Conclusions and Recommendations

11.4.7.1 Problem-Adapted Approach

Choice of program and input should be in accordance with the problem and the answers sought. For simple problems, adequate results may also be obtained with an adapted simple model. Many cases can be solved using a single-zone model; various models are available.17-20 A single-zone model is also described in a CEN standard.21

11.4.7.2 Sensitivity Analysis and Comparative Studies

In certain cases, a precise definition of the input parameters in absolute terms may be difficult. Nevertheless, in many cases this does not cause crucial problems because relative results may be sufficient to compare different design options. The influence on the results of uncertainties in input should be evalu­ated whenever possible by using sensitivity analysis techniques.

11.4.7.3 Multizone Modeling vs. CFD

As outlined earlier, in multizone models, perfect mixing is assumed in the individual zone. The spatial distribution of velocities, contaminant concentra­tions, and air temperatures in a zone can be determined only by using CFD. On the other hand, wind effects are easily accounted for in multizone models, and unsteady-state simulation is normally performed. On the combined use of the two methods, see Schaelin et al.22

11.4.7.4 Multizone Modeling and Thermal Models

Many natural ventilation problems are related to the thermally driven air­exchange in a building. Such cases most often must be treated using combined thermal and ventilation models or thermal models with an integrated natural ventilation model. This is outlined in more detail in Section 11.5.

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