Abstract
Recently, there is a sign that an insulated and air-tight house, which is popular in cold area, is also built in hot and humid area. But a percentage of water content in the house frame or the thermal insulating material increases after the rainy season, so there is probability that an internal dew condensation is induced in the wall in a cooling time during summer season and deteriorates the wall. A purpose of this study is that a guidance for a design of the wall constitution and a prevention method for the internal dew condensation are suggested about the insulated and air-tight house in hot and humid area. This paper clarifies the heat and mass transfer phenomenon in the wall by numerical calculations and some experiments, and investigates the optimal insulated wall constitution. The main results obtained are as follows.
(1) The heat and mass transfer equation adopting water potential (thermodynamic quantity of state) is suggested, and the equation is examined for its validity by comparing calculated values with measured ones of the mass transfer experiment on the wall with glass wool.
(2) By the outdoor exposure experiment on a test house, it becomes clear that the internal dew condensation occurs in the conventional wall-1, but it doesn't occur in the outside ventilated wall-2 with inner vapor proof layer which intercepts mass flux of transmission and in the outside ventilated wall-3 with inside cavity layer which exhausts moisture.
(3) The temperature and humidity in the wall-2 and in the wall-3, which are used as exterior wall of the highly insulated and air-tight house (R-2000) that is located at Kiyama in Saga prefecture, are measured in a cooling time during summer season. By the measurement, it is confirmed that each value of the relative humidity near the hidden side of interior finish material is about 80% and is 67%--75% respectively, and internal dew condensation is not generated in both walls.
(4) The results of the outdoor exposure experiment on the test house are reproduced by the experiment on test walls, in which the bilateral air temperature and humidity of them and the amounts of heating their surfaces are controlled, under conditions that the initial relative humidity in the wall is high (90%) and the wall surface is heated.
(5) The region and azimuth orientation characteristics of moisture fluctuation in various walls are analyzed using the heat and mass transfer equation proposed by the authors. In the vertical east and west-facing wall-1, the internal dew condensation occurs in the four regions (Osaka, Fukuoka, Kagoshima, Naha) . The wall-3 has a property of preventing the internal dew condensation, and can keep the value of the relative humidity near the hidden side of interior finish material under 90% regardless of the wall orientation in Fukuoka.
