Return Air And Co2? Hvac Guys

Slowitdown · Dec 16, 2014

Whats going on everyone! So, I got a room that about 2000 sq ft. It has two rooftop AC units that have the return air duct in the room. I was told that the return air is pulled and goes in a circle and right back in the room meaning the air in the room is the same. Basically, I am running CO2 in this room and ran through a 20lb tank in 24 hours. Obviously, the air being pulled out of the room is going outside somehow because the tank didn't last at all. Is the return air really pulling out of the room and dumping the same air in? If so why am I losing all the co2?

Natural · Dec 16, 2014

some of those all-in-one RTU's are designed to use partial outside air to freshen the workspace. some of them use 100% outside air, with no return air at all .

fishwhistle · Dec 16, 2014

Maybe your not losing it,Sounds like your regulator is constantly on to blow through a tank in 12 hours (should only run at lights on) but 2000 sq ft is alot of space,my rooms are only 150 sq ft ea sealed and i use a 20lb tank every 5-7 days so for 2000 sq ft your not doing bad at all.In a room that big id think you might have a few bottles going in different parts of the grow.What PPM are you trying to achieve and does your room ever reach that point all over?
Post in cannabis johns AC thread and he will give you the low down on the return air.
https://www.thcfarmer.com/community/threads/grow-room-a-c.46645/

Slowitdown · Dec 16, 2014

fishwhistle said:
Maybe your not losing it,Sounds like your regulator is constantly on to blow through a tank in 12 hours (should only run at lights on) but 2000 sq ft is alot of space,my rooms are only 150 sq ft ea sealed and i use a 20lb tank every 5-7 days so for 2000 sq ft your not doing bad at all.In a room that big id think you might have a few bottles going in different parts of the grow.What PPM are you trying to achieve and does your room ever reach that point all over?
Post in cannabis johns AC thread and he will give you the low down on the return air.
https://www.thcfarmer.com/community/threads/grow-room-a-c.46645/

My tank is connected to a regulator, the regulator is connected to a Helios CO2 controller (Atlas 1) which is set at 1500 ppm. They are also connected to a timer for when the lights turn off even though my Atlas 1 has a photocell so it turns off when lights off anyway. So, it can not be that. I have another sealed room about 400 sq ft where a 20 lb tank on the same setup (helios, regulator) will last me over 3 weeks.

Slowitdown · Dec 16, 2014

Natural said:
some of those all-in-one RTU's are designed to use partial outside air to freshen the workspace. some of them use 100% outside air, with no return air at all .

Neither of my units bring in outside air. If that was the case I would of never put the return ducting in the same room.

Natural · Dec 16, 2014

Slowitdown said:
Neither of my units bring in outside air. If that was the case I would of never put the return ducting in the same room.

you had these units installed or someone gave you the specs on existing? A pix or model number would help. Sometimes there's a small port that "mixes" in fresh air..other ones have what is called an economizer..uses dampers to regulate mixed outside air in as a fuel saver. If you have none of those..you have fan coil unit..basic bare bones filter, coil, and blower.
Hard to say anything certain without knowing what the unit actually is. Other than that..is there a duct leak somewhere..or the air handler covers loose? Bad CO2 regulator? That's about all I got

sixstring · Dec 16, 2014

If its a newer unit it probably has makeup air coming in somewhere.here in michigan makeup air is code and they are getting really bad about how big and how close to the air handler it needs to be.its more for the combustion side of a handler or furnace, but maybe your rooftop unit has it built in somewhere? Unless the fans or air handlers are inside the room I doubt its airtight, much like a window shaker where they exchange some outside air.

Slowitdown · Dec 16, 2014

Natural said:
you had these units installed or someone gave you the specs on existing? A pix or model number would help. Sometimes there's a small port that "mixes" in fresh air..other ones have what is called an economizer..uses dampers to regulate mixed outside air in as a fuel saver. If you have none of those..you have fan coil unit..basic bare bones filter, coil, and blower.
Hard to say anything certain without knowing what the unit actually is. Other than that..is there a duct leak somewhere..or the air handler covers loose? Bad CO2 regulator? That's about all I got

I had the two rooftop units installed new. One of them is 4 tons the other is 3. I will have to find out the model # and stuff or take pics to show. My hvac guy who installed them is the one who told me the air in the room is sucked out cooled and then dumped right back in like its going in a circle but never leaving the room. That could be a duct leak like you said or the regulator could be bad. The regulator is brand new but I was thinking something when I hooked it up to a fresh tank and it said the gas in it was low. I am not fully sure though. One of the units looks like this -

Slowitdown · Dec 16, 2014

sixstring said:
If its a newer unit it probably has makeup air coming in somewhere.here in michigan makeup air is code and they are getting really bad about how big and how close to the air handler it needs to be.its more for the combustion side of a handler or furnace, but maybe your rooftop unit has it built in somewhere? Unless the fans or air handlers are inside the room I doubt its airtight, much like a window shaker where they exchange some outside air.

It is a brand new unit. Not sure if it has makeup air coming in I will ask my guy tmw. This was my whole issue with putting the return air ducting inside the actual room. I personally wanted them on the outside of the room but my guy said it has to be inside so it can suck up the hot air and the unit doesn't work to hard.

Natural · Dec 16, 2014

sixstring said:
If its a newer unit it probably has makeup air coming in somewhere.here in michigan makeup air is code and they are getting really bad about how big and how close to the air handler it needs to be.its more for the combustion side of a handler or furnace, but maybe your rooftop unit has it built in somewhere? Unless the fans or air handlers are inside the room I doubt its airtight, much like a window shaker where they exchange some outside air.

I've seen those in a restaurant I built..for the grill hoods..man those hoods can steal your hat. Make-up is mandatory. Alot of the older units use fresh air..the bigger the unit the more likely it does. The new Fan Coil Units are pretty slick..even on the furnace side..you can use 4" double stack and can be inside with absolutely no make-up at all.
I think the answer here is that he's gonna need some big mini-splits if he wants to keep that CO2.

Natural · Dec 16, 2014

Slowitdown said:
I had the two rooftop units installed new. One of them is 4 tons the other is 3. I will have to find out the model # and stuff or take pics to show. My hvac guy who installed them is the one who told me the air in the room is sucked out cooled and then dumped right back in like its going in a circle but never leaving the room. That could be a duct leak like you said or the regulator could be bad. The regulator is brand new but I was thinking something when I hooked it up to a fresh tank and it said the gas in it was low. I am not fully sure though. One of the units looks like this -

That unit you linked has an economizer with option..meaning you might have that engaged, letting outside air in. I would call them in the morning..I'm sure it will help.

sixstring · Dec 16, 2014

Natural said:
I've see in a restaurant I built..for the grill hoods..man those hoods can steal your hat. Make-up is mandatory. Alot of the older units use fresh air..the bigger the unit the more likely it does. The new Fan Coil Units are pretty slick..even on the furnace side..you can use 4" double stack and can be inside with absolutely no make-up at all.
I think the answer here is that he's gonna need some big mini-splits if he wants to keep that CO2.

Yeah or like you and he both mentioned, maybe that co2 controller is bad

Slowitdown · Dec 17, 2014

sixstring said:
Yeah or like you and he both mentioned, maybe that co2 controller is bad

I was thinking lets say the controller is bad. If the controller is bad it is just releasing the co2 into the room non-stop. If the room is not losing CO2 due to the AC then the co2 is still in the room. Basically, I have a manual CO2 tester that shows how much PPM is in the room. Next time I will test it out and figure out if it is the controller.

Canalchemist · Dec 17, 2014

How high are the ceilings in your 2000 sqft grow, and is this your first tank, is your space completely sealed from top to bottom for sure. If it is your first tank you will need to saturate the entire volume of air in your grow space. Any wholes or leaks near the first few feet of the floor will leak like a bucket with holes in it.

Your other space 400 square foot 8 foot ceiling 400 x 8 = 3200 cubic feet 1 tank 21 days

Your current large space 2000 square foot 8 ceilings 2000 x 8 = 16000 cubic feet 16000 / 3200 = 5 so you should be using 5 tanks in the same time frame that your 400 sqft uses 1, and for every 1 foot of ceiling height over and above 8 feet you can add another a little over 2/3rds of a tank every three weeks.

You should be going through a tank every four days

Or everything is okay and you have no leaks and you are growing in an area with 30 foot ceiling's ;)

sixstring · Dec 17, 2014

yeah but 2000 sq ft of 8 inch cuts wont eat co2 like 2000 sq ft of 5 foot tall flowering plants so those time frames are really gunna change alot.
@Slowitdown i would def try that hand held co2 meter to see what the controller is doing.

Slowitdown · Dec 17, 2014

Canalchemist said:
How high are the ceilings in your 2000 sqft grow, and is this your first tank, is your space completely sealed from top to bottom for sure. If it is your first tank you will need to saturate the entire volume of air in your grow space. Any wholes or leaks near the first few feet of the floor will leak like a bucket with holes in it.

Your other space 400 square foot 8 foot ceiling 400 x 8 = 3200 cubic feet 1 tank 21 days

Your current large space 2000 square foot 8 ceilings 2000 x 8 = 16000 cubic feet 16000 / 3200 = 5 so you should be using 5 tanks in the same time frame that your 400 sqft uses 1, and for every 1 foot of ceiling height over and above 8 feet you can add another a little over 2/3rds of a tank every three weeks.

You should be going through a tank every four days

Or everything is okay and you have no leaks and you are growing in an area with 30 foot ceiling's ;)

Ceiling are about 15 ft this is the second tank. This room was designed for the seal. We spent a lot more money and time to make sure it is sealed (as much as you could I mean it is not a bank vault) If I went through a tank every four days that would be fine but they are done in 12 hours. I am going to do that test with the manual meter and let you guys know.

sixstring · Dec 17, 2014

Grow room area: 30000 cubic feet
Amount of CO2 required: 36 cubic feet
On time: 216 minutes

At this flow rate:10
If you are using a 20 pound CO2 bottle with a regulator, it will last 17.5 hours.
If you have a CO2 Generator a 5 gallon propane tank will last 54 hours.

that^^^^ was just done using a flow rate of 10 on the regulator,so its saying you will run out in 17.5 hours and i had it set to 1200ppm added.
heres the link to the calculator https://www.hydroponics.net/learn/co2_calculator.asp

Canalchemist · Dec 17, 2014

15 foot ceiling you can expect a tank in 2 days, as long as the plant count is the same as in the 400 square foot room, see what I am saying.

sixstring · Dec 17, 2014

basically i think your gunna need alot bigger bottles :) this is something i would talk to texas kid about,i seen he was using like 50# bottles all tied together.

Canalchemist · Dec 17, 2014

I based my calculation on the fact that his 400 sqft room I am guessing is a 8 foot ceiling, guessing he setup up the CO2 the same as his other room

Return Air And Co2? Hvac Guys

Return Air And Co2? Hvac Guys

Slowitdown

Natural

fishwhistle

Slowitdown

Slowitdown

Natural

sixstring

Slowitdown

Slowitdown

Natural

Natural

sixstring

Slowitdown

Canalchemist

sixstring

Slowitdown

sixstring

Canalchemist

sixstring

Canalchemist

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