Air exchange for air-conditioned room with ACTIVE exhaust?

[weedlover_89]

Hello to everyone...I plan on doing a summer grow in a room that is 8x8x10 feet. I have a 12000 BTU window unit installed inside this room. I am thinking on running 4x600w HPS.

I can't use a c02 setup which i know is the proper thing to do. So i intend on using active exhaust.

I imagine i should be exchanging the minimum for the room (once every 5 min air exchange?) in order not to exhaust quickly the air-conditioned air?

That means 640 cubic feet which are the dimensions of the room/5=120 CFM?

And what i should i do with passive intake? An 8" intake would be more than enough in this case?

Last but not least, i plan on having lights off during the day with ambient temps reaching 90F. That means that even with lights off, A/C would have to be working. Could i turn off exhaust during these hours to make A/C more effective?

Thank you

 

[mowood3479]

running with an exhaust and ac will chew up power fast... I would recommend spending the $ Ull end up spending on electric and get a propane burner....
And btw, there isn't any great way (without co2 monitoring equipment) to give advice on how much exhaust Ull need..
Trial and error is gonna be the way I'd think... But Ud be way better off to get set up with co2.
I just installed my first mini split ac a few months back w/ a propane burner and yields jumped 20%.
I fight it but having the right equipment almost always pays off far better than trying to rough it.
My two cents anyway.
If u can't get co2 set up I guess I'd advise turning ur exhaust fan on for 15 min and off for 15 min and see how that goes and adjust from there.

 

[MileHighGlass]

You can build a little "room" around your AC and use that small space as a lung room. Then have your fans running full time sucking in from that lung room, and blowing out into that lung room.

I did a setup that way a few years ago, and it worked great. I made about a 18" D x 24" W x ceiling height room in front of the AC.

I ran that for many years with no problems.

Just a thought.

Forgot to say make sure to make an access panel so you can access your AC.

 

[Granger2]

You'd be best off to use your intake and exhaust to air cool your lamps, seal the room, add CO2 tank [less heat than burner]. Yes use AC to cool room both night and during the day [your night]. Good luck. -granger

 

[stoned-trout]

get a co2 setup...yeehaw..wont be long before you have paid more for electric then a co2 setup costs...theres many options now...even them bags.. altho all I use is bottled and a co2 generator...

 

[weedlover_89]

Thanks a lot for the responses so far! I am not inclined to use CO2 for a number of reasons. I don't mind paying more for electric than CO2 as the yield will pay off. So far, MileHighGlass suggested the option that suits me the most. To tell you a little bit more about this room, its next to the living room, they are separated by drywall (easy to make holes through it).

I could install the A/C in the living room, make a hole in the drywall and use an inline fan to pull air to the grow room? The creation of a little room where the A/C is sounds a little bit troublesome and would constrict the grow space, its a very nice idea though.

MileHighGlass what setup were you running that way?

 

[mowood3479]

So.. I re read ur original post.. Yes in ur proposed set up u can shut off the exhaust when lights r off. The co2 in the room will rise without light..
An 8" intake should be sufficient.
And as additional info..
In my 12'x 14'x 9' room the co2 level falls very slowly, it take several hours to drop the co2 level from ambient 500ish to 350...
So depending on a lot of different variables u may be alright just exchanging the 1x per hour or 1x per half hour. This will put a lot less strain on the ac if u set the exhaust to run as little as possible to maintain ambient co2 levels 400-500 (depending on where u are).
If u could borrow a co2 monitor from someone u could dial it in more accurately without so much guess work.
Good luck

 

[queequeg152]

Hello to everyone...I plan on doing a summer grow in a room that is 8x8x10 feet. I have a 12000 BTU window unit installed inside this room. I am thinking on running 4x600w HPS.

I can't use a c02 setup which i know is the proper thing to do. So i intend on using active exhaust.

I imagine i should be exchanging the minimum for the room (once every 5 min air exchange?) in order not to exhaust quickly the air-conditioned air?

That means 640 cubic feet which are the dimensions of the room/5=120 CFM?

And what i should i do with passive intake? An 8" intake would be more than enough in this case?

Last but not least, i plan on having lights off during the day with ambient temps reaching 90F. That means that even with lights off, A/C would have to be working. Could i turn off exhaust during these hours to make A/C more effective?

Thank you

id suggest exhausting in a demand wise fashion with a power open damper through a soffit vent or somewhere cool... not an attic airspace.

old school hvac occupancy relied on co2 sensors to detect elevated levels of co2 from people in the office space or where ever. this was back when PIR stuff was shitty and unreliable.

basically when co2 falls below 300 or what ever, fans powers on, damper powers open, and new air is blown in with old air being exhausted passivly outside via barometric damper or static pressure sensor and actuator.

its important that you dont allow this hotish air to re enter your living space as it will introduce additional load onto your central AC system.

have some pride for fucks sake. exhausting hot shitty air into your living space is fucking offensive and unnecessary with a modicum of engineering here.

you should also consider replacing the exhaust air fan with an energy recovery ventilator later on once you get a better idea of the air exchange requirements. it may be possible to use a small 135 scfm erv running long duty cycles instead of a high volume inline blower. i really dont know, im assuming when plants mature, they will simply remove too much co2 for a small ERV like that to keep up... but maby not.

the ERV simply passes hot wet outside air, over cooler less wet inside air and saves like 75-90% of that heat gain that you would otherwise accumulate with just regular exhaust.

 

[Speed of green]

I think your 12k window banger will cool those 4 600's just fine. are the lights air-cooled? even if they aren't you should be fine. The rule is 4000btu for every 1000w.

 

[Asslover]

Hello to everyone...I plan on doing a summer grow in a room that is 8x8x10 feet. I have a 12000 BTU window unit installed inside this room. I am thinking on running 4x600w HPS.

I can't use a c02 setup which i know is the proper thing to do. So i intend on using active exhaust.

I imagine i should be exchanging the minimum for the room (once every 5 min air exchange?) in order not to exhaust quickly the air-conditioned air?

That means 640 cubic feet which are the dimensions of the room/5=120 CFM?

And what i should i do with passive intake? An 8" intake would be more than enough in this case?

Last but not least, i plan on having lights off during the day with ambient temps reaching 90F. That means that even with lights off, A/C would have to be working. Could i turn off exhaust during these hours to make A/C more effective?

Thank you

Your AC will never cycle off...

 

[Asslover]

I think your 12k window banger will cool those 4 600's just fine. are the lights air-cooled? even if they aren't you should be fine. The rule is 4000btu for every 1000w.

Maybe in Alaska that equation would work. Here in Florida we run 30k btu's for 10x10x8 with 4k watts open bulb. Then theirs the dehumidifier he's gonna need.
You can exchange air 1000X/minute but it won't do squat unless the air coming in is cooler/drier. Building a properly sealed room is an Art and quite frankly THEE only way to grow indoors down here.

 

[LastHurrah]

This thread is timely for me. I converted a bedroom recently and installed a window banger (actually it's a "through the wall" unit). The room isn't sealed. I read long ago when I first considered growing that sealing up and adding co2 should only happen "after" you've dialed in "all" other environmental factors.

I'm sure I started a couple of ventilation threads with very few replies. What I've decided to try is to put a scrubber/fan (with speed controller) on a recycle timer, monitor co2 levels, and adjust the frequency/duration of the exhaust cycles as needed.

I can't say how well it's going to work yet since I'm still putting it all together. Here's what I'm working with:



That's a 14k BTU 220v unit and it cools the room wonderfully.

I'll let ya's know how it's going as I fire up the other two tents. Pretty dynamic environment since I have week old seedlings, I'm only using 430 watts right now, and temps are steadily rising in my hot/dry NorCal location.

LH

 

[Speed of green]

Im cooling 8000watts sealed with dehueys, one 30,000btu window ac. Ambient temps rarely get over 90.

exhausting air conditioned air is not really the best scenario, asslover is right about your ac never cycling off, i would size the correct A/C for your environment and go from there.

If you live swamp ass florida you need 7500btu per 1kw.

If you live by the ocean in california 3500-4000 but per 1kw

Elsewhere in between use your best judgement.

SOG

 

[queequeg152]

Im cooling 8000watts sealed with dehueys, one 30,000btu window ac. Ambient temps rarely get over 90.

exhausting air conditioned air is not really the best scenario, asslover is right about your ac never cycling off, i would size the correct A/C for your environment and go from there.

If you live swamp ass florida you need 7500btu per 1kw.

If you live by the ocean in california 3500-4000 but per 1kw

Elsewhere in between use your best judgement.

SOG

just do a manual J ffs.

a manual J is 500 bucks worst case scenario, and 90 bucks if you do if yourself, buying the reference book.

there is literally no way to approximate cooling load based on region only. there are too many variables that goes into the heat gain calculations to broad brush like that.

a single tree can reduce your solar heat gain tremendously in the right circumstances. a longer soffit can reduce your heat gains tremendously.

high windows can reduce your heat gain. different siding materials, roofing materials, house orientation, window construction, screens and what ever else.

a pier and beam foundation will have different heat gain than that of a slab on grade w/o perimeter insulation.

most importantly is interior verses exterior wall areas. a room in the second story corner of a building will have much more heat gain than that of an interior room on the first floor.

im not saying to do an EXHAUSTIVE manual J... blowerdoor testing and duct blasting and shit like that, but if you do atleast a crude one, calculating wall areas, door areas, ceiling areas etc, then punch in your lat, long and engineered indoor air temps and humidity you can get a pretty good idea of your heat gain.

 

[MileHighGlass]

just do a manual J ffs.

a manual J is 500 bucks worst case scenario, and 90 bucks if you do if yourself, buying the reference book.

there is literally no way to approximate cooling load based on region only. there are too many variables that goes into the heat gain calculations to broad brush like that.

a single tree can reduce your solar heat gain tremendously in the right circumstances. a longer soffit can reduce your heat gains tremendously.

high windows can reduce your heat gain. different siding materials, roofing materials, house orientation, window construction, screens and what ever else.

a pier and beam foundation will have different heat gain than that of a slab on grade w/o perimeter insulation.

most importantly is interior verses exterior wall areas. a room in the second story corner of a building will have much more heat gain than that of an interior room on the first floor.

im not saying to do an EXHAUSTIVE manual J... blowerdoor testing and duct blasting and shit like that, but if you do atleast a crude one, calculating wall areas, door areas, ceiling areas etc, then punch in your lat, long and engineered indoor air temps and humidity you can get a pretty good idea of your heat gain.

This is one of the most thorough posts I have seen on here in years.
Great info!

 

[Granger2]

What is a manual J ffs?

 

[LastHurrah]

...the ERV simply passes hot wet outside air, over cooler less wet inside air and saves like 75-90% of that heat gain that you would otherwise accumulate with just regular exhaust.

Thanks for that! Had never heard of one before. The ones I saw were kinda high. Which do you run and for what size op? What kinda climate? It's hot and dry in the summers here. Mild and dry in the winters. You said it passes hot "wet" outside air over cooler "dryer"inside air. Where does your setup "pull" air from? Outside? Good post!

LH

 

[queequeg152]

What is a manual J ffs?

genuinely cant tell if you are serious lol.

manual J- for fucks sake. ffs= for fucks sake.

i feel like ive gone over this so many times, i have to believe that people are atleast aware of manual J load calculations?

Thanks for that! Had never heard of one before. The ones I saw were kinda high. Which do you run and for what size op? What kinda climate? It's hot and dry in the summers here. Mild and dry in the winters. You said it passes hot "wet" outside air over cooler "dryer"inside air. Where does your setup "pull" air from? Outside? Good post!

LH

they are expensive unfortunatly, hence why i suggested considering one and not just buying one outright.

if your electricity is very expensive and its hotter outside for most of the year one might work for you. if its colder outside and power is cheaper? probably not going to make sense, though i admit to not having done the calculations here.

the reason they make sense in houses is because in a house, they operate for 10+ years maby longer. in your average grow room? it may never pay for itself over something equivelant in flow rate, but lacking the heat excanger.

i do not grow indoors anymore beyond grafting, seeding and propagating cactus's and shit. i dont grow cannabis, but i have a very good working knowledge of hvac systems and design and especially duct design and distribution.

my wording on the previous post may have been clumbsy. let me find a picture.

the air streams never touch directly, its simply a heat exchanger with a very large interface. large enough to allow the two airstreams to approach equilibrium.

this is just one type of ERV, there are a shit load of designes.

you can check out the greenheck website if you want to see the very large units... but keep in mind these larger units are going to be like 4-9 feet across and for units taht are in the range of 10's to 100's of tons, not small residential units.

most ERV units like this take air from outside and inside. you do not need an additional fan or anything like that. the box is supposed to be close to air tight, so negative pressure causes outside air to enter the unit.

some units will have TWO fans. one for outside and one for inside air.

2 fans will be better for situations with lots of duct work, or in situations where the building envelope is not very well air sealed.

 

[krunchbubble]

genuinely cant tell if you are serious lol.

manual J- for fucks sake. ffs= for fucks sake.

i feel like ive gone over this so many times, i have to believe that people are atleast aware of manual J load calculations?



they are expensive unfortunatly, hence why i suggested considering one and not just buying one outright.

if your electricity is very expensive and its hotter outside for most of the year one might work for you. if its colder outside and power is cheaper? probably not going to make sense, though i admit to not having done the calculations here.

the reason they make sense in houses is because in a house, they operate for 10+ years maby longer. in your average grow room? it may never pay for itself over something equivelant in flow rate, but lacking the heat excanger.

i do not grow indoors anymore beyond grafting, seeding and propagating cactus's and shit. i dont grow cannabis, but i have a very good working knowledge of hvac systems and design and especially duct design and distribution.

my wording on the previous post may have been clumbsy. let me find a picture.

View Image

the air streams never touch directly, its simply a heat exchanger with a very large interface. large enough to allow the two airstreams to approach equilibrium.

this is just one type of ERV, there are a shit load of designes.

you can check out the greenheck website if you want to see the very large units... but keep in mind these larger units are going to be like 4-9 feet across and for units taht are in the range of 10's to 100's of tons, not small residential units.

most ERV units like this take air from outside and inside. you do not need an additional fan or anything like that. the box is supposed to be close to air tight, so negative pressure causes outside air to enter the unit.

some units will have TWO fans. one for outside and one for inside air.

2 fans will be better for situations with lots of duct work, or in situations where the building envelope is not very well air sealed.

Wow! Never seen one of these...

 

[Gry]

Neat as can be.