There are three principal mechanisms for heat transfer: conduction, convection, and radiation. In the building environment significant heat moments are caused by heat losses and gains through the exterior envelope produced by conduction, short wavelength (or solar heat) transmission, and air leakage. The absorption and heat storage within material in the buildings and the reflection of fenestrations can also have an impact on thermal movement. Source: “Fundamentals of Building Heat Transfer” – Tamani Kusuda. (NIST 1977)
Conduction: When it is colder on one side of an envelope element, such as a wall, roof, floor, or window, heat will conduct from the warmer side to the cooler side. Conduction is driven by temperature differences and is a major component of heating and cooling loads in buildings. Building codes address heat conduction by specifying minimum R-Values (thermal resistance to heat flow or insulation) or maximum U-Factors (the rate of steady-state heat flow) for building envelope construction assemblies.
Next: Steady-State Heat Flow