Airflow for a known sensible duty

Convert a specified sensible heating or cooling duty into airflow using chosen air properties.

How this calculation works

Use this calculation after the sensible duty has already been established. Enter its positive magnitude together with the air temperature-change magnitude, density and specific heat appropriate to the operating condition. Dividing duty by specific heat and temperature difference gives the required mass flow. Dividing that result by density gives volume flow, which is displayed in liters per second. The same balance applies to sensible heating and cooling when magnitudes are used. Reducing the chosen temperature difference increases the flow required to transfer the same duty, so small temperature differences make measurement or input errors more influential. No latent duty is included. The result also excludes outdoor-air requirements and distribution effects, and therefore does not by itself determine room load, ventilation compliance or duct dimensions.

Inputs and units

Sensible duty magnitude (kW)
Air temperature difference magnitude (K)
Air density (kg/m³)
Air specific heat (kJ/(kg·K))

Method and formula

Mass flow = sensible duty/(cp × ΔT); volume flow = mass flow/density. kW and kJ/(kg·K) give kg/s; multiply m³/s by 1000 for L/s.

Worked example

Example inputs

Sensible duty magnitude: 10 kW
Air temperature difference magnitude: 10 K
Air density: 1.2 kg/m³
Air specific heat: 1.006 kJ/(kg·K)

Calculation steps

Required air mass flow = 10 / (1.006 × 10) ≈ 0.994036 kg/s.
Required volume flow = 0.9940357853 / 1.2 ≈ 0.8283631544 m³/s = 828.363154 L/s.

Example results

Required volume flow: 828.3631544 L/s
Required mass flow: 0.9940357853 kg/s

Assumptions

Specified duty is entirely sensible with constant density and specific heat.

Limitations

No room-load estimation, latent capacity, ventilation allowance or duct design is included.
Preliminary educational check; verify inputs and equipment data before design or operation.

Sources

DOE Fundamentals: Thermodynamics: Specific heat, equation 1-17; first-law energy balance
ASHRAE Handbook: Psychrometrics: Sections 5–7 and 10: humidity ratio, ideal-gas properties, moist-air balances