A characterization and modeling process has been conducted in order to better account for ventilative cooling in the evaluation of energy performance of buildings. The proposed approach has been tested using a monitored zero energy Active House (Maison Air et lumière) located near Paris.
The air flow characteristics of a pivoted roof window have been evaluated using a test chamber installed in the CES laboratory. A CFD calculation has been used to model the air movements inside the chamber and derive the relevant location for the pressure sensors. The air flow rate has been measured as well as the pressure difference on both sides of the window. A flow coefficient and a flow exponent of a power law equation have been identified for different window opening angles.
Flow rates have been evaluated in “Maison Air et lumière” using an air flow model (CONTAM) with the characteristics evaluated previously. These results were compared with on site tracer gas measurements.
Indoor air temperatures in the house have been evaluated using dynamic thermal simulation complemented with air flow calculation (PLEIADES+COMFIE) in order to evaluate the potential of ventilative cooling.
Around 5K indoor temperature reduction has been obtained by the use of ventilative cooling, both by simulation and measurement: with similar outdoor conditions, the interior air temperature of the house was 5K lower using ventilative cooling than without any opening of windows.
The air exchange rates were between 10 and 22 air change per hour even with limited wind velocities (between 2 and 3 m/s) and low temperature difference between outside and inside (0-3 K). An acceptable correlation was found between calculations and measurements.
The overall consistency between calculation results and measurements shows that this process, including the evaluation of air flow characteristics and the use of combined thermal and air-flow simulation, is feasible. The aim is to progress towards assessing the effects of ventilative cooling. Such a process could be used in a regulatory calculation, provided that this calculation integrates an appropriate model.