Tools and Rules : The Pressure / Temperature Chart

 

Pressure-Temperature Relationship:

1. Direct Relationship:

   • Principle: As pressure increases, temperature increases, and vice versa. This principle is fundamental in understanding how refrigerants behave within HVAC systems.
   • Boiling Point Control: By controlling the pressure within a closed system, we can control the boiling point (saturation temperature) of the refrigerant.

2. Saturation Temperature:

   • Definition: The temperature at which the refrigerant changes state (from liquid to gas or vice versa).
   • Location: This change of state typically occurs in the middle of the evaporator coil (during cooling) or the condenser coil (during heating).

Example Pressure-Temperature Chart:

• Refrigerants: The example chart provided includes R22 and R410A.
• Usage: When analyzing system performance, you can refer to the chart to determine the expected pressure for a given saturation temperature and vice versa.

Practical Examples:

1. Evaporator Coil:

   • R22 Example:
     • Saturation Temperature: 41°F
     • Corresponding Pressure: 70 PSIG
   • R410A Example:
     • Saturation Temperature: 41°F
     • Corresponding Pressure: 120 PSIG
   • Application: Blowing 75°F air over a 41°F evaporator coil will typically result in air cooled to around 55°F.

2. Condenser Coil:

   • R22 Example:
     • Saturation Temperature: 120°F
     • Corresponding Pressure: Between 255 and 265 PSIG
   • R410A Example:
     • Saturation Temperature: 120°F
     • Corresponding Pressure: Around 405 PSIG

Key Takeaways:

• Different Pressures for Different Refrigerants: Even when the coil temperatures are the same, R410A operates at much higher pressures than R22.
• System Setup: The pressures in a system are manipulated to achieve the desired boiling point, which affects the system’s cooling or heating performance.