How to combine direct and indirect adiabatic cooling into an air handling unit for resilient tertiary buildings

While adiabatic cooling systems is an interesting alternative to air conditioning in office buildings regarding their environmental impacts, their resilience to heatwaves and global warming depends on the location and the system design itself.

In this article, we study the operation of an indirect adiabatic cooling system, which is the typical use for office building with air handling unit (AHU) installations. Our study highlights the system operation, and the adapted sizing for hot climate conditions. We analyze in details the specific dynamic of the different modes: free cooling mode, heat recovery system, indirect adiabatic, and the possible complement of direct adiabatic.

In this study we redefined several indicators regarding the limits of thermal discomfort, the resilience, and the performance regarding the consumption of energy and water. For this analysis, we identified heatwave scenarios for various locations, and we sized the system accordingly. The results reveal significant disparities in the system operation. In more arid climates, increased use of the adiabatic mode leads to higher water consumption. Furthermore, the coefficient of performance decreases in extremely dry climates as well as in humid climates, primarily due to the increased operating time of the fan and water pump. Additionally, the system is less effective in reducing the thermal discomfort in extreme climates.