Calculate leaving-air approach above entering-fluid temperature for a cooling coil.
Why it matters: Approach temperature provides a simple field indication of coil and flow performance.
ΣCALCULATE · VERIFY · INTERPRET
Calculated result
Engineering evaluation
Physically consistent cooling-coil approach
Cooling-coil approach temperature (A)11 °F
Leaving-air temperature (Tla)
55 °F
Entering-fluid temperature (Tew)
44 °F
Engineering interpretation
The entered cooling-coil approach is 11 °F.
Important limitations
Approach depends on load, airflow, fluid flow, coil rows, fouling, bypass, face velocity, refrigerant/fluid temperature, and sensor location.
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Governing relationships
A = Tla−Tew
physical cooling-coil relationship A≥0
Current substitution
A = 55−44 = 11 °F.
Calculation sequence
Step-by-step method
Confirm the selected fluid temperature basis and flow direction.
Use representative leaving-air temperature.
Subtract entering-fluid temperature from leaving-air temperature and check that the result is nonnegative.
Equation legend
Inputs and calculated quantities
Tla
Leaving-air temperature — °F or °C
Tew
Entering-fluid temperature — °F or °C
A
Cooling-coil approach temperature — °F
Tla
Leaving-air temperature — °F
Tew
Entering-fluid temperature — °F
Applications
How this calculation is used
Building design
Compare scheduled leaving-air and entering-fluid conditions.
Construction
Check sensor locations and coil connection basis.
Commissioning
Calculate field approach at a stable operating condition.
Quality controls
Assumptions and limitations
Assumptions
Entered values represent one stable operating condition and use consistent measurement boundaries.
Fluid and air properties are representative of the evaluated condition.
Limitations
This is a preliminary evaluation and field-verification tool, not a final sizing or code-compliance determination.
Manufacturer data, adopted codes, project criteria, and professional engineering review remain controlling.
Field use
Verification procedure
Confirm measurement boundaries, operating mode, and instrument calibration.
Stabilize the system and record simultaneous readings.
Compare the calculation with project requirements and manufacturer data before disposition.
Common engineering mistakes
Mixing values from different operating conditions.
Using nominal rather than measured flow, temperature, power, or fluid properties.
Technical basis
References and source standards
ASHRAE Handbook—FundamentalsPsychrometrics, heat transfer, load relationships, and HVAC calculation context; verify the licensed current edition during professional review.
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
