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  1. #1
    Join Date
    Apr 2010
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    Post Difference between By pass and Pressure independent VAV boxes

    Hi !!!

    I wish to know whath the basic difference between Bypass and Presure Independent VAV boxes in terms of.

    1. Technology
    2. Operation
    3. Energy efficency.

    PLease help me in understanding the difference please

  2. #2
    Join Date
    Sep 2004
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    a bypass is just a component of a vvt system, to dump air into the return instead of a vfd. that is in a nutshell!!!!!!!!!!

    VAV stands for Variable Air Volume. VAV boxes provide constant or variable air depending on the temperature demands of the space. As the temperature rises the VAV damper opens to send a designed amount of airflow to the room. There are many different types of vav units:

    Single Duct
    Dual Duct
    Fan Powered
    Series Fan
    VAV boxes can also be classified as pressure independent and pressure dependent. A pressure independent VAV measures cfm and will maintain the proper airflow regardless of the box inlet static pressure provided by the main air handling unit. A pressure dependent VAV does not measure airflow. The cfm will change depending on the inlet static pressure. VAV systems are also usually designed with a diversity factor which means that the main air handler design airflow is less than the sum of the total airflow of all the VAV's. This is a common design because not all of the VAV's in a building will be in full cooling or maximum cfm all at once. There are three ways that a VAV can be controlled; pheumatic, electric, or Automated Control Systems (ACS). Pneumatic control systems are becoming obsolete. The VAV damper is opened and closed by a controller sending air pressure to an actuator hooked to the VAV damper. Electric simply sends a signal from the thermostat in volts to an electric motor connected to the VAV damper. ACS works the same as electric except there is a main computer set up in the building that gets information from all the VAV's and air handlers displaying it in text and graphics form. The possibilities are endless with automated controls and is truly a huge leap forward in the HVAC industry

    true knowledge exists in knowing that you know nothing.

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