a/c BTU's, room size, wattage.

[greenduck]

thinking of upgrading the 12,000 btu a/c to a 15,000 btu's so i can add another bulb or to potential expand room. is there a calculation or better way to judge how much btu's a room is need based on size and wattage?

things to consider below:

we have a 12x7 room (4x4 table and 4x8 table under 3, 750w hps) co2 at 1500-1600 ppm and a dehumid set at 50%. a couple fans too.

this room is for 12/12. im going to be posted soon on my project when and if i decide to expand this flower room. advice would be appreciated on the air circulation.

 

[Oldmac]

Hello greenduck, the easy way to calculate BTUs to cover the heat from the lights is to treat the lights like they are electric heaters. Your current 3/750w lights are 2,250 watts total, since there are 3.413 BTUs/watt, you currently need 7,679 BTUs just to cover the lights. 4/750w = 3000w or 10,239BTUs to cover the heat from the lights. Add to that the heat generated by the dehumidifier plus the heat differential between the room and the ambient air temp between the walls (and how well they are insulated) and room.

Assuming you want to maintain the room temp at abt 80F, I don't have enough info for the rest.

Keep in mind that not all AC BTUs are the same. A split sytem is more efficent then a window unit, and a windowless AC is the least efficent.

Hope that helps you in the right direction.

OM

 

[habeeb]

this might help :

http://www.icmag.com/ic/showthread.php?t=95259

 

[greenduck]

olmac and habeeb, thanks for the information and link.

we'd like 77 to 80ish degrees...room is insulated with general insulation (standard stuff).

from what mac said, i have a sharp in wall unit (ill findout if it was originally a window made unit, not sure) that has a reading of 12,000 btu's. we tried to add a 4th 750w hps but we could get the temp below 85...even with the ac running when the lights were on. (ive heard we should have 4, 600w vs 3, 750w... gives more focused lumens and more lumens to the plants overall, and that's just 2400watts vs 2250 so the temp change wouldnt be to drastic)

we are planning on knocking a wall down and adding another table (4x8 with 3, 600w hps )so that's why i was thinking of upgrading from the 12k to 15k btu.


but ya, ill look at the link and try to calculate...very much appreciated!!!!!!

 

[greenduck]

we use the window unit and exhaust the heat through the roof. i dont know much about the split units but they are ductless? so where does the heat go? ill have to do some research.

is this what you had in mind?
http://www.drillspot.com/products/522117/haier_hsu12xc7-g_ductless_split_indoor_wall_mount_unit_air_conditioner?s=1

 

[frenzybud]

Hello greenduck, the easy way to calculate BTUs to cover the heat from the lights is to treat the lights like they are electric heaters. Your current 3/750w lights are 2,250 watts total, since there are 3.413 BTUs/watt, you currently need 7,679 BTUs just to cover the lights. 4/750w = 3000w or 10,239BTUs to cover the heat from the lights. Add to that the heat generated by the dehumidifier plus the heat differential between the room and the ambient air temp between the walls (and how well they are insulated) and room.

Assuming you want to maintain the room temp at abt 80F, I don't have enough info for the rest.

Keep in mind that not all AC BTUs are the same. A split sytem is more efficent then a window unit, and a windowless AC is the least efficent.

Hope that helps you in the right direction.

OM

Your calculation is very helpful, I'm also about to add aircon to my room.
One thing though, a High Pressure Sodium lamp has an effeciency of about 50% depending on the type of bulb/ballast you are using. This means that roughly 50% of the total wattage of the lighting system turn into heat.
So 2250 watt HPS will be equivalent to an electric heater with an input power of about 1125 watt. roughly..

This calculation is also dependent on the type of reflector(if any) you are using. A bare bulb system runs slightly cooler than one with standard un-cooled reflectors.

Peace

 

[Work2much]

Greenduck I consider it smart to always oversize the AC purchased for any room. You never know when you'll get a run of freaky hot weather, whether you'll want to add more heat producing appliances in the room later etc. The difference in price from a 15kbtu and say a 24kbtu is small, usually around $100 give or take.

 

[Oldmac]

@greenduck, a split system is like most central AC sytems, inside you have a evaporator coil and some form of air handler (fan) and outside you have the condensor and compressor. The new "mini-split" systems like Mitsubishi make are designed for smaller areas plus have very efficent rotary style compressors. Usually mounted outdoors but if you have a way to exhaust the heat and enough ambient air inlet it would be possible to mount the outdoor unit in an attic.

@frenzybud, I'm not sure what the percent of light vs heat is for a HPS, but you need to allow for the secondary heat that is generated by the acutal light that is produced. Just light itself will generate heat off every surface it hits warming the air. Treating the total wattage as an electric heater may give a little "fudge" factor, which leads to.....

@Work2much, makes an excellent point. It is much better to oversize an AC system then to be at exactly calulated needs. The compressor will have to cycle on less rather that be working nearly all the time.

@habeeb, excellent link. It's interesting to note if you look those calculations over, there is a fudge factor at every step of the calculation.

For everyone, ponder this, a well designed chiller system can be more efficent then an AC system. Recently I needed to up size a 400w MH in my mom/veg room to a 600w MH. I used a thermal cover over a air-cooled hood (to stop radiant heat from hood) and used an "ice box" on one side of the hood and a fan on the other, not ducted in or out. Plus I added a ice box and fan in my work area and another for a hybred light mounted in a glass tube in the flower room. The resivoir is mounted outside the room and is a 30gal pickle barrel. There is a 3/4" soft copper coil in the barrel that is inline between my well pump (52F water yr round) and the rest of the house. All water used in the house passes thru the coil to chill the resivoir, a poor man's geothermal unit.
Thru the use of theromstats to control the fan at each ice box, I can control temps in all 3 rooms. Only electrical expense is a submersible pump in the bottom of the resivoir running 24/7 for the cooling loop and when the fan's kick on. All fans btw are cheap "duct booster" type fans. Extremely cheap system vs AC to build and very cheap to operate.

OM

 

[habeeb]

I went with a mr. slim, and called it a day well done.

also got the SEER 21 unit, as the SEER 26 was out...

 

[krest]

For those of us that cannot, for security reasons, have a professional install a split system, what would be a good recommendation?

 

[mg75]

For those of us that cannot, for security reasons, have a professional install a split system, what would be a good recommendation?

thermoplus a/c
excel air diy mini split
water-cooled heat exchangers
l.e.d. lighting
plasma lighting
lower wattage HPS/MH
bottled co2 injection for higher temp rooms
run lights at night
bigger exhaust/intake
water-cooled lights
new location with dialed in environment before live plants go in

 

[Guest 18340]

For those of us that cannot, for security reasons, have a professional install a split system, what would be a good recommendation?

Learn how to install them yourself. Thats what I did.
Excelair just capitalizes on the fact they cater to growers and know that most growers can't have a hvac tech to their spot so they act like they have gold with their diy system. Not only are the Excel diy mini's over priced, they are nothing but cheap chinese made "white label" units. Buy them in bulk completely blank and slap their sticker on it.
Here's a cheaper price on a diy, http://www.clearanceac.com/index.php?l=product_detail&p=96
Mind you, it's still a very cheap no frills brand.
I was in the same boat as you. No way I could have a tech do it so I studied endlessly and bought the right equipment and did it myself. If I can do, ANYONE can do it
PS. Mitsubishi Mr.Slim's are thee top of the line...

 

[Stagetek]

As usual, I'm confused;

As usual, I'm confused;

the guys at the hydro shops I buy from, are unanimous in their belief that CO2 is pretty much wasted below 85F. Using a/c to keep a room below 80F, with CO2, seems to be at cross purposes; was I misinformed? On a side note, if running a/c does bottled CO2 make sense or is it cost prohibitive compared to gas generators?

I know that running DWC at those ambient temps requires a chiller; does the same hold true for ebb and flow tables?

 

[Oldmac]

the guys at the hydro shops I buy from, are unanimous in their belief that CO2 is pretty much wasted below 85F. Using a/c to keep a room below 80F, with CO2, seems to be at cross purposes; was I misinformed? On a side note, if running a/c does bottled CO2 make sense or is it cost prohibitive compared to gas generators?

I know that running DWC at those ambient temps requires a chiller; does the same hold true for ebb and flow tables?

Your hydro guys are unanimously misinformed. Photosynthesis is most efficent between 25C (77F) and 30C (86F) and actually peaks at 30C. After that it drops off sharply, the warmer it gets the less stomatal conductance becomes. (the leaf pores start to close as temp goes up and photosynthersis decreases) Many growers compensate and add co2 so the plant continues to grow. Plus they have to use 1200-1500ppm of co2 to get any form of accelerated growth. Using co2 at the optimal temp is much more efficent. Ambient co2 levels are abt 350ppm and abt doubling that to abt 750ppm will increase photosynthesis abt 50%. Adding more co2 to say 1200ppm will only increase it another 5-10%, not worth it.

Max coditions for me are; 85F, 750ppm co2 and a light intensity of 1500 umole m2 s1 (micro-mole per meter sq per sec) PPFD (photosynthetic photon flux densities).

Want to have some fun with your hydro guys?... print out the scientific white paper below from University of Mississippi showing the optium light, temp and co2, and show it to them and tell them Oldmac say's that they need to be smarter then the plants they are growing.

OM

 

[Stagetek]

Nothing like peer reviewed research reports; thank-you.

 

[habeeb]

thanks for the info oldmac..

much appreciated deciphering that paper, as I sure has hell couldn't read it

 

[Hammerhead]

Always keep in mind that if yo get one thats to large for the room it will not work properly. It will make the room feel clammy/sticky. Im running 12k in a 12x10 room and it worked fine. This was not for cooling a grow it was for cooling me. Im using the same AC IN A 5X5X10. It has worked perfect from day 1.


You are using allot more power then I did so a 15 or 25k might work better.