Abstract
Glass 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 tempera tures ranged from about -40° to +35°C.
Thermal conductances for the wet insulations increase sharply in warm weather when swings in outdoor temperature cause daily reversals in the temperature gradi ent in the insulations. This is attributed to evaporation-condensation cycles in which water vapor 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 vapor pressures.
Daily average heat fluxes were found for a summer period for a dry insulation specimen and specimens containing 1, 9 and 15% moisture (volume). The differ ence 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.
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