軒裏換気方式における冬期の小屋裏温湿度の解析

Abstract

In this study, a hygrothermal model was proposed for predicting the humidification and dehumidification effects using the measured flow rate through the flow paths of an attic space in an experimental house. The space between the ceiling gypsum board and bagged insulation (hereinafter “ceiling air layer”) was set up. The simultaneous transfer of the heat and moisture in the hygroscopic regime was analyzed. The outdoor air and surface temperatures, as well as the absolute humidity of the ambient air in the room, vented wall cavity and the outdoor air measured in our previous paper were used as given conditions after averaging them over 5 minutes. Air flow rate through each part (from vent opening to eaves space, from vented wall cavity to eaves space, form eaves space to attic space, from room to attic space) measured every 2 s was also used as an input. The time interval of the calculation was set to 2 s. The calculation was performed from February 25 to April 1, and before that, a pre-conditioned calculation using input data from February 22 to 24 was performed ten times. The calculated absolute humidity in the ceiling air layer agreed well with the measured results by assuming that the air-exchange rate between the ceiling air layer and attic space is 2-20 m3/h (equivalent to 0.2-2.0 times/h air exchange rate in the attic space). The calculated temperature and absolute humidity of the attic, relative humidity of the sheathing boards surfaces, and moisture content of wooden elements were also in good agreement with the measured values, showing the validity of the proposed model. By using the model, the following results were obtained; 1) The absorption by the wooden materials in the attic space increases when the sheathing boards starts desorbing. Then the absorption changes into desorption when the desorption from sheathing boards decreases (when the wooden materials in the attic space become sufficiently warm.), and the desorption rate becomes faster than that of the sheathing boards. Then it decreases. During nighttime, the amount of moisture absorbed by the wooden materials is constant and almost the same as that by the northern and southern sheathing boards. 2) The amount of moisture desorbed from the sheathing boards and wooden materials in the attic space during daytime has strong correlation with the amount of moisture exhausted by air exchange. This is because the desorption of vapor by the sheathing boards and wooden materials increases the absolute humidity of the attic space, and consequently the humidity difference between the attic and the outdoor air becomes larger. 3) The amount of moisture absorbed and/or desorbed by the wooden materials in a daily cycle is almost the same as that by each of the northern and southern sheathing boards, and thus had a significant effect. This must be considered when calculating temperature and humidity in attic space.