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How to model night cycling for VRF in OpenStudio?

asked 2016-05-25 10:46:46 -0500

updated 2016-05-25 11:04:14 -0500

Is there a way to use night cycling for VRF systems in OpenStudio 1.11? If I click the "control" tab for the VRF systems, a message says that "control options are currently only available for air systems." I tried putting a schedule for the VRF fans to be on during occupied hours and off during unoccupied hours, but I would like to model these fans similar to with an air loop where they can cycle on and off during unoccupied hours. ASHRAE 90.1-2007 section G3.1.2.4 requires both baseline and proposed HVAC fans providing ventilation air must be modeled as operating continuously during occupied hours and cycled to meet cooling and heating loads during unoccupied hours.

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answered 2016-05-28 12:47:43 -0500

To make the VRF terminal night-cycle:

  1. Create a new schedule that is 0 at night, 1 during the day
  2. Assign this new schedule to the Supply Air Fan Operating Mode Schedule of each VRF terminal.


According to the ZoneHVAC:TerminalUnit:VariableRefrigerantFlow docs:

Field: Supply Air Fan Operating Mode Schedule

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 default schedule for this field is 'Always On Discrete', which always has a value of 1, meaning constant fan/cycling coil operation all the time.

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Thanks @aparker. That is what I had originally tried. I am not sure if it was actually cycling the fans on and off at night because the fan consumption remained about the same as with the always on supply fan schedule.

kramerica's avatar kramerica  ( 2016-05-31 11:12:45 -0500 )edit

@kramerica you could report out Fan Electric Power at the Detailed timestep and see what the fans are doing.

aparker's avatar aparker  ( 2016-05-31 13:26:03 -0500 )edit

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Asked: 2016-05-25 10:46:46 -0500

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Last updated: May 28 '16