gistfile1.txt

building_volume_cu_ft = 8*8*20
natural_ventilation_cfm = 1

# this is for a human at rest.
o2_to_co2_cu_ft_per_minute = 0.009

# starting/natural conditions -- typical
# see http://www.molecularproducts.com/pdf/technical-library/A%20Guide%20to%20Breathing%20Rates%20in%20Confined%20Environments%20Technical%20Article.pdf
co2_percent_start = 0.000314
o2_percent_start = 0.2095

co2_cu_ft = building_volume_cu_ft * co2_percent_start
o2_cu_ft = building_volume_cu_ft * o2_percent_start

co2_percent = co2_percent_start
o2_percent = o2_percent_start

for i in range(60*24*2): # step through each minute over two days
    # account for respiration of one person
    co2_cu_ft += o2_to_co2_cu_ft_per_minute
    o2_cu_ft -= o2_to_co2_cu_ft_per_minute

    # account for natural exfiltration
    co2_cu_ft -= natural_ventilation_cfm * co2_percent
    o2_cu_ft -= natural_ventilation_cfm * o2_percent

    # account for natural infiltration
    co2_cu_ft += natural_ventilation_cfm * co2_percent_start
    o2_cu_ft += natural_ventilation_cfm * o2_percent_start

    co2_percent = co2_cu_ft / building_volume_cu_ft
    o2_percent = o2_cu_ft / building_volume_cu_ft

    co2_ppm = int(co2_percent * 1000000)

    print("{} minutes: {:0.2f}% O2; {}PPM CO2".format(i+1, o2_percent*100, co2_ppm))