Study on dynamic thermal behavior of double glazing unit filled with phase change materials

Abstract

Glazing units are indispensable for a variety of buildings and their thermal behavior has significant effects on improving indoor thermal comfort and decreasing energy consumption. Recently, the double glazed windows that are filled with phase change material (PCM) have been considered as potential glazing units. Therefore, the dynamic thermal behavior of the PCM-filled double glazing unit is investigated in this work. A three-layer glass-PCM-glass model considering coupled conduction-solar radiationphase change is established. Effects of physical parameters of the PCM on the thermal behavior of the PCM-filled glazing unit are examined thoroughly. The results indicate that the filling of PCM can affect heat transfer within the glazing unit significantly by reducing solar energy entering the indoor room through the window. When the glass-PCM-glass model is adopted, the transmitted solar energy can be reduced by 78.82 W/m 2 . Optical parameters (especially absorption coefficient) of the PCM have significant impact on the thermal behavior of glazing units: the larger the absorption coefficient is, the less solar energy will enter indoors, and the larger will be the temperature fluctuation. For different absorption coefficients, the maximum temperature difference on the interior surface can reach 3.57 C. Thermal properties of the PCM also have significant impact on the thermal behavior of glazing units. Decreasing the thermal conductivity or increasing the latent heat of the PCM can reduce the temperature fluctuation of the glazing windows. Selecting a reasonable melting temperature can make full use of the heat storage capacity of PCM. Thus, this Abbreviations: ε g , emissivity of glass; ϕ, radiative source term, W/m 3 ; κ a , absorption coefficient of glass or PCM, m À1 ; λ g , λ p , thermal conductivity of glass and PCM, W/(m K); ρ, reflectance, %; ρ g , ρ p , density, kg/m 3 ; ρ 1 , ρ 2 , ρ 3 , ρ 4 , interface reflectance; σ, Stefan-Boltzmann constant; τ, time, s; τ eg , optical thickness of exterior glass layer; τ p , optical thickness of PCM layer; τ ig , optical thickness of interior glass layer; A eg , absorptance of exterior glass layer; A p , absorptance of PCM layer; A ig , absorptance of interior glass layer; c p,g , c p,p , specific heat capacity, J/kg; f l , liquid fraction of PCM; H, specific enthalpy, J/kg; H s , H l , critical enthalpy of solid and liquid phase, J/kg; I solar , solar radiation, W/m 2 ; L _ , latent heat, kJ/(kg K); n a , n g , n p , refractive index of air, glass and PCM; q solar , transmitted solar energy, W/m 2 ; q trans , total transmitted energy, W/m 2