Trying to cool a terrarium (with diagrams!)

[sigesti]

So in my previous house, the ambient temperatures were always around 75 F (23 C) and I kept my terrarium down in the basement where the temperature would get to about 65 (18 C) at night with the fluorescent lights off.

I recently moved and am now in a house at around 80 degrees with no basement, and am about to go mad trying to figure out how to achieve a temperature drop to keep my nepenthes happy. I recently tried a method I read somewhere about pumping air from a minifridge to the terrarium, but my results have been dismal.

Here's a diagram of my current setup.



Few basics, it's a 4x2.5x1.5 tank, 55 gallon. Acrylic sheets are between the lights and the terrarium (lights are about half a foot above). I have a humidity pump on either side keeping the humidity from 80-100%.

The recent thing I've tried involves the minifridge. I've got a piece of tubing that leads to the open air of the fridge out to a funnel and fan in the terrarium (sealing hole in the fridge with silicone putty around the tube). The idea being to suck air from the fridge into the terrarium. My results have been poor, and I'm sure there's all sorts of reasons why that might be the case (tube too thick, tube too long, terrarium not sealed enough, fan not powerful enough). The air coming out just doesn't seem all that cold.

I'm not sure what to do now and am welcoming all advice from people more experienced than myself. Before the fridge thing, I tried bottles filled with ice with a humidifier blowing across them, but that only got the temperature down to 74 at the least. That was a wee bit of a hassle and required a lot of attention.

I've read about peltier coolers, but those seem frightfully expensive and difficult to get it working perfectly.

I've also considered instead of using air, using a waterpump that takes cold water from inside the fridge (from some kind of tank), and then lining the inside of the tank with tube, to then lead back to the fridge to cool again.


Thanks in advance for any help.

[sigesti]

This thread was very interesting and I'm going to make a note of it:
icps.proboards105.com/index.cgi?board=indoor&action=display&thread=2098

[BarryRice]

Hi Sigesti,

Do you know any physics or chemistry? It might be very illustrative to do a few calculations. I'm concerned that merely chilling the air via a fridge might be inadequate, since both the heat capacity and conductivity of air is low (if I recall correctly).

I'd suggest you definitely toy with using water as your chilling agent. You'd want to make a few volumetric calculations to make sure that your large reservoir of water in the fridge is big enough, so that the water has plenty of time to chill before being sent to the terrarium.

By the way, I've got some experience in this, having adapted the refrigeration unit from a drinking water dispenser to cool the water for a Darlingtonia tank. It was a pain in the bum, and ultimately I ended up keeping the Darlingtonia too cold! So I can tell you that you're in for an interesting project! Good luck, and keep us posted!

Barry

[David Ahrens]

It would be interesting how long the fans last before they pack up. I used a small computer fan a while ago to help circulate the air in my terrarium, but not to cool it. The bearings soon packed up in the humidity and the fan broke down.

[sigesti]

An engineering friend did a bit of research for me, and gave me a lot of very good advice. The big thing I took away from all of it is that I was fighting a losing battle with my house's ambient temperature. Getting the terrarium down in the feasible range that I wanted (around 60 degrees F) was just going to be pretty difficult.

The solution I went with ended up being that I'd be better off placing the terrarium in a place where the ambient temperature would help and not hinder the process.

In my old home that was a cellar. Thus, I decided to try creating an artificial cellar.

I talked to some hydroponics fellows, and they mentioned how a grow tent could do a decent job of keeping a temperature in. That paired with a portable air conditioning unit might get me what I wanted.

All that, and it kind of looks like a monolith.


Its size is 4x4x7, but let's peek inside, shall we?


Inside, there's the control tower. The air conditioner sits on top because the venting tube needs to reach a window, and longer tubes can decrease efficiency. You can also see where I've taped up vents to insulate the tent.


The side of the grow tent, showing the vent leading to a window.


Electrical stuffs (+ cat tail). I still need to clean this up a bit to make sure it's all organized. The timers are there to control the two sets of fluorescent lights, and the rest of the plugs are for the terrarium humidifiers and fan.


The tank currently sits on the bottom of the tent (where the colder air will gather).


I also ran a tube of air from the AC directly to the terrarium (although I need to check just how much this helps). The AC has an auto setting and a cool setting. I just wish the auto-setting worked a bit better. I set it for 62 and the thing just stops around 72. I've taken to switching it to auto during the day and cool during the night.


A view of the AC tube. The AC itself sucks humidity from the air, but the terrarium is enclosed and thus keeps a happy humidity of around 80-100%


Regrettably, as the tent is big and opaque, it's tricky monitoring the thing. I went to a hardware store and picked up a remote temperature sensor that let's me monitor how things are going.


Results:
Daytime terrarium temperature: 80 degrees F
Nighttime terrarium temperature: 63 degrees F
Terrarium humidity range: 80-100%

Ideally, I'd like to push the nighttime temperature to 55, but I think for now this is as good as it's going to get. I'm at least pleased to be at a decent point that I believe I can build and develop upon.

On the happy side, my plants appear to be improving greatly. A number of them that had stopped producing new leaves are now starting to pick up their growth again. Even the N. Lowii seems to be pitchering well.

Costs:
There is the unfortunate 'cost' of having an enormous black cube like this thing taking up space in a room and blocking a window. Unfortunate, but one I'm willing to make to ensure plant health and happiness. I am open to decorating solutions to the cube though.

This was not a particularly cheap solution, but overall I found the costs not too horrid.
The tent itself was around $180.00 (www.texashydroponics.com/shop/product.php?productid=2843&cat=329&page=1)
The air conditioner was $340.00 (www.amazon.com/gp/product/B000PGQ8YQ)

On the other hand, I'm intrigued at the idea of using this tent (as it stays fairly cool) into a make-shift root/wine/cheese cellar as well.

Anyhew, that's the direction I went. I welcome any comments/critiques as I'm still feeling my way in the dark with all this.

[sigesti]

Talking to someone, they suggested moving the AC out and venting its cool air into the tent. That would certainly give the AC more air to suck in. However, I'm wondering what length of tubing would be the maximum I could use without the air losing too much of its coldness.