軒裏換気方式における冬期の換気口と通気層の小屋裏除加湿効果: 温暖地における木造住宅の小屋裏温湿度形成に関する研究 その2

摘要

A mock-up, one-story test house with eaves ventilation was built in a suburb of Tokyo to examine the hygrothermal conditions in its attic space. A series of measurements were conducted to clarify the effects that the vent opening area and vented wall cavity had on the hygrothermal conditions. In addition, to estimate the airflow rate through the vented wall cavity and eaves vent using the air velocity measured by an anemometer placed therein, the relationship between them was measured by changing the fan flow rate in an experimental setup. The dehumidification of the attic space by the eaves vents, vented wall cavities and room was calculated during the experimental period. The main findings are as follows:1) Of the total flow rate through the vented wall cavity on the southern side, the proportions among upward flow into the attic space, upward flow into the ventilation opening, and downward flow were approximately 5:1:4. 2) Considering that 20% of the upward airflow through the vented wall cavity did not contribute to the ventilation of the attic space, the eave space should be added as a calculation node for hygrothermal models to predict the proper size of the attic ventilation opening. 3) Glass fiber insulation wrapped a vapor tight film (bagged insulation) is generally employed as a insulation layer of ceiling in mild climate regions of Japan. The air gap between the insulation materials has an impact on moisture flow passing through the ceiling gypsum board to the attic space.%本報では、軒裏換気方式の実験住宅において、各経路の空気流量を推定するために風速計や差圧計を設置し、また前報の実験では十分でなかった測定点を増設して、冬期の実験(2014年2月22日～4月1日)を行った。含水率の測定結果から、①前報での推測、野地下部合板の含水率が中央部より高いことについては、今回の測定により確認されたと考えられる(3.2節)。本報では加えて、換気口などの流量を推定するための試験を行い、小屋裏と連通する各経路の流出入量を推定し、得られた流量を用いてそれぞれの除加湿量を算出した。その結果、②前報での「小屋裏絶対湿度が夜間に外気より低くなるのは、(野地合板や小屋裏内木材の)夜間の吸湿量が多くなることで起こる」との推測については、居室からの移流および換気口からの外気流入が加湿となっていることから、野地合板などの吸湿によるためと説明できたと考えられる(5.2節)。