PIR panels better for ducts, says Pearl
Polyisocyanurate technology is set to revolutionise the fabrication of ducts given its numerous advantages over galvanised iron ductwork, says Ahmed Hindawi of the Dubai-based Pearl Industries.
01 April 2007
Ducting technology is set to take a giant leap forward, thanks to the latest polyisocyanurate technology.
While ducts for central air-conditioning have traditionally been made from galvanised iron (GI) sheet metals, panels made from polyisocyanurate – more popularly known as PIR panels – have overtaken the use of GI for fabrication of ducts due to their distinct advantages.
Table 1 gives a comparison of GI vs PIR ducts, highlighting the benefits offered by the latter. Apart from these salient features, these pre-insulated panels and ducts offer a number of other advantages, making them increasingly popular among consultants and the MEP (mechanical, electrical and plumbing) contractors.
The advantages of pre-insulated panel ductwork are built into it right from the production process, as these panels are environmentally-friendly, being totally CFC (chlorofluorocarbons) and HCFC (hydrochlorofluorocarbon) free, unlike GI ductwork which utilises CFCs.
During the fabrication of GI ductwork, fibreglass is dispersed in the cutting process, causing a health hazard, whereas PIR panels do not disintegrate while cutting.
Quality
In terms of quality, PIR panels are offered by a single quality-assessed (ISO 9002 manufacturer and requires only a minimum of supervision as it is factory-supplied in a semi-finished condition, hence deviations from set procedures and material specifications cannot occur. It meets the requirement of IAQ (indoor air quality), which is especially important in clean room applications such as hospitals, laboratories, food processing etc.
GI ductwork is manufactured by at least five different manufacturers and distributed by numerous vendors in the UAE. It requires continuous supervision to ensure conformity to material specifications, work methodology and workmanship. In addition, adhesives used in their fabrication have a much shorter shelf life. In a warm and humid environment, the lagging adhesives used in the insulation work give rise to the eventual growth of fungus, bacteria, mildew (typical 'black spots).
Space requirements
This apart, being space-consuming, GI makes greater demands in terms of transportation to site, site storage facilities, and requires the use of service lifts, hoists and heavy scaffolding. Pre-insulated ductwork – being site fabricated and installed – minimizes storage area requirements and only calls for lightweight handling equipment. Panels and accessories are moved and fabricated into ducts at the actual workplace itself (such as at various floors of a multi-storey building).
Installation of GI ductwork also require a bigger workforce and a longer time frame for completion compared to its polyisocyanurate counterpart that offer faster completion with a smaller workforce. A large workforce translates into added costs in accommodation, sanitation, transport, mess/dining space, government departmental costs, gratuity, travel costs, added supervisory staff.
Efficiency
When installed, PIR ductwork is 15 to 20 per cent lighter than its GI counterpart. When in place, PIR ductwork offer the advantages of reduced heat losses as it has a 'U' value of 0.0247 (20 mm panels), compared to GI ductwork which has a U' value of 0.033 (with 25 mm-thick insulation). Thanks to the reduced energy losses, pre-insulated panels offer energy savings and supports energy conservation programmed/environmental protection.
GI ductwork is designed for three different grades of construction for low, medium and high air-velocity class, whereas PIR ductwork is universally suitable for up to 1500 Pascals of positive or negative pressure.
In the case of GI ductwork, the slightest damage to the aluminium foil vapour barrier results in condensation on the duct surface and consequential damages to ceilings/finishes with the damp areas being susceptible to mildew/ fungal growth, while the fibreglass absorbs water and loses its thermal properties. In PIR, however, the closed cell content is very high, thus minimising water absorption as confirmed by a water immersion test. If the aluminium laminate of PIR panels is damaged, it can be repaired. Hence the chances of vapour condensation and water drip-off are practically nonexistent, thereby eliminating the risk of consequential damages to ceilings/finishes.
Pre-insulated panels also scores in terms of its longevity. Thanks to the use of aluminium laminate, coated with 2 gm/sq m of special anti-rust lacquer on both sides (all panels). In addition, special panels – with additional polyester film on the aluminium laminate – are available for highly corrosive environments. In the case of GI ductwork, the galvanisation begins to oxidise/deteriorate over a period of time, especially when the installation is external or exposed to weather.
Turning to the ultimate deciding factor in selecting ductwork – cost: pre-insulated panel ductwork proves to be more economical by a margin of at least 40 per cent!
Consultants and the MEP contractors in the UAE – where all projects are fast track – would find the use of PIR ducts to be a boon. Given these facts and current trends, GI ducts look set to become a thing of the past!
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