Comment: Ducted vs. ductless air conditioning systems

By Tariq Al Ghussein, chief executive officer, Taqeef.

Tariq Al Ghussein, chief executive officer, Taqeef.
Tariq Al Ghussein, chief executive officer, Taqeef.

The AC market in the region was built on ductless AC units – indeed, it was Fujitsu General’s first ever desert specified window unit which originated the AC market in the region in 1972. Following this, split AC units – wall mounted ductless designs which offer direct and easily controllable cooling for single or multiple rooms or spaces – became the most popular choice.
In more recent years, we’ve seen the market evolve, and witness a move towards ducted designs which are largely hidden in the walls and ceilings of a building, with cooling delivered from a central air conditioner via wall and ceiling vents. While many consider this to be the most aesthetically unobtrusive cooling option, it comes at considerable cost. Ducted units are not usually the most efficient as improper installation, insulation and maintenance impact the safety, effectiveness and emissions of these designs.

Ducted Systems
When opting for a ducted system, several factors need to be looked at to ensure the best possible outcome in terms of energy efficiency and maintaining air integrity. The first, and probably the most important of these, is the design of the ducting itself.  Unfortunately, as a region, we don’t routinely specify return air ducting, which undermines the efficacy of the whole system. In simple terms, contractors and specifiers often reduce the amount of ducting they use as a cost-cutting measure. This means that the dust that’s routinely generated by the system simply collects within the false ceiling, compromising air quality and safety. And, while many of us routinely have our ducts cleaned, false ceilings are tricky - if not impossible - to access, which means the problem is an ongoing one.
Simplifying the structure of the ducting design (through the use of shorter ducts and less bends) is also preferable – resulting in easier cleaning and maintenance of the units. Using optimum specification, professionally installed insulation also contributes to the ease with which the maintenance is carried out.
Another issue related to ducted designs is improper sizing and installation; a primary cause of high energy bills, reduced performance, poor indoor air quality and irregular air distribution of cooled air. All these factors can culminate in uncomfortable hot and cold spots due to the uneven distribution of cooled air.
A large percentage (20%) of the air circulated through the ducting system can be lost due to leaks and poor connections. So, it’s imperative that professional air duct sealing is completed to avoid these issues. Despite the initial cost and inconvenience of the process, users will have increased energy efficiency and lower utility bills, meaning the initial cost outlay is recovered over time.
The inaccessibility of ducts often causes a challenge when it comes to maintenance and cleaning. Not only do dust and allergens accumulate but the ducts can also provide a haven for vermin infestation, which can be very expensive to treat, all the while compromising the health and wellbeing of the residents. To avoid such issues, it’s important that ducted systems are properly insulated. In addition to protecting against moisture-related problems, duct insulation will also improve energy efficiency by preventing external variable temperatures from affecting the temperature inside.
While the above looks at the ways to ensure the best results from a ducted system, research still points to unducted designs (i.e. wall mounted split units) as the most energy efficient and air preserving method of cooling in harsh desert conditions. A design scheme where ducts are avoided - or at least reduced - should always be promoted as a manageable alternative as we pursue an energy conserving standard.   And, while there will be some exceptions to this (for those chiller fan coil units which are larger and noisier, a complex ducted design is often necessary) this should not be standard practice.


Ductless Systems
Split ACs or ceiling concealed DX systems work in a very different and more direct way. They are easily and instantly controllable, offer maximum energy efficiency, and remain the most popular choices when it comes to units installed in residential and commercial properties.
The benefits of ductless systems aren’t restricted to increased energy efficiency and regulated temperature control. One of the most common risks mitigated by split units is the problem of mold, which can be caused by introducing cold air into a warm room and the resulting condensation.
Foregoing a ducted system for a wall mounted unit not only alleviates the problems associated with having to clean and insulate ducts, but also greatly impacts building costs. By foregoing the additional space needed to accommodate ducts, it possible to reduce building costs by shaving up to 50cm off each floor. Ducting can be replaced with a sleek and modern unit design (which can also be concealed in cupboard or alcove if preferred) resulting in higher ceiling and reduced construction height. On a 30-story building this could mean as many as an additional three floors.

The future
As an industry, we need to get better at designing schemes with maximum efficiency as a priority. That means only using ducted designs where and when they’re absolutely necessary – in large scale projects which require bulky and noisy fan coil units where ducting is essential to reduce the noise. Otherwise we should use wall mounted units or ceiling concealed as the standard – as they do in Europe and Asia - ensuring the ducting is sufficient (supply and return), minimised in length by good design and properly insulated. 
Whichever system is chosen, mindful consideration of environmental impact should be a key driver. After all the best cooling should provide comfort that promotes a greener, cleaner world.

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