📊 Percent of Rated Total Capacity
💧 Sensible Heat Ratio
Test Results Breakdown
Full Calculation Table
| Component | Basis | Value | Result |
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How to Use the Coil Performance Test Calculator
Measure the actual system airflow across the coil using a flow hood, pitot traverse, or the system's known design airflow. See the pitot traverse calculator if measuring duct airflow directly.
Measure entering and leaving dry-bulb and wet-bulb temperature at the coil using a calibrated psychrometer or equivalent instrument, taken as close to the coil face as practical.
Enter the coil's rated sensible and total capacity from the equipment nameplate or submittal data for comparison against field-measured results.
Click Calculate Coil Performance to see field-measured sensible capacity, total capacity, sensible heat ratio, and percent of rated capacity delivered.
Understanding Coil Performance Field Testing
Field-testing a coil's actual delivered capacity confirms whether an installed system performs close to its rated specification, a standard commissioning step that catches airflow, charge, and installation problems before they become comfort complaints. This calculator estimates total capacity from the enthalpy of the entering and leaving air, worked out from the wet-bulb readings, and sensible capacity from the dry-bulb temperature drop, each multiplied by the measured airflow. It is the same basic method used throughout HVAC commissioning and diagnostic work.
Why Field Capacity Rarely Matches Nameplate Exactly
Nameplate capacity ratings come from a standardized test condition, typically 80°F dry-bulb and 67°F wet-bulb entering air at design airflow. Real field conditions almost never match that rating point precisely, so some deviation between field-tested and rated capacity is normal and expected rather than automatically indicating a problem. At that rating point the air carries about 31.6 BTU/lb of enthalpy, which is a handy figure for checking a calculation, and the enthalpy calculator lets you cross-check the enthalpy of any other air state. The goal of a field test is catching results meaningfully outside the expected range, not demanding an exact match to nameplate.
Airflow Is Usually the First Thing to Check
Low airflow across the coil is one of the most common causes of underperforming field capacity, since reduced airflow lowers total heat transfer even when refrigerant charge and entering conditions are correct. Confirming measured airflow against design airflow, using the air flow measurement tool, is usually the fastest diagnostic step before investigating refrigerant charge or coil condition. Field surveys summarized in a U.S. Department of Energy peer exchange presentation found measured airflow ranging from 130 to 510 CFM per ton, with 70 percent of the units in one study below 350.
Sensible Heat Ratio as a Diagnostic Signal
The sensible heat ratio, sensible capacity divided by total capacity, shifts in a predictable direction when airflow is off from design. Airflow that's too low gives air more contact time with the coil, increasing moisture removal and lowering sensible heat ratio below what the equipment's rated SHR would suggest. This calculator treats a ratio below 0.65 as lower than typical. A sensible heat ratio significantly different from the coil's rated SHR is often a faster clue than total capacity alone, and the sensible heat ratio calculator is a quick way to check the ratio on its own.
Documenting Results for Commissioning Records
Recording field-tested coil performance as part of a startup or commissioning package establishes a baseline for future service comparisons and satisfies commissioning documentation requirements on many commercial projects, and Natural Resources Canada's commissioning guide for new buildings shows how that testing fits into the wider commissioning process. Pair these results with the HVAC test report generator or commissioning report generator to build a complete documented record.
Frequently Asked Questions
A properly functioning coil operating close to its rated entering conditions and design airflow typically delivers 90 to 100 percent of its rated capacity in the field. Results below roughly 85 percent usually point to a specific cause such as low airflow, incorrect refrigerant charge, entering conditions that differ from the rating point, or a fouled coil surface, and warrant further investigation before assuming the equipment is undersized. This calculator flags results below 85 percent of rated total capacity as below the expected range.
Nameplate capacity is measured at a specific standardized set of entering air conditions and design airflow, and field conditions rarely match that rating point exactly. Actual entering air temperature and humidity, real system airflow versus design airflow, and refrigerant charge accuracy all shift measured capacity away from the rated number, which is why comparing field results to rated capacity is a diagnostic tool rather than an exact pass or fail test.
A lower than expected sensible heat ratio, meaning the coil is removing more latent heat, moisture, relative to sensible heat than design intended, often points to airflow that is too low across the coil. Slow airflow gives air more contact time with the cold coil surface, increasing dehumidification but reducing total delivered cooling capacity and comfort at design conditions. This calculator treats a sensible heat ratio below 0.65 as lower than typical. See the air flow measurement tool to confirm actual airflow.
Yes, accurate wet-bulb temperature measurement matters significantly for a valid coil test, since even small wet-bulb measurement errors translate into meaningfully different calculated capacity results. Uncalibrated or poorly maintained sling psychrometers and some digital probes can introduce enough error to make a properly functioning coil appear undersized or oversized, so instrument calibration is worth confirming before relying on test results for diagnostic decisions.
Related HVAC Tools
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Document these results
Full commissioning documentation