© 2018 Emerson Climate Technologies, Inc.
15
AE4-1431 R1
system from operating outside the operating envelope
published by Emerson, whatever the climatic conditions
and the capacity demand.
However, in some extreme cases
– such as loss of
system charge, extreme heat transfer restriction at the
evaporator, any defect or blocked flow control
component (expansion valve, screens, etc.)
– the
evaporating conditions may be such that the
compressor will operate outside the published operating
envelope limits. These conditions may result in
compressor failure.
Therefore, Emerson requires that all ZB*KAU
compressors without exception be fitted with a low-
pressure protection in the suction line. The mandatory
inclusion of a low-pressure switch will stop the
compressor operating outside the published envelope
limits or below atmospheric pressure.
4.4. Discharge gas temperature protection
Inadequate lubrication! Scroll set damage!
All
ZB*KAU compressors must be equipped with an
external discharge gas temperature protection.
A good system control shall prevent the system from
operating outside the published operating envelope and
acceptable superheat range, whatever the climatic
conditions and the capacity demand. However, under
some extreme operating conditions (such as loss of
charge or improper control operation), the internal
discharge gas temperature reached can cause
compressor damage.
To guarantee positive compressor protection,
it’s
required that discharge gas temperature protection be
used for any application with Copeland brand
compressors. This protection must not be used as an
operating envelope controller. If not used, the warranty
of the compressor will be lost.
The maximum discharge gas temperature is 275°F
(135°C) for Internal limitation. The external DLT is set
1
The ATEX directive consists of two EU directives describing what
equipment and work space is allowed in an environment with an
explosive atmosphere.
for 250°F (121°C) for all ZB*KAU models. These
compressors
have
no
internal
discharge
gas
temperature protection. Therefore, an external protector
is required. See Section
4.4.1. Excessive discharge gas temperatures
A few of the possible consequences are listed below:
•
Since the oil circulates in the system with the
refrigerant, it is subjected to high discharge gas
temperatures. If the discharge gas temperature
becomes too high, the so-called "coking" effect will
occur (heating of oil under exclusion of air). Carbon
deposits can form at points of high temperature, for
example on the valves, oil channels, oil filters, etc.
The oil lubricity will be reduced and a progressive
wear process will occur which will prematurely
damage the compressor.
•
The stability of the refrigerant can also be affected,
particularly if traces of contaminant are present.
•
The problems listed under the first 2 points
frequently occur simultaneously, particularly since
the chemical reaction time approximately doubles at
every 20°F (10°C) temperature rise. This directly
leads to chemical reactions of the oil with the
refrigerant and the compounds extracted from
sealants and insulation material. Therefore,
contaminants of various types, among them acids,
will form inside the system.
4.4.2. Discharge gas temperature protection
Discharge gas temperature protection is the "fall-back"
for failure of the system control. It is essential that proper
control of the evaporating and condensing pressures
and the superheat is maintained and has the ability to
cope with all likely conditions and high loads. Reliance
on
protectors
will
cause
inadequate
system
performance and short cycling. Emerson offers a
discharge line thermostat, which complies with the
ATEX
1
requirements. This thermostat is marked with a
CAUTION