiling in the basement and to the floor on the first floor. With a little planning you could get another vent to a second floor.
The other advantage of the floor truss is ease of wiring and plumbing. Just run the wire through the openings. Plumbing is easy also, as you can more easily set your drain slope in certain situations depending on layout.
Of the three systems I have built with, I rank the floor truss easiest, followed by trus-joists, and finally dimensional lumber. My buildings are commercial, mobile buildings, but the issues are the same.
Dimensional lumber is easy and stout, but in a smaller rectangle floorplan the utilities become an issue.