Use of Partial Recirculation to Limit Build-Up of Cabin Carbon Dioxide Concentrations to Safe Limits per ASHRAE Standard-62 2020-01-1245
Carbon dioxide exhaled by occupants remains within the cabin during operation of HVAC unit in recirculation mode. The CO2 inhaled by the occupants goes into their blood stream that negatively affects occupant’s health. ASHRAE Standard-621 specifies the safe levels of carbon dioxide in conditioned space for humans. The CO2 concentration limit per ASHRAE is 700 ppm over ambient conditions on a continuous basis.
ASHRAE Standard-62 has an additional requirement for maintaining good air quality within the ambient condition. Per this requirement, we need to introduce a min of 15 cfm/person in the conditioned space to maintain good air quality. Even though this requirement is primarily for elimination the body odors, the author has investigated if this airflow requirement is also sufficient to maintain cabin CO2 concentrations as stated above.
The author2 has conducted experimental studies by conducting tests on a vehicle to see if ASHRAE’s additional requirements to maintain good air quality is also sufficient to maintain cabin CO2 concentrations below ASHRAE Standard-62. Detailed results will be presented in the paper.
1. ASHRAE/ANSI, Standard 62-1999, Ventilation for acceptable indoor air quality, American Society of Heating Refrigerating and Air Conditioning Engineers., Inc., Atlanta, GA, 1999.
2. Mathur, G.D. 2019. Influence of partial recirculation on the build-up of cabin carbon dioxide concentrations, SAE Paper # 2019-01-0908.