Indoor comfort evaluation of a sustainable wooden house with a novel vapor-open envelope system in subtropical climate

Abstract

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 very challenging because they have both heating and cooling demand. Also the prediction of indoor air humidity is acquiring a greater interest concerning the envelope durability, the comfort and the energy consumption, which is very relevant to such regions. Meanwhile, there is a need of developing a new construction system and its design method for subtropical regions since it is inappropriate to simply use the established construction systems for cold regions which have only heating demand. Based on the transient hydrothermal model of the envelope and the whole building heat and moisture balance model taking into account the moisture buffering by hygroscopic interior materials, the authors have developed an envelope system and its insulation optimization scheme which considers lifetime environmental impact, lifetime cost, durability, users’ behaviour and local climate. The envelope consists of natural materials such as wood and clay and thus allows the moderate transfer of the water vapour in both directions i.e. from exterior to interior and from interior to exterior. A detached house with this system was realized in Ohmihachiman (central Japan) in June 2013 and the indoor temperature and humidity have been monitored at several points. The measured indoor climate was analysed and it was revealed that 1. the indoor climate in summer has a certain improvement potential and 2. the indoor climate in winter is satisfying. As the monitoring of electricity generation by the photovoltaic panels and the electricity consumption of the whole house has showed a positive balance (more generation than consumption), it is suggested to either use the cooling radiator more actively or install an active dehumidifier into the mechanical ventilation system to provide a more agreeable indoor climate in the summer. The former recommendation will be implemented in summer 2015 and its impact on the comfort and energy consumption will be further analysed.