Possible bug in infiltration reporting

[mleachNREL]

The output from the following variables doesn't seem to make sense:

Zone Infiltration Current Density Volume Flow Rate Zone Infiltration Standard Density Volume Flow Rate

In the IDF there are 4 ZoneInfiltration:DesignFlowRate objects. Each of those is assigned to the same fractional schedule. If I sum the design flow rates for those 4 objects, multiply by the current schedule value, and then multiply by the current density, I get an exact match with the mass flow rate output (Zone Infiltration Mass Flow Rate). But the conversions between kg/s and m3/s (current and standard) don't make sense. For example, the conversion between kg/s and m3/s current should just be the current density, but it is not.

What I'm actually interested in is the ACH output variable (Zone Infiltration Air Change Rate). I can use the zone volume to convert m3/s current to ACH and that checks out, but the reported ACH value looks wrong because the m3/s current reported value is wrong.

Details

Some additional details for this issue (if relevant):

• Platform: Windows 64 bit
• Version of EnergyPlus: 9.4

infiltration_output_test.zip

[mjwitte]

@mleachNREL Are you using the outdoor current density? That's what the ZoneInfiltration: and ZoneVentilation: objects use to convert from volume flow to mass flow.

[mjwitte]

But the ACH will be based on the current zone density.

[shorowit]

It is indeed incredibly confusing.

Until https://github.com/NREL/EnergyPlus/issues/4422 is addressed, as @mjwitte alludes to, you can calculate an output flow rate that matches the inputs to the ZoneInfiltration:DesignFlowRate object by using this calculation:

Flow Rate [m3/s] = (Infiltration Mass Flow Rate [kg/s]) / (Environment:Site Outdoor Air Density [kg/m3])

[shorowit]

Another user confused by this: https://unmethours.com/question/99734/zoneventilationdesignflowrate-fluctuates/