Downlighting and Ducted Heating/Cooling

Using FirstRate, we currently model both downlights and roof based ducted heating/cooling as ceiling penetrations (as per previous advice received from CPD webinars) as follows: 

Downlights (LED type, that allow insulation over the top of the light itself, with just the transformer sitting on top of the insulation – so no break in insulation) are modelled as a 90mm x 90mm penetration, with 0mm clearance, and marked as sealed.

Ducted heating/cooling (the ducts themselves are insulated to R1.0, with the return air vents un-insulated) is modelled as 150mm x 150mm penetrations (exhaust fan) for each of the vents, and a 900mm x 550mm penetration (exhaust fan) for the return air unit (both with 0mm clearance and marked as sealed). 

Is this still the correct way to be modelling these two elements (the downlights given there isn’t an actual penetration as they are the type that does not require a break in the insulation, and the ducted heating/cooling given the duct work itself is insulated (albeit not to the same level as the ceiling itself))?

TechLink Response: 

• Recessed light fittings come in a range of different configurations and performance characteristics.
• The IC (Insulation Contact) rating is critical in understanding whether ceiling insulation is interrupted or not.
• IC4 fittings can have insulation placed continuously over the fitting.
• If IC4 recessed fittings are specified the number must be included in a NatHERS rating but penetration size and clearance values can both be zero.
• It is critical that the number be included so that there is no confusion about the final inspection by the building surveyor even though there is no impact on the rating.
• If not IC4 fittings there will need to be appropriate dimensions of interruption and clearance entered.
• And
• R1 insulation on ducting is an indication of an extremely low standard specification.
• Large amounts of heat and cold will be lost to the roof cavity prior to conditioning the rooms but this is not measured by NatHERS.
• At times when the house requires heating or cooling there will be no leakage through the grilles because hot or cold air will be flowing through them from the appliance into the zones.
• At times when the unit is not running the understanding is that the internal and external ambient temperatures are in reasonable equilibrium.
• Accordingly, there is no requirement to enter ceiling penetrations for insulated heating/cooling ducts in a NatHERS model.