Ventilation efficiency measurements - a comparison between three supply air methods

University essay from Lunds universitet/Energi och ByggnadsDesign

Abstract: This study compares the two traditional ventilation methods ; mixed ventilation and displacement ventilation, with a new type of dif fuser which attempts to solve the problem with blockage of the diffuser for the displacement ventilation. This new diffuser called Airshower is a product developed by Airson engineering AB whom is also the company where all simulations and tests for this study were performed in a built office space. The study compares in term of ventilation efficiency, ventilation index, air exchange efficiency and mean age of air. The Airshower diffuser did prove to be the most efficient ventilation solution in comparison to the other systems when measuring with constant heat loads but the worst one with variable loads. The uncertainty of the results is estimated to be of consequence since the built office space had some flaws such as leakage, issues with the adjustable floor and control system. In ventilation index terms however, the mixed air system is the only system which yields any expected results, this fraction between room- and exhaust air once again lacks confidence due to the unsealed laboratory. The displacement system would do a lot better if the mean age of air in the exhaust air would be older. The mean age of air does not differ much from system to system, it is in the interval of 20-30 minutes for all the systems with the exception for one point in the room for both of the displacement system with the probable cause of turbulence causing air currents reducing the efficiency of the system. This study is not enough to conclude that any system is significantly better than any other but both the results and the conclusion of this study could change a lot for the displacement systems should the floor and walls be sealed. Keywords: Ventilation efficiency, air exchange efficiency, local ventilation index, mean age of air, comparison, mixed ventilation, displacement ventilation

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