Denise, Shading is a very important component to reducing heat in the greenhouse. However, this time of year I am trying to maximize light into the greenhouse, so I look at shading as a last resort. I am more interested in ways to move cooler air into the greenhouse and heat out without compromising the amount of sunlight the plants are getting. I agree it is great in the summer if you can open up your greenhouse so it gets as much ventilation as possible and the temperature inside is the same as outside.
I am trying to collect as many winter ventilation ideas as I can. If you have an unlimited budget you can just open roof vents and other vents, but I find that I have to seal all of my vents for November, December and January to keep the cold out and heat in. I get almost no sunlight those months so I get little heat input except from my furnace. I will put up a page on my web site when I get everything I have received on winter ventilation. thanks, Tom On Mar 21, 2007, at 10:34 PM, Denise Nash wrote: > Ed and Thomas - > > I can see that ventilation is a science. You two seem to have very > large > greenhouses. I own a 18 x 11 greenhouse, and I vent with ridge > vents. I > have two ridge vents, one on either side of the peak of the roof of > the > greenhouse. They are set to open at 80 and 82 degrees. At the end of > February, I begin to notice that the sun has regained some of it's > power > here in the north country. At this time, on a sunny day, at least one > ridge vent will open. That tells me it's time to unroll my light > colored > 70% shade cloth. > > I love my set up. I have 6 awning type windows and a screen door, > and in > summer, it is never any warmer in the greenhouse than it is outside. I > have two ceiling mounted fans, going almost full blast, also. > > In the fall, about mid November, I will notice that on a sunny day, > the > vents don't open. So it's time to roll up the shade cloth once again. > Simple! Works like a charm. > > ~Denise, in SE Lower Michigan > > > Ed Merkle wrote: > >> Thomas, >> >> All greenhouses should have a way to ventilate excessive heat out. >> The >> best way to do this is with automated exhaust fans and power intake >> vents of the proper size. It is usually recommended that the exhaust >> fan(s) should be able to make a complete change in the greenhouse air >> every 60 to 120 seconds. Your 14 ft x 32 ft greenhouse, if it has >> a 10 >> foot roof, probably holds close to 4,000 cubic feet of space. >> Therefore your exhaust fan(s) should have a total exhaust capacity of >> about 3,000 to 4,000 cubic feet per minute. Your intake vents should >> equal roughly twice the area of your exhaust fan(s). (One 24 inch fan >> = 48 inch vent(s).) Most orchid greenhouses should also have an >> evaporative cooler or wet pad system to cool and humidify the >> greenhouse. >> >> During the winter and transitional seasons when the sun warms the >> greenhouse too much on cold days, an exhaust fan and vents are still >> necessary. Due to the cold outdoor temperatures, plants should not be >> exposed to cold breezes coming in through the intake vents. You can >> either move the plants, or provide a second set of vents that does >> not >> open directly onto the plants. Some growers have been known to >> place a >> blower fan (100 to 900 cfm) at roof height, opposite of the intake >> vents, and a tube system that pumps the heat down and out, gradually >> making a change of air over a longer period of time on those cold >> sunny days. >> >> In addition, an orchid greenhouse should have constant air movement >> throughout by using several fans running 24 hours a day. These fans >> should constantly mix the air so that temperatures at the roof are >> not >> too different than those near the floor. Even in this kind of >> situation you should still be able to find micro-climates for the >> cool >> and warm growing orchids. >> >> For my own 20 x 50 foot greenhouse here in Nashville, Tennessee, I >> have a 10,000 cubic feet per minute exhaust fan set on a thermostat >> that turns it on at 78°F. I have a bank of vents that measures 2 x 16 >> ft, and two 36 inch vents, that open when the fan comes on. I have a >> wet pad (Stuppy) measuring 4 x 16 ft. that runs during warm >> weather. I >> also have four 1500 cfm fans inside the greenhouse that run 24 >> hours a >> day...probably could use a couple more. My object is to provide >> enough >> air movement that the leaves and flowers are constantly moving in a >> breeze nearly everywhere in the greenhouse. >> >> I hope this helps, and I'm sure others may have additional ideas. >> >> Ed Merkle >> Merkle's Orchids >> 1008 Maplewood Place >> Nashville, Tennessee 37216 >> >> _________________________________________________________________ >> It’s tax season, make sure to follow these few simple tips >> http://articles.moneycentral.msn.com/Taxes/PreparationTips/ >> PreparationTips.aspx?icid=HMMartagline >> >> >> >> --------------------------------------------------------------------- >> --- >> >> _______________________________________________ >> the OrchidGuide Digest (OGD) >> [email protected] >> http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com >> >> > > > _______________________________________________ > the OrchidGuide Digest (OGD) > [email protected] > http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
