No Load Airflow Through Fancoil

asked 2017-01-18 11:49:49 -0500

willyJohan
1520 ●1 ●5 ●10

updated 2017-08-05 07:42:24 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Can some one please tell me what the inputs for "supply air flow Rate When no Cooling is Needed" and "supply air flow Rate When no Heating is Needed" do for the object OS:ZoneHVAC:TerminalUnit:VariableRefrigerantFlow when coupled with a DOAS?

Feels like these should be hard sized to zero but the default seems to be autosize when creating a VRF system using measures (and then EnergyPlus just autosizes the values to be the same as the airflow rate when heating or cooling is needed). At the most I would expect the no heat/cool airflow to be equal to the outdoor airflow but even this does not make sense given that the DOAS air loop does not seem to be integrated with VRF terminal units.

I feel like I must be missing something obvious, any insight would be appreciated.

answered 2017-01-18 12:17:36 -0500

rraustad

13599 ●72 ●12 http://www.fsec.ucf.edu/

HVAC systems can provide a different air flow rate when the coils are off and the fan continues to operate. These inputs denote the flow rate when the coils are off and constant fan mode operation is selected. If cycling fan mode is used the fan turns off when the coils are off. If the fan operating mode schedule is not entered (blank input) constant fan operating mode is always used and these inputs show the fan flow rate when the coils are off.

When these inputs are autosized the results are a single speed fan that runs at the same cooling or heating speed when constant fan mode is used.

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Thanks @rraustad

So, if i understand correctly, I need to set the "Supply Air Fan Operating Mode Schedule" to a constant value of 0. Should i also hard size the "supply air flow Rate When no XXX is Needed" to 0 or just leave auto sized?