Air flows in building components

Abstract: This work deals with different aspects of air movements in building components . The investigation shows to what degree the concept of fluid mechanics can be applied to problems concerning air flows in building Components. The applicable parts of fluid mechanics are presented as thoroughly as possible. Based on this concept, routines are outlined to make it possible to handle complex flow and pressure distribution problems. Both manual and computer calculation routines are described and the way they can be used is demonstrated in a number of examples. Experimental investigations concerning determination of surface roughness of plates - instead of that of pipes which almost always has been investigated earlier were carried out. A test device for this purpose was designed and tested on a number of building materials. Also magnitudes of contraction and bend loss factors were investigated experimentally. Since, in practice, pressure differences acting across building components are seldom steady the influence of fluctuating pressure differences was investigated theoretically. The analysis shows that rapid fluctuations influence the flow rate only a little. If the fluctuations are slow it is possible to calculate the flow rate as if the problem was a steady state one, using time averaged pressure difference values. Leakaqe characteristics of different building components are reviewed and the air leakage behaviour of whole building envelopes is discussed. The great effect of entrance, bend, exit and orifice pressure losses is emphasized, and their influences on both leakage rate and flow characteristics are shown. An additional part of the so called pressurization test, taking the form of the leakage rate - pressure difference curve into account, is suggested. Such a procedure could imply a new possibility of detecting larqe, and maybe hidden, flow paths giving rise to substantial contributions to the total leakage rate of a building. Some tables are also included. They cover surface roughness, permeability and porosity data of different building materials. An extensive list of references is given.