105+ temps - exhaust design issues?

[SmokinErb22]

Not sure what the issue is. In theory, this should more than suffice.

Ambient temps ~ 60f +/-

Flower cabs(x2) - 4 x 4 x 6.5 = 104 cu ft (2) = 208 cu ft to be exhausted.

870 cfm exhaust. Assume 50% CFM lost with carbon filter = 435 CFM. And I doubt I'm actually losing 50%, less than 10ft duct runs.

435 cfm / 208 cu ft = 2x per minute air exchange.

2x 400w bulbs, stacked vert. 50w/sqft, to give an idea of bulb heat output.

The small utility chamber on top of my veg cab houses all of my fans and ballasts. It works on the vacuum it creates. I see all runs going to the utility chamber as intakes, so I doubled 'em up and ran two "exhausts" and two intakes to minimize drag - I have two 6" duct runs for each 6" exhaust fan as per the normal standard of 2:1 passive intake to exhaust ratio.

I imagine I have closer to 3x per minute air exchange, but regardless 2x is more than sufficient and is what DHF and many others constantly preach. 50w/sqft, 2x per min exhaust. This whole cab was designed around that very concept. I recently spent nearly $1k on adding a second light and fan, only to be shocked to see my temps rise to 112f, and then level off around 102-105. They actually got up to 125f while I was in the process of installing it and the face cover of the utility cab was off, thus no vacuum. This is way too hot and a pretty significant (~30f) jump in temps.

I'm not sure if its a design issue with my duct runs or what? Should I add a 3rd run from the vacuum to each flower cab? Should I seal one off?

 

[SmokinErb22]

I should explain my design a bit. The reason I opted for the vac chamber is because it was initially a 6" and a 4" fan exhausting both cabs with 400w each. It was sufficient for mid 70's temps.

Probably gonna try and fit the 4" back in there, but I'm not sure it'll fit.

Edit:

It appears that *part* of the problem is I need a new thermometer. It was reading 103 when I checked on it with only 400w, wasn't even warm in there. Blew on it a few times and it started dropping Got down to 78 before I fired up the 2nd light again. Gonna let it warm up and see where we're at again.

If temps are too high, my solution is going to be to add another passive run for each cab and see what happens.

 

[SmokinErb22]

Left it running two bulbs overnight - with my digital and a second analog thermometer - both showed readings of 86f, and that "feels" about right.

But when I did post this, I was running from 103-112, and the cab was obviously radiating massive amounts of heat.

Thanks for stopping in, anyway!

 

[tokersmoke]

i am building a room and was trusting a thermometer that read ten degrees off.After i purchased a better thermometer i felt very foolish.def have to have a high quality thermometer.i have three different ones at the moment and they all read different.The one thermometer reads ten off is on a alarm clock.the other two are cheapos from the hydro store and read 2 degrees apart?

 

[dank.frank]

http://www.bhphotovideo.com/c/product/43102-REG/Doran_DOL1212_L_1212_Light_Tight_Darkroom.html

Put one of these in the side wall on each of your flowering sides...bringing in better passive air flow with less resistance and still remaining light tight.

You should certainly have enough air flow...but perhaps the air you are bringing in isn't cool enough to drop the temps accordingly anymore...ie exhausting heat raising ambient temperatures.


dank.Frank

 

[frankenstein2]

These temps are without any plants in there? I ask because the temps will change with some plants in there. Also where is your thermometer located. I like to keep mine right at where the top of the canopy is/will be. Then I know what kind of temps my tops have to deal with. How are ya gonna keep it regulated when it get's warmer outside?

 

[SmokinErb22]

DF - air being pulled in is about 60f. I've had my eye on some of those for a while, its extremely difficult to pick and choose what to upgrade each time,but they are definitely on the list.

I'd like to set up one 6" to each flower cab with a climate controller for my fans to keep the lights off temps from getting so low. These along with those darkroom intakes should be my next upgrade.

Frankenstein - temps are with plants in cab. I typically keep my temps in the room where my cab is no more than 70 year round, usually closer to 65. Temps are measured at canopy. I'll be getting a couple new thermometers with probes after work today.

I'm just confused as to why, for several hours my cab was obviously too hot only to cool down 20f hours later with no change to any aspect. It climbed from 75 to 112 and, despite a flawed thermometer, you could feel it was significantly warmer in there. And then cools down for no apparent reason?

Either way,holding steady right now at 85, with no changes to anything.

 

[SmokinErb22]

i am building a room and was trusting a thermometer that read ten degrees off.After i purchased a better thermometer i felt very foolish.def have to have a high quality thermometer.i have three different ones at the moment and they all read different.The one thermometer reads ten off is on a alarm clock.the other two are cheapos from the hydro store and read 2 degrees apart?

I usually keep two different thermometers in each cab. Really good idea to do so IMO, so long as they read fairly close to each other a degree or three doesn't bother me much.

 

[dank.frank]

Were you home when the temperatures spiked?

I gather you are using an A/C in the room you cab is in to keep ambient temperatures in check then?

If so, is there any reason the A/C could have shut off for a period of time resulting in a rise in the temps?

The other thing I was considering is as the ballasts warm up after being on for extended periods of time - however, with you running flip-flop I suppose that really isn't a variable because the ballasts are one constantly...



dank.Frank

 

[SmokinErb22]

I use an ac in the summer months, but right now my temps stay pretty stable without it running. It's in my garage and my cab acts as a heater keeping temps pretty consistent. 800w running 23 hrs a day (30 min downtime for each flip, digital ballasts) and 4ft 6 lamp t5 on 24 hrs daily. Hasn't gotten colder than 59 in my garage and no warmer than 63.

In really cold months I have a 5kw heat exchanger I run to keep temps up (an extra $175/mo elec!!! More than my entire grow). Summer months a 12k btu doesn't let temps go over 70.

All of my investments in the near future will be environment control items. I want a lung. Badly.

 

[SmokinErb22]

New thought. Brand new fan and filter. The filter specifically. I'm wondering if it wasn't clogged with dust and took a while to work it all out?

 

[dank.frank]

At most you are looking at roughly a 15 - 20% drop in CFM from using a filter.

Then for every 25 ft of ducting another 7%. For every 90 degree angle figure another 4%.

"a filter at the maximum exhaust CFM rating has approximately 0.7 wg. pressure drop"

All this info taken from the can-fan website...



dank.Frank