Calculate tower approach, range, and temperature effectiveness from hot water, cold water, and entering wet-bulb temperature.
Why it matters: Approach and range directly describe cooling-tower operating performance.
ΣCALCULATE · VERIFY · INTERPRET
Calculated result
Engineering evaluation
Physically consistent temperature relationship
Cooling-tower approach (A)7 °F
Cooling-tower range (R)
10 °F
Temperature effectiveness (ε)
58.82 %
Engineering interpretation
The entered tower condition has 7 °F approach, 10 °F range, and 58.82% temperature effectiveness.
Important limitations
Confirm representative entering wet bulb, water flow, fan staging, cell distribution, drift, recirculation, sensor calibration, and stable load.
Engineering knowledge center
Understand the calculation—not just the answer
2026-08-07 · Free Library
Governing relationships
A = Tc−Twb
R = Th−Tc
ε = R/(Th−Twb)×100
Current substitution
A = 85−78 = 7; R = 95−85 = 10; ε = 58.82%.
Calculation sequence
Step-by-step method
Subtract wet bulb from leaving cold-water temperature for approach.
Subtract cold-water from hot-water temperature for range.
Check that range and approach are nonnegative and effectiveness does not exceed 100%.
Equation legend
Inputs and calculated quantities
Th
Entering hot-water temperature — °F or °C
Tc
Leaving cold-water temperature — °F or °C
Twb
Entering-air wet-bulb temperature — °F or °C
A
Cooling-tower approach — °F
R
Cooling-tower range — °F
ε
Temperature effectiveness — %
Applications
How this calculation is used
Building design
Relate scheduled water temperatures to wet bulb.
Construction
Check sensor placement and flow basis.
Commissioning
Calculate field approach, range, and temperature effectiveness.
Quality controls
Assumptions and limitations
Assumptions
Entered data describe one stable operating condition and use consistent measurement boundaries.
Time, energy, and performance values are representative of the stated interval.
Limitations
This is a preliminary evaluation and commissioning-support tool, not an automatic acceptance determination.
Project sequences, manufacturer data, tariffs, codes, and professional review remain controlling.
Field use
Verification procedure
Confirm the operating mode, test boundary, and instrument calibration.
Collect simultaneous readings or a documented trend interval.
Compare the result with the approved sequence, submittal, and project criteria.
Common engineering mistakes
Combining measurements from different operating modes or time intervals.
Ignoring sensor uncertainty, trend sampling, or the defined equipment boundary.
Technical basis
References and source standards
ASHRAE Handbook—HVAC Systems and EquipmentHVAC equipment, central-plant, air-system, and control-performance 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.
