A building envelope is a physical interface between the conditioned i.e. inside and unconditioned i.e. outside environment of a building. It protects the interior space from the effects of the environment like precipitation, wind, temperature, humidity, and ultraviolet radiation.
The role of energy efficiency of the building envelope shouldn’t outlast its purpose to protect the building occupants and give them shelter, fire protection, and comfort but rather enhance the experience. The challenge is to design a building with an envelope that reduces energy consumption without compromising occupants’ needs.
29 % of the total energy is used by the buildings, where 20% by residential buildings and 9% by commercial and the numbers are rising fast.
Heat gains from the envelope play the most significant role in influencing thermal comfort and consequently energy efficiency in buildings. Hence, by judicially designing the building envelope parameters i.e. orientation, shape, walls, fenestration, shading device and roof, the HVAC load can be reduced in buildings.
Orientation: The orientation plays a vital design consideration with regards to solar radiation, daylight, and wind. The most appropriate orientation is such that it gains most solar radiation in winters and least in summers. A brief study of the climatic conditions of the area of prevailing wind direction and solar path can determine the right orientation.
- Building Components: The building envelopes determine the climate inside the building, amount of radiation and wind that will enter the building. The materials for the fenestration, roof, and walls have to be chosen according to the requirements. The heat gain in a single-storey building occurs through the roof, whereas in multi-story buildings through walls and windows.
- Walls: constitute a major part of the building envelope and receive a large amount of direct solar radiation. By increasing thickness in exposed walls resistance to heat flow may be increased (thermal mass), through the cavity wall, by the use of insulating material or by applying light-colored whitewash or distemper on the exposed side of the wall.
- Roof: A significant amount of heat is gained through the roof. Insulating materials should be used to reduce heat gain.
- White or special reflective pigments that reflect sunlight, coatings are like very thick paints that can protect the roof surface from ultra-violet (UV) light and chemical damage, and some offer water protection and restorative features.
- Green roofs also provide insulation, lower the need for heating and cooling, and can reduce the urban heat island effect.
- Fenestration: Provide with ventilation, day-lighting and heat gain. Appropriately designing the shading devices and openings can allow or keep out light and ventilation with reducing heat gain. Glass is transparent to solar radiation but opaque to longwave radiation, can be used to heat a building interior by promoting heat gain. According to ECBC, the maximum Wall window Ratio (WWR) less than 60%. Using louvers, Shading devices or protective glazing transmission of heat can be reduced.
- Shading devices or overhangs: should be designed according to the solar path of the site and size of the windows, reducing the amount of heat gain.
- Glazing: Use of double or triple glasses with air space in between the direct transmission of solar radiation can be reduced. Reflective Glazing can reduce heat gain without obstructing viewing. They are usually used for windows that cannot be shared externally.
Energy-efficient building envelopes enhance the quality of living and make comfortable environments for users naturally and reduce energy consumption. Properly designed fenestration, wall thickness, and roof can significantly reduce the heat gain making the building energy efficient.