Air leakage in parallel fan-powered terminal units

[lymereJ]

Pull request overview

Add new inputs/outputs to model air leakage in parallel fan-powered terminal units.

Pull Request Author

• Title of PR should be user-synopsis style (clearly understandable in a standalone changelog context)
• Label the PR with at least one of: Defect, Refactoring, NewFeature, Performance, and/or DoNoPublish
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[mjwitte]

@lymereJ Is this targeted for 25.2?

[lymereJ]

@mjwitte - Ideally, yes, but it's not quite ready. I'm hoping to be able to get back to it sometime next week.

[github-actions]

⚠️ Regressions detected on macos-14 for commit e0cfaf5

Regression Summary

• Audit: 4
• RDD: 4

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on ubuntu-24.04 for commit 002d49a

Regression Summary

• Audit: 4
• RDD: 4

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on ubuntu-24.04 for commit e0cfaf5

Regression Summary

• Audit: 4
• RDD: 4

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on macos-14 for commit fe079e3

Regression Summary

• Audit: 4
• RDD: 4

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on ubuntu-24.04 for commit fe079e3

Regression Summary

• Audit: 4
• RDD: 4

• View Results
• Download Regressions

[lymereJ]

The following plots show results generated using this branch for the new example file, for two cases: with and without leakage for the parallel PIU terminal serving "Space1-1". The terminal fan pulls air from "Space5-1", that is also the zone that is impacted by the leaks since they occur through the backdraft damper.

Heating and dead-band operations:

• Air is leaking only when the terminal fan is off
• During dead-band the flow to the zone (SPACE1-1 IN NODE) is equal to the primary air flow rate - the leaks

**Cooling operations:**

• During cooling operation, the primary air ramps up, so do the leaks (top, maroon)
• The impact of the leaks on "Space5-1" are shown on the bottom panel

These results for the new example file are still relevant.

I conducted additional tests on a model that uses an AirLoopHVAC:ZoneMixer instead of an AirLoopHVAC:ReturnPlenum as the return path. The results appear to be as expected. For example, when analyzing the return air, its temperature during simulations with leaks is lower compared to the case without leaks. This outcome aligns with expectations, as backdraft damper leaks only occur during dead-band and cooling operations, causing the return air to be cooler. In the figure below, the top panel illustrates the return air temperature (blue for leaks, orange for no leaks), while the bottom panel depicts the return air mass flow rate (maroon for leaks, dark green for no leaks).

I compared the temperature of the zone designated as the destination of the leaks for both configurations: using an AirLoopHVAC:ZoneMixer and an AirLoopHVAC:ReturnPlenum object. In both cases, the designated zone is a plenum, and the annual temperature profiles are almost identical. In the figure below, the orange line represents the temperature of the plenum zone without leaks, the maroon line corresponds to the case with leaks using an AirLoopHVAC:ReturnPlenum object, and the blue line represents the case with leaks using an AirLoopHVAC:ZoneMixer.

I also ran similar models in different climate zones. As expected, simulations with leaks have more impact in hotter climate zones.

Here are the additional models:

• Climate zone 5A:
  • Without leaks: large_office_5A_piu_out.txt
  • With leaks and AirLoopHVAC:ReturnPlenum as a return path: large_office_5A_piu_pl_out_leak.txt
  • With leaks and AirLoopHVAC:ZoneMixer as a return path: large_office_5A_piu_out_leak.txt
• Climate zone 1A:
  • Without leaks: large_office_1A_piu_out.txt
  • With leaks and AirLoopHVAC:ReturnPlenum as a return path: large_office_1A_piu_pl_out_leak.txt
  • With leaks and AirLoopHVAC:ZoneMixer as a return path: large_office_1A_piu_out_leak.txt

I think that this is ready for review.

[github-actions]

⚠️ Regressions detected on ubuntu-24.04 for commit 6171962

Regression Summary

• Audit: 4
• RDD: 4

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on macos-14 for commit 6171962

Regression Summary

• Audit: 4
• RDD: 4

• View Results
• Download Regressions