The foundation of building physics is based on the understanding that heat conveys both energy and momentum. The foundation of building physical requirements for building physics is the knowledge of heat transfer through surfaces and through the air or surrounding space. A building envelope includes the glazing, insulation, frames, doors, windows and floors. Understanding how these building envelopes work leads to building physics concepts and methods for evaluating building materials.
Thermal energy transfer is a function of the building envelope, building materials and surroundings. There are four layers involved in thermal energy transfer: surfaces, surroundings, air and ground. The presence of one layer does not affect the performance of the other layers. For instance, a concrete slab, whether flat or pitched, is effective at providing thermal resistance if it is properly sealed and differentiated from the surrounding concrete. The seal is not affected by differences in temperature between the slab and surrounding concrete or of different concrete mixes.
Surfaces are the interface with which thermal energy exchanges from warm to cool air. In most buildings, the building envelope is made from materials that absorb thermal energy before they leave the building. The mixing and construction of the building envelope, therefore, depends on the quality of the materials used and the nature of the building. Good construction requires skilled labor and quality control.
Surrounding the building, the environment has an impact on the building envelope as well. The climate affects the thermal resistance of materials and the building envelope. A building envelope determines the energy consumption of a building. Greenhouse gases, for example, become a major problem during cold seasons, when heating bills rise due to the warming air, and during hot seasons, when the sun’s rays increase cooling the building envelope. Temperature variations and extremes can have a significant effect on building physics.
A proper thermal design minimizes the use of thermal bridging. Thermal bridging occurs when materials that are not designed to reflect heat are combined with materials that do not suffer from thermal conductivity reduction. The end result is that the same heat source, typically a hot air heating system, is conducted through the poorly-insulated building envelope. Materials with higher R-value (thermal conductivity) provide better thermal bridge. A building may require more than one thermal bridge.
The envelope’s shape also plays a role in building physics. A building envelope’s shape should allow passive solar heat to be integrated into the building envelope. This promotes thermal insulation, a key building physics principle. Passive heating systems minimize the energy needed to heat a building. A building envelope that incorporates effective materials for insulation and design reduces energy consumption.
A good building envelope should allow a building to retain its stored heat during the summer and cold weather. Air movement between floors is another key factor in building climate. Air movement is constrained by building column obstructions such as skylights, doors, windows, walls, ceiling, etc. When air movement is constrained, convection causes the heated air within the building to rise to the top and cool off at the bottom. A good building envelope design allows convection to be efficient and balance the ventilation and heating requirements for a building.
Thermal energy management is an important part of building envelope design. A building envelope must contain proper insulation, air distribution, vapor barriers, and heat recovery. Thermal energy management is achieved by optimizing natural light, ventilation, and temperature. Thermal energy management is the process of optimizing building functions to prevent energy wastage and environmental damage. An effective building envelope will provide energy efficiency and help reduce building maintenance and operating costs.