Energy conservation potential of an indirect and direct evaporative cooling assisted 100% outdoor air system

This study aims to present the fundamentals in which operation of a 100% outdoor air system integrates with indirect and direct evaporative cooling systems and to estimate its energy saving potential. The simulation of the proposed system is performed using a commercial equation solver program, and the annual operation energy saving potential with respect to a conventional variable air volume system is determined. This paper shows that significant operation energy savings (i.e. 21–51% less energy consumption) is possible principally by the pre-conditioning of supply air due to the waste heat recovery using the indirect evaporative cooler and the sensible heat exchanger units. By components, the proposed system shows a 16–25% less annual cooling coil load and an 80–87% reduced annual heating coil load with respect to the conventional variable air volume system, while there is no fan energy savings expected.

Practical applications: This paper provides practical insight on how the evaporative cooling based 100% outdoor air system operates and how each essential component, such as the indirect evaporative cooler, cooling coil, direct evaporative cooler, heating coil and sensible heat exchanger should be controlled during the seasons for realising energy conservation benefits. The sequence of operation presented in this paper can be implemented to actual control logic.