1. CO2 concentration and Stady-state mass balance model
Marianna Luoma

2. Carbon dioxide CO2 is odourless gas Indicates contaminants from humans
Outdoor air concentration ppm
Good air quality: when the concentration is less than 750 ppm
D2: Concentration should not exceed 1200 ppm
Higher levels of CO2 in indoor air indicate poor air quality and too low outdoor air flow per person

3. The need for ventilation to maintain air quality
The CO2 production of a sitting person:
qCO2 = 5,37 cm3/s (19,3 dm3/h)
When the outside air concentration is 380 ppm and we do not want to exceed the indoor concentration of 1200 ppm, the air flow rate needed per person is:
Qiv = qCO2 / ΔCCO2=(5,37 cm3/s/( ) cm3/m3) =
6,5 dm3/s (compare to D2: 6 l/s, person)

4. CO2 concentration in steady state conditions
Source: Demand Control Ventilation
using CO2, ASHRAE Journal, 2001.

5. Demand Controlled Ventilation DCV
Energy savings possible
For example auditoriums
CO2 sensor in the room
Supply air flow rate is controlled according to the indoor air concentration
The set value could be for example 750 ppm.
MAMK D-building

6. TSI IAQ-Calc –mittarilla mitattu CO2-pitoisuus
ja rakennusautomaation tallentama CO2-pitoisuus
luokkahuoneessa

7. Steady-state mass balance model
In the text book page 125

8. Air change rate n = q/V Unit: 1/h Example:
n = 6,73 m3/h /37,9 m3 = 0,18 1/h

9. Nominal time constant Nominal time constant T = 1 / n Unit: h
The concentration changes 63 % of the total change during 1 time constant.
After a time corresponding to 4 nominal time constants, the indoor concentration will equal 98 % of the final, steady- state concentration.