Design strategies for naturally ventilated building
Given below is a list of design strategies for natural ventilation by wind action that can be adopted to demonstrate compliance with Appraisal-1 ( Mandatory for 0 points ), Part 2, Alternative 2. These strategies are taken from NBC 2016.
- A building need not necessarily be oriented perpendicular to the prevailing outdoor wind; it may be oriented at any convenient angle between 0° and 30° without losing any beneficial aspect of the breeze. If the prevailing wind is from East or West, the building may be oriented at 45° to the incident wind so as to diminish the solar heat without much reduction in the air motion indoors.
- Maximum air movement at a particular plane is achieved by keeping the sill height of the opening at at least 85% of the critical height (such as head level) for the following recommended levels of occupancy: For sitting on chair (0.75 m) and For sitting on floor (0.40 m)
- For the normal-sized rooms with identical windows on opposite walls, the average indoor air speed increases rapidly by increasing the width of window up to at least two-thirds of the wall width; beyond that, the increase is in much smaller proportion than the increase of the window width.
- The air motion in the working zone is the maximum when the window height is at least 1.1 m. A further increase in the window height promotes air motion at a higher level of window but does not contribute additional benefits as far as air motion in the occupancy zones in the buildings is concerned.
- The greatest flow per unit area of openings is obtained by using inlet and outlet openings of nearby equal areas at the same level.
- The total area of openings (inlet and outlet) should be at least 25% of the floor area; however, even under the most favourable conditions, the maximum average indoor wind speed does not exceed 40% of outdoor velocity.
- The size of the inlet should be kept within at least 45% of the total area of openings.
- In case of rooms with only one wall exposed outside, provision of two windows on that wall is preferred over a single window.
- Windows located diagonally opposite to each other give a better performance than other window arrangements for most of the building orientations.
- Provision of horizontal sashes inclined at an angle of 45° in an appropriate direction helps to promote the indoor air motion. Sashes projecting outwards are more effective than projecting inwards.
- In the case of narrow buildings, cross ventilation can be obtained through one side of the building to the other (with single-loaded corridors) by the provision of large and suitably placed windows or a combination of windows and wall ventilators for the inflow and outflow of air.
- A verandah opening on three sides is preferred since it causes an increase in the room air motion for most of the orientations of the building with respect to the outdoor wind.
- Provision of a partition with spacing of 0.3 m underneath helps in augmenting air motion near floor level in the leeward compartment of wide-span buildings.
- Air motion in two wings parallelly oriented to the prevailing breeze is promoted by connecting them with a block on downstream side.
- In case of multiple buildings on-site, under the purview of the building owner, air motion in a building is not affected by constructing another building of equal or smaller height on the leeward side but it is slightly reduced if the leeward building is taller than the windward block.