Thursday, June 22, 2017

Beating the Heat with an Extremely Efficient DIY Air Conditioner (Evaporative Cooler)

So, I thought the wind would be enough to keep me cool, but with the dry air and the amount of work I've been doing outside I started to get very sick--signs of fatigue, dehydration, and heat exhaustion.

I had to face the facts: I needed some way to cool my place down or I might end up dying, and I certainly couldn't do that. I have two little ones what depend on me. Being a single mom and living off grid is quite challenging.

I had a small AC unit that I used when I lived in my mom's driveway in my RV, but I had to get rid of that. It used 500 watts of power. My solar panels max out at 400 watts and my fridge uses about 130 watts when it's on. So I needed to build an air cooler that used less than 100 watts for it to be practical.  The lowest powered AC units on the market use around 400 watts and honestly, they don't work that well. They also dry the air out, and I would need to run a separate humidifier which just adds to the impracticality.

So here was my challenge: build a system that humidifies the air and cools it down significantly using under 100 watts.  A swamp cooler (or evaporative cooler) was the obvious solution.

The evaporative coolers on the market are all really big, they use extremely huge blower motors that use a lot of power and they cost $300 and up, but the physics behind evaporative cooling is so simple and building them yourself is equally as simple.  As a physicist I'm quite qualified to explain how it works.

How an evaporative cooler works:

Heat is simply energy from the motion of the particles in a system (usually air in our every day experience). Cooling the air requires transferring energy out of the particles in the air.

Changing water from a liquid to a gas requires energy. So evaporation takes heat energy from air or the surface it's in contact with (like your skin when you sweat) and in the process cools the air or the surfaces in contact with the liquid.

So, to make an effective evaporative cooler you need to maximize the wet surface area and maximize the airflow through the wet surface.

So, I bought/used the following:

  • A $20 window fan from Walmart (the fan uses about 50 watts on high)
  • A $26 fountain pump from Lowe's (I got one that uses 6 watts)
  • A $7 DuraCool Pad
  • A plastic file crate
  • Some leftover fiber glass window screen I had
  • A hot glue gun
  • Cable ties
  • 4.5' of tubing that fits the pond pump.
  • A plastic storage container that the shorter side of the crate fits snuggly in.
  • 4 long screws
How to build it:
  1. Cut out two pieces of windows screen. One for one of the short sides and the other to line the bottom of the crate and the two lager sides. Just glue them in place using hot glue. This does two things: keeps the bugs out and stops water droplets from squirting out  from the DuraCool pads.
  2. Cut the blue DuraCool pad to fit inside the box. Two pieces just like with the window screen. One for one short side and one for the longer sides and the bottom of the crate. Hold them in place with cable ties (the cable ties easily push through the window screen).
  3. Kink the hose and one end and hold the kink in place with a zip tie. Then make a loop that fits snugly inside the part of the crate that will become the top. With a dremel tool or a drill with a small bit carefully drill small holes around the areas of the loop that are close to the DuraCool pads. Make sure to drill the holes about 2" apart in areas where the water will squirt down towards the top of the pads and not sideways through the pads or up into the pads, or too far down missing the pads all together.  Then hold the tube in place with some cable ties.
  4. Connect the tube to the pump and place the pump and crate in the plastic container
  5. Using a drill and 4 long screws screw the short side of the crate without the foam and screen to the top of the plastic container.
  6. Fill the plastic container with water--I discovered that even warm water works.
  7. Mount the window fan securely in the window and attach it and the pump to a power strip to allow you to switch in on an off easily as the cooler will cover up the switch on the fan.
  8. Place the cooler in front of the fan and use tape to cover up any gaps where the fan might not blow through the cooler. You could figure out a way to mount this system outside so the fan pulls air through like a standard evaporative cooler, but I chose to mount it inside so the fan pushes air through for several reasons:
    1. I didn't want to spend time drilling holes in my siding and building something to secure it to the outside of my house.
    2. I had the counter space conveniently below my fan.
    3. The temperature outside would heat up the water and reduce its efficiency.
    4. I didn't want to fan to have to suck wet air into it because it would reduce the life of the fan (remember this is not a swam cooler blower designed for pulling humid air.
    5. Having the box inside makes it a better humidifier because all of the evaporated water is left inside.
See the pictures for details: it should be fairly straight forward:
 I just used a few textbooks to prop the cooler into the best position over the fan and a piece of duct tape to cover up the top part of the fan because the fan was slightly taller than the cooler.

So why did I create a box instead of just having a flat system that goes over the fan? Simple: I wanted to maximize the wet surface area that air blows through.

It was 92 degrees when I first switched it on, and within an hour it cooled down my house to 84 degrees.

Today it was 84 outside and it cooled it down to 75 degrees.

When I measure the air coming directly out of the cooler it registers in the low 60's.
The above picture was taken when it was 80° outside.

It uses somewhere around 4 to 10 gallons of water per day. Which means it's an excellent humidifier.

Overall, this little swamp cooler actually outperforms my 500 watt air conditioner and it uses less that 60 watts of power when on high, plus it humidifies the air and gets rid of those nose bleeds, dry skin and waking up with a dry throat.

The really cool thing about this is when it is windy I don't even need to turn the fan on. The wind here is often strong enough to effectively push air through the box meaning when it's windy it only uses 6 watts!

This is by far the most energy efficient design for an air cooling system that I have ever seen at 6 to 60 watts and it cools a 130 square foot space down 5 to 10 degrees.

Air conditioning was the most challenging thing to figure out how to power from a small 400 watt solar grid, but I solved it! I'm freaking amazing! I just have to pat myself on the back for this one.

This is probably the most exciting thing I've built in a long time and I'm loving the results. Living in the desert has never been so comfortable, and I'm looking forward to finding ways to maximize the efficiency of this system in the future.

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