Fault Detection and Diagnostics for Rooftop Air Conditioners

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1.2.3 Decoupling of Component Faults
In section 1.2.1, rooftop unit faults were divided into two classes according to two
different criteria: component-level or system-level faults according to fault impact scope,
and service or operational faults according to fault cause criterion. The characteristic of
component-level faults is that their source impact can be confined to a component and
this source impact is independent of other faults locally. So, the independence features
for individual component-level faults can be found by investigating their source impacts.
The independence features for service faults can be found by investigating their impact
when the system stops.
1.2.3.1 Compressor Valve Leakage Fault
A compressor pumps a certain flow rate of refrigerant with certain
thermodynamic state to the whole system. At steady state, the compressor is mainly
driven by three conditions: any two independent thermodynamic parameters of the
compressor inlet conditions, say pressure P
suc
and temperature T
suc
, and compressor
outlet pressure
P
dis
. These three driving conditions determine all the outlet
thermodynamic parameters and refrigerant mass flow rate
&
m
ref , pred
. For a certain set of
driving conditions:
P
suc
, T
suc
and P
dis,
T = ref P , h )
(1-10)
dis, pred
(
dis dis,
pred
where,
h
dis, pred
( Psuc,
Tsuc
, Pdis
) = hsuc
( Psuc
, Tsuc
) + wpred
( Psuc
, Tsuc,
Pdis)
− Qloss
(1-11)
w
pred
( P
suc
, T
suc
, P
dis
W&
) =
m&
pred
( P
suc
( P
, T
suc
, T
, P
dis
, P
ref , pred suc suc dis
)
)
is the compressor specific power consumption,
h ,
is the predicted discharge line
dis pred
refrigerant enthalpy,
enthalpy.
T
dis
is discharge line temperature, h
suc
is suction line refrigerant
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