By Benjamin Brits
No matter if you’re bringing fresh air into a space or extracting it from a contaminated area, ventilation plays a critical role in meeting various application needs and standards.
A definition of ventilation is the movement of outdoor air into a building or a room, and distribution of that air within that space with the purpose of providing ‘healthy air’ for occupants. Air quality is affected by both diluting any pollutants originating inside the space and, in certain cases, removing or cleaning out any pollutants by means of extraction or a circular process. This function is completed through the incorporation of fans, ducting and diffusion products.
Ventilation is achieved through three possible methods used in commercial and retail applications: natural, mechanical, and hybrid (a mixed-method solution).
Building ventilation has further elements to consider:
- Ventilation rate – the amount of outdoor air that is provided into the space (outdoor air quality is of course also an important factor).
- Airflow direction – the overall airflow direction in a building, which should be from ‘clean zones’ to ‘dirty zones’.
- Air distribution or airflow pattern – the external air should be delivered to each part of the space in an efficient manner and any pollutants or concentrations generated in each part of the space should also be removed in an efficient manner.
From a design aspect, above what has been stated already, other elements of consideration on this topic related to buildings include indoor air quality and air changes – per hour. Ventilation in buildings may also include a series of ducting (standard steel, fabric type and flexible option), and conditioned air (heating and cooling) through an air handling unit. Ventilation will also usually include various means of air filtration.
A fabric duct installation catering to the ventilation and conditioning required in a gymnasium. Photo by ©RACA Journal | Benjamin Brits
“The quality of air supplied into a building is obviously very important. All outdoor air supplied into the space must be filtered and must be drawn from a clean zone as mentioned before. Extracted air, from kitchens and toilets for example, must be discharged in a manner that doesn’t cause annoyance in the environment for people around the area. Further, extracted air from spaces like a TB department in hospitals must be filtered before it gets discharged to the environment. Filtration systems can be installed in mechanical ventilation systems to eliminate harmful microorganisms, particulates, gases, odours and vapours,” says Siphiwithemba Dube, mechanical and fire engineer at VMG Consultants.
“One of the biggest misconceptions in the market is the understanding and interpretation of efficiency.”
Dube continues, “The air movement in a space, also refers to as the required air changes per hour, is dependent on the space occupancy-classification – and is a mandatory inclusion. In South Africa, the ventilation requirements for different building/space classifications are outlined in SANS 10400 Part O – Lighting and ventilation – and includes the table that shows the minimum requirements of air per person using the room.”
Where spaces or rooms are, for example, open to smoking, a considerably higher supply of healthy air is required.
Fans, as an integral part of a building’s ventilation system also require several design considerations which include:
- The air flow rate to be extracted or supplied
- The system resistance or pressure drop
- The flow rate and the system resistance then determine the selection of the fan, that is, mixed air flow fan, centrifugal fan or axial flow fan
- The efficiency of the fan
- Fan speed (number of poles)
- The noise levels or sound pressure
- Power consumption
- Operating latitude and temperature (depending on the operating environment)
- Physical size of the fan – where or if there is a space limitation
The occupancy classifications of the ventilated space, for example the use of non-ferrous fans for flammable stores
“Some errors in design or installation in ventilation that I have observed, stem from not conducting a noise analysis resulting in noisy fan installations. The other common error is installation of normal canvas collars on kitchen canopy extractors that get damaged by heat over time and result in air leakage leading to inefficient extract systems. Further, inadequate ventilation systems result in build-up of carbon dioxide to above 1 000ppm – which is the accepted concentration in an indoor occupied space. High concentration of carbon dioxide and lower oxygen levels will result in drowsiness, shortness of breath, headaches, and fatigue of occupants. In ‘wet’ areas like bathrooms, incorrect ventilation designs will result in high levels of moisture causing, amongst other effects, wrinkling and peeling of the paint and formation of moulds on the walls and ceilings,” Dube adds.
Other than the makeup air supplied to a building or space, air extraction as part of a building’s ventilation system in many applications is vital. For example, some hospitals as already mentioned, but also in such applications as processing and industrial facilities where toxic fumes may be present, flammable gases or chemicals, laboratories, kitchen and food preparation areas, extraction of various particulates such as overspray in manufacturing, and more commonly, smoke extraction.
A common building extract fan installed at a rooftop plant. Photo by ©RACA Journal | Benjamin Brits
“Smoke extraction, as part of a building’s ventilation system is critical and is required in cases of emergency. BS EN 12101 – Part 3, covers the emergency evacuation of smoke from a building intending to allow occupants to escape with minimal harm. Any building constructed now over a certain size must have a smoke extraction system included by law. This particular element also involves a significant number of fans that can be as much as 50 in an installation,” notes Murray Anderson, group national sales and export manager at Elta Group Africa.
Ventilation (and extraction) systems can be configured in a number of ways, depending on the design of the engineering team and building setup. These can include systems per building level, one main system ducted to each level, and more recently plant rooms or service areas at different levels in a building catering to different building sections. As is common today mixed-use buildings have become an increasingly popular client request and this results in varying ventilation functions.
Basements are another area where air change (specifically extraction) is required and can include sensors to monitor carbon monoxide or smoke levels. Sensor technology can also aid in energy consumption as impulse fans can operate only when needed as concentration levels reach set limits. This also allows that not all fans have to operate simultaneously. To note, smoke and fume extraction design is done and signed off by persons with the appropriate competence.
Selecting the correct fan
Fans for HVACR applications come in a variety of sizes and configurations from very small units to large custom-made units measuring as much as two metres in diameter. They can be made from different materials including plastics, steel and aluminium, further be fitted with various blade quantities, and run at different revolution-per-minute ranges.
Depending on the application environment, bearings are the only real failure-susceptible or ‘wear component’ in a fan and indirectly determine the fan’s lifespan, measured in work hours which can run into tens of thousands of hours. Some fan-mechanisms can be maintained, thus prolonging life expectancy. Newer technology includes magnetic driven motors without any bearing.
As with most industries there are a number of cheap imports available in the country which is difficult to compete against the supply of good quality, more expensive products. The South African mentality remains very much aligned to the cheapest options with the hope of making a 12-month guarantee. Under the current economic environment, securing contracts has become tough, and looking to the bottom-line means looking for cheaper products. What is also happening more and more regularly, and is pulling the wool over people’s eyes, is that quality brands are being copied and sold cheaper when in fact they are poor quality.
“Certainly, many engineers are applying principles to ensure efficiency and good practice, and this is often driven by the client or those who seek green building accreditation. But South Africa is lacking regulations in efficiency, essentially allowing the industry to use whatever products they choose. This is a particular challenge for suppliers as often products are not evaluated on an even playing field in an increasingly price-sensitive environment. Off-the-shelf extraction systems are generally not very energy efficient and often misleading information results in selecting old or poor technology,” says Anderson.
Extract fan selection needs to meet application requirements and regulations, and should further be certified, for example if set to run at 300ͤ degrees C for two hours. Some suppliers build fans and then don’t have them certified. This is a potential risk for the engineers and contractors who wouldn’t necessarily be able to tell the difference. “This is something that is often overlooked, but in an emergency situation a fan failure resulting in harm or death means someone is going to possibly find themselves in jail,” Anderson stresses further.
When selecting a fan, two main elements need to be considered: air volume required, and pressure drop (system resistance) as Dube has mentioned. A particular error in these factors revealed by suppliers is that often the distances that air needs to travel are miscalculated. This can be due to factors such as additional ducting added that would stress the fans or ducting challenges on installation deviating from planned paths. Each fan is designed to produce a certain air volume against a certain pressure. If the parameters change, the output will change. Reducing pressure means volume decreases.
The pressure calculation would be determined by the size of the ventilation space as well required volume, as mentioned. The actual pressure is then determined by the ducting, whether there is any means of filtration or an air handling unit, how many bends are included, how many outlets are in the design, and so on. When all the parameters are known, suppliers are able to identify which model will work for the application, mostly suggesting one size larger to accommodate any inefficiencies.
When it comes to the bigger axial flow fans, these have adjustable-pitch propeller blades that can be set to exactly what the engineer specifies and thus the fan is then made according to specification. To note, changing the blade angles will increases or decreases the amount of power on the motor, so adjusting blades can result in drawing a whole lot more power from the motor resulting in premature failure. The addition of variable speed drives for these fan types is another method of electronically controlling the exact duty required.
“When considering fans generally, there are two aspects that stands out specifically pertaining to the product ranges in the HVAC category that engineers and contractors should be aware of. One of the biggest misconceptions in the market is the understanding and interpretation of efficiency. South Africa has representation of products from around the world, however because the local market leans heavily towards American standards through various guidelines based on ASHRAE documents, the way the industry compares technology is very different. So, when a product has an EU standard, there is often a misunderstanding in whether the product complies. Very often too, one gets lost in standards documents because of many external references and therefore interpretations vary. Secondly, products are not compared equally because of misleading information as Murray has already stated – which is also a very sensitive issue to address in the first place. Apples are not compared with apples,” says Francois Schoombie, technical manager – EC Specialist at ebm-papst South Africa.
“Today smart diffusers coupled with various sensors in a building offer an array of options to continually monitor and control air quality, air flow as well as space conditioning.”
Comparison of efficiencies goes back to the research and development of a product, where testing results are the most important, and where many variances can occur. Although standard testing mechanisms are deployed by manufacturers, extraction and reporting of the data is what is important. Specific conditions of testing include, tolerances, volumes and pressure being some of the elements to generate accurate data. Further, standards refer to noise, vibration, construction material and mounting means for testing. All of which can produce different results.
From a calculation point of view, if an engineer designs a system, they would calculate the total pressure drop. The OEM or supplier needs to be given this information that is based on external static pressure and downline pressure that the fan needs to be capable of overcoming, or, otherwise known as the resistance in the total system. Further, location plays an important role in the calculations because as you move away from sea level, air density is lowered, which must also be factored in. Most fan curve diagrams are based on sea-level conditions.
An internal cutaway view of a variable air volume diffuser. Photo by Rickard Air Diffusion
The progression of fan technology
”When it comes to extraction, inline fans have seen the most progress with a big move towards silent or ‘quieter’ fans. Energy efficiency has also become important for all HVAC components and is probably the biggest area of improvement over the last 10 to 15 years. Unfortunately, South Africa is taking longer to adopt energy-efficient products than for example Europe that has structured directives according to Energy-related Product (ERP) regulations that must comply to certain efficiency parameters. Sound attenuation has also seen a lot of development (silencers), and as mentioned, the development and incorporation of variable speed drives that add control thus bettering efficiency are other points to note. For other applications, Electronically Commutated (EC) fans have shown the most development,” says Anderson.
Conventionally, and many years back, fans operated by belt-driven means. As technology progressed, aerodynamic properties and principles have been improved, as well as fan control leading to the latest innovations. EC is a term now widely used in industry and has produced very good results in the HVAC market, particularly for comfort cooling applications. These typically include, rooftop air handling units and a major portion of local manufacturers have adopted this technology in their products too.
The biggest advantage gained for direct-drive fans was that the belts were eliminated. It was initially determined that approximately 15% savings were gained by removing pulleys and belts from a system. In line with the drive of energy efficiency, was natural progression and evolution of the fan where today fans use half the energy consumption from the belt-driven era. From those days, it was simple to reduce consumption by those margins, while today a mere couple of percent proves great advances in technology.
“Considered pioneers of the EC technology, ebm-papst in fact started producing these fans in the 70s for small or compact fan ranges. EC fans essentially make use of direct current (DC) motors. Although these products are supplied with AC connectivity, internally they are converted into DC. The reason for this is that DC motors run at a much higher levels of efficiency. The physical construction of the motor is also different. In a conventional motor your winding is on the outside, and the rotor sits on the inside. You add AC current through the windings that creating a secondary induced magnetic field in your rotor, thus creating movement. Conversely with EC fans, the winding sits on the inside, and the exterior rotates,” adds Schoombie.
Remote monitoring of various building diffusers is possible. Photo by Rickard Air Diffusion
EC technology has seen the largest development because with the configurations using VSDs, control obviously meant being able to limit capacity and when you don’t need the fan, to be able to slow it down or turn it off obviously saves a lot of energy. Incorporating this methodology into an inline EC unit achieved the same results with fewer components, additional cabling, noise management and harmonic disturbances.
Fan sizes and blade or impeller designs have also seen development over years as more compact units are required by the markets. Blade orientation and shape have also seen changes through scoop or push (depending on forward or backward design) that allow fans to operate under different parameters.
“Forward curve impeller blades are used in higher air volume application, but not for high pressures. Backward curve blade fans on the other hand can handle much higher pressures. The fan type was developed to be installed into, for example, an air handling unit that has multiple filters. In the past there was a primary and maybe a secondary filter in an AHU, where today tertiary filters, HEPA and ULPA filters need to be considered that greatly increase the pressure a fan must handle,” says Schoombie.
Further, fan blade shapes have been improved, again based on aerodynamic principles with the intention of reducing noise levels. These include, the physical blade shape, thickness and tapering, inclusion of additional blade fins or ‘winglets’, and symmetry.
Permanent magnet motors have also gained traction due to their further increased efficiency and are used in several fan models today. Fan speed ranges also continue to be developed to produce varying outputs.
“Looking forward, ebm-papst has in fact moved their focus away from the development of AC products. Within the next 5 to 10 years, AC products will no longer be manufactured in the European market at all as technology aligns to the ERP regulations. A manufacturer’s biggest job now will be to educate the end users to the benefits of new technology and the results they bring. This will be a challenge for all manufacturers who unfortunately sit in the middle of the supply chain. Users persist to select products as cheap as possible, but when cheap products are put forward against a comparative quality overall solution the benefits are seemingly insignificant for the client and they don’t yet realise the long-term results,” notes Schoombie.
Air distribution and diffusion
Generally, grilles, and more so, diffusers, are perceived as the horizontal or vertical split sections in walls, ceilings or bulkheads that are seen around any commercial, retail or hotel room settings, to distribute the air flow in a particular direction.
An example of a large cone-screw adjustable-face diffuser. Photo by Rickard Air Diffusion
Today smart diffusers coupled with various sensors in a building offer an array of options to continually monitor and control air quality, air flow as well as space conditioning, and can further be connected wirelessly. Remote connection and control has seen great drive over recent years.
“Diffuser technology, like other elements of a building’s ventilation has also seen large developments in recent years. It is a product that has seen incorporation of intelligent mechanical devices and now offers users variability – essentially meaning control or modulating of any environment’s airflow and temperature to their requirement. Further, through a buildings management system (BMS), the occupancy, temperature conditioning demand and ventilation demand in a space can be determined offering better management and thus operational efficiency,” says Mark Rickard, director at Rickard Air Diffusion.
This VAV or Variable Air Volume diffuser technology contains an actuator and damper that modulates the space requirements through the various add-on sensors by opening or closing to allow more or less air into the space, thus providing more accurate room conditioning. Through the BMS, groups of diffusers can be connected offering building-section information. With this data, it is possible to identify areas, that for example need to be flushed with more fresh air where higher concentrations of ‘stale air’ sits, or open and close diffusers in emergency situations where smoke or hazardous air is present.
There are different styles of diffusers available for different applications. These include drop-in ceiling or tile type, wall mounted or bulkhead, floor type and linear options. Shapes and styles have also seen development with improved aesthetics to make the product more appealing for the client. Style and design can also be custom engineered.
“Starting off with just a grille or diffuser as has been mentioned, you can see how suddenly this seemingly simple product can become quite complex and intelligent. Intelligent control solutions are going to continue to come into focus as users seek out more and more optimal ways to manage buildings and facilities. Many spaces also require very different conditions, even if they are in adjacent rooms. Look at how cell phone technology has developed – starting out as a simple device, they now have light and motion sensors, face and fingerprint recognition and GPS. Now, combining all that technology allows you to do much more. Better control also leads to better occupant productivity as Siphiwi mentioned earlier – better air supply monitoring and control avoids all the symptoms of unhealthy air. Further, in future we may be able to control or mitigate things like the spread of airborne pathogens like the Coronavirus by being able to quickly action isolation, space flushing or extraction of air through smart ventilation systems and inclusion of other technologies such as UV sterilisation,” says Rickard.