Webinar on “How to use Air-Conditioners in COVID – 19 Times”

Indian Buildings Congress (IBC)  in association with ISHRAE  held the webinar  on 29th April, 2020 on the topic “How to use Air-Conditioners in COVID – 19 Times”. Eminent speakers/ experts delivered their technical lecture.

Shri M.P.Aggarwal, in his initiating note informed that COVID-19 pandemic has adversely impacted the lives of millions of people across globe and highlighted the importance of precautions to be taken in use of air conditioners in conditioning the indoor air quality.

Shri Pradeep Mittal, President in his welcome speech  welcomed Shri Anant Kumar, Additional DG, CPWD; Shri Richie Mittal, National President, ISHRAE; Shri Vishal Kapur, Chief, Technical Committee, ISHRAE; Shri Gautam Baliga, Chair, Technical Group, Healthcare, ISHRAE; Shri C.K.Varma, Chief Engineer, CPWD; Shri O.P.Goel, Founder President, IBC; participating EC and GC Members of IBC, and all other participants. He briefed the viewers about the history, vision, role and activities of IBC in Built Environment. While informing the prevalent circumstances as to how India along with most of the countries of the world is facing the adverse effects of Covid-19-Corona virus where millions of lives are suffering from this disease, he expressed the necessity of the webinar in knowledge sharing on protection measures to minimize the risk of COVID 19 infection in the indoor environment.

Since the topic selected for webinar was very much relevant to the present day demand in COVID-19 circumstances, there was overwhelming response of the participants.

Shri Anant Kumar, Additional DG, CPWD, gave the introduction of the expert panelist/ speakers who spoke and made their presentation on the topic.

Shri Vishal Kapoor, Chief, Technical Committee, ISHRAE, while expressing relevancy of the topic of webinar  in line with the vision of IBC on Built Environment informed about the role and activities of ISHRAE. It was informed by him that ISHRAE has already issued “COVID 19 Guidance Document for Air conditioning and Ventilation”. While informing the different transmission routes from corona virus infected person through direct contact and indirect transmission, he made his presentation on the indoor environment requirements. Most of large cough and sneezing droplets from patients infected by this disease, falls on nearby surfaces and objects, where people can get infected by touching those infected surfaces or objects.

Much smaller infected particles released during coughing and sneezing stay airborne for hours and travel over larger distances which may also aid in spread of the disease. He mentioned there is no such reported data or studies to rule out the possibility of the air borne particles route in spread of this disease. Infectious disease can spread by several routes including transmission through air. Small particles (less than 5 microns) released during cough/sneeze stay airborne for hours and can be transported over long distances. Small droplet nuclei or residue are formed from droplets usually within milliseconds) in the air, which shrink in size due to the process of evaporation and desiccation in low humidity. These smaller particles in air can travel with dust particles, shoes and clothes etc.

Another path for transmission is when virus-laden aerosols are deposited on apparel and on the floor through shoes and then get re-suspended into the air due to the movement of people. That is why sanitizing the floors frequently and limiting the movement of people is helpful in curtailing this route of transmission. In healthcare facilities sanitization of apparel is recommended.

Mechanical ventilation –HVAC can reduce the airborne concentration of the virus and thus reduce the risk of transmission through air. He informed the importance of range of indoor environment temperature and humidity so as to make the virus ineffective. He mentioned that with relative humidity band of 40-70%, indoor temperature of 24 degree centigrade for humid climate and 30 degree for drier climate regions like Delhi was optimum to reduce the risk of this virus.

For Residential units using air conditioners, it was advised that recirculation of cool air by room Air conditioners, must be accompanied by outdoor air intake through slightly open windows and exhaust by natural ex filtration. Fresh Air intake through a fan filter unit will prevent outdoor dust entry (containing high levels of PM 10 and PM 2.5 particles) and exhaust through kitchen and toilet exhaust fans kept operational.


Horizontal-flow Evaporative Coolers installed in windows can effectively cool a room or a section of a room. Windows must be kept open to release humid air. Portable evaporative coolers that do not draw outdoor air are not recommended, since their cooling reduces with humidity rising inside the space. Evaporative coolers must draw air from outside to ensure good ventilation.


Fans should be operated with windows kept partly open. If an exhaust fan is located at a nearby location then it must be kept running to exhaust air for better ventilation.


The best action to limit risk of COVID-19 infection by air is to ventilate indoor environments with outdoor air as much as possible. Mechanical ventilation systems and air conditioning systems, which provide ventilation, can perform this function more effectively than simply opening the windows, because they improve the quality of the outdoor air with filtration.


He informed key operating guidelines for all categories of ACs which included for keeping the AC filters always clean, providing adequate ventilation and allowing fresh air entry inside through fresh air fans. Inspecting and cleaning the indoor unit coils, Mool mantra is replacement of inside air with fresh air continuously preferably by keeping negative pressure inside. Keeping heat recovery wheel on off mode to reduce cross contamination, keeping toilet and kitchen exhaust fans in operating mode,

In buildings without mechanical ventilation systems it is recommended to actively use open able 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.

Shri Gautam Baliga, Chair, Technical Group, Healthcare, ISHRAE, made presentation on healthcare issues. As hospitals are the first line of defense in this pandemic situation, he suggested to change the existing rooms into non-circulatory system isolation rooms for COVID 9 Patients to meet the huge requirement of isolation rooms/ spaces.

On an emergency basis, this Non-circulation can be achieved by blocking off the return air vents in the COVID-19 patient room.

He stressed to make sure that the AHU has the provision to receive adequate outdoor air supply. The outdoor air source for the AHU shall not be from within the building and all care shall be taken to avoid intake of outdoor contaminants, to the best possible extent. Additionally, an independent exhaust blower shall be provided to extract the room air and exhaust out into the atmosphere, preferably, after suitable “exhaust air treatment”. The exhaust air quantity shall be greater than the supply air quantity such that a negative pressure of minimum 2.5Pa (preferably >5 Pa) is achieved in the room. It is advisable to install differential pressure meters to measure this metric. The supply air quantity shall be such that it will provide a minimum of 12 air changes per hour. The position of the extract air in the room shall be just above the head of the patient’s bed.

The exhaust air is most likely to contain particles carrying a viral load and hence a suitable technique should be deployed to prevent the spread of infections. Treatment of exhaust air can be done preferably by HEPA filtration which is the best method.  HEPA filters shall be tested and certified for performance in accordance to international standards and shall be of minimum of H13 (EN1822-1) filter class or equivalent. When HEPA Filtration is not possible, treatment of exhaust air by Chemical disinfection is acceptable. When both the methods are not viable, the exhaust air shall be let off into the atmosphere through an upward plume at a height of 3 m above the tallest point of the building, thereby lowering the viral load concentrations to insignificant levels by dilution. This exhaust discharge shall be well away from other air intake points and populated places.

The other two options available for exhaust air treatment are UV irradiation and heating.

Since the exhaust systems could have viral load deposits, some of which may be active, therefore, Suitable personal and environmental protection protocols shall be followed during any maintenance activity on the exhaust system, for personnel protection and to avoid environmental spill.

To avoid the  significant risk to the health care workers as well as a possibility for environmental spread of virus laden particles in keeping many COVID 19 patients together in a single room, he suggested, make-shift individual patient isolation enclosures to provide the necessary protection. This could be a temporary makeshift cubicle or tent constructed out of a skeleton structure (of plastic or metal) and plastic sheet or canvas covering. The tent shall be covered on all sides excepting the front, where PVC strip curtains can be provided. Arrangements for light and a fan inside the tent can be provided for the comfort of the patient, as necessary. The tent shall be provided with an exhaust blower to extract the air inside the enclosure and exhaust out into the atmosphere after suitable treatment.

For those who are not yet ill, but have been exposed to COVID-19 and have potential to become ill, quarantine/ separation of individuals is necessary. A quarantine centre shall be well ventilated and preferably be maintained at a negative or neutral differential pressure.

He also informed of the necessary guidelines as how to start offices and public facilities/ commercial establishments before opening to public use after lifting the lockdown  alongwith safety guidelines for the technicians  to follow necessary protocols.

Most Commercial establishments have remained closed during the lockdown. These establishments will need maintenance for both Engineering and Health safety. The air-conditioned spaces of establishments under prolonged lockdown will pose health hazards due to fungus and molds in the ducts and open spaces depending on the humidity and temperature prevailing within. Further there may be bird droppings, and excreta of rodents as well increased level of insects. Therefore, before opening the commercial facility to public use and staff, the user or the owner should get the area sanitized, study the fresh air and exhaust system adequacy as per the guidelines and inform the user to modify the system if found inadequate. Carry the preventive maintenance on all the units as per manufacturer’s guidelines including disinfecting and cleaning of all the filters, grills, diffusers, internal surfaces, condensate drain pans and coils etc., besides other precautions for making the existing indoor environment neat and clean.

Few question of the participants were also answered by Shri Vishal Kapur

Before the session was summed up, Shri Pradeep Mittal, President, IBC expressed his satisfaction and appreciated the speakers for their useful suggestion to remove the doubts from the mind of participants about use of air conditioners by following the necessary precautions/ guidelines explained. He also made a call to all the participants to become members of IBC if they have not yet enrolled themselves.

Shri C.K.Varma, Chief Engineer, CPWD while summing up the session, expressed that it was a very exhaustive but short session where viewership was maximum. The people are very much concerned about the use of ACs and coolers in this situation and many of their doubts have been removed. He expressed his hope that this session has addressed maximum concerns of the viewers. Those questions of viewers which could not be answered due to paucity of time have been forwarded to ISHRAE for resolution. He also expressed his profound thanks to Shri Anant Kumar, Additional DG, CPWD and Shri Pradeep Mittal, President, IBC for their initiative in organizing this seminar.