SR362 Kotuku Apartments thermal modelling - design stage (December 2019)

Wellington City Council upgraded the Kotuku Apartments as part of an extensive renovation and redevelopment process over the 2013-2016 period. This study focused on examining the apartments' thermal performance - both existing and that resulting from various possible design upgrades. Existing performance was examined using thermography, while detailed computer thermal simulation was used to compare the design upgrades.

In terms of existing thermal performance, thermal imaging found that water ingress into the external polystyrene wall panels and soffit heat loss were two problem areas that needed rectifying.

Various possible construction scenarios (i.e. thermal upgrades to the external envelope) were explored via thermal simulation. It was found that for the original building, when no external space heating was provided, all of the apartments fell below 12°C at some point during the year. When re-simulated using the finalised specification, the number of days with temperatures dipping below 12°C fell to just 2–6% of the original number of days, depending on the placement within the building. When active space heating was provided, simulations found that in the original specification, the four-bedroom ground units were predicted to cost between $1,900 and $2,290 per year to heat. The final plan specification reduced these heating costs to around half that, at $1,090–1,140. These figures are based on an electricity tariff of $0.28 per kilowatt hour.