Ventilation air flow through window openings in combination with shading devices.

In the UK the increased use of natural ventilation in buildings is being encouraged, particularly during hot weather as an alternative to air conditioning or mechanical ventilation. In order to take advantage of this option building designers need to be able to estimate potential air flows. Conventional calculation methods assume windows to be simple openings, however in practice the situation is more complex since during hot weather the opening is likely to be shielded by some form of solar shading device. This paper reports the results of a laboratory based investigation of the pressure difference-flow relationship for air movement through windows when a venetian blind is also in position. A variety of window opening variations and blind angles have been tested. The results indicate a significant reduction in air flow when blinds are in use in the closed position (angle 850); the results for partially closed position (450) show little reduction in flow. The form of the window opening also has an important effect. Care must therefore be taken in setting blind angles so as to avoid reducing beneficial natural ventilation air flow whilst maintaining shading.