Bjarne W. Olesen, Angela Simone, Michal Krajčík, Francesco Causone and Michele De Carli
Bibliographic info:
The International Journal of Ventilation, Vol. 9 N°4, March 2011

Mixing and displacement ventilation are common systems in commercial buildings, while mixing ventilation is used in residential buildings. Displacement ventilation provides fresh air to the occupied zone in a more efficient way than mixing ventilation but it is important to know how well it works with a floor system for heating or cooling. Can, for example, a floor heating system warm up the supply air too fast and destroy the displacement effect? Will floor cooling, combined with displacement ventilation, result in too high a vertical temperature difference and too low a temperature at feet level?

The required amount of ventilation depends on the ventilation effectiveness. In standards, the recommended values for ventilation effectiveness depend on the position of the supply and exhaust device and on the difference between supply and room air temperature. Among others, for warm air heating the ventilation effectiveness is always less than 1 and can be as low as 0.4. This would then require an increased amount of ventilation.

A combination of floor heating/cooling, radiators, air cooling, displacement ventilation, mixed ventilation and different combinations of supply and return grilles have, in this study, been experimentally tested. The studies on a displacement ventilation system show lower vertical air temperature differences and higher ventilation effectiveness when it is combined with a floor heating system. With floor cooling, the displacement ventilation system should be designed with a higher supply air temperature. Furthermore, the buoyancy flows from warm or cold windows and occupants influence the airflow pattern and increase the mixing of supply air into the occupied zone.