Greenhouse Cooling!

alan_davisJuly 10, 2013

Good Morning!
New to forum and my first post.
I am a full time market farmer and will be starting a hydroponic lettuce operation soon. I am looking for advise, comments or suggestions on how to cool my 750 sq ft greehouse.

I am located in south central Kentucky where just yesterday we had outside temperature of 93 degrees. With 50% shade cloth and exhaust fan running the house was 99 degrees inside.
I am considering, misters, wet wall evaporative cooling or a chiller on the nutrient reservoir. Maybe a combination of some of these techniques.

I will be doing NFT gutters.

Any advise would be greatly appreciated!

Alan Davis

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PupillaCharites(FL 9a)

Good luck starting up your new hydro-venture! I wish I had advice (I'm in Florida where misting and evaporative cooling are no where near as effective as dryer climates), but I can only offer a comment or two.

1) Is there any economical film or material that blocks IR decently and is transparent to visible light? What are the domes of tubular skylight tubes made from, since they have the same issue.

2) Evaporative cooling and misting fail to do a good job in high humidity situations like hydroponics produce in an enclosed area. So people put vents they can open at the highest point of the greenhouse to allow the warmest, most humid air to escape. That is great for the exit. But I wonder about the entry of air. The dryer the air coming in the more cooling capacity it will have. Perhaps this is the ranting of an inexperienced grower, but I have done a lot of wondering lately about the inlet in dry air (from a dehumidifier to blow over evaporative trays, instead of simply using ambient outside air which may be laden with moisture. Essentially in my thinking, you certainly don't want to dehumidify the greenhouse, but rather swap the inlet air of a swamp cooler with air from a dehumidifier which the hope would be provides not too warm air economically. In that way in my thinking, you get the exit covered by removing the hottest air on from above, and the inlet a much more effective evaporative cooling which comes out humidified but cold. Just food for thought. Good luck.

One other thing I just thought of. If you can economically seal the floor, you would remove the ground from overly humidifying/acting as a water sponge in the area closest to the plants and get more bang per unit effort the evaporative coolers do.

This post was edited by PupillaCharites on Wed, Jul 10, 13 at 13:54

    Bookmark   July 10, 2013 at 1:13PM
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Here in NC when they want to cool greenhouses in the summer the most common method is a swamp cooler with the supply water burried at 6 feet into the earth. Even then the ambient temperature on a 95ð day will only drop to maybe 85 and the humidiy in the greenhouse is almost unbearable.It may be that the nutrient temperature is more critical in successfully growing lettuce. If that is the case, the feasibility increases as it is much easier to cool a nutrient reservoir by burying it than it is to cool the ambient temperature with a swamp cooler.

    Bookmark   July 10, 2013 at 2:04PM
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PupillaCharites(FL 9a)

Seems like a losing battle to me. Not because it can't be done, but simply because fighting the summer heat is going to be very costly unless you have some expensive restaurants locking up your production.

Since the problem really ends up being the soaking humidity, maybe the best thing is to forget about the greenhouse completely and put up that or an appropriate 50% screen in a V shape pitch above the lettuce to cut the Sunlight to a good level and maybe even with gutters to send the water on its way. Since so much will be evaporating, with that sort of setup whatever smaller amounts of rain that gets in the system will most likely be needed, and if a bad storm is coming you could maybe toss a light cover over it and pray for low winds. Maybe that, combined with the buried rez idea will be ok if you have the land and no enormous pest problem

    Bookmark   July 10, 2013 at 6:04PM
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IMHO cooling the Nutrient rich water bathing the root will beat the air temperature heat. Running a Nutrient feed line through a coil inside a simple freezer or refrigerator is an easy fix.

Here in Florida we use SHADE HOUSES not green houses. In fact Tomato farmer will have acres of shade cloth hanging over tomatoes. So my suggestion is shade cloth a water cooling.


    Bookmark   July 10, 2013 at 9:34PM
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Thanks, everyone for your replies. I actually have 2 -16'x48' PVC high tunnels right now modified to be a shade house and we're growing several different greens in raised beds. I have been considering setting up the hydro outdoors under one of these shade structures. They are covered with plastic and shade cloth. The sides are rolled up and the ends have been removed.

This may very well be my most economical way to go for the summer and then move the hydro system in the greenhouse this fall and grow there until summer. I may still have to cool the nutrient solution. I have customers and one restaurant waiting for me to come up with a solution to this summer lettuce. I have been selling a spring mix lettuce for $6.00 per 8 ounce bag and sell out every Saturday. I jsut need to find a way to produce more and to beat the Kentucky heat and humidity!

I have read several times that the evaporative cooling pads (wet wall) will not work efficiently in high humidity but a fellow grower just yesterday told me he uses one in his greenhouse and he loves how it works. He has a commercial ice machine and dumps 5 gallons of ice at a time in the reservoir.

Thanks again!

    Bookmark   July 10, 2013 at 10:11PM
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In my small Homeowner operation I used Frozen plastic water bottles to cool my reservoir and had trouble staying consistent . I don't like the Idea of dumping loose Ice into my reservoir and upsetting my nutrient balance. I am not so sure the Plants can metabolize all the additional water from the Ice. Plus this requires a human factor that can be subject to inconsistencies.

I believe a simpler method is to run your Nutrient line through a Coil in a small refrigerator before it reaches your plant's roots. Once set up it wouldn't depend on a Human factor to stay consistent.

I also considered using Geothermal as a way of cooling my water. Other than the Obvious half burying the Reservoir, Burying water line deep enough to get sufficient cooling would mean digging half way to China here in Florida.


    Bookmark   July 11, 2013 at 3:53AM
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Even in florida, if you dig down 2 feet, the ground temperature will be about 65ð

    Bookmark   July 11, 2013 at 7:21AM
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We are looking into the same thing, I plan to do basically what Ricone said and run my nutrient through a fridge. At some point I plan to. Build a digger bucket for my skid steer the we will bury a looping he ground.

We are planning to do the same with a loop for geo thermal heat in the winter. If I had to pay for the digging it would be cost prohibitive.

I still don't have my larger hoop house built yet. Won't need it until October. We have a small shade house that we will be expanding next year.

Where are you in KY I am in Indiana just a short swim to Kentucky.

    Bookmark   July 11, 2013 at 2:02PM
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PupillaCharites(FL 9a)


Can't keep out of this when talking about Florida ground temperatures. Ricone's comments are accurate in my experience. If you compare Florida to Kentucky (or NC) our underground temperature is up to 20 degrees hotter than those numbers. The whole country except the Rio Grand Valley and Florida penninsula follow Grizz's idea, but we are tropical and sandy. Two results - ground temperatures can go off the scale, and when it isn't raining, the soil holds little water and you might as well take a slow walk on the desert beach dunes on the summer solstice and smell the burn skin off your calloused feet. I put a thermometer on my lawn a few days ago. It is 130 degrees in the burnt out areas and 110 elsewhere. Shade is 90.

I don't have direct experience with burying a rez, but I have lots of other tips over the years. The main one is, burying things is ok, if you happen to have land where the water table is 2-3 feet deep like me, is that you would need to make a pit and change the soil to a much higher field capacity to make the burying the rez worthwhile. But, rather than going through all that trouble, since in tropical places like this, agressive roots seem to travel football fields underground picking up first downs daily it seems - is to simply keep the rez above ground and make a mound of a soil around it with the evaporative characteristics that work best. Sure beats weilding the pick ax. You could be creative and actually put a couple of drip lines strategically into the soil to semi-automate this pot-in-soil refrigerator.

Because of the humidity extreme here, Ricone's recommendation about adapting a refrigerator IMO is really the best way to go. This is because when humidity is a problem, closed refrigeration systems are more efficient since their electrical 'coefficient of performance' is a multiple of the energy input (because you are not actually paying to generate cold, only to move the heat and dump it elsewhere). In a place like Arizona, someone can wrap a beer in napkins and put it on the roof of a car and get a cold beer out of it in a few minutes. In Florida, if you do that, you just get a hot beer :(

see deep ground temperatures (not quite to China, but getting there...):

    Bookmark   July 11, 2013 at 2:12PM
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Hey Rio_Grande I am in south central Kentucky near Bowling Green. My son-in law is from Madison.

I like the idea of a nutrient res being buried but what about building an insulated box of 2" rigid insulation foam board to place the res in and keep it above ground. Maybe even put 2 layers of this foam board making for 4" of insulation keep the thing in the shade under the benches and chill and still chill the nutrient solution with a frig or chiller.

I found a couple of studies on evaporative greenhouse cooling and both say a fogging system would be more effective than a wet wall. That kind a surprised me! It would need to be a fogger and not a mister. The water droplets have to be very small.
Anybody use a fogging system?

    Bookmark   July 11, 2013 at 8:56PM
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I live 30 min north of Madison, small world. When I drive to Florida I spend the night in bowling green. Never seen the town but the beds sure are nice!

I know my buddy who has a small system had his tank as you described.

I don't fog, but I mist our shade house with about 1/2 gallon per hour, very small amount, and it brings the temperature down. The only complaint is getting soaked every time I work in there lol. The shade house dosent retain near the heat as a hoop house.

    Bookmark   July 11, 2013 at 10:17PM
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My little hydro grow is nothing like the scale you are attempting, but here is my two cents anyway.

In southern Ohio, my rez is a light beige plastic container that is buried about 18" in the ground. I have no issues to date keeping the water cool enough to keep it oxygenated with a few air stones in the drip system I am using for pepper plants. NFT wouldn't have an issue with my set up either because both NFT and drip allow plenty of air to get to the roots besides the dissolved air. I might have issues if I were using a DWC bucket, but that is one of the several reasons I didn't think DWC would work outside.

    Bookmark   July 12, 2013 at 12:40PM
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Thanks Jeff H. I'm thinking I will be doing some digging.

    Bookmark   July 12, 2013 at 9:36PM
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Burying a reservoir works, but remember to plan for a heavy rain that will flood the hole you buried it in. If there is no drainage, then the rain water will float your reservoir out of the hole

    Bookmark   July 21, 2013 at 4:27AM
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My solution is buried at ground level, it might be a little cooler. But every time it rains, the totes (35 and 30 gallons) will float up if not full of solution. I have a fan to keep it a little cooler during the summer time, but not enough to make a difference to plant lettuce.
During the winter time it is a different story in the greenhouse. I heat at night with a couple of space heaters and it keeps the greenhouse warm enough to grow tomatoes and peppers (started during summer).
I am here in middle TN, just south of Nashville and it is hot and muggy today.

    Bookmark   July 21, 2013 at 12:00PM
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