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General Air Conditioning Tips

For Cooling thermostats should be set between 23 – 26°C. Every 1°C lower can increase running costs by up to 15% or cost you for repairs because they do like a break every so often. If there is a hot day forecast, then pre-cool your house the night before. This is especially effective if your house has a high thermal mass such as solid brick. This will allow your air conditioner to work at its optimum during the cool evening, saving power and wear and tear on the unit. It also allows the unit to keep on top of the heat load as it begins to warm up during the heat of the day.

Power Kilowatts and Refrigeration Kilowatts

Electrical input wattage or Hp, and refrigeration wattage are two different things.

Systems are judged on their efficiency by their Coefficient Of Performance (COP) in the case of heating, or the Energy Efficiency Ratio (EER) for cooling. The EER and COP are calculated by dividing the capacity output divided by the electrical input. More info on EER and COP and how they relate to star ratings can be found here. An interactive side-to-side comparison of air conditioners, showing energy efficiency ratings, power consumption and estimated running costs can be found here.

To work out how much your unit will cost to run multiply the kW input figure (electrical) by how much you pay per kilowatt hour for your electricity.

Note: It is worth doing your own calculations before making a purchase. Some of the star ratings on the energyrating site are derived from incorrect manufacturers EER/COP figures and can give a false efficiency rating.

Single phase (240v) systems are available in ducted splits up to 18kW and non ducted splits up to ~14.5kW. Systems larger than this would require three phase power (415v). If you don’t have it, you’d need to run new mains, replace the meter and rewire the main switchboard. This would be in the vicinity of $1500–$2000 as a rough guide. More if existing boards etc. need to be replaced.

Air conditioning sizing calculators

To get an approximation of the kWs required to cool an area please contact our professionals today.

Refrigerative Cooling

All installations are not equal – be very careful on which contractor you use to install your air conditioner, ask about what materials they use and what advantages their chosen product have, if they don’t know or tell you they are all the same they are likely using inferior materials. Why spend thousands on your air conditioner and then save a few dollars having it poorly installed? Most refrigerated systems fail due to poor installation practice not defective units. A good way to protect yourself is to use a knowledgeable refrigeration mechanic, ask questions, you are making a big investment. Also make sure that your installer is actually a refrigeration mechanic that can repair your unit and properly commission it. There are many plumbers and electricians who install split systems as a side line that would have no idea how your units internals actually work let alone properly commission your unit for maximum performance and efficiency (there are a select few that do). Many cowboy installers and low quality installers do not spend the time planning, installing and commissioning units and it will cost you in the long run, not only in failures but in decreased efficiency.


The difference between inverter and non inverter is the inverter units can alter their speed in response to cooling demand. Some units have an initial over-speed period where they will run at a slightly higher capacity for a set time to pull down the temperature of a hot room. When they reach the set point temperature they can reduce capacity to maintain that level without cycling as much as a normal unit would. This saves power although it’s arbitrary as it would still take a while to recoup the increased purchase costs.

The inverter unit increases the power usage slightly as it converts the incoming power into a suitable style for the air conditioner although the ability to run at a reduced power level helps to drop the overall usage to below that of a typical non-inverter unit. Most of the advertising claiming 30% lower bills using inverters are based on very carefully set up laboratory scenarios. In reality, while they may cost less to run than a conventional unit, buying an efficient conventional unit will still be cost effective.

**consideration ask your salesperson what refrigerant metering device is fitted to your unit, likely they won’t know. Time to speak to a refrigeration mechanic instead. There are three main types of metering device fitted to units and these make a considerable difference to how a unit operates, its efficiency, comfort and time taken to manage heat load.

-capillary- the lowest quality systems refrigerant flow is varied only by the speed of compressor

-ax valve- (piston oriface)- very similar to capillary but less chance of blockages requiring service calls

-tx valve- or thermostatic expansion valve (electronic or mechanical) the best type, most high end systems are fitted with these, refrigerant flow is controlled by speed of compressor as well as heat load in room, allow for faster cooling and heating more efficiently. Where an identical capacity system with a capillary or ax valve is compared to a tx valve system the tx will always be in front. (All current Mitsubishi Electric and Daikin units are fitted with tx valves)

Ducted Systems

Most home ducted systems are in the form of split ducted systems. There are two main types used in residential cooling.

Add-on cooling which is most competitive in terms of price but is a compromise due to sharing heating components and ductwork. Air conditioning is best installed in the ceiling as cool air falls, but most ducted heating is in the floor and there’s a minimum duct size of 6” for heating whereas cooling requires 8” so ducts have to be redone.

Dedicated ducted splits are slightly more expensive to install but offer the benefit of being an engineered package. You also have more choice of manufacturers than add on solutions.

Either way you can zone the ducts to allow a smaller unit to cool sections of a house or to turn off unwanted sections on a whole house setup. In my opinion ducted is preferable to multi head splits as they have fewer parts, fewer electronics and fewer potential refrigerant leaks. It is said that split systems are more efficient, but this is only because a ducted split system has heat losses in the ductwork. Comparative systems are just as efficient. (ducted systems also provide far less accurate temperature control and uniformity)

Evaporative Coolers
  • Costs less to install in some instances.
  • Costs less to run. (careful some can have 1600w fans! that isn’t necessarily cheap tor run)
  • Allows you to vent heat from the house if it cools down outside by drawing in cool ambient air.
  • Increases humidity.
  • They can only cool relative to that day’s dew point.
  • Generally require slightly more maintenance than air conditioning.
  • Consider carefully before purchasing in water restricted areas or where dependant on limited water as water consumption can be up to 80 litres per hour.

An evaporative cooler requires doors or windows open to allow airflow. As a guide, the entire volume of the room should be flushed through every two minutes (or around 30 air changes per hour).

During winter, older ducted units on the roof should have covers placed over them and ceiling vents closed to stop heat loss. Alternatively, consider purchasing a unit with a motorised damper. (many new units have a automatic spring or gravitational shutter)

Legionella Risks

Legionnaires disease has been overblown by the media and it is not something you can contract from domestic air conditioning. The majority of cases are caused by incorrect cooling tower maintenance. Cooling towers are primarily used in commercial air conditioning to cool water cooled condensers and industry to cool recirculated water. They provide an ideal place for Legionella bacteria to grow (temps between 28 to 40°C) and the operation of the towers causes drift which aerosols the bacteria allowing people to breathe it in. There’s probably more danger handling potting mix than from a cooling tower because by law all towers have to be maintained and treated with biocide. Evaporative coolers have been suggested but not verified as potential disease transmitters. Modern evaporative coolers also have dump valves which further lessen the risk.

The disease does not affect everyone who comes into contact with the bacteria. The groups most at risk are:

  • People over 50 years of age (predominantly males)
  • Heavy smokers
  • Heavy drinkers
  • Diabetics
  • People with chronic lung disease
  • People with impaired immune systems (ie body defence mechanisms)

The old adage ‘You get what you pay for’ exists for a reason. The dearer units such Fujitsu & Actron are generally (not always) more efficient and or quieter. They also go together better and give you a better finished product. This translates to easier servicing should the need arise which in my opinion makes the additional purchase costs worth considering. However, some of the cheaper brands provide excellent value for money and offer very good performance. Final decisions should be based on specific unit performance and value for money. There is very little difference between the mainstream and top units sold these days. It’s only in the very cheap units that quality begins to suffer. Some of the very best brands to consider for refrigerated air conditioning would be – Fujitsu, Actron, Samsung. For evaporative air conditioning try – Bonaire or Summer Breeze.


Evaporative coolers: the newer ones self drain but they still need flushing periodically and the pads also require changing when they begin to rot. They also need the water distribution cleaned or you can lose cooling due to the pads drying out. (Chemical dosing is a far better option that washing out your unit, high pressure water will damage your cooler pads)

Air Conditioners: the return air filters require cleaning. The frequency depends on how dusty the house is. If not cleaned the unit can ice up and stop working. They also need the condenser (outside radiator bit) dust free with an unobstructed air flow. This can be cleaned by brushing in the direction of the fins or blowing it out using compressed air/gas. Ensure the drain outlet is unrestricted. Wipe the surface of the inside unit down at regular intervals as they do gather dust

Split Systems

A standard back-to-back split system installation including wiring and appropriate permits will cost approximately $600 to $800 depending on season and quality of work. You may find them cheaper but you get what you pay for. The potential exists for a poor installation to cause expensive repair costs down the track and that should be considered. A non-standard split system installation with brackets, ductwork, a long run, or additional power requirements will obviously cost more. All split installers in all states are required to be licensed by the Australian Refrigeration Council and the person doing the wiring needs to hold a restricted electrical licence at a minimum. You should also get a certificate of compliance for the electrical work.

Multi-Head Splits

They are the best option for whole house cooling where you can’t run ductwork, i.e. a slab floor with a flat or cathedral roof. Or where efficiency, comfort and aesthetics are important, consider bulkhead mounted split systems, the ultimate in control, efficiency and comfort but very very expensive to install.

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