Introduction to Compressors

Types of Compressors

• Reciprocating Compressors: Traditionally common.
• Rotary Compressors: Generally for smaller units.
• Scroll Compressors: Increasingly common in refrigeration and air conditioning.
• Screw Compressors: Used in large applications.
• Centrifugal Compressors: Used in large applications.

Function of Compressors

• Compressors compress refrigerant vapor by decreasing the volume to increase pressure.
• Vapor compression moves refrigerant as high pressure seeks low pressure.

Energy Source

• Most compressors use electrical connections through fusite plugs.
• Types of compressors:
  • Hermetic Compressors: Completely sealed, not meant for access.
  • Semi-Hermetic Compressors: Can be accessed by removing bolts.
  • Open Drive Compressors: Uses a separate motor connected via a shaft (prone to leaks).

Important Considerations

• Superheat Measurement: Ensures refrigerant entering the compressor is fully vapor to prevent damage.
• Temperature and Mass Flow Rate: Essential for cooling compressors, especially refrigerant-cooled types.

Compression Ratio

• Calculated as absolute discharge pressure divided by absolute suction pressure.
• Higher compression ratios result in increased waste and higher temperatures.

Oil Control

• Oil is necessary for lubrication, typically found in the compressor's crankcase.
• Problems with oil:
  • Liquid refrigerant can cause foaming and oil loss.
  • Overheating can degrade the oil.
  • Flooded Starts: Liquid refrigerant accumulates during compressor off-cycles and boils off upon restart, causing oil loss.
• Prevention tools: solenoids, pump down solenoids, crankcase heaters, hard shut-off TXVs.

Compressor Operation

• Vapors enter via the suction line and exit through the discharge line.
• Temperature Disparity: Suction line is low temperature (e.g., 50°F), discharge line is high temperature (e.g., 165-170°F).
• Compression Process: Increases temperature by compressing vapor, causing molecules to move faster.

Heat and Temperature

• Temperature increase due to compression and motor operation.
• Heat from motor windings but mainly temperature increase is due to decreased volume and increased pressure.
• Heat is rejected in the condenser to turn vapor into liquid.

Misconceptions

• Compressors do not turn vapor directly into liquid, this requires heat rejection in the condenser.

This lecture provides an overview of compressors and their role in air conditioning and refrigeration systems. Further details on failure and diagnostics will be covered in subsequent discussions.