With the improvement of thermal building Insulation the percentage of energy losses due to air exchange becomes an increasingly· important factor in building energy demand. In order to optimize infiltration and ventilation and to minimize the energy demand of low energy buildings, it is necessary to install an appropriate mechanical ventilation system. Different ventilation strategies can be used: Extract ventilation and supply I extract ventilation systems for buildings as well as single-zone ventilation units with or without heat recovery.
To ensure indoor air quality an efficient ventilation system should provide fresh air in those parts of a room where it is required. To assess whether the ventilation system fblfils the main objective, different definitions of local ventilation efficiency (the local mean age of air, the local ventilation rate, the local purging flow rate and the local air exchange rate) are reported in literature.
The study concerns the ventilation of a parallelepiped shape room by means of several systems whose supplying and extracting methods differ, so the different thermic conditions applied to limits. To qualify the efficiency of each of these systems in relation with the various current criteria, we carried out measurements by means of a tracer gas, both with a transitory and a permanent flow. At the same time, numerical simulations were carried out by means of a CFD code which solves the equations of the fluids mechanic, material and heat transfers associated with flows.