Mixed Air Control With Economizer Cycle (Ventilation System Only) - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

AIR HANDLING SYSTEM CONTROL APPLICATIONS

MIXED AIR CONTROL WITH ECONOMIZER CYCLE (VENTILATION SYSTEM ONLY)

Functional Description
6
9
9
PERCENT
OPEN
10
ECONOMIZER DECISION.
REFER TO PREVIOUS
ECONOMIZER OPTIONS
Item
No. Function
1-3 Control system energizes when fan is turned
on (See FAN SYSTEM START-STOP
CONTROL).
4 MA temperature maintained by modulating
mixing dampers.
5,6 OA and EA dampers close and RA damper
opens when fan is off and modulate for
temperature control when fan is on.
7 Setpoint for MA temperature control.
8 Setpoint value for minimum ventilation
damper position.
9 Determines when OA is suitable to assist in
cooling.
10 Control program coordinates MA, minimum
ventilation, and economizer control of mixing
dampers.
FEATURES
1. The proper proportions of OA and RA are admitted to
maintain the desired MA temperature during economizer
operation periods.
2. A minimum quantity of OA, determined by the software
adjustable setpoint value, is assured at all times.
3. The OA economizer changeover program returns the OA
damper to the minimum position when OA is not suitable.
NC
EA
83
NO
OA
NC
83
5
ON
11
RA
3 ON
NORMAL
MA
ON
1
12
CONTROL
PROGRAM
22
8
OA MINIMUM SETPOINT
(NOTE: THE TEST AND BALANCE INITIAL
VALUE FOR PROPER VENTILATION IS 22)
CONDITIONS FOR SUCCESSFUL OPERATION
1. Adequate mixing of OA and RA. Mixing may be obtained
using a special mixing chamber. The temperature sensor
should be in the fan discharge when possible. The fan in
a blow-through system usually provides adequate mixing.
2. An MA averaging element sensor is used on draw-
through units.
LIMITATIONS
If the manual positioning value is set to admit a large quantity
of OA and the OA temperature falls below the temperature at
which only minimum OA is required for MA temperature control,
a source of heat is necessary to maintain the MA temperature.
SPECIFICATIONS
See FAN SYSTEM START-STOP CONTROL.
Anytime the supply fan runs, the OA, exhaust, and RA
dampers shall position to a minimum ventilation position and
shall be further modulated by an MA PID control loop to
maintain the MA temperature setpoint. Anytime the OA
conditions rise above the economizer setpoint, the MA
temperature control shall be disabled.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
220
2
13
4
13
7
M15157