This post is quite accurate. A radiant barrier does work well for conventional vented attics (which themselves make little sense in a hot humid environment), and better yet (for that same hot, humid environment), use the spray foam (which should completely seal the house at only the exterior surfaces like a giant Igloo cooler) and forgo the barrier (which would be covered by foam and negate any effect on the underside of the roof deck). Dang...finally go to use my engineering degree!!
OK, I am a little confused about what would be best for me. I live in a climate that will see 90-100 in the middle of summer with a good amount of humidity (not the jungle, but enough that you feel like you are in a oven on hot days). My house has a 5 ton 2-stage, zoned (4) HP for the main floor. It is located in a vented attic. I know I need additional blown-in insulation in the attic, but am waiting until I finish a few more automation projects.
On the hottest days, the HP will just not cool the house to the level we like as we have a tremendous heat load on the front. So in the eveing, we have to shut down the main zone to be able to cool the bedrooms. I know I am getting some cooling loss from the attic duct work (ductboard & flexibles) and my inital thought was to build some barriers and cover the ducts with insullation and seal the joints with mastic.
Then I watched a home repairr show where they were using the radiant barrier. I have full access and could put the barrier between all the roof joists, but is seems like the heat would just come through the joists. Then I thought about some type of spray foam, but have heard it can cause your roof to heat up and lower your shingle life. We plan on being in this house for another 10+ years, so a roof replacement is probably in my future anyway.
So would insulating my attic with spray foam help cool my attic down enough that it would provide a benefit to the HVAC system?
One other option I have is putting back a compressor in the original system. When we moved into this house, the previous homeowner had replaced one system entirely, but left the main floor compressor and a-frame, but replaced the air handler and furnace. Well the old compressor died and instead of replacng it, we put the zoned system in the attic as the old system didn't heat/cool evenly. We kept the furnace as it was gas and use it as our auxillary heat and try not to use the heat strips in the HP.
So I also thought about putting in a compressor back in the orignal system to use as the baseline and then use the zoned system to tailor each zone.
Any suggestions. I know nothing will be cheap.
