Specifications

Catalog WSC/WDC-4 29
For these abnormal conditions, McQuay compressor designers have developed a protective
control system that senses the potential for a surge, looks at the entire chiller system operation and
takes corrective action if possible; or stops the compressor, to help prevent any damage from
occurring. This protection, called “ESP” is provided as standard on all McQuay centrifugal
compressors.
Refrigerant Comparison
The table at the right compares refriger-
ants in common use today in centrifugal
compressors.
Note that required compressor tip speeds
are all within eight percent of each other.
All McQuay centrifugal chillers use
refrigerant R-134a. The machine design
characteristics of this refrigerant (and its predecessor, R-12) such as small moving parts, low
mass, low inertia, quick spin-up and coast-down, and simplicity of design, have continuously
proven themselves since the first chiller was introduced in 1962. The small and lightweight
rotating parts lend themselves to easy servicing of the compressor and its associated parts and
piping.
Environmentally and Operator Safe - The Real Facts
As the air conditioning industry prepares for the future, R-134a stands out as the logical choice
when using a balanced approach. The "balanced approach" takes into account the following facts
on environmental concerns:
• Ozone Depletion Potential (ODP)
; measures the impact of a substance on the depletion of the
ozone layer in the upper atmosphere. With refrigerants, this action is caused by chlorine, the
first “C” in HCFC (R)-123. R-134a contains no chlorine and has a zero ODP and zero
negative effect on the ozone layer.
• Global Warming Potential (GWP)
; measures the contribution of a substance to the greenhouse
gas effect which causes global warming. This is a pound-to-pound comparison, discounting
the application of the substance and any other effects caused by its use. The numbers, relative
to CO
2
for a 100 year integration time horizon are, R-123=90, R-134a=1300, R-22=1500.
Manufacturers utilizing R-123 would have you believe that GWP is the primary and important
measurement of global warming potential of a refrigerant. This is untrue as is explained in the
following description of Total Equivalent Warming Potential.
• Total Equivalent Warming Impact (TEWI)
; is a combination of the refrigerant GWP, unit
refrigerant emissions rate, and the refrigeration system’s energy efficiency. Science has
agreed that a systems approach is necessary to evaluate the
real effect of a substance on global warming. This is TEWI.
In a chiller, the contribution of the GWP is insignificant when
compared to the effect of a unit’s power needs translated to
power plant CO
2
emissions. There is no meaningful
difference between the TEWI of R-134a, R-22 or R-123. The
percentages shown on the right will vary slightly depending
on unit refrigerant loss and on the efficiency of local power
generation. Bottom line, equipment operators should keep
equipment leak free and operate as efficiently as possible.
Since annualized energy consumption (think power plant
output) is a basis for measurement, McQuay’s superior part
load efficiencies result in lower overall power plant CO
2
emissions and can actually deliver a lower TEWI than
competition.
Refrigerant
R-123 R-134a
Condenser Press. psig @ 100°F
6.10 124.1
Evaporator Press. psig @ 40°F
(Inches of Mercury Vacuum)
(18.1) 35.0
Refrigerant. Circulated lbs/min./ton 3.08 3.00
Gas Flow cfm/ton 18.15 3.17
Tip Speed ft./sec. 656 682
Ozone Depletion Potential (ODP) 0.02 0.00