Research On Coupled Natural Ventilation And Infiltration With Building Thermal Modeling

Natural ventilation and infiltration have very important effect on building loads. On one hand, the energy loss caused by ventilation and infiltration accounts for a considerable proportion of heating and cooling loads; on the other hand, in mild condition, the passive cooling systems which use natural ventilation could take place of traditional air conditioning systems, and therefore cut down the amount of used energy. However, the lack of reliable tools to predict airflows extremely limits analyses of building energy consumption, dynamic thermal building simulation and passive cooling system design. So far, considered the characters of natural ventilation and infiltration, the author tried to develop a program used on ventilation and infiltration calculation, and integrate it into DeST, a design simulation toolkit. This tool could be used in predicting ventilation and infiltration rates and assist to design passive cooling system. Several issues were studied in this paper.Firstly, through literature review, the author pointed that the coupled calculation of multizone airflow model and thermal building model was an effective approach to the issues mentioned above. The theories of multizone airflow modeling were summarized. The conditions under which the unique solution to the flow network was guaranteed were proved. It was also discussed the issues related to program development and integrating airflow modal into DeST.Secondly, the approach to wind pressure on building envelope in multizone airflow modeling was analyzed, and a correction to the Cp value in the condition of the area of openings in large proportion to surfaces was proposed.Thirdly, the resistance models of openings and cracks, which were familiar in airflow network, were summarized. Under a reasonable assumption, an analytical solution of large openings was educed, which could accelerate the calculation a lot.Fourthly, three experiments were carried out and the measured data were compared with the result of airflow model. The results showed that the airflow model was valid for most engineering uses.Lastly, the coupled program of airflow model and thermal model was used in analysis of three practical issues and some conclusions were drawn, which provide demos to researchers and designers. The research results of this paper had established the application bases for calculating ventilation and infiltration in engineering. It also provided a software platform for the research of natural ventilation and infiltration problems and design of passive cooling systems.