Experimental study on augmentation of mixing within a stratified indoor environment by erosion of density interface

Department of Building Engineering, Energy Systems and Sustainability Science, University of Gävle, SE-801 76 Gävle, Sweden

^* Corresponding author: alan.kabanshi@hig.se

Abstract

The current study aims to address the problem associated with warm air heating in passive houses. Warm air eating is cheaper and easy to operate in passive houses, however, this creates problems of shortcut ventilation and thermal discomfort due to stratification as warm air is confined to the ceiling. In the current study, we explore a new method of creating resonance between stratification frequency and the periodic variation of the ventilation supply frequency to increase mixing of the supplied warm air and the room air consequently destratifying the room conditions. A basic water model study is used to understand the interaction between the frequency variations and the resulting standing waves with stratification characteristics in a room. Measurements at three different input frequencies and at three input paddle locations have been performed, gathering vertical temperature gradients and visualization data from them. The results show the shift in the inversion point because of an increase augmentation across the inversion between the fluids with different densities close to resonance. There is also a dependency on paddle location showing that the type of ventilation system will have different mixing rates due to different fluid energetic behaviours.