Economizer Cycle Control Of Space Temperature With Supply Air Temperature Setpoint Reset - Honeywell AUTOMATIC CONTROL Engineering Manual

AIR HANDLING SYSTEM CONTROL APPLICATIONS
ECONOMIZER CYCLE CONTROL OF SPACE TEMPERATURE WITH SUPPLY AIR
TEMPERATURE SETPOINT RESET
Functional Description
EA
83
6
OA
83
5
12
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 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
ventilation 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.
ENGINEERING CMANUAL OF AUTOMATION CONTROL
RA
3 ON
MA
ON
1
14
CONTROL
PROGRAM
11
22
OA MINIMUM SETPOINT
(NOTE: THE TEST AND BALANCE INITIAL VALUE
FOR PROPER VENTILATION IS 22)
FEATURES
CONDITIONS FOR SUCCESSFUL OPERATION
LIMITATIONS
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.
222
13
8
2
NORMAL
TEMPERATURE
SA
TEMPERATURE
RESET SCHEDULE
SUPPLY AIR
TEMPERATURE
59
SETPOINT
4
7
10
75
59
9
55
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.
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.
If the manual positioning value is set to admit a large quantity
74
74
SPACE
MIXED AIR
SPACE
COOLING
DEMAND
0
100
M10457