Island Life
Island Life
(OP)
Here I am on a small south pacific Island w/out access to Ashrae...what are the best practices for HVAC design here? I see a lot of sweating walls and rusting duct. Whats best: Alum duct, flex duct, sstl, corrosion restiant coatings on equipment. Its 89 deg and 80RH here most of the time.





RE: Island Life
You have internet so you have ASHRAE access.
Small island means your dewpoints will be very close to the sea surface temperatures. Your condition of 89F at 80% Rh is about an 82 dewpoint, I will get them that high every now and then but more like a consistent 78 to 80 here.
So if the coast is not far away, galvanized fresh air ducts will rot. The thicker the galvanizing, the longer it lasts, but it will fail. Need aluminum or stainless fresh air ducts.
If you run the fresh air duct through conditioned space you need to insulate it so that the air inside the duct does not condensate. The condensation speeds corrosion and there is a good chance that there will be organic matter in the duct- pollen, insects. You do not want wet organic matter at room temperature laying around in ducts.It will be a spore generation factory.
You want to keep your buildings under a positive pressure to keep that humidity out. You bring in fresh air directly to a cooling coil, cool it off and then blow it into the space.
http://www.masongrant.com/html/samples.html
Order "The ASHRAE Guide for Buildings in Hot and Humid Climates" and the ASHRAE "Humidty Control Design Guide"
here is a free chapter from the latter
http://w
You live somewhere, where the ambient dewpoint is higher than the temperature people will set their thermostats at so you need to be careful.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Island Life
It was an Arizona design recycled here-- it was a negative pressure ventilation scheme, as you can see it is disasterous. The decking is the underside of a floor slab, it was 78F, the ceiling space was demonstrating the rain cycle like a primary school lesson. There was over 1/2 inch of water in the sheet metal channels holding up the ceiling
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Island Life
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Island Life
http://www.baileyeng.com/paston_effect.htm
RE: Island Life
Mike will be a lot more humid than Florida though
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Island Life
RE: Island Life
never ever on the inside in a hot humid climate
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Island Life
If you place a vapour barrier inside the water will build up and be a real problem
In my experience I would insulate on the outside with styrofoam
If you insualte on the inside between those studs, use something that breathes
For a commercial building, ASHRAE 90.1 would not require those concrete walls to be insulated in your climate the thermal mass cuts down on the heat coming in during the day, it releases the heat at night
If you insulate on the outside, you cut down on the heat that gets into that concrete in the first place.
If you seal the attic and insulate the roof deck and any gable walls, the building will tend to be very dry, and I doubt the attic gets much hotter than 80F.
A white metal roof is a no brainer, keeps the heat out, reflects it away.
Driest condos in the caribbean (hurricane panels up for Hurricane Dean)
sealed unconditioned attic averaged 80.5F and 47% RH in Aug 2007
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Island Life
The roof is about R7, I figure it is more effective then R30 at the ceiling plane with a vented attic.
The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install