Approach temperature is the difference in degrees Fahrenheit between the leaving air temperature from a heat exchanger and the entering water or refrigerant temperature, measuring heat transfer effectiveness. Lower approach temperatures indicate more efficient heat transfer, with well-designed systems typically achieving 5 to 15 degree approach temperatures. This parameter is critical for sizing and evaluating heat pump and air conditioning system performance.
Technical Measurement
Approach temperature is calculated by subtracting the entering water temperature from the leaving air temperature at the coil outlet. A standard air conditioning system with a 45 degree entering water temperature and 50 degree leaving air temperature has an approach temperature of 5 degrees. Larger approach temperatures suggest fouled coils, inadequate airflow, or undersized heat exchangers requiring maintenance or replacement.
System Evaluation
Technicians use approach temperature calculations to diagnose performance degradation and capacity loss. Increasing approach temperatures often indicate coil scaling, refrigerant charge problems, or airflow restrictions reducing system efficiency. Maintaining optimal approach temperatures through regular coil cleaning and proper maintenance preserves cooling or heating capacity while minimizing operating costs.