Objectives Psychometrics Examples in AHUs

Humidification hw Specific enthalpy of water added to system hg Specific enthalpy of saturated water vapor

Evaporative Cooling (air washing)

Air Washer Sprays liquid water into air stream Typically, air leaves system at lower temperature and higher humidity than it enters

Air Washers/Evaporative Coolers Heat and mass transfer is mutually compensating Can evaluate based on temperature drop, humidification, or comparison to other energy exchangers

Evaporative Cooler 8

Cooling Tower Similar to an evaporative cooler, but the purpose is often to cool water Widely used for heat rejection in HVAC systems Also used to reject industrial process heat

Processes in AHU and buildings

Systems: Single-Zone Air Systems Zone – any space with a thermostat

Air conditioning 12

Reheat 13

Recirculation 14