How to do the Air Turnover Calculat

[JohnsonMadukayil]

How to do the Air Turnover Calculations for a space (our machine shop here) which is 200, 000 cubic feet and there are two ceiling exhaust fans which are 6000 cfm each. Like for how much time should both the fans be kept on in an hour to ensure at least one air turnover per hour? There is no air makeup unit inside the plant. The air leakage into the plant is primarily through the numerous doors and windows. If the outside temperature is cold, then keeping the fans on for a longer period of time lowers the temperature inside the plant and workers complain. At present the fans are kep on for one minute in an hour and this serves to increase the pollution in the plant. In summer (25°C) it is ok to keep all the doors and windows open and run the fans for longer periods.

Is there any formula which might help me calculate the air turnover time requirement?

 

[ChrisConley]

Well Johnson, the quick answer is: 12,000 cubic feet per minute will generate 12,000 cfm* 60 minutes = 720,000 cubic feet in an hour. Which means that in order to exhaust 1 ACH you need to run your fans just under 20 minutes an hour. 16 minutes * 12,000 cfm = 192,000 cubic feet. My concern would be that without any make-up air that you will have problems with any vented equipment (boilers, furnaces), have you considered make-up air?

 

[quark]

Johnson!

Chris is correct. Use the formula cfm = volume(in cu.ft)*air changes per hour(ACPH what you call as turnover)/60.

To check whether the leakage through doors and windows is sufficiently maintaining the required air change of 1 per hour check the actual cfm of each fan by a velometer (not on nameplate) and then back calculate.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[la45]

Well Jhonson
I have gone through both the answers above but frankly I think insteaed using bigger fans like you have in your factory try using four small size fans (one on each side facing each other) at some where MIDDLE of the room height .
By doing this you may help in changing room air (polluted and staled air ) with out letting insiders to know anything .
good luck jhon.
alley.

 

[cjw81]

Another option- install a variable frequency controller on one of the fans, along with a CO2 controller for a demand ventilation strategy. CO2 is NOT an absolute indoor air quality remedy but CO2 levels are related to indoor air pollution and VOC's (volatile organic compounds) because of it's solubility with other gasses.Go to the Trane website and look up a good article about demand control and CO2. By using a variiable frequency drive you can maintain a constant low flow to get your air changes, it will be cost effective and won't freeze up your crew. You may not eliminate VOC's during low flow but you will minimize dangerous concentrations that you will get with an on/off strategy.