One request per entry, as a line of text or an object. Duct sizing: the airflow ('1000 cfm', '500 L/s', '1800 m3/h') with a friction rate ('0.08 in wc/100 ft', '1 Pa/m'; 0.1 in/100 ft or 0.8 Pa/m by default), a maximum velocity ('900 fpm', '5 m/s') or both, and optionally a height limit for rectangular ducts: the standard round size, the exact diameter, and rectangular options. Duct check: a size ('12 in round', '400 x 250 mm') and an airflow: velocity, friction rate, velocity pressure. Duct runs: add a length, fittings ('4 elbows', '1 tee', 'mitered elbow', 'vaned elbow', '45 elbow', 'wye', 'takeoff', 'damper', 'fire damper', 'exit') and components with their pressure drop ('filter 0.3 in wc', 'coil 120 Pa', 'diffuser 25 Pa'): the total pressure drop; several sections as an object. Airflow: a sensible load ('24000 Btu/h', '2 tons', '5 kW') with ΔT or supply and room temperatures, or air changes ('room 20 x 15 x 9 ft, 6 ACH'); the duct for it. Materials: galvanized (default), aluminum, pvc, duct board, lined, flex. Air at another temperature ('air at 120 F') or altitude ('altitude 5000 ft'). Object fields: type (duct, system or airflow), q, d, w, h, fixed, friction, velocity, material, roughness (mm), design, length, fittings, components, sections (name, q, d or w and h, length, fittings, components, material), load, dt, supply, room, ach, volume, altitude, temperature, units, title, text.
