Ask Erik: September, 2009
I just read your article titled Grow Room Construction 2004 from an old issue of Maximum Yield and it’s amazing. But, you didn’t talk at all about the relay system. Do you still think CEA is best served by that flip flop method? How do you deal with CO2 levels not getting too high in the side where the lights are off? I understand having small 250 cfm fans blowing into the lung, creating negative pressure, but does that not draw air in from somewhere else? Where do you recommend I seek two of those things that stopped air entering the dark side? Can vegetative CO2 levels really go to 4000 ppm?
Thanks a lot,
Matthew Mint
Matthew,
Glad you enjoyed the article. It’s nice to get a question to see if my thoughts have changed on a subject. In this case, I think the non-relay set-up makes for a more straightforward installation (one big grow room versus two rooms), but the relayed set-up is most efficient.
Yes, 4000 ppm of CO2 can be used. This is a relatively high concentration, and should be lowered when people are entering the area. The plants will grow at an accelerated rate provided other growing parameters are in check, i.e. lighting, temperature, nutrients, moisture, etc. High CO2 levels can be maintained throughout flowering, but are best lowered (1500 ppm) a couple weeks before the anticipated date of harvest.
In CEA (controlled environment agriculture) three rooms are used. Two rooms are for growing and a separate or preferably larger room will act as the “lung.” The lung should be located between the two independent sealed growing areas. In this room, the air is cooled, scrubbed, de-humidified and enriched with CO2 (carbon dioxide). The air from this room is vented into the active growing room. It is also discharged from the active growing room back into the lung. When the lights “flip” into the other room, the air from the lung is "flipped.” Instead of the air from the lung going into and drawing from room “A,” it is now going to and being drawn from room “B.” This is most often accomplished with electric dampers (“gates” in ducting) and relayed fans. For specifics, consult with your hydroponics retailer or an HVAC technician.
The relayed CEA is more efficient because:
- the ballasts run for 24/7
- only one A/C is required
- environmental equipment can be serviced away from the growing area (no interruptions of dark periods)
- more space for growing; environmental equipment does not need to be located amongst the crop
- fewer appliances to install; two rooms typically requires two times the equipment (versus non-relay)
Hope this helps.
Cheers, Erik
