Specification J5.2b Ductwork Insulation and Sealing

clarifies that contains the required performance for the insulation and sealing of ductwork and fittings, where the ductwork is part of an air-conditioning system.

outlines that for the purposes of this Specification, 'fittings' includes passive or static components of a ductwork system and excludes active components of a ductwork system such as those used in an air-handling unit.

This means passive or static components of a ductwork system must meet the requirements of this Specification and may include items such as plenums, bends, branches, transitions, reducers, offsets, spigots, cushion heads, attenuators and fixed air balance dampers.

Active components of a ductwork system are exempt from the insulation and sealing requirements of this Specification. This exemption recognises that there are practical difficulties applying insulation to components that move or where access is regularly required.

Active components may include Variable Air Volume (VAV) boxes, electric duct heaters, actuated volume control dampers, access panels and doors, fire and smoke dampers, fans or humidifiers.

Air-conditioning ductwork has joints, and unless sealed these joints will allow heated or cooled air to escape. To limit this heat loss or gain, ductwork must be sealed with adhesives, mastics, sealants, gaskets or the like in accordance with AS 4254 Parts 1 and 2 for the static pressure in the system as stated in . AS 4254 is the standard covering ductwork for air-handling systems in buildings. These requirements do not apply to ventilation ductwork where the air is not heated or cooled.

The exemption in outlines that the requirements in do not apply to ductwork in the space being conditioned or the last room served by the system, as the air is intended for that space anyway.

Ductwork and fittings in an air-conditioning system need to be insulated to reduce energy loss. The insulating requirements do not apply to ventilation ductwork where the air is not heated or cooled.

outlines that insulation must comply with the requirements of AS 4859.1.

requires that insulation applied to ductwork and fittings must comply with the minimum material R-Values specified in or for flexible ductwork must achieve an added minimum material R-Value of 1.0, where the flexible ductwork is not more than 3 metres in length to an outlet or from an inlet. Where flexible duct is more than 3 metres in length it must comply with . This means that flexible duct runs (single or joined) greater than 3 metres in length must comply with the requirements in .

Note that the insulation levels in are minimum material R-Values of the added insulation and are based on the location and climate zone of the installed ductwork and fittings.

outlines specific requirements of the insulation, such as (i), that states the insulation must be protected against the effects of weather and sunlight, which will likely reduce its insulating properties over time.

requires insulation to be installed so that it abuts adjoining insulation to form a continuous barrier as any gaps in the insulation allow heat loss or gain. The insulation should also maintain its position and thickness other than at flanges and supports as any compression of insulation can reduce its effectiveness.

requires a vapour barrier to be installed around the insulation on ductwork that conveys cold air to assist in the control of condensation resulting from the cold surface. Without a vapour barrier, the likelihood of condensation forming increases. Condensing moisture can saturate the insulation, thereby reducing its effectiveness and causing it to deteriorate. states that where the vapour barrier used is a membrane, it must overlap by 50 mm and be bonded or taped together to ensure the vapour barrier membrane can function as intended.

exempts a number of situations where ductwork and fittings do not need to be in accordance with the requirements of as it may be impractical or pointless to do so.

exempts ductwork and fittings located within the only or last room served from being insulated on the basis that the heating or cooling effect is intended for that room anyway. If a room where the ductwork is not insulated is sub-divided then insulation will need to be added to the ductwork that passes through the first room to serve the second room. This needs to be considered if the exemption is applied to a part of a building or storey likely to be sub-divided as part of a fit-out.

exempts fittings that form the interface with the conditioned space such as air registers, diffusers, outlets, grilles and the like as there would be minimal heat transfer occurring.

exempts return air ductwork in, or passing through a conditioned space from meeting the minimum insulation requirements as there would be no heat transfer across the ductwork.

exempts ductwork containing unconditioned outside air or exhaust air ductwork where the air is to be discarded anyway. There would be no benefit gained, in terms of reducing energy consumption, by requiring insulation to be installed on this ductwork.

exempts the floor of an in-situ air handling unit from the insulation requirements of .

exempts packaged air-conditioning equipment that comply with MEPS.

Note that air-handling ductwork must also comply with .

The application of the ductwork insulation requirements of are shown in the following example.

Example

Example

Figure Spec J5.2b(1) APPLICATION OF DUCTWORK INSULATION

The building is located in climate zone 5 and the ductwork is greater than 3 m in length.

Space A is not conditioned; therefore insulation must be installed to the supply and return ductwork with a minimum R-value of R 2.0 as per .

Space B is a conditioned space; therefore insulation with a minimum added R-Value of R 1.2 from is required to be installed on the supply ductwork. No insulation is needed for the return ductwork in Space B as it is exempted by .

Space C is a conditioned space. Since it is the last room served by the system the insulation requirements of do not apply to the ductwork.

In Space B and C the diffuser forms the interface with the conditioned space and is therefore exempt from the insulation requirements of by .

The exhaust ductwork is exempt from the insulation requirements of by .

Note that the requirements of may also apply.