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Air conditioners, airborne infection prevention and air pollution in buildings in New Delhi

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R. Singh,  A. Dewan

Dear Editor,

The focus on airborne spread of SARS CoV-2 started even before WHO declared it to be through airborne mode of transmission.1 A critical method of airborne infection control for both TB and COVID-19 is dilution ventilation.2,3 This means the flushing out of aerosolised droplets of exhaled breath or cough or sneeze that would otherwise linger in the interior air of built spaces. Air conditioners, such as split air conditioners,4 simply recirculate the indoor air, thereby increasing the duration and concentration of pathogen-containing aerosols when an infected person is present. The proposed solution is to use operable windows and doors to allow outdoor air to enter and replace the indoor air.5,6 This process of dilution can happen through diffusion (when windows are open) or be accelerated using mechanical ventilation methods such as exhaust fans and air handling units with fresh air dampers. However, open windows have disadvantages with regard to thermal comfort, increase in noise, entry of insects (when used without wire meshes) and entry of ambient pollutants. This last problem, especially the entry of suspended particulate matter, leads to a double paradox for most urban dwellers. In India, New Delhi has a severe air quality crisis due to the presence of high concentrations of particulate matter of 2.5 μm diameter (PM2.5) in the ambient air.7 The inhalation of PM2.5, when present at high concentrations, is a cause of lung diseases.8 Opening windows for dilution ventilation to occur is therefore a choice between preventing the spread of airborne infections and the possible risk of lung damage due to high levels of PM2.5. There is therefore a reliance on mechanical ventilation, as it ensures thermal comfort in New Delhi’s climate and is also perceived to act as an air filter, making the supplied air free from PM2.5. Heating, ventilation and air conditioning (HVAC) systems also have the advantage of being able to integrate ultraviolet (UV) germicidal irradiation or UVGI systems for sterilisation,9 as well as carbon dioxide monitoring for ventilation feedback. Conversely, HVAC systems may cause harm in cases where (due to energy efficiency constraints) there is recirculation of indoor air.10 The HVAC system may also lack appropriate filters capable of separating a significant portion of PM2.5 in the supplied ambient air.

To appraise the airborne control features of air conditioners, a series of applications were filed under the Right to Information Act, 2005,11 for various important buildings in India. These buildings include the Indian Parliament, the Supreme Court of India, the venue for the G20 intergovernmental forum meeting in 2023,12 the Assembly Hall of Delhi, the Rashtrapati Bhawan (President’s House) and other such buildings. These buildings should set the tone and serve as role models for other buildings in the country. The aim was to discover the current level of air conditioning and airborne infection control measures in these buildings. We also assessed the filtration capacity of fresh air intake by HVAC systems.

Of all the buildings studied, the Indian International Convention and Expo Centre, the building likely to host the G20 in 2023, had exceptional results (Table). All other symbolically important buildings lacked adequate HVAC systems. For example, the Assembly Chamber in the Parliament building did not have UVGI installed in the HVAC. Fresh air accounted for a maximum of only 10% of the total supply. The Darbar Hall and the Ashoka Hall in the Rashtrapati Bhawan did have 100% fresh air provision, but only had filters capable of filtering particles with a diameter of 10 μm, not 2.5 μm. The Chanakya Hall in the Hotel Samrat (used for important government functions) had a provision for 79.89 cubic feet per minute (CFM) of fresh air per person, but was only using 50 μm filters. These buildings are at the heart of the Indian Government and the health of users of these buildings affects that of the entire country. The use of the Right to Information Act, 2005, is also worth noting, as it is an indispensable tool for researchers to obtain information from government departments in a timely manner, bypassing bureaucracy and making data available transparently.13

This study highlights the importance of appropriate HVAC systems in public buildings, as these play a key role in preventing the spread of airborne diseases, as well as other particulate matter. We suggest that there should be information about the HVAC system at the entrance to every building to increase awareness among visitors. The current focus on ventilation due to COVID-19 could benefit the global fight against TB, as the mode of transmission is similar for both and adoption of HVAC systems is a priority in many settings. Our observations in India may also be true for urban buildings in other countries, which are dealing with a similar air pollution crisis and require dilution ventilation.



1       World Health Organisation. Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations: Scientific Brief. WHO/2019-nCoV/Sci_Brief/Transmission_modes/2020.2. Geneva, Switzerland: WHO, 2020. Accessed December 2021.

2       World Health Organisation. Practical guidelines for infection control in health care facilities practical guidelines for infection control in health care facilities. Geneva, Switzerland: WHO, 2004: p 110.

3       Escombe AR, et al. Natural ventilation for the prevention of airborne contagion. PLoS Med 2007; 4(2): 309–317.

4       Singh R, Dewan A. Rethinking use of individual room air-conditioners in view of COVID 19. Creat Space 2020; 8(1): 15–20.

5       Central Public Works Department, Government of India. Guidelines for running of air circulation, air cooling and air conditioning equipment during COVID-19. CE CSQ(E)/COVID-19/2020/028. New Delhi, India: Government of India, 2020: pp 1–4. Accessed December 2021.

6       Indian Society of Heating, Refrigeration and Air Conditioning Engineers. COVID-19 guidance document for air conditioning and ventilation. New Delhi, India: ISHRAE, 2020. Accessed December 2021.

7       Rizwan S, Nongkynrih B, Gupta S K. Air pollution in Delhi: its magnitude and effects on health. Indian J Community Med 2013; 38(1): 4–8.

8       Xing Y-F, et al. The impact of PM2.5 on the human respiratory system. J Thorac Dis 2016; 8(1): E69–E74.

9       Escombe AR, et al. Upper-room ultraviolet light and negative air ionization to prevent tuberculosis transmission. PLoS Med 2009; 6(3): 312–323.

10     Hobday RA, Dancer SJ. Roles of sunlight and natural ventilation for controlling infection: historical and current perspectives. J Hosp Infect 2013; 84(4): 271–282.

11     Republic of India. The Right to Information Act, 2005; No. 22 of 2005. New Delhi, India: pp 1–23.

12     Wikipedia. List of G20 summits. Accessed December 2021.

13     Singh R. RTI for research: using the Right to Information Act, 2005 for research in India. New Delhi, India, 2020: pp 1–60.

14     Comparative guide to norms for the classification of air filters: Venfilter Air filters and industrial ventilation. Accessed November 2021

15     Bureau of Indian Standards. SP-7: National Building Code, 2016. New Delhi, India: BIS, 2016.

Read the PDF for more information, including the Figures and Tables