HUMIDIFICATION, DEHUMIDIFICATION, AND PSYCHROMETRICS
Most refrigerated cooling processes also include dehumidification. The process has been studied from many angles. There are some very interesting approaches that are available from a variety of sources. A good start- ing point is a quick review of what you know about temperature and its measurement.
For air-conditioning and heating for comfort purposes, it is necessary to also know something about humidification. The word “sensible” implies that the heating or cooling takes place at a constant humidity. Al- though the humidity ratio remains constant, there can be a change in the relative humidity. As the dry-bulb temperature increases, the air will hold more moisture at saturation.
If an air stream is passed through a water spray in such a way that the departing air is saturated adiabatically (without heat loss or gain), then the process can be shown on charts. A constant wet-bulb process and the final wet and dry bulb temperatures are equal. In practice, the process is called evaporative cooling, and saturation is achieved. The efficiency of an air washer or evaporative cooler is the ratio of the dry-bulb temperature difference from point 1 to point 2 to the initial difference between the dry- and wet-bulb temperatures.
Psychrometry (from the Greek psychro-, meaning “cold”) is the science and practice of air mixtures and their control. The science deals mainly with dry air, water-vapor mixtures, and the specific heat of dry air and its volume. It also deals with the heat of water, the heat of vaporization or condensation, and the specific heat of steam in reference to moisture mixed with dry air. Psychrometry is a specialized area of thermodynamics.