Hello fellas, In a room that is 3,5m x 3,3m x 2,9m I have decided to use an extractor fan that will be around 2000 m3/h. I will also use a carbon filter to this. This area will have nine 600w HPS lamps. Can someone help me out on chosing the right size for an intake fan in m3/h or explain to me the right way to calculate it myself? Kyriakos
You don't need an intake fan unless there's absolutely not enough "leakage" to function by passive. An underpressure system is a GOOD thing. However, if you still want the calculations, it's easy enough...calculate the volume of your tent, calculate the volume of air moved out by the exhaust fan every minute (usually already given on the box, no need to do math). If you're trying to balance pressure, you want to move the same volume. Unless there's overpressure building, it will naturally balance. You are aware that that's an 1166 CFM/33M^3/Minute fan you're talking, right? And you only have 33.5 M^3 total volume? Total air exchange in about 1 minute 1.5 seconds. Hurricane force winds at intake and exhaust. Not good for plants exposed directly to it. A smaller tent manages full exchange once a minute with farrrrrr less volume of air being moved, so the force of the wind is a lot lower. That said, I run a pair of 745 CFM fans in a 5 by 10 by 10 foot setup, passive intake, and it keeps 2280 true watts under 75 degrees in there. I ran ONE of them, dialed down to about 90% (just under 700 CFM) in a 4 by 4 by 7 foot, passive intake in a tent kept indoors in a house I keep at around 72 to 74 degrees (F), where the tent had direct light from a window on it for most of the day, and not once did internal temps crest 80. Why I said passive...wind is high pressure moving to low pressure. Expansion/decompression cools (why a computer air duster can gets freezing cold as you use it). Create underpressure, the inside stays cooler, and the air that's drawn in wasn't compressed (heated) by a fan to blow it in. The air that is pushed in due to outside pressure being higher than inside expands rapidly, so it cools the area just by coming into it and expanding, quite a bit better than blowing compressed air that will have picked up heat compared to the outside air, due to compression. If you absolutely can't get enough air in via passive, go for lower pressure fans (wider outlet diameter to volume moved ratios--a 10 inch fan moving 50M^3 a minute does so with less pressure and windspeed than a 6" delivering the same volume, by FAR) that will move less air than the exhaust, to maintain the lower pressure situation inside the tent. The less compression at any point for air being released into the area, the lower the temp it's introduced at, the faster it expands upon entry (larger the pressure differential) the more it cools the tent. Then all you have to worry about is that the plants are getting enough CO2 in the process...since they grow as well outside Denver, CO as they do waterfront in WA state, 2ppsi, plus or minus a couple tenths of a pound per square inch isn't going to create a circumstance where there's "too little air for them to breathe".
Thank you for a very informative answer. Do you believe I would have problems with the heat from the lamps in this area? The intake air will be between 10-20 degrees celcius.
External air 10-20C? Honestly, I expect not. I could be wrong, but with an outside temp of 50-68 (F), and "target temp" ranges being "by the book" 70-80(F)/21-26.6(C), should be manageable. Pressure differential of 2.32 PPSI, suction over bulbs, household air at 73-74(F)/22(C), passive intake, and sporadic (couple times a week) "ghetto tricks" to augment CO2 while cooling, I usually easily stayed under 80(F)/26.6(C) in a 4 by 4 by 6 foot.