Bypass factor. The fraction of the air a cooling coil leaves untouched; the rest leaves at the coil's surface temperature. The coil model computes it from the geometry.
A cooling coil's bypass factor is the fraction of the air that passes through as if it had never touched the coil; the rest leaves at the coil's apparatus dew point — effectively the surface temperature — and the actual leaving air is the mix of the two. It is a one-number picture of how completely the coil contacts its air: more rows, closer fins and slower air lower it, and typical values run from 0.05 on a deep coil to 0.3 on a shallow one. It decides the moisture a coil removes, because only the contacted air is brought to the surface where condensation happens — a shallow, sparse coil cools sensibly and dries poorly.
The factor is exp(−NTU) on the air side, so it comes from the air-side heat-transfer coefficient and the surface area. In this model the coefficient is computed from the coil's geometry through a published correlation with one calibration, and the fin-to-tube contact resistance is kept as its own term rather than folded into the air-side coefficient — folded in, it would inflate the bypass factor and misread the latent duty of a shallow coil by twenty percent, which is what the Carrier rating matrix the model is held against showed.
Open the builder — the examples in the Design tab's sources list include a machine of this kind, and the Simulate tab runs it against a year of weather.
DOAS — dedicated outside-air system · SZVAV — single-zone variable air volume · VAV terminal box · Economiser · Waterside economiser · Demand-controlled ventilation · Face-and-bypass · Head-pressure control · Humidity ceiling and floor · Cycling and modulation · Coupling · Priority · Category · Nested system · Design point and TMY year · Superheat · Subcooling · Sensible heat ratio (SHR) · Wet-bulb temperature · Dew point · COP and EER · Compressor map · Evaporating and condensing temperature · Range and approach · Heat-recovery (three-pipe) VRF · Typical meteorological year (TMY)