Ventilation Rates in the New Houses
The ventilation rates measured at the time of air sampling ranged from 0.14 to 0.78 air changes per hour (ach). These rates are shown in Figure 2. For the manufactured houses, the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) minimum recommended "by volume" rate of 0.35 ach is applicable. Two of the site-built houses had ventilation rates that were measurably below ASHRAE guidance.

Figure 2. Ventilation rates measured by tracer gas decay at the time of air sampling in 4 new manufactured and 7 new site-built houses. (LBNL-43519)

VOC emission factors in new houses
Net area-specific emission rates termed "emission factors" were calculated by a steady-state mass balance model for the predominant VOCs in the manufactured and site-built houses. Normalization to the floor areas facilitates the comparison of contaminant generation in houses of different sizes. Geometric mean (GM) emission factors in µg/m²-h, geometric standard deviations and emission factor ranges for 28 predominant VOCs in the manufactured and site-built houses are presented and compared in Table 11.

The compounds with the highest emission factors in the two house types included alpha-pinene, beta-pinene, ethylene glycol, hexanal, trimethylpentanediol monoisobutyrate (TMPD-MIB), and acetic acid. Only 11 of the 28 VOCs had GM emission factors that differed by more than a factor of two between the house types.