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Latent and Sensible Conduction in building’s porous walls subjected to high levels of temperature and wet

In this article was studied, the wet influence in the cooling loads in walls putted under rain, solar radiation, convection and phases change condition. Is analyzed the dependence between the wet level profile’s time, temperature and the cooling loads on the wallsof different materials in a summer week at the Florianopolis City (warm/wet). It’s researched also, the influence of rainy days with intense solar radiation after a period of time, in thermical charges and wet contents.

We describe the use of a dynamic and mass transfer model to analyze the effect on cooling loads of transient moisture storage and transport throughwalls with porous building materials, under varying boundary conditions. It is analyzed the influence on cooling loads of high moisture content due to rain soaking materials, and the influence of solar radiation on sunny and cloudy days. It is shown that neglecting moisture migration may result in large errors in sensible and latent heat transfer.

In buildingsenergetic analysis, usually, is evaluated the heat transfer through the walls, looking down on storage and transport of wet in the wall’s porous structure. As the heat flow, the wet needs a consideration. This one, presents others implications, especially in warms and wet weathers where it would cause building’s structures damages and would promote the mushrooms grows, affecting the people’s health.Burch and Thomas (1991) unwrapped the MOIST code to composite wall study, about normal isotherm conditions, they propose that the heat transfer when is considered constant, presents in a limited program, low wet levels. Liesen (1994) used the evaporation-condensation theory and the answer factor method to unwrap and implement a heat and mass transferring in the thermo-energetic simulationIBLAST (Integrated Building Loads Analysis and System Thermodynamics). The transport coefficients from this program were considered constants.
For heat and wet transport to high levels was used a dynamic model that evaded some restrictions in the wet content. Convection, solar radiation and gas-liquid phase movement were considered to walls. According to Mendez (1997) in this model thephysical quantities as matter, thermical conduction and specific heat transport coefficients, are variables and depend of wall temperature and wet level.
This research analyzes cooling loads for three different materials, irate reinforced concrete, brick and mesela. Analysis is accomplished in the most critical summer week on Florianopolis weather, in Brazil. Is analyzed also the coolingloads influence and wet levels to two types of rain conditions: a rain followed by a sunny week, and a rain followed by a cloudy week.

Math Model:
Principal differentials equations to show the heat and wet transfer are given by the equations (1) and (2) who were derivate through the energy and matter balance in a porous material’s control volume

(1)Mass ConservationEquation

(2)Energy Conservation Equation


The parameter Cm is the specific heat and is a θ function. The variable λ is the thermical conductivity of environment in phase movement absence who normally depends a lot of θ and a little of T. The coefficients Dι, Dθ, Dιν, Dθν are responsible about the wet transfer inside the porous material according tothe Phillip and De Vries model (1957). The wall’s external surface is exposed to the solar radiation and phase movement. The conservation equations associated are the next.

(3)Conservation of mass in the outer surface (x = 0)
(4)Conservation of energy in the outer surface (x = 0)

[pic] ( Heat Convection
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