Outcome 5.1 Refrigeration: Measuring, Understanding, and Diagnosing the Vapor-Compression System

Temperature

A measure of the average kinetic energy of the particles in a substance, indicating how hot or cold it is.

Pressure

The force exerted per unit area; in HVAC, often refers to gauge or absolute pressure in refrigeration systems.

Gauge pressure

Pressure measured relative to atmospheric pressure, often indicated as psiG (pounds per square inch gauge).

Absolute pressure

Pressure measured relative to a perfect vacuum, often indicated as psiA (pounds per square inch absolute).

Saturation temperature

The temperature at which a refrigerant changes phase at a given pressure; critical for understanding refrigerant state.

Evaporator

The component in a refrigeration system where the refrigerant absorbs heat and changes from liquid to vapor.

Condenser

The component in a refrigeration system where the refrigerant releases heat and changes from vapor to liquid.

Superheat

The temperature of a vapor above its saturation temperature at the same pressure, important for compressor protection.

Subcooling

The temperature of a liquid below its saturation temperature at the same pressure, ensuring only liquid refrigerant reaches the metering device.

Pressure-temperature (P-T) chart

A graphical representation showing the saturation temperature corresponding to given pressures for refrigerants.

Conduction

The transfer of heat through a solid or between solids in contact; heat flows from warmer to cooler areas.

Convection

The transfer of heat between a surface and a moving fluid, often attributable to airflow in HVAC systems.

Radiation

The transfer of heat via electromagnetic waves, such as heat from the sun warming a refrigerant unit.

Thermal energy

Energy that comes from the temperature of matter; in refrigeration, it moves from low to high temperature areas.

Cubic Feet per Minute (CFM)

A measure of air volume flow rate, indicating the volume of air displaced in one minute.

British Thermal Unit (BTU)

The amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

First Law of Thermodynamics

A principle stating that energy cannot be created or destroyed, only transformed from one form to another.

Latent heat

Heat transfer associated with phase change, such as the heat released when water vapor condenses into liquid.

Sensible heat

Heat transfer that results in a temperature change without a phase change; related to temperature differences.

Thermodynamic cycle

The series of processes that refrigerant undergoes in a refrigeration system, continuously circulating and changing state.

Compressor

The component that compresses refrigerant vapor, increasing its pressure and temperature in the refrigeration cycle.

Metering device

The component that regulates the flow of refrigerant into the evaporator and creates a pressure drop.

Energy conversion

The process of changing one form of energy to another, such as electrical energy to mechanical energy in compressors.

Temperature difference

The difference in temperature between two points which drives heat transfer in a refrigeration system.

Cooling capacity

The ability of a refrigeration system to remove heat, often measured in BTU/h.

Flow hood

A device used to measure airflow at supply and return vents, typically used in HVAC diagnostics.