Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual page 232

AIR HANDLING SYSTEM CONTROL APPLICATIONS
Item
No. Function
1-3 Control system energizes when fan is turned
on (See FAN SYSTEM START-STOP
CONTROL).
4 SA temperature maintained by modulating
mixing dampers.
5,6 OA and EA dampers close and RA damper
opens when fan is off and modulate for ventila-
tion and temperature control when fan is on.
7 Setpoint for SA temperature control.
8 Space temperature demand resets SA
temperature setpoint.
9,10 Calculates SA temperature setpoint (7) based
upon space temperature cooling demand.
11 Setpoint value for minimum ventilation
damper position.
12 Determines when OA is suitable to assist in
cooling.
13 Space temperature setpoint and PID function.
PID output (0 - 100) inputs to reset schedule.
14 Control program coordinates space
temperature, SA temperature, minimum
ventilation, fan interlock, and economizer
control of mixing dampers.
FEATURES
1. The system admits only the minimum quantity of OA
required for ventilation when the OA is unsuitable for
cooling assistance.
2. During intermediate weather the system admits OA for
cooling to satisfy the space temperature demands, subject
to SA temperature schedule setpoints.
3. A minimum quantity of OA, determined by the software
adjustable setpoint value, is assured at all times.
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. A satisfactory schedule of all settings must be determined.
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 SA temperature
control, a source of heat is necessary to maintain the SA
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 SA PID control loop to
maintain the SA temperature setpoint. The SA temperature
setpoint shall be varied from no less than 13 C to no more than
24 C as the space temperature PID loop cooling demand varies
from 100 to 0%. Anytime the economizer program is invoked,
the SA temperature control shall be enabled.
PSYCHROMETRIC ASPECTS
For the psychrometric aspects of this application, refer to
MIXED AIR CONTROL WITH ECONOMIZER CYCLE. The
psychrometric aspects of the two applications are the same.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
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