HVAC System Capacity Calculator

Use this HVAC System Capacity Calculator to estimate the sensible, latent, and total cooling capacity currently being delivered by a system. Enter the measured system airflow, jobsite elevation, and entering and leaving dry-bulb and wet-bulb temperatures.

The calculator uses psychrometric relationships to determine changes in air temperature, moisture content, and enthalpy across the indoor coil. Results include sensible capacity, latent capacity, total capacity, sensible heat ratio, and equivalent cooling tonnage.

Outdoor ambient temperature is not required to calculate the system’s measured airside capacity. However, outdoor conditions should be recorded separately when comparing the calculated capacity with the manufacturer’s published performance data.

For reliable results, allow the system to stabilize before collecting measurements. Use properly calibrated instruments, measure dry-bulb and wet-bulb temperatures at the same entering and leaving air locations, and enter measured airflow rather than nominal equipment airflow. Calculated values are diagnostic estimates and should be evaluated with the applicable product data and service literature.

SYSTEM AIRFLOW

Enter the measured total system airflow.
Use measured airflow, not nominal equipment airflow.
Enter 0 for sea level. Elevation is used to adjust atmospheric pressure and actual air mass flow.

ENTERING AIR CONDITIONS

Measure dry bulb and wet bulb at the same entering-air location.
Return-air dry-bulb temperature entering the equipment.
Wet bulb cannot be greater than entering dry bulb.

LEAVING AIR CONDITIONS

Measure dry bulb and wet bulb at the same leaving-air location.
Supply-air dry-bulb temperature leaving the evaporator coil.
Wet bulb cannot be greater than leaving dry bulb.

CALCULATED SYSTEM CAPACITY

Psychrometric calculations adjusted for dry bulb, wet bulb, atmospheric pressure, moisture content, and actual dry-air mass flow.
Entering dry bulb minus leaving dry bulb.
Entering-air enthalpy minus leaving-air enthalpy.
Calculated using actual dry-air mass flow and moist-air specific heat.
Calculated from actual dry-air mass flow and the full entering/leaving enthalpy difference.
Total capacity minus sensible capacity.
Sensible capacity divided by total capacity.
Total capacity divided by 12,000 BTU/h per ton.
Correct flagged measurements before relying on the calculated capacity.
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