Empirical Validation of a Transient Computer Model for Combined Heat and Moisture Transfer.
Empirical Validation of a Transient Computer Model for
Combined Heat and Moisture Transfer.
(1361 K)
Rode, C.; Burch, D. M.
U.S. Department of Energy (DOE); Oak Ridge Natiional
Laboratory (ORNL); American Society of Heating,
Refrigerating and Air Conditioning Engineers (ASHRAE);
Building Environment and Thermal Envelope Council
(BETEC). Thermal Performance of the Exterior Envelopes
of Buildings VI Conference. Proceedings. Thermal VI.
December 4-8, 1995, Clearwater Beach, FL, 283-295 pp,
1995.
Keywords:
heat transfer; moisture; validation; computer models;
condensation; mass transfer; measurement; modeling;
siding
Abstract:
A computer program for transient modeling of combined
heat and moisture transfer in building constructions is
introduced. The model's predictions are compared
against moisture content and heat flux data obtained for
six typical North American lightweight wall
constructions that have been exposed to climatic
conditions in a calibrated hot box. A special aspect of
the work was that the basic moisture and thermal
transport properties were determined for each individual
material in the walls. The experiment, and thus the
validation, was restricted to diffusive transport
mechanisms taking place in the hygroscopic region.
Using the detailed information on the material
properties, the program was able to predict the measured
moisture content of the walls' siding and sheathing
materials to within approximately 1% moisture content by
weight, and the heat flows were predicted with a
satisfactory accuracy. In a subsequent sensitivity
andalysis, the moisture transport properties were
described as simpler functions or selected arbitrarily
from a database of ordinary building materials. In some
cases, this had a noticeable effect on the resulting
moisture contents. It is suggested that transient heat
and moisture transport models can be used in the design
and analysis of constructions if the user is
knowledgeable about the workings of such models and
cautious in interpreting the results.
