Detailed investigation of ventilation rates and airflow patterns in a northern California residence

Abstract

Building ventilation rates and indoor airflow conditions influence occupants' exposure to indoor air pollutants. By making time- and space-resolved measurement of 3 inert tracers steadily released in a single-family house in California for 8 weeks in summer and 5 weeks in winter, this study quantifies the air change rate of the living zone with 2-hour time resolution; estimates airflow rates between the living zone, attic, and crawlspace; and characterizes mixing of air in the split-level living space. Occupant behaviors altered the air change rates, primarily through opening windows and secondarily through operating the heating system. The air change rate correlated with the number of window openings, accounting for 57% of the variability measured across 2 seasons. There were substantial upward interzonal airflows between the crawlspace, living zone, and attic; downward airflows were negligible by comparison. More than 70% of the airflow entering the living zone in the winter and at night during summer came through the crawlspace, rather than directly from outdoors. The airflow from the living zone to the attic increased with the attic-outdoor temperature difference, indicating that buoyancy associated with solar heating of the attic induced airflow from the living zone, increasing the air change rate.

Characterizing sources and emissions of volatile organic compounds in a northern California residence using space‐ and time‐resolved measurements

“…Key approximations made in this calculation are (a) that the occupied internal volume of the house can be effectively considered as well‐mixed and (b) that only indoor emissions and air change between indoor and outdoor air influence indoor‐air concentrations. These approximations are supported by three important observations: (a) tracer results showed that air in the upper and lower living spaces mixed fairly well; (b) the crawlspace and attic generally served as one‐way paths for airflow into and out of living zone, respectively; and (c) VOC composition in the crawlspace was similar to that outdoors. Under this approximation, the mass balance of a VOC in the living zone is given by the following equation:where C in = C in ( t ) and C out = C out ( t ) are the concentrations in the living zone and outdoors (ppb; part per billion by volume); V is the volume of the living zone (m 3 ); E = E ( t ) is the emission rate in the living zone (mg h −1 ); ρ is the gas density for the compound (mg mm −3 ); and A = A ( t ) is the living‐space air‐change rate (h −1 ).…”

“…The time‐dependent indoor concentration, C in , is approximated as the weighted mean of VOC concentrations measured in the kitchen and bedroom area. The procedures to calculate values of , , and are described in the supplement and are consistent with the procedures to determine the air‐change rate using measured tracer concentrations …”

“…The second period (winter campaign) spanned 5 weeks from late January to early March 2017. A detailed description of the studied house and of the two observational campaigns has been reported . We provide a brief recap here of aspects essential for understanding and interpreting the VOC data.…”

“…Time‐resolved emission rates in the living zone were determined for VOC signals using indoor air‐change rates determined with 2‐hour resolution . Key approximations made in this calculation are (a) that the occupied internal volume of the house can be effectively considered as well‐mixed and (b) that only indoor emissions and air change between indoor and outdoor air influence indoor‐air concentrations.…”

Sources and dynamics of semivolatile organic compounds in a single‐family residence in northern California

“…House airflows and air exchange rates were acquired through high–time resolution measurements of an inert tracer (butene‐d3, CD 3 CH 2 CH=CH 2 , 98%; Cambridge Isotope Laboratories, Inc,) continuously released inside the residence. The tracer was detected using proton transfer reaction time‐of‐flight mass spectrometry (PTR‐TOF‐MS) following previously reported methods . Using the determined flow rates (m 3 h −1 ), the effective emission rate ( E , mg h −1 ) of gas‐phase SVOCs from indoor sources to the indoor air was estimated using the following equation:Here, C Indoor and C Outdoor refer to the SV‐TAG measured indoor and outdoor gas‐phase SVOC concentrations, respectively (in mg m −3 ), obtained by subtracting the particle‐only SVOC concentration (denuded sample) from the total gas‐plus‐particle SVOC concentration (undenuded sample).…”