Disease Resilient and Covid Safe Existing Air Conditioned Buildings

IAQ standards are useful but must now respond to an unusual situation like the COVID-19 pandemic. In the absence of specific knowledge to meet this challenge of air-borne infection, it is essential to depend on the old faithful “dilution Ventilation” to reduce the pathogen load in the occupied spaces.

Present ventilation standard is designed to dilute the concentration of pollutants like Biological Pollutants, Carbon Monoxide (CO), Formaldehyde/Pressed Wood Products, Lead (Pb), Nitrogen Dioxide (NO2), Pesticides, Radon (Rn), Asbestos, Indoor Particulate Matter Secondhand Smoke/ Environmental Tobacco Smoke and Volatile Organic Compounds (VOCs)

ASHRAE Standard 62, and its subsequent incarnations as Standard 62.1 (commercial, institutional, and high-rise residential) and Standard 62.2 (low-rise residential), has served as the most prominent ventilation standards since it was first published in 1973.

In those days, It was a table with ventilation rates for nearly 300 individual space use types. A large number of space use types and the ability to arrive at ventilation rates for each space type were quite simple and impressive, but the justification for those values was not documented.

For commercial office spaces, the 1973 standard had a minimum requirement of 7.5 L/s (15 CFM) per person, the recommendation was 7.5 L/s(15CFM) to 12.5 L/s(25 CFM) per person. Classrooms had a minimum requirement of 5 L/s (10CFM)per person and a recommendation for 5 L/s (10CFM) to 7.5 L/s (15CFM) per person.

Ventilation rate requirements for different space types have been revisited in subsequent versions of Standard 62 since it was originally published in 1973. The determination of these values has always been challenging based on limited research results to support specific values.

There have been pressures by some to lower the ventilation rates based on operating cost considerations and pressures by others to raise them based on IAQ benefits.

The development of ventilation and IAQ standards has progressed significantly since the first ventilation standard was issued almost 50 years ago, but more work is required to make the standards more successful in supporting safer indoor environments in existing air-conditioned buildings.

For instance, Covid-19 has introduced airborne infections as an additional indoor pollutant which is airborne. This would involve reviewing the ventilation standard with new enhanced control protocols to monitor the quantity and type of airborne contamination.

Post-Pandemic IAQ guidelines will have more of an impact if they address infection control in existing buildings by recommending the retrofits

Normally, only healthcare buildings have airborne infection control and even that is often compromised and results in a high risk of Hospital Acquired Infections (HAI), especially in developing countries.

Presently, no sensors capable of tracking viruses directly are known to exist however there is a possibility that real-time monitoring of transmission risk based on some proxies similar to Co2 may be possible. We need to recognize the urgent demand of the building owners and operators who are striving to give the occupants confidence in returning to the workplace safely. Commercial, as well as all kinds of other air-conditioned public buildings, will be safe to reoccupy only when we can reduce the Virus loads in these spaces.

Bringing in more than the mandated amount of fresh air into the facility is one such solution being considered by all professional HVAC organizations.

The only argument against this solution is that the make-up air units increase the operating costs of the HVAC system.

Patented Dual Path Technology (based on SSLC technique with condensate energy recovery) addresses this issue excellently well to mitigate the pathogen dilution problem without impacting the operational costs of the existing HVAC systems significantly.

Marginal additional capital investment in these advanced energy-efficient retrofits by each building will save the society from incurring colossal economic costs and human misery.