HVAC design guides

Short, practical explanations of the methods behind the J1 Pro calculators, written for working engineers and students.

How to calculate duct external static pressure (ESP)

Index run, duct friction, fittings, accessories and the fan selection margin, with a worked example.

Pick a friction rate, size each section, check velocity and aspect ratio.

What goes into a room cooling load, and why area-based rules of thumb mislead.

The one formula for CHW flow, ΔT choice, and quick conversions for kW, TR and US gpm.

Dry bulb, wet bulb, dew point, humidity ratio and enthalpy, and the three air-side load formulas.