Find the line for 78F, which runs vertically through the chart.You must have JavaScript enabled in your browser to utilize the functionality of this website.LEARN HOW TO STOP THE INVASIVE SPOTTED LANTERNFLY Coronavirus: Information and resources for the Extension Community Home Psychrometric Chart Use Psychrometric Chart Use A psychrometric chart presents properties of air in a graphical format useful for troubleshooting greenhouse or livestock building environmental problems.Save For Later Print Articles Updated: July 12, 2016 Psychrometric Chart and Air Characteristics A psychrometric chart presents physical and thermal properties of moist air in a graphical form.
It can be very helpful in troubleshooting and finding solutions to greenhouse or livestock building environmental problems. 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. This fact sheet explains how characteristics of moist air are used in a psychrometric chart. Three examples are used to illustrate typical chart use and interpretation. Properties of moist air are explained in the Definitions Sidebar for your reference during the following discussions. Figure 1. Psychrometric chart Psychrometric charts are available in various pressure and temperature ranges. Figure 1, is for standard atmospheric pressure (14.7 psi) and temperatures of 30 to 120F, which is adequate for most greenhouse or livestock housing applications. Psychrometric properties also are available as data tables, equations, and slide rulers. A psychrometric chart packs a lot of information into an odd-shaped graph. If we consider the components piece by piece, the usefulness of the chart will be clearer. 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. The chart shows other important moist air properties as diagrammed in Figure 2: wet-bulb temperature; enthalpy; dewpoint or saturation temperature; relative humidity; and specific volume. See the Definitions Sidebar for an explanation of these terms. Moist air can be described by finding the intersection of any two of these properties. Use Figures 2 and 3 with the psychrometric chart in Figure 1 to verify whether you can find each air property. Figure 2. Properties of moist air on a psychrometric chart. Wet-bulb temperature and enthalpy use the same chart line but values are read off seperate scales. An understanding of the shape and use of the psychrometric chart will help you diagnose air temperature and humidity problems. Note that cooler air (located along the lower, left region of the chart) will not hold as much moisture (as seen on the y-axis humidity ratio) as warm air (located along right side of chart). A rule of thumb for inside typical greenhouses or animal buildings during winter conditions is that a 10F rise in air temperature can decrease relative humidity 20 percent. Use of a psychrometric chart will show that this is roughly true. For example, to decrease relative humidity in a winter greenhouse during a critical time period, we could heat the air. Use of Psychrometric Chart in Greenhouse and Barn Example 1 Find air properties A sling psychrometer gives a dry-bulb temperature of 78F and a wet-bulb temperature of 65F. ![]() Relative humidity is an indicator of how much moisture is in the air compared to desirable moisture conditions, and dewpoint temperature indicates when condensation problems would occur should the (dry-bulb) temperature drop. Find the intersection of the two known properties, dry-bulb and wet-bulb temperatures, on the psychrometric chart, Figure 1. The dry-bulb temperature is located along the bottom horizontal axis.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |