3D Numerical Simulation of the Transient Thermal Behavior of a Simplified Building Envelope Under External Flow

Understanding building envelope performance and thermal mass effects is becoming increasingly important under the scope of low energy building construction and energy conservation. In the present paper, a three-dimensional computational fluid dynamics methodology is presented for the numerical simulation of the flow and heat transfer that determine the thermal behavior of simplified building envelopes. This is dominated by a conjugate heat transfer approach, which involves conduction, convection, solar heat gains, ambient temperature variation, and the effects of thermal radiation losses to the sky. Validation results include comparison both with measurements from fundamental laboratory studies of heat transfer from surface mounted cubes and with numerical results from well established commercial building energy simulation software. Numerical issues, such as temporal and spatial discretization, are addressed, and parametric studies are performed with regard to the effect of external flow Reynolds number and temperature variation in the building envelope, depending on the individual orientation of the external walls with respect to the flow and on the thermal properties of the building materials. Results from the parametric studies performed indicate that the transient three-dimensional calculations provide important information regarding the effect of external flow properties, such as the approaching flow temperature, velocity, and direction on the thermal behavior of the building envelope. In addition, it has been clearly demonstrated that the methodology is also capable of taking into account the complex effects of parameters such as the building material properties.