Handbook of air conditioning and refrigeration / Shan K

● Central plant control
Multiple-chiller optimizing control
Multiple-boiler optimizing control
Condenser fan cycling
Demand limit control
● Safety controls
Commissioning and Maintenance
A properly designed and installed EMCS needs commissioning to test and tune its controllers and
system components according to the design specification. A sufficient, clear, and well-followed
operations manual and a well-implemented maintenance schedule are key factors for an effective
and efficient EMCS. Commissioning and maintenance are covered in detail in Chap. 32.
5.15 FAULT DETECTION AND DIAGNOSTICS
Basics
Modern air-handling units (AHUs), packaged units (PUs), and chillers become more and more
complicated because of the IAQ, thermal comfort and energy efficiency requirements, and the use
of DDC. An HVAC&R operator is hardly able to monitor and detect the fault operations of the
AHUs, PUs, and chillers; find their causes; and correct them. An automatic fault detection and diagnostic
system is important for the effective operation and control, for the monitoring and maintenance,
and for the optimizing of utilization and continuous improving of the HVAC&R systems.
As of the late 1990s, fault detection and diagnostics are already a standard component in many
large PUs.
In HVAC&R operations, faults occur when the actual measured operating parameters deviate
from the normal operating values. There are two types of detected faults: complete failures and
performance degradations. Complete failures are abrupt faults that often cause discontinuation of
the operation of a system or component. Symptoms of abrupt faults can be easily observed. Peformance
degradation is the result of an evolving fault accumulated during a certain time.
The differences between the actually measured values of an operating parameter, such as temperature
T, °F (°C); pressure p, in. WG (Pa); volume flow rate , cfm (m3 /s); or mass flow rate ,
lb/s (kg/s) and the expected values (estimated, simulated, or set points) of temperature Texp, pressure
pexp, volume flow rate , or mass flow rate under normal operating conditions are
called residual. A fault can be detected by investigating and analyzing residuals.
A temperature residual Tres, °F (°C), a pressure residual pres, in. WC (Pa), or a volume flow rate
residual , cfm (m3 V˙
m˙
V˙
exp
m˙ exp
/s), can be calculated as
V˙ res
ENERGY MANAGEMENT AND CONTROL SYSTEMS 5.61
T res � T � T exp
p res � p � p exp
V˙ res � V˙ � V˙ exp
(5.21)
where the subscript exp indicates expected (predicted) values and the units of Texp, pexp, and are
the same as those of T, p, and V˙ . Most of the measured operating parameters in a fault detection and
diagnostic system are the same monitored parameters (sensed or measured) in an EMCS.
Residuals are often normalized so that the dominant symptom may have approximately the same
V˙ exp