Refrigeration Basics with Elliot & Bert – Part 1

There are four main components: compressor (high-temperature; pressure increaser), condenser (heat rejector), metering device (pressure dropper), and evaporator (heat absorber). When you start by memorizing components and their order, you can start to absorb information about HVAC systems with greater ease since you will have the vocabulary at your disposal.

Pressure is one of the main driving forces of the HVAC refrigerant circuit; it is the force exerted on an object. It may be measured in absolute pressure (PSIA) or gauge pressure (PSIG), the latter of which deducts atmospheric pressure (14.7 PSI). We usually use PSIG in the field; we may use PSIA for some PT charts and calculating the compression ratio. In the HVAC industry, we primarily measure air pressure in inches of water column (“wc or in. wc.), refrigerant pressure in PSIG, and vacuum pressure (in microns; 1/1,000,000 inches of mercury column).

Temperature is an average measurement of molecular velocity (how fast molecules are moving). It is not the same thing as heat; heat is the amount of energy a substance has, not the average speed of the molecules. Something may be cold to the touch but still have heat. In the HVAC industry, we are moving heat; temperature is an indicator of it, but it’s not the exact same thing. Temperature measurements might be wet-bulb or dry-bulb. Dry-bulb temperature only accounts for sensible heat, and the wet-bulb temperature accounts for latent heat (moisture or humidity) and is usually cooler than the dry-bulb temperature.

The compressor manipulates temperature by manipulating pressure according to the Ideal Gas Law (PV = nRT); as pressure rises, the temperature also rises. Temperature also decreases as pressure decreases, so the metering device drops the refrigerant pressure before it enters the evaporator again.

The Second Law of Thermodynamics states that hot goes to cold; heat moves from hot to cold and will attempt to continue to do so until both objects are at the same temperature (thermal equilibrium). HVAC systems use the evaporator as a means of heat transfer; heat from the space is moved into the colder refrigerant, and refrigerant that is hotter than the outdoor temperature gives off that heat to the cooler space. Imbalances in pressure will cause the refrigerant to move, and imbalances in temperature will allow heat to move.

Voltage, or electrical pressure, also follows a high-to-low rule. Whenever there is a difference in electrical potential, electrical energy will move from a higher concentration to a lower concentration due to the energy imbalance.

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