Can naturally ventilated office buildings cope with dusty outdoor air?

Naturally ventilated (NV) buildings, when well designed and operated, can provide adequate indoor environmental quality (IEQ) while reducing the building energy demand. However, in dusty outdoor air, this ventilation technique may increase the penetration of outdoor particulate matter (PM) indoors, leading to adverse health effects. Given the increasing frequency of outdoor dust episodes in Mediterranean climates, an important research question is whether NV buildings can provide adequate indoor air quality (IAQ) during increased outdoor air dust episodes. We monitored indoor and outdoor concentrations of size-resolved PM for six months in an occupant-operated NV low-energy office building in Cyprus, an island with frequent episodes of airborne dust. In parallel, the building was monitored for its energy consumption, indoor air temperatures, relative humidity, and CO2 concentrations. We also interviewed the building occupants regarding their perceived IEQ conditions. The results revealed that the NV provided adequate IAQ conditions in 4 out of 5 investigated indoor spaces for PM2.5 and in 2 out of 5 investigated spaces for PM10. The average indoor concentrations were in the range of 4.4-5.1 μg/m3 for PM2.5 and 13.8-19.9 μg/m3 for PM10, while the average outdoor concentrations for the same period were 7.4 μg/m3 for PM2.5 and 38.1 μg/m3 for PM10. Additionally, unlike the outdoor air, the indoor PM concentrations respected the WHO short-term 24-hour limits, indicating that the building addressed well the dusty days. In terms of other IEQ parameters, the CO2 levels remained below 1000 ppm for more than 90% of the time, while more than 90% of the occupants were satisfied with the thermal comfort conditions. The final actual energy consumption was ~164 kWh/m2/yr, drifting only by 7% from the predicted energy use. The results of this case study indicated that well-designed low-energy NV office buildings can provide adequate IEQ conditions, even in outdoor environments with dusty air.