Long-term durability of humidity-based demandcontrolled ventilation: results of a ten years monitoring in residential buildings

In-situ performance of mechanical humidity-based mechanical exhaust ventilation (RH-MEV) is characterized in this study. This ventilation system includes fully-mechanical air inlets in the dry rooms and exhaust units in the wet rooms: the extensions and retractions of a hygroscopic fabric modify their cross-sections upon hygrometric changes in their environment without the need for motors or electronic sensors. 
This demand-controlled ventilation (DCV) system was invented 35 years ago; it is now widely used in Europe, and the first ventilation system in new French residential buildings. 

A large-scale monitoring on thirty new occupied apartments in two residential buildings, equipped with this system, was held from 2007 to 2009. The equipment included indoor air quality (IAQ) sensors in different rooms of each dwelling (temperature, humidity, and CO2), as well as pressure and volume flow sensors for monitoring the ventilation system. Recordings were performed every minute over two years. This former study showed: 

• The good IAQ in terms of CO2 and humidity provided by the ventilation system, despite the over- occupation of some apartments. These results showed the system’s appropriate reaction to human occupation resulting from a good correlation between CO2 and airflows. 
• The statistical real-field savings on heat losses of 30 % in average compared to constant airflows from the French regulation. 
• The good agreement of the heat loss measurements with the simulation models used for the French DCV technical agreements. 

Ten years later the acquisition system is turned back on with the intention to assess the ventilation system behaviour/performance after a prolonged in-situ functioning period. We present in this article the results of a preliminary study: 

• At start-up, more than 80 % of the metrology is still in working conditions. 
• Using this rough data, the average in-situ drift of the hygroscopic devices after 9 years of operation is estimated below ± 1.5 %RH and is lower than the announced accuracy of the electronical humidity sensors at installation (± 1.8 %RH). 
• The observed drift of volume flows on some of the exhaust units is typical of an absence of maintenance. 
• The battery of the presence-based toilet exhaust is often (90 %) discharged. 

These first promising results will be followed by a thorough IAQ and performance study which shall include: 

• The collection of the ventilation devices for a full quality control before and after the recommended maintenance. 
• The collection of the metrology sensors for re-calibration and drift-correction on the measurements. 
• A new set-up for each apartment including pollutant (VOC, particle matter) sensors to follow the latest interests of IAQ research.