Introduction to Refrigeration Systems : Pressure and Temperature Terminology

 Key Points:

1. High-Pressure Terms:

   • Interchangeable Terms: High side, high side pressure, head pressure, discharge pressure.
   • These terms all refer to the pressure on the high side of the system, which typically remains constant.
   • Temperature Changes: Significant temperature changes occur on the high side.

2. Temperature Terminology:

   • Discharge Temperature: The superheated vapor leaving the compressor.
   • Condensing Temperature: The temperature where the refrigerant changes state from vapor to liquid.
   • Liquid Line Temperature: The sub-cooled liquid temperature leaving the condenser.

3. Diagram Review (High Side):

   • High Side Pressure: 278 PSIG.
   • Saturation Temperature: 125°F.
   • Discharge Line Temperature: Superheated vapor (superheated by 50°F).
   • Condensing Temperature: 125°F, where the state change occurs.
   • Liquid Line Temperature: Sub-cooled liquid temperature.

4. Low-Pressure Terms:

   • Interchangeable Terms: Low side, low pressure, suction pressure.
   • These terms all refer to the pressure on the low side of the system, which also remains constant.
   • Temperature Changes: Different temperature terms used to describe the low side conditions.

5. Temperature Terminology (Low Side):

   • Suction Temperature / Evaporator Temperature / Saturation Temperature: The temperature at which the refrigerant evaporates or changes state.
   • Suction Line Temperature: The temperature measured after leaving the evaporator, always a superheated vapor.

6. Diagram Review (Low Side):

   • Low Side Pressure: 69 PSIG.
   • Saturation Temperature: 40°F.
   • Suction Line Temperature: Initially superheated by 10°F to 50°F, may increase to total superheat or compressor superheating.