Controlling Grow Room Odors
deally, use a 2-prong approach for the best results. This entails running an ozone generator and an exhaust fan with a carbon filter.
You can run carbon filters in a couple of different ways.
1. First, is pre-exhaust where you need to exhaust heat (and / or humidity) from the grow room. In this setup, the carbon filter goes into the grow room, where air is drawn first through the filter, then exhausted out of the room. The size of the filter has to be matched to the size of the fan so that the air going through the filter has enough contact time with the carbon to do it's thing. If you pump the air through the filter too fast, the carbon can't do it's job. So, depending on how much heat you've got to remove, you first determine the necessary fan size, then pick the correct filter for the fan. With the right fan/filter combo, all of the air being exhausted will be clean enough of organic fertilizer odors to blow directly outside (or into your house in the winter to utilize the heat and high quality oxygen rich air).
2. The other way to run a carbon filter is to simply connect the fan to the filter and put it into the area that you're concerned about with no ducting. This is called "polishing" the air and a larger fan with more air movement can be used because the air is being repeatedly drawn through the carbon filter. With this approach, the larger the filter and fan you choose the better.
Overkill is a good thing!
CFM (cubic foot per minute) FOR AIR MOVEMENT:
The air movement (or CFM) isn't the only important part in matching the fan to the filter. It's also the 'pressure' of the fan's output. If you were to run a squirrel-cage type fan on a carbon filter (or an in-line duct fan, or an axial computer fan), they won't have the same torque as a centrifugal fan, so the CFMs aren't the same when you restrict the air movement with the carbon filter. It's hard to get a good match between different types of fans with the carbon filters but it can be done. It's just kind of a hit/miss approach to find the correct air movement with a fan other than the sizes that the manufacturers recommend.
As for the air movement, you can push or pull through the filter, and it will work just as good either way, but in the long run you want to pre-filter the air to get all of the dust out before the air enters the carbon filter. The CAN filters come with a white poly outer pre-filter to remove all of the dust before it can create dust pockets in the carbon. If the dust is allowed to enter the filter (without the use of a pre-filter), it creates pockets of dust that promote bacterial growth, and this bacterial growth limits the overall life of the carbon. So, a pre-filter is important either way whether you push or pull through the filter.
Ozone use for odor control has a long list of pros and con's, but one of the good things is that itkills bacteria, not only in the growroom, but in the exhaust fan and carbon filter. So, if you've got an ozone generator treating the air in the room before it enters the carbon filter, it will kill the bacteria that can limit the life of the carbon.
This dual approach, using ozone and carbon (filter) to deal with your organic fertilizer odor issues is probably the best overall approach if money isn't an issue.
Here's a list of some ozone pros:
Removes all odors from the air very effectively.
Creates an environment that spider-mites don't like (it won't get rid of a problem, but it will help keep spider-mites from getting out of control).
Controls mold and powdery mildew both on plants and in the room.
Here's some con's:
It's so effective at removing odors it can affect the flavor of your produce, or the aroma of flowers.
Supposedly it's not healthy for our lungs to be exposed to ozone for prolonged periods of time.
Ozone has a half-life of about 15 minutes, meaning that if you plug an ozone generator into a timer that runs the generator 15 minutes on / then 15 minutes off, you've still got 100% ozone enriched air. I'd recommend taking this timer approach to ozone, running it for as little as possible. This way, you've got minimal effect on your plants, and your lungs.
Air polishing lets you clean the air without chemicals or outside venting. Learn more about it here.