air exchange in terrarium - Orchid Board

travelfin · #1 12-21-2007, 02:41 PM

Anybody have facts on how much should the air change per hour. To my knowledge the air in a building changes once per two hours. Greenhouses run between once an hour to once per minute. If the air doesn't change how long does co2 last for the plants.
It is easy to have high humidity if the air changes slowly and very difficult if it changes fast.
Searched the net for an answer but found nearly nothing. Only for greenhouses.
Which is better slow change and high humidity 90%
or fast change and 70% humidity.

Ross · #2 12-21-2007, 03:15 PM

I don't have the info you are asking, however I would like to share my setup as it works great. I have two passive vents on one end of orchidarium and a thru-wall fan on opposite wall. I run this for 3 hours every night. During the lights-on period (right now 12 hours) there is no air exchange at all except if I open the doors to water. There is, however, a 12volt DC fan running 24/7 inside the tank blowing directly on the orchids. This arrangement has kept them happy and blooming for almost a year, now. Hope this helps.

travelfin · #3 12-21-2007, 03:25 PM

Thanks for the answer, if no scientific answers then answers based on experience help.
Running air in and out myself 24/7 and no fan inside

Ross · #4 12-21-2007, 03:28 PM

Quote:

Originally Posted by travelfin

Thanks for the answer, if no scientific answers then answers based on experience help.
Running air in and out myself 24/7 and no fan inside

Nothing wrong with that, at all. It's just that I want really high humidity for my Angraecoids, and running air thru the tank would defeat that (in my case.)

travelfin · #5 12-21-2007, 03:42 PM

Just trying to find out is air exchange co2 or high humidity more important and which one is the more important factor. And basically why in scientific terms.

Ross · #6 12-21-2007, 04:06 PM

I can tell you this - plants use CO2 during lights-on periods (day) to run processes necessary for growth, etc. They expell Oxygen during this same period. Related to chlorophyl production and maintenance. During lights-off periods, the process reverses and they consume Oxygen and expell CO2. The production of CO2 is at the heart of the war on "greenhouse gas production".

My personal observation is that (if growing humidity loving plants) the rating of the three things would be #1- humidity, #2-air exchange to reduce likelihood of molds and rot and I would not be concerned about CO2 at all. I doubt your tank is sealed so well as to be a mini-environment (a biosphere.) So normal opening of the doors for various tasks will cause a certain amount of air exchange on a basis directly related to the frequency you open the doors.

As to "scientific terms", I think it may relate to what you are growing. I grow mostly Angraecoids and they depend on high humidity and a steady source of "rain" because of the home territory. So in my case I can state, unequivocally, that humidity is the most important factor of the three you cite. Other important factors for me are control of temps, amount of light, a brief drying out to control rot and mold on the mounts, constant air movement, and brief (yet regular) mistings to simulate the ocean fog they might have experienced in nature.

This is a really interesting discussion. I wish some others would join in, because I am not an expert - I just have a bunch of success and observations.

travelfin · #7 12-21-2007, 04:47 PM

You are right, should I lower the air exchange for higher humidity for night time and have a higher humidity or mist more daytime for a higher humidity daytime.
Which is better more internal airflow inside the terrarium and less air change or the other way arround. Easy to do with timers. So what is the best and why

FinnBar · #8 12-21-2007, 04:55 PM

I don't think a universal answer exists. so much depends on the species, watering habits, and whatnot.
I prefer to mainly circulate the air but like Ross' my tank has mainly Aerangis. I've got a pretty vigorous fan on 24/7 which i moved to another angle as it was drying plants a little too well, even with 90+ humidity.

the tank is sealed quite well and most of the air exchange takes place while watering.
the conditions seems to suit the Aerangis but for example bulbophyllums i might try a little less air movement for starters..
the air moving up one side certainly creates microclimates within the limited space. maybe now i've learnt how to make use of it better.

i'd rather keep the humidity above 90 and circulate the air inside heavily than exchange the air more at the cost of humidity.

FinnBar · #9 12-21-2007, 04:58 PM

i've understood nighttime humidity is more important while plants open their stomatas at night. during the day they keep them shut as a preventive measure from drying out.

Ross · #10 12-21-2007, 05:06 PM

I run three timers feeding off each other. Here is set-up: appliance timer (simple on-off) set to come on and off at "day length" I choose. Into that timer I have an interval timer plugged that runs the misting system (MistKing). Also the lights and a cooling fan for the lights are plugged into same appliance timer. I have a second timer set to run for 3 hours at night to clear out the tank, so to speak. I feel three hours are plenty to dry things off a bit and I prefer to do it at night because wet nights are bad for plants. Humidity tends to run a bit higher once lights go out, due to lower ambient temps (it's relative humidity, right?) Three hours has provided plenty of drying so far. I still run a fan 24/7 inside the tank to just circulate air (doesn't do anything for air exchange) because it's easier to do it this way. My experience has been that to hold higher humidity for day periods, one needs to NOT do any air exchange (other than passive) during the day. Hope this makes sense. Internal airflow is a MUST if you have no air exchange. Otherwise you will see mold and fungus build up real quickly. As ambient temps of the room the tank is in decrease (like during winter) then it isn't quite as important for air exchange to hold back the mold. That seems to grow best when temps climb in summer (in my experience.) I fought mold all summer using daily sprays of Physan 20 and now I rarely spray, but mold is all gone. Ambient (basement) temps this time of year run approx 18C at night and 22C day. In the tank, I read a bit over 22C at bottom of tank (away from lights) and 24C at top under lights. In summer, figure at least 5 degrees C higher for all readings.