With summer waining, it might not be the best timing for this post, but maybe somebody will stumble across it before next summer. This is a viable off-grid cooling method, requiring approximately 33 watts of electricity and 3-5 gallons of water per day, if run 24 hrs. per day.Barstow, CA, where I live must be the swamp cooler capital of the world. Probably 90% of the homes here have one and they work quite well here most of the time.
About 4 years ago or so I began living in my 20' RV. When summer came it didn't take long to realize an aluminum sheathed RV makes an excellent solar oven. So I started experimenting with making a swamp cooler.
The one I am using now has got me through 3 summers and I can tell you, I wouldn't want to attempt living here in summer without it. It's not perfect, but it's sure better than without. I have measured the temperature of the air coming out of it on a 100 degree day, it's 70! But then I can measure the wall 1 foot to the side and it measures close to 100. But still, all in all, I am happy.
If you already have a "fantastic fan" or similar exhaust vent in your roof, you will find that this helps much.
This swamp cooler is quite unique in that it does not have a fan. What's that you say? Yes, it's true. Unlike every other swamp cooler I have ever seen there is no internal fan in this one. That makes it much easier to construct.
But anyone who has experienced swamp coolers (or more properly, evaporative coolers) would know that a major part of their cooling effect is created by lots of air flow.
Well, that's where the fantastic fan comes in. It is actually the fan for the swamper, just doing it's job a little differently. In a nutshell, this cooler is a water tank with an excelsior pad that is kept moistened that hangs outside my window, butted up against the window frame with foam weather stripping. Since my RV is completely sealed, every square inch (by me!), if I shut off all possible air intake like windows and stove vent, as the fantastic fan exhausts air, more air must come from somewhere to replace that exhausted air. It comes through the moistened excelsior pad! Nice, cool air. It is mounted about 4 feet away from where I normally sit at the dinette table, blowing that air directly upon me, increasing the cooling effect by way of "wind chill." On the hottest 100+ days, I have held a thermometer where I sit, it says 85.
I made a WOODEN box, off the top of my head it's about 20" tall, 25" wide, 8" deep. Cut a hole in it the size of my window frame, and bordered that with some 1/2"x1/2" square moulding. Fits in my window perfectly, then super glued some 1"x1" gray foam sold for air conditioners at Home Depot to it. I like the super glue, 'cause when summers over I can just rip the foam off easily, throw it inside the cooler and it's still good for next summer, otherwise the sun eats it alive if it's exposed. Just a drop here & there to hold it in place.
The box is made of 1/2" plywood (I think, maybe it was 3/8", that would be fine). I also cut a hole in the rear of the box for the air to come through the excelsior, about 13" x 18". The bottom of this hole should be lower than the window opening hole as a safety drain, in case the float valve doesn't shut off (happened to me twice this summer). Before screwing and gluing the box together, I stapled "hardware cloth" over the inside of this hole, it acts to help hold the excelsior pad into place. About 3/8"x3/8" or 1/2"x1/2" hardware cloth works fine. I originally used window screen and it didn't work very well, the holes were too small, calcium deposits began blocking airflow.
I also put in some staples on either side of this hole halfway pushed in, they act as guides to tie to later. Due to that gravity thing, you must somehow hold the excelsior pad against the hole where air flows through. I did this by tying nylon string to these staples, a bit like shoelaces in your shoe. The nylon string has worked very well for 3 years, 3 new pads, even though nylon is not waterproof. Technically I guess polypropylene string would be the proper choice.
Oh, a word about the pad. Since my pad is much smaller than any typical swamper cooler, I make my own. Just buy the cheapest one you can find, it'll be too large, and then, using scissors cut it slightly bigger than your intake hole. Stuff as much extra excelsior in it as you can (for best cooling) from the unused section. Then I use a sewing machine to close up all the open ends of the mesh that encases it. Works great, custom. If you don't have a sewing machine handy, probably just some needle & thread, stiff wire, perhaps even glue (like 3m weatherstrip cement) would work fine.
The wooden box also has a removable top to make it easier to change pads, which should be done yearly for best results. I used the same 1/2"x1/2" square moulding to make a lip on the outside, on all four sides of the top. Then I glued some round rubber weatherstripping (also Home Depot) on the tops of lip, leaving space to allow screws on the same surface. Finally, cut another piece of plywood for the top cover.
It may sound strange to make a water tank out of wood, but it has worked very well, amazingly. Initially, I used spar varnish on the inside to make it waterproof, but found it really didn't work that well, confirmed also on boat forums & the like on the web. The spar varnish they sell up at Home Depot, wooo, makes a real pretty shine & all, but it isn't any good for weather. Go figure. It's not REAL boat spar varnish, which is so expensive you don't even want to know. But what I have found that works great is everyday EXTERIOR house paint. I buy it from the OOPS rack at Home Depot, you know, where they made the wrong color for someone. I don't much care what color it is as it is never seen, and that is 3X cheaper than the make-believe spar varnish. I got the info from the pro-woodworkers & boaters, they know their stuff.
So now we have a water tank with a pad over the air intake that weatherstrips up to a window. Somehow that pad must get moistened. Since I am on the landline powergrid here, it was a no-brainer, just got a pond pump from Home Depot (garden dept.). I have a 15 watt version in there currently, but I also got a 5 watt version and that works just fine too, not a difficult pumping task here. I mention all of this because in an offgrid situation you may not wish to use either of these, they are both 120V models. However there is a Chinese seller on ebay that specializes in all sorts of water pumps, I have seen several 12 volt models they sell that would work just great. They are quite detailed in their specs also, so you can really zero in on what to get.
I got a brass fitting that adapted the output of the pump to 1/4" plastic tubing, sold also at the Home Depot evaporative cooler section as water supply tubing (to your swamper up on the roof). I cut a length of this tubing to go from the pump (which sits in the bottom of the box, in a pool of water) up to the top of the pad, then making a sweeping 90 degree turn and running along the entire length of the pad. I took a nail and punched a small hole about every 2" in this tubing across the top of the pad. The water squirts out of those holes like a squirt gun constantly, keeping the pad moist. Oh, of course, you want to try and punch all of the holes along a centerline pointing down towards the pad, that's kinda tricky, and it's easy to have water squirting in directions you don't want. No problem, just take some aluminum foil and wrap it around those stray squirters, the water will collect up and drip on the pad anyhow. You make end up making a couple of these waterlines for practice
I made the waterline about 6" too long on purpose. Now with the "open" end bend back about 6", this seals it quite well and water comes out only thru the squirt holes. To hold that bent back section in place I used two wire ties, 1 tying the wire ties to the tubing, the other just a loop about 3/8". The bent back section goes thru this loop, holding it in place. Works quite well, and I find about once per season I must clean the water tubing, as little stray bits of sludge eventually get pumped into it and it clogs. I have some plastic covered steel cable whose OD is exactly the size of the tubing ID, and works great as a "pipe cleaner." Just unbend the end of the water tubing, opening it up, pop it off the pump and ream the steel cable thru there like a pipe cleaner until it reaches the other end and the sludge pops out. Slide the bent end of the tubing back into the wire tie loop & you're done!
I would like to say more about this way of moistening the pad. Those of you who are familiar with swampers might recall that the universal method is to have a "V" shaped trough above the pad with holes in the trench, then they simply bring one tube squirting water into the "V". While this works quite well and cheaply normally, I found this tubing system superior on an RV. I did try that system in my experiments but it was difficult to get to work properly due to leveling. Now, of course I level my RV, but inconsistencies in the leveling of the cooler just cause too much headache for that to work. This squirting tube system always works fine, irregardless of any leveling.
OK, now we have a functional swamp cooler. It must have a water supply. The source will vary according to your circumstances, here I have that same 1/4" tubing going to a brass 1/4" fitting adapter on a hose. But the part I wish to detail is how it comes into the water tank. I purchased a thick steel "L" framing piece from Home Depot (hey, it ALL came from Home Depot!). This would be like what framers would use to maybe add support to a 4"x4" fastened to the concrete, just an L shaped piece of steel, about 4"x maybe 2" roughly. This is the float valve support. Drill a hole in the upper part of the 4" section of the L bracket the size of the mount fitting for the float valve. Now you can screw the 2" leg of the L to the bottom of the box and the float valve will be suspended at a proper level to regulate the water. Of course you'll have to reason about where that is, I suggest you have _just enough water in there to cover the pump, at 9 lb. gallon don't want any more weight than necessary.
I drilled a hole in the side of the box large enough to pass the AC plug from the pump thru, and that wire plus the water supply line pass thru that hole into the interior. I then cover the hole, wire & tubing with plumbers putty to make it airtight.
I made 4 "ears", at least they look kinda like square ears, and attached them to the top 4 corners of the box. This is for mounting support, which I do from the roof. Thru each set of ears I put a 3/8"(?) threaded rod, with a nut & lock washer on each end. Then I got 2 turnbuckles, one eye of the turnbuckle is on the threaded rod, the other end is attached to a chain hung down from the roof. Two nuts on each threaded rod act to position the turnbuckle on the horizontal plane, and the turnbuckle of course adjusts in the vertical, giving me lots of latitude for positioning. On the roof I have 2 2"x4" about 6' long. Bricks at the far end of the 2"x4" 's act as a counterweight, and the chains are wrapped around the 2"x4" 's. I like this setup because I don't have to poke any holes, screws, anything into my RV. However, after 3 years the strain of holding up that weight has been too much for the ears, they are starting to rip off, gonna have to do something before next season. I had to repair them by adding more screws before this summer and I thought they were mighty sturdy, but apparently not. Haven't checked that out yet, it's coming down in a week or two, then we'll see what's up.
Paint, paint, paint & there you have it. About 4 coats ought to be good for the inside the 1st time, then a couple before every summer is what I do. The outside needs paint too, to your liking.
A couple of years ago I bought a box fan from Walmart that is exactly the size of my rear bedroom window. I hung it from the luggage rack with chains on the outside wall, with 1" foam butting it up against the window and airflow direction outwards. It adds greatly to the airflow and I often use it only to save wear & tear on my fantastic fan. Yes, cheating I know, because I do have the landline power. Don't worry, it works great with the fantastic fan only too.
By next summer I hope to make a homemade Coolerado cooler. If you haven't seen those yet you will be AMAZED. Swamper type power requirements, and fantastic full-fledged air-conditioning. It's the offgrid dream...
Well, I certainly didn't intend for this to be so long, and I'm sure there's some ambiguity, but I tried to cover all aspects of the basic design, at least briefly. I'll be happy to give any clarification or answer questions. I like to make things work spending as little as possible and I love to see others doing the same, as the folks here do. And this works well on the cheap. All of my Barstow friends agree, and after all, they know swamp coolers.