To determine the most efficient air conditioner for your home you need:
- to have an efficient air conditioner
- to have the correct sized air conditioner for the area you are treating
- to maintain and use the air conditioner in accordance with manufacturers’ instructions, and
- with ducted reverse cycle air conditioners, the air conditioner must be designed to meet your needs and operated in accordance with that design.
Efficient Air Conditioner
Reverse Cycle Air Conditioners
Nowadays there is not much difference in air conditioning efficiency across similar sized models if you choose a quality brand.
The efficiency of reverse cycle air conditioning is measured as Energy Efficiency Rating (EER) on cooling and Coefficient of Performance (COP) on heating mode. They both measure the amount of heat or cooling for every unit of energy input. These measures are shown on the air conditioning manufacturers’ brochures. The higher the number the better.
You can check and compare the efficiency of different Australian model split system air conditioners (which includes ducted reverse cycle air conditioners) at the Australian government’s Energy Rating website.
Furthermore, if you enter the number of hours you plan on using the air conditioner and your electricity tariff it will provide an indicative annual running cost.
The actual efficiency of your home’s air conditioner and its running cost will be different from the Energy Rating website and manufacturers’ brochures because your home’s design and local climate differs from standard test conditions. With ducted reverse cycle systems, how you use the zones and the thermal rating and air tightness of components (ductwork and fittings) will further affect efficiency and running costs.
Evaporative Air Conditioners
The efficiency of evaporative air conditioning is not addressed by the Energy Rating website.
The Australian evaporative air conditioning standard (AS/NZS 2913-2000) does not require cooling capacity, electricity consumption or water consumption to be tested by evaporative air-con manufacturers.
Instead the standard requires measurement of evaporation (saturation) efficiency which indicates how close the cooled air is to saturation point. Saturation point (100%) is the maximum limit for direct evaporative air conditioners.Typical evaporation efficiency values are 70 – 85%. Evaporative air conditioners with higher evaporation efficiency generally require less power and water to provide an equivalent amount of cooling. However:
- Evaporation efficiency doesn’t take into account the temperature and humidity in different areas of Australia which has a significant impact on efficiency. Evaporative air conditioners are not suitable for use in Brisbane or Darwin (high humidity) but are perfect for Perth, Adelaide and Canberra (low humidity).Manufacturers are not required to publish their evaporative efficiency rates.
- Even if they did, because of permitted variations in testing, comparisons across brands would not be useful.
- Furthermore evaporation efficiency doesn’t provide a complete indication of efficiency because of the dramatic difference in climate across Australia.
- A measure of seasonal efficiency energy rating was proposed in a 2010 government funded study but limited progress has been made and there is no indication when or if a better measure of evaporative air conditioning efficiency will be introduced.
The standard does not evaluate indirect or two stage evaporative air conditioners. These systems are uncommon because they are costly to buy.
Air Conditioning Sizing
What ever type of air conditioner – evaporative cooling, portable, split system or ducted reverse air conditioning – it is vital that the air conditioner is sized correctly otherwise it will affect its efficiency. The greater the under sizing of the air conditioner the more dramatic the drop in efficiency.
Sizing Reverse Cycle Air Conditioners
As a rule of thumb, use 145 watts per square meter of cooling output for reverse cycle air conditioners. For a more accurate answer for a room only split system air conditioner based on your home, use AIRAH’s sizing tool. To understand the factors that affect reverse cycle air conditioning sizing and heat load read our article “What size air conditioner do I need?”
Over sizing reduces the efficiency of reverse cycle air conditioners, but is less of an issue with inverter air conditioners than non-inverter air conditioners because inverters work more efficiently at less than full capacity. Since new Minimum Energy Performance Standards were introduced in 2010, inverters have become commonplace.
A specialist air conditioning dealer will be able to advise you on the size of air conditioner you need for your home.
