Air conditioning
Refrigerative air conditioners remove heat from the air inside your home and transfer it outside, cooling the air to a temperature determined by a thermostat. They cool, dehumidify and recirculate the room air. Unlike evaporative cooling systems, if they are sized correctly, they work effectively in any climate. Most modern air conditioners are reverse cycle, meaning they can be used to both heat and cool your home.
Types of air conditioners
Portable units – these are an option for cooling a small room where it’s not possible to have a split system. The most common type are single-duct systems where the internal unit, which includes both the compressor and air handling unit, is connected to an exhaust duct used to vent the hot air from the compressor to the outside via a window. They can create localised cooling in a small room but, as they draw in air from the room and vent some of it outside as part of the cooling process, this brings hotter air into the home from outside, making other parts of the home hotter. This means that overall, portable air conditioners are not as effective as split systems. They are also noisier as the compressor is located inside the home.
Window/wall units – box-like air conditioners installed through an external wall or a window, designed to cool a single room or open plan area. These units are cheap to install, are only suited to smaller rooms or areas, and are generally much less efficient that split systems. Installation into windows can negatively impact natural ventilation strategies, and the units should not be installed into the only opening window in a space.
Split systems – designed to cool a single room or open plan area, they have a separate indoor air handling unit connected to an outdoor compressor unit by refrigeration piping. Most commonly the indoor units are wall mounted, however, more discrete options are available including bulkhead units, where only a grille is visible, and ceiling cassette units, which are recessed into the roof space. Most split systems are reverse-cycle units which can both heat and cool and are the more efficient inverter type system.
Multi-split systems – designed to cool several rooms or areas of a home, they have several indoor air handling units connected to a single outdoor compressor. One such system might provide good coverage for a unit or small house, but several multi-split systems might be required for a large house if you require heating and cooling throughout. They can provide a similar cooling (and heating) service to a ducted system but are more efficient as they don’t suffer from ‘duct losses’. They are also very controllable as the air handling units can be switched on only in the areas where cooling (or heating) is required and can have their thermostat settings independently controlled.
Ducted systems which cool the whole house through multiple ceiling or floor outlets – have a central air handling unit that is usually located in the ceiling space (or under a suspended floor) and a single large compressor unit located outside, connected to the air handling unit by refrigerant piping. The systems can usually be zoned, allowing different areas of the home to be switched on and off, as required, and the more sophisticated control systems can allow independent temperature control in these zones. These systems are less efficient than split systems and multi-split systems as there are energy losses in the ductwork that distributes the cooled (or heated) air to the outlets. Most ducted systems sold are reverse-cycle systems that can both cool and heat.
Running costs
Inverter air conditioners have a variable speed (or inverter-driven) motor. Rather than switching the compressor on and off, they automatically vary the speed of the compressor, running it at full speed when cooling demand is high and at a much slower speed when cooling demand is low. Over a whole day, they operate more efficiently than the older style systems that have a compressor that is either fully on or off.
Inverter air conditioners are quieter to run and have lower running costs compared to the standard air conditioners. Most modern split system air conditioners are inverters. Ducted air conditioners may be either inverter models or standard models.
Sizing
The best way to ensure that you have the right-sized unit is to have a full heat load calculation carried out by an authorised air conditioner installer or manufacturer before you purchase a system. This is best done in your home so that factors such as ceiling heights, window sizes and orientations, and insulation levels can be taken into account. If this is not possible, it is a good idea to provide the installer with a floor plan of your home that contains this information.
If your system is too big for the space it is cooling, it will have short cooling cycles (switching on and off) resulting in increased power consumption and excess wear and tear on your unit. This is likely to be a greater concern with standard air conditioners than with inverter models.
If your system is too small, it won’t provide adequate cooling. This will result in the unit working harder than it is designed for, increasing maintenance requirements and potentially shortening the life of the unit.
If you have a split system servicing a single room in your home, it is important to ensure this space is zoned adequately with doors closed to prevent cool air escaping and the unit working overtime in an attempt to cool the space.
Choose energy-efficient cooling
Once you’ve established what size you need, use the Energy (star) ratings to choose an energy-efficient cooling system for your home. Air conditioners are rated between 1 and 10 stars for their cooling and heating performance, with a higher star rating meaning that the unit is more efficient and has lower running costs. The new zoned energy rating labels show performance in three main Australian climate zones – cold, mild and hot. Most of Victoria is covered by the “cold” climate zone, but the warmer northern parts of the state are covered by the “mild” zone. It's also important to understand how to use your cooling system efficiently to save even more energy and money.
