Results From Laboratory Testing of Embedded Air Handling Unit and Variable Air Volume Box Fault Detection Tools.
Results From Laboratory Testing of Embedded Air Handling
Unit and Variable Air Volume Box Fault Detection Tools.
(6849 K)
Schein, J.; Bushby, S. T.; House, J. M.
NISTIR 7036; 38 p. August 2003.
Keywords:
air handling units; air bolume box; tests; fault
detection; air temperature; BACnet; building automation
and control; direct digital control; energy management
systems; fault detection and diagnostics; cybernetic
building systems
Abstract:
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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899