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MarketManager » Loads and Sizing
Q: When I auto-size the Fans and Zone Air in the Plant data form, what formulas are used to adjust both the supply and return fan cfms?


1. The Zone | Sply Air form:

First, let me explain how the Zone | Sply Air form works.

    1. MarketManager already knows the zone loads for the zone (as they are recalculated each time you input something).
    2. MarketManager also knows the zone design temperatures for heating and cooling (which are located at the bottom of the Zone data form).
    3. In the Zone | Sply Air form, there are inputs for supply air temperature for heating and cooling. The defaults for these are 110F and 55F. The Zone | Sply Air form uses the equation listed below to determine cfm requirements for heating and cooling (they are not the same):
    4. Zone Loads = 1.08 X cfm X T

      where T = (Tdesign - Tsupply) for cooling and (Tsupply - Tdesign) for heating

    5. When you autosize zone air, MarketManager will take the maximum of:
  • the cooling supply air requirement (cfm),
  • the heating supply air requirement (cfm), and
  • the ventilation requirement (cfm) (which come from the Use Defaults form).

The greatest of these three will be the Zonal Supply Air requirement.

2. The System Form:

The System form will sum all the Zonal Supply Air requirement for all zones attached to the system. You can see this near the bottom of the System | Detail form. (It says "sum of zone cfm = " and some number.)

3. Fans

When you autosize fans, the fans will be sized to match the total zonal cfm requirement as shown in the System | Detail form (mentioned above).

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Otherwise feel free to contact our Tech Support staff at (805) 329-6565, or via email at helpdesk@abraxasenergy.com.

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