Swamp cooler: passed final inspection

Today marked the final inspection on the swamp cooler. Since I had to run a short duct from the swamp cooler through the attic to the living room ceiling, I had to pull a "mechanical" permit in my jurisdiction. That's a good thing: improperly sealed ductwork can cost you a lot of money on your heating/cooling bill, so it's nice to have another pair of eyes checking up on your HVAC contractors' (or lazy/cheap homeowners) work ethic. In my case, not only did my cute little baby duct pass, but Lemontree tells me the inspector liked what he saw. Aw, shucks.

Anyway, I learned a couple things. One, ductwork is not a science, it's an art. (And I am not an artist.) Two, mastic will cover many sins.

Mastic is this lovely gluey stuff that's approximately the consistency of sour cream. When dry, it provides an airtight yet flexible rubbery seal, since metal ducts expand and contract with temperature changes. Actually, most of my joints ended up pretty tight so it didn't take much mastic to seal them up. However the final joint just didn't line up quite right... even though I took great pains to use a plumb bob to transfer the roof duct location to the ceiling duct location, I ended up a tiny bit off so the duct is a tiny bit crooked and I ended up with a quarter inch gap on one side of joint. I don't know if 1/4" is a decent tolerance for HVAC pros or if they're all shaking their heads sadly as they read this, but in any case it's not going to leak air any time soon because I put a couple layers of foil tape (NOT duct tape!) on the outside and filled the gap on the inside with about a pint of mastic. Do pros use a spatula to apply mastic? Maybe not, but it sure works great!

Luckily, we had a couple of unseasonably hot days this May so we've already had a chance to actually run the swamp cooler. Our outside thermometer said 96°F, and I'm pleased to report the cooler made Lemontree and the kids cold enough to put on sweatshirts. So, I guess that means it works.

So far it seems ridiculously oversized, though. I got a 5,000CFM cooler with a 1/2 horsepower blower motor for a 1,700 sqft home. The recommendation is to replace all the air in the house every 3 minutes. On low, it moves a good amount of air. On high, it's a freakin' wind tunnel. It's almost like rolling your car's windows down on a highway. So, I fully anticipate running the blower on low 99% of the time. Maybe when it hits 110°F I'll be glad to have a highway speed -- er, I mean a high speed -- available, but for now low is good and costs half the electricity as high... and this thing already uses about 1/3 the electricity of "normal" A/C, so the savings are even more than I expected.

I was right about the noise thing, too. Our neighbor's outside central A/C unit is probably 50 feet away behind a wood fence and I often hear it growling when I'm outside. Our cooler, on the other hand, is almost silent. On low, I can't really hear the blower when I'm outside. The hissing of the water valve letting in a trickle of water is actually the loudest thing, and even that sounds like a whisper at ground level. From the inside of the house, you can definitely hear the hum of the blower motor but it's about the same noise level as a central A/C blower, so it's not objectionable.

In short: I'm happy. :)

One step closer to cool

Been super busy installing the swamp cooler, as the weather is getting downright warm at times. I finally got the duct, but haven't installed it yet because the electrical conduit needs to run behind the duct. Installing the duct first would have made the electrical a nightmare (and it's already pretty nasty).

There are two ways to control a swamp cooler; one is line voltage. Line voltage is when you run big full power (120V) wires to a switch on the wall, then run a bunch more big wires to the swamp cooler. That's a lot of expensive wire (copper ain't cheap!) and those switches tend to burn up in a few years when run that way.

I chose the alternate way, which is low voltage. If you have a furnace or central A/C with a thermostat, that's exactly how those are all controlled. Your furnace or A/C has a little transformer in it, that produces a small amount of safe, low (24V) voltage which goes through inexpensive little wires to your thermostat. You'd get a tickle from it, but it shouldn't kill you or start any fires.

Ordinarily, you'd need to purchase a swamp cooler specifically designed for low voltage ($$$), or purchase a $150 conversion kit which is an ugly box mounted to the outside of the cooler. I didn't like those options, so I used something called a RIB from a company called Functional Devices. A RIB is a "Relay In a Box", and a relay lets you use low voltage to control line voltage. Neat, eh? The other nice thing about these RIBs is they're individually replacable, so if one fails I'm just replacing one $20 RIB and not a $150 control board.

So, I tapped into the low voltage source from our gas furnace:

You're not required to do low voltage connections inside a box like you are for line voltage, but I put mine in a box anyway just because I wanted things to be tidy. I'm saving a ton of money by doing this myself vs hiring someone, so a couple more bucks isn't going to break the budget.

The inspector actually didn't like how short I left the above wires, so if you do something like this be sure to leave 6" free length on each conductor. But, the inspector let me slide this time.

Rather than have these RIBs mounted inside the swamp cooler (subject to moisture damage!), I mounted them in the attic on a scrap of 2x6 lumber. Mounting everything to the lumber beforehand let me do most of the work in my cool, clean, well-lit workshop standing comfortably rather than laying facedown in nasty insulation at 100°F:

The blue box off to the right side houses all of the low-voltage connections, so that only line voltage connections exist in the main gray box. (Don't want to mix the two together, for safety reasons.)

The inspector passed my work (and by the way I also got a plumbing permit for the water line and that passed inspection as well) so now I can try to figure out how to install the duct... hopefully before we start getting too many 80°F days!