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Pondering over porosity, permeability

Air filters are at the heart of efforts for achieving good Indoor Air Quality. What are the factors that ensure effective filtration solutions for sustained performance?

| | Sep 12, 2018 | 10:17 am
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Air filters play a pivotal role in determining the Indoor Air Quality (IAQ) in a built-environment. However, the air filter market is influenced by a number of factors.

Dr Iyad Al-Attar

Dr Iyad Al-Attar, an independent air filtration consultant, says: “Industrial air filtration is a multi-billion-dollar industry, worldwide, and the market today is driven by five main factors: A strict government emission regulation; a growing demand for highly efficient and aerodynamic filters; an increase in demand for global energy, frequent epidemics and outbreaks; the increasing, but insufficient awareness of air pollution and its impact on human health, vegetation and the climate.”

Though there are drivers that lead the air filtration market towards growth, Al-Attar insists there are several challenges influencing the market. He says: “Factors like the declining oil prices, lacklustre HVAC maintenance practices, the fluctuating development of real estate and economic recession all have a part to play when we talk about roadblocks to progress in the air filtration market.” On the other hand, he says, the number of filter suppliers has increased in the Middle East, and market shares in different application segments seem to be scattered. Over the years, Al-Attar says, air filters have served the HVAC industry and play a crucial role in providing clean air. However, IAQ is often compromised, when contaminants settle on the heating or cooling coil, as a result, impeding the level of air quality being provided to occupants.

He says: “Well-being and the importance of clean air go hand in hand and, hence, there is a need for air filters to perform, making accurate filter performance prediction essential to saving on energy and operation costs.”
In addition to performing well, Al-Attar highlights how the application of air filters is no longer limited to the HVAC sector alone; instead, it has found acceptance and application across sectors. He says, “Today, air filters are used in space applications, gas turbines, healthcare facilities and sewage plants.” For instance, he says, data centres today have their own HVAC system requirements, as do the micro-machining industry and the semiconductor industry, where the control of sub-micron dust particles is of paramount importance. He says that the application of air filters for indoor cabin air across the automotive and aviation sectors has also gained momentum in the last 15 years. “Smoking cabins are another space, where chemical and mechanical air filters are used,” he says. “This is in addition to In Vitro Fertilisation (IVF) facilities, where air quality is very important.”

Elaborating on the use of air filters in IVF facilities, Al-Attar says: “Human gametes and embryos cultured In Vitro are extremely sensitive to oscillations in temperature, humidity and contaminants. Several reports suggest that toxic agents, such as bacteria, particulate matter, dust and chemicals like Volatile Organic Compounds (VOCs), influence fertilisation and embryo development.” He adds that in IVF facilities, mechanical and chemical filters are
installed to encounter solid and gaseous contaminants respectively.

Another interesting, yet odd, application of air filters is ‘Exhaust Filtration,’ which Al-Attar says, has gained international attention. Elaborating on the concept, he says: “Though it may seem odd, the application finds its use in the hospitality sector (professional kitchens) and in hospitals.

This requires the HVAC and filtration system to be responsive to variations in heat load, contamination and ventilation rates.” Pointing to gas turbines as another application for air filters, Al-Attar says: “Air filters installed in gas turbines confront several atmospheric contaminants in varying concentrations. The situation may lead to a decrease in engine performance, where contaminants are capable of fouling the compressor assembly. Compressor fouling is responsible for 70% to 85% of gas turbine performance degradation, hence, leading to a reduction in power output and an increase in heat rate and fuel consumption.”

The permeability of an air filter 
While understanding the nature of air filters, Al-Attar elaborates on the role of air filter permeability with reference to its level of productivity. He says: “Let’s examine the basic principle of permeability, which according to the Filtration Dictionary can be defined as ‘the ease with which a porous substance permits the passage of a fluid’. This is often confused with porosity, which is ‘the ratio of void volume to the total volume of the filter media’.” “The higher the filter permeability, the lower the filter pressure drop, which then has a well-pronounced effect on energy consumption.”
Usually, introducing a higher surface area, Al-Attar says, is a method used to lower the pressure drop. “Unfortunately, the increase in pleats, depth or the number of pockets in an air filter can have a counter-productive effect on filter performance, resulting in the deterioration of the overall efficiency of the air filter.”

What’s rocking the boat?

Mohamed Shafiq Ur Rahman

Mohamed Shafiq Ur Rahman, Senior HVAC Engineer, Gulf Consult, Kuwait, gives a fitting analogy, saying: “The importance of air filters is like the heart. If the heart is strong, healthy and vibrant, then the person will be healthy. Similarly with air filters. However, for this to happen, it is important to know which air filter will work best, based on the end-user’s requirements.” He adds that air filter performance, in terms of pressure drop and efficiency, along with manufacturing craftsmanship and the materials used, are all factors that must be taken into consideration when choosing an air filter. He says, “End-users are often unaware of these factors and, hence, it is important to trust the engineering consultant.”

Al-Attar echoes Rahman, saying: “In the past, high-efficiency filters came with a hefty pressure drop, which was a major turnoff for both designers and users. This again emphasises that air filter acquisition or purchasing should be conducted under the immediate direction of the filtration engineer,” adds Rahman. “As a consultant, the salient features for the selection of air filters are the efficiency, particulate size, pressure drop, media and aerodynamic design, which play an important role in understanding which air filter is ideal in a particular setting.”
Al-Attar highlights a trend that exists in the air filtration market, where filters are acquired without consulting a professional filtration expert and calls it the “fit all application”. Elaborating, he says: “It is like asking the pharmacist directly for medication to avoid the cost of consulting a doctor.”

The person who selects the filter, Al-Attar says, must be certified by the government and held responsible for the selection. He says: “This is a matter that needs to be taken very seriously, as employing state-of-the-art filtration to provide for people’s respiratory systems is not an experiment.” Here, Attar raises an important question, saying, “Today, the advances in filter media and cartridge design have brought better answers to the aspect of
enhancing air quality.” However, he insists that we ask ourselves how many times we re-visit filtration specifications to update and synchronise them with the latest filtration technology made available to the end-user. Al-Attar also highlights the technical challenges with regard to how air filters are released into the market. He says: “There is a deep ambivalence between the demand for good IAQ and how air filters are manufactured, specified, acquired, installed and replaced. There is also an unusual infatuation with washable metallic filters, in addition to dust loading, which is a chronic filtration problem that shortens the life of a filter.” Interestingly, experts believe that the need for consultation while choosing the right air filter is just one obstacle to achieving the desired result.

Highlighting the many other challenges influencing the air filter market in the Middle East, Al-Attar says: “Often in the HVAC industry, performance filtration signifies efficient air filters that are aerodynamic; however, status quo dictates price as the standard for performance. While that’s not all, other challenges, like filter failure, inappropriate filter selection and regeneration of disposed-off filters with water and air to re-use them, is a major syndrome in the Middle East. One of the biggest misconceptions is that extending the life of a filter, helps save costs. Re-installing wet filters in the AHU can promote micro-organisms and expose the entire HVAC system and human occupants to greater health risks, which defeats the entire purpose of good IAQ.” That’s not all, Al-Attar highlights the role of recognising good technicians in helping the market grow and says: “No one has ever recognised the best AC technician of the year or month. We expect to confront the dusty filters, the excess heat and humidity without any sort of appreciation.” Technicians, Al-Attar says, need to be provided with advanced tools and instruments, and their health and safety should be taken into consideration. An ideal start, he says, would be to establish a programme for HVAC maintenance teams and staff, where there would be qualification, training and appropriate examinations, leading to certification and recognition.

Al-Attar also highlighted that filtration requirements are application- and location- sensitive; however, the drivers for current requirements range from demanding high filter efficiency of sub 1μm to striving for an aerodynamic filter design. He says: “Regionally, filter performance is still assessed by how long a filter lasts in operation, irrespective of its operational conditions, sustainable efficiency and pressure drop response. I still recall when I read some pre-filter specifications 25 years ago, and the term ‘permanent’ filter caught my attention. I learnt that ‘permanent’ is used to refer to the aluminium mesh filters. It is ironic to encounter such filters corroded in the air-handling units, suggesting their inability to protect themselves, let alone protect the subsequent filter and/or the human occupant/application at hand. Yet, it is still widely used in the region. If we are really serious about
achieving and inhaling better indoor air, then we must have the courage to change trajectory, in the way we approach air filtration systems.”

Tactics to ensure an improvement in Air Quality
The first step, Al-Attar says, is to rely on “increasing awareness”, and get everyone involved in the selection process, to source the latest, ideal, filtration technology. He says, “We need a standard measure for filter performance to get rid of any malpractice.” Further elaborating on the role and need for international standards, Al-Attar says: “If international standards are understood appropriately and implemented professionally, then yes, they can have an impact. However, while filtration technologies can contribute substantially to reducing emissions, we are in need of a revolution to abandon our conventional practices that turn HVAC systems into an engine that spreads contaminants. Therefore, I believe in a governmental Air-filtration testing facility inspired by the International Standards, without which our plans and actions appear arbitrary.”

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