Influence of building envelope on indoor air quality: Field measurements, analysis, and method development related to indoor odors

Sammanfattning: The ventilation system should provide occupants with fresh air while removing excess pollutants from the building. However, increasing ventilation may inadvertently draw more pollutants into the occupant area or prove ineffective in altering emission rates from building materials and furnishings. If not addressed properly, this can make raising the ventilation rate inefficient, resulting in unnecessary heat losses or, in the worst case, reduced indoor air quality. This thesis addresses two previously insufficiently understood situations of contaminant transport within buildings, both manifested as unpleasant indoor smells: contaminant transport from adjacent compartments and early-stage emissions of air pollutants in new buildings. The former, inspired by school buildings in Sweden demolished due to 'moldy' smells, was thoroughly explored in my Licentiate thesis, Contaminant Transport by Air Infiltration from Crawl Space to Occupant Area-Numerical Simulations and Field Measurements in Swedish schools, and is presented here as a summary. The latter focuses on indoor air quality in new buildings, which often have initial high volatile organic compound (VOC) levels, typically perceived as a 'new smell.' In Sweden, it is common to run the ventilation system at full rate for several months as a remedy due to the negative effects of high VOC levels on occupants. However, the drawback of this strategy is the risk for over-ventilation with unnecessary energy losses. Two methods, ‘VOC-passport’ and ‘Ventilation threshold’, are developed to assess how ventilation can improve indoor air quality in more energy-efficient ways. Results show that with VOC-passport, it is possible to simulate dynamic variations in VOC concentrations in new buildings based on passive VOC measurements and building physics modeling. With this method, it is possible to find an optimal ventilation strategy for low VOC concentrations and minimal energy losses. In addition, an analytical analysis of the diffusion of VOCs in materials shows that if ventilation rates exceed a certain threshold, further increases will not affect the emission rate. A quantified ventilation threshold is useful for setting the ventilation rate regarding optimal off-gassing and an important complement to the VOC-passport.