Modelling Accumulation of Respiratory-CO 2 in Closed Rooms Leading to Decision-Making on Room Occupancy
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ORIGINAL PAPER
Modelling Accumulation of Respiratory-CO2 in Closed Rooms Leading to Decision-Making on Room Occupancy D. Majumdar1*
and S. Chatterjee2
1
Kolkata Zonal Centre, CSIR-National Environmental Engineering Research Institute, i-8, Sector C, EKDP, EM Bypass, Kolkata 700107, India 2
Rabindra Bharati University, 56A, Barrackpore Trunk Road, Kolkata 700050, India Received: 07 January 2020 / Accepted: 18 April 2020 Metrology Society of India 2020
Abstract: A model predicting time required to attain undesired levels of respiratory-CO2 in closed rooms is described. The model works under the following assumptions: (1) room air is well-mixed, (2) indoor CO2 does not exchange with outdoor CO2, (3) there is no effect of individual occupants on CO2 exhalation rate of other occupants, (4) there is no indoor CO2 sink and all exhaled CO2 end up increasing CO2 concentration in the room, (5) apart from respiration, there is no other source of indoor CO2, (6) breathing rates of occupants are constant throughout the period of occupation of room. The model makes use of anthropocentric parameters like body weight, height, du bois surface area, MET levels, etc., to calculate dedicated individual CO2 exhalation rate and uses room volume and number of occupants to predict time required to reach user-earmarked levels of CO2. A model run showed that in a closed room of 12 9 12 9 10 m3, respiration by one person at rest (65 kg body weight, 1.7 m height, basal respiratory quotient of 0.83) would take 4.37 h to reach 2000 ppmV indoor CO2 when background indoor CO2 level was 380 ppmV. This model would help allocating desired number of occupants in closed rooms to help avoid building up of undesirable levels of CO2 in poorly ventilated offices, schools, hospitals or households that might frequently experience high levels of indoor CO2, undermining health and performance of occupants, patients and workers. Keywords: Activity level; Air quality; Du-Bois surface area; Exhalation; Indoor air; Occupational health 1. Introduction Indoor CO2 concentration can range from an equivalent level of background outdoor concentration (about 400 ppmV) to many thousands of ppmV, depending on the prevailing CO2 generating activity indoors [1]. In the absence of a combustion source, indoor CO2 build-up from human respiration relates to room occupancy, body height, weight, activity level and metabolic rate of occupants [2]. Erickson et al. [3] defined ‘occupancy’ as total number of people present in a defined part of a building. Occupancy measurements have been done through direct techniques like use of camera, passive IR sensors, ultrasonic sensors, motion detection sensors, CO2 sensors etc. [4]. Human respiration itself could lead to attainment of 3000 ppmV CO2 in indoor areas and indoor appliances like kerosene
stoves, cooking gases, etc., could aggravate it further (National Collaborating Centre for Environmental Health, http://www.ncceh.ca/documents/practice-scenario/carbondioxide-indoor-air). Other crucial factors influencing CO2 accumulation
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