Systems with large dimensions and high evaporator capacity

Commissioning of large cold stores or distribution centres often entails special requirements, such as partial commissioning of individual construction sections and compliance with temperature reduction curves for screeds and floors.

• Long pipe runs on the suction side can lead to low suction pressures after commissioning of the first evaporators and, in the worst case, to operation with high suction gas superheat and low compressor frequencies. Monitoring the thermal limits of the compressors is therefore mandatory. Note the position of the discharge gas temperature sensors and the thermal inertia of the measuring points!
• Large ambient temperature cold stores include the risk of overload conditions for compressors, especially if a lot of liquid refrigerant is injected into the evaporators when the first evaporators are commissioned. Carefully select, set and check the parameters for the evaporator and suction pressure controllers accordingly!

Recommendations:

• Fill the system on the suction side with more gaseous R744 (>10 bar) to avoid suction gas and discharge gas temperatures which are too high.
• Open the discharge and suction gas shut-off valves of the compressor, but keep the suction gas shut-off valve in the throttle position for the time being. After switching on the compressors to "automatic mode" and starting the first evaporators, observe the suction pressure and, if necessary, take the evaporators out of operation again if the suction pressure rises too quickly. After lowering the suction pressure, select a smaller evaporator capacity for start-up.