We know how stressful it can be to have a new initiative and limited time to come up to speed on how to address it. Largely using the Department of Education’s “Room Air Cleaner Guidance for Schools” and earlier releases, we have put together some information to assist you in your decision making that will cover issues such as the correct unit you need to buy for your classrooms, how many units will be required and what technical specifications are required for your school.
Selecting your Product
The Department of Education advised when selecting an air cleaning unit, the following should be considered and compared:
- Matching the cleaning unit to the room in which it is to be located
- The effectiveness of the air cleaner
- Filter types in the unit
- Noise levels
- Additional features
Matching the Unit to the Room
Understanding the role Clean Air Delivery Rate (CADR) plays.
Air cleaning consists of the removal from the air of suspended particulates that potentially carry the Covid-19 or other virus. Filtration is the simplest and most effective method of air cleaning. To assess the efficiency of the filters it’s important to understand a key term CADR or Clean Air Delivery Rate. CADR levels indicate how fast an air purifier can filter the whole air (volumetric) of a room within a specific time.
The effectiveness of the air cleaning unit
Identify the CADR of air purifiers that you are considering. The CADR defines an air cleaning unit’s effectiveness in reducing particles and is typically expressed in M3/hour. In general, the higher the number, the more particles the air cleaner can remove and the larger the room the device can reasonably be expected to clean.
To compare various units, you can calculate the air change rate of cleaning equivalent to the air cleaner’s CADR as:
ACR (cleaning) = The CADR divided by the Volume of air in the room
The ACR represents the number of times per hour that air is either purified by a device or exchanged by opening windows in the classroom.
Another way to look at this formula is to decide your goal for ACR – how many times per hour do you want to have the room cleaned?
In one of the recent updates from The Department of Education, a Harvard University study on schools was referenced. The graphics below provide a quick reference guide from this study. The Harvard study indicated school’s goal should be to refresh the air in classrooms at least 5 times per hour. The Department of Education suggested one way to achieve this goal would be to establish a goal of 3 ACR from an air purification device and a goal of 2 ACR by opening a window.
Calculating the required ACR is relatively straightforward. Take the length, times the width of each room, times the height of the ceilings to calculate the cubic metres of air in the room (M3) and then multiply the M3 times the desired ACR.
In the example below, you’ll note each of the examples have the same sized rooms. The only variance is the desired ACR. If your budget allows, the Harvard school study recommends going with the higher ACR.
We’ve heard from some schools who have gotten a head start on ordering air purifiers that they simply took the total allocated budget and divided it by the number of rooms in the school and then purchased the same air purifier model for each classroom. This approach is understandable, but we’d suggest schools consider a slightly different approach.
All rooms do not need the same CADR. The formulas above can be used to calculate the CADR for different sized classrooms, but these simple formulas don’t take into consideration the number of teachers and students who will be breathing in the classroom – rooms with more people will require a higher ACR.
Take an example of two rooms of equal size as shown in the example above. If one classroom has half the students in the other classroom, the school can achieve a similar level of protection by adjusting the desired ACR to reflect that more or less people will be breathing air in a given room. This amended approach can help the school develop a customised CADR for each classroom and help allocate their budgets in a more scientific manner. The Harvard study provides a much more detailed formula to account for this and we’re happy to help schools work through these formulas without incurring any consultation fees or any obligation to purchase air purifiers from us.
Filter types in the unit
A HEPA filter removes harmful particulates from the air. HEPA is an abbreviation that stands for 'High-Efficiency Particulate Air'. The Department of Education recommends choosing an air purifier with a HEPA filter, sometimes referred to as True HEPA, HEPA13 or HEPA 14. They caution against “HEPA-type” filters since these won’t have the same level of air purification, which is particularly important when trying to capture the tiny particles of the Covid-19 virus.
A HEPA filter may sound complicated but in effect, they are made using glass or synthetic fibres. The filter itself is like a dense matting that allows air to pass through it but the fibres in there stop the vast majority of air particulates from getting through.
Air purifiers generate noise from internal fans that pull air through a series of filters. The Department of Education notes that it is important to choose a device that suits the required noise levels of the space the unit is serving, whilst delivering the required ACH and CADR at its mid/lower speed settings.
Airify Tech provides the CADR level at each fan level. We believe you can make a more informed decision if you understand the trade-offs between effectiveness of the CADR if you know the performance at different fan speeds. While there may be times when teachers will want to reduce the noise level by turning down the fan speed, they need to understand students will not benefit from the same number of air changes per hour with the lower settings as they would get with the higher settings.
HEPA filters are disposable and must be entirely replaced. It is important to compare the replacement filter costs and expected life of each unit you are considering. Keep in mind that expected life is measured in hours of use. So, if your classrooms are in session for 6.5 hours per day and you only use the devices during times when school is in session, a filter with an average life of 1,500 hours will last for 230 days of use on average, which when you consider that schools are in session for 183 days on average, will mean you only have to change the filter about one time per year. In general, Hepa filters are easy to change and should not need any specialist skills.
Some air cleaners have additional features. Look for useful features such as the following:
- Sensors indicating how clean the air is in your classroom, or when it is time to replace the HEPA filter
- UV lights that are fully enclosed in the device that effectively kill virus trapped in the HEPA filter.
- Remote controls
Quick Summary Check List
- There is no single air cleaner that's right for every situation.
- Determine the air volume of the space to be served, and ACR (cleaning)
- Request that your suppliers give you the information on the CADR ratings and filter types and noise ratings and confirm to you how effective the air cleaning will be for your specific needs. We’re available to consult with you on your specific room requirements.
- Look for a table similar to the Airify Tech table below. Please note we calculated the ACR on an assumed room of 56M2 with a 3-metre ceiling.
We encourage you to register for our webinar in January where we’ll cover more of this material and will be available to answer your questions. In the meantime, please email or call us if you need further information.
Office 045 254 256 Mobile 089 430 6599