![]() ![]() Boundaries of the psychrometric chart are a dry-bulb temperature scale on the horizontal axis, a humidity ratio (moisture content) scale on the vertical axis, and an upper curved boundary which represents saturated air or 100-percent moisture holding capacity. If we consider the components piece by piece, the usefulness of the chart will be clearer. Psychrometric properties also are available as data tables, equations, and slide rulers.Ī psychrometric chart packs a lot of information into an odd-shaped graph. Figure 1, is for standard atmospheric pressure (14.7 psi) and temperatures of 30° to 120☏, which is adequate for most greenhouse or livestock housing applications. Psychrometric charts are available in various pressure and temperature ranges. Properties of moist air are explained in the Definitions section below for your reference during the following discussions. Three examples are used to illustrate typical chart use and interpretation. This article explains how characteristics of moist air are used in a psychrometric chart. Understanding psychrometric charts can help you visualize environmental control concepts, such as why heated air can hold more moisture or, conversely, how allowing moist air to cool will result in condensation. It can be very helpful in troubleshooting and finding solutions to greenhouse or livestock building environmental problems. The definition of STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure.Psychrometric Chart and Air CharacteristicsĪ psychrometric chart presents physical and thermal properties of moist air in a graphical form. STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure The relationship between the psycrometric chart and the Mollier diagram. Moist Air - Transforming the Mollier Diagram to a Psychrometric Chart - or vice versa The Mollier diagram is a graphic representation of the relationship between air temperature, moisture content and enthalpy - and is a basic design tool for building engineers and designers. Moist Air - Psychrometric Table for Pressure 29.92 inHgĭry and wet bulb temperatures, saturation pressure, water vapor weight, specific volume, heat and more.ĭry and wet bulb temperature, specific volume, relative humidity, enthalpy and more. Relative humidity in moist air can estimated by measuring the dry and wet bulb temperature. Air-condition systems temperatures, absolute and relative humidities and moisture content in air.Īir - Heating, Cooling, Mixing, Humidifying or Dehumidifying Processesīasic air changing state processes - heating, cooling, mixing, humidifying and dehumidifying by adding steam or water - psychometric diagrams and the Mollier charts.Īir - Humidifying by Adding Steam or WaterĪir can be humidified by adding water or steam.Īir - Humidifying with Steam - Imperial UnitsĮstimate the amount of steam required (lb/h in 100 cfm) in humid air.Īir - Humidity Measurement from Dry and Wet Bulb Temperature Psychrometric charts and Mollier diagrams. Heating, Cooling, Mixing, Humidifying and Dehumidifying Air Processes by Adding Steam or Water - Visualized in the Mollier diagram.* grains of water is commonly used in psychrometrics The state of air with dry bulb temperature 70 oF and relative moisture 60% can be visualized in a psychrometric chart as indicated below:įrom the chart - the saturation temperature is approximately 61 oF and that the humidity ratio is approximately 66 grains of moisture per pound of dry air.Īir with saturation temperature 63 oF and dry bulb temperature 7 5 oF can be visualized in the psychrometric chart asįrom the chart - the relative humidity is approximately 50 % and the humidity ratio is approximately 66 grains* of moisture per pound of dry air. ![]()
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