Seasonal variations in the modes of heat transfer in a moist porous thermal insulation in a flat roof

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Journal titleJournal of Thermal Insulation
Pages5466; # of pages: 13
SubjectRoofing; thermal insulation; heat transfer; glass fibres; seasonal variations; summer; winter; porosity; flat roofs; moist porous insulation; heat flux transducers; outdoor testing; Moisture performance; Couvertures; isolation thermique; transfert de chaleur; fibre de verre; variation saisonnière; été; hiver; porosité; toiture terrasse
AbstractGlass fiber insulation specimens 60 mm thick, with moisture contents ranging up to 15% by volume, were placed on the roof of the Outdoor Test Building of the Institute for Research in Construction, National Research Council of Canada in Saskatoon, Saskatchewan. The specimens were sealed in polyethylene to prevent the loss of moisture. Temperatures were measured at the top and bottom surfaces of each specimen and at the quarter points inside some of them. Heat fluxes were measured with calibrated heat flux transducers. Measurements were recorded every 20 minutes at all seasons of the year. Thermal conductances were calculated using transfer functions. The results showed an increase in thermal conductance when the weather was warm enough to produce daily reversals in temperature gradient across the wet specimens. This was attributed to latent heat transfer produced by evaporation of water at the warmer side of the insulation and its condensation at the cooler side. In winter, the moisture was deposited in the upper, colder part of the insulation. It was apparently distributed through the upper part of the insulation and not deposited as a solid layer at the top surface, since its effect on thermal conductance, indicated by the interior temperature gradient, extended well down in the insulation.
Publication date
AffiliationNRC Institute for Research in Construction; National Research Council Canada
Peer reviewedYes
NRC number28548
NPARC number20377514
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Record identifier12387f7e-ce4d-4c76-b837-ec6ea21ff967
Record created2012-07-24
Record modified2016-05-09
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