Hanbell RC2-AVI Series, Manual

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35
7. Applications
7.1 Additional cooling
When compressors operate in the following application conditions, installation of an additional auxiliary cooling
apparatus is recommended to lower discharge temperature, maintain proper temperature of lubricant and additional
cooling for motor coil to ensure safe running of compressors.
 Air-cooled system
 High compression ratio system such as heat pump, low temperature and refrigeration system
 High discharge temperature system such as heat recovery system
 Any other heavy duty application
There are two types of additional cooling of compressor that described separately as below:
a. Liquid injection applications
In areas with high condensing temperature and/or low evaporating temperature as in the limitation diagram, additional
cooling is required in order for the compressor to work properly. A relatively simple method of additional cooling is
direct refrigerant injection in the compressor either in the motor side or compression chamber side.
The purpose of installing a liquid injection system is to prevent the compressor from overheat. The system installed a
liquid injection expansion valve between the liquid line and compressor for cooling down the compression chamber and
motor to ensure the continuous and safe running of the compressor. The suction superheat should be controlled
between 5K~10K for the application of air-cooled and heat pump chillers by means of expansion valve devices. These
devices can be adjusted by the stem of the expansion valve to control the suction superheat by means of refrigerant
flow rate. When the initial startup, the loading of the chiller is heavy due to the high temperature of chilled water, so the
liquid injection devices capacity should be selected or calculated enough to reduce the overheat of the compressor.
Calculating the cooling capacity of liquid injection devices
Liquid injection devices can be calculated with the HANBELL selection software or manually. For manual calculation,
consider the most extreme conditions to be expected during actual operations i.e. minimum evaporating temperature,
maximum suction gas super heat and condensing temperature.
Liquid injection applied with low temperature expansion valve
When the compressor applied in the low temperature system (E.T.
≦
-10°C) the compression ratio is high at this
condition, also the discharge temperature will be very high. The design of the liquid injection system for low
temperature application is similar to the illustration shown in figure below. There are two connectors for the liquid
injection in the compressor, one is in the motor side to cool down the motor temperature and reduce the discharge
temperature. The other is in the compression chamber side and its function is to reduce the discharge temperature and
increase the compression efficiency. However, when additional cooling in compression chamber like economizer
operation, oil cooler application is used or when condensing temperature is low, discharge temperature be kept low
and liquid injection may not be turned on, although motor load is severe and motor coil temperature is high. This may
lead to motor failure. Therefore, in application mentioned above Pt100 or Pt1000 for liquid injection to motor is
recommended instead.
Figure 7.1: Liquid injection connected to motor Figure 7.2: Liquid injection connected to compression chamber