Does HVAC/ Air-conditioning spread Covid19?

Published on Jun 13, 2020

Since the spread of the novel Coronavirus, panic has spread among all of us on the usage of Air-conditioning. The most common questions circulating have been: Can we use it at our homes? Can we use it in our stores, shops and offices? What should be the settings? What are the regulations?

We are addressing some of these concerns in this blog.

Where it all started?

There was an outbreak of COVID-19 reported in a restaurant based in Guangzhou, China in the first week of February 2020. The infected persons had their lunch on January 24. The below pic is the seating arrangement of the restaurant, with the infected people highlighted at the tables TA, TB, TC. The family TA travelled from Wuhan with index patient A1. The TB & TC families were sitting on either side as shown in the picture below. Subsequently, three members of Family A, three members of Family B and two members of Family C were infected with SARS-CoV-2.

The seating arrangement of the restaurant. Source: Centre for Disease Control & Prevention

Scientists studied this arrangement and simulated the situation to know what caused the spread of droplets from the Index patient.

Since none of the waiters or 68 patrons at the remaining 15 tables became infected, the study was concentrated on simulating the distance, time spent, airflow and ventilation around these 3 families in the restaurants.

The families spent nearly 1 hour seated beside each other. The reason for other families and staff not getting affected has been attributed to the minimal time spent around this Index patient (purple).

Owing to the Chinese New Year, the restaurant was crowded and extra tables were added. The study also said “The measured average air flows of 1.04 L/s and 0.75 L/s per patron in the non-ABC and ABC zones respectively. These rates are considerably lower than the 8–10 L/s per person as per ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers). Further evidence comes from the low ventilation rates: the observed high concentrations of the simulated contamination result from the lack of outdoor air supply. The exhaust fans in the walls were found to be turned off and sealed during the January 24 lunch, meaning that there was no outdoor air supply aside from infiltration and infrequent and brief opening of the fire door due to the negative pressure generated by the exhaust fan in the restroom. This outdoor air was mainly distributed to the non-ABC zone, thus exacerbating the ventilation deficit of the ABC zone.”

The scientists concluded the article by saying “The transmission of SARS-CoV-2, which subsequently resulted in an outbreak of COVID-19, thus occurred in a crowded and poorly ventilated space.

So far, so-called airborne transmission by some sort of air conditioning unit really has been reported only once and I think is likely to be a very odd event,” said Dr.William Schaffner, an infectious disease expert from Vanderbilt University Medical Center in Tennessee.

“People have been going to pharmacies and grocery stores and liquor stores and other venues for some time now. We’ve had no reports here in the United States of infection related to a single source that could be attributed to air conditioning,” Schaffner told Healthline.

“What will be important for restaurants is that the wait staff wear masks and attend to good hand hygiene,” Schaffner said. “And that they disinfect surfaces between patrons.”

Dr.Amesh Adalja at John Hopkins University Center for Health Security said: “But I do think that as we open restaurants and places where air conditioning is going to be running, they are going to have to think about what their airflow is like.” Adalja added, “They’re likely going to have to modify the way their seating is done to make it less crowded, to encourage social distancing, and hopefully that would eliminate these kinds of things from happening.”

REHVA, the European Federation of HVAC Associations, has advised that humidification, air conditioning and duct cleaning has no practical effect on the transmission of the coronavirus.

What are the rules in India?

Residential Applications:

Set Room Temperature between 24°C and 30°C. Maintain a relative humidity between 40% and 70%. (In humid climates set temperature closer to 24°C for de-humidification and in dry climates close to or at 30°C and use fans to increase air movement).
In dry climates, do not allow Relative Humidity to fall below 40%. Water evaporating from a pan kept in the room will increase humidity if it falls below 40%.

Commercial or Industrial Applications:

For the purpose of Guidance for operation during a Pandemic like COVID-19, Air Conditioning is categorized based on the types of Indoor Units installed:

i) Multiple Cassette Units: Ceiling-mounted units that can each cool up to 50sq.m and can be controlled individually or as a group.
ii) Multiple Hi-Wall Units: Used due to ease of installation and low cost.
iii) Tower Units: For larger spaces, where most occupants are not stationary thus allowing for higher drafts.
iv) Ducted Units: A mini central Air conditioning system that is easy to operate.
v) Fan Coil Units: Installed in guest rooms, individual office spaces or patient wards.
vi) Air Handling Units: Can provide better ventilation, filtration and Coil disinfecting.

Operating Guidelines:

A) Air Filters & coils must be kept clean

a.Filters, grilles, diffusers & internal surfaces: it is recommended to use 5% Cresol solution (containing 50% Cresol and 50% Liquid soap solution). Mix 1 litre of this solution in 9 litres of water. The surface shall be sprayed with this solution, left for 10 minutes and then washed/wiped clean with water/cloth. (the above methodology is only for washable filters)
b. Condensate drain pan: Disinfecting/treatment of condensate drain pan is suggested using UV treatment or 1% sodium hypochlorite dosing. This will apply only if the HVAC equipment is working on a re-circulatory mode.
c. Coils: Follow standard recommendations of coil cleaning and then sanitize using the same protocol as that of the filters specified above

B) Provide adequate Ventilation ( Fresh Air and Exhaust ).

C) Set Room Temperature between 24°C and 30°C. Maintain a relative humidity between 40% and 70%.
(In humid Climates set temperature closer to 24°C for de-humidification and in Dry Climates closer to or at 30°C, use Fans to increase air movement)

D) Heat Recovery Wheel (HRW): It is advisable to keep this wheel in off mode to reduce cross-contamination. Upon restarting, the wheel must first be sanitized.

E) Toilet and Kitchen Exhaust Fans must be kept in operating mode.

Recommendations suggested by ISHRAE:

In case you want to take further steps which will make your place feel much safer, here are the recommendations by ISHRAE:

For Categories i), ii), iii):

If fresh air is not provided, it is advisable to introduce a fresh air duct attached to a central inline fan filter unit and distribute the fresh air by grilles into space or near the indoor units. For Cassette Units the fresh air duct may be connected to the available port of the Cassette Unit. In case fresh air cannot be provided through a fan it is recommended to actively use operable windows. A separate Treated Fresh Air DX Unit may be provided in the case of multiple-unit installation. This will reduce the impact of reducing available cooling capacity by supplying non-treated fresh air.

For Categories iv, v, vi:

Fresh air must be provided by an inlet duct and fan. It is advisable to provide a MERV 13 or higher filter fitted on the Air Handling Unit. If a filter of higher filtering capability is retrofitted into an existing system, care shall be taken to ensure that the fan and motor capacities are adequate to handle the higher pressure drop.


In buildings without mechanical ventilation systems, it is recommended to actively use operable windows. Add a TFA(treated fresh air) unit if recommended Fresh Air intake impacts cooling performance. Install UVGI(Ultraviolet germicidal irradiation) for larger Ducted Units and AHUs to keep Coils continuously clean and disinfected. It is advisable to inspect the AHUs and ducts for Air-tightness and low leakage.

Written by Zodhya

About Zodhya

We are Zodhya, a start-up that provides AI-based tech to reduce energy bills and lower emissions for commercial buildings and industries.