I'm planning on installing a portable spa in a small 12' x 12' sunroom (which is now unconditioned). I will be using screened double hung low-e windows and doors in the room.
Obviously, I need an exhaust vent, and makeup air if I want to keep the windows closed. I don't feel heating the room will be needed as much as cooling in the summer. (located in the mid-atlantic region)
I could open the sliding patio door between the sunroom and conditioned house for some heating and cooling. But I also have a spare Aprilaire fresh air exchanger that I could incorporate in the vent system.
So what are some setup and control options for exhausting spa moisture, making up with cooler air using existing HVAC and in turn making that air up with the Perfectaire unit? Looking for a way to switch from either conditioned air or outside air easily.
PS. I'm a retired HVAC-R commercial service tech, so will be doing the work myself.
Your spa puts in a load of humidity in that room, as well as a good amount of heat. You need (in my experience) negative pressure, to keep the humidity out of the house as well as the Bromine, Chlorine or other sanitizer smell out of the house. You should use a V/S air handler with a two stage condensing unit at the very least. The ducts should wash the windows with air to keep them clear. You have not mentioned the size of the room, flooring, roofing, insulation or the temperature and humidity you want to mantain. I've seen great indoor spa rooms with terrific humidity control and ventilation as well as some moldy disasters. There have been many cases of hot-tub lung from improperly mantained and ventilated indoor hot tubs. I am also of the belief that Chlorine is the only acceptable sanitizer for an indoor spa, as such the ventilation must be adequate.
The room was originally framed to be a screened-in patio, but that being said, the shell was built to the same specs as the rest of the house. 12' x 12' with an 8' ceiling. 4" concrete slab floor with perimeter insulation. 4" walls with R-13 insulation and vinyl "nailite outside siding, not sure what the inside finish wall will be yet. Six 40" x 60" double-hung Farley vinyl windows with low-e/aragon glass. One 32" insulated steel door with no glass to the outside. Tongue and groove ceiling with R-30 insulation, ridge vented gable roof. Window shades will be used to control excessive sunlight.
Other than the outside wall thing, which I know makes a big difference on the heat load, we"re talking about a room the size of a large walk-in closet!
Now since my other option would be to have this spa outdoors, I really don't expect to maintain the same temperature and humidity as the rest of the house. The wall between the spa room and the main house will be moisture and temp proof, as if another outside wall.
If I get one of the higher quality tubs with an insulated cover, I've been told the humidity level only goes up during use, which would be 1/2 to 1 hour a day. I am hoping to try this summer without an extra zone for this room, we'll see how it goes. The negative pressure idea makes sense.
How would I determine the minimum proper amount of air changes for the room while in use? Let's assume for now that my existing cooling equipment can handle the load (it was sized for the future completion of a large attic bedroom, which may never materialize).
My thinking is to put the "stale air" intake of the Aprilaire unit in the spa room. then install the rest of the heat recovery vent system as per a normal installation. I could then run a cooling outlet into the spa room, which I would close when using the windows.
Or I could just go with a simple seperate ventilator and makeup opening (like crackin' the windows)
Any better ideas?
About a 300CFM exhaust ventilator should do, check out the Broan insulated units, they are quiet. A unit of this size should require about a 8" exhaust. The insides are pretty much all plastic, so rust shouldn't be too much of an issue. Get yourself a variable speed control to go with it and you can decide how much exhaust you need. Depending on the construction of the room, you might not even need to crack a window. I would stay simple, as the humidity carries chlorine residue that tends to screw up the exhaust system. I just cleaned the blower wheel on a small mini-split used in a spa room, it was unbalanced from the build up of Chlorine residue. As far as cooling, if the shades are open, you'll need alot! Usually, you'll need a seperate zone at the very least for a comfortable sunroom. Good luck.
Thanks, Rob, great advice!