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

applicable to simple configurations and geometries with well-mixed assumptions and a limitednumber of zones, such as a single room attached to an atrium.The numerical solution is a more complex version of the mathematical model described above,in that it is a system of algebraic relationships that are solved simultaneously. The computationalmodel provides point-like solutions, with unique values for a series of determined points. Acommon numerical solution in the area of ventilation is the use of computational fluid dynamics(CFD) software, such as PHOENICS, to quantitatively predict fluid flow in or around objects.CFD software packages have the ability to model the interactions of temperature, heat flow,buoyancy and air flow in and around buildings. A grid is used to solve the mechanical andthermodynamic relationships throughout the environment under analysis, taking into account thelayout, ventilation opening(s), geometry and heat loads.Experimental solutions are obtained through the use of physical models to examine the behaviorand interaction of physical systems in a controlled environment. They are also used indetermining the relationship among variables, as physical modeling allows for the adjusting andmeasuring of specific parameters of interest. Physical models are created at a variety of scalesand normally using one of several working fluids for investigation. Scale modeling has beenused extensively in the field of ventilation, at both small scales and large scales, on specificsystem components, such as flows in fume hoods and whole systems, such as buildings andsurrounding sites. The size of these models varies from full scale to 1/200 th scale or smaller,particularly for wind tunnel investigations. In this work the focus will be on reduced scalemodels used for understanding the internal flow within spaces in buildings, rather than the flowaround them. In this case, the scales range from full scale single rooms to 1/120 th scale models,though it is difficult to use models smaller than 1/50 th scale as there is not necessarily adequatespace within which to make measurements (Szucs 1980).The selection of the scale at which the model is created depends on several fators, including theworking fluid used. The following sections present the methods used at full-scale and reducedscale,focusing on the most common working fluids used and associated flow visualizationtechniques. Each of these areas has a significant contribution to the overall effectiveness of scalemodeling as a method to assess the prototype counterparts. The application presented is onreduced-scale models that are used to investigate airflow patterns and behavior in internal,occupied spaces within buildings, specifically those that use natural ventilation.4.1.1 Full-Scale ModelingFull-scale models are created for specific, single room applications to predict and analyze thethermal environment of that space in the design phase. When designing a passively ventilatedspace, a mock-up of a portion of the space, at full-scale, can be useful to evaluate that space withthe appropriate internal loads, including computers, people, and lighting. This method is timeconsuming and requires a lot of space, but may be useful for isolated spaces. However, thismethod only works if the space being analyzed is in isolation and does not interact with adjacentspaces or zones.Existing buildings are often assessed in a post-occupancy evaluation of the design of a space andbuilding at full-scale. Though this does not help in the design phase, it does provide information72