Investigation of different ventilation profiles to avoid stratification in Nearly Zero Energy Buildings

Abstract: This research paper examines possible solutions for the problems that warm air heating is suffering in Nearly Zero Energy Buildings. These NZEBs are passive houses constructed to have high energy efficiency where the quantity of power used is equal to the power created annually, produced locally or in the surroundings by renewable energy sources. The problem is that this type of houses are facing problems when it comes to the heating system, where temperature of air in the ceiling is greater than on the floor, so temperature stratification happens and thermal comfort is not reached in the occupied zone. For this reason, this study is carried out and tries to find optimal solutions for warm air heating. To accomplish the investigation, an experimental study has been performed using water as the working fluid in a small-scale model. Here, paddles moved horizontally located in the center of the model at the inversion level have been used to simulate the effect that the diffuser does in the air when heating. Measurements with different paddles were made to analyze the importance of the size in the mixing and one of the paddles has been positioned on a side, next to the wall, to analyze the influence of an obstacle. It has been concluded that the area of the paddle does not have a great influence on the mixing rate, but the height of it. Also, the obstacle introduced when having the paddle next to the wall showed good results in the mixing rate. Finally, the potential energy of the water tank has not suffered any change at the surface but it has decreased at the bottom for all of the paddles, so it has been wound up that the area does not have influence on the change of potential energy. All in all, two main conclusions have been reached. On the one hand, the configuration of the air inlet diffuser significantly influences the rate of mixing. Specifically, a greater vertical size of the diffuser leads to a higher speed of mixing attainment. On the other hand, it is recommended to position the diffuser towards an obstacle, such as the adjacent wall, in order to induce turbulence. As a consequence, these findings can be investigated later in a real scale model using air as the working fluid. In this way, a solution for problems of warm air heating could be found.