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Building Systems

Automated Diagnostic Algorithms for Chillers, Boilers, Cooling Towers, and Chilled Water Distribution

Boiler Picture
Commerical building HVAC equipment.

Laboratory researchers in collaboration with staff of Architectural Energy Corporation (AEC) developed logic for diagnosis of problems with chillers, cooling towers, and chilled water distribution systems in commercial buildings. This work was done in a project funded jointly by the California Energy Commission Public Interest Energy Research Program (PIER) and the U.S. Department of Energy Building Technologies Program. The logic was derived from diagnostics based on visual interpretation of data plots developed and used over many years by AEC staff. The logic is documented and requirements specified for software for automating the diagnostics in a PNNL report (Automated Diagnostics Software Requirements Specification Version 1.1) as well as a final report to the California Energy Commission (Final Report Compilation for Pattern Recognition-Based Fault Detection and Diagnostics).

The methods rely on fixed data that characterizes the equipment (e.g., rated current or power of electrical motors, temperature set points for water flows) and on metered data (e.g., outdoor ambient conditions, electrical current to fan and pump motors, and temperatures of water at various points in systems) sampled over time. Fixed data are input during set up of the software, and metered data are collected from sensors during equipment operation.

The outputs of the diagnostic processes are indicators of the condition of the various equipment. Improper operating conditions or faults lead to energy waste and accelerated wear on equipment. The major faults detectable with the diagnostic logic follow. Some of these faults have several subcategories, which isolate or specify the fault to higher resolution.

Cooling tower faults:

  • Cooling-tower fans are cycling too frequently
  • Cooling-tower fans are not staged correctly
  • Poor cooling-tower-fan and sump-temperature control
  • Cooling-tower range is too small and a problems exists with cooling-tower heat rejection
  • Cooling-tower approach is too large and problems exist with cooling-tower heat rejection
  • Cooling-tower fans and condenser pumps are not interlocked properly

Chiller faults:

  • Compressor is cycling on too frequently
  • Compressor is cycling off too frequently
  • Chiller is operating outside its scheduled times
  • Secondary and primary chilled-water pumps are not interlocked properly
  • Supply fans and chilled-water pumps are not interlocked properly
  • Compressor and condenser pumps are not interlocked properly
  • Compressor and condenser fans are not interlocked properly
  • Compressor and chilled-water pumps are not interlocked properly

Boiler faults:

  • Boiler is shut off when it should be operating
  • Boiler is running when it should be shut off
  • Hot-water pump is not synchronized properly with the boiler or controlled correctly
  • Boiler is cycling on and/or off too frequently
  • Hot-water supply temperature is too low
  • Hot-water supply temperature is too high
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