new room Ventilation ?'s

[inreplyavalon]

So i am setting up a new room that is going to be 13.5 x 13 ft. I have a couple vent dilemmas and was hoping someone could blow some fresh ideas into my repetitive thought circle.

The decision is whether to go sealed w/ CO2 or to you standard intake/outake.

I have way more experience with the later. The issue i am continuing battling in a intake/outake room is the fluctuation in temperatures of the outside ambient air. The temperature where i live ranges from 15f-55f in winter and 35f-95f in the summer. So just when i think i have enough airflow, the temperatures are dropping too low because the intake air at night is so cold.

I plan on running 8x600W in a 12x6ft footprint. leaving the rest of the room for equipment and such as i am sick of working in overcrowded spaces and also and following medical guidelines and that is all the space i am going to need to use.

So how can i supply enough CO2 to my room without the heat dropping into the sixties?

For the A/C options i wonder is there is an efficient A/C that i can run in the room and duct the air outside. Would that waste the supplemental CO2 by pumping it outside?

Thanks for the fresh ideas folks.

peace and blessings

 

[Vincent Vega]

You could go non-sealed, and set a thermostat to control your intake fan(s), or go sealed and run a window AC boxed in or a mini-split if you have the extra $$. You will most likely have to open up the window AC and seal any leaks with spray foam/caulk to minimize CO2/smell leakage.

"

I plan on running 8x600W in a 12x6ft footprint

Not sure how you plan on running all those bulbs in that space. That's enough bulbs to light up the whole area 12x6 area, with no walking space.

 

[inreplyavalon]

Thanks for the tips VincentV.

I am not very familiar with mini splits. I just looked them up and it looks like the cold generating part needs to be outside the room? How big is that part of these units as i would need to cut a hole in the ceiling and put it into an attic. Also would this not add positive pressure to a sealed room and in turn push some smell out of the room? Probably small amounts, just wondering.

As for the footprint and wattage, the room is 13x13.5 ft. So the wattage is for the 6x12 footprint within the larger room. Bout 3x3 ft per 600W.

 

[inreplyavalon]

What i don't like about having a thermostat control my intake is that if it is a perfect temp then the fan won't come on and will starve the plants of wanted CO2. i think...

 

[Lazyman]

Thanks for the tips VincentV.

I am not very familiar with mini splits. I just looked them up and it looks like the cold generating part needs to be outside the room?

Yes, make sure you get one that is inverterless and works in cold temps outside. Sanyo and Mitsubishi are very popular with growers for good reason.

How big is that part of these units

Usually about 2'X2'x2' high, and they often weigh 150-250 pounds and have a drain line, and require 240v power.

as i would need to cut a hole in the ceiling and put it into an attic.

Highly unlikely this will be feasible unless you're building a dedicated attic lung room just for the compressor. They pretty much have to be outside.

Also would this not add positive pressure to a sealed room and in turn push some smell out of the room? Probably small amounts, just wondering.

No there is no air exchange between the units. The interior part cools and recirculates the air in the room, perfect for sealed room /CO2 grows.

As for the footprint and wattage, the room is 13x13.5 ft. So the wattage is for the 6x12 footprint within the larger room. Bout 3x3 ft per 600W.

Sounds good, air cool the hoods if you can to reduce the strain on your ac.

 

[Lazyman]

What i don't like about having a thermostat control my intake is that if it is a perfect temp then the fan won't come on and will starve the plants of wanted CO2. i think...

Tstat control of intake or exhaust is the only correct way to grow, if you're running CO2 you should not be air cooling your room. It must be sealed and airtight to keep the CO2 in and reduce burn time or Co2 tank usage. This is where the forementioned AC comes into play. Can't have one without the other!

 

[Lazyman]

So how can i supply enough CO2 to my room without the heat dropping into the sixties?

Propane or natural gas fired Co2 generator, look up Sentinel and Green Air units.

For the A/C options i wonder is there is an efficient A/C that i can run in the room and duct the air outside. Would that waste the supplemental CO2 by pumping it outside?

Mini split or split AC are the best, some window units leak, and all portables do somewhat, even the dual hose ones. The single hose units are worthless.

 

[inreplyavalon]

Lazyman thanks for the info on the A/C's. It has been very educational.

I am trying to decide between a sealed room and a non sealed room. I understand that with a sealed room an intake and outake are not used.

The reason having my outake or intake on a tstat is problematic is because of the cold air outside this time of year. I am helping with a room that has 7200 non aircooled watts of HPS and having a ten inch intake has proved problematic. That much air is dropping the room temperature to the low sixties WITH ALL THE LIGHTS ON.

thats what i am trying to avoid, but the plants need their fresh air for natural CO2. Anyone have any ideas how to work out this dilemma?

Thanks!

 

[Some1uKnoOf]

You have a big problem with the temperature swings. I bet it fluctuates about 25 degrees from night to daytime, average. That's tough to overcome.

The best way to handle variable intake temperatures is with a variable speed fan that is hooked to a controller. The fan speed will crank up/down until you get the right temperature. The thermometer is not continuous control. It is either on or off, and there is no in between.

One way to do it is with a series of fans and a thermostat for each one. For instance, if it gets down to 70, all fans turn on and stay on. If it gets down to 65, one fan cuts out. If it gets down to 58, the next fan cuts out, etc. With this method, the main fans are all set to add more air to a common duct that goes to the room. As it gets cooler, the fans stops because you need to bring in less air.

The problem with this method is that it is tough to balance. You can do it but you have to know your numbers. It will get you a rough amount of air but you still need to adjust the final flow with a continuously variable fan so that you can keep temps right where they need to be.

I was never a big fan of the "air changes per minute" theory of CO2 replenishment. I think it is a rule of thumb that someone made up for small grow boxes. How can it make sense for the same plant and light to need a different airflow just because the box is 20 cubic feet bigger? I think someone just made it up and everybody else repeats it for lack of anything better.

If you use CO2, you really need to have a sealed room. The problem is that you need sooo much cooling for the lights that the CO2 is just swept out of the room as soon as it is released. There is too much fresh air coming in to allow any kind of control. This can be improved if you isolate the light from the room and then cool each area separately so that less overall air it pulled into the plant area. Still, it is pretty much a losing battle if you are going to do CO2 right.

If you run A/C, you MUST (I repeat, MUST) have the A/C vent the heat beyond the room. The hot side needs to be out of the room somewhere with lots of air circulation over it to move heat away. Options are through-the-wall units and split units that have two parts. It sounds like 4800 watts, so you aren't going to get away with the cheapo window units. You are going to need about 1.5 tons of air conditioner cooling power (not tons of weight, A/C units are measured in tons, with 1 ton being equal to ~3.5 Kwatts/hour)

One thing you could think about is sizing your cooling fans for the worst case temperature and then using a "lung" room next to your growing area. I don't know what a better name for it is, but a "lung" room acts like a lung. If the air from outside gets colder, you bleed hot exhaust from the the room into the lung room and it mixes with outside air to effectively warm it up. This decreases your overall outside air coming in and keeps you at the right temperature. Of course, you still have the problem of knowing just how much exhaust to allow back into the lung room to get the right temperature. The benefit here is that you always run your fans at the same speed and just use feedback of exhaust to control temperatures. Now, you just need a damper that can adjust itself to open/close and bleed back enough air. Rather than changing fan speeds, you just recycle some air to reduce the effectiveness of the fan.

You could adjust the amount of recycled air manually, but this means you have to be living in your grow house and checking the temps constantly to adjust in case outside air cools or warms. This is a pain to do and leads to problems when you forget.

A variable speed fan controller is the best choice if you vent your hot air outside. You have to get a controller that can handle the full wattage of your fan, or you have to use more than one fan and just run the second/third/fourth fans at 100% when temperatures climb. The controller only has to handle a relatively narrow range of load changes and the other fans are manually plugged or unplugged when weather changes. This avoids a larger and more expensive controller but means you need to visit regularly to activate the other fans when needed.


-SomeoneYouKnow

 

[deepforest]

got some q's about intake/exhaust room that should fit into this thread. i usally run sealed rooms so im all new to this. id just run sealed but pigs stole my equipment so i gotta make do:


i have 2 x 4" intake holes from outside drawing fresh air

havent cut the exhaust hole yet...

need to cool 4000w in winter, temps around 15-17 celsius outside

any idea how big exhaust fan i need? is passive 2x4" intake enough? also, i assume its the exhaust fan that is thermostatically controlled. i want to get one of those fancy fans that adjusts itself depending on the temperature of the air flow going through it!!! can fan makes a couple on smaller sizes i think, anyone know of a company that does them in 8"-12"?


to the OP: if you wanna run co2 just seal the room and get a good a/c unit. it sounds like you would be well off with a water cooled a/c unit cause then you don't need intake or exhaust holes, just water and a drain.

 

[Some1uKnoOf]

DeepForest,

17*C is equal to 63*F. Difference between 81*f and 63*F is 18*F. That's a decent difference.

The formula you want is CFM = 3.16 x watts / Tdff. That gives:

CFM = 3.16 x 4000 / 18

CFM = 702 CFM


If you use a 2x4" vent, that gives you 8 square inches, or 0.05555 square feet. You want to squeeze 702 CFM through that tiny hole? Good luck. Air will have to move through that hole 702 / 0.05555 = 12,636 feet per minute, or 143 miles per hour. I don't think that's going to happen and the noise would be terrible. If you used a 1 square foot hole (12x12 inches) then air is moving more like 8 miles per hour and is possible. You should probably use the rule of making your passive intake about twice the size of your fan hole. If you have an 8 inch circular hole on the fan, you should have two 8 inch holes for intake (and more intake area would be better).

Look for a fan that can move about 750 or 800 CFM. You will need a bigger fan if things heat up in the summer and you still want to grow.

I agree that having a fan that will adjust speed based on inlet temperature is a good thing. I would definately try to find one of those.

-SomeoneYouKnow

 

[inreplyavalon]

Someone you fu#@*&^ ROCK! That explanation is really well written. Thanks for sharing all that.

I like the idea of a split AC, the problem is that i have read it is illegal to install myself. That is a huge security concern because i live in a place that folks typically don't have AC's. So a window unit with a box is likely my best option.

Thanks for pushing me in a direction i have wanted to move...supplemental CO2!

 

[Lazyman]

Someone you fu#@*&^ ROCK! That explanation is really well written. Thanks for sharing all that.

I like the idea of a split AC, the problem is that i have read it is illegal to install myself. That is a huge security concern because i live in a place that folks typically don't have AC's. So a window unit with a box is likely my best option.

Thanks for pushing me in a direction i have wanted to move...supplemental CO2!

Nah, check out excel air AC systems, self installs with precharged lines. They sell 2-5 ton systems, including a really quiet stealth series.

 

[inreplyavalon]

Thanks Lazy! thats officially on my wish list!

 

[Seed Buyer]

I own quite a few Excel Air systems and can vouch for their quality and value in the garden. However, the outside condensers are large and based on your prior comments you will need to find a way to hide them(plant bushes around it). On the flip side nobody is going to know if it is an ac used to grow herb or a central heating system used to keep a family warm. As far as co2 the main expensive is buying the gear. Propane tanks are so cheap to refill don't stress about not being 100% efficient and losing some gas. Burn that stuff and go buy more!