Aren't they close to useless in high humidity?

This is true, but out humidity is somewhat strange here, perhaps a micro climate. For example, yesterday at 1:00pm it was 28% relative only 55 at 5:00pm. I understand the real cut point is abut 45 or 50. This is not everyday here, but unless it rains it seems to hold true. I am noe monitoring it here as I have a gauge and also have access to the net with a private system that is reasonablly close. Still in the research stage and if fact I would want to try and build it myself. Thanks for the response
1eyedJack and the Dawg

Wow, you live in pleasantville then. I grew up in fla without ac; I remember summer as 90/90 on the nice days. I would soak my shoes with sweat from the effort of tying them.

About ten years ago we were driving north out of fla in late august (without ac in the vehicle), and I do remember the remarkable drop in humidity as we drove up onto the piedmont in SC/NC. Then it gets swampy again in the tidewater.

Evaporative coolers are frequently used in orchid greenhouses. That just happens to be where I have seen them. Pads of some sort of course fiber which resembles excelsior (I can find out what it is if you want me to) are installed at one end of the greenhouse. They cover a large portion of that wall. Water is dripped into the pads from above and collected at the bottom and recirculated. Large fans pull air through the pads and into the greenhouse. It exhausts from the other end.

Jim

They used to make an evaporative cooler for the old VW beetle that hung out of the window. It looked like a jet engine.

I have seen the ones that hung on car out West, but they will never work in FL. Some days up here they wouldn't either, but my thought is one for a green house. I had thought to take a fake chamois and cut it in strips and cris cross it so that the air can flow thru. wet it and put it in front of a fan and see if it will work. If it does I will figure out some way to keep it wet and have at it.
Thanks for the comments
1Eye and the Dawg

I purchased an evaporative cooler from one of the big box home & garden stores, and installed it on the northeast side of my greenhouse. It sat on a concrete block pad (I placed/leveled a few concrete blocks on the existing dirt ground) outside the structure. I also attached it to 2 hanging chains/hooks for additional support. The unit's cooling outlet poked through a small side window into the structure.

The water resevoir (on the outside) was automatically refilled using a floatation on/off device connected to a tube which connected to my greenhouse water faucet. I did have some issues with the tubing leaking at the stepdown connection (from garden hose size hose to 1/4 inch tubing.)

I have a greenhouse controller connected to an outlet specific for "cooling" and just plugged the evaporative cooler's electric plug into the special outlet. My controller was able to turn on/off the unit (by supplying power or removing power from the outlet) as needed with my set temperature requirements.

It probably brought the temperature down by 10 (maybe 15) degrees at most. It also blew cooling/humid air which was a nice benefit--the plants in its direct path were cooler than the ambient temperature.

Unfortunately, algae grew in the resevoid and the unit's pump it died after the first winter (likely froze since the resevoid was outside the structure) even though I attempted to weatherize it (guess my weatherization wasn't effective.)

After it died, I just left it in place, but covered it on the inside with plastic to prevent cold air leaks in the winter.

It was rather inexpensive to purchase and to operate. And, because I was able to self-install (and I'm very much NOT an HVAC installer type) I am considering another one to replace it.