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SHF, RSHF, BPF and ADP

Short answer

SHF = Q_s/(Q_s+Q_l); RSHF is SHF of room loads. ADP is the coil mean surface temperature (saturated state of perfect contact). BPF is the fraction of air bypassing the coil unchanged; contact factor = 1-BPF. For a cooling coil, BPF = (t₂ − t_A)/(t₁ − t_A) = (ω₂−ω_A)/(ω₁−ω_A) = (h₂−h_A)/(h₁−h_A).

Define sensible heat factor (SHF), room sensible heat factor (RSHF), bypass factor (BPF), contact factor and apparatus dew point (ADP) of a cooling coil. Derive the relation between BPF and the entering, leaving and ADP temperatures.

TermMeaning
SHFRatio of the sensible heat load to the total (sensible + latent) load: SHF=Qs/(Qs+Ql)\text{SHF} = Q_s/(Q_s + Q_l).
RSHFThe same ratio for the room load only (the heat gains of the room); it is used to fix the supply air condition.
Apparatus dew point (ADP)Mean surface temperature of the cooling coil; the saturated state to which the air would be cooled if it came into perfect contact with the coil.
Bypass factor (BPF)Fraction of the air that passes through the coil without contact and leaves unchanged.
Contact factorFraction of the air that comes into contact with the coil: β=1−BPF\beta = 1 - \text{BPF} (coil efficiency).

Relation

In a real coil, a fraction BPF of the entering air (state 1) remains unchanged and a fraction (1−BPF)(1 - \text{BPF}) is cooled to the ADP (state A). The leaving air (state 2) is their mixture, so it lies on the straight line joining 1 and A.

  w ^              saturation curve
    |       .-'
    |    .-'               o 1
    |  .'               /
    | /          o 2       line A-2-1
    |/        /
    |   A o  (on the saturation curve)
    +----------------------------> DBT

Energy and mass balance on the mixture:

t2=BPF t1+(1−BPF) tAt_2 = \text{BPF}\,t_1 + (1 - \text{BPF})\,t_A BPF=t2−tAt1−tA=ω2−ωAω1−ωA=h2−hAh1−hA\text{BPF} = \frac{t_2 - t_A}{t_1 - t_A} = \frac{\omega_2 - \omega_A}{\omega_1 - \omega_A} = \frac{h_2 - h_A}{h_1 - h_A}

Contact factor =t1−t2t1−tA= \dfrac{t_1 - t_2}{t_1 - t_A}. BPF decreases with more coil rows, closer fin spacing and lower air velocity.

✓ Answer checked by Claude Opus 5.5 (high effort)

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