10 C6.2.27/0716-0219/E
4.1.3 Compressor or valve service
When replacing a ZF compressor using the DTC valve it is recommended to replace both the DTC
valve and the compressor at the same time. The filter in the liquid line should also be replaced.
4.2 ZF*K5E compressors with vapour injection
4.2.1 Economized Vapour Injection technology (EVI)
The Economized Vapour Injection (EVI) technology has been developed to provide improved
capacity and efficiency.
Scroll compressor models ZF*K5E are equipped with a 1" - 14 UNS 2A injection connection, which
can also be used as a vapour injection connection for economizer operation. Economizing can be
accomplished by using a sub-cooling circuit similar to the circuit shown in Figure 7. The line
diagram shows a system configuration for the economizer cycle. A heat exchanger is used to
provide additional sub-cooling to the refrigerant before it enters the evaporator. This sub-cooling
process provides the increased capacity gain measured in the system. The refrigerant evaporated
through the heat exchanger is injected into the compressor and provides additional cooling at
higher compression ratios.
Figure 7: Vapour injection line diagram
During the sub-cooling process a small amount of refrigerant is evaporated and superheated. This
superheated refrigerant is then injected into the mid-compression cycle of the scroll compressor
and compressed to discharge pressure. This injected vapour also provides cooling at higher
compression ratios, similar to liquid injection of standard ZF* Scroll compressors. The benefits
provided will increase as the compression ratio increases, thus, more gains will be made in
summer when increased capacity may actually be required.
Best sub-cooling effect is assured if counter flow of gas and liquid is provided. In order to guarantee
optimum heat transfer, the plate heat exchanger should be mounted vertically and vapour should
exit at the top.
4.2.2 Multiple compressor applications
Multiple EVI compressors can be used with either a single heat exchanger for each compressor
or a common heat exchanger for all compressors. In case of a common heat exchanger, a solenoid
valve should be installed on each individual vapour injection line.
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