8
ACZ 010A through 039A
IOMM ACZ1
For normal comfort cooling applications, where the cooling load changes relatively slowly, we
recommend a minimum system volume of five minutes times the flow rate (gpm). For example, if the
design chiller flow rate is 50 gpm, we recommend a minimum system volume of 250 gallons (50 gpm
x 5 minutes).
Since there are many other factors that can influence performance, systems can successfully operate
below these suggestions. However, as the water volume decreases below these suggestions, the
possibility of problems increases.
Variable Chilled Water flow
Variable chilled water flow systems are not recommended for this class of equipment due to limited
unloading capability.
Flow Switch
Mount a water flow switch in the leaving
water line to shut down the unit when water
flow is interrupted.
A flow switch is available from McQuay
(part number 017503300). It is a “paddle”
type switch and adaptable to pipe sizes
down to 1 1/4” (32mm) nominal. Certain
minimum flow rates are required to close
the switch and are listed in Table 2. Install
the switch as shown in Figure 5. Connect
the normally open contacts of the flow
switch in the unit control center at terminals
4 and 5. There is also a set of normally
closed contacts on the switch that can be
used for an indicator light or an alarm to
indicate when a “no-flow” condition exists.
Freeze protect any flow switch that is
installed outdoors. Follow installation instructions provided with the flow switch. Calibrate the flow
switch to open at one-half of nominal flow rate.
Caution:
Differential pressure switches are not recommended for outdoor installation. They
are subject to freezing-up at low ambient temperatures.
Table 2, Flow Switch Settings
inch
1 1/4
1 1/2
2
2 1/2
3
4
Pipe Size
mm
32
38
51
63
76
102
gpm
4.8
6.3
9.9
15.3
24.4
33.3
Flow
Lpm
18.2
22.7
37.5
57.9
92.4
126.0
gpm
3.0
3.6
5.9
9.5
15.4
21.1
Minimum
Adjustment
No
Flow
Lpm
11.3
13.6
22.3
36.0
58.3
79.9
gpm
7.7
10.0
15.8
23.7
35.5
61.4
Flow
Lpm
29.1
37.9
59.8
89.7
134.4
232.4
gpm
5.9
7.0
11.0
17.0
29.2
37.7
Maximum
Adjustment
No
Flow
Lpm
22.3
26.5
41.6
64.3
110.5
142.7
Figure 5, Flow Switch Installation