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Window design guideline for non-conditioned/mixed mode buildings. The following may be considered in selection of type of windows.

1) Horizontal pivot windows

  • These produce very effective ventilation because large open areas are created at a separation equivalent to the window height.
  • Air will tend to enter at the lower level and exit via the top of the window.
  • These are easily adjustable to provide control of the ventilation rate.
  • These are often used in taller buildings, as both sides of glass can be cleaned from the inside of the building with ease.
  • The main disadvantage of this type of window is that, when opened, the top of the sash interferes with the curtains.

2) Vertical pivot windows

  • These are less efficient than horizontal pivot windows because the open area is uniformly distributed throughout the height of the window rather than concentrated at the extremes; but these can work well in combinations.
  • There is an advantage that these can be both opened and closed by pushing and are easy to clean from the inside.
  • When fully open these offer a safe vertical barrier.
  • The inward opening section may interfere with curtains when fully open.

3) Casement windows

  • These offer the same advantages as vertical pivot windows but are susceptible to gusts.
  • The most commonly used are double sided hinged outward opening windows which have great versatility with respect to air flow control.
  • Most casement windows are designed to open outwards, which poses a problem for installation of window air conditioners.

4) Top/bottom hung windows

  • These are less effective as ventilators than pivot windows as all the opening area is concentrated at one end, the top or bottom of the window.

5) Sliding windows

  • These have similar characteristics as horizontal or vertical pivot windows.
  • Sliding windows are easy to open; these slide to the side instead of having to be pushed  inside/outside.
  • A  good  seal  is important in reducing draughts and energy loss when closed.
  • Cleaning the inside of slider windows is easy, but cleaning the outside may be difficult.

6) Tilting top vents

  • These provide smaller opening areas than the other systems as these occupy only a relatively small proportion of the window height.
  • However, these can provide good  draught-free  ventilation, especially in cross-ventilation mode.
  • The inward opening function of tilt and turn windows limit the available space.
  • The window may also be provided with fixed/sash/ sliding/roller insect screens to allow fresh air without the inlet of mosquitoes and other insects through openable windows.
  • As compared to air-conditioned spaces, the window design in non-conditioned/mixed mode buildings takes a different approach.
  • The glazing system for windows in non-conditioned/mixed mode spaces is usually single pane/panel glazed units as the windows will be opened to allow ventilation.
  • Thus there is less relevance to install double glazing units with low SHGC and U- values.
  • However, in the non-conditioned/mixed mode buildings the shading device plays a crucial role in the thermal performance of a window.
  • Windows on facades, for different orientations, should be provided by the shading devices which can cut the direct incident solar radiation for the critical solar angles.
  • In  the  non-conditioned  buildings/mixed mode buildings, penetration of direct solar radiation needs to be regulated.
  • The critical Horizontal Solar Angle (HSA) and Vertical Solar Angle (VSA) (see Figure below) for fenestrations located on the cardinal directions should be regulated by designing appropriate shading devices.
  • The horizontal solar angle at critical hours can be regulated by the vertical fins provided as external shading devices.
  • The vertical solar angle at critical hours can be regulated by the horizontal fins provided as external shading devices.
  • The maximum permissible WWR on a facade should not exceed 60 percent.
  • Window opening requirements for naturally ventilated low rise residential and office buildings include the following
  1. In order to allow outside air to enter the space, window openings should be oriented appropriately to optimize heat and solar heat gain.
  2. In order to facilitate cross ventilation, location of window openings should be located opposite to each other on walls parallel to each other.
  3. In order to achieve the required air change per hour in a given space, cross ventilation and  stack  ventilation  mode  of  natural ventilation should be adopted.
  • The external shading devices can be designed in various ways to stop the solar radiation entering through the window.
  • Figure below shows the commonly used shading devices.

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