Backyard Aquaponics
A place to discuss aquaponics

Being new to all of this, I reserve the right to be stupid. My stupidity may be showing below, I'm not sure

I've been contemplating building a system in a greenhouse. I know with your typical greenhouse setup (non aquaponics) air circulation and exchange is always a big concern - not only due to temperature, but also due to carbon dioxide/oxygen levels.

Ignoring any concerns about temperature, is air circulation and/or exchange necessary for a aquaponics system in a closed greenhouse? If I understand things correctly, the fish should be releasing some amount of carbon dioxide that the plants will use, while the plants should be releasing some amount of oxygen that the fish and plant roots will utilize. Correct? Are the ratios in balance? Does a human(s) in the greenhouse throw them out of balance?

What are the general thoughts on both air circulation and exchange in a aquaponic greenhouse?

Circulation and air exchange is probably more of a concern in terms of humidity... leading to possible fungal and mildew problems...

And reality is... you'll probably be opened the door... and going in and out to check/feed/look at... the fish and plants anyway...

No real problem that anyone has ever reported....

I just can't figure out if I should be installing a fan(s) for air circulation, and whether I should be installing vents for air exchange (or temperature control if I can't manage the heat through other means). I live in an area that get's quite cold in the winter, and fairly hot in the summer, with really low humidity year around (I live in a "cold" desert with two nearby massive lakes for good "lake effect" from time to time).

I'm hoping/planning for a 400-500 sqft greenhouse that I have hopes of running year around. Not really entertaining commercial aspects right now, just want to feed myself, my wife, 4.5 kids, my wife's parents, and a brother-in-law. My estimates for staggered year around growing (using typical commercial field production numbers) seem to indicate that's about the right size. If I have a little extra room then I can sneak in more of those space hogging crops I really love like watermelon and muskmelons.

Thanks,

Gene

I was told that anything over 50mtrs long (sorry about the metric ) you will probably need a fan to help move the air in the middle area, the direction it faces can make a big difference with air flow too, mine runs east west just for that reason, afternoon breeze will go straight through

Hi gblack

My system is sitting in a greenhouse that is 8m x 2.5. I have lattice panels every couple of metres to allow air flow and so far they seem to be working (no mildew issues). My water temps are rising up to 21 degrees during the day and only falling to around 18 at night (in Wollongong), so the greenhouse is definitely helping to keep my silvers happy and feeding.

Cheers

Air circulation is definitely needed for fungal/moisture problems in cool weather as well as for cooling in hot weather.

Well, I think I'm going to be under 50 meters, but my width may be more than whatever was considered for that calculation. I'll keep that in mind.

It sounds like the big item here I hadn't properly considered was humidity. I'm kind of considering this as an add-on to my house anyway as local regulations may make it easier to expand the house with a "sun room" than throw a greenhouse in the back yard. Given that I live in a desert and low humidity is a problem around here, I'm wondering about the possibility of using the greenhouse as the intake for my furnace/AC system for the house - this would possibly save me the trouble of installing a humidifier in the house, and get the humidity out of the greenhouse (to a degree).

I'm still in the dark though on where I'll stand with oxygen/C02. Any thoughts?

Thanks!

Gene

Gblack.... fish respire ammonia... not carbon dioxide...

The only real exchange of carbon dioxide/oxygen would be between the air and plants... or perhaps between the oxygen in the water and carbon dioxide due to algael processes...

As we avoid algael growth... and are continually oxygenating our water... no problems...

The plants also benefit from the highly oxyganted water... and normal photosynthesis of carbon dioxide from the air isn't a problem...

Fish also respire Carbon Dioxide.
http://bio-isu.tripod.com/id3.html

+1. I believe most of the O2 we add to the water comes out as CO2 (the gas exchange goes both ways)....and the plants love it. I understand that CO2 is sometimes added to greenhouses for better growth and that critters (I've heard of chickens as well as fish) will do the job admirably. I do not know if the CO2 levels in GHs are lower than fresh air, but would guess so when the sun is shining.

Bringing that warmed, moist air into the house (use a fan and forget the furnace? Just let it drift by convection?) and exhausting some of your stale warm air to the GH would be a real winner, I would think: the rich, moist, warm, live smell of a greenhouse would be welcome in the winter.

Thanks, BRB. I was about to set the record straight. All animal life respire CO2, even our beneficial bacteria (see the demise of Biosphere II, when all the oxygen was depleted but there was no correlating CO2 rise- the scientists discovered that the CO2 sequestered in the concrete that was still curing)- so there is plenty for the plants. Additional CO2 is unnecessary, which is normally a huge on-going expense in greenhouse horticulture. Try to capture as much of that as possible by using some sort of free fall to release the trapped CO2 and it will exchange for O2 given off by the plants inside the greenhouse itself. The O2 in the greenhouse will be a higher concentration so that is also better for the fish. However, if you smoke or have any open flames, you do risk the chance of an ignition. It has happened in greenhouses before. Just a heads up- I don't think anyone has ever mentioned that on this forum yet.

You will likely still need some sort of venting for the greenhouse on occasion and do careful research before assuming you really want to draw your household air from the greenhouse since it may be more humid than you really want.

Granted, I am in a climate where we have to run the dehumidifier to keep indoor air quality good.

During winter when I had my AP system all covered up by greenhouse plastic I had problems with condensation and excess humidity as well as things getting way too hot during a sunny day and still getting cold at night. My "greenhouse" was really more like a giant cold frame and hence no automatic vents or fans or anything like that.

Thanks guys, this is some really good feedback here.

I *think* (correct me if I'm wrong) most of what has been said here with gas consumption/emission is pretty much in line with what I have been thinking so far. To summarize:

1. Oxygen is used by fish and by plant roots.
2. Fish produce CO2.
3. Plants (the green leafy parts) consume C02 and emit Oxygen.

Because plants do like CO2, I've suspected that the possibility existed for an aquaponic greenhouse to have not only higher CO2 levels than a typical greenhouse, but also possibly higher CO2 levels than outside air. If this is the case, then I'm worried about what venting might do to those valuable CO2 levels - and also wondered if venting was needed for gas exchange at all (maybe for other reasons, but I want to separate that as there may be other methods to meet those needs).

I've also thought that even if air exchange wasn't needed, air circulation might be needed. My thinking being that one of the things AP people seem to tend to do to help oxygenate their air is to "spray/aerate" it in some fashion back into the fish tank. Well if anything related to oxygenation is occurring over the top of the fish tank where presumably a lot of that CO2 will be surfacing, that may be air with a low oxygen content being mixed back in - also, that valuable CO2, is over top the fish tank, not necessarily in the growing section where it's needed. Hence I can kind of see the whole circulation thing going on - particularly if the circulation helps to stir up the water and aid aeration in some fashion in the process.

Hence my questions about air exchange and circulation. So, what are your thoughts guys/gals? I'm sure all of you have a lot I can learn from you.

Thanks!!

Gene

Remember that plants only use CO2 during the day when they are getting sun and photosynthesis is taking place. At night, plants us O2 and give off CO2 just like us animals. (This is why fish gasping at the surface for O2 is more common around dawn, the algae has been using the O2 and giving off CO2 overnight.

I don't think most of us have been paying much attention to extra CO2 for plants and most of our fish tanks are not so heavily stocked that the air over them is going to be O2 depleted just by being over the fish tank. We are also usually not spraying the water super fine into the air. In general spraying the water back into the fish tank is to break the surface tension of the water and allow as much gas exchange as possible.

Well that was a bit of a howler... apologies... no idea what my tired over-extended brain was thinking when I posted that...