Product Manual PM WSC/WDC 7
• Toxicity and Flammability Rating; per 1997 ASHRAE Fundamentals Handbook
• HFC-134a ⇒ A-1
• HCFC-123 ⇒ B-1
Where A=No toxicity identified
B=Evidence of toxicity identified
1=No flame propagation in air at 100°C, 50% rh and one atmosphere pressure
A certain future for HFC-134a:
The Clean Air Act of November 1990 allows the EPA to accelerate the phase-out schedule of Class I (CFC) and
Class II (HCFC) refrigerants if it deems it necessary. This leaves the future of HCFCs (which includes HCFC-22
and HCFC-123) uncertain. HFC-134a will not be regulated or phased out by the Clean Air Act or the Montreal
Protocol. The commercial air conditioning, home appliance, and automotive industries are just a few of the
many markets that will be using HFC-134a for years into the future. This large market demand for HFC-134a
translates to a readily available and competitively priced product.
Compressor Design
Gear Drive Offers Greater Operating Efficiency Than Direct Drive
Centrifugal compressor efficiency is a function of impeller design and application to the refrigeration system.
The increased heat transfer surface and efficiency of modern heat exchangers have changed compressor head
and impeller tip speed requirements. Direct drive designs limit the manufacturer’s ability, within a single
compressor size, to select impellers at or near peak impeller efficiency. While a unit selected at poor impeller
efficiency might produce the required performance at peak load, its operating characteristics over the entire
range of part load performance are sharply curtailed, resulting in increased annual operating costs. McQuay
gear drive centrifugal chillers provide a variety of tip speed ratios to permit selection of impellers for maximum
efficiency over their entire part load to full load range and are ideal for 50 Hz application. Mechanical gear
losses are limited by design standards to less than one-half of 1%. The impeller efficiency obtained by alternate
gear selections may increase chiller efficiency by as much as 7%. As energy costs continue to rise, the
economic advantages of gear drive to obtain maximum efficiencies will be universally sought.
Extended Motor Life
McQuay’s modern compact compressor design equates to many operating advantages that improve its overall
reliability and durability. One such advantage is prolonged motor life. A motor draws locked rotor current until
it reaches break away torque at approximately 80% of its running speed. While drawing locked rotor current the
stresses on the motor are over six times that of full load. The McQuay compressors absolutely minimize this
stress through the unique gear drive and light weight drive train that allows a 500 ton (1750 kW) compressor to
reach running speed in less than three seconds. The owner benefits from a longer motor life.
Safe Compressor Coast Down
Another advantage is the short coast down time. Under normal operating conditions the electric driven oil
pump continues to feed oil to the bearings during coast-down. However, if a power failure occurs, the pump is
unable to provide positive coast down lubrication. With McQuay’s design, coast down takes less than 15
seconds and this short time allows an internal reservoir to provide positive oil flow to the bearings.
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