HVAC Essentials: A Free Hands-on Workshop

A: 0.022 is Darcy, not Fanning, and at 18 L/s in 100 mm the velocity lands near 2.3 m/s, which drives the loss term. That combination yields about 7 m over 180 m once units are kept straight. The trap is double-counting the loop or mixing friction factor definitions, both of which DFMEA loves to flag.

A: 100 W/m² is the anchor that separates sanity from fantasy for offices without heroic glazing. Multiply by 1,200 m² and you're in the low hundreds of kilowatts, not tens. Estimation lives on first principles and scale, not on optimistic single contributors.

A: 1,000 Pa is the tell. That excess static drives VAV damper hunting, which then fights the temperature loop. Backing off pressure and tuning hierarchy restores loop decoupling instead of masking the symptom.

A: Chlorides plus moisture is the threshold condition. Once insulation gets compromised, localized pits form fast on copper, long before velocity or temperature-driven mechanisms wake up.