Commissioning booster systems for medium and low temperature applications

Be sure to observe the following:

Always commission the medium temperature compressor stage before the low temperature stage.
From a commissioning point of view, the parallel compressor stage is only an extension of the medium temperature compressor stage. Depending on the ambient temperatures, the number and capacity of the compressors, the parallel compressor stage should be ready to operate before the load is connected.
If the parallel compressor stage is running, stable operating conditions should be achieved in the medium temperature compressor stage.
When only the medium temperate compressor stage is in operation: Take the influence of the flash gas bypass into account!
Observe the system configuration and adjust the commissioning procedure if necessary.

DANGER

Liquid R744 evaporates quickly, cools down at the same time and forms dry ice!

Danger of cold burns and frost bites!

Avoid uncontrolled deflating of R744!

When filling the system with R744, wear gloves and goggles!

NOTICE

Oil foam formation and therefore insufficient lubrication!

Avoid strong pressure reduction in the crankcase during the compressor start and during operation!

Checklist for the commissioning of R744 booster systems
1. Check pressure strength and tightness, mount pressure relief valves: Pressure and tightness test only with dehydrated nitrogen, not with air or oxygen! Compressor: Was already subjected to a pressure strength test at the factory. A tightness test is therefore sufficient. Test pressures must not exceed the maximum values on the compressor name plate! Distinguish between the high and low pressure sides! Piping: Pressure strength according to EN 378-2: MOP x 1.43 or min. 1.1 ( ≥ category II) // subsequent EN12799 (brazed joints), EN12517 (welded joints). Decouple individual sections of the system, record (measure) pressure and temperature. Mount the pressure relief valves: HP, MOP_____________________ Serial number(s):___________________________ MP, MOP_____________________ Serial number(s):___________________________ MT LP, MOP_____________________ Serial number(s):___________________________ LT, LP, MOP_____________________ Serial number(s):___________________________
2. Fill oil into oil separator and oil reservoir: Use BSE85K or BSG68K oil, do not mix POE and PAG oil! BSE60K oil is not permitted for compressors in the low temperature compressor stage in booster systems! Document the oil type and charge.
3. Install filter drier cartridges: Model 48-DM
4. Evacuate: It is difficult to dry systems merely by evacuating. Evaporating water by evacuation is time-consuming. Therefore: Break the vacuum of 20 mbar 2–3 times with dehydrated nitrogen during the evacuation process. Avoid ice formation in the system (triple point) – no temperatures below 0°C! Recommendation for "standing" vacuum: Approx. 0.7 mbar (500 microns).
5. Break vacuum with gaseous R744: Connect R744 refrigerant cylinder with pressure reducer and suitable filling lines to the system. Evacuate filling lines or flush with gaseous R744. Open the filling connection and break the vacuum with gaseous R744 up to approx. 10 bar (-40°C). If the refrigerant cylinder cools down considerably, heat the cylinder in a water bath at max. 40°C! Close the discharge and suction gas shut-off valves of the compressors in the medium and low temperature compressor stages.
6. Check safety and control components: Connect laptop to compound controller (FRIGO DATA, Plant Visor, Service Tool, etc.). Switch the compound control digitally to "on". Load circuits of the compressors remain switched off (fuses removed). Calibrate pressure transducer and temperature sensor. Signal tests on the analogue and digital inputs and outputs. Check temperature sensor assignment (cold spray). If necessary, check arrangement of the wiring and electrical connections. Check correct mounting of the temperature sensor on the gas cooler. Check correct mounting of pressure transducers and temperature sensors on the evaporators. Check the rotation direction of the gas cooler fan. Check the rotation direction of the evaporator fan. Check the parameters of the superheat controller at the evaporators. Activate protection function "Close expansion valves at MOP and minimum superheat". Set/check parameters for MOP. Set/check parameter for minimum superheat. Check the parameters of the suction pressure control on the compound regulator. Allow for short time delays for the compressors during the initial commissioning phase.
7. Switch on the oil heater(s): (Do not switch on the compressor!) Oil sump temperature(s) should be at 35– 40°C, but at least 20 K above the ambient temperature. Check the oil level in the compressor.
8. Further charging with refrigerant (small to medium-sized systems) ➔ Not for systems with large capacities and long piping distances between evaporators and compressors. Set the evaporators digitally to "off". Close the shut-off valves at the outlet of the intermediate pressure vessel. Continue charging the system with liquid R744 into the intermediate pressure vessel. Use a pressure reducer when removing R744 from cylinders without a riser tube! If necessary, switch on standstill cooling. Before the first evaporator goes into operation, the minimum liquid level in the intermediate pressure vessel must be reached. Stop filling the intermediate pressure vessel at 30 bar (depending on the design (MOP) of the system at this pressure level) and ensure that the pressure remains below the set point for the flash gas bypass valve.
9. Commissioning Open the discharge, suction and oil shut-off valves of the compressors, switch on the compressor load circuit. Switch the compressor to "automatic mode" ready for operation. Slowly open the liquid line shut-off valve from the intermediate pressure vessel. Start up the evaporators of the medium temperature application one after the other in "automatic mode". Note the capacity of the evaporator(s) in relation to the capacity of the compressor! Switch on the load in 3 to 5 steps in proportion to the nominal evaporator capacity. After commissioning an evaporator, wait to see how the control parameters change and adjust. Observe the following parameters: High pressure Intermediate pressure Suction pressure medium temperature compressor stage Suction pressure low temperature compressor stage Suction gas temperature medium temperature compressor stage Discharge gas temperature medium temperature compressor stage Opening degree of high pressure control valve Opening degree of flash gas bypass valve Superheat and opening degree at the evaporators Reduce the room/refrigerated display cabinet temperature to approx. 10° to 8°C before the next group of evaporators is switched on. Start up the low temperature application evaporators one after the other. Process is the same as that previously described. Reduce the room/refrigerated display cabinet temperature to approx. -5°C° to -10°C° before the next group of evaporators is switched on. ➔ Adjust/supplement refrigerant charge as required.
10. After successful commissioning of the system, check the operating data and create a data protocol: Operating temperatures. Evaporation and condensing temperatures. Suction gas temperature. Discharge gas temperature > 50°C (40°C). Oil temperature > 30°C (20°C). Cycling rate Medium temperature compressor stage: Min. time for one start-up and shut-off: 10 min. Low temperature compressor stage: Min. Operating time: 2 min. Maximum number of compressor starts per hour: Medium temperature compressor stage: 6. Low temperature compressor stage: 8. Voltage and operating current in all three phases. Filter change: Suction gas filter and filter drier after max. 200 h. Oil separator after 50 h.

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