Air Supply & Circulation.
 

Growing in a terrarium presents one with many dilemmas, along with encouraging successes. One such dilemma is Air. I hope this thread will provide specific air-handling solutions for at least some of the various enclosed growing environments.

SO, feel free to provide any pertinent Q's and A's, and I will try do do the same.

Good growing!
tyler

Well, I guess I'll start this off and say that in my (admittedly limited) experience, circulating the air inside the terrarium with a small fan as opposed to bringing new air in has proven the best way for me- the plants seem to love it, it discourages mold, and humidity stays highest. Air exchange in my setups only occurs when the doors are opened for whatever reason, or through any small gaps in the construction, but this doesn't seem to be an issue.

One question I might pose is how people keep airborne water from a misting system or the like out of their fans when the system kicks on. Not only does it seem to burn the fans out really quickly, it tends to redirect the flow of the misting nozzles to a degree as well, in my experience.

This is something I've been experimenting with for a while, and would agree that simply moving the "same" air around is good enough. However, in my situation, generating a large amount of internal circulation poses a problem: too much heat. My tank is such that the bulbs are not totally isolated, and I use CFL's which get quite warm. My initial thinking was to exhaust the warm air occasionally, to maintain intermediate temps. The problem there is humidity. Only recently I re-installed the circulating fan, but instead of running it "openly" in the tank, I've cut a roughly fan-sized hole in the undergravel filter which sits on the bottom of my tank, and placed the fan blowing into it. This (so far) is working wonderfully. Tank temps dropped significantly, and airflow is very even, and slow, throughout the tank. Now, I exhaust for 15 minutes every 4 hours in this tank, daytime temps 70-72, nighttime 66-68.

A question I pose is how to increase day-night temp differences. My strategy has been to increase air intake (by running exhaust every 2 hours for 15 min)
to cool by evaporation. But, once again, humidity drops below acceptable levels. My plants reside in a living area, so an open window wont work. It's like the air is so dry outside the tank, evaporation inside can't keep up. I am in the process of building a cool growing tank, with an external evaporating cooler, and wonder if anyone has used something like that for similar purposes. I guess I could put an ultrasonic next to the tank! (or cough up dough for a mist system)
good growing
tyler

I'm able to get a 10 degree diurnal range just from the lights during the day (78 to 68, or thereabouts), but I guess if you're trying to push more intermediate temperatures you may not be able to do this. The CFLs do get quite warm- I'm assuming you're referring to the self-ballasted ones. Can you give some details as to how your lights are set up? A fan moving air away from your lights outside the tank may help somewhat if you're hoping for a cooler tank, though it sounds as though your low-mounted fan's working out well.

I've seen that people have good results using an external humidifier with the output routed into the tank- in your case it may also have the benefit of drawing cooler room-temperature air into the tank in the evening, while ensuring that said air is good and humid.

An external evaporative cooler might work in creating those cooler temperatures, provided the air going into the device is dry- I'd presume it is in MN, but I could be wrong. I don't know how low you'll be able to go with this setup, though- perhaps someone else can chime in. I've seen some very inspiring setups in which a mini freezer was used to cycle cool air through a large terrarium- I'm trying to look for the link now. It was the fellow who developed Epiweb that designed it- basically just a small freezer with ducts on either side blowing air up into the display area by way of fans wired to a humidistat. It looked great (the freezer was inside a cabinet below), and he got some seriously cool temperatures, with full control over day/night.

I have a question about air circulation. I just got my first orchids and I want to house them in my terrarium with ferns.

How much circulation is considered as 'good' circulation? Is it quantifiable? Can one create too much circulation?

I see photos where there are one or two 12V CPU fans for a 1.5'x1'x1' set up. My terrarium is 4'x2'x2' and I would like to find out how feasible is it to house these wonderful orchids in the terrarium.

Cheers.

Firstly, what sort of orchids are you wanting to grow in the terrarium?

The idea of air circulation is to maintain a level of humidity wihout alowing water to sit stagnant on the plants.

I supply fresh air 24/7 for cool growing plants in this manner:
http://www.alienflora.com/gallery/airduct.jpg

There is a 4" PC fan attached to the window frame which blows into the flexible aluminum duct. The air travels through the duct and empties out on each level of the plant shelf then no fans get ruined by high humidity.

This setup is currently servicing 3 shelves of mainly African succulents so I do not have an ultrasonic humidifier attached to the duct tube after the intake fan in this pic. If I did then it would show you exactly how I cool everything down for montane pitcher plants and orchids who need fresh cool air and high humidity. Just keep the fans out of the air's path after the humidifier and you'll be fine.