Emerson Copeland Scroll Introduction Manual page 42

Compressors
ZB50K* to ZB114K*
Summit
Figure 7: Mounting parts for multiple operation
7. Design points
7.1 Suction line header
The suction lines running from the evaporators to the compressors should be led to a common main suction header in which
the suction pressures can equalize. From the main suction header to the compressors, preferably short and similarly constructed
pipes have to be provided symmetrically arranged. This serves to achieve a most perfect pressure equalization necessary for the
crankcases already at the compressor inlet. Naturally, the lower the speed in the suction line header the more perfect the pressure
equalization. Pipes running into the suction line header must not be right opposite outgoing pipes, so that an equalization of the
returning oil quantities can take place in the suction line header.
According to the capacity requirement of the system, compressors will be switched on or off. Occasionally however liquid
refrigerant can possibly flow into the compressors operating. Therefore, the suction line header should be designed in a manner
to simultaneously serve as a liquid separator. Consequently, one has to construct each pipe from the suction line header to the
compressor so that the oil return is guaranteed by using additional bores or capillaries. Liquid refrigerant should not return to the
compressors when not operating via the oil returning device.
Since installations with parallel compressors mostly have long pipe runs fitted on site, suction filters are commonly used. These
filters may just as well be equipped with drier cores as with dust filters only. The filter housings will be rigidly fitted into the system
during first installation before the common suction line header. Thus one can employ the appropriate filter core according to the
individual requirement, ie, acid absorbing driers too if necessary.
7.2 Discharge line header
The discharge line should slope downwards from the compressor to a lower positioned discharge line header. This is so any liquid
returning to the compressor from the condenser on the off cycle does not enter the compressor discharge port.
7.3 Oil separator
One of the features of a parallel compressor installation is the higher refrigeration capacity. With an increasing capacity generally
the entire pipe work is extended, more complex and not easy to survey, sometimes resulting in problems with the oil return. It is
therefore recommended to install oil separators regardless of the refrigerant and evaporating temperature. Pay careful attention and
obey the rules on how to install the pipe work. With the installation using an oil level regulating system the oil separator is already
included in this system hence the oil return line has to be fitted to the oil reservoir.
7.4 Oil supply
The more complex a system pipe work is the more influence the installation has on oil return. The extreme possibilities of capacity
control resulting in frequent changes of gas velocities inside the suction line will render the oil return difficult as well. Particular
attention should be paid to the lubrication problems involved. The oil level in the compressor crankcase should be controlled by
using an OMB oil level regulator having oil level detection. This device interrupts the compressor control circuit when insufficient oil
is in the compressor crankcase.
7.5 Installation
All compressors should be installed as close as possible to each other in order to keep the lines as short as possible. By changing the
priority of compressors in operation and keeping running time constant the compressors oil temperature can be kept at a certain
level which will reduce the amount of refrigerant absorbed into the compressor oil. Refrigerant flowback into the compressor during
standby periods is not possible because the suction line header is below the compressor inlet port. If there is a requirement for
isolating the installation against vibrations the frame should be mounted on vibration absorbers. Of course the connecting pipes on
suction and discharge sides have to be flexible as well.
39
Ident Number
8609592
527-0206-03
Variation = 8602466
Characteristics
Hard
steel
Drawing