Center for the Built Environment

Today’s high performance green homes are reaching previously unheard of levels of airtightness and are using new materials, technologies and strategies, whose impacts on IAQ cannot be fully determined by past efforts.  This research assessed IAQ in 24 new or deeply retrofitted homes designed to be high performance green buildings in California using pollutant measurements, home inspections, diagnostic testing and occupant surveys.  Measurements included six-day passive samples of nitrogen oxides (NO2 and NOx), formaldehyde (HCHO), acetaldehyde (CH3 CHO) and air exchange rate (AER); time-resolved data loggers were used to measure carbon monoxide (CO), particle counts (PN), temperature (T) and relative humidity (RH), as well as ultrafine particle count (UFP) during stovetop testing. 

Only 13 of 24 homes provided continuous mechanical ventilation, and no relationship was found between mechanical venting and either AER or pollutant levels, with the exception of particulate, which was actively filtered by 12 of 13 ventilation systems.  Naturally vented homes were much less airtight, on average (6.7 vs. 2.3 ACH50).  Numerous faults were observed in complex mechanical ventilation systems, suggesting need for more rigorous commissioning.  AER did not significantly determine either formaldehyde or particulate levels, but they did for NO2.  Median formaldehyde concentrations in bedrooms and kitchens (17.5 and 20.1 μg/m3) were approximately half those found in conventional new CA homes by previous research (36 μg/m3) (Offermann, 2009).  Source control (engaged in by 22 of 24 households) was most likely responsible for this result.  NO2 concentrations were generally low, with concentrations in gas cooking kitchens 2.4 times higher than electric (13.1 vs. 5.4 ppb).  Three gas cooking homes exceeded the CalEPA annual ambient air standard for NO2.  Those homes that provided active particle filtration had lower indoor particle count levels than unfiltered homes.  UFP emissions were dramatically lower on induction electric cooktops, compared with either gas or resistance electric models.  Kitchen exhaust fan usage rates were low, with occupants believing that everyday cooking was harmless, suggesting a lack of education on IAQ impacts of cooking.  Finally, shortcomings affecting high performance green homes were identified in current U.S. codes and standards.  The results of this research suggest that with better occupant education, careful system design and commissioning, particle filtration and source control, high performance green homes can provide acceptable or enhanced IAQ.