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The tables below compare approximate annual running costs for various types of cooling systems for a range of room sizes.
* Approximate energy costs per year, rounded to nearest $5. Based an average existing (pre-2005) 2 Star house in a Melbourne climate, cooling all day on the weekend, and in the morning (midnight to 8am) and evenings (5pm to midnight) on weekdays when internal temperatures are high. Based on an electricity tariff of 31.9c/kWh. This is based on a typical Melbourne peak tariff, but does not include any pay on time discount. Note that the evaporative coolers will also use water, and the cost of the water is not included in this table. Actual costs for your house will depend on the area cooled, how long you run the cooling for, your thermostat settings, how well insulated and shaded the house is, your energy tariffs and your local climate. To estimate the running cost for a cold climate (e.g. Ballarat) multiply these figures by 0.85, and for a warm climate (e.g. Mildura) multiply these figures by 3.2. To estimate the running cost for a 5 Star house located in Melbourne, multiply these figures by 0.95, and for a 6 Star house multiply these figures by 0.85.** GHG = Greenhouse Gas coefficient used is 1.18 kilograms of carbon dioxide equivalent emissions per kilowatt hour.*** The figures for "zoned" operation assume that cooling in the bedroom areas is switched off during the day (8am to 5pm) and is only operated in the living rooms from 6am to 10pm when the house is occupied, e.g. on the weekends. On workdays, it is assumed that the cooling in the living rooms is only operated from 6am to 8am in the morning and from 5pm to 11pm at night. Other zoning arrangements are possible, and would change the saving achieved by zoning.
Remember, regardless of the type of air conditioner you have, if you operate and maintain your cooling system wisely you can reduce your cooling costs and still be comfortable.