The work presented in this report does not represent performance of any product relative to regulated minimum efficiency requirements. The laboratory and/or field sites used for this work are not certified rating test facilities. The conditions and methods under which products were characterized for this work differ from standard rating conditions, as described. Because the methods and conditions differ, the reported results are not comparable to rated product performance and should only be used to estimate performance under the measured conditions. v Contents List of Figures .
Air flow in buildings is a complex flow and pressure distribution problem that makes quantification difficult. However, certain parameters have recently become easy to quantify – specifically the air pressure relationships within buildings. The measured building air pressure field can be used with network analysis to solve the building flow and leakage regime creating an analytical macro model of the building flow and leakage regime. The response of the analytical model can be further tuned by perturbing both the building air pressure field and the analytical model. Building analysis typically focuses on flows and requires that all flow paths into and out of a control volume be defined. The flow path resistances need to be characterized. Determining all air flow paths and determining the flow path resistances directly is difficult. As such, estimates of these flow path resistances are commonly used. These estimates are based on limited field data and laboratory measurements. The literature provides some component values that vary by orders of magnitude and their application is often unable to predict building flow fields (ASHRAE, 1997). Standard building analysis develops the building pressure field from the flow field. This paper argues that developing the flow field from the building pressure field is more powerful. Determining the characteristics of the building pressure field directly is considerably easier than determining flow path resistances. It allows closing of the gap between the mathematical sophistication of available multi-cell air flow models and the necessary input information defining the building boundary conditions. This approach allows the pressure response of the building to be used to ‘‘tune’’ the models extending the range of their applicability and accuracy.
This paper reviews work that has led to the development of a number of multi-zonal airflow models (network models). At present, the network analysis and perturbation methods cannot be used to solve the interstitial flow, pressure and resistance regimes. Network analysis and perturbation may suggest that such flows exist, but the complexity and workmanship dependence of the interstitial flow, pressure and resistance regime requires direct measurement. In other words, at present, the boundary conditions of the interstitial regime can be defined analytically using traditional methods, but the pressures and flows within the interstitial spaces cannot be predicted with certainty using analytical means.Difficulties in obtaining the detailed information on mechanical systems and the leakage areas of building assemblies make the traditional approach of measuring airflows and constructing models using leakage areas impractical for diagnostic purposes. Additionally, a pressure difference across an assembly alone, where interstitial pressures are not considered, is not enough to describe performance of the building envelope. The interstitial air pressures are usually small and until recently have been beyond measurement.Research on building envelope durability and indoor air quality has shown the significance of these small, but persisting interstitial air pressure fields. To enhance the capability of network models, a relational model was developed. This approach permits the measured building air pressure field to be used with the network analysis. Furthermore, the response of the analytical model is calibrated by comparing the effect of a specific perturbation on both the building air pressure field and the analytical model. This paper is written in two parts, the first reviewing issues in prediction of airflow in the buildings and building envelope, the second analyzing the actual data of measured pressure response of buildings. sake of clarity. When some relations are deemed less important than the others,
Control of airflow is essential to several important performance aspects of the building system. Air carries moisture which impacts a material’s longterm performance (serviceability) and structural integrity (durability), behavior in fire (smoke spread), indoor air quality (distribution of pollutants and microbial reservoirs) and thermal energy. Typical case studies are presented to illustrate how each of the above characteristics is affected when unintended airflow occurs as a result of poor construction. In some cases, there was simply a lack of understanding of the consequences of ignoring potential leakage paths and the interaction of the mechanical conditioning systems with the building structure. Rehabilitation of a troubled building requires that these interactions be understood. In general, the approach to developing that understanding is not involved.
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