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PsyRhoAirFnPbTdbW: RhoAir (Density of Air) is calculated <= 0

asked 2022-08-29 08:31:24 -0600

ecroftFoE's avatar

updated 2022-08-30 09:03:22 -0600


I have read through the other posts that are related to this error and am still unable to fix my error. I am brand new to OpenStudio, so I am unsure of how to continue with my simulation. I'm working on the severe errors before I work through the warning errors. The only error I am receiving is below.

* Severe * PsyRhoAirFnPbTdbW: RhoAir (Density of Air) is calculated <= 0 [-0.52081]. * ~~~ * pb =[98088.00], tdb=[-914.65], w=[1.4285632E-002]. * ~~~ * Routine=CorrectZoneHumRat During Warmup, Environment=EAU_CLAIRE ANN CLG .4% CONDNS DB=>MWB, at Simulation time=07/21 00:00 - 01:00

I have natural gas fired furnaces with exhaust fans for each thermal zone, I do not have the furnaces autosized. They are 80% efficiency at 80,000 btu/h. I am just trying to establish a baseline for a small office before working with higher efficiency equipment. When running my simulation I currently have the OS measure surface matching and Energy+ measure add output diagnostics. Am I missing anything to just run a basic energy evaluation on a building?

I'm new so I cannot upload documents as of yet. I can send the error document and photo if needed. Thank you in advance.


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@ecroftFoE instead of uploading documents & photos, you can store them on Google Drive, Dropbox, etc. and then share the URL to those files in your post here on Unmet Hours.

Aaron Boranian's avatar Aaron Boranian  ( 2022-08-30 09:04:17 -0600 )edit

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answered 2022-08-30 09:03:38 -0600

This type of warning, where tdb=-914.65 C, typically means the zone is not getting heated. You might add reporting during warmup and reports (output:variable) for the zone temp and furnace performance to see why the zone does not get heated.

Output:Diagnostics, ReportDuringWarmup;

Output:Variable,*,Zone Mean Air Temperature,hourly;

Output:Variable,*, something showing how your equipment is operating , hourly;

See the rdd file for available output report variables.

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Thank you for this answer. This prompted me to go deep into all my HVAC to make sure everything had the proper schedules and setpoints. I was missing the heating schedule on one of my thermal zones. I successfully got a full simulation to run this morning, and can now start adding in different measures and parameters. Thanks again!

ecroftFoE's avatar ecroftFoE  ( 2022-09-01 09:35:37 -0600 )edit

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Asked: 2022-08-29 08:31:24 -0600

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Last updated: Aug 30 '22