A FAULT DIAGNOSIS TOOL FOR HVAC SYSTEMS
USING QUALITATIVE REASONING ALGORITHM
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ABSTRACT
! ! " #"$% " & ' INTRODUCTION
' ( ) ( " *+,-. " / ' QUALITATIVE MODEL
0 123 4 1 2 3 5 123 6 43
5 3 " 123 " 787 4
5 77
4 5
The value of the state variable being normal, higher
than the normal value, or lower than the normal value
is represented as "0", "+" or "-" respectively. The
combination of the signs assigned to the nodes of the
SDG is defined as a "pattern" and represents the state
of the system.
' 4 #+ 45 5 #9 #+ #,
:+ :, ' " 123 # +45 " 787
' 77 " 787 #9 :+ #9 45 :+ 45 " 7
7 #+ :+ #+ 45 :+ 45 # ' "'+ "' , #,
F0
F1
L1
L2
Fig. 1 Tank system
F2
F0
L1
F1
L2
F2
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0 123 797 " 3 $
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In the above explanation of CE-graph, we assumed
all signs of nodes are given. However, there are few
cases where all nodes with their signs. Usually, some
nodes are measured by sensors, but the others are not
measured. Iri [1] proposed an effective algorithm to
find all candidate causes. The algorithm uses an
assumption; "There is only one cause (origin) of the
failure." This assumption is used in many fault
diagnosis systems, because the probability that two
(or more) causes occur simultaneously is very small.
1!' *,. = " + , + , #- ( 787 + < ( 78>7
+< ( 6< + 797 , <6 ( <6 + 7>7 , <6
( < , 77 ( < ,
+
0
-
+
+?
0
-?
-
F0
L1
F1
L2
F2
0
+
-
-
-
Fig. 3 CE-graph
SYMPTOM GENERATION
" " *+. - ( 787 ( ; + 797 ,< ( 6<
+ 77 ( < +
- '
Signs thus determined are called 5-range signs, and a
combination of them is called a five-range pattern.
The sign "+?" means "+" or "0" and the sign "-?"
means "-" or "0". Shiozaki at al. [2] have given an
efficient algorithm to find all candidate causes.
DIAGNOSIS TOOL
0 +5 2 3 1
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3) Reasoning Subsystem
4) Man-Machine Interface Subsystem.
5) Engineering Subsystem.
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! EXPERIMENT
The T-Building VAV air conditioning system is
shown schematically in Fig.8. The system has eight
VAV units. Fig.9 shows the signed directed graph
of the VAV air conditioning system. It has 83 nodes
and 129 branches. The number of the preliminary
registered causes is 132.
CTA
TA
C5
F5
T5
C6
F6
CFA
T6
C7
F7
T7
Fig. 8 T-Building VAV Air Conditioning System
Fig.9 SDG of T-Building VAV Air Conditioning System
Table1 Nodes of the Signed Directed Graph
Fi
SFi
Ti
STi
Ci
CCi
Di
SDi
FAHU
SFAHU
CAHU
TAHU
STAHU
CTAHU
VAHU
FW
SFW
STWIN
TWIN
Air flow rate of VAV unit
Air flow rate sensor value of VAV unit
Temperature
Temperature sensor value
Output of temperature controller
Output of flow rate controller
Damper open rate
Damper open rate sensor value
AHU air flow rate
AHU air flow rate sensor value
AHU air flow rate controller output value
AHU air temperature
AHU air temperature sensor value
AHU air temperature controller output
Valve open rate
Water flow rate
Water flow rate sensor value
Water temperature sensor value
Water temperature
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