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Can OpenStudio do LEED 62.1 multizone calcs?

asked 2015-09-09 13:06:32 -0500

Is it possible to use OpenStudio to do 62.1 multizone calcs for LEED EQp1 and EQc2? I would like to use OpenStudio to calculate the required outdoor air intake for multizone systems rather than the 62MZCalc spreadsheet. To do this would require a critical zone for each multizone system based on zone area and population.

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answered 2015-09-09 15:33:21 -0500

Yes, you can do VRP with OpenStudio. Ostensibly the engineers who designed the systems also did these calculations, and therefore your modeled results should match the mechanical schedule. However, differences between their assumptions about space type, design occupancy, and zone air distribution effectiveness could lead to differences in results. Given these caveats, here's how to do it in OS:

  1. Make sure your spaces have DesignSpecification:OutdoorAir objects setup with the correct per-area and per-person values. The OpenStudio templates have these setup already.
  2. Click on the dashed line in the middle of your AirLoop
  3. In the Inspector (right column), scroll down to Sizing:System and set the "System Outdoor Air Method" to "VentilationRateProcedure"
  4. After you run the simulation, open the EnergyPlus Results file. There will be a 62.1 section that breaks down the values used in the VRP calculation, which you can double-check.

For more info on how E+ implements VRP, read this section in the engineering reference.

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@aparker I noticed when I select 'VentilationRateProcedure' in the 'Sizing:System' object the translated E+ file shows the 'Controller:MechanicalVentilation' still maintaining its 'ZoneSum' value for the System Outdoor Air Method. Is there a reason for this?

Lincoln's avatar Lincoln  ( 2015-09-11 09:48:02 -0500 )edit

@Lincoln, specifying "VentilationRateProcedure" does something different in each object:

Sizing:System Specifying VRP does the multizone equations once, up-front, and sets the system min OA flow rate to the resulting value. Assuming you have no other fancy controls, this will be the lowest flow rate the VAV system can drop down to during the simulation.

aparker's avatar aparker  ( 2015-09-11 13:35:57 -0500 )edit

Controller:MechanicalVentilation Specifying VRP means that at every timestep, the multizone equations are run, and overall OA can sometimes be reduced. This is typically used to model "Multiple-zone VAV System Ventilation Optimization Control" as specified in 90.1 Section Section of this document has a pretty solid description of this type of control.

aparker's avatar aparker  ( 2015-09-11 13:36:47 -0500 )edit

Thanks for the calirification @aparker

Lincoln's avatar Lincoln  ( 2015-09-13 22:19:36 -0500 )edit

@aparker, can you help me in other question about to EnergyPlus X ASHRAE 62.1? Thanks!

Geraldo Pithon's avatar Geraldo Pithon  ( 2016-01-18 15:23:47 -0500 )edit

answered 2015-09-09 14:54:32 -0500

nfonner's avatar

I have not seriously attempted this with OpenStudio, but yes, there is an option to show compliance with Minimum Ventilation (VRP) using modeling software for LEED. I would caution that it is much more important that the air handling equipment schedule be the basis of the modeled ventilation rate rather than flicking the switch for VRP calculations in OpenStudio and toying around with the max Z ratio. The Min Ventilation credit is only to show that enough outdoor air is provided as scheduled. I have seen projects go through appeals in order to get this right.

I usually just fall back to using the 62MZCalc on suspected critical zones.

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Asked: 2015-09-09 13:05:48 -0500

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Last updated: Sep 09 '15