There Is No Such Thing as Cold—Only the Absence of Heat

            When an air conditioner or refrigerator is cooling a space, it isn’t adding cold air into the space. The purpose of the refrigeration cycle is to remove the heat in a given area and eject it outside. Less heat means a colder room.              

         In simple terms, a refrigeration cycle's mission is heat absorption and heat rejection. As any HVAC instructor will tell you (emphatically), you can't make cold, you can just remove heat. The refrigeration cycle, sometimes called a heat pump cycle, is a means of routing heat away from the area you want to cool. This is accomplished by manipulating the pressure of the working refrigerant (air, water, synthetic refrigerants, etc.) through a cycle of compression and expansion.

The Refrigeration Cycle in HVAC

A refrigeration cycle has four major components: the compressor, condenser, expansion device, and evaporator. Refrigerant remains piped between these four components in the refrigerant loop.

1. The compressor -refrigerant begins as a cool vapor and heads to the first component—the compressor. The compressor is the engine of the refrigeration cycle. It consumes the most power of an HVAC system’s components and forces refrigerant through the system. As the HVAC compresses the cool, gaseous refrigerant, it transforms into a very hot and high-pressure vapor.

2. The condenser - the condenser’s job is to cool the refrigerant so it turns from a gas into a liquid, or condenses. This happens when warm outdoor air blows across a condenser coil filled with hot, gaseous refrigerant. This allows heat to transfer from the refrigerant to the cooler outdoor air, where the excess heat diffuses to the atmosphere. The condenser coils wind through the condenser to maximize the surface area of the piping—and heat transfer to the air. The refrigerant turns from a vapor into a hot liquid due to the high pressure and reduction in temperature.

3. The expansion device - the refrigerant then approaches the expansion device as a hot, high-pressure liquid. The expansion device is responsible for quickly driving the pressure of the refrigerant down so it can boil (evaporate) more easily in the evaporator. And that’s it! The expansion device has one sole purpose: to reduce refrigerant pressure. Because the pressure drops so rapidly at the expansion device, the refrigerant turns into a combination of a cold liquid and vapor.

4. The evaporator - once the refrigerant is a cold mix of liquid and gas (vapor), it begins to move through the evaporator. The evaporator is responsible for cooling the air going to a space by boiling (evaporating) the refrigerant flowing through it. This happens when warm air blows across the evaporator as cold refrigerant moves through the evaporator coil. Heat transfers from the air to the refrigerant, which cools the air directly before being vented to a space. Like the condenser coil, the evaporator coil also winds through the evaporator to maximize heat transfer from the refrigerant to the air. The low-pressure liquid refrigerant is easily boiled by the warm air blown across the evaporator and heads back to the compressor as a cool gas/vapor.

The refrigerant is hottest when it leaves the compressor and coldest when it leaves the expansion device.

To summarize—refrigerant in the evaporator absorbs heat (cooling the air), and is expelled from the refrigerant to the outdoor air via the condenser. Simultaneously, the expansion device and compressor help manipulate the pressure of refrigerant to make the cycle possible.

References

Delahunt, J. (2021). Understand Your HVAC—The Refrigeration Cycle. Retrieved on May 13, 2022 from https://www.buildingengines.com/blog/knowledge-refrigeration cycle/#:~:text=When%20an%20air%20conditioner%20or,heat%20means%20a%20colder%20room.

Super Radiator Coils (2021). The 4 Main Refrigeration Cycle Components. Retrieved on May 13, 2022 from https://www.superradiatorcoils.com/blog/4-main-refrigeration-cycle-components#:~:text=The%20refrigeration%20cycle%2C%20sometimes%20called,cycle%20of%20compression%20and%20expansion.

Submitted by: DAISY JANE D. ECHAVEZ - HVACR 3
Submitted to: Prof. Gretchen Cabunita