With 35 years of existence and more than 10 million equipped dwellings, mechanical humidity-based demand-controlled ventilation (RH-DCV) can provide a comprehensive feedback on installation, aging, and maintenance of its components. Their working principle is based on the extensions and retractions of a hygroscopic fabric, which pulls on a shutter to modify the device’s cross-section – hence the airflow – upon humidity changes in their environment.
In 2006, before generalizing the usage of RH-DCV in French residential buildings, the Ministry for Housing ordered an evaluation of these systems after prolonged on-site operation. For this purpose, the COSTIC laboratory selected 21 social housings in the Parisian suburb, and collected 57 exhaust units after 6 years of in-situ functioning.
During the collecting phase, the first on-site observations were the following:
- 12 % of the exhaust units were installed in incorrect rooms (kitchen/bathroom swap, for instance).
- 14 % of the units had suffered damage, either due to voluntary modifications by the occupants (e.g. blocking of the shutter), or to bad re-assembly after maintenance. In 1 out of 3 dwellings, at least one device presented such defects.
- 75 % of the units showed an absence of sufficient maintenance (dusting), when 58 % visually exhibited clogging of the canal.
The devices were first characterized on a laboratory test bench as-collected (i.e. still soiled). Characterization of RH-DCV units consists in plotting the volume-flow crossing the unit as a function of relative humidity.
- 100 % of the non-damaged exhaust units exhibited a conform hygroscopic behavior or showed a slight shift of their characteristic when still soiled.
- 46 % of the kitchen units complied with factory specifications despite the absence of maintenance.
- 100 % of the bathroom exhaust units showed an airflow reduced by 5 m3/h.
Devices were then cleaned and properly re-assembled. The shutter and shutter-case (passive elements) were replaced when irreversible damaged was observed.
- 75 % of the units complied with factory specifications after cleaning.
- Among the other 25 %, the kitchen elements showed an increase of volume flow lower than 3 m3/h, while bathroom units exhibited a decrease lower than 2 m3/h.
For the same study, self-adjusting exhaust units were also collected and tested. These devices were installed in utility-rooms. Their working principle is based on the deformation of a membrane solely due to pressure forces to maintain a constant airflow despite pressure variations in the ventilation ductwork.
- 100 % of the soiled units were out of their specification, with volume flows 4 to 10 m3/h (25 to 65 %) lower than their initial setting.
- Once cleaned, 100 % of the units complied with factory specifications.
The results of this samples collection highlight the necessity of ventilation units’ maintenance; it also shows the robustness of RH-DCV settings after prolonged in-situ operation.