Keeping Greenhouse Cool

[Manchua]

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?

[uncasteeb]

Living in a climate where temps rarely get(i can only remember 100f once) i haven,t looked into active cooling.I,ve just had a browse & it would seem that price is major factor.
Came up with Aquafog400

Not cheap.

[Manchua]

Yeah, I've heard of the Aquafog 400. It's what my searching for the last few weeks has sort of settled on. It's about $4-500 and seems to be the one recommended for hobbyists. Advantages are that you don't have to use superfiltered water and you don't need extremely expensive compressors and lines. It also doesn't draw a lot of power. It's drawback is that the droplet size is 35 microns, which seems to be getting into the mist category, which can fall out of the air. Why that's such a problem, again, the books fail to mention. Supposedly, the smaller the droplet, the quicker and more effective the cooling. And I have read that fogging, assuming the droplets are small enough, is more efficient a method of cooling than the pad and fan method. With fogging, wet bulb temps can be obtained at 100% I have read. Not bad.

No book or greenhouse site seems to talk much about electrostatic or ultrasonic foggers though. One site mentioned that they draw lots of power and don't produce much fog. There seems to be no efficient AND inexpensive way to cool a greenhouse. What you save in one end of the equation, you're probably going to lose in electricity bills.

Hmm, I wonder about going down to the grocery store every day and loading up on the dry ice they use to pack meat in. Dump it all in the greenhouse. It's cold and free. Plus, the plants will probably love the CO2. Hmmmmm. A bit labor intensive though.

[scopinox]

Only thing a can say is that the smaller the water droplet, the larger the surface area to volume ratio you are getting. Heat absorption, and thus cooling relies on the surface area, and that's why I think the ones that produce smaller droplets cool the air much faster.

[Gin]

My green house is 12x16 on an old cement patio slab . I have a mist system from one of the box stores under a bench with a wind machine fan blowing through the mist , also another smaller fan the blows thru. an ultrasonic fogger from another discount store , bought when on sale . also an exhaust fan on a thermostat as high as it will go . On the outside is alumnet shade cloth. I checked into the larger foggers and they are to rich for me . Mine is low tech . but has kept the Temp. no higher than 85 on the 100 degree days we have had . If ever put up another green house it will have the turret ventilators on the ridge pole or an attic fan on the ridge pole . another thing that worked well in a green house I had before this one was a dropped ceiling made of clear rigid solar panels it trapped the heat up high and the exhaust fan got rid of it . Gin

[WEA]

My understanding is that the 20 micro fog set at 8-10 ft. high will never hit the leaves of plants on waist high benches. This would not create free standing water on/in your plants to harbor disease. It just cools ... and humidifies. My concern is that if I use a auto drip system to create a large particle fog or small particle mist, then depending on the heat, humidity and air flow, I'm liable to end up with that free moisture on leaves (crown and/or new growth). This has in the past lead to heavy losses of plants and new growth. If there is a chance of leaf wetting, then the 24/7 circ fans must be able to eliminate any free standing water, after the fogging/misting cycle during the hot part of the day, and before night fall. Night fall in my area (N. FLA) during the summer brings high humidity (70-80% R/H especially if you mist during the day) and little hope of good evaporation. I'm thinking of using misters under the benches on a long count of 5+ minutes twice an hour from 1200-1700 and/or single line of overhead foggers at 7 ft. high on a short count of maybe 15-30 seconds every 15 minutes for same period. Times will have to be experimented with. I have to choose. I either open the G/H up completely and accept ambient outside temperature minus what ever the mister/foggers can get me in an open system, or close the G/H up and use the thermostatically controlled exhaust fan and assoc inlet shutters to work on the mist/fog to lower the temp. Currently: Outside 90-100. Inside 100-105+. G/H is 10x25', up against a CBS wall, concrete floor, 3' hi CBS block side walls with 4x4' triple hung plastic windows, clear corregated Lexan slant roof 7 to 9' hi., Aluminet 50% shade cloth stretched on PVC frame, propane heater, thermo controlled exhaust fan and inlet shudders, 2 small circ fans with plans for larger units 24/7. My hope is to get system set so that I can be away on vacation for several weeks at a time ... and have my plants survive the experience. But the high temperatures have got me house bound.

If I were in North or Central Texas, I'd go with a swamp cooler in a heart beat, but here in North Florida I seem to be sliding along the wrong side of the dew point to be really effective. Cost if $400-800 for my size G/H ... and there conflicting method for determining the "real" CFM airflow to acheive good results.

[WolfinKW]

Ummm I may not be seeing why this wouldn't work... but there are portable air conditioners available that have an outside vent... They are around 400 bucks I think at most box stores. Why not buy one or two of these and use them for cooling and forget about all the mist/foggy/wetting options?

[Diane]

I thought the same thing as Wolf, except add a mister or too. But all this reconfirms why I am in no hurry to get a greenhouse. This is way too complicated. Too much math - all these microns and parts per billion or whatever....

[Forrest]

conventional air conditioners actually pull water out of the air. so your greenhouse would get dry. Though in a high humidity area like Texas you may be able to counteract this, I am not sure.

[WolfinKW]

Yeah but with humidification in a greenhouse am sure that could be controlled... Also with this air conditioner it has a drip pan that would have to be emptied... If you just let that drip onto the floor of the greenhouse it would evaporate again and help maintain humidity. It doen't pull the moisture to the outside like a window air conditioner does.

8000 BTU Portable Air Conditioner. Single hose with 2 fan and cooling speeds. Covers up to 340 sq. ft.

This 8,000 BTU portable air conditioner will cool up to 340 sq. ft. of living area. Casters allow for easy movement from room to room. Comes with a single exhaust hose, 2 cooling speeds and 2 fan speeds. Includes window kit for exhaust hose. Electronic control with 12-hour timer. 5-year carry-in warranty. Exchange only-no refunds.

those are the details of waht I was talking about. I think it may be worth a try.