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4.3
Pressure safety controls
4.3.1 High-pressure protection
The high-pressure protection should be installed according to EN 378.
4.3.2 Low-pressure protection
IMPORTANT
Loss of system charge and lubrication! Bearing malfunction and
compressor breakdown! A low-pressure control is highly recommended.
Do not bridge or by-pass the low-pressure cut out.
Heat pumps in some geographical areas have to operate at low evaporating pressure because
of the low ambient temperatures, sometimes combined with a high level of relative humidity.
Good evaporator sizing and adequate defrost strategy control should prevent the system from
operating outside the operating envelope published by Emerson Climate Technologies, whatever
the climatic conditions and the heating or cooling demand.
However, in some extreme cases – for example loss of system charge, extreme heat transfer
restriction at the evaporator, any defect or blocked flow control component (expansion valve,
screens...) – the evaporating conditions may be such that the compressor will tend to operate
outside the Emerson operating envelope limits. All those conditions may starve the compressor
in refrigerant and oil, and may result in compressor failure.
Therefore, Emerson Climate Technologies strongly recommends the installation of a low
pressure limiter in the suction line that will shut down the compressor when it operates outside
the published envelope limits.
4.4
Discharge gas temperature protection
IMPORTANT
Inadequate lubrication! Scroll set damage! Compressors ZH04K1P to
ZH19K1P and ZHI05K1P to ZHI46K1P must be equipped with a discharge
gas temperature protection.
A good control should prevent the system from operating outside the published operating
envelope and acceptable superheat range, whatever the climatic conditions and the heating
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. In order to guarantee positive compressor protection, discharge gas
temperature protection is required for any application with Copeland brand compressors. This
protection must not be used as an operating envelope controller but as a safety device.
For compressors ZH04K1P to ZH19K1P the maximum discharge gas temperature is 140°C. For
compressors ZHI18K1P and ZHI23K1P single BOM 526 and ZHI05K1P to ZHI14K1P it is
135°C. These compressors must be equipped with an external discharge gas temperature
protection (see Figure 16). The protection shall be installed 120 mm from the compressor shell,
along the straight or bended pipe.
Figure 16: Sketch of discharge gas temperature protection for compressors with external sensor
For compressors ZHI18K1P and ZHI23K1P tandem-ready BOM 477 and for compressors
ZHI27K1P to ZHI46K1P, the maximum discharge gas temperature is 135°C. These compressors
are equipped with a NTC-temperature sensor in the top cap (see Figure 17). This sensor
measures the discharge gas temperature in the top cap and must be connected to the controller,
eg, EXD TEVI (under development, please contact Emerson Climate Technologies). The
controller has to stop the compressor when the maximum discharge gas temperature is
exceeded.
18
C6.2.26/1013-1116/E
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