Indoor Air Quality in Passive Houses

Passive houses are a simple idea: construct a building that is well-insulated with a tight envelope, and the result is a very energy-efficient home. A proclaimed benefit of these homes, in addition to the energy-efficiency, is improved indoor air quality due to continuous mechanical ventilation and filtered incoming air. Filtering the ventilation air only solves one issue, however. Many air pollutants in homes come from indoor sources. The goal of this study is to observe and quantify how passive houses are impacted by common indoor pollutants.

In this project we are measuring fine particulate matter, carbon dioxide, carbon monoxide, ozone, nitrogen dioxide, total volatile organic compounds (TVOCs), and radon inside passive houses in Colorado and the surrounding areas. The homes will be studied while unoccupied to determine a baseline condition, and then again while we perform a series of repeatable activities, like cooking and walking around. Bedrooms will also be monitored overnight to determine if high temperatures or carbon dioxide build-up from respiration may be an issue.

A pilot study was conducted in a passive house near Fort Collins November of 2017. Results indicated that outdoor PM had little effect on indoor levels, while walking and cooking greatly increased indoor PM.  TVOC levels appeared to be independent of any inside activities. CO2 levels were significantly increased by both activities, with cooking having a larger impact. Due to very low air exchange rates, CO2 and PM levels were slow to decay once elevated. In the bedroom, CO2 levels increased at night to above 1000 ppm. Overheating was not an issue in late fall, with an average temperature of 21.7°C and a maximum of 26.0°C. Relative humidity ranged from 12.2% to 34.2% with a mean of 25.3% Overall results show generally good air quality that degrades during cooking. Thus it is recommended to supplement ventilation with open windows or doors while cooking.