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Define the term By Pass factor used for heating or cooling coil Also explain apparatus dew point temperature

Subject:- Refrigeration and Air Conditioning

Topic:- Psychrometry

Difficulty:- Low

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By-Pass factor:

The inability of a coil to cool or heat the air to its temperature is indicated by a factor called by-pass factor (BPF) or Coil Bypass Factor. This inability is due to the coil inefficiency and some amount of air just bypassing the coil without getting affected by it. A coil with low BPF has better performance. BPF can also be defined as the ratio of air which is unaffected by the coil to the total quantity of air passing over the coil.

BPF= $\frac{(t_d2-t_s)}{(t_d1-t_s )}$ for cooling coil

Apparatus dew point temperature

Dehumidification is removal of water vapour from air. This process is possible when air is passed over a cooling coil which is at a temperature below the dew point temperature of entering air.

The surface temperature of this cooling and dehumidification coil is known as ‘Apparatus Dew Point’ temperature, also called ‘coil

ADP’ or simply ‘ADP’. The process of cooling and dehumidification is shown in figure as line 1-C. A part of air passes over the coil to reach ADP temperature and remainder air is bypassed. Hence the actual resultant condition is point 2 .