Effect of Increased Cabin Recirculation Airflow Fraction on Relative Humidity, CO2 and TVOC
- Minimum cabin air pressure limited to 750 hPa (equivalent to pressure at an altitude of 8.000 ft. or 2.400 m above sea level)
- Temperature range in the cabin between 18.3 and 23.9 °C (65 to 75 °F)
- Minimum outside airflow rate per passenger of 3.5 L/s (7.5 cfm)
- Recommendation of 9.4 L/s (20 cfm) total flow, to be met by outside and filtered recirculated air
2.1. Flight Test Facility Test Setup
- Temperature: Four-wire PT100 thermocouples with an accuracy ±0.1 K @ 20 °C according to DIN EN 60751  class A.
- Humidity: Rotronic HygroClip HC2-C05 sensor with ±1.5% RH 
- CO2: Vaisala GMW20, range: 0–5.000 ppm, accuracy ±2%. Sensors were calibrated with 4.000 ppm calibration gas both at ground pressure (~940 hPa for Holzkirchen due to the place’s elevation) and low pressure of 755 hPa in the vessel and a pressure correction was derived.
- Pumped tubes: samples drawn for 20 to 60 min with flow rates of 0.1 to 1.0 l/min (depending on target compounds) and analyzed by GC-MS (gas chromatography-mass spectrometry QP2010 SE, Shimadzu, Duisburg, Germany) or HPLC-DAD (high performance liquid chromatography with diode array detector, Agilent 1260 Infinity, Agilent Technologies, Waldbronn, Germany). VOCs were analyzed according to DIN ISO 16000-6  and carbonyl compounds according to DIN ISO 16000-3 .
- Flow rate: Schmidt SS20.500 Sensors 0–35 m/s with an accuracy of ±3% .
2.2. Test Matrix and Sequence
- Baseline: Replication of today’s typical CO2 levels reported in aircraft
- ASHRAE: Replication of the minimum requirement for outdoor airflow rate (3.5 L/s/passenger) set out by ASHRAE 161
- ASHRAE half: Half the required outdoor airflow rate (1.8 L/s/passenger). Because the CO2 level follows the inverse of the outdoor airflow rate, this point was chosen because it was pre-assessed to be in the middle between the ASHRAE and the Max. CO2 condition.
- Max. CO2: Lowest outdoor airflow rate designed to remain below 5.000 ppm limit .
- Baseline–uncongested 1 (1st Session)
- Baseline–uncongested 2 (2nd Session)
- Baseline–fully booked
- ASHRAE–uncongested 1 (1st Session)
- ASHRAE–uncongested 2 (2nd Session)
- ASHRAE–fully booked
- ASHRAE half–uncongested 1 (1st Session)
- ASHRAE half–uncongested 2 (2nd Session)
- ASHRAE half–fully booked
- Max. CO2–uncongested 1 (1st Session)
- Max. CO2–uncongested 2 (2nd Session)
- Max. CO2–fully booked
2.3. Assessment of Air Quality
- rate the smell in the cabin on a five point scale (How would you assess the odor intensity in this flight? no odor; slight odor; moderate odor; strong odor; overwhelming odor),
- evaluate the air quality with a five point Likert scale (How would you rate the air quality in this flight? very poor; poor; average; good; very good/excellent)
2.4. Test Preparations
2.4.1. Considerations on Heat Balance
2.4.2. Subject Safety
3.1. Flow Rates
3.3. Cabin Humidity
3.4. CO2 Concentration
3.6. Trained Panel Votes
3.7. Subject Votes
- Relative humidity, CO2 and TVOC clearly increase with decreasing outdoor airflow rate
- Singular effects like an ethanol or cleaning agent event showed higher impact on the TVOC levels than the airflow regime
- Neither a trained sensory panel nor subjects could differentiate smell or acceptability for the different airflow conditions. Only in a fully booked cabin slightly worse votes were given at lower outdoor air intake.
- Low outdoor airflow rates necessitate additional cooling capacity in the recirculation path. This would result in a possible need for redesign of the ECS compared to today’s architecture.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
- Zavaglio, E.; Le Cam, M.; Thibaud, C.; Quartarone, G.; Zhu, Y.; Franzini, G.; Roux, P.; Dinca, M.; Walte, A.; Rothe, P. Innovative Environmental Control System for Aircraft. In Proceedings of the 49th International Conference on Environmental Systems ICES-2019-171, Boston, MA, USA, 7–11 July 2019. [Google Scholar]
- Oehler, B. Modeling and Simulation of Global Thermal and Fluid Effects in an Aircraft Fuselage. In Proceedings of the 4th International Modelica Conference, Hamburg University of Technology, Hamburg-Harburg, Germany, 7–8 March 2005. [Google Scholar]
- ASHRAE. Standard 161-Air Quality Within Commercial Aircraft; ASHRAE: Atlanta, GA, USA, 2007. [Google Scholar]
- Umweltbundesamt: Beurteilung von Innenraumluftkontaminationen mittels Referenz- und Richtwerten. Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz 2007, 50, 990–1005. [CrossRef] [PubMed]
- DIN EN 15251:2012-12: Indoor Environmental Input Parameters for Design and Assessment of Energy Performance of Buildings Addressing Indoor Air Quality, Thermal Environment, Lighting and Acoustics; German Version EN 15251:2007; Beuth Verlag: Berlin, Germany, 2012.
- Zavaglio, E.; Le Cam, M.; Quartarone, G.; Thibaud, C. An overview of indoor air quality and ventilation standards in commercial buildings and aircrafts. In Proceedings of the Indoor Air Conference, Philadelphia, PA, USA, 22–27 July 2018. [Google Scholar]
- Giaconia, C.; Orioli, A.; Di Gangi, A. Air quality and relative humidity in commercial aircrafts: An experimental investigation on short-haul domestic flights. Build. Environ. 2013, 67, 69–81. [Google Scholar] [CrossRef][Green Version]
- Vaisala: Application Note-How to Measure Carbon Dioxide. 2019. Available online: https://www.vaisala.com/en/file/66231/download?token=k98ud14E (accessed on 1 October 2020).
- Cao, X.; Zevitas, C.D.; Spengler, J.D.; Coull, B.; McNeely, E.; Jones, B.; Loo, S.M.; MacNaughton, P.; Allen, J.G. The on-board carbon dioxide concentrations and ventilation performance in passenger cabins of US domestic flights. Indoor Built Environ. 2019, 28, 761–771. [Google Scholar] [CrossRef]
- EU Funding and Tenders. Available online: https://ec.europa.eu/info/funding-tenders/opportunities/portal/screen/opportunities/topic-details/jti-cs2-2015-cpw02-sys-02-02 (accessed on 19 June 2015).
- DIN EN 60751:2009-05: Industrial Platinum Resistance Thermometer Sensors; German Version EN 60751:2008; Beuth Verlag: Berlin, Germany, 2009.
- Rotronic: Gesamtkatalog 2009/10–Feuchte- und Temperaturmessung. 2009. Available online: https://www.rotronic.com/de-de/productattachments/index/download?id=419 (accessed on 1 October 2020).
- DIN ISO 16000-6:2012-11: Indoor Air—Part 6: Determination of Volatile Organic Compounds in Indoor and Test Chamber Air by Active Sampling on Tenax TA® Sorbent, Thermal Desorption and Gas Chromatography Using MS or MS-FID, German version ISO 16000-6:2011; Beuth Verlag: Berlin, Germany, 2012.
- DIN ISO 16000-3:2013-01: Indoor air—Part 3: Determination of Formaldehyde and Other Carbonyl Compounds in Indoor Air and Test Chamber Air—Active Sampling Method; German Version ISO 16000-3:2011; Beuth Verlag: Berlin, Germany, 2013.
- Schmidt Technology: Flow Sensor SS20.500. 2020. Available online: https://schmidttechnology.de/wp-content/uploads/wpallimport/files/api_files/downloads/Instr_SS20.500_dt.pdf (accessed on 1 October 2020).
- Federal Aviation Administration (FAA). Airworthiness Standards: Transport Category Airplanes. Federal Aviation Regulation-Part 25; FAA: Washington, DC, USA, 2005.
- DIN ISO 16000-30:2015-05: Indoor Air—Part 30: Sensory Testing of Indoor Air; German Version ISO 16000-30:2014; Beuth Verlag: Berlin, Germany, 2015.
- Wargocki, P. Measurements of the effects of air quality on sensory perception. Chem. Sens. 2001, 26, 345–348. [Google Scholar] [CrossRef] [PubMed][Green Version]
- Wargocki, P. Sensory pollution sources in buildings. Indoor Air 2004, 14, 82–91. [Google Scholar] [CrossRef] [PubMed]
- DIN EN ISO 7730:2006-05: Ergonomics of the Thermal Environment–Analytical Determination and Interpretation of Thermal Comfort Using Calculation of the PMV and PPD Indices and Local Thermal Comfort Criteria; German Version ISO 7730:2005; Beuth Verlag: Berlin, Germany, 2006.
- Herbig, B.; Ivandic, I.; Ströhlein, R.; Mayer, F.; Norrefeldt, V.; Lei, F.; Wargocki, P. Impact of different ventilation strategies on aircraft cabin air quality and passengers’ comfort and wellbeing-the ComAir study. In Proceedings of the ICES-International Conference on Environmental Systems, Lisbon, Portugal, 12–16 July 2020. [Google Scholar]
|Conditions||Baseline||ASHRAE||ASHRAE Half||Max. CO2|
|Outdoor airflow rate in L/s/passenger||5.2||3.5||1.8||1.1|
|Recirculation airflow rate in L/s/passenger||4.2||5.9||7.6||8.3|
|Total airflow rate in L/s/passenger||9.4||9.4||9.4||9.4|
|Fully booked (~70–80 PAX)||1 session||1 session||1 session||1 session|
|Uncongested (~35–40 PAX)||2 sessions||2 sessions||2 sessions||2 sessions|
|Conditions||Baseline||ASHRAE||ASHRAE Half||Max. CO2|
|Outdoor airflow rate in L/s/PAX||5.2||3.5||1.8||1.1|
|Required outdoor air temperature||7 °C||−1 °C||−23 °C||−52 °C|
|Recirculation cooling power||n/a||n/a||4 kW||8 kW|
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Norrefeldt, V.; Mayer, F.; Herbig, B.; Ströhlein, R.; Wargocki, P.; Lei, F. Effect of Increased Cabin Recirculation Airflow Fraction on Relative Humidity, CO2 and TVOC. Aerospace 2021, 8, 15. https://doi.org/10.3390/aerospace8010015
Norrefeldt V, Mayer F, Herbig B, Ströhlein R, Wargocki P, Lei F. Effect of Increased Cabin Recirculation Airflow Fraction on Relative Humidity, CO2 and TVOC. Aerospace. 2021; 8(1):15. https://doi.org/10.3390/aerospace8010015Chicago/Turabian Style
Norrefeldt, Victor, Florian Mayer, Britta Herbig, Ria Ströhlein, Pawel Wargocki, and Fang Lei. 2021. "Effect of Increased Cabin Recirculation Airflow Fraction on Relative Humidity, CO2 and TVOC" Aerospace 8, no. 1: 15. https://doi.org/10.3390/aerospace8010015