Almost the “hot months” here in East Texas.  During June through the end of September, going outside can be a miserable task because it’s usually 80 F by 9:00 AM and the heat doesn’t really break until after sunset.  100-105 is not uncommon to  these parts and it may not break under 85-90 till past midnight.

Obviously, under these conditions, there’s a need for some kind of cooling.  According to experts, the right solution here is an air conditioner.  16 SEER heat pump was not quite free.  Are swamp coolers the answer?  Maybe…But there are lots of caveats and asterisks.  No two people’s results will be the same and your experience will vary.

First a word about the operating principles.  An air conditioner is well-understood.  A compressor liquefies a refrigerant which is then piped to an evaporator” and that moves heat around.  Magic of state-change.

With a swamp cooler, there’s a simple water pump that makes an air penetrable set of pads wet as air is blown through this “pad.”  Evaporation takes care of the rest.

The US is set up into evap cooling zones A through D.  Out west, zone’s A and B are up a ways from the Mexico sieve (used to be a border, lol).  In those areas, like much of New Mexico, Arizona, and desert parts of California – where the humidity is low – you can use a simple swamp cooler and remain very comfortable.  The problem in Zone C (which is where our slice of Texas is) the swamp cooler becomes a marginal proposition.  A few miles south of us, toward the Gulf and Houston you transition into Zone D and a swamp cooler won’t do much good. Just never gets really dry-enough air.

The key thing is to understand is what your local relative humidity is  when you will need cooling.  Here’s a chart that I borrowed from a physics discussion site here (and looks like they borrowed it, too…) but I have made some “bright yellow highlights” to show where our new 2250 CFM evaporative (swamp) cooler is chilling to:

I don’t spend a tremendous amount of time in the shop, but it’s nice to be able to jump out from my office (air conditioned, 73 F and 40% or less humidity) into a shop that might have been 90-95 F previously but is now a much more comfortable 79-81 F at the workbench.

There are several things about the shop that make it suitable for a swamp cooler.  First and foremost is it has a high roof.  The peak is about 20-feet off the ground and since it’s an open truss poll building, heat can rise and go out the ends of the building which are open (but screened).

Second thing is the doors are not tight and lots of air can move around. With a swamp cooler, you want a “loose” building so the static pressure doesn’t build up…because that small pressure will reduce the airflow over your pads in the cooler.  Think catalytic converter back-pressure if you’re a gear-head.  Same idea.

Monday of this week was about typical for this time of year,.  Outside, the Temp was 87 F and the outdoor humidity was 56%.

You can look at the chart above and see that the output temperature ought to be between 77 and 82 F on the cooler output.

As the summer moves along, there will be continued drying.  It’s not uncommon here for the relative humidity where we live to drop to the 45 and even 35% range on hot days. Like a 100 F and higher.

Again, referring to the chart, the 35% humidity and the 100-degree day is what I live in hopes of to justify this expendiment.  The cooler will likely chill to the 82 F range under those conditions.

The nice thing about the swamp cooler is it doesn’t use too much water under these conditions.  Maybe 20-gallons a day.  Where the real savings comes in is from much smaller electrical use.

In the Monday comparison numbers, my office was running 73 F but the air conditioner was running about 60+ percent of the time and during that it was pulled a bit more than 13-Amps from the power center.  Yeah, it’s a big unit and power-hungry, to boot.   Pencils out to an 8 Amp draw.  Remember, that’s running 60 percent of the time at 13 Amps when it’s 86 F outside.

We can run our first simple calculation here.  86 F – 73 F = 13 F of cooling.  At the 8 Amp level, that’s 960 watts worth of power.  Then, we divide the 13 into this 960 watts and we see 73.85 watts of power.

At the same time, the swamp cooler was running on the middle fan setting (200 watts) and the temperature drop was from 86 F to 78 F…and it climbed up later to 79 F…so let’s roll with that.  7-degrees of cooling.  Here’s the thing:  200 watts divided by 7-degrees is a bout 28.6 watts/per degrees.  Yeah, I like 2/3rd’s less energy…you bet!

Still, it’s not all peaches and creme (or is that cream?).  First and foremost, until the temperature hits 80 F, there’s no point  turning on the shop evap cooler.  Evap coolers are standard fare for cooling chicken farms in the Mississippi River region in the summer…read a lot on those.  Don’t bother with ’em until 79-80 F.

The Ag Extension services say pretty much the same as what I’m telling:  Not only do you need a bigger cooler than you thought, but helps to have lots of “tunnel fans” too, to make sure the hot air is being blown out of the building.  (Did you know chickens don’t sweat?  They do, however. pant…thrilling huh?)

One more visit back to the chart.  This time, let’s see what a high of 92 degrees and 15% humidity would chill down to with a swamp cooler:   70 to 72 degrees on the output, maybe?  Can’t beat that with a stick.  Which is why so many homes in Phoenix, Arizona and other dry arid places have both swamp coolers AND conventional a/c systems installed.  The swamp cooler will be cheaper to operate, but if you get monsoon rains come through “the Valley” (PHX) in late summer, well, then there’s nothing like the “no humidity-added” feature of conventional AC.

Which means what to preppers?

Well, if you are cheap, you will still want to avoid those 100 F days if possible.  You can do it a bit with misters, but only outside.  Evap coolers work, but you won’t be reaching for an overcoat until the air is thoroughly dry.  And right out of the box, the first half-hour, or so, an evap cooler will smell like wet cardboard (or gym socks) because the pads look like cardboard that’s specially built for cooling use.

On the plus side, they do offer reasonable bang for the buck and if you have the option to slip into a real “cold room” to take off a light sweat from working in 80-83 F every 15-30 minutes or so (gotta check the market anyway, right?) then one might make sense.

Oh, a light dusting of Lysol Spray on the outside of the unit while running, but not right on the plastic, freshens up the air in the shop to something approaching a pleasant aroma…Bang! fresh smelling shop.

The one we’re using is a Hessaire MC37M portable Evaporative Air Cooler for 750 sq. ft.. As a practical matter, always go larger than you need.  The shop (all in) is about 1,000 feet and we could have used larger.  But, do I need to keep the paint storage rack cold?  Hmm….

As I closed up the expendiment Monday, the outside air was 86 and 50%.  Output of the evap cooler (which is sitting outside an open window that has cardboard air baffles now) was 75F and 76% humidity.

Over at the main workbench the air temp was 81F with  70% humidity.  I use a small (20″) box fan to “help the air along” to the bench.  It’s sitting on the table saw where the temp is about 79 F and 73%…

Thus ends today’s new hybrid learning program:  Science project and prepping all in one omelette.  Figure we can run lots of evap in a pinch in a grid-down condition and still have the energy for the fridge and freezer.

Beer?  Almost warm enough now….

Write when you chill,  (pop!)

george@ure.net