Air Conditioning Unit Help

[macnasty]

Hi.

Does this work:

10,000 BTU portable a/c unit, cooling a 1000W HPS in a 4' x 6' x 8' room (192 cubic feet), exhausting air 20' UP through the attic and out the roof. The unit's exhaust is roughly 250 CFM.

If this doesn't work, could someone give me suggestions on how to make it work? For example, what size a/c unit would work? Or, could I 'assist' the unit by installing an inline fan half way up the ducting, at around 10'? The problem with this latter solution is I don't know how to sync the inline fan with the a/c unit, so it will be running on all the time while the a/c unit might be off. Any way around this?

Thank you very much.

macnasty Reviewed by macnasty on 03-19-2011. Air Conditioning Unit Help Hi. Does this work: 10,000 BTU portable a/c unit, cooling a 1000W HPS in a 4' x 6' x 8' room (192 cubic feet), exhausting air 20' UP through the attic and out the roof. The unit's exhaust is roughly 250 CFM. If this doesn't work, could someone give me suggestions on how to make it work? For example, what size a/c unit would work? Or, could I 'assist' the unit by installing an inline fan half way up the ducting, at around 10'? The problem with this latter solution is I don't know how to Rating: 5

[Dutch Pimp]

if the unit is in good working order?...it should work fine. window units are better

[oldmac]

Hi Macnasty,

Saw you said hi to me on another thread, did not mean to ignore you just ran out of time....then continued my self imposed "time out".

Like Dutch said it should be fine.

Portables and windowless are the least efficent ACs, better is window or sleeve and best are the small split AC systems. With that said, there are advantages to the portable...like easy venting of the heat, simple one hose. I used a Sharp's 12,000btu windowless in a sealed room and it works great and deals with 1320watts of LEDs and 2,000watts of PSMH.

For you and others, I'll repeat this advice. When dealing with sizing AC or other cooling treat the lights like they are electric heaters. Since there are 3.413 BTUs in 1 Watt, so in mini-mac's example 1000w of HPS means 3,413 BTU to be cooled. Once you cover the wattage producing heat, you then need to figure out and guessimate what, if any, cooling you need between the room and ambient temp outside the room.

OM

[macnasty]

Dutch and OM, thank you very kindly for the quick reply. The 20' of vertical exhaust was confounding me and I was actually concerned the air wouldn't make it up without the assistance of an inline fan, but if 3,413 BTU + outside ambient temps is all I need to cover then I think I'm in good hands. That is a great formula btw I won't forget it. Funny enough om, I was just thinking about you (as per my regular habit) and that nifty sharp a/c unit sitting so handsomly in one of your setups, but I wasn't aware that there were 2000watts of PSMH there too. Here goes!

-mini-mac (hah!)

[TANKJR]

"...but if 3,413 BTU + outside ambient temps is all I need to cover then I think I'm in good hands."

While OM's formula (LOL! Is this like Ohm's Law?) is good for compensating for the lights, (3413BTU/H there is always a time factor guys!) there is a lot more to doing a heat load calculation on a room, any room, and especially a grow room...10,000BTU/H should work for you unless you've got some kind of extreme conditions outside. If the A/C runs constantly trying to hold setpoint, or ices up, tho, you will know it's too small for the conditions you have. If it does not run long enough to control the humidity to at least 50%, but reaches setpoint easily, it's too big. (By too big or small I am referring to the BTU/H rating {yes, it's just a rating, it may or may not achieve that number}number, not physical size, sorry, but you'd be surprised how many think that's how you measure an A/C!) If you find a need to rig another booster fan that runs when the A/C does, let me know and I'll draw you up the circuit...it's easy, you just need a fan relay in line.

[Dutch Pimp]

the cool air flow should go between the light bulb and the canopy. keep this space 75-85 degrees

[oldmac]

WoW Mac, you got a real good memory. I had to go look for where I showed that (Hydro: Aero/fog LED grow table) to see what/where we were at then. It was the first trial run of 1/2 of Fogfognugen (4x4 tray with 660w of LED). After a couple of more trials the second tray was added and 2 more TI Pro blooms where added.

About six months later I built another fogfognugen (I had bought parts for 4 trays originally) that sits lower and the orignal was mounted higher, one set of trays above the other. I could not convince my partner to spend another $5,000 on LEDs so we experimented with HPS first. We tried a 600w HPS and did have have enough light, then went to 1,000 HPS, we found the LED could match finished wgt but the LED bud was better. So, tried the expensive bulb PSMH and they have worked great. 3k PSMH for most of flowering and change to a 10k bulb for last week to mature the trichomes.

Hey Tank,

I think I said above that using the light wattage/ BTU was just for lights, take a guessimate for the rest, if needed. Actually as a HVAC guy you know that if we have the insulation R factor for the 4 walls and ceiling and know the max temp differential between room and outside the walls we can calculate the BTUs needed to cool the room and maintain wanted temp.

Speaking of Rules:

Murphy's Law; "what ever can go wrong will go wrong"

Oldmac' Law; "Murphy was a bloody Irish optimist"

OM:jointsmile:

[TANKJR]

LOL! Yep, OM I'm a firm believer in Murphy's Laws...ALL of them...no other "natural" law is more proven on a day to day basis, 'cept maybe gravity...

Yes, OM, the R factor will get you closer, but to do a complete "J-sheet" heat load calculation, there are many, many other factors needed to do a complete evaluation to get the exact heat load...I just estimated 10K BTU/H would be sufficient and added how to tell if it's too big or little after that, so if what he has doesn't work, at least he'll know whether to go bigger or smaller. Not pickin on ya...just wanted to give him some options on direction if it doesn't work correctly....again...Trying to help him overcome Murphy...LOL!! It's all good!

Hey OM...I never told ya this before, but I find the fogfognuggen stuff fascinating! Thx! We need more innovators like you!
PS Gravity is how us Irish Optimists tell when we've had too much to drink...

[Rusty Trichome]

You might want to have a look at my "Dealing with heat issues" thread. (in my signature)
I flower in an outdoor shed, and I live in the desert where outdoor temps exceed 100 degrees daily.

I'd go bigger if you can afford it. Larger units are usually a tad more efficient during the heat of summer, and it's best not to have a smaller A/C on full-blast all the time. (electricity and wear-n-tear)

[oldmac]

@macnasty; I forgot to mention another advantage to (some) windowless units. They have a dedicated dehumidifier setting. When we first started that room we had a humidity problem from water comming thru the floor, we'd run that thing just to get the water dried up many times.

@TankJR; I knew you were not picking (nit-picking?) on me, just wanted you to realize that I understood more went into sizing an AC then just the lights. BTW you are correct about BTUs, they are not created equal. A windowless 12k will compete with a 10k window unit which will compete with a 8k split system.

@Rusty; I got to give you credit for all the help you provide, especially in the plant problem department. I think I have to look into starting the ball rolling on Sainthood for you. I know I'm familar with your "dealing with heat issues" thread, I hope mini-mac reads it too. Good point about sizing the AC larger, it truly is more energy efficent that way.

For everyone: As good as AC's are at cooling don't overlook chillers.

IMHO a well designed chiller system is more energy efficent then AC.
[I can hear the keyboards starting up now]

OM :jointsmile: