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Sigesti

At my wit's end trying to cool a terrarium

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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.

terrarium.gif

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.

alternative.gif

Thanks in advance for any help.

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Hi Sigesti,

Seems the main challenge is to remove enough heat from the tank (your fridge or whatever cooling agent needs to be powerful enough to do this) and prevent heat from the outside from replacing it fast enough.

I've a 2 ft tank insulated all around on the inside (except the front glass pane) with a layer of bubble wrap and then abt 1/4" polystyrene. The outside is further insulated with polystyrene sheets as well. Once it's evening (when I cool the tank), a polystyrene sheet covers the front pane as well.

Perhaps you'd want to try something similar with your set up - I've found that lots of insulation helps keep the heat out.

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Hi Sigesti,

Seems the main challenge is to remove enough heat from the tank (your fridge or whatever cooling agent needs to be powerful enough to do this) and prevent heat from the outside from replacing it fast enough.

I've a 2 ft tank insulated all around on the inside (except the front glass pane) with a layer of bubble wrap and then abt 1/4" polystyrene. The outside is further insulated with polystyrene sheets as well. Once it's evening (when I cool the tank), a polystyrene sheet covers the front pane as well.

Perhaps you'd want to try something similar with your set up - I've found that lots of insulation helps keep the heat out.

I may need to invest in insulation, as right now I'm not using anything really. I was concerned about the insulation would keep a lot of heat from the lights in as well though. How do you handle that?

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Yes u're right.. it's a challenge getting enough light in while keeping heat from the lamps out.

My set up is more or less the same thing you did - I've a sheet of 3mm thick acrylic separating my aquarium lamp from the tank (I use a 35w lamp in an aluminium housing. The aluminium housing gets really hot in the afternoons).

I've also 2 pcs 3mm thick spacers (cut from the same sheet of acrylic) sitting underneath each lengthwise edge of the lamp housing - to create a 3mm gap betw the lamp housing and the acrylic sheet cover. This is to minimise heat transfer from the lamp thru contact/conduction. I think ideally I'd have a small fan blowing air betw the gap when the lamp's on, but I've not had to do this.

I've also insulated the outside surfaces of the acrylic sheet cover - where the lamp does not come into contact with - to further reduce heat gain from outside.

Hope this helps.

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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.

doomcube.jpg

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

opening.jpg

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.

controltower.jpg

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

airvent.jpg

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.

electronics.jpg

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

planttank.jpg

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.

acvent.jpg

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%

tube.jpg

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.

monitor.jpg

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 (http://www.texashydroponics.com/shop/produ...=329&page=1)

The air conditioner was $340.00 (http://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.

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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.

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Putting the air conditioner outside of the tent may be a good idea. The AC produces heat itself which means that it will be increasing the ambient temperature within the tent which it then has to cool. If you were to put it outside the tent then the larger and shorter the feed tube the better, I would have thought similar or larger diameter to the vent tube. If the tube is too restrictive then the AC air might take a less restrictive path instead of going into your tent. I guess that if you were to put it outside of the tent, you would need a remote sensor/thermostat in order for the AC to control the temperature.

Edited by mobile

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That's a pretty innovative soln Sigesti.. Well done

I'm wondering it'd be more efficient if u directed the cool air from the aircon directly into a sealed tank by way of your orig set up. In the tent config, there's much more space and things to cool (including the air conditioner itself as the others have indicated).

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That's a pretty innovative soln Sigesti.. Well done

I'm wondering it'd be more efficient if u directed the cool air from the aircon directly into a sealed tank by way of your orig set up. In the tent config, there's much more space and things to cool (including the air conditioner itself as the others have indicated).

I think that'd be more efficient for cooling, but I think it could potentially kill the humidity.

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Yes tt's true.. the air would be dry.

Keep us posted on any other mods u'd be doing (I'm thinking of dismantling a used mini-fridge and somehow installing cooling unit into back of my tank - but the thot of all the work puts it off).

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I have only skimmed through the above posts but here is my take.

the tube from the fridge is a good idea but your set up has a fundamental problem.

1. the fan is not drawing air from the fridge (merely turbulance) as you are creating a vacuum!

2 the fan is creating heat.

Solution:- create hole in fridge big enough for fan and pump air into the fridge, this will force cold air out through the tube into the tank.

if you also add a good coil of copper pipe inside the fridge attached to the outlet pipe (tank feed) this will ensure that the air forced out to the tank is at its coldest. also if you fill the fridge with old thin ribbons of metal (say from an old car rad or old drinks cans) this will increase the cold surface area in the fridge and make it much more efficient!

The idea with the air con unit and the tent will be more efficient if the air drawn in to the a/c unit actually comes from the tent (but with the unit outside the tent) as it becomes more efficient as the intake temp drops.

Whilst this does strip humidity, it also creates negative pressure so you can have a swamp curtain in front of an inlet to replace humidity as the vacuum draws fresh air in.

By having the unit outside you are creating positive pressure with cool but dry air and the temp will only drop so far (to probably 16 deg c) this you can pass through a swamp curtain to add humidity and then vent the tent at high level.

To reach lower temps you will probably need to bypass the units thermostat.

If you choose to use an electric stat to switch of and on, make sure it has a 3 min rest between cycles or the unit wont last!

any questions feel free

Edited by Dicon

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The idea with the air con unit and the tent will be more efficient if the air drawn in to the a/c unit actually comes from the tent (but with the unit outside the tent) as it becomes more efficient as the intake temp drops.

Do you mean drawing the air out of the tent via the a/c intake then feeding it back in from the a/c? A recirculation system?

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Do you mean drawing the air out of the tent via the a/c intake then feeding it back in from the a/c? A recirculation system?

Yes, that way the a/c unit is working at a lower input temp (after a short while) instead of the higher ambient temp outside....win win!

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Yes, that way the a/c unit is working at a lower input temp (after a short while) instead of the higher ambient temp outside....win win!

That's what the manufacturer of my car recommends when running the a/c, turn the vent to internal rather than external intake.

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