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Air conditioning overview

Air conditioning - what is it? A building's air conditioning can be described as the ‘lungs’ of a building. The air conditioning system draws in outside air and filters, heats or cools, humidifies, circulates and then expels a portion of it to the outside environment.

By definition, air conditioning is the control of the different properties of the air within that space. These properties include temperature, humidity, air speed and the cleanliness of the air (amount of dust, odour and other contaminants).

Air conditioning systems assist building occupants in these ways:

  • They help maintain proper temperatures.
  • They provide fresh air for building occupants, i.e., they operate as ventilation systems.
  • They remove contaminants from the air.

How air 
conditioners work

Air conditioners employ the same operating principles and basic components as your home refrigerator. An air conditioner cools your room with a cold indoor coil called the evaporator.


The condenser, a hot outdoor coil, releases the collected heat outside.


The evaporator and condenser coils are serpentine tubings surrounded by aluminium fins. This tubing is usually made of copper.


A pump called the compressor moves heat transfer fluid (or refrigerant) between the evaporator and condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils.


The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling the building.


The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid giving up its heat to the air flowing over the condenser's metal tubing and fins.

Types of air conditioners

The basic types of air conditioners are room air conditioners, split-system central air conditioners and packaged central air conditioners.

Room air conditioners

Room air conditioners cool rooms rather than entire homes. If they provide cooling only where they're needed, room air conditioners are less expensive to operate than central units, even though their efficiency is generally lower than that of central air conditioners.

Central air conditioners

Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors or ceilings covered by grills) carry cooled air from the air conditioner to the room. This cooled air becomes warmer as it circulates through the rooms; then it flows back to the central air conditioner through return ducts and registers. A central air conditioner is either a split-system unit or a packaged unit.

In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. The air conditioner's evaporator coil is installed in the cabinet or main supply duct.

In a packaged central air conditioner, the evaporator, condenser and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab outside the building. This type of air conditioner also is used in domestic or small, commercial buildings. Air supply and return ducts come from indoors through the building’s exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils.

Regular maintenance

An air conditioner's filters and coils require regular maintenance for the unit to function effectively and efficiently throughout its years of service. Neglecting necessary maintenance ensures a steady decline in air conditioning performance, a decline in indoor air quality and an increase energy use. Negligence is no excuse for duty-of-care.

Air conditioner filters

The most important maintenance task that will ensure the efficiency of your air conditioner is to routinely replace or clean its filters. Clogged, dirty filters block normal air flow and significantly reduce a system's efficiency. With normal air flow obstructed, air that bypasses the filter may carry dirt directly into the evaporator coil and impair the coil's heat-absorbing capacity. Filters are located somewhere along the return duct's length. Common filter locations are in walls, ceilings or in the Air Handling Unit.

Some types of filters are reusable; others must be replaced. They are available in a variety of types and efficiencies. Clean or replace your air conditioning system's filter every month or two during the cooling season. Filters may need more frequent attention if the air conditioner is in constant use or is subjected to dusty conditions.

An antimicrobial filter treatment can extend filter life by minimising premature blockage caused by the fungal root system and improve indoor air quality.

Air conditioner coils

The air conditioner's evaporator coil and condenser coil collect dirt over their months and years of service. Clean filters prevent the evaporator coil from soiling. Moulds and bacteria love the condition presented by the evaporator coil (cool temperature, food and moisture). This microbial growth causes blockages on the coil and provides a source of indoor air quality contamination. See the before and after example below.
clean coil


clean coil


Coil contamination will increase your energy cost by reducing air flow and the ability to absorb heat. Your evaporator coil should be cleaned and sanitised annually. The cost of coil maintenance is quickly recovered with increased system efficiency and mitigation control.

Outdoor condenser coils can also become very dirty if the outdoor environment is dusty or if there is foliage nearby. You can easily see the condenser coil and notice if dirt is collecting on its fins. You should minimise dirt and debris near the condenser unit. Dryer vents, falling leaves and lawn mowing are all potential sources of dirt and debris. Cleaning the area around the coil, removing debris and trimming foliage back at least 0.6 metres allow for adequate air flow around the condenser.

Sealing and insulating 
air ducts

An enormous waste of energy occurs when cooled air escapes from supply ducts or when hot air leaks into return ducts. Recent studies indicate that 10% to 30% of the conditioned air in an average central air conditioning system escapes.
For central air conditioning to be efficient, ducts must be airtight. Hiring a competent professional service technician to detect and correct duct leaks is a good investment since leaky ducts may be difficult to find without experience and test equipment.

Obstructions can impair the efficiency of a duct system almost as much as leaks. You should be careful not to obstruct the flow of air from supply or return registers with furniture, drapes or tightly fitted interior doors. Dirty filters and clogged evaporator coils can also be major obstructions to air flow.

The large temperature difference between roof space and ducts makes heat conduction through ducts almost as big a problem as air leakage and obstructions. Ducts in roof space should be insulated heavily in addition to being made airtight.

Cleaning air ducts

Duct cleaning generally refers to the cleaning of various heating and cooling system components of forced air systems, including the supply and return air ducts and registers, grilles and diffusers, heat exchangers, heating and cooling coils, condensate drain pans (drip pans), fan motor and fan housing and the air handling unit housing.

If not properly installed, maintained and operated, these components may become contaminated with particles of dust, pollen or other debris. If moisture is present, the potential for microbiological growth (e.g., mould) is increased and spores from such growth may be released into the building’s living space. Some of these contaminants may cause allergic reactions or other symptoms in people if they are exposed to them.

Failure to clean an entire contaminated system can result in re-contamination, thus negating any potential benefits. NADCA recommends source removal method of duct cleaning. Source removal methods remove the dust, which is a food source for microbial contamination.

Some service providers may also suggest applying chemical sealants or other encapsulants to seal or cover the inside surfaces of the air ducts and equipment housings. They believe sealant will control mould growth or prevent the release of dirt particles or fibres from ducts. These practices have yet to be fully researched, and you should be fully informed before deciding to permit the use of encapsulates or sealants in your air ducts.

Encapsulants covering dust create a rough surface within the ductwork. This disrupts the air’s flow through the ductwork. Most encapsulants will break down with moisture, exposing the contaminant once again. Source removal is the preferred option.

Duct sanitisation involves applying chemical biocides, designed to kill microbiological contaminants, to the inside of the ductwork and other system components. The treatment is used in treating the walls, floors and ceilings of these air handling rooms and ducts, preventing the growth of bacteria and fungi for up to 12 months.

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South Coast, Sydney Metropolitan and Blue Mountains areas
Call : (02) 8407 9727 
North Coast, Newcastle and Central Coast
Call : (02) 4971 4525
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