A DX coil, or direct expansion coil, is a cooling heat exchanger where liquid refrigerant directly evaporates within the coil tubes to cool passing air. DX coils are the most common cooling method in residential and light commercial air conditioning systems, functioning as the indoor component of split-system and packaged air conditioning units.
Technical Details
In a DX coil, refrigerant enters as a liquid-vapor mixture through an expansion device, then fully evaporates as it absorbs heat from the air passing over the coil. Operating pressures range from 70 to 150 psig depending on refrigerant type (R-410A, R-454B, etc.). The coil temperature sits 15°F to 20°F below the desired discharge air temperature to achieve proper dehumidification while preventing ice formation on the coil surface.
Applications and Significance
DX coils are preferred for their efficiency and simplicity compared to chilled water systems. They eliminate the need for separate chillers and water circulation pumps, reducing installation and maintenance costs. Common refrigerant capacity ranges from 1.5 to 5 tons in residential systems. Proper superheat control ensures optimal performance and compressor protection.