Year-Round System Control Processes; Heating, Cooling, And Economizer - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

AIR HANDLING SYSTEM CONTROL APPLICATIONS

YEAR-ROUND SYSTEM CONTROL PROCESSES

HEATING, COOLING, AND ECONOMIZER

Functional Description
EA
NC
100
5
NO
OA
NC
PERCENT
21 OPEN
100
18
4
ECONOMIZER DECISION.
REFER TO PREVIOUS
ECONOMIZER OPTIONS
7
Item
No. Function
1-3 Control system energizes when fan is turned
on (See FAN SYSTEM START-STOP
CONTROL).
4-6 Mixing dampers modulate to maintain
minimum ventilation value and free cooling
SA temperature setpoint.
7 Economizer enables free cooling when OA is
appropriate.
RA
ON
3
2
NORMAL
SUPPLY
FAN
20
18
19
36 0
22
CONTROL
PROGRAM
6
22
OA MINIMUM SETPOINT
(NOTE: THE TEST AND BALANCE
INITIAL VALUE FOR PROPER
VENTILATION IS 22)
SPACE TEMPERATURE
CHILLED WATER COOLING
SETPOINT = FREE COOLING
SETPOINT PLUS
1.1
10
(0.8 MINIMUM)
FREE COOLING
SETPOINT
HEATING SETPOINT = FREE
COOLING SETPOINT MINUS
1.1
12
(0.8 MINIMUM)
15
SA
SUPPLY AIR
TEMPERATURE
15
SETPOINT
1
14
ON
16
SUPPLY AIR
TEMPERATURE
SETPOINT
17
SUPPLY AIR
TEMPERATURE
SETPOINT
18
8 Space temperature dictates heat and cool
demands.
9-13 Free cooling setpoint and heat/cool dead-
band values determine the SA temperature
setpoint for hot and chilled water control
setpoints. Software has a minimum 0.8
kelvins heating and cooling deadband.
14 Heat demand varies SA temperature setpoint.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
248
8
24.5
SETPOINT
24.5
11
9
23.5
SETPOINT
22
13
SPACE
HEATING
DEMAND
100
41
0
13 0
FREE
COOLING
DEMAND
0
24
100
100
14
CHW
COOLING
DEMAND
0
24
96
13 100
M15176