Download Ventilation impact of outdoor CO2 concentration increase

Ventilation impact of outdoor CO2 concentration increase
Moon Keun Kim1,*
1
Xi’an Jiaotong – Liverpool Univeristy, (XJTLU), Suzhou, China
*
Corresponding email: [email protected], [email protected]
SUMMARY
This study aims to identify a ventilation impact of outdoor CO2 level increase. The main part
of ventilation impacts occurs during the use phase because of indoor air quality. According to
the IPCC report 2014, the observed atmospheric CO2 level increased at a rate of 1.9 to 2.1
ppm per year. This paper analyzes existing knowledge regarding the ventilation impact of
atmospheric CO2 concentration increase in buildings. The outdoor airflow rate must be
increased to maintain acceptable indoor CO2 level and to adapt increased atmospheric CO2
concentrations. Therefore, energy loads of buildings for heating and cooling are also
increased. By the analysis of indoor CO2 concentration level, it can be identified various
possibility of advanced improvement methods of ventilation strategies to maintain acceptable
CO2 level and to save ventilation energy in buildings.
PRACTICAL IMPLICATIONS
Increase of atmospheric CO2 concentration highly influences ventilation effects in buildings
Change of atmospheric CO2 level also produces an effect on energy loads of buildings.
KEYWORDS
CO2 concentration, ventilation impact, indoor air quality, building energy
1 INTRODUCTION
Recently concentration of greenhouse gases have been increased. According to the IPCC
report 2014, the observed concentrations of atmospheric CO2 have steadily increased 300 to
390 ppm. And during 1990-2011, the observed atmospheric CO2 level increased at a rate of
1.9 to 2.1 ppm per year. The IPCC report shows predicted scenarios of atmospheric CO2
concentration increase in next 30 years. Based on guidelines and standards lists, a maximum
acceptable CO2 concentration is generally 800 or 1000 ppm (volume). And typically standards
suggests recommended outdoor airflow rate, 7.5 L/s per person to maintain the steady state
CO2 concentration below 1000 ppm (volume) assuming the outdoor CO2 concentration to be
350 ppm (volume). However, if outdoor CO2 concentration level is increased, actual
recommended outdoor airflow rate should also be adjusted.
2 METHODS
In order to analyse the CO2 concentration considering infiltration and scheduled occupancy
diversity factor from ASHRAE standard 90.1-2004, numerical modelling was carried out
based on the following equation for CO2 concentration (ASTM D6245-12, Lu et al. 2011,
Wang and Jin 1998). The mass balance is shown in the following equation:
𝐶 𝑡 = 𝐶! +
!(!)
!
+ (𝐶 𝑂 − 𝐶! −
! !
!
)𝑒 !!"
(1)
where V is the space volume, C(t) the indoor CO2 concentration at time t, Q the volumetric
flow rate, Co the outdoor CO2 concentration, I = Q/V is the air change rate and G(t) is the
CO2 generation rate at time t. If Q is assumed, and Co and G(t) are constant.
This case study assumed air volume flow rate of 8.0 L/s per person, which is around 1.0 air
change per hour (ACH) in a volume of 800 m3. It is assumed that outdoor atmospheric CO2
concentration are 350-500 ppm and occupants CO2 generation is 0.0052 L/s per person
engaged in office work (ASTM D6245-12). And this study assumed that the breathing zone is
well mixed as is predicted for office buildings.
3 RESULTS
We simulated the indoor CO2 level with 100% atmospheric air for a typical weekday from 6
AM to 9PM based on the occupancy diversity factor from ASHRAE 90.1 2004. It is shown in
Figure 1. With atmospheric CO2 level 500 ppm, the office CO2 level peaks more than 1100
ppm. In order to maintain indoor CO2 level below 1000 ppm, outdoor air ventilation rates
should be increased 10% per every 50 ppm of atmospheric CO2 concentration increased.
Figure 1. Change in indoor CO2 concentration with variable outdoor CO2 concentrations (350500 ppm) for typical weekday in the office based on ASHRAE 90.1.
5 CONCLUSIONS
This paper analyzes existing knowledge regarding the ventilation impact of atmospheric CO2
concentration increase in buildings. The outdoor airflow rate must be increased to maintain
acceptable indoor CO2 level and to adapt increased atmospheric CO2 concentrations.
Therefore, energy loads of buildings for heating and cooling are also increased.
6 REFERENCES
ASHRAE. 90.1 Appendix G. 2004. Building performance rating method. ASHRAE 2004,
Atlanta.
ASTM. 1992. ASTM Standard D6245-12, Guide for using indoor carbon dioxide
concentration to evaluate indoor air quality and ventilation.
IPCC 2014. Climate change 2014 synthesis report, Intergovernmental panel on climate
change, 2015
Lu T, Lü X, and Viljanen M 2011. A novel and dynamic demand-controlled ventilation
strategy for CO2 control and energy saving in buildings, Energy and Buildings, Vol. 43,
Issue 9, September 2011, pp.2499-2508
Wang S.W, Jin X.Q. 1998. CO2-based occupancy detection for on-line outdoor air flow
control. Indoor and Built Environment, May 1998; Vol. 7, 3: pp. 165-181