Profroid MiniCO2OLcompact Notice D'instructions page 74

11.4.3 CO2 Pump
The CO2 pump aims at compensating the differential pressure generated by the ejectors when it is not sufficient to ensure proper operation of
the consumer expansion valves.
The uplift delivered by the ejectors is between 1.5 and 6.5 Bar depending on the operating conditions. The pump starts usually when the pressure
uplift is below 2 Bar. That value can be adjusted in the controller to be adapted to the specific conditions of each installation.
11.5 RECOMMENDATIONS TO DESIGN AN INSTALLATION USING EJECTORS:
11.5.1 Liquid receiver pressure
When using ejectors, the pressure of the liquid receiver will reach higher values than usual. The receiver design pressure PS (and as a
consequence the entire liquid line of the installation) must thus be set at 52 bar minimum. Higher pressure levels > 52 bar are also available under
request.
11.5.2 Receiver volume selection
Recommendations of chapter 6.1.7 apply.
To be noticed that in an installation using ejectors, higher refrigerant charge is required compared with a traditional installation requiring the
same cooling capacity. Indeed, operating in semi-flooded mode induces higher refrigerant content in the consumers as well as a small liquid
fraction in the main suction line. Therefore, fluctuations of liquid content inside the liquid receiver are more important than in a traditional CO2
transcritical system.
11.5.3 Selection of the consumer expansion valves
To enable the semi-flooded operation with a small pressure difference between the liquid inlet and suction outlet of the consumers, their expansion
valves must be selected with a pressure differential value between 1.5 and 2 bar, which usually leads to one or two bigger orifice sizes compared
with a traditional CO2 transcritical system.
11.5.4 Limiting the pressure drop of the refrigeration lines
The systems using ejectors operating with a quite low differential pressure between the liquid and suction lines, it is required to reduce the
pressure drop generated by the refrigeration lines, as well as the pressure at the consumer level and especially of their liquid line.
11.5.5 Use of consumers with high Delta Pressure
In the case when a few consumers create more pressure drop than the others, it is recommended to, position them closer to the suction line of
the rack if possible to reduce the impact on the overall installation.
Last generation cabinets, air coolers should be prefered to maximize the energy efficiency of the overall system.
When using low performance MT consumers (low evaporating temperature) having a limited cooling demand compared with the total capacity of the
system, it is recommended to connect them into the LT stage instead using a pressure regulating valve.