Roof penetrations and other swamp cooler questions
 

I just moved into a house with no A/C. I'd like to install a swamp cooler on my roof (She-Who-Must-Be-Obeyed has flatly vetoed a window- or wall-mount). I understand roof-mounting is common in AZ but I see few swamp coolers here in Idaho and none on roofs, so I need some schooling.

I think I understand the rest of the install, my questions are just about electrical so I'm posting here instead of in HVAC.

How large of a roof jack should I use for the electrical feed (I will feed plumbing separately)? It will contain at least 5 wires (blower lo, blower hi, water pump, neutral, ground). I was thinking of feeding 3/4" or 1" PVC conduit through the roof jack. Is there some kind of outdoor-rated flex conduit I can use from the roof jack to the cooler?

Since the wire is enclosed in conduit, can I run NM (probably 12-4 or a 14-2 and a 14-3) or do I need to use THWN/THHN?

Can I tie into an existing general purpose circuit or must it be on a dedicated breaker? The blower is 1/2HP, the pump is 1A.

How does one make a rain-tight seal at the top of the roof jack where the conduit comes out?

Finally, I may want to tie the cooler into a thermostat at some point. Is there a code-approved way of connecting a low-voltage relay to the power feed to the swamp cooler? I've wired plenty of 12VDC automotive relays before so I know what connections to make, I'm just not sure what codes will require -- enclosure, wire terminations, etc.

I will be pulling permits and getting everything inspected. No hacks. If I'm in over my head, I'm willing to use an electrician.

Thanks for any comments...

As an update. The roofers were here so in between tear-off and re-shingling I had them install a 20x20 roof jack for the vent. I also found some Oatey "Solar" pipe jacks with 1/2" openings, so I had them install two (one for water, one for electric).

Based on my research, I should use liquidtight flexible PVC conduit as the roof is a wet location. THHN is also required. (Once inside the attic I can use a junction box to transition to Romex.) It appears I must consider the THHN as a 75°C conductor instead of 90°C since it is in a wet location, so there's some de-rating.

I believe I may also need to de-rate because there are more than three conductors in the conduit (blower high, blower low, water pump, neutral). However since blower high and blower low both go to the same motor, they may not be considered separate conductors so I don't need the extra 80% de-rate. My guess is I'll have to ask the AHJ on that one but I'd love to hear your opinions.

Due to high ambient temperatures in the attic I must de-rate further. How much to de-rate, I'm not sure. Some discussion forums suggest 140°F for an attic but I cannot find a code reference. I found some ASHRAE guidelines but not anything in the NEC. Sure be nice if I can only de-rate to 122°F, as 12ga 25A * .80 * .75 = standard 15A breaker.

If I need to de-rate for 140°F AND for more than 3 conductors, it seems I must go to 10ga THHN (12ga comes out to 12.9A, so a 15A breaker is unsafe). 10ga THHN is 35A * .80 * .58 = 16.24A, so use a 15A breaker.

However, it appears I can still use 1/2" liquidtight flexible PVC conduit even with 10ga, as 1/2" allows up to six x 10ga conductors and I only need five.

Thoughts?

Huge differance in humity and tempertures from AZ to Idaho. What works in on area does not mean it's going to work someplace else.
It would be like trying to use a heat pump in Alaskia.
Unless it's extremly hot and dry there usless.
http://www.homedepot.com/webapp/cata...rative_Coolers
What's her issue with real AC?

Oh it's not the wife that wants evaporative, it's me. :) She just doesn't want it on the side of the house (ugly).

Based on the climate here, a swamp is effective 99% of the summer -- only rarely do we get humid days in the summertime.

go master cool.get one set for 240.only need two hots and a ground.low voltage t-stat uses 24v from unit.ckt board does all the rest.very easy to do.and you better find out what roof jack is needed so you don't have to tear it out.go online for mastercool or PMI pheonix manufacturing inc.

Where were you guys in September? ;) It's too late now, I'm afraid. 5000CFM Champion is already on the roof, pipe jacks are already shingled in.

It's more the electrical code questions I'm worried about now...

are you using line voltage t-stat?

No, a 24VAC thermostat will control RIB2401B relays.

but did you run the five wires?thats the idea of just running 240 or 120 and let ckt board control hi-lo-pump ect.

No, haven't run any wiring yet. Will the Mastercool ckt board work in a Champion cooler?

they did make a add-on box.still might.dial has one also.dial is a cooler parts mfg'r.go to homedepot,ace,lows and look.they will accept 120 or 240.they mount on cooler.champion may have one also.

This is true,
swamp coolers or evapouritive coolers
just dont work very well in a humid enviroment.
But if your heat is dry,
then they will work.