Kenny, somewhere on here I believe I posted how an early spring day went from 27F outdoors in the morning to 45F in the afternoon . . . Nothing remarkable about that, especially here where clouds usually interfere with further warming at that time of year - somewhat, unlike Colorado.

However, the clouds were not in the sky that afternoon. Instead, it was very clear - with sustained wind above 20mph!

The result was I was dancing all afternoon to keep the temperature down inside the greenhouse! With an exhaust fan and a vent open, it still reached 82F!

This is where even automatic systems would have limited value. I mean, I didn't want 40 degree wind BLASTing thru the greenhouse on top of the plants! Keep it "buttoned up" and the interior would quickly soar above 100F!

I could have the same problem on a clear, still day with temperatures in the 20's. Fully automated systems would go crazy unless they were carefully adjusted and absolutely could NOT be trusted with these kinds of conditions.

I know - "wet foliage = bad" but "roasting = worse." If nothing else can be done, wet down everything! Temperature 95F, interior soaked . . . it will be okay. Can't let it happen when the temperature is 45F outside. I mean, full ventilation is required so that the plants dry by sundown.

Steve

This past Sunday, we had one of those glorious spring days where the outside temps went from 28F in the early morning to 88F in the afternoon, along with 40 mph winds. My tomatoes and peppers were already planted outside, assuming the prone position, covered up with grass clippings.

Just my 3rd year with a (little) green house, but I kinda laugh when every one talks about ventilation and fans. I know that ventilation is good up to a point, but what good to ventilate when the outside temp is 100 or better? which is not at all unusual here. That swamp cooler with a thermostat kick in and a swinging door on the air exit was great. Size? about 5 times what is normally recommended for fans. Remember, humidity can be 10 percent or less here and I figure the plants can use the moisture too.
Kenny.

I think I've posted about my greenhouse and the fan issue. The room is about 20 x 25, and I put in two huge chicken house fans, blowing the hot air out of the room. So its as you say, turn those things on with the doors and windows open and almost instantly, its the outside ambient temperature. However......

close the doors and the windows, and the suction and vacuum created is enough to suck the water up out of the floor drain, and the doors are almost impossible to open.

IOW, pretty useless. One of these years, I will replace at least one of them with a swamp cooler.

In the commercial greenhouses, we would sometimes lose a water pump for the pads in the end wall. You could see the moisture being sucked out of them on a summer day, in not much longer than it takes to tell about it . . . it was very disturbing!

And then the heat . . !

But, those big greenhouses were giant swamp coolers in themselves. We were still using the aspen pads when I got there, just like a swamp cooler. 150 feet away were the fans but stopping in front of the pad on a hot summer day was blessed relief from the heat.

Hanging around the monstrous fans at the other end of the structure was only good for making strange noises that carried into the parking lot.

We installed a misting system for each house - just on a timer. Helped but nobody really like to be out there hot, wet, soaked, hot . . . did I say hot?

We could always go up on the roof and go blind from the glare, burn like a slice of bacon and fall thru the roof . . .

Steve