Home Air Conditioning Tips And Advice For Energy Efficient Homes.


Heating and cooling

Very little energy is needed to run your air conditioner if your house is well-designed. Appropriate insulation, which is essential for a comfortable house, combined with passive solar design and a draught-proofed building, can create low energy requirements for heating and cooling. Highly efficient homes with low heating or cooling input are possible across much of Australia.

For existing homes, installation of high efficiency heating and cooling technologies, with modest building improvements and behaviour change, may be cheaper options to reduce energy bills and greenhouse gas emissions than major home renovations.

Your money is better invested in an energy efficient building combined with heating and cooling air conditioners.

At 40% of household energy use, heating and cooling are together the largest energy user in the average Australian home (DEWHA 2008). However, since most home heating uses gas, heating is responsible for a lower proportion of energy bills and greenhouse gas emissions than its share of energy use suggests.

Use passive design principles to increase comfort and reduce the need for heating and running of the air conditioner. Insulate the roof, walls and floor, seal off draughts, let in winter sun and draw curtains at night. Zone your existing or new home and only heat the rooms you are using; use doors to prevent heat escaping into unused rooms (see Passive design).

Central heating can often heat a whole house whether individual rooms are occupied or not. Space heaters usually only heat the room or area where the heater is installed.

For an energy efficient house, use space heating only in rooms that require heating or use a zoned central heater to reduce running costs.

Heat only the rooms that are being used.

Answer the following questions before buying a heater:

Does the room need to be heated or will eliminating cold draughts and improving insulation be enough?

How many rooms need to be heated?

How big are they?

How often and for how long will heating be required?

Central heating

Central heating usually uses more energy than space heating as more of the house tends to be heated. However, an energy efficient house with central heating may use less energy than an inefficient house with space heating. Several types of central heating are available.

Many central heaters have high energy losses from the heat distribution systems, usually through ducts or hot water pipes. They should be as short as possible and well-insulated (at least R1.5 for ducts and 25mm of pipe insulation). Fans and pumps can also be costly to run. When heating requirements are low, distribution losses can be the main contributor to heating costs.

In well-insulated houses with solar gain to some rooms, a central thermostat may not provide comfort throughout: some rooms may have higher heat losses and cool down faster than the rest of the house.

Ducted air

In ducted systems, hot air is circulated through roof or underfloor ducts, supplying convective heat. Reverse cycle air conditioner can be the better option when heating your home.

Design the system so that the extent of the area heated can be controlled and include zoning to allow for shutting off heating to unoccupied areas. Ducted systems should be designed and installed by accredited experts such as Aussie Air Conditioning.

Ensure the ducted system is sized for the house. New, energy efficient houses that meet the requirements of the Building Code of Australia (BCA) require less heating and smaller capacity heating equipment.

Ducts should be the correct size and have adjustable outlets (registers). Ducts need to be larger if also used for cooling.

Insulate ducts to at least R1.5 and make sure all joints are well sealed. (see Insulation)

A return air path from every outlet back to the central system is very important. Without it the warm air escapes and the system sucks cold air in, dramatically reducing its effectiveness. In each room that has a duct outlet installed, a gap under the door between the room and the central return air inlet creates a return path.

Each zone or room should have its own control Temperature control or using the Myair 5 System would be the best option.

Exterior walls behind panels must also be insulated to prevent heat loss to the outside. Use wall cavity insulation or a layer of installed reflective foil on the internal wall behind the panel. Ideally all exterior walls should be insulated to maximise comfort from the heating system, especially in a new home or major renovation.

Reverse cycle air conditioning (or heat pumps) provides convective heat and is the most energy efficient electric heater. The most efficient 5–6 star units may be cheaper to run and generate lower greenhouse gas emissions than gas heaters. Visit the Energy Rating website (www.energyrating.gov.au) to find the most efficient reverse cycle air conditioners.

Systems can also be mounted on external walls or central ducted air conditioning.

Evaporative coolers can increase heating bills and allow a house to heat up faster when not operating, because large volumes of air can be sucked out of the house through the evaporative unit. Many modern units have automatic seals when not in use. Otherwise, close off ducts and cover the roof unit in winter to reduce heat losses.

An indirect benefit of an evaporative cooler is that it tends to pressurise the house, keeping out bugs and dust.

Air conditioners/refrigerated coolers

If thermal comfort cannot be achieved with passive design, fans or evaporative cooling, consider air conditioning.

Air conditioning can give a higher degree of comfort in any climate.

For efficient air conditioning, the house or room should be sealed and highly insulated with bulk and reflective insulation. Windows must also be shaded from the summer sun.

Purchase costs vary depending on the size and type of air conditioner, and efficiency varies widely between units and models.

Choose the most efficient model of the correct size for air conditioning.

Systems using inverter technology and advanced design can show energy savings of up to 40% over standard units. The Energy Rating website (www.energyrating.gov.au) lists the products regulated by energy labelling programs and Minimum Energy Performance Standards.

Always choose the most efficient model for your application.

Air conditioners are available as portable, wall, window, split and ducted systems. Fixed systems need to be installed by a licensed refrigeration mechanic.

Ensure your air conditioner is correctly sized by having an expert calculate the cooling load before purchasing. Use the Australian Institute of Refrigeration, Air Conditioning and Heating’s online calculator (www.fairair.com.au) for cooling requirements based on specific room characteristics.

Portable air conditioner units

Through wall/window units

Through wall/window units are placed in an existing external window or a hole made in an external wall. Smaller units can use a standard power outlet but larger ones may need a dedicated electrical circuit installed.

They are suitable for single rooms up to about 50m2 but are generally less efficient than fixed split systems.

A split system unit can be away from the outdoor compressor.

Fixed split systems

Fixed split systems, especially those using inverter technology, are generally the most efficient domestic air conditioners. The indoor wall or floor mounted unit can be up to 15m from the outdoor compressor.

Multi-split systems have more than one indoor unit running off the outdoor compressor.

Ducted units

Ducted air conditioning units cool large areas or an entire house.

Ducts must be well insulated, to at least R1.5, and joints sealed to prevent condensation and leakage. The roof should have reflective foil insulation installed and be vented to dispel hot air.

Zone systems to cool only occupied areas and allow different conditioning in living and sleeping areas.

Alternative heat exchangers

Reverse cycle air conditioners, in both cooling and heating modes, mostly use an air-to-air heat exchanger, like a refrigerator. They dissipate heat extracted from the room to the outside when cooling or from the outside air into the room when heating.

Ducted units can cool an entire house.

In colder climates, heating and cooling modes must be appropriately selected, as some units may ice up, reducing both efficiency and heating capacity in cold conditions.

Air-to-water or air-to-ground (also called geothermal) exchangers are far more efficient. Heat exchange pipes are run through a body of water or deep into the ground where the temperature is relatively stable all year round.

Cooling system operating tips

Shade outdoor components of air conditioners from direct sun — but don’t limit air flow around them.

Some units are noisy in operation. Split systems (where the compressor is outside) are quieter inside but consider your neighbours when selecting and locating external components.

Reverse cycle models can also be used for heating and can provide low cost, low emission heating (see ‘Heating’ above). Units that use electric heating elements cost more to run and produce more greenhouse gases.

For ducted systems, install a zoning system so only rooms requiring air conditioning are cooled. Ensure that ducts are well insulated and consider installing reflective foil or painting the roof a light colour and ventilating it to reduce the roof space temperature.

Purchase a system that has controls such as a timer to schedule activation and shut-off.

Set the thermostat as high as possible on your cooling system.

Never set the thermostat at a temperature below what you require — that does not make the unit cool faster.

Always aim to set the thermostat as high as possible.

Avoid leaving air conditioning running when no-one is home. It is cheaper to cool the house down when you arrive home, or to set a timer so that the house begins cooling shortly before people return home.

Practical tips for heating and cooling

Do not leave heating and cooling appliances on overnight or when you are out, although slow combustion stoves can be left on in very cold weather. If you must have the house comfortable when you arrive home, install a timer and turn your system on about 15 minutes before your return.

Locate thermostats in the most used rooms and away from sources of heat and cold.

Each degree of extra heating in winter or cooling in summer increases energy consumption by about 5–10%. Set the thermostat to 18–20°C in winter and 25–27°C in summer.

Dress appropriately for the weather. Putting on a jumper is better than turning the heater up.

Maintain your heater. Keep reflectors shiny and free of dust. Clean air filters regularly.

Service all heaters and coolers according to the manufacturer’s instructions. Pay special attention to air filters.

Close windows and doors in areas where a heater or air conditioner is on unless ventilation is required for un-flued gas appliances.

Close drapes or blinds, especially in the evening when you are heating.

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