Specifications

15 Catalog WMC-4
Unit Design Features
• No increase in operating cost due to
displacement of heat transfer surface by non-
condensables
Variable Frequency Drive
Efficiency: The variable frequency drive option
is a technology that has been used for decades to
control motor speed on a wide variety of motor-
drive applications. When applied to centrifugal
compressor motors, significant gains in part load
performance can be realized. The improvement in
efficiency and reduction of annual energy cost is
maximized when there are long periods of part
load operation, combined with low compressor lift
(lower condenser water temperatures).
• No crevice corrosion and tube failure due to
moisture in the system
• No annual service expense to maintain and
rebuild purge unit
• No abnormal annual service expense for oil,
filter, and refrigerant replacement
• No periodic emissions of refrigerant into the
atmosphere
Combining the attributes of VFD drives and the
efficient McQuay WMC Dual Centrifugal Chiller
produces one of the industry's most efficient
chiller based on the all-important IPLV value. See
“
Heat Exchangers
McQuay WMC centrifugal chillers are equipped
with high performance heat exchangers. The
unique design greatly increases heat transfer and
reduces unit footprint and refrigerant charge.
Vessels are designed, constructed and tested in
accordance with ASME Section VIII, ASHRAE
Standard 15 requirements and TEMA
recommendations.
IPLV/NPLV Defined” on page 18 for details on
the ARI IPLV efficiency rating.
Starting Inrush: The use of a VFD on
centrifugal chillers also provides an excellent
method of reducing motor starting inrush-even
better than "solid state" starters. Starting current
can be closely controlled since both the frequency
and voltage are regulated. This can be an
important benefit to a building's electrical
distribution system. The low inrush feature,
combined with two one-half size compressors
having a staggered start, is particularly attractive
where chillers will be asked to operate on
emergency generators. Since inrush has much to
do with sizing the generators, much smaller
generators can be used. See page
The replaceable water tubes are internally rifled
and externally enhanced copper, and are
mechanically bonded to steel tube sheets. Standard
tubes are 0.025-inch wall thickness. Optional
tubes include 0.028 or 0.035-inch wall thickness
on either vessels and 90/10 cupro-nickel, 304
stainless steel or titanium material. Clad tube
sheets and epoxy-coated heads can be provided.
Vessels are available for 1, 2 or 3 pass water flow.
A 3/4" or 1-1/2 thick layer of vinyl/nitrate polymer
evaporator insulation is optional. All seams are
glued to form an effective vapor barrier. Detailed
information on the insulation can be found under
“Physical Data” on page
42 for further
details.
HFC-134a
31.
McQuay Positive Pressure Design:
• No Purge
Pumpdown
• No Vacuum Prevention System
Pumpout systems provide a means to collect and
contain the refrigerant charge without loss when
access to internal chiller components is required
for service.
• No Contaminants
HFC-134a operates above atmospheric pressure in
the entire refrigerant circuit and at normal
temperatures. All McQuay centrifugal chillers use
a positive pressure refrigerant, with the following
benefits:
McQuay condensers and evaporators are sized to
hold the entire unit refrigerant charge when not
more than 90% full and at 90°F (32°C) ambient
temperature. They are equipped with valves in the
compressor discharge lines, suction lines, and in
the liquid line. These valves, coupled with the
vessel design, satisfy the stringent requirements of
• No absorption of impurities into the
refrigerant circuit
• No breakdown of motor insulation, refrigerant
or lubricant