Hello. I also live in Texas. First, I really hate it when people who don't know the "answer" respond with a completely different solution so in this case...I hate me.

BUT, my neighbor has 12ft x 20ft hoop house and in the summer plans to throw a shade cloth over the top and rolls up the ends. He then has two large box fans that will push air through it. He also has the option to roll up the sides. Anyway, I know that this doesn't really answer your question but I think this will do just fine for him.

its ok, any response can sometimes spark an idea. in my case, im doing research on aquaponics and need to keep a closed environmnet ,so i cant roll up my sides or have the plants exposed to so many "outside" variables. so i need to know if i can keep temps in the 80s with my setup

I doubt you'll be able to keep it at 80F if the outside temp is 100F. you've got 12m^2 = about 12kW of heat from the sun for 8 hours, plus a surface area of about 30m^2 with an R of about 0.03 giving 1kW/degree K difference, i.e. about 11kW heat loading from the boundary over say 12 hours.

This is 0.34 + 0.5GJ = 0.84GJ.

You want to store all of this in 1.5kL of water over a day which means your water has to start the day at -100C...(ignoring freezing) Not a hope. Blowing air in will not get the temperature below ambient without cooling.

If you want to keep the temperature below ambient the cheapest option is evapourative cooling. I have a similar sized greenhouse which I can keep at 28C in 45C strong winds using a single commercial window-mount evapourative cooler running full bore. I picked mine up in a curbside hard rubbish collection, but I think it would sell for a few hundred dollars. Mine is controlled using a surplus split-cycle controller which cost me $50 new. A simple thermostat would work but I found the temperature tended to cycle a long way. New ones probably have a temperature set-point built in. If you buy one make sure it has autofill on the water reservoir, rather than requiring manual filling.

Also look at SolaRoof if uniform temperature is very important. My new greenhouse is being designed around that approach, and due to the efficiency I should be able to use compression cycle cooling with less energy than the old system. Solaroof will reduce the first time by about 20% and the second heat term to about 5% according to claims, giving a total of about 0.3GJ heating effect.

In my proposed greenhouse I'm looking at about 8kL of thermal mass water, meaning my starting temperature only needs to be about 20C to regulate the temp completely on average, which I think is practical, particularly with a dew point of around 10C.

so will my window ac unit combined with active exhaust and water heat storage be enough?

Is your window ac unit evaporative or refrigerative? If it is refrigerative it will probably have the coolnig power on the nameplate. And I doubt any refrigerative window cooler on the market can deliver 30kW of cooling power (you'd need about 10kW of electricity to run it!).

If you have an evapourative cooler (known as swamp coolers in some places) then it will probably do by itself (no water storage).

The conversion factors:

1 KW of cooling power = 3413 BTU
1 Ton of air conditioning = 12,000 BTU/hr = 3.5 KW/hr

Here is a link that might be useful: Conversion Units Tables

thanks everyone for your help. i guess im going to go get a swamp cooler. they have some that can deliver 12,000 of cooling for under $300.

would a mister system from home depot hinder the swamp cooler or help keep temps down?

what about if i add a dehumidifier,swamp cooler,mister system?which should i run together and which isnt needed?

cottagefarmer: I use the unix utility called units, which does everything you could possibly want for these sorts of calcs :)

A mister (i.e. tap pressure pipes with fine holes) will bring the temperature down to around the dew point and is very effective. On my controller I have the highest fan speed also drive a solenoid for the misters, so when the temp gets above 2C above the set point the misters kick in and cool everything down. Generally this only happens around early afternoon and the misters tend to run for 20 seconds then off for 5 minutes etc.

A dehumidifier is basically a refrigerative cooler. You would just waste energy trying to dehumidify the air! Much better to bring in fresh air through the swamp cooler all the time (mount the swamp cooler through the wall - a good design won't even let pollen through). The misters make a good back up, though they will use a lot of water.

Another possibility is to use a fog generator (based on either very high pressure or spinning disks). These produce much finer droplets of water which evapourate rapidly, cooling the air quickly. Last time I looked it was about $300US for the pump and another $200 for the plumbing. You will still need to bring in fresh air and design a control loop, which makes it less compelling than an all-in-one swamp cooler with thermostat.

ok, i think im set. going to go get a swamp cooler/dehumidifier combo and set it up to my thermostat. i already have an exhaust setup,so i should be just fine with the swamp i guess.

A swamp cooler without fresh outside air is almost useless, btw. The reason they work well is that they convert hot dry air into cool wet air. If the incoming air is hot and wet they can't do anything. If you ran a dehumifier in the same room as a swamp cooler without any fresh air you will not get any cooling because the total heat in the system is fixed. It really is important to use outside air! An exhaust fan will not work at all well, as you will be diluting your dry air before you try to cool it.

Things to read:
http://en.wikipedia.org/wiki/Swamp_cooler
http://en.wikipedia.org/wiki/Evaporative_cooling
http://en.wikipedia.org/wiki/Dehumidifier

oh, i will be pulling in outside air through the swamp cooler. isnt exhausting air in the greenhouse absolutely important,am i wrong? should i build a separate housing outside the greenhouse for a dehumidfier,than pull tht air through the swamp cooler?

I'm not sure why you're planning on running a dehumidifier at the same time, or is that intended to run in winter?

In my set up the vents open automatically when they get hot, then the swamp cooler kicks in. The swamp cooler pushes a lot of air through already, so you don't need exhaust fans. Maybe you could put a plan online so we can all sit round and criticise it (hmm, not the most tactful way of putting it, but that's what will happen :).

There is the possibility of constructing a two stage evaporative cooler that extends the operating range of humidity and improves efficiency. The page at the link below describes its operation. The two stage unit apparently introduces less humidity into the enclosed environment than a single stage would.

Here is a link that might be useful: Two Stage Swamp Cooler

nathan, where i live in texas the humidty gets very high. so a swamp cooler wont work very well in a 95F at above 70% humidity. i wasnt planning on running a dehumdifier in the same room as the swamp cooler, but to build a small 4'X4'X'6' unit to house the dehumdifier in outside the greenhouse,then pull the air from this through the swamp cooler into the greenhouse.

this way the swamp cooler will be using dry hot air.

Using the dehumidifier first is pointless, as you are using lots of energy to dry the air, only to wet it again! What is actually happening is the dehumidifier will produce air which is warmer, but dry. When you cool it again it will return to where it was (or as cool as the air would have been had you just used a swamp cooler by itself). Your dehumidifier will not keep up with the swamp cooler.

If the humidity really is 70% at 95F (which implies a dewpoint of around 27C) then the evap cooler will do nothing. You will have to use refrigerative cooling which means big dollars. Remember that 30kW? That means you need a 10 ton cooler.

cottagefarmer: Yes, two stage coolers are more efficient as they can bring the air temp right down to the dewpoint (and possibly below, I'm not clear on that). For a greenhouse the higher humidity isn't a big deal so you can run a two-stage cooler to a lower temperature (sensible heat) than you would for comfort. However, if the dew point is 27C (83F), then I suspect that cooling to 80F is impractical.

I think we need some hard data from utsharpie about swamp cooler performance in Texas before we can predict much more.

utsharpie. Go with the swamp cooler - it will be a cheap option whenever the dewpoint is significantly below 80F, but you'll probably have to shut it down and use a split-cycle cooler when the humidity goes up. I think you need to get some practical experience with a swamp cooler in your climate and see how well it performs.

In melbourne we regularly get to 45C (115F) but when that happened a week ago the dewpoint was -6C so even a modest swamp cooler could provide dramatic cooling.

my 1st question is why operate a greenhouse in the summer.i cover mine with black plastic,and tarps in the summer-do all my growing outside in the summer.my greenhouse serves no purpose in the summer-i can grow anything out in the yard.i only use mine to keep the plants above 50 at night in the winter.and in early fall,and late spring,it's still difficult to keep from overheating.why do u want to use a greenhouse in the summer?

We discussed this in another thread. In some climates it is hard to keep the water up to small plants at high temperatures and it is more effective to make an enclosed space with high humidity. Plants will take quite high temperatures as long as the humidity remains nearly saturated (humans don't :).

I suspect that in georgia you would never get a day with 45C, -6 dewpoint and a 60km/hr wind, so growing outside is quite practical. Contrarywise, I never have frost so techniques to deal with it sound rather over the top (yet I know that people in such climates must make precautions or they could lose everything!).

To give you a feel for how it affects people read this thread:

http://www.au.gardenweb.com/forums/load/oznative/msg012020129072.html

i need to keep constant temps for my research purposes.

I did find a useful chart. Its oriented for CA and lower humidity conditions but shows that there is some noticeable cooling from an evaporative cooler even at higher humidities. As it says somewhere else in the article as the daytime temperature increases, usually the humidity decreases so the evaporative cooler will become more efficient. Perhaps, with a somewhat more intelligent control system, one could use a combination of evaporative cooling and air conditioning to achieve the required results.

The problem, cooling a large enclosed space with a high solar load and high humidity, seems to be beyond the more conventional greenhouse issues that are addressed with lower cost methods we have, as greenhouse owners, at our disposal.

One method that I think might help here is using a shade cloth or a system of motor driven "venetian blind" style shades. The motor could be the solar powered type, located within the greenhouse and linked to the external shade system. Something like this:

{{gwi:288491}}

Here is a link that might be useful: Evaporative Cooling Chart

i really appreciate all the help. another idea

since energy consuption isnt a factor in my setup(ill be growing enough food a month to offset the cost) what if i built a small housing outside the greenhouse and used a window ac unit with or without a dehumid. than ran that air into the greenhouse and the swamp cooler intake?would the window ac keep up with the swamp cooler?

or would just running a swamp and a window ac unit in the greenhouse work better?

are my thoughts wrong that drying the air being brought into the swamp cooler would help create desert like air, thus allowing the swamp cooler to perform like it would in UTAH or ARIZONA?

utsharpie, the short answer is 'I would recommend against that'. You will probably get a small additional cooling effect, but at a tremendous increase in both capital and running costs. Is maximum sunlight really that important for your experiment in summer? Putting shade cloth over makes a big difference, and in mid summer the plants don't actually like full sun when they are young.

Are you more concerned with worst case behaviour or average case behaviour?

Perhaps you can tell us a little about your experiment. It sounds quite interesting and other may have ideas to improve it. Perhaps a few days at 90F won't affect your results significantly.

well im doing an experiment on aquaponics. I need to have as many variables locked down as i can to accurately measure my bacteria performance in my biofilter and nutrient absorption by the plants.

will a shade cloth be bad for sun loving crops such as tomatoes and melons?a few days at 90F will be ok, but will i be able to keep temps around 88F with my setup? the temps dont need to be at 80F but just under 90F...the MOST important is being able to keep temps at 1 constant temp in day.

what about fog systems? i found one for 400 bucks american that says it covers 400square feet.

again thanks so much

It is probably way too late for this.

You say you are doing an experiment, well I don't know how much money you have set aside for this but if I were to attempt what you are doing I would set your system up totally differently.

In any experiment you need to keep all the factors constant (light, temperature, humidity, day length, total weight of fish, water temperature, nutrients.... and 14 other factors I can't even think of!)

I would have tried to do this experiment in a cave. Using metal halide and or HPS lamps to provide the "sunshine". that way you are in control of the seasons (day length) but you do not need to deal with the unwanted effects of the sun, the heating effect. You pay more in energy for artificial light but your cooling costs go way down.

Not many people have a spare cave handy however. The next best thing would be in the middle of a barn. Set up your experimental hoophouse environment in the middle of a barn. Nathen is good with numbers, he can work it out in 10 mins, but my gut feeling is your equipment costs by providing artificial LIGHT will be much less than your costs for providing the cooling you need by using free light from the sun.

Yep, I know I am nuts, but my plans are to expand my seed starting operation by digging a big hole in the yard, building a "bunker" and using artificial lighting. (zone 4 it is really starting to make economic sense)

I agree with Chris, if you really want a controlled environment room you should build one. Get a well insulated barn or similar (a cool room is good) and use metal halides etc. We use them for cloning where you don't want to cook plants in their little flasks.

The sun is a mighty big light and hard to control so a special environment is probably a better choice.

Alternatively, get some good logging equipment, accept you won't be able to precisely control everything and use a swamp cooler alone. It will keep your greenhouse below a little above dew point, takes very little water and electricity to run and is easy and cheap to install.

Chris is also right that heating is a big problem with sunlight. What you want is a magenta low emissitivity glass that stops all colours besides the bands for chlorophyl (or whatever you want the light for?). I have no idea whether this even exists, but it would probably mean you could get away with fairly low power cooling and stay within your opperating bands.

Finally, if you are interested in bacteria for water filtering, why not keep the bacterial filter and tank in a well insulated box and refrigerate the water directly. I find that temperature transfer to water from air across a pond is very slow unless you have significant aeration. That's why outdoor heated pools are practical. A similar design is the supermarket chest freezers that have no lid.

In that case a simple high volume extraction fan will be quite adequate.

well i was using a spare bedroom with 4 tables each under a 400watt m/h....but we are remodeling so i no longer have access and i already have the hoop house built so no luck changing, plus ill be able to grow more plants and test more in a place under the sun.

so i guess its down to a swamp cooler or fog system...which would be better? here is the fogger site.

http://www.advancegreenhouses.com/greenhouse_foggers_misters.htm

Either swamp coolers or foggers are fine. They both work on the same principle, but foggers often make surfaces damp whereas swamp coolers don't. Constantly damp leaves can cause rot.

On the other hand, a fogger will probably use less electricity for a given cooling rate. Buy what you feel is right. You probably should find out how easy it is to configure each approach - do they require a separate thermostat, can they change fan speeds to minimise fluctuation, how good are they at stopping air movement when they're stopped, etc.

i just found this website on waco texas weather history (i live in waco)could you take a look and tell me if an evap cooler will work? i feel much better that it will, and than we can put this one to bed. much thanks to all!

http://www.cityrating.com/cityweather.asp?city=Waco

Sorry, but that site was useless. I'm not sure why people collect relative humidity, it's really quite useless. Even more useless is posting the average or maximum relative humidity without reference to temperature.

Why? Because to a human, a RH of 80% is quite dry at 30F, but 80% at 110F is oppressive (if not lethal). What you need is a list of ave and maximum dew points over summer. Looking at that list I would guess that you'll be fine based on the supposition that the dew points are the maximum and were actually recorded fairly early in the day before it really warmed up. In my mind Waco has a similar climate to coastal new south wales, and swamp cooling is fairly popular there.

Try this site for your weather history.

Here is a link that might be useful: The Old Farmer's Almanac

farmers almanac, thats the site i was originally looking for. well i guess im going to look for an evaporative cooler with the highest cfm for my price range. thanks guys you were a great help!

if i learn how to post pictures ill show you my hoophouse i rigged up to be airtight. not too bad for only $250 even though i have duct tape all over the door areas. not the prettiest but oh well

Yeah, I had a look through some days in June July August and you seem to get a fairly reliable dewpoint of 70F, which means that 80F sensible heat is quite doable. I think you're set. Good luck, remember to come back with some data so the next person can be better advised!

what if for the intake air on the swamp cooler i run some coiled hoses underground and created a SCHS for the intake air? this would supply cool dry air?

or did this SCHS for circulation in the greenhouse?constntly recooling and drying the air that is being cooled by the swmp cooler?

or used it with compost bin for heat?

Using the ground to store energy is certainly a possibility. However, unless you are made of money, I would just build a simple system and see what its performance is like.

I've seen some mighty big swamp coolers made using a panel of special folded cellulose at one end and a big fan at the other.

You might also look into 2-step swamp coolers which use a heat exchanger and swamp cooler to pre-cool the air before using a second swamp cooler to cool the air right down.

I think the time and effort digging those pipes in will take many years to pay off.

"I think the time and effort digging those pipes in will take many years to pay off."

I think that depends on where you live. Here they lay hundreds of miles of that 6 inch corrugated drainage pipe a year in fields. I see it go past on large flat bed trucks, it must be cheap. Also where I live there are many young adults who would pay me to let them rip up a big hole in my back yard on a Saturday afternoon just so they could play with their dad's "John Deere"

As to paying real world prices for the pipe and the excavation then the cost is probably way too high.

in my setup i wont be excavating. The greenhouse has 8 55gallon rubbermaid continers each side has 4 side by side lengthwise.

I was planning on building a box perimeter round the containers at 3 feet tall,the fill in the area with dirt to as tall as the containers,serving 2 purposes.
1.support for the continers holding water
2.a large above ground storage for the piping.

or do i HAVE to bury the pipe ubder the ground soil?

what about pipe size?cubicft/min?

im going to use 1" pvc pipe since i have so much leftover after building the hoophouse. will this work?

Any suggestions for how many feet of pipe id need to wrap around the containers?

ive been reading this thread and i have a few ideas for you.

im curious that no one has talked about lowering the grow area. i know this sounds labor intensive but without massive energy inputs, i dont see how u plan on getting temps @ 80F with the outside temps over inside temps with the addition of the 2x poly. a few feet down will help some.

also, i think shade cloth is a must in this situation. not only are u trying to be under ambient but u are adding the sun's heat inputs.

maybe 2x poly isnt the answer either. seems like overkill in tx anyhow. im in freezing wisconsin and i need 2x poly but in the summer, i lift the sides. which brings me to the pt that this absolutely needs some sort of upper air escape. maybe fan's at the tippy top of ur endwalls.

u mentioned that u have 8x 55gal drums in the house. what temp is that water at during the daytime? vs night?

anyhow, here is a totally different way to approach a solution. u mentioned that $$$ is no matter. that i dont believe but if it really isnt...

lower the flooring, use radiant heating tubes in reverse, using the cooling waters of the earth. then get a big tank of CO2 with all the valves and meters to turn it on & off at the right PPM. this will do a few things for u.
1) co2 increases the heat tolerance. u can grow @ higher temps.
2) co2 is under pressure and cold as the dickens.
3) 1200ppm+ will give u exceptional growth.
4) if u use dryice (solid co2), then u will get a cooling effect off of the 'melting' as well as the gains of the co2. but not really too sure what kinda cooling u would get or how much ice u would need. it sells for about .75$/lb. and im sure there are some smart ppl on here that can calculate how much u would need.

lastly, not sure why u have a greenhouse in texas anyhow? again, in wisconsin i would but im not sure about tx.

froggy

ok,

after some begging with my family, they allowed my to use half their back deck for my fruiting plants when it starts to get warm. this means i can use the greenhouse for growing leafy crops only.so this allows for me to still have better control over my environment for my research but be ble to use shade cloth to help lower temps.

so i think with shade cloth, active exhaust/intke,SCHS,swamp cooler, ill be able to keep summer temps in the mid to high 80's. and winter and spring temps at lower 70's to high 80's.

which i guess is even better because it simulates tropicl environments where i want to actully use the systems once reserch is done.

Excellent news! It's always good to plan things carefully.