Impact of the building airtightness and natural driving forces on the operation of an exhaust ventilation system in social housing in Chile

Chile has 1,626 social housing complexes with a total of 350,880 dwellings. Several studies have demonstrated a low thermal performance and high air permeability of the envelope of social houses throughout the country, causing surface condensation on walls, high heat losses in winter and low levels of thermal comfort for their occupants. The presence of high levels of indoor pollutants and/or indoor humidity has also been observed, causing respiratory and cardiovascular diseases in the occupants. This highlights the urgent need to renovate social housing in Chile to achieve better standards of habitability, well-being and quality of life for its inhabitants. Current retrofitting programs for social housing focus mainly on reducing heat losses and condensation problems inside the dwellings, although they also include the installation of a mechanical exhaust ventilation system with natural air inlets. However, there is currently no evaluation of the performance of such ventilation systems in the country. In fact, we do not know if the natural air inlets provide the required airflow rates to the different living areas of the dwelling and how the airflow rates are affected by the airtightness of the building envelope and the natural external driving forces (wind and thermal buoyancy).
This study has evaluated the performance of a commonly used mechanical exhaust ventilation system in a representative social house in Chile, for two sets of climatic data, using the airflow and contaminant transport calculation software CONTAM. It has highlighted the significant effect of the building airtightness and the natural driving forces, mainly the wind effect, on the performance of the ventilation system. For the house investigated in this research and considering a n50-value of 10h-1, the supplied airflow in one of the bedrooms is drastically reduced to almost the half of the value obtained for a perfectly airtight house when all the interior doors are open. When the doors are closed, the effect is even more pronounced. The decrease in the supplied airflows in the bedrooms leads to a significant increase in the CO2-exposure of the occupants. In the most unfavourable case analysed – n50 of 10h-1 with closed interior doors – the child of the family spent only 35% of his time in an indoor environment with a CO2 concentration below 950 ppm.
These results emphasize the need to work also on improving the airtightness of social housing for a better operation of the exhaust ventilation system. They contribute to a better knowledge of the performance of the ventilation systems currently installed in the renovation of social housing in Chile, as well as to the identification of ways to improve these systems so that they can guarantee sufficient indoor air quality to the occupants.