What purpose does the VRF Supply Air Fan Operating Mode Schedule serve?

I am having some issues with unmet hours on my VRF system in OpenStudio and am trying to better understand the various fields associated with OS VRF systems. Which fan does the Supply Air Fan Operating Mode Schedule refer to? This appears to be separate from the overall Terminal Unit Availability Schedule as well as the availability schedule under the OS:Fan:OnOff section.

When I ran the ZEDF VRF with DOAS measure, this field came populated with an Always Off Discrete schedule. I am having significant difficulty resolve unmet hour for heating and cooling (seemingly a common complaint with this system) and am wondering if it could be related to this.

Thanks

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1.2k

jbatt

asked 2021-05-10 14:52:02 -0500

4.4k

__AmirRoth__

updated 2021-07-09 17:47:04 -0500

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I agree that it's confusing. To understand what's happening, note the EnergyPlus documentation for this field:

This alpha field defines the name of the supply air fan operating mode schedule. Schedule values equal to 0 denote cycling fan/cycling coil operation. All other schedule values denote constant fan/cycling coil operation.

In OpenStudio, the "Always Off Discrete" schedule is a generic schedule with a constant value of zero throughout the year, while the "Always On Discrete" schedule is a generic schedule with a constant value of one throughout the year.

Therefore using the "Always Off Discrete" schedule for the Supply Air Fan Operating Mode Schedule field is telling EnergyPlus that the fan cycles with the system (whereas using the "Always On Discrete" schedule would tell EnergyPlus that the fan is continuously running).