Refrigeration Cycle Principles

This article will cover the basic fundamentals to the refrigeration cycle. When it comes to troubleshooting an industrial refrigeration system, referencing the refrigeration cycle is always a great starting point. Overthinking can make valuable time unproductive. When evaluating the problem at hand, practice "mindfulness" and start with the basics. The key foundation for any skilled operator/technician is having a sequence they follow when presented with an operational problem.

The Water Cycle is a term that was taught to us back in grade school. Who would have guessed that we were learning about the basics of the refrigeration cycle at an early age? The principles for the water cycle (hydrologic cycle) are identical to the principles of the refrigeration cycle.

The Water Cycle

The Refrigeration Cycle is the process of relocating heat from one location to another. Heat is moved to a place where it makes little or no difference, like condensers that are located outside. Four main components make up the basic refrigeration cycle:

Expanding is the process of using a device to remove pressure from the liquid refrigerant to allow expansion or change of state to occur.

Evaporating is the process of absorbing heat into the refrigerant which changes from a liquid to a gas (evaporation).

Compressing is the process of raising the pressure and temperature of the vapor (compression).

Condensing is the process of rejecting heat from the vapor, to allow for the (condensation) of the refrigerant back into liquid.

Basic Refrigeration Cycle

Let's discuss some scenarios where the basic refrigeration cycle can assist in identifying system mis-operation.

Scenario #1: Compressor suction pressure setpoint is "25psig" and the actual suction pressure has dropped to "18psig". The compressor machine is operating properly, and the slide valve is fully unloaded.

If you refer to the above image, you will trace back to the equipment that is connected to the suction side of a compressor (low pressure gas). In this case it would be the "evaporator" that is providing the "load" to the compressor. I would investigate the evaporator for proper operation, you could follow the refrigeration cycle rotation and go to the condenser and then to the expansion valve, but that would be the "long way" to identify the problem.

We'll say that this evaporator had the fans fault out and that stopped the process of absorbing heat into the system which also provides a "load" to the compressor machine.

Scenario #2: The condensing pressure (head pressure) is normally around 150psig +/- 10psig and head pressure is currently operating at 192psig. In this scenario if your compressor suction pressure is still operating at its desired setpoint you would trace the next piece of equipment after the compressor.

That component would be the "condenser" and while inspecting the condenser you found that no water from the pumps was being delivered to the condenser.

We'll say that the condensers water sump tank was not properly re-filling with water and pumps shutoff for a low-level condition.

Having that knowledge is the framework for adding tools to your mental toolbox for future problems you face. Whenever you have a problem presented to you that has you stumped, always remember to start with the basics and check those "refrigeration cycle boxes" first.

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