This requirement presents a conflicting challenge when designing an energy efficient building, because the windows are part of the insulation barrier and need to provide insulation to varying degrees to ensure the efficient operation of any air-conditioning equipment. This becomes a balance between cost, window size and energy efficiency.
This project is a multi storey residential building with a ground floor retail area and a multi-level car park below. The residential part of the building is covered by BASIX, while the retail floor and basement car parks are covered by Section J of the BCA. The standard Deemed to Satisfy (DTS) approach required three different glazing types on each of the North, West and South facades to achieve compliance with the minimum requirements of the Building Code. The DTS assessment required double glazing on the west façade, tinted windows on the north façade and clear low-E windows on the south facade.
Using the Verification Method (JV3) from the BCA, all the windows and doors were rationalised to one specification of tinted low-e glass in aluminium frames and the floor insulation above the car park was avoided. This solution provided an overall energy usage better than the DTS building, and reduced the construction cost by $12,500.
The verification method (JV3) takes into account the estimated energy usage for the proposed new or modified building and compares it to the estimated energy usage of the DTS requirements for the proposed building. This allows for a high level of flexibility in how the best energy outcome can be achieved. In this case the tinted low-E glazing all round the building was used to compensate for the removal of the floor insulation above the car park and provide an overall cost saving.
The estimated annual energy demand of the JV3 solution was 215.5MWh which is less than the DTS solution and achieved an overall cost saving of $12,500.