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Critical Plane Analysis of Wall Assembly in a Hot, Humid Climate
Abstract
Condensation plane analysis for determining critical
planes at which condensation may occur can be
performed for building assemblies in any climate.
Procedures for doing so in heating climates where
buildings dry to the outside of envelope assemblies
are given in 1997 ASHRAE Fundamentals
Handbook, Chapter 22 "Thermal and Moisture
Control in Insulated Assemblies - Fundamentals."
Little original work is available elsewhere in the
literature to guide analysis for buildings in hot and
humid climates.
Example 1 in Chapter 22 of the Fundamentals
Handbook gives step-by-step calculations, for a
heating climate. To analyze envelope assemblies in
hot and humid climates where drying predominately
occurs to the indoors, no direct discussion or
examples are available. This paper presents this
detail for a typical light commercial wall assembly,
and provides the basis for analysis of any envelope
assembly in hot and humid climates.
Analysis of an envelope assembly in hot and humid
climates seeks to determine if there is a critical plane
in the wall towards which water vapor flows more
rapidly from the outdoors than it flows to the indoors.
(In heating climates, the analysis is reversed). In
order to do this, weather data must be examined to
yield outdoor conditions, and indoor conditions must
be identified. Water vapor and thermal resistance of
the materials in the wall assembly must also be
established. These data are then used to perform
calculations using the basic diffusion equation and
methods described in the Fundamentals Handbook.'
Each potentially critical plane is analyzed to
determine if water vapor can accumulate more
rapidly than it dissipates. This potential
accumulation would signify a heightened risk of
equilibrium relative humidity sufficient to amplify
microbial growth, or to promote the deterioration of
building materials.
Citation
Turner, S. C. (2000). Critical Plane Analysis of Wall Assembly in a Hot, Humid Climate. Energy Systems Laboratory (http://esl.tamu.edu); Texas A&M University (http://www.tamu.edu). Available electronically from https : / /hdl .handle .net /1969 .1 /6792.