I've been thinking about putting up a hobby greenhouse in my backyard, as an excuse to buy more orchids to fill it. Anyway, the issue of keeping it cool obviously comes up. I live in Central Texas and three weeks ago, it was 100F every day. Simple physics dictates that, even if I recycled the air constantly, the temp would at the very least be 100. So what other methods are there to actively cool greenhouses besides the pad and fan method? Passive methods such as shade will only keep temps from rising above the outdoor temp....which is already too high.

I read an article in the 4/03 issue of Greenhouse Product News about the use of the evaporative cooling properties of fog on the order of 5-20 microns to cool greenhouses. Most books and web sites seem to gloss over this method. It seems that the standard method in use today is still the fan and pad. Something tells me that there must be a serious disadvantage to using fog, otherwise, more people would be using it. Does anyone know why companies offer complex 1000+ psi fogging systems when there are much less expensive fan-generated or ultrasonic foggers available? Again, I feel that there must be a disadvantage to the latter. I also suspect that fogging will not work in a small greenhouse, on the order of 1000-1500 cubic ft. And I don't mean misters, but foggers. Anyone know more about this?