One of the questions we are always asked is how much does it cost to run air conditioning?
In short, the type and size of air conditioner has the biggest impact on air conditoning running cost. When choosing between brands and models look at their energy efficiency rating.
Type of Air Conditioner
Costs in order of the cheapest to most expensive air conditioner to run are:
- Evaporative coolers
- Room only split systems – wall splits, cassettes and floor standing units
- Multiple head split and variable refrigerant flow (VRF) systems
- Ducted reverse cycle (refrigerative).
Portable and window wall air conditioners are not as efficient as split system air conditioners and are relatively expensive to run for the amount of air they treat (heat or cool).
The South Australian government provides an estimate of running costs of different types of air conditioners. Note these calculations are based on a unit of electricity costing 36.5 cents compared to 23.366 cents per watt in Perth in 2015/16. It does not appear that zoning has been factored into the ducted reverse cycle (refrigerative) calculations.
For an overview of each type of air conditioner read our Ultimate Guide to Buying Air Conditioning. Note evaporative air conditioning and ducted air conditioning is not suitable across all ofAustralia’s climates.
Evaporative Air Conditioning (Coolers)
Evaporative air conditioning is very cheap to run as the motor is only around 1kW and power is only used to run the motor and a fan.
Australian brands with centrifugal motors, like the Breezair and Rinnai S Series, are the cheapest consumers of electricity. Breezair is advertised as costing the same as a light bulb to run. Brands with a standard co-axial motor, like Bonaire, Cool Breeze and other Rinnai models cost a little more to run and may be cheaper to buy depending on their other features.
Evaporative air conditioners are really only coolers as they do not refrigerate the air and instead add water to the air to cool it. So water consumption should be factored into the operating cost. In Australia domestic models have an automatic water management system to prolong the life of the pads by minimising the build-up of lime and other minerals. When there is excessive mineral build-up water runs down, rather than through, the pads and there is reduced cooling of the air. Depending on the aircon brand the water is dumped around 10 minutes after the unit is turned off and replaced at periodic intervals when it is operating (4-12 hours depending on the setting chosen to suit the water quality). The amount of water dumped is around 9 litres (a bucket) depending on the size and brand of system. Your local evaporative air conditioning dealer can provide this information for the models they supply and install.
Split System Air Conditioners
Split system air conditioners use refrigerant to heat or cool the air. They require much larger motors than evaporative coolers and so cost a lot more to run. The power output of split systems is expressed in kilowatts (kW) and is stated on the manufacturers’ brochures. The higher the kilowatts the bigger the area treated and the more the unit costs to run. That said do not choose a smaller model than you should (under sizing) thinking you will reduce running cost as the unit could cost more to run as it has to run longer to reach the desired temperature and may reduce the life of the unit as it has to work longer hours. Over sizing air conditioners, within reason, is not such as an issue nowadays as split systems use inverter technology to reduce their fan speed when your chosen temperature is reached.
All residential split systems sold in Australia are measured by an independent government authority for energy efficiency. Use the Energy Rating website to calculate and compare the running costs of different model split systems based on your cost of the electricity and hours you intend running the system. These calculations do not allow for zoning of ducted systems and make assumptions about temperatures inside and outside the home. Wall split systems must display energy efficiency label making comparison when shopping easier, bear in that smaller units will consume less energy (more stars) than larger models.
Room Only Split Systems
Air conditioners which treat a single room are efficient and thus relatively cheap to run. With a room onlysplit systemthe treated air is distributed through the room and circulated back into the indoor unit for further heating or cooling. As long as windows and doors are kept closed and are well sealed there is minimal loss of treated air.
Wall splits are the most common type of domestic air conditioners to heat or cool one room. They range from 2kW to 9.5kW. Dakin’s US7 is the most efficient wall split on the market. It comes with a range of other features including a dehumidifier so it is also the most expensive wall split available.
Multiple Head Split and VRF Systems
Multi head split systems and Daikin’s domestic variable refrigerant flow (VRF) systems use one outdoor unit to power multiple types of indoor unit. Systems range from 5kW to 22kW. They consume more power than a room only split system as they have a larger motor as they are sized to run single or multiple units at one time. They consume less electricity than comparable sized ducted air conditioners because they treat individual rooms.
Ducted Reverse Cycle
Ducted reverse cycle air conditioning treats the whole home and is the most expensive to run because it needs a large motor (systems range from 6kW to 25kW) and some treated (heated or cooled) air is lost as it is distributed through the home. The indoor unit is located in the roof space. Treated air is distributed through the home through ductwork located in the roof space and expelled through ceiling outlets. The air is circulated back to the indoor unit for further heating or cooling via a return air grille, usually located in the hallway,
Zoning is commonly used in parts of Australia to reduce the size of air conditioner required and reduce running cost by treating only part of the home at one time.
There are three factors which make ducted less efficient and cost more to run per kilowatt than room only split systems:
1. loss of treated air as it travels through the home, particularly through untreated areas,
2. incorrect system size,
3. incorrect zone configuration.
Minimise the impact of these factors by:
- Looking for duct that has a high thermal rating (R1.0 is standard and R1.5 is the most efficient option). Look for components that are guaranteed leak free, likeiMaxi by Airstream, so treated air does not leak into your roof space.
- Have your system designed by a specialist air conditioning dealer so you have the appropriate sized air conditioner, which has the best air flow and the zones are set up for how you live. Get three quotes so you can see if the system size and design is the same from each sales person. Ask for the heat load calculation to verify the air conditioner is sized correctly.
- If you want an air conditioner to treat your whole home but often want to run only a small area like a baby’s bedroom or study, get the premium Daikin model or Actron ESP or Ultima models as their fan speed can slow more than other brands. Otherwise install a wall split in that room.
To reduce your need to run your ducted air conditioner also install a fresh air intake system, which uses air from outside to distribute through your home. iSave is a stylish fresh air intake system that integrates seamlessly with your air conditioner’s controller.
More tips and information on how to keep your ducted reverse cycle air conditioning costs down is available on our blog.
I trust this blog will help you as you start researching air conditioning. Running cost is only one factor to consider when buying air conditioning. Contact Air and Water Residential if you are looking for air conditioning in Perth and a specialist will advise you in the right system to meet your needs and budget.
This article was written by Don Curnow, owner of Air and Water Residential. Don has 20 years experience in air conditioning in Western Australia and Victoria. Air and Water Residential supply and install all types of air conditioner for both domestic and commercial use.
