CONTENTS PAGE Executive summary ----------------------------------------------------------------------------------------- 8.118 Written description of issue ------------------------------------------------------------------------------8.119 Illustrations of operational modes ------------------------------------------------------------------- 8.120 Standard psychrometric chart ---------------------------------------------------------------------------8.121 Enthalpy comparison benefit -----------------------------------------------------------------------8.122 DEFINITIONS DRY BULB TEMPERATURE A measurement of temperature usually expressed in degrees Fahrenheit or degrees Celsius, measured with a thermometer. WET BULB TEMPERATURE The lowest temperature that evaporation of water causes, measured using a thermometer with a wet wick over its bulb. RELATIVE HUMIDITY The percentage of moisture contained in air relative to the air saturated at that dry bulb temperature. ENTHALPY The total heat content of air, considering the dry bulb temperature and the relative humidity. (Every pound of evaporated water contains 970 BTU of latent heat, as well as its sensible heat.) SENSIBLE HEAT Heat added or taken from a substance that changes the dry bulb temperature of that substance. LATENT HEAT Heat absorbed or discharged from a substance as that substance changes state from solid to liquid, liquid to solid, gas to liquid or liquid to gas. Latent heat loss or gain does not change the dry-bulb temperature of the substance. VALUES -1- 7,000 grains of moisture = one pound -2- 13.35345 cubic feet of air = one pound -3- 970 BTU’s are required to evaporate one pound of water -4- 970 BTU’s are produced in condensing one pound of water vapour -5- .018 BTU’s are required to raise one cubic foot of air one Fahrenheit degree 8.117
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