Specifications

6 Catalog WSC/WDC-4
No Vessel Heating Blankets
When negative pressure chillers are expected to be inoperative for a long period of time, during
winter shutdown for example, it is common to apply an electric heating blanket to the evaporator
in order to raise the refrigerant pressure above atmospheric. In other words, try to force it to
behave like a McQuay R-134a unit! The initial and operating costs of these blankets are not
necessary with a McQuay chiller.
No Refrigerant Availability Issue
R-134a is considered a solution to refrigerant environmental issues because it does not have a
phase-out date. R-123 cannot be used in new equipment after the year 2020. History has shown
us that a practical refrigerant phase out occurs well in advance of the Montreal Protocol’s
mandate. Since R-123 has been primarily used only in chillers and only since 1995, there is a
limited quantity available for recycling to meet service needs to 2030. It is already capped in the
United States and will be reduced to 0.5% by 2020 for service use only until 2030. It is
considered highly unlikely that the phase out dates will be extended.
Lower Health Risk with McQuay’s R-134a
R-134a is listed as an “A1” refrigerant as defined by ASHRAE Standard 15, which means that it
has the lowest toxicity and flammability rating. R-123 is rated as “B1”, which means it is toxic to
humans and also carries a low flammability rating. In the event of a refrigerant release, the
likelihood of personnel risk is lower with R-134a.
Smaller Equipment Rooms
As a general rule, the physical size of an R-134a positive pressure chiller will be smaller than a
negative pressure chiller, reducing equipment room size. R-123 requires a much larger refrigerant
flow rate than R-134a, with a subsequent increase in component size. Also, Equipment room
ventilation requirements are greatly reduced when compared to chillers with open drive motors,
which reject heat directly into the room ambient air.
Gear Drive Advantage
Lower Vibration
A gear-driven compressor runs at higher impeller rotational speeds but tends to have less vibration
than the larger, much heavier, direct drive units. All McQuay compressors must pass a stringent
vibration test while running on the production test stands. Spring isolators are normally not
required for most applications.
Unique Lubrication System
With the higher rotational speeds and much lighter running components compared to direct drive
units, efficient hydrodynamic bearings can be used. The shafts are supported on a film of
lubricant, rather than running with metal-to-metal contact, typical of rolling element bearings.
Under normal circumstances, the McQuay bearings have a theoretical infinite life while rolling
element bearings do not.
Selectable Impeller Speeds
Another gear drive advantage, over the older design direct drive units, is the ability to select gear
ratios that will provide the optimum impeller tip speed for a given application. Impeller speeds
can be selected to provide sufficient pressure lift ability without the excessive tip speeds that lead
to inefficient compressor operation.
Also, the gear options allow for excellent compressor performance on 50 Hertz power.