Calculation sequence
Step-by-step method
- Calculate dry-air mass flow from volumetric airflow and density.
- Subtract leaving from entering moist-air enthalpy.
- Multiply mass flow by enthalpy difference.
MechanicalIntermediateHeat Transfer
Airside Total-Heat Calculator
Calculate total airside heat transfer from airflow, air density, and moist-air enthalpy difference.
Why it matters: Enthalpy captures both sensible and latent effects that dry-bulb temperature difference alone cannot represent.
Calculated result
Engineering evaluation
Airside total heat transfer (Qt)360,000 Btu/h
- Dry-air mass flow (ṁda)
- 45,000 lb/h
- Moist-air enthalpy difference (Δh)
- 8 Btu/lb
Engineering interpretation
The entered air condition represents 360000 Btu/h of signed total airside heat transfer.
Important limitations
- Use simultaneous representative psychrometric measurements and a dry-air mass basis. Leakage, fan heat, casing heat transfer, and measurement uncertainty require separate review.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
ṁda = ρQ×60
Δh = h1−h2
Qt = ṁda·Δh
Current substitution
ṁda = 0.075×10000×60 = 45000; Δh = 32−24 = 8; Qt = 360000 Btu/h.
Equation legend
Inputs and calculated quantities
- Q
- Airflow — cfm or m³/s
- ρ
- Dry-air density — lb/ft³ or kg/m³
- h1
- Entering moist-air enthalpy — Btu/lb or kJ/kg
- h2
- Leaving moist-air enthalpy — Btu/lb or kJ/kg
- Qt
- Airside total heat transfer — Btu/h
- ṁda
- Dry-air mass flow — lb/h
- Δh
- Moist-air enthalpy difference — Btu/lb
Applications
How this calculation is used
Building design
Screen total coil or air-system capacity.
Construction
Compare scheduled and installed airside capacity conditions.
Commissioning
Estimate field total heat transfer from simultaneous airflow and psychrometric readings.
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.
- NIST Guide for the Use of the International System of UnitsFederal unit-system and conversion reference used for SI/I-P presentation.
Engineering calculation disclaimer
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.
Read the full use and limitation statement