View Full Version : AC ideas for closed in screen porch
05-14-2007, 12:26 PM
Hello group, I am looking for suggestions and ideas and possible ideas for sizing..We have a east facing covered screen porch which we closed in with acrylic panels. It has house on two sides (rear and one side) plus roof and floor to ceiling acrylic panels on the long and short walls one one side. We had a 12K BTU portable AC/Heat pump which we have installed out there but it doesn't seem to quite cut the mustard. This last winter we installed a gas wall heater which took care of the heat but now am thinking of redoing the AC. Originally the porch was screen and the cover is part of the roof although the hardy board ceiling is not insulated yet. The porch is roughly 10X30 with the backside of the fireplace taking out a bit of that. We also have a hot tub in there but is covered and not used daily. In the morning the sun heats up the porch and at this point that portable is not able to bring the temp below 84 when it's running full blast. In the afternoon when the sun is on the other side it is better(outside temps have been reaching near 90 and this is central Texas)..One would think that one ton of Ac would be more than enough but I have read these things are very inefficient. We are thinking of replacing it with a ductless split system which would be super easy given the power is right there and the compressor could sit right outside the porch. We also intend to blow some insulation over the ceiling. Given the "windows" are single sheet acrylic I am sure the heat load is more than usual for this size of space. I have been pricing out these units in the same size of the portable but I have read that they are way more efficient, would a 12K be too much given my situation? I know you can't see it so if there is something I need to look at or take into concideration I am all ears. the panels are very well installed and we don't have much air leakage that I can see. WHen I run the portable I leave one of the doors to the porch open as I know it needs to draw air since it exausts air from the living space but it still seems to work way too hard(figured with the house door closed it has to draw warm damp outside air in somewhere).
Thanks so much!
PS. The reason we put the gas wall heater in was last winter we had a very cold (for Texas) period and that heat pump ran solid for three days and could only bring the temp up to about 65 degrees. THe heat pump feature on this unit is marginal at best anyway but given we had three foot icicles it was pretty cold.
05-14-2007, 12:42 PM
If you install a mini-split, get one with the inverter compressor. They are fully modulating. I use Fujitsu but your local contractor will make his/her recommendation. A 12k btu unit will go as low 3,800 btu's and as high as 14,500 depending on the load. Or you can use the 15k and go as low as 5,500 and up to 17,000. That way depending on the load you are not always using full capacity. They work very well in your application. I have installed about a dozen in 3 season porches such as yours. Hope that helps.
05-14-2007, 12:53 PM
Do yourself a favor and insulate first. You may be surprised at the difference. The space you are trying to cool is nothing like typical residential space. You have very little insulation, don't know how much air infiltration, but probably lots, extra heat gain from the windows, extra heat gain from the hot tub.
You need to insulate and seal the space. THEN see what your heating/cooling requirements are. You may be pleasantly surprised.
05-15-2007, 12:48 AM
What kind of "portable" AC unit? Does it use 1 or 2 exhaust tubes? If it only has 1, then it's useless as it's pushing hot moist air out the 1 tube and hot humid air is rushing in from outside through air leaks in the patio to make up for it. You're on the right path -- a mini-split is the ideal solution for this application...but definitely insulate the roof first and seal off air leaks. I've seen mini-split systems used with open-air patios successfully, but it requires a very oversized unit.
The other issue is that you have the hot tub, which is going to put substantial amounts of moisture into the air, which will have to be removed with the mini-split. Inverter-based is going to be the best solution, as a non-variable system won't be able to adequately remove humidity in this case. If humidity gets to be a real problem, a good dehumidifier might not be a bad idea.
05-15-2007, 10:40 AM
Thanks guys for all the tips..I had seen a reference to the "inverter" technology but steered away because of the price being nearly 50% higher but might have to go back and look. I didn't realize it was worth the difference in price.
Working on sealing everything up now and plan to blow some insulation over the ceiling. I didn't seal it up tight over the winter as with the gas wall heater it expects a bit of fresh air for combustion. Hopefully we will only need that in extreme cold which we don't get here often.
On the hot tub, Been toying with the idea of putting in an exhaust vent fan of some sort to use when the tub is open with a small opening window. We don't use it that often specially in the summer..More of a winter thing but do keep it running. It has a really good top but I am sure some humidity leaks out. Figure it would be best to try to pull out the access moisture from using the tub that way instead of expecting the AC to do it.
Oddly enough in the afternoon when outdoor temps are highest it seems to work better but at that time the sun is over the house. It really has a tough time in the morning when the room is in full sun. I see the point of needing the unit oversized but also don't want to go too far so it won't run long enough.
The portable is a one tube Chinese unit and we didn't know the downfall of that when we bought it. That is why I try to allow it to pull air from inside the house rather than from outside, I know this isn't a good solution and is why I am looking at this other unit..I see several online vendors sell them so been looking..Trouble I have seen so far is most of them are Asian and most of the manuals are poorly translated.
Anyway this all gives me some ideas of what I need to do first. As always thanks for all your help!
05-16-2007, 07:44 AM
Just get a PTAC if cost is an issue.
05-16-2007, 08:04 AM
Just get a PTAC if cost is an issue.
I looked at those but all that I found have electric heat and not heat pump. Plus not sure if I want a big box hanging off the side of the porch.
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