Welcome to the latest installment of our ongoing series breaking down ASHRAE standards and their impact on modern commercial HVAC design, energy efficiency, and indoor environmental quality (IEQ).
Standards like ASHRAE Standard 62.1 and 90.1 manage everyday indoor air quality (IAQ) and energy performance. Yet, the COVID-19 pandemic proved that typical ventilation baselines fall short during public health crises.
In this installment of our ASHRAE Standard series, we dig into what Standard 241 is and how ERVs can help with meeting this standard.
In 2023, ASHRAE addressed the need for more stringent ventilation requirements during public health events by publishing ASHRAE Standard 241, Control of Infectious Aerosols. Groundbreaking in its scope, Standard 241 was designed specifically to reduce the risk of disease transmission from airborne viruses and pathogens in commercial and institutional facilities.
Why ASHRAE Standard 241 Was Created
During early pandemic responses, authorities turned to time-tested ventilation protocols. These strategies were designed based on historical responses to the 1918 Spanish Flu pandemic. Operators opened outdoor air dampers 100% and continuously flushed facilities with raw outside air.
While flushing buildings successfully reduced airborne contaminants, it created a secondary issue: soaring energy consumption. Recognizing the need to balance pathogen control with building performance, ASHRAE approved Standard 241 in 2023. This framework established actionable guidelines for infectious aerosol control during public health crises without overwhelming mechanical equipment or utility budgets.
Facility managers or authorities having jurisdiction (AHJs) can activate this standard during specific events, such as a localized measles outbreak, a severe seasonal flu surge, or a declared airborne health emergency.
During normal operating conditions, commercial facilities would operate under traditional baseline ventilation codes or standards like ASHRAE 62.1. However, when an airborne outbreak occurs, the building could transition into IRMM to deliver heightened pathogen protection only when it is needed most.
When Standard 241 Applies: Infection Risk Management Mode (IRMM)
Forward-thinking in its development, Standard 241 was not intended for every health emergency. Instead, the standard specifically targeted infectious aerosols and airborne contaminants—pathogens like influenza, measles, or SARS-CoV-2 that remain suspended in air and travel through HVAC systems. Public health events originating strictly from waterborne, foodborne (such as recent Cyclospora or E. coli outbreaks), or surface-contact transmission fall outside its scope.
Additionally, unlike traditional ventilation codes that dictate continuous daily operations, Standard 241 requirements apply only when a facility enters Infection Risk Management Mode (IRMM).
IRMM is an operational state activated during identified periods of elevated airborne transmission risk. Facility managers or authorities having jurisdiction (AHJs) can activate an IRMM when a specific public health event occurs like a localized measles outbreak, a severe seasonal flu surge, or a declared health emergency.
During normal operating conditions, commercial facilities operate under traditional baseline ventilation standards like ASHRAE Standard 62.1. However, when an airborne outbreak occurs, the building transitions into IRMM to deliver heightened pathogen protection when occupants need it most.
How to Prepare for Standard 241: The Building Readiness Plan (BRP)
Before a facility can ever enter Infection Risk Management Mode, Standard 241 requires building owners to lay the groundwork. This starts with creating a site-specific Building Readiness Plan (BRP).
The BRP serves as the operational blueprint. It documents exactly how a facility will transition its HVAC systems and air-cleaning equipment to deliver heightened protection during an airborne risk event.
Key components of a complete Building Readiness Plan include:
- System Assessments: Evaluating baseline ventilation rates, filtration capabilities, and available clean-air capacity across all occupied zones.
- Operational Procedures: Outlining clear instructions for activating an IRMM event, adjusting control sequences, and engaging supplemental equipment.
- Maintenance Protocols: Establishing routine inspection schedules so ventilation hardware operates reliably during an emergency.
By establishing these protocols ahead of time, facility teams can execute their risk-mitigation strategy instantly when an outbreak occurs.
How Standard 241 Measures Protection: Equivalent Clean Airflow (ECAi)
When a facility transitions into IRMM, building operators use a calculation, Equivalent Clean Airflow (ECAi), to protect building occupants against the airborne pathogens.
During normal circumstances, ventilation standards would only count raw outdoor air exchange. In IRMM circumstances, however, Standard 241 defines ECAi as the total flow rate of pathogen-free air delivered to occupied spaces. This allows facility managers to use a much more robust strategy—combining multiple air-cleaning methods rather than relying on outdoor air alone.
To reach high targets cost-effectively, Standard 241 relies on a layered defense strategy. Facility managers can choose from a flexible mix of clean-air options to reach their total compliance goal:
- Balanced Outdoor Air Ventilation: Diluting indoor pathogen concentration by continuously replacing stale indoor air with fresh, filtered outdoor air.
- Advanced Air Filtration: Capturing airborne particulates and pathogens through high-efficiency mechanical filters like MERV 13 or HEPA.
- Air Disinfection: Inactivating active pathogens using validated technologies, such as germicidal ultraviolet (UV-C) systems.
Balancing ECAi Targets with Energy Efficiency
Building teams are not required to implement every option. However, filtration and air cleaning alone cannot replace the foundational need for fresh outdoor air dilution. During an IRMM event, HVAC systems must deliver high amounts of outdoor air.
For facility directors, this can bring on another issue. If their building’s HVAC system is not energy efficient, it can overload mechanical equipment or drive up energy costs.
The Challenge: Increasing Outdoor Air Rates During IRMM Events
Increased outdoor air ventilation forms the core of Standard 241’s layered defense strategy. Fresh outdoor air serves as the primary mechanism for diluting indoor airborne viruses. Ideally, systems should balance this ventilation so equal parts of contaminated indoor air exit the building while fresh, filtered outdoor air replaces it.
However, scaling up outdoor airflow during an IRMM event creates a major operational challenge. Conditioning massive volumes of unconditioned outdoor air drives up energy costs and strains mechanical equipment.
How ERVs Support Standard 241 Compliance
RenewAire energy recovery technology plays a critical role in solving this operational challenge.
RenewAire energy recovery ventilators (ERVs) provide balanced ventilation. Our systems recover energy from the exhaust airstream. During operation, our static-plate units transfer total energy—both heat and moisture—between outgoing exhaust air and incoming outdoor air.
This process reduces ventilation energy costs and equipment loads by up to 70%. By pre-conditioning incoming fresh air, RenewAire ERVs allow building operators to meet heightened ECAi targets during IRMM events without overwhelming HVAC systems or spiking utility bills.
The Path Forward for Standard 241 Compliance
ASHRAE Standard 241 set a new benchmark for indoor health and safety without forcing facility teams to choose between risk mitigation and energy efficiency. By documenting activation protocols in a Building Readiness Plan and combining flexible clean-air layers to achieve ECAi targets, building owners can prepare for public health crises responsibly. Integrating RenewAire energy recovery ventilators into this layered strategy anchors your facility with balanced, fresh air ventilation—ensuring occupants stay protected while operational expenses stay under control.
Frequently Asked Questions (FAQs)
What is the difference between ASHRAE 62.1 and ASHRAE 241?
ASHRAE Standard 62.1 sets mandatory baseline ventilation rates for normal, day-to-day building operation to control typical indoor air contaminants.
ASHRAE Standard 241 is an infection control standard designed to reduce the risk of disease transmission from airborne pathogens during periods of elevated risk (Infection Risk Management Mode). Standard 241 requires significantly higher clean airflow rates than Standard 62.1.
Is compliance with ASHRAE Standard 241 mandatory?
By themselves, ASHRAE standards are never mandatory. However, these voluntary standards often serve as the framework for local building codes. Standard 241 could become legally binding if adopted into code by an Authority Having Jurisdiction (AHJ) or required by government agencies.
Does Standard 241 require 100% outdoor air?
No. Standard 241 relies on Equivalent Clean Airflow (ECAi). This allows building managers to reach targets through a combination of outdoor air, high-efficiency filtration, and air disinfection.
However, outdoor air ventilation remains a widely researched and successful strategy for diluting airborne pathogens. Standard 241 gives facilities the flexibility to mix these clean-air layers based on their specific equipment capabilities.
How do ERVs help with Standard 241 compliance?
Yes! Energy recovery technology brings in fresh outdoor air energy-efficiently.
When buildings with traditional HVAC systems increase ventilation rates, heating and cooling loads rise. Why? The incoming outdoor air must be conditioned to match indoor temperatures.
Energy recovery technology solves this challenge. RenewAire ERVs capture energy from the exhaust airstream to precondition incoming air. This process allows facilities to increase ventilation protection while keeping utility costs under control.