Dark Room Louvers: Worth the money?

[messn'n'gommin']

Essentially, yeah. The formula is used to figure how much fan you need for what temp you want inside the growroom. The total lamp wattage multiplied by 3.2, is then divided by that difference to figure the fan CFM. I don't think it is all that exact because of all the possible ways a room can be set up, but, I do believe that it will be close enough for government work!

I took the inside temps at just above the shadow line of the reflectors. For a more accurate number you could take temperature measurements at various places and average them out, but, I'm a lazy bastid

Namaste, mess

 

[petemoss]

Essentially, yeah. The formula is used to figure how much fan you need for what temp you want inside the growroom. The total lamp wattage multiplied by 3.2, is then divided by that difference to figure the fan CFM. .....

Namaste, mess

The problem with that formula is that it assumes you are using a non-air cooled light. Most people with bigger lights (250 watts and up) have some form of air cooling for their light. So to use the formula for an air-cooled light, you need to substitute the Watts figure with an effective watts number. For instance, you have a 600 watt light in an air-cooled hood. If you use 600 watts for the total lamp wattage, you'll get a CFM number that is too high. You have to use a lower figure such as 200 watts (assuming your air-cooled light gives off as much heat as a bare 200 watt lamp). Here's a nice table based on the heat transfer equation:
http://www.greenpassion.org/f45/what-size-vent-fan-do-i-need-intake-area-size-3704/

 

[guest 77721]

I found some info on louvers that came with a matched fan and spec's. The fan was pulling 1/2 rated airflow so I'm assuming the louvers block at least 1/2 the airflow and require double the area of unblocked intakes.



This chart is pretty useful. It's the CFM=(3.2 * Watts)/delta T formula. I use it as a diagnostic tool to calculate actual CFM. If you know the Watts and you can measure the temperature rise from ambient, just look up the chart and there's your effective CFM.

I can tell with these two values if someone's box is working properly. You need to take temperature readings in the exhaust duct on the fans as a starting point as well as the temp rise in the cabinet.

Petemoss is dead on that the chart gives high numbers for air cooled lights. What it does give you is the air flow rate for the exhaust through the light box. With an aircooled light the majority of the heat is taken away but you don't need 10*F cooling on waste exhaust. I have found using 1/3 of the calculated airflow gives the same as 100% using a bare bulb. Who cares if the exhaust is 20*-30*F higher. An airchange of 3-5 mins gets rid of the radiant heat.