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Air leakage is the next big front on the way to net zero buildings

Stopping air leakage in buildings is one of the next big wins in the journey to a zero-carbon built environment, according to the Australian Sustainability Built Environment Council (ASBEC).

But it’s not just a building envelope issue – HVAC ductwork can be a major contributor to leaky buildings.

Leakage from HVAC ductwork means that heating and cooling systems are forced to work harder and use more energy to ensure thermal comfort, but it can also impactthe lifespan and maintenance needs of mechanical system parts such as fans, pumps and air handling units, according to Kingspan Insulation marketing manager Neil Cox.

The National Construction Code recognises the relevance of ductwork sealing when it comes to overall building energy performance. Section J has set down rules that define the acceptable parameters for air tightness.

Medland Engineering mechanical design engineer John Peacock says the higher the air tightness, the better. Air tightness reduces time wasted during commissioning, and also wasted fan energy during operation, he says.

Insulation of ductwork is also an important factor in energy efficiency and overall thermal performance of a building.

The challenge for designers, specifiers, builders and subcontractors is coming up with a solution that delivers high performance while meeting other project parameters, such as space available for ductwork, budget, the load-bearing capacity of support structures and project timelines.

Kingspan’s KoolDuct system aims to address all of these challenges with one product, Cox says. It is a pre-insulated duct system that has been shown to provide lower air leakage and higher R values than many conventional solutions. The integrated ductwork has been shown to reduce air leakage by up to 80 per cent compared to conventional sheet metal ductwork insulated with fibreglass blanket.

Reducing leakage means plant can be right-sized, and this can deliver a capital cost saving for both new build and refurbishment or retrofit projects, Cox says.

Samsung Head office with kingspan Kool duct

Samsung HQ, Seoul

Smaller and more agile

The integrated ductwork system is also smaller in dimensions than the standard sheet metal duct solution with added insulation. And because there is no need to leave space for insulation to be installed separately once ductwork is in place, it can be installed flush to walls, floors and ceilings.

Overall it also has a slimmer profile, saving up to 150-200mm compared with standard ductwork that has externally-installed insulation.

There are a number of challenges when designing ductwork systems to fit available space. They include shallow ceiling voids; multiple ducts crossing over one another, particularly in plantrooms; and ductwork passing through in between internal members of roof trusses, Peacock says.

Smaller dimensions offer definite advantages, Cox says.

“Flange widths and duct insulation on conventional ductwork is always an issue in tight roof spaces.”

Being lighter than conventional solutions also means it requires fewer supports, and it can potentially be used in retrofit projects where the building structures may not have sufficient load-bearing capacity for the heavier duct and insulation combinations.

The all-in-one, lightweight nature of the product also makes it fast to safely install, with only two people required for lengths of up to four metres.

The insulation incorporated into KoolDuct is a fibre-free combination of a phenolic layer and high-performance aluminium foil.

Good for IEQ

Having no fibres, unlike mineral wool insulation and some other products, means there is no risk of insulation fibres being transported into the building’s indoor environment via the HVAC system if there is a leak in a ductwork joint – a plus for indoor environment quality.

The insulation structure comprises 90 per cent closed cells, and the material is non-wicking and has a high degree of resistance to moisture and vapour permeability. This also addresses another of the major IEQ challenges – mould growth. KoolDuct is resistant to both fungal and mould growth, and is also odourless and free from CFCs and HCFCs.

Kingspan kool duct

Safety bonus

In addition to its performance benefits, there is a safety in design dividend with an integrated pre-insulated ductwork product.

Federal legislation cites an example of this in the Work Health and Safety (Safe Design of Structures) Code of practice. The case study of lightweight pre-insulated ductwork that was installed in a large nursing home project observed that the product was of assistance during a labour-intensive installation process that takes place in congested roof spaces and ceiling cavities.

The lightweight nature of the product meant it could be handled without the need for mechanical lifting equipment, and there was no need for workers to undertake manual lagging of the ductwork within confined spaces following ductwork installation.

Fewer hours working at height or in confined spaces reduces the overall amount of risk to workers involved in this kind of project.

KoolDuct has been used in projects across Asia, the US, Europe and Australasia, including Marina Bay Sands in Singapore, the Perth Convention Centre in Australia and Selwyn Aquatic Centre in New Zealand.

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