Case Study on Ventilation for Improving the Hygrothermal Behaviour of Emergency Temporary Housing under Japanese Conditions

Emergency Temporary Housing units consisting of a light-gauge steel brace construction were built following the Great East Japan Earthquake of March 11, 2011 (see Appendix). About 30,000 of these units are still in service following a delay in rehabilitation and reconstruction. The heat bridge portion in this kind of construction causes surface condensation in rooms. In addition, condensation damage on the steel roof surface in the attic space is also relatively large. This is because ventilation is inadequate and the amount of moisture production is relatively large despite the small volume of indoor air. Case studies on various ventilation methods have been carried out using whole building heat, air and moisture transfer simulation. The results obtained are as follows:

1) An exhaust fan is commonly used to prevent condensation problems in the attic space, however, conversely it has resulted in enhancing the condensation risks. Introducing outside air to the attic space would be a better method to reduce condensation risk.

2) An appropriate amount of airflow volume in residential spaces is required since the moisture buffering effect of the room air becomes small thus causing some condensation problems. Simulation results also confirmed that even a low volume heat exchange ventilation system would be enough to minimize condensation risks.