Implementation of Models for Building Envelope Air Flow Fields in a Whole Building Hygrothermal Simulation Tool

Simulation tools are becoming available which predict the heat and moisture conditions in the indoor environment as well as in the envelope of buildings, and thus it has become possible to consider the important interaction between the different components of buildings and the different physical phenomena which occur. However, there is still room for further development of such tools. This paper will present an attempt to integrate modelling of air flows in building envelopes into a whole building hygrothermal simulation tool. Two kinds of air flows have been considered: 1. Air flow in ventilated cavity such as in the exterior cladding of building envelopes, i.e. a flow which is parallel to the construction plane. 2. Infiltration/exfiltration of air through the building envelope, i.e. a flow which is perpendicular to the construction plane. The new models make it possible to predict the thermal and moisture impact of these air flows which represent either (1) a part of the building envelope which has hitherto not been offered much focus in building simulation, or (2) a transport form which in most cases should be kept minimal but which has immense importance on the overall heat and moisture flows when it occurs. The paper presents the models and how they have been integrated into a whole building simulation tool. Furthermore, the paper shows some calculation results for validation and for illustration of the importance of the phenomena.