Fresh air in a building brings health benefits and increased comfort level to its occupants. Fresh air provision is considered as an efficient and a healthy solution as it reduces the need for mechanical means to ventilate a building.

For NZEB design goal, passive design measures can be judiciously used to influence movement of outside air into a built space by bringing in fresh air. These interventions can reduce and in some cases (in certain climates) completely eliminate reliance on mechanical means to ventilate a building. Thus largely affecting air-conditioning loads.

Various forms such as appropriate orientation and form, openings in building envelope (windows, doors and ventilators), operable windows, internal space planning, etc. are various natural ventilation strategies that can be adopted. Other advanced ventilation techniques are courtyard effect, stack effect, wind tower, or air earth tunnels.

• For good natural ventilation, building openings should be in opposite pressure zone ( since natural ventilation rely on pressure to move fresh air through buildings).
• The building can be oriented 0° to 30° with respect to the prevailing wind direction (wind rose diagram) / most preferably orientating longer facades of the building towards predominant wind direction.
• Maximum air movement is achieved by keeping the sill height at 85% of the critical height.
• Greatest flow per unit area of the opening is achieved by keeping the inlet and the outlet of nearly same sizes at nearly same levels.
• Windows should be staggered rather than aligned( see fig)
• If the space has only one façade exposed to the exterior, it is preferred to provide at least 2 windows on the façade.
• Total area of openings should be a minimum of 30% of floor area.
• Window-Wall-Ratio (WWR) should not be more than 60%.
• Along with orientation to breeze, design of windows to collect direct breezes is important. Use casement windows to catch and deflect wind from varying angles.

Opening controls like louvers, sashes, canopies and screens can be used to control the direction and velocity of air stream flowing into a space. Comparatively permanent controls like canopies can alter the pressure build up at the face of fenestrations and must be designed keeping this factor in mind.

Climate specific recommendations

• In hot and dry regions, the windows should generally be kept closed during the day to minimize solar heat gains to interior spaces. For regions experiencing high diurnal temperature differences (of the order of 12°C to 15°C cooler in night), Interior spaces should be opened to night time ventilation.
• In warm humid regions, openings should be designed to capture wind as ventilation is the key comfort defining criteria throughout the day.
• In cold regions the openings should be kept shut with controlled ventilation.