The pandemic has highlighted, how rapidly and how effectively we are adapting to the ‘new normal’. At Godrej & Boyce, we have taken several initiatives. Keeping the well-being of its people first, Godrej initiated practices such as WFH, deep disinfection of the workspaces and stringent implementation of all Covid protocols. Amongst these, Indoor Air Quality (IAQ) was an important factor that was re-examined considering the workspaces for future.
It is known that HVAC systems can have a major effect on the transmission of infectious microscopic airborne particles and contaminated aerosol droplets. If air conditioning is not maintained properly and used as per pre-covid norms, it may lead to a further spread of infection. Considering this, a whole new approach has been devised for the existing Air Conditioning systems in the new normal.
In the absence of a readily available solution for the retrofit of Air Handling Units (AHUs), reengineering with a unique design to suit the size, space constraint and performance under increased static pressure is the key.
After extracting, examining and analysing the information on the behaviour and transmission of the virus, we came up with a solution to remodel the air-conditioning system. A McKinsey analysis pointed to filtration, irradiation, thermal heating and ionisation methodologies to improve indoor air quality (IAQ), air filtration being the most common and preferred technique, followed by irradiation. Solutions were benchmarked to control the transmission of infectious aerosols in indoor environments and retrofitting the existing central air-conditioning systems.
Improvisation in Air Filtration
The idea of filtering the air we inhale, as a protection from health risks, is not new. The filters of an air conditioning system function in the way the nose does for humans. Minute hair inside the nasal cavity helps filter the air we breathe, blocking dirt and dust particles from getting into our lungs. Similarly, the Air Handling Units (AHUs) of the central AC systems have air filters installed at their surface that restricts, or rather captures the microscopic airborne particles and contaminated aerosols.
The chart data shows that MERV 13 lowers the influenza infection risk by nearly 14% as compared to the erstwhile MERV 7 filters. The change from MERV 13 to HEPA however would barely reduce the infection risk by 4% and would need high investment. Hence, we selected MERV 13 as the suitable fine air filter for AHUs. Additionally, MERV 5 and MERV 8 filters are installed before MERV 13 so as to reduce the dust loading and to increase the life of MERV 13 filter. Three layers of filtration are thereby selected and implemented as shown in the next table.
Before retrofit of AHUs, the total pressure drop was 56 mm while after retrofit, the total pressure drop is 89 mm. The fan curve of the existing blower is referred to and the maximum pressure handled is reviewed (as shown in figures below), which proves that the existing AHU blower does not come under the surge region and can sustain and work satisfactorily in higher pressure conditions.
Sterilisation of AHU Coils with UVGI (Ultraviolet Germicidal Irradiation)
Filtration by itself cannot reduce the fungal or bacterial count. Hence, the UVGI technique was implemented along with filtration. UV light of wavelength 254nm is harmful for pathogens that potentially spread the Covid infection but it can harm humans too. Hence, UV is utilised but in a controlled environment. While it protects humans against the virus, there is control over the UV light by cutting it off when AHU is accessed.
UVC germicidal ultraviolet wavelength (254 nm) is effective in penetrating the cell membrane, breaking the DNA structure of a microorganism. DNA sterilisation inhibits reproduction.
The intensity and dosage of UVGI was selected as per the air velocity specified in ASHRAE 2012 Systems and Equipment Handbook. Microorganisms such as mold, bacteria and viruses are destroyed with the required concentrations of germicidal irradiation. Across a 15,000 cfm AHU, with 2000 x 1490 mm coil, the required intensity and wattage as per the guide is 220 µW/cm2 and 300 W and the UVGI selected has an intensity of 1915 µW/cm2 and net wattage of 300 W. The CFD profile of UVGI across the AHU coil is shown below.
The UV is thus able to cover the entire surface of the coil.
Modification of Fresh Air Supply
The pandemic has necessitated a rethink on fresh air requirements for indoors. The air-conditioning systems have been modified to infuse more fresh air into the occupied spaces. Fresh air is a natural disinfectant with rich natural oxidant properties that act as a barrier against the coronavirus and other pathogens. Further, maintenance of humidity between 40% and 70% and temperature from 24°C to 27°C helps to activate the virus killing properties in the air. The fresh air dampers are also integrated with MERV 5 filters to filter the incoming fresh air.
Improved Air Recirculation
Recirculation implies the same air passes through the system whereas ACPH (air changes per hour) is the no. of times the air moves through the same bank of filters in an hour. Lower air recirculation rates affect the filtration efficacy, hence the system is reconfigured to ensure 10-12-10 ACPH (recirculation) rates, to improve filtration.
Robotic Cleaning of Air Distribution System
Air ducts are defined as structures for distribution of fresh and hygienic air. Air-conditioning ducts are the most contaminated parts of the central AC system. As per the latest research conducted by health associations, unclean air ducts can seriously affect occupants’ health. Cleaning them on a regular basis is a critical step in the direction of improving health, wellness and safety of the occupants. Consequently, besides improving air quality of indoor spaces, a cleaned air duct system runs more efficiently than a dirty one, resulting in lower utility bills.
Robotic cleaning of air duct helps in eliminating the particulate contaminants that may act as potential carriers of the virus. Hence, it is carried out to maintain healthy indoor environment and enhance the life of fine filters (MERV 13).
The operational practices and cleaning methodologies and its frequency for the AHU coils & filters were also relooked at to further restrict microbial growth. Further, a provision of double doors at the AHU room entrance helped reduce the particle concentration.
Using a scientific approach, a decision to appoint an accredited (ISO/IEC 17025) laboratory professional for pre and post measurement of outcomes was taken. The results have been extremely encouraging ensuring our readiness for the ‘new normal’. There is a drastic reduction of 84% and 90% in fine particles and microbes (at rest condition) respectively, which are responsible for transmission or spread of virus through air conditioning.
The retrofit results are summarised in the tables, and we have now achieved ISO 14644-1 Class 8 environment.
Provision of clean air is acting as a shield in the fight against the virus.
Take a breath of fresh air and stay safe and healthy.
Mukesh Suthar is a mechanical engineer with over a decade of corporate experience across diverse industries including manufacturing, engineering, projects and process cooling. He joined Godrej & Boyce Mfg Co Ltd in January 2015 and handles the utility operations and projects.