Coil Bypass Factor and Apparatus Dew Point
How much air slips past a coil untouched, and how much actually contacts it.
Example
You enter
- Entering-air dry-bulb (°F) 80
- Leaving-air dry-bulb (°F) 55
- Apparatus dew point ADP (°F) 50
You get
- Bypass factor BF 0.167
- Contact factor CF 0.833
Details, formula, and sources
Bypass factor BF = (t_lvg - t_adp)/(t_ent - t_adp), contact factor CF = 1 - BF, off the apparatus dew point (coil-surface temperature). 80 -> 55 F off a 50 F ADP -> BF 0.167, CF 0.833; a shallower coil bypasses more and dehumidifies worse. A design aid; the coil rating governs.
BF = (t_lvg - t_adp) / (t_ent - t_adp); CF = 1 - BF.
The coil bypass / contact factor and apparatus-dew-point definition from the ASHRAE Handbook - Fundamentals, by name.
The bypass-factor / apparatus-dew-point construction is a standard coil-performance result. The coil rating and ADP selection govern.
Estimate. AHJ and licensed professional govern.
Field names used by the API: t_ent_f, t_lvg_f, t_adp_f, bf, cf
- Bypass / contact factor BF = (t_lvg - t_adp)/(t_ent - t_adp); CF = 1 - BFASHRAE Fundamentals
- Apparatus dew point ADP is the effective coil-surface temperatureASHRAE
- Physical band leaving air lies between the ADP and the entering temperaturescope of this tile