Calculation techniques and numerical models are essential for any design process. They provide the means by which the designer can develop and investigate an idea before being committed to the final product. Typical design aspects cover system sizing, performance evaluation, indoor air quality prediction, energy impact assessment, and cost benefit analysis. A calculation technique or model is used to analyse the interaction of design options with fixed constraints. Such a process is necessarily iterative, with adjustments made to parameters over which control is possible, until an optimum design solution is achieved.
A wide range of methods of varying complexity have been developed with no single method being universally appropriate. Selection varies according to the required level of accuracy, the availability of data and the type of building under investigation. As designs have become more complex and performance tolerances more demanding, it is increasingly important for the designer to be able to understand and use calculation techniques. This need has resulted in the development of improved algorithms and wider availability of design data. In addition, sufficient guidance and data are provided to enable basic calculation methods to be performed.
Techniques cover methods to determine:
• air change rates in buildings and rooms,
• the flow rate of air through infiltration and purpose provided flow openings (network methods), see Figure 1.5,
• air flow pattern in a space (computational fluid dynamics).
Figure 1.5 Representing the Building as a Flow Network (Courtesy C-A Roulet, Switzerland)