System information

4
© 2015 Emerson Climate Technologies, Inc.
AE4-1287 R8
Introduction
Energy effi ciency regulations drive continuous change
in the availability of refrigerants to the marketplace. With
the introduction of R-22 as a replacement for R-502,
compressors began to experience internal discharge
temperatures that exceed the safe operational limits for
long term stability of refrigerant oil. In response to this,
Demand Cooling was developed as a reliable method
to keep discharge temperatures reduced to a safe level
without inhibiting the operating limits of the compressor.
With the phase out of R-22, the following refrigerants
have become viable alternatives for R-22 applications:
R-407A, R-407C, R-407F, R-448A, R-449A. All of the
above mentioned refrigerants require special attention
to discharge temperature control.
CAUTION
POE must be handled carefully and the proper
protective equipment (gloves, eye protection, etc.)
must be used when handling POE lubricant. POE
must not come into contact with any surface or
material that might be harmed by POE, including
without limitation, certain polymers (e.g. PVC/CPVC
and polycarbonate).
Updated Discharge Temperature Guidelines
Emerson Climate Technologies developed and
released the Demand Cooling
™
system for Copeland
Discus
™
compressors to provide a solution for
applications with high discharge temperatures
such as the R-22 low temperature refrigeration
applications. Without Demand Cooling, these high
temperatures typically resulted in overheating of the
lubricant leading to compressor failures.
Since additional refrigerant solutions such as R-407A,
R-407C, R-407F, R-448A, and R-449A became
available to the marketplace, there have been
numerous requests to operate Discus compressors
without Demand Cooling in applications where it is
possible to control both condensing temperature and
the return gas temperature to low enough levels to
avoid overheating related failures. Emerson Climate
has re-evaluated operating guidelines for these
refrigerants for the following reasons:
1. R-407A/C/F, R-448A/R-449A discharge
temperatures are higher than R-404A, but lower
than R-22.
2. Many new refrigeration systems operate at lower
compressor superheat/return gas temperatures
than AHRI rating condition at 65°F return gas.
3. Since February 2011, Copeland Discus
compressors come standard with more
comprehensive compressor protection via
CoreSense™ technology
Due to these factors, Emerson is pleased to offer
updated operating envelopes and guidelines for
low temperature R-407A/C/F and R-448A/R-449A
applications. For details on specific applications with
Demand Cooling and without Demand Cooling, refer
to page 8 of this bulletin.
Operating Range
Demand Cooling is designed to protect the
compressor from high discharge temperatures over
the evaporating and condensing temperature ranges
shown in Figures 2, 3, and 6. Additionally, in instances
where compressor return gas temperature and
condensing temperature is closely controlled, the
envelope in Figure 2 is achievable without the addition
of Demand Cooling components to the compressor.
Demand Cooling System
Demand Cooling is compatible with single (conventional)
units as well as parallel racks.
The Demand Cooling module uses the signal of
a discharge head temperature sensor to monitor
discharge gas temperature. If a critical temperature
is reached, the module energizes a long life injection
valve which meters a controlled amount of saturated
refrigerant into the compressor suction cavity to cool
the suction gas. This process controls the discharge
temperature to a safe level. If, for some reason, the
discharge temperature rises above a preset maximum
level, the Demand Cooling module will turn the
compressor off (requiring a manual reset) and actuate
its alarm contact. To minimize the amount of refrigerant
which must be injected, the suction gas cooling
process is performed after the gas has passed around
and through the motor.
Injection valve orifi ces have been carefully chosen
for each body style to be large enough to provide the
necessary cooling when required but not so large
that dangerous amounts of liquid are injected, or that
excessive system pressure fl uctuation occurs during
injection valve cycling. Normally, pressure fl uctuations
are no greater than 1 to 2 psi. It is important to
use the correct valve for each compressor body style.