ASHRAE 241- Is it a realistic option?

 

 

Background

ASHRAE have recently published ASHRAE 241, a Standard for the Control of Infectious Aerosols. Standard 241 effectively incorporates and goes beyond ASHRAE 62.1 in establishing minimum requirements aimed at reducing the risk of disease transmission through exposure to infectious aerosols in new buildings, existing buildings, and major renovations.

ASHRAE 241 is the result of the work of a group of academics and engineers who were set the challenge of how to specify mechanically ventilated / air conditioned systems where, specifically during a pandemic, the system could go into an 'enhanced mode' which would go a long way in protecting the occupants from infection by a Covid 19 like virus.

The key factors that influence the model they have derived are the population density (because some of the occupants will emit virus), the size and rate of a supply of 'clean' (i.e. free from virus) air, and the speed with which the mechanical systems must circulate that air to dilute the average level of airborne virus to a 'safe' level.

ASHRAE promote 241 as:

‘A framework for increasing occupant wellness in indoor spaces by minimizing the risk of human airborne transmission (infectious aerosols)'

And defines acceptable indoor air quality (IAQ) as:

‘Air in which there are no known contaminants at harmful concentrations, as determined by cognizant authorities, and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction’

The drive to improve mechanical ventilation systems to ‘dilute’ any airborne virus concentrations to a ‘safe’ level arises primarily from the Covid pandemic, when it became clear that traditional mechanical ventilation systems and filters had little positive effect and where, at the time, no other solution (other than sending people home) was available to protect building occupants from cross-contamination.

According to 241 the supply of 'clean' air that can be used to ‘dilute’ virus concentrations elsewhere in the building can come either from outside the building or from a reservoir of inside air where filters or some other means have been employed to remove the virus.

On the face of it that all makes sense. However, as usual the devil is in the detail.

Costs vs Benefits

The fundamental problem is simply the cost (both capital cost and in use cost) of creating an installation that meets the requirements of 241.

Compared to a traditional HVAC system, say any commissioned before 2022, meeting the additional requirements of 241 involves, either:

• Importing far more air from outside (most existing systems take only a little air if any from outside due to expense of changing the temperature up / down of the outdoor air to the target indoor temperature), or
• Creating a constant supply of ‘clean’ air by passing sufficient internal air through high quality MERV 14 filters.

And, in either case, the quantities of ‘clean’ air to be sourced will be very substantial, and the ventilation rates, depending on the space, will typically need to increase by a factor of three to six throughout the system.

Indeed, with required air changes per hour likely needing to be increased in healthcare and schools to 10, waiting rooms to 30, restaurants to 40 and lecture halls to 50 we can quickly conclude that only relatively sparsely occupied spaces, such as offices, are a practical targets for 241 application.

The authors fully appreciated the impracticality / high costs of routinely implementing 241, including the cost of sophisticated filters such as  MERV 14, which is why, even where implemented, the systems should only be run in this enhanced mode during emergencies. However, that being the case, the capital cost might be spent and infrequently or never used within its lifetime!

Costs may be manageable for more sparsely occupied spaces, such as offices, but as critics have remarked – what if staff cannot get to work safely? and wouldn’t it be better and more robust to implement enhanced IT systems that can be easily accessed and used from the home?

In terms of sustainability, 241also raises the obvious climatic concerns that go alongside increased emissions arising from more aggressive air change rates, especially as typically some 40% of all GHG emissions arise from buildings.

Does ASHRAE 241 meet the objective of providing a safe place to work in a pandemic?

Clearly in terms of significantly reducing virus aerosol levels, it does. But future pandemics, unlike Covid, may be equally transmitted by touch or through intermediate surfaces, where 241 provides no protection, and even with Covid and future airborne viruses, transmission by close contact or ‘sneeze’ will not be materially reduced by 241.

Sadly, overall, the additional costs associated with 241 could likely only be borne in high risk / high value circumstances, for example mission critical control centres.

But there is a better way…

Airora makes ASHRAE 241 redundant

Airora’s revolutionary technology has been demonstrated to destroy 99.9999% of ‘hard to kill’ MS2 airborne virus in minutes, and the CDC confirms that as Airora’s technology kills MS2 virus, it will kill all types of virus and bacteria without exception. Indeed, unlike increased ventilation based solutions such as 241, Airora is so powerful it has been shown to destroy > 99% of bacteria in a sneeze before it travels just 600mm!

Airora’s technology is based on replicating nature’s outdoor atmospheric chemistry indoors, and as such is entirely safe and can operate continuously and invisibly with people present, continuously decontaminating both the air and surfaces.

In addition to germs, Airora’s technology destroys or neutralises all types of moulds, allergens and odours and most other irritants and harmful pollutants throughout entire indoor spaces.

Given Airora’s unique germicidal power, and other obvious Indoor Air Quality benefits, it provides a far more rational response to pandemic protection than ASHRAE 241.

Unlike ASHRAE 241, Airora’s solution:

• Provides 24/7, 365 days a year unrivalled protection from all types of potential pandemic infections, be they transmitted through the air or via surfaces. 
• Practically eliminates, not just reduces as with ASHRAE 241, airborne germ concentration.  
• Practically eliminates surface borne germ concentrations, unlike ASHRAE 241 which only effects airborne germs.
• Has capital costs that are very small compared to ventilation dilution solutions such as ASHRAE 241.
• Has operating costs (and CO2 emissions) that are very small compared to those inherent with ASHRAE 241.
• Requires no changes to existing forced ventilation or air conditioning systems.
• Makes retrofitting / upgrading any existing building a minor task compared to the complexity of ASHRAE 241.
• Is equally effective in naturally ventilated and mechanically ventilated buildings.
• Does not require that the resultant installations are subject to compulsory certification, does not require post installation testing and verification, does not require a Building Readiness Plan, nor Infection Risk Management Mode (IRMM) documentation.

 

You can find out all about Airora at airora.com

And contact us at support@airora.com