The image above of the ground floor area of a 2 storey dwelling shows the separate zoned areas.
Note that the Kitchen / Meals / Family area has been divided up to depict the tiled and carpeted areas within the space. As the 'Kitchen area' is not separated by a doorway the entire area is classified as a Kitchen Zone (with it's higher heating and cooling loads) for the purpose of the rating.
The Laundry area to the bottom left is zoned separately ("other-day zone") with lower energy loads as it is separated by a closable doorway.
As the Study area, to the bottom right, is open to the Entry/Hallway, the entire area is classed as Living Zone. (the red line indicates a separation of carpeted floor in the Study and tiling through the Entry).
The Garage is nominated as a 'Garage Zone' with the floor covering designated as 'none'.

Once the basic details are put into the software then the assessor can then start to look at adjusting the levels of insulation and glazing types to a point where the 6 Star level is achieved.
Other factors may come into play such as adjusting eave widths, reducing or enlarging window sizes if the assessment falls short of the required level.
In this particular home, with a concrete slab floor, altering the carpeted area in the Family area to tiles may help to increase the assessment.
Winter solar heat gain through the large glass area facing north will be absorbed into the slab whereas currently the carpet acts as an insulator.

A major role of the Thermal Assessor is to provide the Builder or Owner with economical and viable options to enable at a minimum the required energy efficiency level to be achieved.
This home in Melbournes northern suburbs achieved a 6 Star level - 113.3 mj/m2 - with R4.0 insulation to the ceilings, R2.5 insulation to both the external walls and the internal Garage walls and standard glazed aluminium windows throughout except for one double glazed window to the upper storey. One of our suggestions included installing large bifold doors to the study area to regulate and separate heating/cooling loads and to reduce air transferrance up the open stairwell. This would have either increased the rating or removed the need for the double glazed window.
The Owners opted to stay with the double glazed window but provision is being made in the framing for the bifolds to be easier to install at a later date if required.

At the end of all that waffle, a main point is that 'open plan' living is good but the layout does, more than ever, need careful detailing in regards to orientation, winter solar gains and the like

If you require any further information in regards to this or other topics, dont hesitate to contact me.