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OpenStudio: DOASVRF design and warning of not enclosed zones

asked 2025-06-17 11:57:50 -0500

LIANG Peijun's avatar

updated 2025-06-17 12:46:53 -0500

Hello everyone!

I am currently working on a DOASVFR system design that only applies to a few zones, but cannot solve humidity problems. The DOASVFR system consumes much more energy than the VAV system, and has little effect on the cooling condition. Besides, the warnings keep reporting the not enclosed zone problems, even though I had already hard-sized the zone volume. Can I do anything to fix these problems?

 ** Warning ** CalculateZoneVolume: The Zone="ELCT ALL" is not fully enclosed. To be fully enclosed, each edge of a surface must also be an edge on one other surface.
 **   ~~~   **   The zone volume was calculated using the floor area times ceiling height method where the floor and ceiling are the same except for the z-coordinates.
 **   ~~~   **   The surface "SURFACE 863" has an edge that was used 4 times: it is an edge on three or more surfaces: 
 **   ~~~   **   The surface "SURFACE 1440" has an edge that was used 4 times: it is an edge on three or more surfaces: 
 **   ~~~   **     It was found on the following Surfaces: 'SURFACE 1441' 'SURFACE 1445' 'SURFACE 1446' 
 **   ~~~   **     Vertex start { 5.8000, 95.2500, 27.4000}
 **   ~~~   **     Vertex end   { 5.8000, 95.2500, 22.0000}
 **   ~~~   **   The surface "SURFACE 1441" has an edge that was used 4 times: it is an edge on three or more surfaces: 
 **   ~~~   **     It was found on the following Surfaces: 'SURFACE 1442' 'SURFACE 1445' 'SURFACE 1450' 
 **   ~~~   **     Vertex start { 5.8000, 95.2500, 27.4000}
 **   ~~~   **     Vertex end   { 5.8000, 91.8000, 27.4000}

This is my osm. filelink text.

I am a complete freshman in HVAC system design, and do not have many ideas about the parameters, like the design air flow or the equiments sizing.

Does anyone know how to solve the problem?

Thanks, any assistance would be greatly appreciated!

Sincerely, Peijun

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Looks like a variant of the model discussed here. The OSM holds a degenerate surface (triggers a SEVERE error), and +dozen interzone surface mismatches. The enclosed volume issues are just reported as warnings, and as such would not be the main source of worry for now. Tested with OS App v1.9: got a fatal error with SetpointManager:OutdoorAirReset="OA TEMP RESET". I'd look into fixing the latter, and the degenerate surface first ...

Denis Bourgeois's avatar Denis Bourgeois  ( 2025-06-17 14:15:32 -0500 )edit

Thank you, Denis. The model is similar to the one you refer to. But during my simulation, there was no alert about the Setpoint Manager. Can you explain a little bit? Thanks a lot.

LIANG Peijun's avatar LIANG Peijun  ( 2025-06-17 21:26:04 -0500 )edit

I have v3.9.0 (App v1.9.0) installed, so I simply ran your v3.8.0 .osm file with the latest App. That's something you should try, or else share your generated run/eplusout.err file.

Denis Bourgeois's avatar Denis Bourgeois  ( 2025-06-18 11:14:26 -0500 )edit

@Denis Bourgeois Thank you so much for your time! This is the latest version of my OSM. file, and the eer. file. I tried to solve the mismatched surfaces by reversing them through the SketchUP plugin, and it seems that the warning would not come up again. But I still don't have much ideas about the SetpointManager.

LIANG Peijun's avatar LIANG Peijun  ( 2025-06-18 11:35:40 -0500 )edit

@LEUNG Peijun It looks like you still have some spaces that are separated from each other, like in your previous post https://unmethours.com/question/10139...

Ski90Moo's avatar Ski90Moo  ( 2025-06-20 09:25:33 -0500 )edit

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answered 2025-06-23 14:19:57 -0500

Some zones still have an unrealistic occupant density. The building code minimum is 5sqft/person (0.46sqm/person) for standing, assembly without seats. Some spaces have less than this. (see building code https://codes.iccsafe.org/content/IBC...).

The main problem appears to be the DOAS. It accounts for 99.9% of the zone load.

One problem is that you have specified a very low humidity ratio for the DOAS sizing. 0.004 is saturated at freezing; I doubt the DOAS system will be operating the dehumidification coil at freezing temperatures. It will cause convergence problems. More realistic would be to set the humidity ratio closer to the expected space design humidity (60%RH @ 24°C = 0.011). Or use the default Humidity Ratio Difference method and value (0.005). I think the difference method is more realistic as it would prevent oversizing/convergence issues and it is better for a steady state operation. It is unrealistic to expect the system to be sized for maximum dehumidification during high humidity startup.

Another problem is that the specified Zone Humidistat Dehumidification Set Point Schedule (Inlet Air Humidity=0.6 constant) was specified as a dimensionless positive schedule. Per the InputOut reference, this schedule should be a percentage schedule that specifies Relative Humidity. Create a percent schedule set at 60 and assign this instead.

Another problem is that the design outdoor airflow per person has been specified as 31,783 cfm/person (15m3/s/person). This is way too high. For assembly type spaces the ventilation per person can range from 7.5-10 cfm/person (0.0035-0.0047m3/s/person) (see building code https://codes.iccsafe.org/content/IMC...).

Another problem is that there are many zones with zone exhaust fans; each with a high airflow of 42,377cfm (20m3/s). These zones are not associated with the DOAS, so it would not affect the DOAS sizing. However, if they are attached to an airloop system, it will cause the airloop outside airflow to be very large. You should review the size of these to ensure they are realistic.

https://imgur.com/a/FVRMYG9

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@Ski90MooThanks so much for your time and patience! Your insight was really helpful. I knew there were issues with my space type and DOAS parameters, but I had no idea where to start fixing them. Your answer really cleared things up for me. Thanks again!

LIANG Peijun's avatar LIANG Peijun  ( 2025-06-23 22:59:56 -0500 )edit

No worries, cheers! :)

Ski90Moo's avatar Ski90Moo  ( 2025-06-24 00:10:12 -0500 )edit

Hi,Ski90Moo! I solved most of the problems of my model, so I started to build the HVAC system. I separately modeled a VAV and DOASVRF system on the same building. However, I found that the DOAS system consumed much more energy than the VAV one, and the warning kept reporting PLR>1. Does that mean the outdoor unit is inadequate for cooling demand? I use the Mitsubishi in/outdoor VRF unit uploaded by you.

LIANG Peijun's avatar LIANG Peijun  ( 2025-07-03 04:33:37 -0500 )edit

These are my models: DOASVRF, VAV. Thanks again for your assistance and advice.

LIANG Peijun's avatar LIANG Peijun  ( 2025-07-03 04:35:37 -0500 )edit

I think, but I am not sure, that the main problem is that you are using a Coil:Cooling:DX:TwoStageWithHumidityControlMode with three stages. It appears that this object has four dx coils attached to it. You should read up on the proper application of this object: https://bigladdersoftware.com/epx/doc...

Ski90Moo's avatar Ski90Moo  ( 2025-07-03 08:22:08 -0500 )edit
3

answered 2025-06-18 15:07:54 -0500

updated 2025-06-19 09:02:09 -0500

@LEUNG Peijun : This is not a list of definitive fixes for your model - just highlighting a few below.


I ran the latest version of your .osm file using the OpenStudio Application (App) v1.9.0 (EnergyPlus 24.2.0). EnergyPlus again halted the simulation with 2x FATAL errors. It's probably worth testing (a copy of) your model against the latest App to compare reported errors/warnings between EnergyPlus releases. Here's the relevant excerpt of the generated eplusout.err file:

image description

The EnergyPlus feedback is fairly clear on the error. I suggest you go over the concepts here, and input parameters here. This seems to be the culprit entry:

image description

Admissible values should be "1" or "2" - not "0".


The eplusout.err file reports an unusually high occupancy density:

image description

... which may be at the root of other occupant-related errors, e.g. calculated (billions!) m3/s:

image description


On interzone surfaces & constructions: Fix the default interior wall construction ...

image description

... so it's symmetrical (Layer 1 should be the same as Layer 3). This should get rid of numerous related warnings:

image description


Again, this is just a selection of issues/fixes. I suggest you adopt an iterative QAQC approach to fixing your model:

  • prioritize an issue to fix, then fix
  • re-run the simulation
  • go over (in detail) the generated eplusout.err file
  • start over

Until you have fixed the bulk of the errors and warnings, I wouldn't pay too much attention to reported energy use at this point ...


EDIT : Finally ran the model using OpenStudio Application 3.8.0. As you indicated, the model runs without FATAL errors from EnergyPlus. That's interesting. It's not as if EnergyPlus recently changed policy on outdoor air reset parameters. That said, many of the same anomalies (discussed above) are reported in the eplusout.err file, such as the (huge) calculated design max air flow rates.


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@Denis Bourgeois Thank you for your time and suggestions provided, which were greatly helpful. I figured that the problem with the setpoint manager is due to the incorrect schedule name, and that warning disappeared after changing the schedule value to 1. The construction conflict resulted from dragging the same material from the library to the construction where the system would automatically rename the material. It can be easily solved by dragging the same material from my model tab.

LIANG Peijun's avatar LIANG Peijun  ( 2025-06-19 09:16:16 -0500 )edit
1

I opened the model and separated everything into its own thermal zone and assigned ideal air loads. This is the best way to troubleshoot model problems (except for HVAC systems). It appears you have several zones with very high occupant densities: https://imgur.com/a/mcPrmBP This issue will cause problems with convergence as Denis noted.

Ski90Moo's avatar Ski90Moo  ( 2025-06-20 12:57:09 -0500 )edit

@ Ski90MooThanks for your time and effort. I separated all the thermal zones and tried to test the HVAC system. Therefore, I applied the measure: NZEHVAC to the 1st floor of the building and shortened the simulation period to 3 days. However, the Design load and Design Air Flow were strangely huge. The dehumidifier was also not working. All the data seems to be weird. How can I make the HVAC system work normally?link text

LIANG Peijun's avatar LIANG Peijun  ( 2025-06-22 12:29:18 -0500 )edit

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Asked: 2025-06-17 11:57:50 -0500

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Last updated: Jun 23