The psychrometric chart is used in many other calculations related to heating or cooling of the air (Kodama et al. These properties are needed when you need to calculate 1) the time to turn your irrigation system on, 2) the time to turn your irrigation system off, and 3) the danger of frost damage (Parsons and Boman 2003). In this introduction to psychrometrics, you will learn the relationships between dry bulb temperature, relative humidity, wet bulb temperature and dew point temperature and how to use the chart and any two of these properties to determine the other two properties.
Learning how to read a psychrometric chart will help to understand how relative humidity and air temperature can be used to predict freezing and frost conditions and how it can be used as a tool to time the use of frost protection methods. Relative Humidity (RH)-The ratio of actual water vapor pressure to the vapor pressure of saturated air at the same dry bulb temperature. This quantity may also be called Absolute Humidity. Humidity Ratio-Weight of water vapor in pounds per pound of dry air or grains of water vapor per pound of dry air or kilograms of water vapor per kilogram of dry air expressed as a decimal. Wet Bulb Temperature-The lowest possible temperature to which an air mixture can be cooled solely by the addition of water.ĭew Point Temperature-The temperature at which moisture starts to condense from air cooled at constant pressure and humidity ratio. Moist Air-A mixture of dry air and water vapor.Īir Mixture-A mixture of dry air and water vapor.ĭry Bulb Temperature-The temperature measured by an ordinary. A psychrometric chart is commonly used to establish variations in the environment based on changes in the air heat-moisture. Psychrometrics is the study of the physical and thermodynamic properties of air-water mixtures (Gatley 2004 Knox et al. Haman, Haimanote K Bayabil, and Sandra M Guzman
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