![]() ![]() At 100% RH, db temperature is equal to wb temperature. ![]() The RH lines are curved and the values appear in increments of 10%, representing the degree of saturation, or the ratio of the pressure of the vapor (pv) to the pressure of the vapor at saturation (pvs). In SI unit charts, the scale is in ☌.įigure 34-6 shows RH lines. 34-7 Specific Humidity (Humidity Ratio) Lines. 34-4 Sketch of Psychrometric Chart Highlighting One Specific Set of Conditions.įig. 34-2 Psychrometric Chart (English units). The scale called db temperature is laid out horizontally at the bottom of the chart in ☏, with the incremental lines extending Fig. These are shown as straight vertical lines. Each highlights particular scales and lines associated with each one of the seven conditions shown jointly in Figure 34-4.įigure 34-5 shows db temperature lines, i.e., the temperature of air measured on a standard thermometer. If any two properties of an air mixture are known, the chart allows a quick determination of all of its other properties.įollowing are a series of skeleton psychrometric charts. The darkened circle pinpoints the location of the specific condition and the intersecting horizontal and vertical lines show the scales from which the condition can be identified. Included are db and wb temperatures, RH, specific humidity, vapor pressure, dewpoint temperature, and enthalpy. Figure 34-3 is a psychrometric chart in SI units.įigure 34-4 is a basic sketch of a psychrometric chart the scales and lines of the chart are highlighted as they relate to one specific set of air conditions. The numbered lines or scales highlight the functionality of the chart. Figure 34-2 is a psychrometric chart in English units. The chart can be used to make calculations to determine the sensible and latent loads associated with HVAC equipment processes. It relates db temperature to absolute moisture content of the air and includes all of the possible combinations of temperature, moisture content, density, and heat content properties that can occur in air. It is essentially a graphic representation of the condition of air (air-water vapor mixture) at each point in the AC process. It graphically illustrates the relationship between db temperature, wb temperature, RH, humidity ratio, and enthalpy. If dbt and % Relative Humidity (RH) are known, then also it is possible to locate the point on the chart to read other properties of air.The psychrometric chart is a plot of the properties of atmospheric air. In majority of situations, dbt and wbt of the air are measured to find the location of the point on the psychrometric chart. After locating the point of quality, many other properties can be easily obtained from the chart. It is necessary to know to parameters to locate the quality of air on psychrometric chart. The actual psychrometric chart is depicted in Fig. under different conditions using various psychrometric relations. The constructional procedure is of psychrometric chart is based on the calculations for relative humidity, enthalpy, specific humidity etc. ASHRAE has also developed psychrometric charts for other temperatures and barometric pressures. Psychrometric charts are readily available for standard barometric pressure of 101.325 kPa at sea level and for normal temperatures (0-50 oC). Fig.26.4 shows the schematic of a psychrometric chart. The left hand side of the psychrometric chart is bounded by the saturation line. Standard psychrometric charts are bounded by the dry-bulb temperature line (abscissa) and the vapour pressure or humidity ratio (ordinate). It saves lot of time and labour required for calculation of different properties of air and such values can be directly read from the chart. Using the chart, it is easy to obtained psychrometric properties of air and it helps to decide the various processes to be followed to achieve required quality of air. Psychrometric chart shows the inter-relation of all the important properties of air. ![]()
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