Unit installation

8 ACZ 010A through 039A IOMM ACZ1-2
System Volume
It is important to have adequate water volume in the system to provide an opportunity for the
chiller to sense a load change, adjust to the change and stabilize. As the expected load change
becomes more rapid, a greater water volume is needed. The system water volume is the total
amount of water in the evaporator, air handling products and associated piping. If the water
volume is too low, operational problems can occur, including rapid compressor cycling, rapid
loading and unloading of compressors, erratic refrigerant flow in the chiller, improper motor
cooling, shortened equipment life and other undesirable occurrences.
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
Minimum Flow gpm 4.8 6.3 9.9 15.3 24.4 33.3
Figure 5, Flow Switch Installation