Advice and News •
Ducted air conditioning is a complex system that uses a range of components to control a property’s climate. When you think of ducted air conditioning, the first thing you think about might be the ducts themselves, which run through the ceiling of a property and circulate the conditioned air.
But how does air con ducting work, exactly? In this article, we’ll explain how ducts help to deliver conditioned air, what they’re made of, the different types available, and more.
How does ducting work?
Ducted air conditioning is a climate control system that allows you to cool or heat specific zones (areas) in a property. Conditioned air is delivered to each zone by a network of ducts, which extend outwards from the indoor unit, and branch off into each unique zone, similar to how your body uses veins to deliver blood to your organs.
Air is delivered to each zone through ducted air con vents (or registers), and is returned to the system via the return grille. The return grille helps to relieve air pressure throughout the system, and includes a filter to trap dust and other pollutants.
When conditioned air is being delivered, it’s important to preserve its temperature along the way, which is achieved by using a number of insulating materials in the ducting. Insulation is measured by something called an r-value, which is the amount of thermal resistance that a surface offers.1 To achieve a favourable r-value, air con ducting can be made of various materials such as aluminium, polyester, plastic, and fibreglass. It can also be given an extra layer of insulation with a mastic sealant.
What are the types of air con ducting?
There’s two main types of air con ducting in Australia: flexible ductwork, and rigid ductwork.
Flexible ductwork (flex)
As its name suggests, flexible ductwork is a flexible type of ducting that is suited to tight spaces, and for this reason, is commonly used in homes. The ducts are typically made of a steel wire coil, covered in flexible polyester, and surrounded by insulating material such as aluminium or glass wool.2 They can also be made of rubber, PVC, silicone, and polyester fabric, and are a much cheaper option than rigid ducting.
Flexible ductwork comes in different diameters, which affects the air pressure in the system—the smaller the diameter, the higher the pressure, and the faster that air can flow through the system. There’s also other options to choose from such as thermal resistance (r-value), and the level of noise produced as air passes through them. Each type of ducting also has an operating temperature range (e.g. -20°C to +80°C), and range of pressure that it can handle (e.g. -190pa to +1200pa).
For flexible ductwork to be effective, it needs to be properly secured and supported, with lengths five metres or less, as few bends as possible to improve airflow. Under no circumstances can there be any kinks in the ducting, as the airflow will be compromised. This makes it important for the ducting to be installed by a professional who knows what they’re doing, as installation errors can lead to high energy bills, extra maintenance, regular repairs, and even entire replacements.
As most ducted air conditioners cover entire homes, it’s necessary to create branches in the ducting, which leads to its own unique zone in the property. Branches are created using y-piece or branch take off components, which are designed specifically to divert air flow and minimise temperature loss.
For flexible ducting to be safe and effective, it must adhere to the Australian Standard 4254.1-2012, which considers processes such as temperature, strength and rigidity, tensions, pressure, and susceptibility to mould.3
Flexible ducting is usually installed in the roof cavity of a property, but it’s also possible to install underneath the floor. This type of ductwork tends to be cheaper than rigid ductwork, and is fairly easy to install.
Rigid ductwork is a hardier type of sheet metal ducting, which requires a little more space compared to flexible ductwork, making them more popular for commercial spaces such as offices. As with flexible ductwork, rigid ductwork is created with different diameters, based on the amount of desired air pressure. It’s much more expensive than flex, as it needs to be custom made, as well as transported to the property. But because sheet metal has better natural insulation than flex ducting, it’s more effective at regulating the temperature, and can lead to energy savings. It also lends a cool industrial look to commercial spaces, and its durability makes it last for much longer.
Rigid ductwork is typically made of two different types of metal: galvanised steel or aluminium.
Galvanised steel ductwork
Galvanised steel is popular because it contains a zinc coating that prevents it from rusting, and so doesn’t require painting (or re-painting). This type of ductwork is typically fabricated in metal shops, which are manufactured in sections, and then joined during installation. It can be rectangular or round.
Aluminium is a lightweight material, which makes it easier to install when used in an air conditioning system. As with galvanised steel, the ductwork is usually custom-made in metal shops, and connected using joints and sealants. Aluminium ductwork usually has a rectangular shape.
To dampen the noise of the air conditioning system, rigid ductwork can include an internal fibreglass lining. However, the acoustic benefits of fibreglass are offset by its difficulty to clean, and susceptibility to mould and bacteria, which can create health problems. More importantly, if enough time passes, fibreglass can deteriorate and release fibreglass particles into the air, which are a major health concern.
Rigid ductwork can also be made entirely of fibreboard, which is naturally well-insulated. But this material suffers from the same problem as fibreglass, being difficult to clean and prone to mould and bacteria growth.
For rigid ducting to be safe and effective, it must adhere to the Australian Standard 4254.2-2012, which considers similar processes to flexible ducting, including temperature, strength and rigidity, tensions, pressure, and susceptibility to mould.4
Due to its size and lack of flexibility, rigid ductwork is usually installed in a building’s roof cavity, where there tends to be more space. It’s rare for rigid ductwork to be installed underneath the floor.
To connect the system of rigid ducts to the indoor unit, it’s common to use flexible ducting, as this is much easier than fabricating a precise piece of metal to connect to the unit.
Ducts are just one component of a ducted air conditioning system, but a critical one. Whether flexible or rigid, they transport conditioned air around your home, forming a network that allows you to control the climate with exact precision.
Ducted air conditioners are complex. If you’re having an air conditioning system installed by a company (which you almost certainly should be), you won’t need to worry about how ducting works, or the nuances and differences between them. A professional will be able to recommend the ideal system for your home, based on their experience. At H&H, we’ve been installing air conditioning systems for over two decades, and can recommend the perfect solution for your property.
- R-value (insulation), Wikipedia
- 2015, Different Types of Ducts for Central Air Conditioning, Art Plumbing & AC
- Flexible air conditioning and heating duct, Current Force
- Australian Standard, infostore.saiglobal.com