ENGINEERING MANUAL OF AUTOMATIC CONTROL
AIR HANDLING SYSTEM CONTROL APPLICATIONS
258
VAV AHU WITH RETURN FAN AND FLOW TRACKING CONTROL
Functional Description
Item
No. Function
1-5 Control system energizes when supply fan is
turned on (See FAN SYSTEM START-STOP
CONTROL).
6-8 Supply fan loads to maintain duct static
pressure at the end of the longest run.
9-14 Return fan loads to track supply airflow minus
exhaust airflow minus air for pressurization.
15 Manual positioning value determines
minimum summer ventilation mixing damper
position. This position is fixed for the OA and
relief air dampers; but is a minimum position
for the return air damper, the value of which
will be overriden to maintain a constant mixing
box negative static pressure and thus a constant
OA airflow.
16 OA determines SA temperature setpoint.
17 Economizer enables free cooling when OA
is suitable.
18 Mixed air temperature is for operator
information.
63
83
13
0.45
0.45
58ON
OA
SA
RA
EA
ON
ON
13
1.274
360
0.613
PERCENT
LOAD
PERCENT
LOAD
SA
TEMPERATURE
SETPOINT
OA
TEMPERATURE
EXHAUST
FAN
WARM-UP
MODE
M15182
2
9
10
31
4
30
7
8
3
11
29
32
26
25
27
6
15
24
23
28
19
13
14
12
1
5
16
18
22
20
21
NORMAL
NORMAL
EXHAUST
FAN "ON"
DIFFERENTIAL
m
3
/s
4
16.5
22
0.060
32
-21
ON OFF
ECONOMIZER DECISION.
REFER TO PREVIOUS
ECONOMIZER OPTIONS
17
CONTROL
PROGRAM
OA MINIMUM SETPOINT
(NOTE: THE TEST AND BALANCE INITIAL
VALUE FOR PROPER VENTILATION IS 22)
CONTROL
PROGRAM
9
24.5
13
0.060
83
17
14.5
76
00
4.530
6.423
ZERO
CALIBRATION
SPACE
PRESSURIZATION
DIFFERENTIAL
m
3
/s
m
3
/s
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