Specifications

43 Catalog WMC-4
The necessary procedure for reconnecting power
from the generator back to the utility grid is shown
below. These procedures are not peculiar to
McQuay units only, but should be observed for
any chiller manufacturer.
1. Set the generator to always run five minutes
longer than the unit start-to-start timer, which
could be set from 15 to 60 minutes. The actual
setting can be viewed on the operator interface
panel on the Setpoint/Timer screen.
2. Configure the transfer switch, provided with
the generator, to automatically shut down the
chiller before transfer is made. The automatic
shut-off function can be accomplished through
a BAS interface or with the “remote on/off”
wiring connection shown in
Figure 23. A start
signal can be given anytime after the stop
signal since the three-minute start-to-start timer
will be in effect.
Chiller Control Power: For proper operation on
standby power, the chiller control power must
remain as factory-wired from a unit-mounted
transformer. Do not supply chiller control power
from an external power source because the chiller
may not sense a loss of power and do a normal
shutdown sequence.
Optimum Water
Temperatures and Flow
A key to improving energy efficiency for any
chiller is minimizing the compressor pressure lift.
Reducing the lift reduces the compressor work and
its energy consumption per unit of output. The
chiller typically has the largest motor of any
component in a chilled water system.
Higher leaving chilled water
temperatures
Warmer leaving chilled water temperatures will
raise the compressor’s suction pressure and
decrease the lift, improving efficiency. Using 45°F
(7.0°C) leaving water instead of 42°F (5.5°C) will
make a significant improvement.
Evaporator temperature drop
The industry standard has been a ten-degree
temperature drop in the evaporator. Increasing the
drop to 12 or 14 degrees will improve the
evaporator heat transfer, raise the suction pressure,
and improve chiller efficiency. Chilled water
pump energy will also be reduced.
Condenser entering water temperature
As a general rule, a one-degree drop in condenser
entering water temperature will reduce chiller
energy consumption by two percent. Cooler water
lowers the condensing pressure and reduces
compressor work. One or two degrees can make a
noticeable difference. The incremental cost of a
larger tower can be small and provide a good
return on investment.
Condenser water temperature rise
The industry standard of 3 gpm/ton or about a 9.5-
degree delta-T seems to work well for most
applications. Reducing condenser water flow to
lower pumping energy will increase the water
temperature rise, resulting in an increase in the
compressor’s condensing pressure and energy
consumption. This is usually not a productive
strategy.
System analysis
Although McQuay is a proponent of analyzing the
entire system, it is generally effective to place the
chiller in the most efficient mode because it is a
larger energy consumer than pumps.
The McQuay Energy Analyzer™ program is an
excellent tool to investigate the entire system
efficiency, quickly and accurately. It is especially
good at comparing different system types and
operating parameters. Contact you local McQuay
sales office for assistance on your particular
application.
Operating Limits:
Maximum standby ambient temperature, 130°F (55°C)
Leaving chilled water, 38°F to 60°F (3°C to 15°C), ice duty not available
Maximum operating evaporator inlet fluid temperature, 66°F (19°C)
Maximum startup evaporator inlet fluid temperature, 90°F (32°C)
Maximum non-operating inlet fluid temperature, 100°F (38°C)
Minimum condenser water entering temperature, 55°F (12.8°C)
Maximum entering condenser water temperature, 105°F (40.1°C)
Maximum leaving condenser water temperature, 115°F (46.1°C)
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