Design principles - energy

Central cooling

What is the most efficient central cooling system to install?

Generally, a well-designed central cooling system will provide greater efficiency than individual units, but efficiency and stability of operation of central systems can be compromised when only a small proportion of apartments are using air conditioning. A central system is unlikely to be practical for small developments of less than about 50 apartments.

In general, a central chilled water fan coil unit system using high efficiency water cooled chillers will be the most efficient central cooling system choice. Though common in hotels, it is not as common in residential design, due to the challenge of apportioning the energy cost between apartments. If a source of cogeneration heat is available, a central chilled water fan coil unit system with an absorption chiller would not only be energy efficient but would also have energy costs low enough that apportioning may not be an issue.

Gas-driven options have lower efficiency than their electric alternatives, but may actually score better due to the lower greenhouse potential of gas compared to electricity.

A central system using high efficiency water source packaged unit system has the advantage that the majority of the energy cost can be metered at the apartment. Depending on the climate, such systems may have efficiency better than an equivalent chilled water fan coil system, though high efficiency water source units are not readily available.

Low/medium efficiency systems will not score as well in BASIX as high efficiency options.

Systems using an evaporative process for heat rejection (cooling tower, evaporative fluid cooler or evaporative condenser) generally provide better efficiency than air cooled equipment, though not in all climates.

A low efficiency central water source packaged unit system provides better efficiency than a central fan coil unit system with medium efficiency air-cooled chillers, a central variable refrigerant volume unit system or individual unit system.

The sizing (and capital cost) of a central cooling system is very dependent upon the thermal performance of the building envelope – particularly reduction of solar gain. Smart building design and glazing techniques can cut capital costs of cooling equipment, while large areas of unprotected glass can lead to such high peak solar gains that either the local cooling capacity will be inadequate or capital costs will be high.

When choosing a cooling system, energy efficiency is one of many factors that should be considered. Apart from initial cost, other considerations include maintenance cost, health and safety issues, reliability, maintainability and life expectancy.

As with central hot water systems, effective insulation of chilled water or refrigerant pipes is also critical if high efficiency is to be achieved. The Building Code of Australia (BCA) requires minimum level of insulation for insulating of heating and cooling piping, vessels and tanks.

Central hot water

In order to maintain high thermal efficiency of a centralised hot water system it is essential that its design and installation is carried out in association with a qualified hydraulic consultant in accordance with the following principles:

  • Maximise Hot Water Pipe Insulation - Ensure all supply and return hot water piping is well insulated, including connections. The Building Code of Australia (BCA) sets minimum standards. BASIX rewards best practice (See BCA requirements).
  • Optimise Hot Water Heaters - Use the highest efficiency hot water system available (minimum 5 star gas hot water heaters or better). Size the hot water system correctly to suit the demand and minimise tank losses.
  • Minimise Hot Water Pipe Diameter - Size the centralised hot water piping correctly to achieve required flow with minimal heat loss while maintaining acceptable pressure drops.
  • Minimise Hot Water Pipe Length - Minimise the lengths of system piping to minimise energy losses.

Minimising lengths and diameters of pipes from the pumped ringmain to points of use minimises 'dead water' losses– that is, the amount of cooled water a user has to draw off before receiving hot water is minimised.

Hot water pipe diameter and length is not currently assessed in BASIX, since design of these occurs after approval of the development application for the proposed development. It is still important to recognise their importance to good design.

Design the centralised hot water system at the early planning stages of a development to ensure adequate space within the building to position centralised hot water piping, its associated insulation and storage tanks.

Carry out the design of a central hot water system through a qualified hydraulic consultant briefed to aim for best practice.

Cooling systems

Reduce the need for an active cooling system by improving the design of the dwelling. If the cooling load in Thermal Comfort is sufficiently low and it is realistic to have no cooling, then the highest-scoring option is "no cooling to be installed".

Depending on the local climatic conditions, ceiling fans or evaporative cooling may be appropriate and will score well.

If selecting an air-conditioner, choose one with a high Energy Efficiency Ratio (EER) or cooling star rating.

When choosing a cooling system, energy efficiency is one of the many factors that should be considered. Apart from initial cost, other considerations include maintenance costs, health and safety issues, reliability, noise, maintainability and life expectancy.

Central systems

To reduce the energy used by central systems in multi-dwelling developments:

  • choose an efficient central hot water system;
  • choose an efficient central cooling system;
  • choose an efficient central heating system;
  • install a central alternative energy source to offset some or all of the energy demand;
  • choose suitable and efficient lifts;
  • choose efficient pool and spa heating systems;
  • operate pools and spas (especially pumps) efficiently;
  • choose efficient sauna heating systems and operate them efficiently;
  • install a Building Management System; and
  • install active power factor correction.

Additionally, for common areas in multi-dwelling developments:

  • provide common clothes drying lines if individual ones are not provided;
  • provide efficient common clothes drying facilities that use an energy source with low greenhouse-gas intensity; and
  • provide energy and water efficient common clothes washing facilities.

Other energy uses

The greenhouse-gas emissions of appliances can be reduced by:

  • cooking with gas (mains or bottled) if possible, or induction;
  • ensuring the refrigerator operates efficiently by allowing sufficient space around it for ventilation;
  • having outdoor, indoor and/or sheltered clothes drying lines;
  • installing energy-efficient appliances (A list of appliances and their energy star ratings can be found at

Tip: If you install a gas cooktop or oven, ensure the kitchen is designed with good natural ventilation. If installing a rangehood for ventilation, exhaust to the outside wherever possible.

Alternative energy sources

What is an Alternative energy supply system?

BASIX definition

Alternative energy system means a system which generates electricity on the land the subject of the application, using an energy source other than the electricity supply grid, and includes a photovoltaic power system and a wind generator.

In multi-dwelling developments cogeneration systems are also an alternative energy supply option.

Note: The alternative energy system must be located on the same piece of land as the proposed development.

Pools and spas

What is the most energy efficient way to run a pool?

An unheated pool (selecting 'no pool heating') will achieve the highest score in BASIX. If the pool is to be heated, solar pool heating is the most efficient option. In multi-unit developments, the use of cogeneration heat for pool heating will also score well.

The energy used for heating and pumping can also be reduced by:

  • installing a pool cover to reduce heat loss through evaporation– this will also reduce water loss;
  • installing a timer on the pump/filter.

Pool covers also protect the pool from pollutants such as leaf litter, reducing maintenance and chemical requirements.

During high-use periods (summer), recommended pump running times range from 4-6 hours a day, and in low-use periods (winter) 2-3 hours a day.

Contact a swimming pool manufacturer or pool technician for the most accurate advice on pool pump timers, heating systems, filtration times and temperature settings for the pool.

Central heating systems

What is the most efficient central heating system to install?

The most efficient central heating option by a large margin is a central radiator system with cogeneration heat as the energy source. A central fan coil unit system with cogeneration heat is a close second.

If cogeneration heat is not available, or if it could only provide a small proportion of the heating needed, then individual heating by gas fixed flued heaters or heat pumps (reverse cycle air conditioning) in each dwelling are the next most efficient choices. Gas-driven air conditioners score better than all but the most efficient electric air conditioners.

A central variable refrigerant volume (VRV) system provides efficiency similar to having air conditioners of the same coefficient of performance (COP) in each dwelling. It has the advantage of centralised 'outdoor' units, but disadvantages of some limitation of piping length, challenge of apportioning energy costs (though some manufacturers have control systems that can assist in this) and a potential risk of excessive refrigerant concentration if a leak develops within an apartment. Again, gas-driven VRV systems score better than electric systems.

Other central systems are unlikely to be practical for small developments of less than about 50 apartments, and all have the challenge of apportioning energy costs.  Radiator and fan coil unit systems with gas boilers are more efficient than water source packaged units.

A water source packaged unit system with electric or gas driven heat pumps as the energy source scores better in BASIX than one with a gas boiler.

All systems with electric boilers or electric resistance heating score poorly in BASIX.


How do I use lighting to increase my energy score?

The energy used for artificial lighting can be reduced by:

  • using natural lighting;
  • installing energy efficient lights, especially in high-use rooms, such as bedrooms, living areas and hallways;
  • installing fittings that are dedicated to energy efficient lamps– tubular fluorescent and LED lights typically qualify as the lamp can not be replaced with a less efficient type.

Types of energy efficient lights

Energy efficient lights include compact fluorescent, fluorescent and LED lights. It is important to consider the type of light required. Fluorescent and compact fluorescent lights are ideal for lighting rooms. In contrast, halogen lamps provide a small, direct beam of light and typically will not adequately light a room unless several lamps are used and therefore consume a lot of energy.

Halogen lights

Halogen lights are best suited for task lighting, for example lighting a picture or over a bench top. Even then, they may require dimmers, to control the excessive amount of light they generate.

Tip: LED lights can be an efficient replacement for halogen lights.

Ventilation and exhaust

The most efficient option is natural ventilation, typically via windows that can be opened.

In general, individual fans without ducting are likely to be the most efficient of the mechanical ventilation options. Ducted individual fans can also perform well, as long as the intake, ducting and discharge are reasonably sized. Although not a requirement, fans should have automatic dampers or shutters so that air does not leak through them when they are not operating.

A fan with some form of operation control such as manual on/off or interlocking to the light switch will be considerably more efficient than a continuously operating fan.

Additional options for multi-dwelling developments

For multi-dwelling developments, the individual fan options are likely to be the most efficient of the mechanical ventilation options. Even though the small fans themselves have poor efficiency, this is offset by their short operating time.

Of the central systems, the most efficient is an individual motorised damper into a central duct with an efficient control (e.g. interlocked to light); with the central fan having a variable speed drive. Even though the central fan operates continuously, it has a higher efficiency than the small fans, and the VSD allows the energy to be reduced considerably in periods when few of the connected apartments are operating.

The central ducted system operating continuously scores very poorly in BASIX because it exhausts from all apartments all of the time, so has a constant high energy input.

Heating systems

What is the most efficient heating option?

Reduce the need for an active heating system by improving the design of the dwelling. If the heating load in Thermal Comfort is sufficiently low and it is realistic to have no heating, then the highest-scoring option is "no heating to be installed".

If there is a heating demand, then gas fixed flued heaters with a high star rating and air-conditioners with a high efficiency or star rating will score well.

Gas-fired hydronic systems are also efficient and score well; the pipes should be properly insulated.

Hot water systems

Hot water systems can be categorised based on:

  • Mode of operation– storage or instantaneous (continuous flow)
  • Heat source– solar, gas, air and electricity

Mode of operation - storage vs instantaneous

  • Storage systems operate by heating and storing water in an insulated tank. Some of the energy used by these systems is lost as heat dissipating from the storage tank.
  • Instantaneous (continuous flow) systems heat water as it is required and do not use storage tanks. The system senses when taps are turned on and it then begins heating the water. Typically 1-2 litres of water pass through an instantaneous hot water system as it heats up, creating a short delay in hot water delivery.

Heat sources

Solar water heaters use solar collectors to heat water in a storage tank. A solar system with a high STC rating will give the best BASIX score. To ensure adequate hot water at night or on overcast days, solar water heaters are often "boosted" by gas or electric heaters. Solar (gas boosted) will usually outperform solar (electric boost) in BASIX.

Gas water heaters can be either storage type or instantaneous. A high efficiency gas hot water system with a high star rating will score well in BASIX.

Air-source water heaters typically use an electric heat pump to move the heat from the air to the water. These are appropriate for warmer climates. An electric heat pump hot water system with a high STC rating will also score well in BASIX.

Electric water heaters can be either storage type or instantaneous. They use the supplied electricity to directly heat the water. Although common, these are the most greenhouse-gas intensive and are the lowest scoring water heater in BASIX. Electric hot water heaters are not an option in the BASIX Alterations and Additions tool.