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#1
11-19-2009, 06:05 AM
 Unregistered Guest Posts: n/a
Convert BAR to CFH or CFM

Hey guys, need help with converting a pressure to CFH. I have bottle of carbon dioxide (22LB) that i need to be released to my greenhouse at rates 1500PPM . Problem is all online calculators need CFH or CFM, to calculate time i need to release the gas. I can release from 1 to 3 bar but i need to know how many CFM or CFH it is. it does not have to be very precise calculation as ppm can vary in green house.

RedDog
#2
11-19-2009, 06:32 AM
 JohnS Double Ultimate Supreme Member Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,219 Rep Power: 18
Re: Convert BAR to CFH or CFM

Quote:
 Originally Posted by Unregistered Hey guys, need help with converting a pressure to CFH. I have bottle of carbon dioxide (22LB) that i need to be released to my greenhouse at rates 1500PPM . Problem is all online calculators need CFH or CFM, to calculate time i need to release the gas. I can release from 1 to 3 bar but i need to know how many CFM or CFH it is. it does not have to be very precise calculation as ppm can vary in green house. Thanks in Advance RedDog
The pressure won't help you much. The CO2 is actually a high pressure liquid in the bottle. The indicated pressure is more a function of temperature than what is left. (The pressure drops because the temperature drops as some expands to a gas.

You are probably better off using the weight. The molar volume of a gas is normally worked in SI (metric) units. However, people who use english units make up a "pound mole" and proceed. 44 g of CO2 is a real mole, 44 lb is a "pound mole", so you have 0.5 pound moles. In english units, the molar volume at 60 °F, 14.7 psi is 379.5 cubic feet. You have half that, or about 190 cubic feet (measured at that temperature and pressure).

The weight of a full bottle should be 22 lb more than the weight of an empty bottle. In between, the weight (minus the weight of an empty) is your best estimate of what is left. The weight of an empty is called tare weight and may be printed on the bottle.
#3
11-19-2009, 06:44 AM
 Unregistered Guest Posts: n/a
Re: Convert BAR to CFH or CFM

22lb (10KG) is a pure weight of co2 in the bottle (converted to us measuring) whole bottle weight 22.5 kg. I really sucks in mathematics and my english dictionary is limited So could you please help me with timing of releasing the gas like what pressure i should set up (1 to 3 bar) for how many minutes to reach 1CFH or 1CFM

All help is appreciated

Thanks

RedDog
#4
11-19-2009, 12:33 PM
 JohnS Double Ultimate Supreme Member Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,219 Rep Power: 18
Re: Convert BAR to CFH or CFM

Quote:
 Originally Posted by Unregistered 22lb (10KG) is a pure weight of co2 in the bottle (converted to us measuring) whole bottle weight 22.5 kg. I really sucks in mathematics and my english dictionary is limited So could you please help me with timing of releasing the gas like what pressure i should set up (1 to 3 bar) for how many minutes to reach 1CFH or 1CFM All help is appreciated Thanks RedDog
There is no direct conversion of flow to pressure drop. It depends on the dimensional details of the nozzle or pipe through which flow occurs. Usually, only the region of greatest restriction needs to be analyzed; the rest can be ignored. I'm not very good at flow equations. If you had all the dimensions of the orifice, I probably couldn't calculate it.

What is the total interior volume of your greenhouse?
What is the airflow through the greenhouse (this will let some of your CO2 escape)?
What is the rate at which your plants consume CO2 in photosynthesis?
Maybe we can estimate the rate at which it needs to be released.
#5
11-20-2009, 06:37 AM
 Unregistered Guest Posts: n/a
Re: Convert BAR to CFH or CFM

Fantastic, thanks for trying so hard

1. Volume of my greenhouse is 32m3(cubic meter),
2. There is 1200m3 exhaust(out) and 400m3(in) but they will work only once a hour for 15 min to change the air in greenhouse. But from what i was planning this should not be a important factor as i´m planning to build up once an hour co2 to 1500-1600ppm and the then refill again.
3. Plants need from 600ppm up to 2000ppm depending from the plant stage (grow, bloom)

I have order a co2 garden probe tests, but they will arrive in about 3.5 week as i´m living in canary islands, and at the moment i cannot afford a 600\$ computer that will release this co2 automaticly for me Thats why i need your help guys (JohnS) cause i would like to start using it as fast as possible (bigger crop).

In case you will need this gas will be released by electric valve connected to 0.22mm pipe system.

RD
#6
11-20-2009, 05:53 PM
 JohnS Double Ultimate Supreme Member Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,219 Rep Power: 18
Re: Convert BAR to CFH or CFM

Quote:
 Originally Posted by Unregistered Fantastic, thanks for trying so hard 1. Volume of my greenhouse is 32m3(cubic meter), 2. There is 1200m3 exhaust(out) and 400m3(in) but they will work only once a hour for 15 min to change the air in greenhouse. But from what i was planning this should not be a important factor as i´m planning to build up once an hour co2 to 1500-1600ppm and the then refill again. 3. Plants need from 600ppm up to 2000ppm depending from the plant stage (grow, bloom) I have order a co2 garden probe tests, but they will arrive in about 3.5 week as i´m living in canary islands, and at the moment i cannot afford a 600\$ computer that will release this co2 automaticly for me Thats why i need your help guys (JohnS) cause i would like to start using it as fast as possible (bigger crop). In case you will need this gas will be released by electric valve connected to 0.22mm pipe system. Thanks again in advance RD
The 190 cubic feet (at 1 atm) mentioned earlier is about 5.4 m³ of CO2 at 1 atm. If you want concentration of 1500 ppm that is 0.0015 atm partial pressure of CO2. So you bottle will bring a total of 3586 m³ of air to that concentration (ignoring uptake by the plants). If you blow that out every hour and re-enrich the air, you can do so about 100 times.

As long as you are adding CO2, I'm not sure you need to ventilate (unless for temperature control.) If you don't add CO2 artificially, you DO need to ventilate as the plants are pulling CO2 out of the air.

I don't know how to suggest you regulate the flow. Can you keep the bottle on a scale and release about 0.1 kg/0.22 lb each time after vent. cycle is complete?
#7
11-21-2009, 05:21 AM
 Unregistered Guest Posts: n/a
Re: Convert BAR to CFH or CFM

Hey,

I need to ventilate the room cause of hot and moisture climate over here

Unfortunately i can only control pressure release 0.1 - 3BAR.

JohnS thanks very much for trying to help me but i found the solution. One of my mates will lend me his digital co2 controller so i will try to calculate the time of release of gas to the air, and set up my timers similar.

If i have any more problems i´ll let you know.

Thanks Again
RedDog
#8
12-05-2012, 12:46 AM
 Unregistered Guest Posts: n/a
Re: Convert BAR to CFM

How to convert 8.5 bar into cfm.This is required for our air reciever tank

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