Retrofit of Airconditioning to improve Indoor air quality for Safety and Efficiency


RAISE Programme


EESL has undertaken a retrofit of its office air-conditioning and ventilation system to address concerns about
poor air quality and the risk of airborne transmission of COVID-19. This is a part of a larger initiative to “Retrofit of Air-conditioning to improve Indoor air quality for Safety and Efficiency” developed for healthy and energy efficient buildings in partnership with U.S. Agency for International Development’s (USAID) MAITREE program

The retrofits focuses on enhanced indoor air quality (IAQ), thermal comfort, and energy efficiency (EE) in the air conditioning system. The building is predominantly served by a central air conditioning system with additional split ACs in some areas. The key measures taken as a part of the pilot are as follows:

1. Increased ventilation for dilution and lower CO2 levels

a. Fresh air system to retrofitted for increased outside air

b. Automation for demand-controlled ventilation and economizer operation

c. Treated fresh air unit to be installed to offset the additional cooling load

2. Filtration to minimize particulate matter, pollutants, and pathogens

a. High efficiency electrostatic filters installed in the air handling units (AHU)

b. Ultraviolet Germicidal Irradiation in the AHU

c. Portable air purifiers for spot application in small enclosed offices

d. Ceiling mounted ESP and HEPA filtration units for conference rooms

3. Monitoring and display of IAQ and comfort parameters

a. Install high-quality reset certified monitors on all floors

b. Online dashboard and display screen to be installed on every floor after the lift lobby

c. Comprehensive IAQ testing

The retrofit started with the installation of a network of state-of-the-art air quality monitoring system in the first week of June. The main filtration system was installed by the 6th of June, and the rest of the installation is in progress.

The results of the retrofits have been encouraging. The air quality in the offices has dramatically improved with over 90-95% reduction in pollutants and constantly maintaining healthy indoor environment. Along with proactive measures to clean and disinfect surfaces, maintaining social distancing and wearing masks, communicating the improved air quality in the office to the employees has also allayed their anxiety about COVID spread, and returning to the office.

The graphs and figures below are taken from the real-time air quality monitoring system, and show the impact of the retrofit so far. This will only improve further as the remaining measures are implemented.


Poor air quality has been a concern in India for quite some time and has become even more important in light of the COVID pandemic. It is now well established that poor indoor air quality in buildings causes health problems and general discomfort for occupants. As people return to their offices and public spaces,
maintaining good indoor air quality is essential for occupant comfort, well-being, productivity and the overall public health.

The concentration of pollutants like volatile organic compounds (VOCs), combustion byproducts, and airborne particulate matter inside the buildings can lead to problems like headaches, allergies, asthma, and other respiratory conditions2. Issues like poor temperature control and air flow effect comfort and general health of the occupants. New buildings need to factor these in at the design stage. Most existing buildings in India are not equipped to establish and maintain healthy indoor air quality and need to be upgraded. Such retrofit measures, like increasing outside air and additional filtration in the air conditioning system, typically come at the cost of occupant comfort and increased energy use.

Breathing quality, fresh, and clean air indoors is essential for good health and productivity. For example, a recent study on decision-making performance concluded that for seven of the nine scales (basic activity, applied activity, task orientation, initiative, information usage, breadth of approach, and basic strategy), the
higher the CO2 concentration in the air, the worse people performed in these activities


To address these concerns about indoor air quality and energy efficiency, EESL, in partnership with U.S. Agency for International Development’s (USAID) MAITREE program, has developed the “Healthy and Energy Efficient Building”.

EESL corporate office in Scope Complex has been taken up as a pilot for this approach. These retrofits will focus on enhanced indoor air quality (IAQ), thermal comfort, and energy efficiency (EE) in the air conditioning system

Currently, there are no standardized approaches to retrofitting. The EESL office pilot will address this problem by developing specifications for future use in other buildings throughout the country, as well as aid in evaluating the effectiveness and cost benefits of various technologies and their short and long-term impacts
on air quality, comfort, and energy use. The key measures implemented in the EESL office building retrofit are described below.


The ventilation system will take into account the building’s occupancy, design, and use in order to turn air over at a rate that dilutes the air and prevents the buildup of indoor pollution and pathogens.


State of the art filters in the HVAC system to trap pollution coming from indoor sources and also to remove

pollutants from outdoor air sources before they reach the building’s occupants.

b. Electrostatic filtration for central AHUs with low pressure drop

c. Standalone ceiling mounted and portable air filters for high density spaces


Sensors to provide insight into the air quality inside the building. Measuring particle counts, carbon dioxide concentration and volatile organic compounds will help make sure good air quality, and communicate it to the occupants in real time.

d. Install high-quality, certified and calibrated monitors in the breathing zone

e. Ambient air monitoring for reference

f. Online dashboard and display screen to be installed on every floor after the lift lobby

g. Comprehensive IAQ testing done periodically for particulate matter, organic, and inorganic

pollutants. The pollutants to be tested are specified in the Annexure


The air handing unit and the chilled water system to be upgraded to enhance energy efficiency as well as cooling performance. Selection of filtration technology to ensure that the cooling and energy performance of the air conditioning system is enhanced. The filter pressure drop to be as low as possible while maintaining the desired filtration efficiency