How to enforce Duty Cycle for Fan:OnOff object

asked 2016-11-04 15:29:19 -0600

EplusNewb
41 ●2

updated 2016-11-10 11:04:36 -0600

__AmirRoth__

4446 ●5 ●17 http://bleedinggreenna...

Hi, I am using a fan:onoff object within a Zone:HVAC:TerminalUnit:VariableRefrigerantFlow object, and for some reason even though my runtime fractions for the heating and cooling coils within the object are often between 0 and 1 (i.e. 0.5), the runtime fraction for the Fan:OnOff only bounces from 0 to 1, 1 if there is any load, and 0 if there is no load. The engineering and I/O reference seem to suggest that the fan power and runtime fraction should calculate as if the fan cycles with the coils, but in my model this is clearly not the case. I would appreciate any help. Is there a specific input to force the fan to behave the way I want?

answered 2016-11-07 07:57:43 -0600

rraustad

13834 ●79 ●12 http://www.fsec.ucf.edu/

Look at the VRF terminal unit object and check whether the fan operating mode schedule is cycling (0) or constant (anything other than 0). What you describe sounds like constant fan operating mode.

ZoneHVAC:TerminalUnit:VariableRefrigerantFlow,
  VRFFanSchedule,          !- Supply Air Fan Operating Mode Schedule Name

Schedule:Compact,
  VRFFanSchedule,          !- Name
  Any Number,              !- Schedule Type Limits Name
  Through: 12/31,          !- Field 1
  For: AllDays,            !- Field 2
  Until: 7:00,0.0,         !- Field 3
  Until: 18:00,1.0,        !- Field 5
  Until: 24:00,0.0;        !- Field 7

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Thank you, in the schedule I had designated it does appear to cycle between the 2 modes (0 and 1). I did not previously realize that the schedule in the compound object is where I can select the mode. I appreciate the help!