Used swamp coolers are not expensive, especially in January in depressed hot areas like (insert name of appropriate town in your area) where at that time of the year the credit cards are full from X-mas, it's not hot and the swampers are not needed. I bought 2 from there for $100 apiece, one 1/2 years old. They work great but take a lot of space and make plenty of noise, not suitable for a small backyard green house. I'm going to build another couple of units for extra protection and also just for fun. These will be cheap, silent and definitely suitable for anyone's greenhouse.

Start out by making a rectangular box out of 2" x 2"s of the following dimension: 18" x 18" x 5'. Cover the 4 long sides with plywood or redwood planks, leaving the 2 ends open. Fit one of the ends with the smallest 'attic fan' Home Depot has ($82). 1' away from the fan perforate with a 1/2" PVC pipe, immediately make a 90 degree and run another 6" parallel to the roof. There place 3 misters, the type they use in Palm Springs for hot days. The outside end of the pipe is attached to an electric shut off valve such as is used in any sprinkler system (HD, about $15) and fed with city water. Since the valve is low voltage a step down transformer is needed. Granger item #6WU91 $18. Both the valve and the fan are then attached to an all weather 110Volt thermostat which comes with the attic fan and can be placed on the wall of the greenhouse. Total cost is about $115 plus the cost of the wood, should total out for under $130.

This rectangular structure sits on a slant so one end rests on the floor of the GH under a bench, the other end with the fan is elevated a couple of feet off the ground and becomes part of the wall. The fan draws outside air. The discharged air should run parallel to the direction of the bench. The electric motor of the attic fan needs to be protected from moisture.

When the temp reaches the set point, the fan is activated and the valve is opened. Air rushes over the misting nozzles and discharges humid, cool air inside the GH. If there is unevaporated water, it will end up on the floor instead of on the leaves of the plants and adds to the humidity. If there is too much water, remove a mister, if more water is desired add more misting nozzles. The principle is the same as a swamp cooler, air rushes over water, evaporates it thus cooling it and adds humid, cool air to the GH. This system is smaller, quieter and probably cheaper than a quality swamp cooler. Placing misting nozzles on the roof of the GH and using them to cool eventually leaves a grey residue on the plants if city water is used, this system does not. Should be perfect for smaller greenhouses.

Rube Goldberg is alive and well.

Nick.