This paper examines the economics of three-stage indirect/direct evaporative air-conditioning systems. The third stage of cooling is considered to be supplied by mechanical refrigeration, typically direct expansion or chilled water. A parametric study or sensitivity analysis is performed to identify the key variables that influence the economic evaluation required to justify the additional capital expense associated with installing an indirect/direct evaporative air-conditioning system in lieu of a conventional mechanical refrigeration system.

For purposes of comparision in the parametric analysis, a payback period is defined as the number of equivalent full-load operating hours required to amortize the capital cost difference. A series of graphs are presented that will allow the experienced energy engineer or HVAC designer to estimate the economic feasibility of three-stage evaporative air-conditioning for his particular building application and weather conditions.

Units: I-P