Fault Detection and Diagnostics for Commercial Heating, Ventilating, and Air-Conditioning Systems

NIST is working to measure and improve the operational performance of commercial buildings by leveraging previously untapped capabilities within modern automation and control systems.  This requires developing a measurement science that enables automatic detection and diagnosis of equipment faults, sensor failures, and control errors in the heating, ventilating, and air-conditioning (HVAC) systems of buildings.  The resulting fault detection and diagnosis (FDD) software ("FDD tools") will utilize existing sensors and controller hardware, and will employ artificial intelligence, deductive modeling, and statistical methods to automatically detect and diagnose deviations between actual and optimal HVAC system performance.

Objective: To improve the operating efficiency of commercial heating, ventilating, and air-conditioning (HVAC) systems by 10% to 30% through development and demonstration of the enabling measurement science for detecting faults and control errors in commercial HVAC equipment and systems, and transferring the measurement science to the private sector by 2014.

What is the new technical idea? The new idea is to leverage the untapped capabilities of modern building automation and control systems by developing embedded FDD tools that monitor the performance of subsystems and automatically detect faults.  Advances in building automation technologies provide the prospect of very data–rich performance surveillance in buildings that can be applied on system-wide scales that are necessary to optimize overall system performance and achieve the goal of net-zero energy consumption.  The key to realizing efficiency improvements is combining new measurement technology and performance metrics with analysis techniques that can be implemented in building automation and control products.  The resulting systems would have a distributed, embedded intelligence that can detect and respond to faults and operational errors and inefficiencies.  Microcontroller technology has advanced in a way that simplifies the implementation of the proposed embedded intelligence.  Success is likely because of increasing industry demand for the technology as a way to reduce energy consumption and associated environmental impacts^[1]

What is the research plan? NIST will develop and demonstrate a comprehensive set of tools and algorithms for detecting faults and control errors in a wide range of commercial HVAC equipment and systems following a sequence of steps that has proven successful in the past:

• Develop a rapid prototyping platform for FDD algorithms that includes a MatlabÒ interface to HVACSIM+ (a sophisticated system simulation package developed at NIST), along with a database–driven interface to the researcher for configuring simulations
• Develop an expert system framework incorporating FDD and learning algorithms into new FDD tools that adapt to operator feedback, improving FDD reliability and acceptance by minimizing false alarms and helping operators cope with cascades of true alarms
• Obtain building automation system data from real buildings and laboratory studies of normal and faulty operation
• Test rapid prototypes using collected data and simulations
• Extend promising approaches by developing hardware-in-the-loop implementations and test them under a wide range of conditions using the VCBT
• Conduct field tests in cooperation with existing and anticipated industry CRADA partners (e.g., Delta Controls, Automated Logic)

The research plan is staged, in that concentration is directed first to the tools resulting from NIST FDD work to date.  Research will seek to make those tools more autonomous and more adaptive.  Autonomy means tools that are less dependent on a human expert intervening in order to infer critical FDD parameter values from the available data.  Adaptation means the tool improves its reliability by "learning" from its mistakes, through interaction and feedback from building operators, a capability that enhances FDD acceptance.

NIST will leverage existing CRADAs with industry partners to speed commercialization of FDD research results. NIST will also leverage academic ties to sponsor components of the research through contracts and grant solicitations.  The outcome will be a suite of proven algorithms for FDD that can be embedded in hardware that is practical for commercial adaptation.

[1]Turner, C. and M. Frankel.  2008. "Energy Performance of LEED for New Construction Buildings.  U.S. Green Building Council.

Recent Results:

Outputs:

"Detecting Cooling Coil Fouling Automatically – Part 1: A novel Concept", HVAC&R Research Vol. 16, No. 4, Veronica, D. A. 2010.

"Detecting Cooling Coil Fouling Automatically – Part 2: Results Using a Multilayer Perceptron", HVAC&R Research Vol. 16, No. 5, Veronica, D. A. 2010.

"Results from Field Testing of Embedded Air Handling Unit and Variable Air Volume Box Fault Detection Tools", Journal of Research (NIST JRES) 7365

Outcomes:

An initial version of Rapid Interactive Virtual Prototyping for Intelligent Buildings (RIVPIB), a software platform running HVACSIM+ in the interactive MatlabÒ computing environment to enable quicker development and prototyping of new tools for FDD and energy management.

Embedded tools Air–handler Performance Assessment Rules (APAR) and Variable-air -volume (VAV) box Performance Assessment Control Charts (VPACC).

Impacts:

Commercial products and services based on APAR and VPACC are now available in the marketplace.  These products keep surveillance on the energy performance of buildings, allowing maintenance staffs and analysts to find and correct inefficiencies such as malfunctioning valves, dampers, coils, sensors, and controllers.

Standards and Codes: