Ventilation in houses with distributed heating systems.

The LTEE laboratory of Hydro-Quebec, in collaboration with Canada Mortgage and Housing conducted an indoor air quality study involving 30 single family detached houses heated with electric baseboard heaters in the vicinity of Trois Rivières during the 1993-94 heating season. The houses were selected according to the measured air leakage at 50 Pa, so as to have a sample distribution similar to the distribution of air leakage of houses in the province of Quebec. The "source strength" of several air pollutants were calculated from measurements of ambient pollutant levels and total ventilation during a one-week test. In addition, the indoor CO2 and humidity levels were recorded in eight of the houses continuously during the heating season. The level of CO2 in the master bedroom was found to follow fairly closely the CO2 level in other parts of the building including the basement (within about 200 ppm) except when the bedroom door was closed. With the room occupied and the door closed, CO2 levels in the bedroom increased steadily during the night until morning, when the door was opened, to levels in excess of 3 500 ppm with one person, and in excess of 4 500 ppm with two persons. Model studies using the measured pollutant source strengths and measured equivalent leakage areas of the buildings indicated that the recommended health guidelines for airborne respirable solid particles (RSP's), CO2 and formaldehyde are exceeded during periods of low total ventilation, coinciding with mild outdoor temperatures and low wind conditions. It was observed that kitchen and bathroom fans originally installed in some of these houses were not operated by the occupants for sufficiently long times to affect the quality of indoor air. Various different methods of ventilating some of the houses were tested, including quiet replacement exhaust fans, mixing fans for indoor air, and a fresh air intake and mixing system. The effects of operating various air handling systems were monitored by keeping track of indoor CO2 and relative humidity in the master bedroom, and occupancy in person-hours per day. Quiet replacement fans noticeably improved indoor air quality when these were operated over 50% to 100 % of the time. An area of remaining concern is the fact that exhaust only systems accentuate the negative pressure in the basement by raising the level of the neutral pressure zone in the building, and may enhance the flow of soil gases into the basement. A system which mixed indoor air between the basement and the main floor also reduced the average level of indoor pollutants. The system was designed to create a pressure difference between the main floor and the basement, causing a slight pressurization of the basement. A system designed to introduce 5 L/s of outdoor air and to mix it with 55 L/s of indoor air for tempering was installed to draw air from the hallway and deliver the mixed air into each of three bedrooms. This system was capable of maintaining CO2 levels in the master bedroom below 1000 ppm with two occupants in the room and the door closed.