A simple CO2 meter for less than a couple hundred is a excellent device for determining the actual fresh air changes in any occupied structure. The amount of CO2 per person is known volume. Using the number of occupants in a space multiplied by the volume of CO2 per person divided by the cfm of fresh air equals the cfm per occupant.
Attached is a graph of interal ^F temp, %RH, and CO2 ppm. 800 ppm CO2 equals 30 cfm per person fresh air in a house with 2-6 occupants during last week, 7-20-09. A CO2 level of 1,500 ppm CO2 equals 10 cfm per person. Healthy homes should have an air change in 3-5 hours when occupied. Ideally they should not exceed 1,000 ppm for extended periods. This is a handy tool for an modern a/c contractor to estimate the real fresh air infiltration/ventilation rate of home. This technology could put the V back in H_AC. Also the CO2 meter will indicate excessive air leak caused by duct leaks and wind which helps determining wether the a/c is functioning properly. High indoor humidity with extremely low CO2 levels indicates excessive outside infiltration/duct leakage. Normal CO2 levels indicates adequate fresh air and attention to the a/c set-up (air flow/refrigerant charge/etc.) Regards TB