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do I need to multiply the outdoor air flow rate according to zone multiplier?

asked 2017-04-25 11:59:00 -0500

dalin_si gravatar image

updated 2017-04-25 14:02:54 -0500

If one zone needs 32 cfm outdoor air,I set the outdoor flow rate as 32 cfm in PTAC. so if this zone have multiplier 3, do I need to set it as 96 (32*3) cfm?

from this link, I know the Zone multipliers are designed as a “multiplier” for floor area, zone loads, and energy consumed by internal gains during load calculation. The HVAC system size is specified to meet the entire multiplied zone load. But is this 32 cfm included in load calculation? if it include in load caculation, it should be 32cfm, otherwise should be 96, am I correct?

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answered 2017-04-25 14:02:14 -0500

updated 2017-04-28 07:16:55 -0500

Do the experiment yourself:

  • Take an E+ example file that leverages DesignSpecification:OutdoorAir, eg: 5ZoneAirCooled.idf
  • Add the output variable Output:Variable,*,Air System Outdoor Air Mass Flow Rate,Monthly;
  • Create another version were you assign to each Zone a multiplier of 3
  • Loop at the output, and decide...

Zone mult of 1: Air System Outdoor Air Mass Flow Rate sums to annually 1.61, one mult of 3 is 4.83. That does look like it's getting multiplied by 3.

Caveat: If you have hardsized your loop or outdoor air flow rates to a wrong value, it can get capped... so watch out for this.

Please do not read generalize this answer blindly. DesignSpecification:OutdoorAir objects for example are indeed affected by zone multipliers, but there are a number of airflow related objects that aren't (Fan:ZoneExhaust` for example). Please read this question for more info.

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Asked: 2017-04-25 11:59:00 -0500

Seen: 151 times

Last updated: Apr 28 '17