Series Fan Powered Box or Parallel?
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  1. #1
    Join Date
    Nov 2006
    Location
    Columbus, OH
    Posts
    40

    Series Fan Powered Box or Parallel?

    I'm working on a project where there is a space that requires a VAV box. I am using a fan powered box. There is a medium pressure supply main to tap into to get air to the box. How do I know if I should use a parallel or series box?

  2. #2
    Join Date
    Nov 2003
    Location
    Boston
    Posts
    600
    Series box = constant volume to room
    Parallel box = variable volume to room.

    http://www.titus-hvac.com/ecatalog/g...px?fileid=7564
    Edited by powerhead on more than one occasion

  3. #3
    Join Date
    Dec 2005
    Posts
    107
    Series boxes perform better overall in providing comfort to occupants. No on/off periods like a parallel unit with different airflow and noise characteristics. Parallel units are generally less energy intensive.
    The real question is why use a series fan powered unit on a medium pressure ductwork. The booster fan concept of lower pressure main air is not required since you already have the pressure. A single duct box would probably be the best and easiest choice.

  4. #4
    Join Date
    Sep 2010
    Location
    Dallas/Ft. Worth
    Posts
    1
    Many studies now show that the energy usage is equal between series and parallel fan VAV systems. Yes, the fan operates less of the time on a parallel, but since our DDC systems regularly perform load calculations for the zones they serve, they can adjust their supply air temperature and only use the amount of cooling necessary to each zone. The constant flow from a series box means the tenant also doesn't hear the click of the fan relay, only the heat contactor in winter.

  5. #5
    Join Date
    Jun 2008
    Location
    NY
    Posts
    33
    Does your vav require heat or is it an interior space for cooling only? I have usually see the fan powered boxes used for exterior vav's for cooling and with supplemental heating only. Interior cooling only vav's do not usually have fans.

  6. #6
    Join Date
    Dec 2003
    Location
    Princeton Texas
    Posts
    114
    Agree with darter1, all of our parallel systems are for when cooling only is supplied. then parallel fan will energize the box heat and draw the air strait from the attic return, shuting down your cooling side damper. The series usually will be heating then switch to cooling or will have a hot and cold coil in the boxes. Depends on aplication. Hot deck or cold deck or hot and cold deck.

    Redfive

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