Need Grow Room AIR fLOW Advise

[herb4meds]

Room Size- 4'x10' 8' foot ceiling. Contents 3- 2'x3' ebb&flow trays ; 3- 400w hps lights ; 6" inline exhaust fan/ 18" active carbon scrubber on one end room ; 6" Fresh air vent on the other end ; 2- oscillating fans.
I will be growing 18 to 24 plants in the three trays. The fan is rated at 530CFM . With the drag from the scrubber I'm guessing closer to 400CFM. The room is 320 cubic feet. I will run the fan at 15 minute intervals on a timer. How many times during daylight hours do I need to exchange the air for maximum growth ?
The watering cycle is three times a day for 15 min. each on a 12 hr light cycle. 1st watering is 30 min. after lights come. 2nd watering at 6hr and 3rd watering at 11 hrs or 1hr before lights out.
I was thinking of running the exhaust fan at the same as the waterings, which is three times a day.
Will this be enough fresh air for 18 plants or should the fan run more? The room is insulated and sealed. The only fresh air will come through the 6" vent when the scrubber is on.
Is the best way to use a scrubber on the vacuum side of the exhaust fan? I have noticed growrooms usually have them set up this way on the inside of the room. Would you reccommend installing another fan in the fresh air vent to create positive airflow ?
I will have the room built this week and need your input asap so modifications can be made if necessary.

Tell me what you think; any problems you see or ideas to grow plants more efficient.

Thanks. I will send pics when I get it together.

[Muddy]

I think temperature control will be the determining factor in how much you run your fan. My veg light is only 150 watts and it can raise the temperature here in my 10' x 12' office by a couple of degrees. 1,200 watts of HPS is going to create a lot of heat. I wouldn't be surprised if you have to run your fan continuously.

Set your scrubber up so air is pulled, rather than pushed through it.

[herb4meds]

Thanks Muddy, I forgot to mention I have a 5000btu A/C to take care of the heat. I knew it would be a problem especially here in the South.
Also, I am having problems with the seeds I got from Jim @ dopeseeds.com . The Northern Lights and Short Stuff seeds sprout but will not come up. I have tried rockwool, peatmoss pucks, pearlite and potting soil. I still have the White Widow and Ak seeds but needed some advise before trying them.
I put the seeds in a small cup of water in a dark closet and usually in two to five days they sprout. With the strain I have grown for years, I just plant in peat pucks or rockwool and they come up in a few days. These are the first seeds I have bought and I can't get them to come up. After a couple of weeks the sprouts have rotted. I did get one of the short stuff seeds to come up but it died the next day.
Advise needed and appreciated.

[Muddy]

I've not used that method of starting seeds so can't comment on it. I use Rapid Rooters. Seeds go in the middle of the plug and the plugs go into a tray. A quarter of inch of water is added. I then cover with a clear plastic humidome and set it by the window. I also place a heating pad under it to keep the seeds warm. Usually in 2-3 days they sprout and in a week or so I plant the plugs into 4" square pots. My germination rate is usually around 90%.

If I'm understanding you correctly your's sprout but die after transferred to the peat or rockwool?

[darrmann]

I have a 10,000 btu and just cools a 5'x 20'x7' . with 6 600 watters. have exhaust and intake running full time. Exhaust is on a cooling thermostat but still dont shut off till lights out. Best thing to do is buy a cooling thermostat.

[herb4meds]

Thanks for the advise guys. I will try the rapid rooters with these new seeds. I have a cooling thermostat just didn't cross my mind to use it, thanks Darrmann. I always run the lights at night to help with the heat issue. I had hoped the a/c would take care of it but if not the thermostat should.