Dystopia
Active Member
Grownavy1091Mostly that sounds perfect. i was just hearing alot of mixed talk about the cooltube acting like a magnifying glass and burning the canopy of the plants, but I think that the cool tube will be perfect. Quick question for ya, do I need 2 inline fans? Or can I just use 1? I'll be growing in the growlab 120 3' 11''x3'11''x78''. I hope the 400W HPS covers enough ground for the 4-5 plants I'll be doing. I apologize for all of the questions, this ventilation thing is kicking my butt. I really want to go with the 400 Watt for the Stealth Hydro dual spectrum setup, but I want to have it properly ventilated, feel me??
If you go back to Post 308 on page 31 (https://www.rollitup.org/dwc-bubbleponics/220083-bubblehead-gang-31.html) you’ll see I diagrammed out two options for ventilation: 1) ventilate light and tent through one fan; or 2) ventilate light and tent separately using two fans.
Option 1 will work, option 2 is more efficient.
Sizing the fans depends on which option you choose. I’ll show you how I now figure fan sizing:
First, figure the minimum size of the fan using this formula:
Vrate = (3.178 x W)/(T2 - T1)
Vrate is in CFM (required size fan)
W is in watts( bulb)
T's are in degree F. T1 = inlet temperature, T2 = what you want tent temperature to be.
So let’s say you’re using a 400 watt HPS, your inlet temp is 72* F, and you want your tent to run at 80* F.
Vrate = (3.178 X 400)/(80 – 72) = 1271.2/8 = 159 cfm
So a 159 cfm fan is where you start.
Add 20% if you are adding a filter in line with the fan: 159 + (159 X .2) = 190 cfm
Add 5 – 20% for length of ducting, number of turns, etc. Let’s say you have short ducting with two turns, let’s add 8%: 190 + (190 X .08 ) = 205 cfm.
Add 25% if you live in a hot climate. 260 cfm.
So, if you’re going with option 1 (1 fan to cool light and tent) you would need, at a minimum, a 205 cfm fan if you’re living in a mild climate, 260 cfm in a hot climate. More is better, so I would go with like a 275 cfm fan.
If you’re going with option 2 (2 fans to vent tent and light), then you would split up the fans to equal 205 or 260. For instance, if you’re growing in a 4 X 4 X 7 tent, you have 112 cubic feet. If you want to swap out the air in the tent every minute (for the reasons I enumerated in post 308 ), you would need a 110 cfm fan. Add 20% if you connect a filter to that fan: 110 + (110X .2) = 132 cfm to vent the tent.
205 – 132 = 73 cfm; 260 – 132 = 128 cfm. That means you would need about a 75 – 130 cfm fan to cool the light. I would get two 130 cfm fans to vent the tent and light for option 2.
Hope this helps; I’m retired Air Force myself, always willing to help out a squid.