Tower Free Cooling, Dual Chillers - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

TOWER FREE COOLING, DUAL CHILLERS

FUNCTIONAL DESCRIPTION
41 26
22
100
COOLING
TOWER 1
0
42
40 6
18.9 18.9
CURRENT
22
SETPOINT
5
OPEN TO
P3
CHILLER
ON
36
14
34
11
56
00
P4
37 OFF
OPEN TO
CHILLER
16
00
56
13
Item No. Function
1,2 Chilled water pumps produce flow through
chillers or plate/frame heat exchangers.
3,4 Free cooling mode initiated when OA WB
drops to setpoint.
5 Tower water entering temperature, operator
information.
6,7 Setpoints indicate need for cooling tower and
chilled water.
8 Minimum condenser water temperature setpoint
provides free cooling low limit.
9 In free cooling mode, tower will produce water
about 4 kelvins above OA wet-bulb tempera-
ture, and HX will cool chilled water to within 1
to 1.5 kelvins of condenser water temperature,
so the sum of these dictates when to activate
free cooling.
10-13 Maintains condenser water temperature entering
chiller during period when tower is pulling
ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
43
26
23
100
38
COOLING
3
TOWER 2
0
44
CHILLER
MINIMUM
SETPOINT
CONDENSER WATER SETPOINTS
-
32
20
+
CHILLER 1
22
24.5
10
78
45
LOAD
00
39
24.5
CHILLER 2
24.5
12
35
33
-
16
Fig. 36. Graphic for Tower Free Cooling System with Dual Chillers.
FREE COOLING OA WB SETPOINT = CHILLED WATER
TEMPERATURE SETPOINT MINUS
OUTSIDE
AIR
CHILLER/ FREE
COOLING SETPOINT
DRY BULB
13
5
WET BULB
9
WET BULB
21
8
FREE COOLING
18.9 5.5
MINIMUM
SETPOINT
10.1
PHX 1 30
16.0
31
1
ON
ON
18
P1
STATUS
19
OFF
28
16
ON
P2
PHX 2 16
29
+
water temperature down to free cooling setpoint
value and the temperature is too low for chiller.
14-17 Valves direct water from chiller/condenser to
HX when condenser water reaches setpoint.
18,19 Chiller Status.
20 Operator information.
21 Prevents tower from cooling water below
minimum value that chiller can tolerate (during
chiller cooling mode).
22,23 Tower fans modulate to maintain condenser
water setpoint.
24 CHILLER-AUTO-TOWER software mode
selection function.
25 Prevents chilled water temperature setpoint
from dropping below the design minimum.
26-45 Operator information (see chiller control and
cooling tower control examples).
46 Icon, to display cooling tower control data.
47 Icon, to display chiller control data.
325
5.5
DEGREES
9
CHILLER/ FREE
COOLING
4
CURRENT MODE
CURRENT MODE
CHILLER
24
26
46
TOWER
CONTROL
47
CHILLER
CONTROL MINIMUM
SETPOINT
CURRENT
SETPOINT
OPEN
15
OPEN
17
2
CHILLER/ FREE
COOLING
1
1 = CHILLER
2 = AUTO
3 = TOWER
25
7
10.5
7
10.5
20
16
27
M15265