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Ventilation Revolution: Transforming Schools for Healthier Learning Environments Amidst the Battle Against Infectious Aerosols

Recently, ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) released their DRAFT of Standard 241P: Control of Infectious Aerosols. 

This standard is critical because it frames the likely direction of travel for the flow rates of ventilation systems in the future, to mitigate the risk of infectious aerosols like COVID-19. 

This applies to all spaces, including schools.

For anyone who has been looking at the challenge of improving ventilation in the aging UK and Irish stock, the numbers being referenced as a new standard will make your eyes water. 

25 liters per second per person is a level of air renewal that is at least double the flow rates of most countries’ aspirations, and probably four times higher than what is practically seen on the ground in the UK and Ireland.

The question is, as often is the case. In the pursuit of perfection, do we limit or slow travel in the right direction? 

With the industry already struggling to find solutions to the problem and costs escalating quickly, how do we find the right balance between progress and the right target?

Mounting Evidence

There is mounting evidence in general that indoor air quality (IAQ) affects outcomes in performance, absenteeism, and general health and wellbeing in classrooms.

Like the recent study “Associations between illness-related absences and ventilation and indoor PM2.5 in elementary schools of the Midwestern United States” This study monitored indoor environmental data in 144 classrooms in 31 schools in the Midwestern United States. 

The research team examined the effects of indoor environmental variables on absence rates in elementary schools and found.

  • Higher classroom ventilation rates significantly reduced illness-related absences. 
  • Higher concentrations of indoor long-term monitored PM2.5 were significantly associated with increased illness-related absences. 

Although mechanically ventilated classrooms had relatively low indoor PM2.5, more rigorous control of indoor particles was still beneficial. So it is no surprise that, in the face of controlling infectious aerosols, we see the demand for increased airflow increase.

Ventilation in Schools

With years of under-investment, schools are starting from a place of chronic underperformance when it comes to ventilation. 

Most of the education stock is naturally ventilated, and unless it happened to have been built during the turn of the last century during the TB pandemic, it is unlikely to be able to ventilate adequately, even if you wanted it to. 

Natural ventilation is still relied on even in more modern air-tight buildings relying on false assurance of modeling and proper use of windows. 

This past few, through the COVID-19 Pandemic, even the most modern schools were stretched to provide decent air quality and maintain reasonable temperatures, which will probably be the death knell for natural ventilation in such densely occupied spaces as classrooms.

The challenge now is not our new schools but how to manage the stock we have. 

How do we bring these spaces up to even modest flow rates of 8-10 liters a second per person? In a typical classroom, this will likely equate to flow rates in the region of 800-1200 meters cubed per hour. 

The battle of occupancy levels and rooms size

There are a number of key factors that will influence the path forward.

  • Design flow rates (Litres per second per person or Air changes hour)
  • The thresholds you set (CO2 800ppm? 1000ppm?)
  • Over what time frame (8 hour Average?)
  • The size of the space
  • How many students and teachers

If we decide it’s a hard number on the flow rates of the ventilation system based on a per-person rate, then the reality is with the numbers currently occupying classrooms, this will create significant air change rates, well above reasonable levels. The only choice may be to reduce class sizes.

If we go for an absolute threshold of CO2 then we are setting a metric that may be very hard to hit in the short and medium term, again, particularly in smaller rooms or more densely occupied class sizes.

The challenge is that this is a design flow rate above most domestic-orientated hardware, this puts the solution firmly in the field of specialist equipment. It very easily slides from one cost level to another adding thousands to a solution per classroom or even making it practically impossible to meet a specification.

This is a problem currently being faced in Ireland with a 10 l/s per person requirement and a noise criteria of 35dB(A) based on 35 occupants.

This problem is going to take time and resources to upgrade and a level of investment that the education sector is undoubtedly not ready for. 

But it’s an investment they are going to have to get to grips with.

The underperformance of ventilation in schools and the impact of poor IAQ is now firmly out of the bottle, and schools are not just where we send our children to learn, but they are also workplaces. 

Workplaces that employers have an obligation to provide adequate fresh air and manage risk effectively. And a reasonable expectation from teachers and staff that they have a safe and comfortable place to work. The teacher’s Unions in the UK have just released a guide to members on exactly this.

Investment needs to start now, and schools will need to roadmap how this investment will occur over the long term. We are now monitoring more and more classrooms, and the performance of these spaces is now visible. There are solutions for nearly all spaces, and a program of fix could fall in with the inevitable energy performance measures needed over the next few years. 

In the meantime, there are temporary solutions like air cleaners that if properly sized and specified can provide some interim relief.

But without question, if the direction of travel to protect against the risk of airborne infections like the last pandemic is as described in the new ASHRAE document, there will need to be a significant shift in gear when it comes to schools.

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