Coil Bypass Factor Calculator

Inputs

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Mixed-air dry-bulb entering the coil.
°F
Supply-air dry-bulb leaving the coil. Must sit between the ADP and the entering temperature.
°F
Effective coil surface temperature — where the coil process line meets saturation on the psych chart.
°F

Results

Default result
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Bypass factor(BF)
0.168
Pass

Within the customary comfort-coil band. Lower BF = more rows / closer fins / lower face velocity.

Fraction of air effectively bypassing the coil surface; comfort coils commonly run ~0.05-0.30.

Also computed

Contact factor(CF)0.832

Coil temperature drop(ΔT)25°F

Approach to ADP(T_out − ADP)5.04°F

How close the leaving air gets to the effective coil surface temperature.

Method notes 4 notes
  • Dry-bulb formulation of the bypass model: the same BF applied on the psych chart with enthalpies gives the latent side; this screen covers the sensible picture.
  • BF rises with face velocity and falls with rows/fin density: typical comfort coils ~0.05-0.30, deep dehumidification coils lower, shallow process coils higher.
  • ADP is found where the coil process line extended meets saturation — estimate it from the psych chart or coil selection data; it is NOT the supply air temperature.
  • Measure dry-bulbs with the same instrument either side of the coil; a 0.5 °C error moves BF noticeably at small approaches.

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