11
General Recommendations
System requirements
Rotary compressors are ‘direct suction’. The suction gas enters directly into the compression chamber.
The suction accumulator incorporates a filter to protect the compressor against dirt and debris entering
the pump.
It is essential that all necessary precautions are taken to ensure the system is kept clean during
installation and service e.g. purge the system with Nitrogen whilst brazing.
Pipework design
The function of the pipework is to allow the refrigerant to circulate through the system components in
such a way as to provide optimum operating conditions, i.e.:
> Limited pressure drop,
> Velocity is sufficient to entrain the oil,
> Ensure that the compressor is protected against the return of liquid refrigerant particularly when
the installation is switched off.
> A full head of liquid refrigerant at the expansion device.
As in all refrigerating systems using hermetic compressors, some of the oil from the compressor
circulating within the system is entrained with the refrigerant. The amount varies according to the ope-
rating conditions of the installation. No additional components e.g. oil separator, oil coolers etc. are
required to assist with oil control in rotary compressor systems.
However, it is essential to ensure the oil return to the compressor otherwise its working life may be
shortened and its performance affected.
All pipework in the refrigerating system must be designed to return oil to the compressor. The design
must prevent oil being trapped in the pipework, the system components and the heat exchangers.
Refrigeration best practice must be respected.
Due to the difficulty of controlling the return of oil in a multi-evaporator system, we advise that the
rotary compressors should only be used in a single circuit system.
4.2.1 Pipework design advice/guidance
4.2.1.1 Suction pipework
Suction pipework returns refrigerant gas to the compressor from the evaporator. The main factors
to consider are:
> A partial refrigerant charge caused by a leak or incomplete charging will cause a reduction in
compressor capacity due to the lower suction pressure,
> Reduce the return gas superheat in order to limit the discharge temperature,
> Ensure that the refrigerant velocity is sufficient to return the oil to the compressor which has a small
oil charge,
> Prevent refrigerant entering the compressor during either the running or off cycles. The possibility
of any liquid slugs of oil entering the compressor during the running must also be prevented.
In practice, suction lines are generally designed for pressure drops of no more than 1°C saturated temperature.
4
4.1
4.2
To Next Page
Loading...
