Temperature Control in a Greenhouse

[jewingmd]

Hi, I'm not used to forum discussions, etc, but I'll try to be succinct. I have a small (250gal) reef setup in a non-profit school setting. Their greenhouse, an 800sqft double-walled polycarbonate, has two evaporative coolers and a large propane heater. I have two 24x48x10 acrylic tanks (DIY), and a standard 55gal display tank on top of an 8x4ft table, with two 33 gallon sumps in-line with each other underneath. I'm setting up the two acrylics as an experiment in showing morphological changes in response to different current types (one will be two SCWD devices, the other a surge tank).
I'm having some trouble with temperature control. The non-profit is concerned with propane (on their bill) and not electricity (an bill that is subsumed under a different line), so they let the temp way up in the day (even in CT at 10degF, the air temp can reach 100F at about 3PM now), and down to 40F at night, all to save propane. So I run a total of 1700W of heating at night, supporting about 78F in the water, and fans+1/3HP chiller at the peak of the day. The temp in the tanks still reaches about 83, despite chiller on at 81. In summer, the evaps will be allowed, as long as they don't require propane use during the day. I'm using an Aquacontroller jr. (just setting it up) to try and tighten the control. I've got the Coral Propogation book, Anthony, any suggestions? John

 

[DonW]

Does your chiller have a built in controller like the 1/3hp pacific coast units?

Don

 

[jewingmd]

Yeah, it does (set at 81 until I get the aquacontroller set up)

 

[hammondo]

the hot air will make it hard for the chiller to work effectively, can your tanks be put near the edge of the greenhouse with the chiller outside in the cooler air?

 

[DonW]

Yeah, it does (set at 81 until I get the aquacontroller set up)

I have the same goofy controller. Set at 80 the chiller turns on at 82 and the heater at 78. Would allow 83 to 77 temp swings. They do make a upgrade for the controller that is 1 degree, and inexpensive. Aso as stated above, moving the chiller outside will make it a little more efficient.

Don

 

[Anthony Calfo]

the chiller is not to be used under any circumstance. My "career" as a hobby/industry mentor and consultant has evolved to the point where I consult 2-3 serious coral farms monthly... 'round the word and both hemispheres now. And this one is a commonality... no refridgeration/condenser/chilling equipment. Under the best of circumstances it is obscenely expensive to run and moreover contributes excess heat at the worst time of day in GHs.

Evaporative cooling alone is enough for knocking temps down in New England and as far south as the Carolinas (humidity address). The key is having a ridge or gable-mounted exhuast fan that is controlled by a thermostat. You will see that when it kicks in... the ambient room temp will drop as much as 10F in 3-5 minutes. Quite impressive Find there units in GH supply catalogs (like atlasgreenhouse.com)

Night time temps are boosted by using as much water as possible to serve as a heat sink. Make your tables and benches out of capped water barrels, etc. Do simply get as much water in there as you can.

best of luck/life!

Anth-

 

[Carl]

Something else that might help is to install a misting system that is thermostatically controlled. Keep the nozzles adjusted so they are not over the tanks. The finer the mist the better. In a small older greenhouse I had kept chameleons in I could drop the temp 15f in minutes. With temps in the 90's outside I could keep my montaine species happy with a temp of 75-78.

Another thing that I found that helped was light colored shade cloth in the summer and darker colored shade cloth in the winter. Partialy shaded sunlight is still far more beneficial then the best lights produced by man.

Carl

 

[Anthony Calfo]

misting in the greenhouse however will add to already high humidity (more quickly ruining elctronic quipment) plus it will badly handicap evaporative cooling inside the structure. Add to that the metal rods and purlins sweating contaminants (metals incl) into the tanks and it can get scary.

Misting is very helpful for open air environs and vertebrate animals.

 

[Carl]

I guess I never took notice to the dripping.

Carl

 

[overgrown]

gh cool/heat

I have had great success in temp control . The way my system works is well first I have a geo loop of adout 400 ft that just helps to take a liitle heat not much but it does work then I also have an exaust fan that has humidity control as well as temp control . If that dosnt keep up a 2.5ton air handler will come on and that will maintain interior temps to 75 . the water temp never goes above 84 and never drops below 79.8 . sps are growing like crazy, systems are coming up on 1 year of ops in may. Cant say that it has been free of troubles but for the most part,smooth . oh yea I forgot to mention the floor is 8 inches of concrete this provides insulation

 

[jsmkmavity]

grainger is another good source for the fans. they have all different sizes and thermostatic controls if you want or make your own. size one for at least 3-4 times the air volume of the GH. a smaller size will cost less to buy and run so dont go crazy on the size. also the temp will be more even with smaller more constant airflow. a chiller cant get rid of its heat well in a humid environment and the evap coolers add humidity too so if you use a chiller the unit needs to be outside like already suggested. ag suppliers orweed control/fertilizer companies should have plenty of 55 gallon plastic barrels to get rid of if you check around.

 

[overgrown]

some recent gh pics

just took these they are from a tank that has variety

 

[Travis]

the chiller is not to be used under any circumstance. My "career" as a hobby/industry mentor and consultant has evolved to the point where I consult 2-3 serious coral farms monthly... 'round the word and both hemispheres now. And this one is a commonality... no refridgeration/condenser/chilling equipment. Under the best of circumstances it is obscenely expensive to run and moreover contributes excess heat at the worst time of day in GHs.

Hi Anthony, First let me say I bow down to your experience and expertise in GH aquaculture. I know you consistently repeat all over that chillers should not be used in "for-profit" GH endeavors. Forgive my lack of understanding but what would you do on a 100 degree day at 80% relative humidity to maintain 80 degree water temps in a GH? I can see that a large water volume would be helpful, along with some good ventilation in the GH but I still don't see how you could keep the tank temps down on hot and humid days like this. What other cooling methods are there besides increasing water volume, strong thermostatically controlled exhaust fans/shutters, evaporative coolers on the shutters, and shade cloths?

Also, I know Rick Rottet has mentioned in his thread that water temp in his tanks are usually around 15 degrees cooler than the ambient temp in the GH. Does this sound about right? If so, then on a 100 degree day at 80% humidity, how would one achieve a 5 degree temp pull-down in the GH to keep the tanks at 80?

 

[Anthony Calfo]

evaporative cooling alone can keep large enough pools (an important plan design... minimum 200-300 galls each... larger is much better) easily cool enough during the hottest days. Even in humid climes like the East Coast of the US (we have relative humidity well over 70% much of the summer... some weeks staggeringly high) and even still I have never needed or seen chillers needed in our GHs)

Yes, the tank temps will be usually10-20F cooler than ambient... and with ambient being finessed by adequate fans, and exhaust (ridge or gable vents, recirc fans, etc)... it really can be a small matter. Furthermore, the (large enough) tanks are strong thermal masses. Even without evaporative cooling... the average between a hot 90F day and an uncomfortably hot (to sleep in) 70F night is still 80F - quite comfy for corals Add evap cooling to that and the spikes by day or night are really little trouble to endure.

The temp in your pools will not shift high or low very fast.

The key in any such greenhouse is massive (!) air circulation.

In extreme cases, alts for cooling include:

- using desiccants (cheap calcium chloride road salt) on trays in front of your passive shutters to dry incoming air to improve evaporative cooling

- swamp coolers (do google search)

- geothermal cooling (some great threads on various message boards where coral farmers have tried this)

 

[Travis]

Is having a lot of smaller tanks hooked together with a common sump the same thing as having fewer larger tanks running separately when it comes to the mass of the water's ability to resist temperature change? For example, lets say someone had 10 100 gallon tanks hooked together. Then on the other side of the greenhouse they had one big 1000 gallon tank. Would the water in these 2 systems keep similar temperatures to each other as the ambient temperatures change or will one change temperature faster?

 

[Anthony Calfo]

the first problem with that is "central filtration" which has almost no place in coral farming (or any farming). Thats what holder (wholesalers/retailers) do to optimize profist at the expense of some health vigor and even life for the crowded and exposed animals.

But for coral farmingi, central filtration does nothing more than share the growth inhibiting noxious exudates and worse... system wide. Dreadful truly.

Farming is farming. Monoculture. One species per tank. Big tanks... and big broodstock pools.

Trust me... if an ag farmer could grow chickens, bulls and pumpkins on the same acre of land, he would. But he can't.

And as the smaller tanks relate to temp stability... they are worse too. The many walls/panes of these smaller vessels are more surace areas for cooling (unwanted at night) and they heat up too quickly (you are less likely to be able to run water through them fast enough and efficiently($) to compensate for the difference.

This is one lesson that most coral farmers fail to learn because they still think like reef keepers. They try to keep and grow too many species at once.

Good question, Travis my friend... but not a good solution

 

[Travis]

Ahhh, superb answer Anthony. You definitely hit some things that I never considered. I do understand what you mean by

This is one lesson that most coral farmers fail to learn because they still think like reef keepers.

Since I am a hobbyist I do think that way. I never thought about how a farmer would need to change their way of thinking but I do see the light now.

I also now see your point about the multiple smaller tanks not being as temperature stable. Another thing I hadn't thought of.

Now a question for the opposite end of the spectrum...
Let's say a farmer used huge burial vaults like 8 x 5 x 6 and buried them half way into the ground. Surely this would negate any concern about cooling during the summer months but would the large tanks being half buried in the ground end up giving up extra heat during the cold months compared to if they were just sitting right on the ground? Would it be better to use vaults like 8 x 5 x 3 and just sit them right on the ground?

Not that I am a coral farmer or anything. I'm just finding it fun to follow along on all the GH threads. I think the people doing the coral farms are doing a great service to our hobby as well as the wild reefs. Maybe some day I can have a farm of my own... Well, one can dream, right.

 

[tangdiver]

Bump please

 

[Anthony Calfo]

being partially buried will not help or hurt much here because of the shallow depth. Do so if it seves a practical need for space, but give little weight to thermal mass issues unless we are talking huge pools and greater depth (more than a few feet).

 

[tangdiver]

What about the larger tank buried 3 feet deep...would this help cooling, and would it hinder heating...would ground suck heat from tank if buried 3 feet deep?

thanks,