Examination of Stability of Boundary Conditions in Water Vapor Transmission Tests

Abstract

The diffusion of water vapor through construction materials is driven by the gradient of partial water vapor pressure. Traditionally, water vapor transmission tests (WVT), the `dry cup', and the `wet cup' tests have been conducted with 0 to 50% RH, and from 50% to 100% RH, respectively. Often, desiccants, saturated salt solutions or distilled water are used to generate the required RH. The stability of vapor pressure in WVT tests is of paramount significance because these values are used in calculating permeance. Dry cup tests performed with high permeance materials (>25 Perms) indicated a transient behavior for the two types of adsorbing desiccants; calcium sulfate and silica gel. Monitoring RH inside the dry cup was performed to examine the effect of low and high WVT on the performance of moisture sinks. The results indicate that for highly permeable construction materials, the use of vapor pressures corresponding to 0% RH in calculation of permeance is not appropriate.

Keywords

Moisture transport water vapor diffusivity permeability permeance water vapor transmission solid sorbents ASTM E96 standard.

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References

Astm (2005). ASTM E 96-05, Standard Test Method for Water Vapor Transmission of Materials, American Society for Testing and Materials, Vol. 14.06.

Babbitt, J.D. (1939). The Diffusion of Water Vapor through Various Building Materials, Canadian Journal of Research, 17: 15-32.

Burch, D.M. , Thomas, W.C. and Fanney, A.H. (1992). Water Vapor Permeability Measurements of Common Building Materials, ASHRAE Transactions, 98: 486-494.

CEN TC89 WI 13 (Part 1). Building Materials - Determination fo Moisture Permeability Principles of Testing, (working draft) prepared by Thermal Performance of Buildings and Building Components, European Standard, 10 January 1994.

Chang, S.C. and Hutcheon, N.B. (1953). Performance of Desiccants in the Dry Pan Test for Water Vapor Permeance of Membranes, Canadian Journal of Technology, 31: 175-192.

Greebler P. (1952). Error in Vapor Permeance Measurements due to Diffusion in Lip Section, Unpublished Memorandum, Johns-Manville Research Center.

Hansen, K.K. and Bertelsen, N.H. (1989). Results of Water Vapor Transmission Round-Robin Test Using Cup Method, In: Trechsel, H.R. and Bomberg, M. (eds), Water Vapor Transmission through Building Materials and Systems: Mechanisms and Measurements, pp. 91-100, ASTM STP 1039, American Society for Testing and Materials, Philadelphia.

Hansen, K.K. and Lund, H.B. (1990). Cup Method for Determination of Water Vapor Transmission Properties of Building Materials: Sources of Uncertainty in the Methods, In: Proceedings of the 2nd Symposium on Building Physics in the Nordic Countries, Trondheim, pp. 291-298.

Incropera, F.P. and DeWitt, D.P. (2002). Heat and Mass Transfer , New York: John Wiley & Sons .

10.

Joy, F.A. and Wilson, A.G. (1966). Standardization of the Dish Method for Measuring WVT, Humidity and Moisture, Vol. 4, National Building Institute , Oslo.

11.

Mungo, T. (2003). Water Vapor Transmission Through Weather Resistive Barrier, M.A.Sc. Thesis, Concordia University, Montreal, Canada.

12.

Pazera, M. (2003). Laboratory Evaluation of Weather Resistive Barriers , M.A.Sc. Thesis, Concordia University, Montreal, Canada.