Raising the standards with insulation
The loss of heat and energy through ductwork can have a significant effect on a building's overall running costs and contributes greatly to its CO2 emissions. MEP Middle East looks at the latest developments and standards for the thermal insulation of h&v ductwork.
An airtight, well-insulated ductwork system is key to a building’s heating and cooling installation. If the system is not effectively designed, installed, sealed and insulated, the total heating and cooling costs can be increased by up to 40%.
The sizing of the ductwork is a vital factor in ensuring that comfort conditions and an energy efficient scheme are achieved. Ducts that are incorrectly sized for the areas that they are intended to serve can cause hot and cold spots in a building and will affect the efficiency of the building’s overall operation.
Perhaps more important is the length of duct runs and the potential changes in temperature that these produce. In the Middle East market where the scale of projects means that large duct runs are often necessary, reducing the impact of such losses becomes an essential factor in the system design. The ambient temperature in the region brings the danger of increases as well as decreases in temperature if insufficient insulation is used.
But another factor that must be considered today is that the lack of sufficient insulation on hvac systems has been proven to significantly add to the CO2 emissions from a building. If the UAE is to meet its Kyoto obligations, all aspects of the built environment must be considered and ductwork insulation is being highlighted in other areas of the world as a key way to reduce unnecessary emissions.
One of the key standards covering the ductwork sector, BS 5422: 2001 Method for specifying thermal insulating materials for pipes, tanks, vessels, ductwork and equipment within the temperature range –40°C to 700°C is currently being revised to reflect the importance of insulation to the environmental agenda.
The industry-wide standard includes detailed guidance on the effective use of insulation to conserve energy, prevent surface condensation and protect personnel against extreme surface temperatures. The revision of the standard will involve a change in emphasis over the use of economic benefits as a method to determine the minimum thickness of applied insulation. Although this approach is expected to remain permissible in the foreseeable future, in the revised standard the focus of all the energy-related tables in the standard will be based on the absolute energy use and the associated carbon dioxide emissions.
“It is anticipated that the revised version of BS 5422 will drive forward standards of process efficiency and especially environmental stewardship; plus, equally importantly, be practical,” explains Nick Ralph, technical marketing manager for Rockwool, who is chairing the standards revision committee reviewing BS 5422.
“The revised ‘environmental’ thicknesses of insulation given by BS 5422 will therefore be based on a balance of environmental, financial and practical considerations,” Ralph adds.
The current version of BS 5422 already includes tables of insulation thicknesses that promote the environmental benefits of energy saving. However, changes that are made to these tables as part of the current revision process will also reflect a greater emphasis on the practicality of installing insulation on site.
There is little benefit in selecting the optimum insulation at design stage if the installation method reduces its effectiveness. The two critical factors in obtaining a good insulation performance are thermal conductivity and vapour permeability. The latter is especially vital in climates with high humidity levels such as are experienced in the Middle East.
If moisture in the ambient air passes through the insulation it will condense on the duct surfaces. This would saturate the insulation with water, negating its insulating properties and deteriorating the ductwork metals. Many products available include a vapour barrier on the outer surface to reduce this problem, however care must be taken that this is not damaged during installation.
The choice of insulation material should also be considered. It should protect against rotting, mould, fungal growth and vermin, as well as be suitable for use without degradation throughout the range of operating temperatures to which it will be subject in a given application. Products containing cfcs in their manufacture should not be used for environmental considerations.
Products now available on the market aim to simplify on-site installation while ensuring that the thermal qualities specified in the system design. Insulation in the form of rigid, preformed boards; flexible rolls; blankets; mats and mattresses is available to suit the range of rectangular, circular or flat-oval ducting that is commonly used. Pre-insulated sections of ductwork are also now commonplace and different materials are being used to assist the ductwork installer’s job.
The choice of product for an application will involve a number of factors including mechanical strength, durability and resistance to moisture. The fixing method used should minimise the occurrence of direct metal paths where thermal bridging can cause localised high temperatures at the aluminium foil surfaces, and the vapour seal must continuously cover the entire system.
Dubai-based manufacturer Alpha Duct, a member of the ETA-Ascon Group, offers pre-insulated ductwork that uses phenolic and pir foam which, as well as holding good insulation properties is lightweight and easy to handle. This is already being installed in some prestigious projects in the region including the Burj Dubai Residences and Al Dafna Towers.
Pearl Industries also offers pir foam pre-insulated panels for the construction of air distribution ductwork. And earlier this year, Thermobreak launched a product onto the market that comprises an electron beam crosslinked, closed-cell Polyolefin foam composite that is bonded to a reinforced aluminium foil.
Thermobreak’s insulation can be used on internal and external applications and the manufacturer claims that it gives virtually zero vapour permeability.