This standard 241P is applicable to ALL new buildings, existing buildings and additions to existing buildings.

This proposed standard does not change any requirements for normal operations. It asks that properties create a plan as to the methods that will be taken through engineered, non-engineered systems or a combination of the two to handle emergency conditions – in this case aerosolized infectious agents.

The standard as acknowledged by ASHRAE has been rushed through to this public comment and it shows. The language of the proposed standard is somewhat disorganized and unclear. That said, here’s my take on it.

First, as a prerequisite a building to have met the requirements of either ASHRAE 62.1, 62.2 or 170, based on occupancy before you get to play with the new proposed 241P.

Bottom line. In case of emergency, you need to be able to do something to your building to conform to the Infection Risk Mitigation Mode (IRMM) airflow requirements determined during the assessment phase. IRMM represents a set of interim settings of a building’s operational parameters to help mitigate against aerosolized infectious agents.

Meeting the enhanced outdoor air requirements can be done with an engineered system either central or local or with non-engineered controls. For example, a higher speed on air handling fans to produce additional airflow. Locally, an in-room HEPA filter or an in-duct air cleaner could be used. Operation of airside economizers is an option to introduce additional outdoor air into the system. On the non-engineered side, opening a window (natural ventilation) or reducing occupant count are viable options.

Ultimately, it comes down to creating a plan and implementing it when necessary.

Introducing EOAi

Important new acronym – EOAi the equivalent flow rate of pathogen free air per person that, if distributed uniformly within the breathing zone, would have the same effect on infectious aerosol as a given removal or inactivation mode.

The determination of the required EOAi for a given building will at some point be based on either a prescriptive value or a performance-based procedure. That point hasn’t come yet, so all we have is prescriptive. They will get to performance later – maybe.

Using residential as an example, 50 cfm per person is the prescriptive EOAi requirement.

To help put that into perspective, ASHRAE 62.2 requires 7.5 cfm per person, plus 1% of the house’s square footage. Tabbing that out, using a 2,500 sqft 3-bedroom house, would require (4 x 7.5)+(2,500 x .01) = 30 + 25 = 55 cfm.

So, to be compliant with 62.2 we need to provide 55 cfm. For 241P, the threshold is nearly 4 times that at 200 cfm, assuming all occupants are expected to be in residence during the emergency. For purposes of 241P it is also possible there may be more occupants during the emergency than would normally be there…

Keeping with the residential example, the section regarding airflow distribution patterns can be ignored as it is not applicable to 62.2 projects. Commercial and healthcare projects have requirements for diffuser and register placement, limitations for airspeed in the breathing zone of 50 feet per minute. Equations regarding the ventilation effectiveness of various mechanical system types are provided as is an equation for non-recirculated ventilation systems, commonly known as DOAS systems. 

A clarification of spaces requiring ventilation, in 62.1 and 170 spaces only, any regularly occupied space, 4 foot or wider, 6.7 feet high.

Natural ventilation is allowable in compliance with 62.1 -2022

Provisions are made to allow for air cleaning devices to be utilized to contribute to the required EOAi. Restrictions regarding adverse interaction between systems are discussed.

Air cleaning devices can be installed within the physical space or within the ductwork of the mechanical systems feeding such spaces. Calculations based on the effectiveness of these devices are used to determine the overall contribution of Equivalent Outdoor Air based on cleansed return air. Operating an air-side economizer cycle increases EOAi as the non-infectious outdoor air is introduced with an effectiveness of 1.

So what do we know so far?

Not a lot.

The new EOAi is a lot higher than what was required before. Natural ventilation is OK, and there’s a way to meet the requirements with some kind of air cleaner or filter or something. But how and when and where?

Assessment, planning and implementation are next, starting right in talking about commissioning. The first item on the list regarding Cx is a Building Readiness Plan (BRP). That sounds important – what’s a BRP?

A BRP is a document created after the assessment, planning and implementation phases that describes the engineering and non-engineering controls the facility systems will use to achieve its equivalent outdoor air flow for infection control targets.

Starting with an Assessment

The requirement for the assessment of an existing building as outlined in the proposed Standard 241P would apply to all buildings and their systems that were constructed or renovated before the adoption of the proposed standard.

Should a building be altered or change its use, a re-assessment would be required as well as a re-evaluation of the Building Readiness Plan.

Here’s a big one…an Occupied Space Inventory is required. Remember, this is for all existing buildings. A space by space inventory of occupied space including a categorization based on space usage.

Then, the assessment continues with verification of outdoor airflow, ideally measured with a testing and balancing report no more than a year and a half old. Alternatively, estimates of airflow based on ASHRAE 111-2008 or calculations based on CO2 decay are allowable.

ERVs are specifically called out for assessment to determine if they can be utilized during the IRMM.

What’s an IRMM? 

Infection Risk Mitigation Mode is the control conditions a system or set of systems will be commanded to operate during a specific risk condition. This mode would be initiated by building operators based on information in the Building Readiness Plan.

Basically, the goal of the standard is for each building to work out a plan of operations that they will follow in case of emergency. The building will need to have three unique operational modes Normal, IRMM and Temporary Shutdown. Information regarding temporary shutdown mode has not yet been provided.

Focusing on Residential Properties

There are a few items of note that appear in section 10 affecting only residential properties.

Blower door testing is required, Verifying a leakage rate of 0.2 cfm/SF at 50pa. This is far below the current Phius standard of 0.06 cfm/SF at 50 pa.

There is one last interesting section that talks about a separation area. The idea being that if a family member gets sick, there may be a need to keep them home but in a space that is physically and mechanically separated from everyone else. Now there is a similar requirement in the commercial section, but it is somewhat challenging for a single-family or multifamily home to accomplish this, so it deserves extra notice. 

This separation area would not only need to have its own separate space, but also have its own HVAC system. This is a significant requirement, especially in the passive building arena where finding systems “small enough” is a common challenge. Further compartmentalization of these  systems can cause real issues.

It could happen that the state of emergency lasts for years, therefore, it would be preferable, in new construction at least, to design for compliance with 241 in a way that doesn’t entail a large increase in operational energy use. We expect to have more to say about this later.