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  • Home
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  • SketchUp Models
    • SketchUp Resources
    • Bureaucratic Affairs Building HHW System Logic Exercise
    • Bureaucratic Affairs Building Scavenger Hunt
    • Chilled Water Plant System Diagram Exercise
    • The HIjend Hotel >
      • Chilled Water Plant Scoping Exercise
      • Ballroom AHU Scoping Exercise
      • Cooling Tower Scoping Exercise
  • Tools
    • Altitude Correction Factor
    • Economizer Evaluation Checklist
    • Eikon for Educators and WindLGC
    • Effective Duct Length Tool
    • Excel Third Axis Tool
    • Excel Time Value Conversion
    • Insulation Savings Tools
    • Logic Diagram Tool >
      • Logic Diagram Example - Discharge Air
      • Logic Diagram Example - CHW Plant 01
      • Logic Diagram Example - VAV AHU
    • Mixed Air Calculations
    • Monitoring Plan Spreadsheet
    • Pipe Friction Chart
    • Plot Digitizer >
      • Plot Digitizer Pump Curve Example
    • Square Law Spreadsheet
    • System Diagram Symbols
    • Thermodynamic Diagrams Spreadsheet
    • Universal Translator Data Analysis Tool
    • y = (m * x) + b Spreadsheet
  • Useful Formulas
    • Affinity Laws
    • Circular Equivalent Duct
    • Effective Duct Length
    • FT Guide Appendix C
    • HVAC Equations and Concepts
    • Hydraulic Diameter
    • Pump Power and Energy
    • "Square Law"
  • What's That Thing?
    • Cooling Towers
    • Pumps
    • Valves
  • Resources
    • Bill Coad's Writings
    • Data Logging Resources
    • EBCx Skills Guidebook
    • Energy Design Resources
    • Fisher Controls Valve Cavitation Bulletin
    • Functional Testing Guide
    • Honeywell Gray Manual
    • MCC Powers Bulletins
    • NBCIP Reports
    • PEC Tool Lending Library
    • PID Resources
    • Pneumatic Control Resources
    • Resource List
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    • TAB Resources
    • Vintage Carrier Design Manual
    • VRF Systems
    • Williams' Wisdom
  • Videos
    • Bureaucratic Affairs HHW Logic Answers
    • Cooling Tower Flow Variation
    • Economizer Stratification
    • Functional Testing
    • Induction Principles
    • Monitoring Plans
    • CW Pump Deadheaded by Tower Lift
    • Ripple Effects
    • Testing a Pump
    • The Garden of Low Entropy
    • Variable Flow Systems
  • Training
    • Materials from Classes and Presentations >
      • ACEEE
      • ASHRAE
      • ASHRAE - Engineers Notebook
      • BCxA and NCBC
      • BEST Institute
      • Case Studies
      • ERDC 2020 RCx Academy
      • ELPNW
      • ICEBO
      • Marriott AEP
      • Magazine Articles
      • NAVFAC
      • Pacific Energy Center Design, Performance and Commissioning Issues Classes
      • Pacific Energy Center EBCx Project Review
      • Pacific Energy Center EBCx Workshop Series >
        • EBCx Workshop Series 12
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      • Portland General Electric
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Ripple Effects

These two videos are screen captures I did to convey a problem to the commissioning team instead of writing an annoyingly long e-mail with pictures that explained the problem (which, as some may know, I am very capable of doing).
Both of these videos are from the same project.   The first video illustrates how an upset in one control process can ripple out and cause upsets in other control processes. 

Specifically, int this example, an upset in the fan speed control loop, caused by an operating mode change that needed a larger differential, was rippling out and causing a significant disturbance in the zone temperature control processes;  about a 2°F change in temperature in an hour or so.  
The diagnostic technique involved locking the fan speed down and observing the result.   When we did that, the zone temperature stabilized, indicating that the upset we were seeing in the zone was being driven by the upset we were seeing in the fan speed control process (vs. the zone temperature upset driving the fan speed upset).   

That observation focused our troubleshooting on the fan speed control process, which led us to the realization that there was an operating mode change that was being enabled and disabled too quickly.  When we spread out the differential on that process, the fan speed control process stabilized, as did the zone temperature.

This video also features cameo appearance by Riley Sellers as the dog barking in the background.
This second video is alluded to in the first video.  It is another example of how an upset in one system can ripple out and cause issues in a different system.

In this particular instance, a very minor (3-4%) hunt in the control process for a chilled water valve serving one of three air handling systems in an archival storage facility was causing the chillers in the central plant serving the facility to trip out on low evaporator temperature and pressure.
The diagnostic approach we suggest is identical to the approach suggested in the first video;  i.e. lock down the suspected culprit control process and observe what happens.   

​When we did that the problem went away, which focused our attention on the control processes associated with the errant chilled water valve.   That revealed another mode change issue with a differential that was set too tight.  In this case, the system was jumping from a temperature based control process to a humidity based control process due to very minor variations in the temperature sensed by the sensor triggering the change;  like a hummingbird fluttering by the sensor would likely trigger a change-over event.  Spreading out the differential solved the problem.

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