WEFOUNDpsychrometrics definition of family

Psychrometric charts are available in various pressure and temperature ranges. Figure 1, at the top of the page, is for standard atmospheric pressure (14.7 psi) and temperatures of 30 o to 120 o F which is adequate for most greenhouse or livestock housing applications. Psychrometric properties are also available as data tables, equations, and slide rulers.

An understanding of the shape and use of the psychrometric chart will help in diagnosing air temperature and humidity problems. Note that cooler air (located along lower, left region of 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, inside typical greenhouses or animal buildings during winter conditions, is that a 10 o F 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.

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.