Getting what you want from your air filters (3)

Wednesday - 01 August 2018

Clean Air

We think all our filters are beautiful. But we understand that you might not feel the same way. In fact, the chances of you buying one of our filters just for its aesthetic merits are slim-to-none. Whether it’s to protect other equipment, people or a process, you buy our filters because you need to. Filters are a necessary purchase to ensure the safety of things that are valuable to you. They separate the useful from the harmful.

But do your filters actually meet the purpose for which you bought them? And are they delivering that outcome in the most cost-effective way?

The final of our three-part series looking at getting what you want from your air filters, this article examines why you buy air filters in the first place and how you can choose filters that deliver what you expect them to.

Why buy HVAC air filters?

An HVAC air filter typically serves two purposes – to protect the other components of the air delivery system from dirt and damage, and to provide clean and fresh air for people in the building. There may be other niche applications, such as protecting artefacts in museums, but generally the aim of an air filter in commercial buildings is to protect the health of people and/or equipment.

To do that, an air filter needs to capture contaminant from the incoming air flow. Different filters will perform this function to different levels depending on their size, shape and design. But ultimately, a filter’s stopping power comes down to filtration efficiency. The greater the number and smaller the size of particles that a filter can separate, the higher the filtration efficiency.

In the days of the EN779 standard, F7 was the go-to filtration class for HVAC air filters. We now have a new standard in ISO 16890, but you may well still have an F7 in your air handling unit. There’s potentially nothing wrong with that. But have you ever reviewed your filter system to determine if it’s delivering the outcome that you wanted when you bought your air filter? If not, you are far from alone. But more and more companies are taking a different approach to filter purchasing – one that is based on delivering the standard of clean air that they need.

Outcome-based filtration

Filters must perform in all kinds of settings – from cool and wet cities to dry and hot rural environments. The type and size of contaminant that filters face will vary drastically from location to location, as will the humidity, temperature, air flow and other factors that influence filter performance. In fact, the operating environment and pollutant type will often vary between neighboring buildings. That is why a one-size-fits-all approach to filter selection can compromise air quality and put at risk the things that you are trying to protect. An outcome-based approach that uses hard evidence on the operating environment and your goals, can ensure the safety of the people and equipment in your building – and save you money too. Here’s how it works.

Decide on an outcome

The most likely reason for installing HVAC filters is to protect people and components. Us humans are the most vulnerable and valuable of those two categories, and if it’s safe for people, it’s safe for the rest of the HVAC system. So, your desired outcome for your filtration system will be to provide safe air quality for the occupants of your building. Fortunately, the World Health Organization (WHO) tells us exactly what this safe level is: 20 mg/m³ for PM10 (particulate less than 10 µm in diameter), and 10 mg/m³ for PM2.5 (particles smaller than 2.5 µm).

Find out what you’re up against

Now we know the outcome that we want, we need to determine the levels of the incoming contaminants. Most countries around the world now publish pollution levels across their regions – often with detailed historical records and sometimes in near real-time. So, finding out the levels of PM10 and PM2.5 in your local area can be a quick web search away.

Do some sums

Armed with the local pollution levels you can then calculate what filtration efficiency will remove enough of the contaminant to deliver a safe level of air quality.

For example, if the PM concentrations outside your building are 48 μg/m³ for PM10 and 33 μg/m³ for PM2.5, you need a filter system that can reduce PM10 by 58% and PM2.5 by 69%. This equates to minimum ISO 16890 filter efficiencies of ePM10 60% and ePM2.5 70%.

Use a safety buffer or survey

Of course, the published air pollution levels will not give you a precise picture of your individual building. Pollution levels are far from static, and localized pollution caused by construction or industrial activity can be missed in regional published data. So, we recommend adding a safety buffer and choosing a filter 10 - 20% cleaner than your calculations may suggest. This will cover any periods of high pollution and mitigate the risk from neighborhood sources.

Better still, ask your filtration partner to conduct an air quality survey of your building. We regularly analyze customer sites as part of our eco16 program. We measure the incoming level and type of pollutants, and create a tailored filter solution that guarantees safe air quality at the lowest possible cost. Find out more about eco16 here.

Watch out for over-specified filters

At this point you may be asking yourself why not just choose the highest filtration efficiency possible. And the answer comes down to cost. Higher efficiency filters tend to be more expensive to buy and – as they are designed to trap finer particles – will load with coarse dust much more quickly than lower class filters, shortening the operating life considerably.

But the biggest cost implication of over-specifying filter efficiency comes down to energy consumption. A filter that has too high a filter class will choke the air flow and cause the energy consumption of the whole HVAC system to soar. You can find out more about minimizing your filter costs in part two of this series.