I have a question, What is VCR of Ventilation?

Discussion in 'Boat Design' started by hookcap2017, Sep 12, 2017.

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  1. hookcap2017
    Joined: Jul 2017
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    hookcap2017 Junior Member

    upload_2017-9-12_20-33-21.png

    Before, I usually used what the calculate formula is Required airflow, m3/hr(cfm) =compartment volume x time to change air(hr).
     

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  2. Ike
    Joined: Apr 2006
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    Ike Senior Member

    I don't understand your question? VCR is exactly as described. A compartment has a known volume in cubic feet or cubic meters. The volume of air in that compartment is the same as the compartment volume. If you ventilate the compartment, using an intake and an outlet and perhaps a blower to speed up the process; each time it exhausts a volume of air equal to the compartment volume it has made one complete change of air in the compartment. The number of times it does that in one hour is the VCR. I don't know any other way to explain it.

    To calculate it you need to know how many cubic feet (or meters) of air is being moved. That depends on the size of the openings, ducts if you have them, and the CFM of the blower. From this you determine how many cubic feet (meters) are being moved per minute. Multiply by 60 to get cubic feet (meters) per hour. Divide that by compartment volume to get VCR.
     
  3. hookcap2017
    Joined: Jul 2017
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    hookcap2017 Junior Member

    1st,Thank you very much for told with me.
    2nd,Yes, but I means I always used what the calculate formula is Required airflow, m3/hr(cfm) =compartment volume x time to change air(hr).
    Time to change air is ACH -air changes per hour.
    upload_2017-9-19_7-28-54.png
     

  4. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    That is not correct. It is just the opposite: the reciprocal value.
    The table you posted above says for bilges VCR per hour is 5, that means time to change air is 12 minutes.
    ACH is just another term for VCR, so ACH for bilges is also 5. If you convert the ACH to ACM (Air changes per minute) you will find ACM = 5 / 60 (min/h) = 0.0833
    0.0833 (1/min) is the reciprocal value of 12 (min). 1/12 = 0.0833; 1/0.0833 = 12
     
    Manfred.pech likes this.
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