Large scale experimental investigation of the relative drying capacity of building envelope panels of various configurations
Alturkistani, A.
2007
Dissertation, Dept. of Building, Civil and Environmental Engineering, Concordia University, Montreal, Canada
Alturkistani, A., (2007), "Large scale experimental investigation of the relative drying capacity of building envelope panels of various configurations", Dissertation, Dept. of Building, Civil and Environmental Engineering, Concordia University, Montreal, Canada.
| Abstract: |
| Building envelope performance can be predicted through field investigation, laboratory investigation, modeling, or a combination of these. Large scale testing in the laboratory has been limited because of cost, but it is important in validating mathematical or empirical models since the impact of different variables on the envelope performance can be studied as other variables can be readily and reliably kept constant. In the context of a research project in collaboration with nine companies, three universities and the government, a two-story test hut, with overall dimensions of 16 ft 8 inches in length, 12 ft 5 inches in width, and 19 ft 11¼ inches in height to accommodate 31 instrumented wall assemblies 8 ft high and 2½ ft wide each, has been designed and erected within a large scale test chamber to investigate the drying capacity of 31 different envelope configurations. These wall configurations are reproduced in 31 assemblies that have been built and tested under pre-set loading conditions according to developed protocols: the specimens' protocol, the loading protocol for both moisture loading and climatic loads, and the monitoring protocol. These protocols are combined with the test methodology and data collection methods to yield a unique and state-of-the-an experiment.
The experimental investigation is based on the hypothesis "that the data generated from large scale tests on various wall configurations will yield recognizable patterns that would enable researchers to identify mechanisms relating measurable building envelope parameters to movement and accumulation of moisture in wood-based building envelope systems and that the knowledge gained would support a design process that would better predict the performance of envelope systems" 1 . This can be achieved by investigating the hygrothermal performance of different full-scale wall assemblies in relationship to envelope configurations under the same climatic and loading conditions by performing comparative analytical studies to better characterize the relative performance of different wall configurations.
A new test method was introduced to provide identical and measurable moisture sources for evaporation in the stud cavity of wall assemblies. The moisture source consisted of a water tray on a load cell placed on the bottom plate to represent rain water penetrating the cavity and collecting at the bottom plate. This set up provides a uniform moisture source that submits the different wall configurations to wetting by evaporation and drying by moisture evacuation out of the stud cavity. The test method yielded consistent and repeatable correlations between parameters that can be used to perform comparative parametric analysis.
A new calculation by Mapping Method "MM" was adopted to calculate the moisture absorbed by components surrounding the stud cavity. The moisture evacuated from the cavity is taken as the difference of water evaporated from the tray and the water absorbed by the components surrounding the cavity. The ratio of the water evacuated divided by the water evaporated is defined as the drying capacity of a given configuration over a given period of time. This calculation by the mapping method provides a comparison tool between different wall systems.
The analysis of this drying or evacuation of the building envelope was taken one step further since the mapping method calculates the evacuation through the sheathing material only. A Calculation Evacuation Method (CEM) was introduced to calculate the evacuation through the outer layers of the building envelope including the sheathing, weather barrier, and cladding. CEM takes into account (i) the non-linear profile with height of the absorbed vapor mass which influences the permeability of the sheathing, (ii) and the non-linear profile along the height of the vapor pressure due to the moisture source located at the bottom of the wall cavity.
1 Unpublished internal report prepared by P., Fazio. CRD proposal. NSERC Collaborative Research & Development (CRD) grant, Concordia University, Montreal, Quebec. |
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This publication in whole or part may be found online at:  here. |
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