Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Results from Laboratory Testing of Embedded Air Handling Unit and Variable Air Volume Box Fault Detection Tools



J Schein, Steven T. Bushby, J House


Building HVAC equipment routinely fails to satisfy performance expectations envisioned at design. Such failures often go unnoticed for extended periods of time. Additionally, higher expectations are being placed on a combination of different and often conflicting performance measures, such as energy efficiency, indoor air quality, comfort, reliability, limiting peak demand on utilities, etc. To meet these expectations, the processes, systems, and equipment used in both commercial and residential buildings are becoming increasingly sophisticated. This development both necessitates the use of automated diagnostics to ensure fault-free operation and enables diagnostic capabilities for the various building systems by providing a distributed platform that is powerful and flexible enough to perform fault detection and diagnostics (FDD).The purpose of the research effort described in this report is to develop, test, and demonstrate FDD methods that can detect common mechanical faults and control errors in air-handling units (AHUs) and variable-air-volume (VAV) boxes. The tools are intended to be sufficiently simple that they can be embedded in commercial building control systems and rely upon only sensor data and control signals that are commonly available in commercial building automation and control systems.AHU Performance Assessment Rules (APAR) is a diagnostic tool that uses a set of expert rules derived from mass and energy balances to detect faults in air-handling units. Control signals are used to determine the mode of operation for the AHU. A subset of the expert rules corresponding to that mode of operation is then evaluated to determine if there is a mechanical fault or a control problem. VAV box Performance Assessment Control Charts (VPACC) is a diagnostic tool that uses statistical quality control measures to detect faults or control problems in VAV boxes.This report describes a research study of embedding APAR and VPACC in HVAC equipment controllers in a laboratory setting. APAR was embedded in several air handling unit controllers and evaluated in an emulation environment, while VPACC was embedded in several VAV box controllers and evaluated in a laboratory environment. APAR and VPACC were both found to be successful at finding a wide variety of mechanical and control faults. Both tools appear to be suitable for embedding in commercial control products.
NIST Interagency/Internal Report (NISTIR) - 7036
Report Number


BACnet, building automation and control, cybernetic building systems, direct digital control, energy management systems, fault detection and diagnostics


Schein, J. , Bushby, S. and House, J. (2003), Results from Laboratory Testing of Embedded Air Handling Unit and Variable Air Volume Box Fault Detection Tools, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed April 22, 2024)
Created August 1, 2003, Updated November 10, 2018