I'm getting ready to add co2 to a similar size room but it's all for flowering. 8X9 7 feet tall. 12 plant modular scrooge with 3 plants harvested per month (or 4). What did you end up getting OP? What would I need to buy?
If you are looking for equipment on the cheap. You can get a welding regulator from harbor freight for $29, then go on ebay and get a solenoid for about $15-20. Take those down to a hardware store and get a fitting to connect them. The tanks you can go to a home brew shop, welding supply, or a decent grow shop. There is a calculator out there on the internet for figuring out the space you have to adjust and the time your tank needs to run to hit the levels of co2 you desire.
It will be difficult to find an adapter or fitting to convert most welding regulators unless you are using CO2 to weld with (mig). The fitting that fits a CO2 tank is not the same as O2 or acetylene, it is not something you would find at most hardware stores. I find the best priced regs are the ones used in fish tanks. For some reason they use CO2 to grow stuff in fish tanks. The price is very cheap. The part that will bite your wallet is the controller. $500 is a good deal on a controller. You will waste enough CO2 to pay for a controller after a half dozen completed grows. So going cheap is not a real option unless you plan on growing one crop then quitting.
You can turn a $50 teleaire HVAC co2 monitor into a co2 controller pretty easily. That's all the C.A.P PPM-3 is anyway. Use this guild Making a serial cable for a Telaire CO2 sensor .: Cannaversity Then all you have to do is use the relay contacts on in the box to controll your co2 valve. I've been playing around with one of these units and looking into the serial protocol it uses to talk to the UIP 8000 software. I've figgured out enough of it to read the PPM with serial port on my machine and get the PPM reading with my own software. I plan on making a write up on it as soon as I clean it up a bit and make it more presentable.
I have a near infrared co2 sensor that I am working with just need to get the logic down. The solenoid I am using has a a 1/2 fpt and the regulator has a 3/8 so not to hard to connect them. The other thing is the solenoid is a 12v dc so I can use a transistor to switch it on in off. Added I picked up my sensor from here. http://www.co2meter.com/collections/co2-sensors/products/k-22-oc-co2-sensor-module They also have this for the less tech inclined. http://www.co2meter.com/collections/wall-co2-meters-transmitters/products/co2-level-controller It will close the circuit to relay below 1200ppm then open the circuit at 1500 ppm.They are using the same infrared sensor to figure out the co2 concentration so it will be very accurate. You could add a photo relay in line with solenoid relay to prevent light off operation. Then for venting just have the solenoid line connected to the NC portion of relay and venting on NO portion. This is not the simplest setup but with power adapter only $219.
The sensor I got is from co2meter.com it is from sensair model k22. It has either a sinlge wire setup or can be hooked up to a i2c port for greater resolution. It either be hooked up to a micro controller or direct to a computer via a serial USB breakout. It is a better sensor then what alot ofcompanies use but requires that you build and program a controller so limits those who go this route. There is cheaper sensors out there but harder to use and less resolution.
Thanks everyone for their recent replies. I will look at those meters/pages India. I do not mind spending a little cash on this as it will save me money in electricity (if I choose that usage) in the summer, and give me more goodness in the winter I mean, right now I'm planning on going al lumatek ballasts for my bulbs just because their known to be high quality/reliable.