Do you air condition the whole house? It might be cost effective to get a smaller split system put in and only cool one area. We have splits in all of the bedrooms and one in the living area. When it's hot, the living area goes on and if the kids want to be cool they come out of their rooms and interact with their parents as human beings.
Have a look at the latest post on the website to look at my west-facing windows and, in a similar vein to what you've posted, the current practice is to shut off the hot room in the afternoon and use open windows to keep the air moving if its cool enough.
The ducted has three zones:
1) Living area - including the boy's room (which was the study when we moved in) and the kitchen area which is one of those combined kitchen/dining/family areas in modern houses. This is the middle part of the house.
2) Rumpus room - the room at the west end of the house which is basically the source of the heat issues.
3) Bedrooms - the office, master bedroom, girl's room, spare room, all on the eastern half of the house, with the office having a north-facing window, the master bed having a glass sliding door facing east which only gets limited sun due to neighbour's block being elevated. Warms up quickly though.
Thing is, it doesn't matter which zones you turn on or off, because the grunt from the unit is dependent on ambient temp versus requirement temp. The unit spins up to over 5kW and stays there, pretty much. Does a great job cooling, mind.
I'd love nothing better than to sell this ducted piece of shit at cost and buy two split systems - one for the east end of the house (master bedroom), and one for the west end of the house (rumpus room). There is a ceiling fan in each of those rooms that could push the cooler air through the rest of the house.
Problem is, I've got 10 holes in the ceiling for the ducts throughout the house. It would be ideal if a more efficient system could re-use these, or I'll be adding the cost of the plaster repair or perhaps tying off the ducts somehow.
But the capital cost of doing so would offset any financial gain for another couple of years. Keep in mind I've already outlaid a significant sum to get the system on the house. If I need to pull a few extra kWh in summer a couple of times a week, for now I have to live with it.