Study on heat and moisture balance of a sustainable building envelope for subtropical regions
Paper in proceedings, 2011
Concerning the resource depletion and global warming, the realization of sustainable constructions is crucial because the building industry has a big impact on the greenhouse gas emission. Recently the interest in the buildings in subtropical regions has been growing due to the high growth rate of their urbanized areas. From the view point of building physics, those regions are challenging because they have both heating and cooling demands. Also the prediction of indoor air humidity is acquiring a greater interest concerning the envelope durability, the comfort and the energy consumption. Authors developed a new building envelope system for subtropical regions. This envelope is a vapor-open and sorption-active system which allows the moderate transfer of the water vapor in both directions i.e. from exterior to interior and from interior to exterior. It consists of hygroscopic materials such as wood and clay, and its design system enables the make-up of the envelope to be flexibly changed according to the individual design conditions such as local climate, preferred room temperature and humidity and so on. The wall make-up is optimized so that no occurrence of interstitial condensation is predicted by transient heat and moisture transfer simulations. The energy consumption and the comfort of the building with this system, which will be built in central Japan, was analyzed. The dynamic energy simulation on hourly basis of an example case was carried out by means of a simulation program in accordance with ISO 13790. Furthermore, based on the heat balance simulation, the indoor humidity of the living room was predicted by means of a simplified moisture balance equation. This equation included the ventilation rate, the internal moisture load, and the moisture buffering by the interior materials. The result of the heating and cooling energy need was 13.9 kWh/m2 and 9.8 kWh/m2 respectively. The moisture buffering by the interior finishing reduced the fluctuations of the humidity and the acceptability of the room air. As a result, it was concluded that the utilization of the building envelope system has a high potential to provide the low-energy consuming and durable houses in subtropical regions. However, there still remains a need to improve the indoor comfort situation in summer. The model will be validated by the in-situ measurement in the test house in the near future.