Heat transfer in a wet porous thermal insulation in a flat roof

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Journal titleJournal of Thermal Insulation
Pages165188; # of pages: 24
SubjectRoofing; thermal insulation; flat roofs; heat transfer; glass fibres; moisture content; porosity; thermal insulation; moisture; flat roof; thermal conductance; moisture flux; transfer coefficients; heat flux transducers; outdoor testing; water vapor evaporation-condensation cycle; Moisture performance
AbstractGlass fiber insulation specimens with moisture contents ranging from 0 to 15% by volume were placed on the roof of an outdoor test facility. Heat flow measurements were made, using heat flux transducers at all seasons of the year. Outdoor temperatures ranged from about -40 to +35 degrees C. Thermal conductances for the wet insulations increase sharply in warm weather when swings in outdoor temperature cause daily reversals in the temperature gradient in the insulations. This is attributed to evaporation-condensation cycles in which water vapors is transferred back and forth in the insulation, carrying latent heat. In the analysis, the heat flux was regarded as comprising two components -- a sensible heat component and a latent heat component. The results of the measurements were used to develop relationships, involving transfer coefficients, to express the heat flux in terms of temperature and water vapors pressures. Daily average heat fluxes were found for a summer period for a dry insulation specimen and specimens containing 1, 9 and 15 percent moisture (volume). The difference in heat flux was substantially the same for all of the wet specimens. For each wet insulation, the heat flux was about three times as large as it was for the dry specimen.
Publication date
AffiliationNRC Institute for Research in Construction; National Research Council Canada
Peer reviewedYes
NRC number29215
NPARC number20377532
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Record identifier6d372f75-cacf-40fb-b375-26ed71fea9a4
Record created2012-07-24
Record modified2016-05-09
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