Humidity ratio by mass can be expressed as the ratio between the actual mass of water vapor present in moist air - to the mass of the dry air.

Humidity ratio is normally expressed in kilograms (or pounds) of water vapor per kilogram (or pound) of dry air.

The formation of frost on cooling coils in a refrigerator increases power consumption.

Bypass Factor is part of the total air through the coil which fails to come into contact with the surface of the cooling coil.

By-Pass factor is 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.

The By-pass factor for a cooling coil increases with increase in velocity of air passing through it.

The wet-bulb depression is the difference between the dry-bulb temperature and the wet-bulb temperature. If there is 100% humidity, dry-bulb and wet-bulb temperatures are identical, making the wet-bulb depression equal to zero in such conditions.

The difference between dry bulb temperature and wet bulb temperature, is called wet bulb depression.