M
Mr. McGregor
- 11
- 0
I’m trying to finalize my box design. I’m using a compendium of source material which includes Can Fans specs, an airflow spreadsheet downloaded from an HVAC consultants web site and a rather exhaustive thread on ventilation 101 from ICMag.
3 x 4 x 6 ft grow box. 600W vented hood w/ 6” duct openings. Add’l equip is centrifugal fan, using say 85W
Using the formula “Total watts x 3.16 /20 or 30 suggests that I need between 72 and 108 cfm to remove the heat.
Using can fan specs the 4”HO fan w/ 9000 filter combo results in filtered air of 114 cfm. Using 2 90^ bends adds 0.23” of add’l resistance for final air exhaust of 94 cfm. Probably OK since my box is in the basement where the ambient tend to run about 65^.
First uncertainty: Can filter 9000 specs show max exhaust cfm of 55 cfm @ 0.1 sec contact time. Since I’m exhausting 70% more I’m wondering if I’ll have an odor problem.
Can-Fan 4" HO w/ Can33 filter plus ducting results in 114 cfm. Maximum exhaust for can 33 is 200 cfm so I’m plenty good there but more expensive. Also I’ve read that more than one air change per minute is stressful to plants.
Second uncertainty: My hood has 6” ducts. In order to connect to 4” fan I have to use a duct cap w/ 4” flange attached resulting in an abrupt reduction in duct size. I can’t use reducers due to space constraints. Will the abrupt change in duct size affect exhaust cfm, if at all?
A 6" fan just seems to be way more capacity than necessary.
I see all kinds of design criteria, some conflicting. But I rarely see any empirical data on these types of set ups. I have enough money to do it right just not enough to do it twice. So, all comments and criticisms welcome.
Regards,
MM
3 x 4 x 6 ft grow box. 600W vented hood w/ 6” duct openings. Add’l equip is centrifugal fan, using say 85W
Using the formula “Total watts x 3.16 /20 or 30 suggests that I need between 72 and 108 cfm to remove the heat.
Using can fan specs the 4”HO fan w/ 9000 filter combo results in filtered air of 114 cfm. Using 2 90^ bends adds 0.23” of add’l resistance for final air exhaust of 94 cfm. Probably OK since my box is in the basement where the ambient tend to run about 65^.
First uncertainty: Can filter 9000 specs show max exhaust cfm of 55 cfm @ 0.1 sec contact time. Since I’m exhausting 70% more I’m wondering if I’ll have an odor problem.
Can-Fan 4" HO w/ Can33 filter plus ducting results in 114 cfm. Maximum exhaust for can 33 is 200 cfm so I’m plenty good there but more expensive. Also I’ve read that more than one air change per minute is stressful to plants.
Second uncertainty: My hood has 6” ducts. In order to connect to 4” fan I have to use a duct cap w/ 4” flange attached resulting in an abrupt reduction in duct size. I can’t use reducers due to space constraints. Will the abrupt change in duct size affect exhaust cfm, if at all?
A 6" fan just seems to be way more capacity than necessary.
I see all kinds of design criteria, some conflicting. But I rarely see any empirical data on these types of set ups. I have enough money to do it right just not enough to do it twice. So, all comments and criticisms welcome.
Regards,
MM
