Engineering Manual o.. - HVAC.Amickracing

10152025PSYCHROMETRIC CHART FUNDAMENTALSTHE ABRIDGED PSYCHROMETRIC CHARTFigure 2 is an abridged form of Chart No. 1. Some of thescale lines have been removed to simplify illustrations of thepsychrometric processes. Smaller charts are used in most ofthe subsequent examples. Data in the examples is taken fromfull-scale chartsThe major lines and scales on the abridged psychrometricchart identified in bold letters are:— Dry-bulb temperature lines— Wet-bulb temperature lines— Enthalpy or total heat lines— Relative humidity lines— Humidity ratio or moisture content lines— Saturation temperature or dew point scale— Volume lines in cubic feet per pound of dry airThe chart also contains a protractor nomograph with thefollowing scales:— Enthalpy/humidity ratio scale— Sensible heat/total heat ratio scaleWhen lines are drawn on the chart indicating changes inpsychrometric conditions, they are called process lines.With the exception of relative humidity, all lines are straight.Wet-bulb lines and enthalpy (total heat) lines are not exactlythe same so care must be taken to follow the correct line. Thedry-bulb lines are not necessarily parallel to each other andincline slightly from the vertical position. The purpose of thetwo enthalpy scales (one on the protractor and one on the chart)is to provide reference points when drawing an enthalpy (total.03050.0286015.05000 3000 20001.00.80.60.50.4150015SENSIBLETOTAL HEAT0.3350.2HEAT0.1ENTHALPYHUMIDITY RATIO40-0.1=1000∆H S-0.32025∆H T-0.5∆ h∆ W-1.0-4.0-2.05001.02.04.0∞-10000=3035 40ENTHALPY—BTU PER POUND OF DRY AIR453550 5513.040604565705045SATURATION TEMPERATURE - °F13.55580%75 80 856060%6514.040%7014.5REALTIVE HUMIDITY - %75WET BULB - °F20%DRY BULB - °F8085VOLUME-CU FT PER POUND OF DRY AIRHUMIDITY RATIO(W) - POUNDS OF MOISTURE PER POUND OF DRY AIR.026.024.022.020.018.016.014.012.010.008.006.004.002555045403512.53540455055606570758085909510010511011512030Fig. 2. Abridged Chart No. 1.M10306ENGINEERING MANUAL OF AUTOMATIC CONTROL 41