HVACopediaPsychrometrics
Wet-bulb, humidity, dew point, grains and enthalpy from two readings.
Good to know
- Take the wet-bulb with fast air over the wick and keep the thermometer out of radiant heat; a shielded sling psychrometer is best.
- Enthalpy difference × airflow gives total (sensible + latent) capacity: Btu/h = 4.5 × cfm × change in enthalpy.
- Grains of moisture per pound of dry air: 7,000 grains = 1 lb of water.
More airflow & ducts calculators
Airflow & heating outputcfm, temperature rise, output and cooling airflowStatic pressure & friction rateAvailable static pressure and the friction rate for duct designRound duct sizeDuct diameter from the airflow and the friction rateRound ⇄ rectangular ductEquivalent sizes with the same frictionVentilation & air changescfm for people or air changes, ACH from airflow, blower-door ACH50Fan lawsWhat happens to pressure and power when the airflow changes
Use it on the job
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Calculation aids and reference figures for licensed technicians. Always follow the manufacturer’s data plate and manual for the exact model, and local codes. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Pressures are typical saturation values and change with load and airflow.