Is it Possible? Is it Expensive? Is it Worth it? Cost & Feasibility of ASHRAE 241 — Part 9
How difficult is it to provide the high equivalent clean airflow rates required in ASHRAE 241? How much will this cost businesses? Most importantly, is it even worth it?
ASHRAE 241 provides the airflow rates and methodology necessary to control infectious aerosols. Now that the standard has been created, questions about feasibility and benefit have emerged. This post will explain whether implementation is feasible, its potential costs, and the benefit from implementing this standard.
Feasibility
Acceptable Indoor Air Quality
ASHRAE 241 is designed to control infectious aerosols, not provide general acceptable indoor air quality. Other standards are designed to do that, most prominently ASHRAE 62.1.
The most difficult part of complying with ASHRAE 241 would likely be the first requirement:
4.1.1 The building shall meet the requirements of the applicable version of ANSI/ASHRAE Standard 62.1…[or any other applicable indoor air quality standard].
ASHRAE 62.1 has certain outdoor air ventilation requirements. Providing sufficient outdoor air to a space can be challenging and requires the proper equipment, structural, electrical and heating capacity. However, it states explicitly in ASHRAE 62.1:
1.3 This standard is intended to be used to guide the improvement of IAQ in existing buildings.
Standards for indoor air quality are designed to be used in existing buildings.
Speaking from experience, there are many existing buildings that were not designed for mechanical ventilation, which I have worked on and brought into compliance with ASHRAE 62.1. It can be difficult, but not impossible. Indoor air quality standards are not designed to provide control of infectious aerosols, but are designed to mitigate other air pollutants, including body odours, volatile organic compounds and particulate matter. Buildings that are not in compliance with IAQ standards are not acceptable for human occupancy and should be fixed.
Equivalent Clean Air
Equivalent clean air is not the same as outdoor air. Outdoor air requires ventilation equipment. ASHRAE 241 only requires supplying equivalent clean air that can come from any technology, as long as it is shown to be safe and effective.
Many methods exist to provide equivalent clean air, including different types of in-room air cleaners, upper room UV, increasing outdoor air supplied or upgrading filters in air handling units. While not necessarily an ideal solution, portable air cleaners can be purchased to provide sufficient equivalent clean air capabilities to bring any space in compliance with ASHRAE 241. Providing sufficient equivalent clean air is not only possible, it is pretty easy too.
This underscores that ASHRAE 241 is not solely tailored for implementing in new construction. It is stated at the beginning of the standard:
1.1 The purpose of this standard is to establish minimum requirements for control of infectious aerosols to reduce risk of disease transmission in the occupiable space in new buildings, existing buildings, and major renovations to existing buildings, including requirements for both outdoor air system and air cleaning system design, installation, commissioning, operation, and maintenance.
This standard is designed to be implemented on existing buildings.
Cost
The cost of providing equivalent clean air can be low when designed with cost in mind. A recent publication in the ASHRAE journal compared the cost of supplying more clean air, either by increasing the amount of outdoor air or improving filtration:
As the title of the publication suggests: clean airflow doesn’t have to be expensive.
MERV-13 Upgrade Costs
Filters are generally rated on the MERV (Minimum Efficiency Reporting Value) system. It goes from 1 to 16 where MERV-1 is ineffective and MERV-16 removes 95% of particles at all size ranges. MERV-11 and higher is effective against infectious aerosols. Most places use MERV-7 or MERV-8 filters which are ineffective against infectious aerosols and are designed to protect equipment from dust. Upgrading filters to MERV-13 is the best way to balance cost and effectiveness of filtration.
These upgrades are generally an easy step to take. It is a good idea anyways to protect against outdoor air pollution.
I recently received a quote for a fully ventilated school with approximately 500 students to upgrade from MERV-8 to MERV-13 (costs are in Canadian dollars). Maintenance with MERV-8 cost $5120/year. Maintenance with MERV-13 cost $8040/year. The difference of $2920/500 students = $5.84/student per year CAD or $4.30/student per year USD.
These units supplied 750 cubic feet per minute (CFM) of recirculated air to each classroom, with 22 students and a teacher. Using the efficiencies from ASHRAE 241, the equivalent clean air is 750 CFM x 0.77 = 578 CFM/23 people = 25 CFM/person.
$5.84/student/ 25 CFM/person = $.23/CFM.
Every student requires 40 CFM/student in a classroom based on ASHRAE 241, so upgrading to MERV-13 provides 25 CFM/student, in addition to the 15 CFM/student needed from outdoor air.
Portable Air Cleaner Costs
My favourite air cleaner is the Luggable XL. It costs $375 CAD and provides 320 CFM, roughly $1.20/CFM. In a classroom with 25 people and 40 CFM required per person, this equates to approximately $50/person CAD to comply with ASHRAE 241 using portable air cleaners alone.
Upper Room UV Costs
The effectiveness of upper room UV has not yet been determined in accordance with ASHRAE 241 — no devices have provided lab results in accordance with ASHRAE 241 Normative Appendix A.
Based on CDC, it could cost around $3000/classroom. If this allows for compliance with ASHRAE 241, it would equate to 40 CFM/student and $3/CFM. This equates to $120/person to comply with ASHRAE 241.
It’s important to note these are one-time costs. For upper room UV, although it is $120/person to initially install, over 10 years, it would equate to $12/person to comply with ASHRAE 241 or $1/person/month.
Summary
To use a combination of outdoor air, MERV-13 upgrades and portable air cleaners in a classroom, the additional cost would be as follows:
- 15 CFM from outdoor air — already required from ASHRAE 62.1, no additional cost
- 25 CFM of recirculated air through MERV-13 — $5.84/person
- 10 CFM of air from an in-room air cleaner — $12/person
This equates to an additional $18/person. Compared to many other costs we accept, like sick days and hospital bills, this is minimal.
Benefits
Questions addressing the costs of implementing ASHRAE 241 should not just address the the cost of compliance but also address the cost of not complying.
A recent publication calculated the cost and benefits of compliance with ASHRAE 241. The difference is staggering:
In short, compliance with ASHRAE 241 is not expensive, not difficult and can have significant societal paybacks. It really is an obvious choice to protect public health.
Further Reading
Other posts about ASHRAE 241 can be found here.
Disclosure: I have no conflicts of interest.
