ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
325
Fig. 36. Graphic for Tower Free Cooling System with Dual Chillers.
TOWER FREE COOLING, DUAL CHILLERS
FUNCTIONAL DESCRIPTION
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
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.
21
100
20
22
24.5
24.5
24.5
18.9 18.9
22
18.9
9
13
5.5
10.1
16.0
5.5
7
16
16
16
16
1
-
+
-
+
78
00
ON
OFF
OFF
OPEN
OPEN
OUTSIDE
AIR
WET BULB
WET BULB
DRY BULB
CHILLER/ FREE
COOLING SETPOINT
CHILLER/ FREE
COOLING
CURRENT MODE
FREE COOLING OA WB SETPOINT = CHILLED WATER
TEMPERATURE SETPOINT MINUS DEGREES
CHILLER/ FREE
COOLING
CURRENT MODE
MINIMUM
SETPOINT
CHILLER
MINIMUM
SETPOINT
FREE COOLING
MINIMUM
SETPOINT
CONDENSER WATER SETPOINTS
CURRENT
SETPOINT
OPEN TO
CHILLER
CHILLER 1
CHILLER 2
CURRENT
SETPOINT
PHX 2
P2
P1
LOAD
STATUS
56
56
0
26
26
100
0
5
CHILLER
10.5
10.5
ON
ON
P4
41
22
23
42
40
5
6
44
43
38
3
8
4
9
26
24
TOWER
CONTROL
46
CHILLER
CONTROL
47
25
7
20
15
1
30
31
32
10
45
39
18
19
11
34
37
13
35
16
12
29
28
2
17
36
ON
00
OPEN TO
CHILLER
00
27
PHX 1
1 = CHILLER
2 = AUTO
3 = TOWER
33
14
P3
M15265
COOLING
TOWER 1
COOLING
TOWER 2
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