Solar Control

Shading

A very important strategy to stop heat gain and unwanted direct sunlight is to divert sun's rays before entering the building. This can be accomplished through the use of fixed and adjustable shading. The most important consideration is the orientation of the aperture which is being shaded. South-facing windows are easy to shade, because in summer months, when shading is necessary, the angle of the sun is high. However, east and west facing windows are much more difficult to shade because the sun is much lower in the sky.

One example of shading is an overhand above fenestrations. The length of the overhang must carefully consider sun angles in both winter and summer so as not to block valuable solar gains in the winter. The image below shows an example an excel worksheet designed to recommend overhand depths depending on time of day, year, and orientation developed by MIT student Sephir Hamilton. The goal was to provide designers with tools to size such shading devices. The example below shows solar radiation though a west-facing window with 100% depth overhang and a 10% fin depth on June 21.

In addition to fixed shading devices such as overhangs, we have also considered the use of adjustable shading devices, such as curtains, blinds, and shutters. It is important that screens provide adequate shading while still allowing daylight to penetrate into the rooms. These shading devices can be useful in the winter to add to thermal insulation as well as in the summer as a shading device. It is recommended to place these to the outside of the glazing to reflect unwanted solar gains before reaching the glazing layer.

Special glazing can provide an alternative to fixed and operable shading devices. Such examples are reflective and absorbing glass, but few of these are used on the residential scale. Another alternative to shading devices is shading from vegation or nearby buildings. Ideal plants will maximize protection from solar gains in the summer, while providing minimum shade in winter months.

External Gains

Internal Gains

Ventilation

Natural Cooling

Natural Ventilation

Chinese designers would like to include natural ventilation in the design of their new buildings. This is a complicated issue that involves the design of building interiors and window placement to facilitate airflow. In addition, the proximity of neighboring buildings and the building shape will influence air circulation outside the building and in turn natural circulation throughout the building. There is the desire to include natural ventilation in high-rise buildings, a difficulty compounded by the interaction of buoyancy and wind driven flows. If natural ventilation could properly be designed in a building, our initial simulations suggest that natural ventilation combined with nighttime cooling and thermal storage in the walls would eliminate most of the need for air conditioning in Beijing on an average summer day.

see natural ventilation feasibility study

back to top