Modeling integrated airflow and thermal

Four methods for industrial air technology design are presented in this chapter computational fluid dynamics (CFD), thermal building-dynamics simulation, multizone airflow models, and integrated airflow and thermal modeling. In addition to the basic physics of the problem, the methods, purpose, recommended applications, limitations, cost and effort, and examples are pro vided. 

However, in thermally driven naturally ventilated enclosures, airflow rates and room air temperatures are interdependent and can be determined only simultaneously by using an integrated airflow and thermal model. 

A higher level of integration is achieved when the airflow model is fully integrated in the thermal model and the input for the airflow part is just an addition to the input required for the thermal model. 

This section deals mainly with the interaction of thermal models as outlined in Section J 1.3 and airflow models as described in Section 11.4 for the purpose of integrated modeling of thermally induced (stack-driven) natural ventilation, governed by the thermal behavior of the building. For the integrated analysis ol air velocity fields and radiative and thermal effects in the building using CFD codes, see also Section 11.2 and Ott and Schild.-... 

I FIGURE I (.49 In thermal models, the ventilation airflow rates are input parameters in airflow models, on the other hand, room air tmiperatures must be defined In the output. Since natural ventilation airflows and room air temperatures are interdependent, both parameters must be intcgratly considered in the solution process. This is possible only by an integration of the natural airflow model into the thermal model. 

Integration. Here, at a certain time step in the simulation, the airflow model is repeatedly called within the iterative solution process in the thermal model, and the airflow results are considered within this iterative solution process. Thus, the resulting airflows and room air temperatures fully comply in terms of the underlying physics. 

Also, for this option, several levels can be observed concerning the integration of the airflow model. The lowest level of integration still requires separate input for the thermal and the airflow model respectively with a high degree of redundancy in the input parameters (e.g., zones must be input for both models), and the connectivity of the airflows and the zones in the thermal model must be established manually by the user. More sophisticated levels have reduced redundancy and automatic establishment of the link connectivity. 

The highest level of integration would be to establish one large set of equations and to apply one solution process to both thermal and airflow-related variables. Nevertheless, a very sparse matrix must be solved, and one cannot use the reliable and well-proven solvers of the present codes anymore. Therefore, a separate solution process for thermal and airflow parameters respectively remains the most promising approach. This seems to be appropriate also for the coupling of computational fluid dynamics (CFD) with a thermal model. ... 

The integration of the ventilation model into the thermal building model can be realized on different levels, from simple stack-flow equations to a full integration of a multizone airflow and contaminant transport model. 

Integrated thermal and airflow modeling is needed for problems such. is these ... 

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