I finally got to go camping again a couple weeks ago. Since we were going camping for several days and in a location without electrical hookup and a lot of my neighbors were going (some of whom had never camped), I figured I’d make a portable solar powerbox. The box worked well. It was just a proof-of-concept so there are some improvements that’ll be made to it but it had no problem keeping up with my Yaesu 857d ham radio, lighting, charging electronic devices and filling up air mattresses.
Since this weekend at my house is now 118 degrees (I live in Phoenix), I started thinking hard about what I’d do to survive if I had to live for a while outside in this weather. Obviously, to survive in the desert, you need an ample supply of water. More water than other places. But just drinking water won’t keep you very cool Sweat only goes so far. You need to find a way to get cool.
Provided I had water available, since I have a viable power supply, I thought I’d make a portable evaporative cooler, or swamp cooler as they’re called out here. I figured I’d make this post before my build, as I do some research and get the parts so you’d have enough information to build your own. I’ll post my version 1.0 build once it’s built and working.
In dry environments, they can work very well. They use a LOT less energy than an air conditioner unit so I won’t have to increase the power capabilities of my system to work it, and they can reduce the temperature by up to 30 degrees as well as take out the dryiness in your tent while you sleep. If SHTF, this may be something that could make your life more comfortable or even save it.
Since I have a pretty small tent, cooling it down isn’t gonna be much of a problem. Since I want to be able to be flexible with it in case I want to cool other things (like my second floor bedroom at home), I’m gonna make it bigger than it needs to be.
The first build is gonna be a proof of concept just like the powerbox is. As such, it’s gonna be an experiment to figure out what works and what doesn’t, and give me something to do some tests with to make it better.
This is what I want in this build:
- Runs off 12V DC so I can either use the solar panel or connect to a battery. It’ll have a 12V power plug for this.
- Draws as little power as absolutely possible.
- Has the ability to connect to a larger water source easily so it won’t have to be continually refilled or have a large reservoir.
- Very portable. Backpackable if possible.
That being said, let’s look at how a swamp cooler actually works.
I was at my neighbor’s house last night, where it was 117 degrees after dark. After getting out of the pool a few drinks later, it was quite chilly. The temperature had only dropped 3 degrees while we were in there but it felt chilly enough that it was a little uncomfortable without grabbing a towel. Why is this?
When water evaporates, it takes energy to convert it from a liquid to a gas. All you need is to have dry air contact water. With a swamp cooler, that air that now gave up some of its latent temperature to the conversion is then blown into the room. Simple.
One thing to keep in mind is that the wet bulb temperature of the air is the coolest it can be brought to by evaporation. If you continue to pump in humid air to a room without releasing the wet air, you’ll eventually get to a point where the cooler isn’t gonna help. As time goes on, you’ll then have a hot humid room. Worse than when you started. Let’s make sure we don’t do that with this system.
In a swamp cooler, water is dripped down through a medium, usually a mat or pad that looks like a flat piece of hay or blue fiber. This mat is designed to give the water as much surface area as possible to contact the air going through the system. The more surface area of water, the more efficient the system for the most part. Also, the more air that goes through will cool down the room quicker. But, these two fight each other like two hens with a worm because as you blow air faster, it dries out the pad. Since the pad then has a dry spot, not only is there less wet surface area to convert, the air has an easier time going through the dry part so it doesn’t work as well.
This means that you have to have as much pad area as possible, keep it continually wet somehow, and blow as much dry air through it as you can.
So how are we gonna do this and still meet all the criteria that I mentioned before?
What we’re gonna do is start with the basic idea that a guy named came up with for cooling that is laid out in this instructible. Great way to use easy-to-find stuff to make your life more comfortable or survivable.
Now, as you can see, this design is a bit large. Too large for my purposes. Luckily since the theory is so simple, it’s easily adapted and down-scaled. Figjam (Fuck Me I’m Good, Just Ask Me) did this for his trips to the Playa at Burning Man (always a hotbed of inventions and way hot and dry). He also explained how he did it in this post.
Now that’s more like it. Cheap, portable, low power, and works. He took a 5 gallon bucket, wrapped the inside with two layers of swamp cooler matting, made a loop of hose above it connected to a submersible pump and ran a fan out the top with piping. You could then attach that pipe to a vent hose and pump it into your shelter.
So, I’m gonna base my design loosely on that one but make a couple changes.
One, I don’t like having to use both AC and DC to run the thing, especially since the AC will take more power. Not much, mind you, but the more efficient I can make the system, the less power I’ll have to supply. So to that end, I’m gonna use a 12V DC submersible pump. It draws about 350 milliamps, which at 12Volts is about 4.2 watts. For that, I get a hair over a gallon per hour. Should be just about right. I may end up changing this pump later for a better one but whatever.
This pump will hopefully give me the flowthru rate I need to keep the padding wet at all times but not take too much energy. If it doesn’t work, I’ll just switch to either a larger 12V pump or scrap the idea altogether and go AC. For about $10 though, I gotta at least try it. If it does work, I may look for an even more efficient DC pump for a bit more money.
Another thing I wanna change is the fan. I was originally going to use the same kind of computer fan that Figjam used but then decided it didn’t have enough flowthru. This is what he’s using:
At maximum speed, this one pulls about 45 CFM (Cubic Feet per Minute) and should draw about 1.8 Watts.
The one I’m gonna start with is the Attwood Blower H20 Resist. It pulls 2.7 amps but blows at 240 CFM, and since it’s inline with the pipes, it pulls all the air through more efficiently. It’s like having over 5 of those fans above and if the DC pump works, I’ll be able to afford the increased amps in this area. Like the pump, this one may get changed out in the final build. 2.7 amps is a LOT more amps than the 150-200 or so milliamps that the computer fan’ll draw but we’ll see. Due to the static pressure that may end up building in the system with so much airflow, and the effect that velocity may have in the cooling efficiency, I may have to either switch to a slower fan or modify the input to the fan to make it run slower somehow.
Another thing I wanna do is be able to hook the box to other water somehow but not have to worry about it overfilling. To do this, I’m gonna hook up a simple mechanical float shutoff valve.
With that, I can keep the internal reservoir full but not have to either keep filling it every hour (the system is gonna go through somewhere around a gallon an hour or so) or have to have a gigantic reservoir. I want this thing to be something you can carry with you if possible, and if not, at least not take up a lot of room in a vehicle.
I haven’t yet figured out what I’m gonna use as a box to hold it all. I may end up using a 5 gallon bucket like Figjam did but I need to see how my current setup is gonna work. What I’d rather do is come up with a way to make it collapsible somehow so it can fit into a backpack or something but I don’t want to make this build so technical that people with little fabrication skills would have a hard time with it.
I have a couple of other ideas that are gonna be quite novel if I can get them to work but I don’t wanna give up that info just yet.
If you’ve built one of these at home that’s portable, please feel free to post in the comments below how you did it.