Negative Tent Pressure

[Zeez]

Hi Everyone, I need some advice. This is a 5x9 tent with two carbon filters, one recirculates, and one exhausts. They run on re-cycle timers. The portable 10,000 btu a/c and dehumidifier vent hot air outdoors. There is a third fan on full time that pulls outside air into the tent.

The problem is that there is always negative pressure in the tent and there is concern that the a/c and dehumidifier will not get adequate cooling from short supply of air. Should I just add another fan pushing air into the tent? Or, is there a better way to get this done? Thanks.

 

[bigganjabud]

Wtf a recirculation carbon filter?
What gave you that idea

ALL that aside all tents are supposed to have negative pressure as it stops botritis and also means the smell is getting taken out quickly rather than just stagnant air and odour mate

The recirculation carbon filter is a waste id swap with a desk fan

I ain't roasting you man

Seriously I'd do a bit more research if I was you bro look in the grow room design section

 

[bigganjabud]

Oh and from the diagram I'd swap the side the extract is on aswell

Ie opposite the intake

 

[Zeez]

The recirc fan through the second filter goes on for 20 minutes ever two hours. It keeps the smell down when exhausting through the other filter. It was pretty stinky outside until doing this and the ac exhausts unfiltered air. It works. A room with a mini split eliminates all this I know. Maybe some day.

 

[GOT_BUD?]

Wtf a recirculation carbon filter?
What gave you that idea

ALL that aside all tents are supposed to have negative pressure as it stops botritis and also means the smell is getting taken out quickly rather than just stagnant air and odour mate

The recirculation carbon filter is a waste id swap with a desk fan

I ain't roasting you man

Seriously I'd do a bit more research if I was you bro look in the grow room design section

Recirculating carbon scrubbers are fairly common, especially in a closed system.

 

[sdd420]

Negative pressure is good

 

[Chunkypigs]

View Image

Hi Everyone, I need some advice. This is a 5x9 tent with two carbon filters, one recirculates, and one exhausts. They run on re-cycle timers. The portable 10,000 btu a/c and dehumidifier vent hot air outdoors. There is a third fan on full time that pulls outside air into the tent.

The problem is that there is always negative pressure in the tent and there is concern that the a/c and dehumidifier will not get adequate cooling from short supply of air. Should I just add another fan pushing air into the tent? Or, is there a better way to get this done? Thanks.

it shouldn't hurt your appliances in there, if the pressure goes positive then you are forcing unfiltered air out of the tent.

why are you stressing on the smell now that we are legal here?
my house is a dank festival with 2 lights just harvested and drying.

 

[Zeez]

it shouldn't hurt your appliances in there, if the pressure goes positive then you are forcing unfiltered air out of the tent.

why are you stressing on the smell now that we are legal here?
my house is a dank festival with 2 lights just harvested and drying.

No stress really, keeping it on the down low. There was plenty of house dank here. Drying tent helped allot too.

 

[Raho]

Have a speed controller on the exhaust fan and adjust it until you have just the right amount of negative pressure you need, no more. Problem solved.

I love the hyperfan line, comes with it's own controller, cheap, light, quiet and powerful.

Fitered recirc is smart. Well done Zeez.
Cops aren't the only people interested in a house of dank.
Being discrete is always a good idea.

Doesn't your exhaust from the dehu send out "dirty" air?
Seems you'd be better letting your AC handle that heat.

Unrelated question, but have you built a filter box on your intake air to keep out mold spores, insects and other undesirables?

 

[Zeez]

I think you nailed it. Throttling air being pushed in to get the right amount of negative pressure would be optimal. All fans used so far get flat spots and are reliable only on full speed, a better controller or fan would fix that.

The recirc scrubber is the only way to go. It works. I have used several big filters on exhaust fans that do nothing more than share the dank. Both the dehu and a/c exhaust unfiltered air but the scrubber covers it. The hope was that a/c would handle the dehu job too, but a separate dehu was needed. Had to exhaust the dehu heat with the a/c heat. Maybe taking the exhaust carbon filter and making it a second recirc scrubber would be cool. There's plenty of exhaust with the Dehu and a/c.

On the intake air, I get a forced air furnace filter at Depot (dust and pollen) and cut pieces that get taped over the tube.

 

[OldPhart]

I had a couple questions and concerns. Is the room that the tent is sitting in a climate controlled and/or insulated room? I ask that because I was wondering why you don't run the ventilation full time. If you are venting the dehuy outside, you are using it for nothing more than a power eating, over priced, unfiltered exhaust fan.

 

[Zeez]

I had a couple questions and concerns. Is the room that the tent is sitting in a climate controlled and/or insulated room? I ask that because I was wondering why you don't run the ventilation full time. If you are venting the dehuy outside, you are using it for nothing more than a power eating, over priced, unfiltered exhaust fan.

That's a good thought. The deal breaker was the accumulating house dankness. Our clothes had dankness and it was too much. Running two big carbon filters in the tent, exhaust still has to go outdoors. Our house does have central a/c. The dehumidifier is a heat maker too. Prior to the dehumidifier, I saw night time tent humidity going to 90% due to transpiration. Guaranteed bud rot. I tried fans running on a humidistat to supplement and just couldn't get a handle on it. For anyone interested, this gizmo is great for monitoring temperature and humidity.

If there is some way to do what you say, I'm definitely interested.

 

[OldPhart]

Ok, so it is in a controlled environment, that is good. If it were me I would move the dehuy and AC both outside the tent. I would make both carbon filters into exhaust, and vent them back into the room the tent is sitting in, and run them both 24/7. I would take the out put of the AC and direct it to the intake of the tent, along with your current air intake. It wouldn't have to be a tight seal, because you will have a high neg. pressure; you are just trying to get the cold air to enter the tent to off set the heat load inside the tent, but you will probably need to open all of your lower air intakes for passive air intake. If balanced properly, the air coming out of the tent should be about the same as the room temp. Then your AC will cool/dry the air before it enters the tent again. I would try this and see if the dehuy is even needed. Basically I am describing a classic lung room. Given this setup, all air is filtered before leaving the tent, and the only air leaving the house is the AC exhaust.

This is just one idea, and I'm sure it would need tuning. There are many ways to set this up, I'm just a major fan of the lung room, and high air turn-over in the tent/box.

 

[Zeez]

I really like the concept and am not trying to be contrary, (don't take this the wrong way) but what about the control on the dehumidifier and a/c? They need to be in the tent for sensors to pick up the ambient temperature and humidity and then control? It would be possible run both on separate controllers which I already have.

 

[OldPhart]

First, you don't have to worry about offending me. Second, I wouldn't worry about the temp/humidity in the tent, because the air will only be in the tent about 20-30 seconds if you hit the type of ventilation I like to see. BTW, what is the CFM of the fan/filter combo? If the fan/filter can pull 150-200 CFM *each* out of the tent, you will hit the 20-30 second turn over that I like to target. Then I would just look to control the environment in the lung room. This will make for more stable environment, with less swing. But this will also create a nice day/night temp swing in the tent, by just maintaining the temp in the room.

 

[Zeez]

Right now using three 315cfm fans. They probably do less with the filters attached. I have a couple spares.

 

[OldPhart]

Right now using three 315cfm fans. They probably do less with the filters attached. I have a couple spares.

Oh crap, I can't do simple math today. I started thinking about those numbers and it wasn't coming out right. So I broke out the calculator, and sure enough, I was off by a factor of 2 somewhere. The volume of the tent is somewhere around 300 CF, so with 2x315's w/filters, I would guess you are getting somewhere around 300 CFM. 60 seconds/exchange isn't bad, I usually like to overkill things though.

Maybe some people that have more experience will drop some information on us both, I hate giving random advice about what has worked for me, as it may not work in different situations, such as the portable AC.

This has been my go to cooling method, but I only run a 600w in a 40"x40" box. I just take that flex duct, and point it at the air intake at the bottom of the box, then vent out the top. I find that the air coming out the top of the box, is about 1 degree below the room temp, but if you put a sensor at canopy level, it is almost exactly room temp due to the radiation from the light. I have ran this combo with 5000 btu with a 600w box, to a 12000 btu with a 1800w box and have had great results. But there is normally a little tuning to be done.

At least I think I may have given you some different ideas. I haven't looked, but I bet there are threads here about using a lung room, they are great for stability and odor control.

 

[Zeez]

The dehumidifier is outside now. I can see where this was a huge mistake. Thanks. On to the a/c, It is working out very well with the dehumidifier outside the tent. The dry air being pumped in form the dehumidifier is replacing the hot exhaust air going outdoors from the portable air conditioner still in the tent. I'm thinking that may be enough flow through and that both carbon filters could be scrubbers for the unfiltered a/c exhaust. This would have to be reconfigured for winter mode.

What do you think?

 

[OldPhart]

If it works, it works, there is not a single 'right' answer. At least now your getting some benefit of the dehuy, and lowering the air exchange in your house, your central AC will thank you for that.

Of course things will have to change for the winter, or for those 65 degree days at the end of July, crazy ass weather!

Edit, it is actually 56 degrees at 3pm .. thinking about turning on a portable heater, but refuse to, just because it is july.

 

[Zeez]

Really good advice. Thanks. I was using an old dehumidifier that was cranking out hot air and thinking that it was like the a/c with a hot side and a cold side. Dumb mistake.