I want to go with in-floor heating using gypcrete or something similar but I'm wondering what to use for cooling in the summer.

 It's a new house build and the HVAC guy told me it costs about the same, minus that furnace, to run the ducting for air conditioning. He quoted me about $15000 complete with the air exchanger. Is there another way to do this without resorting to window or wall mount systems?

 I'm doing most of the build myself, is A/C hard to run ducting for? I've only ever installed a garage furnace and ducting.


Sean

Do a manual-J cooling load calc, and a manual-D duct design first or your AC performance is gonna suffer...

In low humidity climates radiant cooling can work using the same tubing as your heating, but it'll take some design work on both the cooling & control end. Having some radiant wall or ceiling (or panel) helps the efficiency of the cooling end enormously, allowing you to get there with warmer water, avoiding having to make the gypcrete uncomfortably cool to bare feet.

In low average-daily-load climates & tight well insulated houses just thermal mass (which you have with gypcrete) and controlling solar gain with (mostly exterior) shading can get you there without a cooling system. What is your annual cooling degree day ( CDD)load (look here for your nearest city or the one with the most approximate climate: http://ggweather.com/ccd/nrmcdd.htm ) Mine's under 500CDD- we have central-air, but with recent insulation & air sealing upgrades it runs less than 20 hours/year- could get by without it by adding more thermal mass to the interior and some dehumidification. (We use it primarily for subduing latent-loads anyway, otherwise passive nighttime ventilation is usually more than sufficient.)

To reduce solar gain south facing skylights should be blocked 80-90% with (preferably exterior) reflective shading or high-quality very reflective window film, and south facing windows need overhangs or shades (low-E windows just won't cut it.) Something like 50% of the incident gain is from indirect/scattered light, so in high-intensity sunlight areas like FL, AZ or NM overhangs alone aren't enough.

 I'd imagine from the chart somewhere in Montana might be the closest, they have 4-500 annual??? Not to sure what this means. It's a pretty dry climate here as well,

 I've never had air conditioning in my house but I think having a second floor now it might get quite hot so my wife wants it. I agree with the nighttime cooling being enough, it's always worked for me, but it's out of my hands.

I was looking at the Spacepak and Unico systems and they seem pretty interesting, not sure of the cost though, I have to check. I was wondering about the noise if it's really a problem. If it's not too bad I think we could live with it since it won't run all that often. I don't really understand if an air exchanger system can be hooked up with these as well.

I realize I'll need someone to plan this out for me but I need to know which direction to go, not just to code, but a quality system. More research required I guess, thanks for the help though,

Sean

If you're building your house very tight and installing a heat-recovery ventilator (aka "HRV" or "ERV", if it's swapping humidity as well as warming/cooling the ventilation air with the exhaust air) you can probably come up with a system for chillng the ventilation air and running it longer than the minimum required. In the German PassivHaus concept the HRV's input air comes ducted underground to temper the incoming air stream closer to earth-temp (probably ~50F in MT, except under some active volcanic areas- I'm sure it's higher than that on a thin spot of a caldera. :-) ) But unless your house has pretty high R-values, that might not meet your peak cooling load.

This li'l ERV has an evaporative chiller option that may very WELL work for low-moderate cooling loads in dry climates like yours:

http://www.mtd-solutions.com/heatrecoveryproducts/documents/MTD600brochure-1st-edition-April2009.pdf

(Don't know if they sell in N. America yet, or of similar products, but it might be worth searching a bit.)

It's a bit of work, but a ACCA manual-J (or similar) cooling load calculation can come up with your peak cooling load, after which you can figure out what your best options are. If you're building 2x better than code or more on all insulation, then it's all about designing the glazing/shading to minimize solar gain during the warm season. With a gypcrete slab for increased thermal mass and an HRV, if you can kill the solar gain a bit it'll coast along closer to the average daily temps, and your peak AC load will get averaged down to near-nothing (just turn on the HRV for longer cycles and tell "the boss" that it's the air conditioner. ;-) )

Like I say, in my place (~375CDD/annum) we only turn on the AC to bring the humidity down. With reflective shades on the two skylights and 2' overhangs on all the windows, with trees on the SW & W sides to killl the afternoon gain that we'd otherwise get through the substantial W facing glazing, it never gets much over 80F on the first floor, 85F upstairs even on days it hits the high 90s outside. But when the dewpoints outside are over 70F, that's too sticky to be comfortable at 80F. And this isn't anything LIKE a super-insulated house.