HVAC Tech Tip: Introducing ASHRAE Standard 241

In the ever-changing landscape of the HVAC&R industry, staying informed about the latest standards and guidelines is crucial to providing top-notch services to clients. To help you do so, we’re giving you some highlights of the new ASHRAE Standard 241 titled “Control of Infectious Aerosols.” In this article, we explore the essential aspects of the standard and its implications for mechanical contractors.

ASHRAE Standard 241 was developed to create minimum requirements for mitigating disease transmission via infectious aerosols in occupied space in new buildings, existing buildings and major renovations. The standard addresses a range of factors related to indoor air quality during an infectious event including equivalent outdoor air requirements, filtration, disinfection and control strategies to minimize the potential spread of infectious aerosols.

Before we begin our brief overview of Standard 241, here are some pertinent acronyms and definitions:

• ECAi – equivalent clean airflow rate in units of flow per occupant in a space. This can be met by outside air, filtered recirculated air or disinfected air.
• BRP – building readiness plan – a document detailing engineering and non-engineering controls and practices to enact in response to an infectious event. This first appeared in ASHRAE’s building readiness guide in early COVID-19.
• IRMM – infection risk management mode – an equipment mode to react to an infectious event.
• _PR – infectious aerosol reduction efficiency.

Let’s take a look at certain notable sections in the standard.

Section 5: Equivalent Clean Airflow for Infection Risk Mitigation

Section 5 details how to calculate the minimum ECAi value. This value is independent of minimum ventilation rates defined by ASHRAE Standards 62 and 170 and is intended to be used during an equipment’s IRMM mode. One important takeaway is that even if an ECAi value is calculated to be lower than a space’s minimum ventilation level due to lower occupancy, ventilation rates should default to their regular minimum while in IRMM. Section 5 also includes Table 5-1 that details minimum equivalent clean airflow per person in the breathing zone in IRMM for various building types.

Section 6: Air Distribution and Natural Ventilation

Section 6 goes into further detail of how to calculate ECAi using the summation of equivalent clean airflow resultant from air cleaning systems and outdoor air intake. It then discusses air distribution of ECAi and air cleaning systems.

Section 7: Air Cleaning

Section 7 is of particular interest as it, along with Appendix A, lays out testing requirements and procedures for air cleaning systems. This is an extremely useful section as there are many air cleaning systems of varying efficacy and – until now – there hasn’t been a way to compare them. The effectiveness of air cleaners in air-handling units, ductwork, plenum or occupied space will be reported as an air cleaning system equivalent outdoor air flow rate. This is determined by the product of infectious aerosol reduction efficiency, _PR , and the recirculated cleaned airflow rate. Included in the section is Table 7-1, which provides an equivalent _PR for filters based on their MERV and/or MERV-A ratings.

Section 8: Assessment, Planning, Implementation; and Section 9: O&M

Section 8 details what should be included in a new and existing building’s BRP and how to document, assess, plan, implement and commission those items. Section 9 details operations and maintenance procedures for the BRP and IRMM. Table 9-1 is of particular interest, as it details minimum maintenance activity and could provide a great opportunity for improved engagement and service with your customer.

You may be asking how Standard 241 relates to Trade Ally Network NW and energy efficiency. In truth, much of the guidance found therein could actually lead to greater energy usage. Fortunately, there are ways to limit the intensity of these technologies, which include heat recovery ventilators (HRVs), advanced rooftop unit controls (ARC) and connected thermostats. HRVs allow for improved ventilation while recovering heat from the exhaust air stream. ARC and connected thermostats can include interfaces and software designed to be incredibly responsive. These can also be configured with settings or schedules that could be part of a BRP. Many of these systems qualify for BPA energy efficiency incentives through participating local utilities.

Please keep in mind this discussion of Standard 241 is meant to inform you about the new standard and in no way replace it. The Network encourages you to review Standard 241 on your own. If you have questions, please reach out to your local field specialist. By embracing ASHRAE Standard 241 and applying these key points, you can create healthier and safer indoor environments and demonstrate real value to your customers.