---
title: "SHF, RSHF, BPF and ADP"
subject: "Applied Thermodynamics"
chapter: 4
key: "semester_3/applied_thermodynamics:shf-bpf-adp-definitions"
source: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/shf-bpf-adp-definitions
site: BCT Engineering
---

# SHF, RSHF, BPF and ADP

Applied Thermodynamics · Chapter 4: Air-Conditioning

- Asked in: year not given, 5 marks
- Video: [Psychrometry ( part-5)#Concept of BPF,ADP,SHF,RSHF,GSHF,ESHF](https://www.youtube.com/watch?v=G4peXzCiiac) — Anil kolli
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/shf-bpf-adp-definitions
- Whole chapter: https://www.bctengineer.com/md/semester_3/applied_thermodynamics/chapter-4

## Question

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.

## 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).

## Answer

| Term | Meaning |
|---|---|
| **SHF** | Ratio of the sensible heat load to the total (sensible + latent) load: $\text{SHF} = Q_s/(Q_s + Q_l)$. |
| **RSHF** | The 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 factor** | Fraction of the air that comes into contact with the coil: $\beta = 1 - \text{BPF}$ (coil efficiency). |

#### Relation
In a real coil, a fraction BPF of the entering air (state 1) remains unchanged and a fraction $(1 - \text{BPF})$ 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.

```text
  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:

$$
t_2 = \text{BPF}\,t_1 + (1 - \text{BPF})\,t_A
$$

$$
\text{BPF} = \frac{t_2 - t_A}{t_1 - t_A} = \frac{\omega_2 - \omega_A}{\omega_1 - \omega_A} = \frac{h_2 - h_A}{h_1 - h_A}
$$

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

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Sensible heat factor is:
   A. Q_l / (Q_s + Q_l)
   B. Q_s / (Q_s + Q_l)
   C. Q_s / Q_l
   D. Q_total / Q_s
   Answer: B. SHF is the sensible load divided by the total (sensible + latent) load. (Key point: SHF definition)

2. Bypass factor of a cooling coil is:
   A. Fraction of air that contacts the coil
   B. Fraction of air that passes through the coil unchanged
   C. Ratio of ADP to DBT
   D. Coil efficiency
   Answer: B. BPF is the uncontacted fraction; the contact factor 1 - BPF is the contacted fraction (coil efficiency). (Key point: Bypass factor)

3. Which expression for BPF is correct?
   A. (t1 - t2)/(t1 - tA)
   B. (t2 - tA)/(t1 - tA)
   C. (tA - t2)/(t2 - t1)
   D. (t1 - tA)/(t2 - tA)
   Answer: B. Leaving air is a mixture BPF x t1 + (1 - BPF) x tA, so BPF = (t2 - tA)/(t1 - tA); the same holds for omega and h. (Key point: Derivation of BPF)

4. On the chart, where does the leaving air state 2 lie?
   A. On the straight line joining entering state 1 and the ADP state A
   B. On the saturation curve
   C. Vertically above state 1
   D. On the constant WBT line of A only
   Answer: A. State 2 is a mixture of unchanged air (state 1) and air at ADP (state A), so it lies on line 1-A. (Key point: Leaving state location)

5. BPF decreases with:
   A. Fewer coil rows
   B. Wider fin spacing
   C. More coil rows and lower air velocity
   D. Higher air velocity
   Answer: C. More rows, closer fins and lower velocity give better contact, so less air bypasses. (Key point: Factors affecting BPF)

## Related in Applied Thermodynamics

- [Cooling and dehumidifying coil load](https://www.bctengineer.com/question.md?key=semester_3%2Fapplied_thermodynamics%3Acooling-dehumidifying-coil-numerical) — Applied Thermodynamics, chapter 4
- [Sensible heating of air numerical](https://www.bctengineer.com/question.md?key=semester_3%2Fapplied_thermodynamics%3Asensible-heating-load-numerical) — Applied Thermodynamics, chapter 4
- [Supply air quantity for a conditioned room](https://www.bctengineer.com/question.md?key=semester_3%2Fapplied_thermodynamics%3Aroom-supply-air-numerical) — Applied Thermodynamics, chapter 4

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