Methodology for the Evaluation of Natural Ventilation in ... - Cham

Chapter 4.0Modeling and Visualization TechniquesAnalysis of full-scale buildings can prove difficult for several reasons, including the vast amountof space to analyze, amount of instrumentation required to adequately monitor all importantaspects, time requirement and cost. In the design stage, it is normally impractical to build a fullscaleversion of a building to test configurations to ensure adequate airflow and thermal comfort.For this reason, modeling techniques are employed for the prediction of performance inbuildings. Several methods exist, including computer simulations, partial full-scale modeling,and reduced-scale modeling. Visualization techniques are incorporated into all of these methodsin order to evaluate the flow patterns for various configurations and ventilation schemes within asingle room or for an entire building.This chapter covers both modeling techniques and visualization methods currently used for theabove mentioned physical models. The focus will be primarily on the application of thesemethods on the analysis of airflow patterns with respect to buildings. Both airflow patternswithin the building and exterior flow patterns around the building will be addressed, with a focuson internal airflow analyses. Techniques presented are currently used to evaluate bothmechanical and natural ventilation schemes. However there is particular attention paid to thosemethods being used to evaluate airflow and temperature distributions in buildings and roomsusing natural ventilation.4.1 Overview of Modeling as a MethodOften it is not convenient to evaluate full-scale buildings in either the design or the occupancyphase of a building, so reduced-scale versions of the building are created to simulate the fullscaleversion. The goal of the reduced-scale modeling is to gather data at a more manageable,smaller size, then scale the data back to full-scale and apply it for use in the full-scale systems,using some sort of scale factor. Scale modeling has been used for a wide variety of systems,both to investigate flow around objects and within spaces and buildings. Details on therequirements for similarity between the full-scale prototype and reduced-scale counterpart areprovided in Chapter 5.Three types of models are currently used: mathematical models that provide an analyticalsolution, computational models that provide a numerical solution, and physical models used forexperimental solutions. Analytical solutions are mathematical analyses that describe thephenomena under investigation through a series of equations. These mathematical models canprovide a basis for the primary governing phenomena of a system. An analytical solution isassumed to have a closed-form solution, in that at least one solution can be expressed as amathematical expression in terms of a finite number of well-known equations. If no closed-formsolution exists, the equations must be solved numerically. The governing, analytical flowequations for buoyancy, wind, and combined flow were presented in Chapter 2. They are71