Figure 1b gives the ventilation rate of room G1 obtained
by the fan and CO2 methods. The ventilation rates obtained
by the fan method were much higher than those obtained by
the CO2 method (annual means of 22.4 and 5.3 m3/s,
respectively). Similar results were obtained from all the other
rooms. The fan method may have an uncertainty of about
15% due to dust buildup and power supply variations. The
CO2 method has an unknown uncertainty. One reason is that
the CO2 production rates of pigs were measured in the late
1950s (ASAE Standards, 2004). Animal breeds, diets, and
production systems have changed over the years; therefore,
the CO2 production rates may have also changed. Another
reason is that the CO2 produced by manure stored in the room
was unknown and assumed negligible as compared to that
produced by animals. Hence, the ventilation rates obtained
by the fan method were used for the purpose of determining
odor emission in this study. The ventilation rate of room G1
varied between 5.6 m3/s in January and 52.6 m3/s in May
when the measurements were taken.