Greenhouse Cooling - Beat the Heat.
Greenhouses can become a kiln in summer / I'm building one for wood drying! Here are some things (opaque
roof, ventilation, shading, and evaporative cooling) to combat the summer heat but allow for the most winter light:
(1)- Opaque or partially opaque roof: Either white or bronze
polycarbonate will reduce the light transmission approximately 50%. Used this material on the roof and clear on the walls to capture the most winter light. I went with white on my courtyard:
Notice the small triangles open to vent. The various sections are separated by box
gutter. Insulated Solid roofs with or without skylights is also a good option.
(2)- Ventilation fans or/and removable panels: Textbooks recommend that
volume of air is changed out every minute or so your 12x16' greenhouse holds 1,920 cubic feet of air and I sized a fan with that will handle 2,240 CFM (cubic feet per
minute). If you don't want a fan, at least 20% of the floor area is needed for roof and floor ventilation. I think the removable panels will help but may not get you all the way there.
(3) - Shade cloth: You're right-on!
(4) - Evaporative cooling: This works best in arid climates. But doesn't do much
when humidity is close to 100%. The Hydrofogger(tm), misting nozzles http://www.azmist.com , evap. coolers are all good options. I wanted to try pumping cool water
from the ground (50 degrees here), run it through nozzles with air and use the water for irrigation. This is called geo-thermal air-conditioning with water mist heat exchanger.
Here's a plan for one out of the Ortho Greenhouses book:
- According to the Ortho book: "Previously, most pads were made of aspen
shavings, excelsior or plastic. Now on the market are cellulose pads impregnated with insoluble antirot salts. Another modern cooling pad system
consists of a bonded plastic fiber pad coated with an absorbent cellular foam. Unaffected by continual exposure to moisture, disinfectants, chlorine or water
acidity, these new pads are so efficient that you do not even see water trickling down the side. All of the new evaporative cooling pads fit existing systems; they are easy to install and clean.
- "The size of the pad is important. It is determined by dividing the required air
flow by 150. Thus an 8- by 12-foot greenhouse needing an air exchange of 2,000 cfm requires about 13 square feet of pad (2,000 /150 = 13.3). The most
effective pad is one that extends across the entire wall."
Here's a link to a supplier or two: