Is the largest source of greenhouse gas emissions from an average Australian home and the second largest segment of household energy use in Australia, after space heating and cooling. It accounts for about 21% of the energy and generates about 23% of the greenhouse gas emissions (DCCEE 2010). In Australia, about 48% of the energy used for water heating comes from natural gas, 45% from electricity, 3% from liquefied petroleum gas (LPG) and 4% from solar (DCCEE 2012). Electric water heaters in particular contribute to these emissions: only half of Australian homes use electric water heaters, but they contribute 80% of hot water greenhouse emissions. Reducing your hot water use and using renewable energy sources to heat water are great ways to reduce your environmental impact. By installing the most appropriate and efficient water heater for your household size, water use patterns and climate you can save money and reduce greenhouse gas emissions without compromising your lifestyle. An efficient hot water service (HWS) can also add value to your home and help meet state, territory or local government regulations. 21% of energy used in the home heats water. Energy use in the Australian residential sector 1986–2020. Data are projected energy use for 2012.
Household energy use %
- Heating and cooling 40
- Water heating 21
- Appliances and equipment including refrigeration and
- cooking 33
- Lighting 6
More than half of hot water use is in the bathroom, a third in the laundry and the remainder in the kitchen. One of the best ways to reduce energy bills is to reduce hot water use by installing water efficient showerheads and taps — and save on energy and water. Behaviour change also saves energy and water: take shorter showers, use cold water for clothes washing, use water-efficient appliances, rinse dishes in cold water, and use mixer taps in the cold water position when hot water is not required (see Reducing water demand).
Water heaters Both of the two basic types of water heater
— storage systems and continuous flow (or instantaneous) systems — can use a variety of energy sources to heat water including solar, gas (LPG and natural gas) and electricity.
Storage water heaters Water is heated and stored in an insulated tank for use when it is required. These systems can operate on mains pressure or from a gravity feed (constant pressure) tank.
Mains pressure— Hot water is delivered at a similar pressure and flow rate to cold water so more than one outlet can usually be turned on without greatly affecting pressure. The storage tank is usually located at ground level inside or outside the house. Mains pressure systems have been the most popular systems in recent decades but heat losses from storage tanks and their associated fittings and pipes can be substantial. Large electric storage tanks and their fittings can waste up to 1,000kWh each year; a typical 5 star gas storage HWS wastes 3,500MJ.
This is equivalent to the energy required to heat 50–60L of hot water each day. Constant pressure or gravity feed
— Hot water is delivered at lower than mains pressure from a tank located in the roof of the house. Pressure depends on the height difference between the tank and the point of use. Gravity feed systems are most common for older properties and properties not connected to mains water.
In a gravity feed system, the storage tank is installed in the roof cavity, still above the collectors. Active (or pumped) systems In active systems (also known as pump or split systems), solar panels are installed on the roof and the storage tank is located on the ground or another convenient location that does not have to be above the solar collectors. Water (or another fluid) is pumped through the solar collectors using a small electric pump. Because active systems do not require a roof-mounted tank they have less visual impact, particularly when the solar collectors are mounted flush with the roof. However, active systems are usually more expensive to purchase and require more maintenance than passive systems. Active systems generally use more energy than passive systems because extra energy is required for pumping. There are also additional heat losses in the pipes between the tank and solar collectors. However, if renewable energy is used to power the pump and a high level of insulation is used for the pipes and tank, active systems can reduce greenhouse gas emissions as much as a passive system (see Renewable energy).
For either type of system, storage tanks may be made of copper, glass (enamel) lined steel or stainless steel. Copper and glass- lined tanks typically have a sacrificial anode to reduce tank corrosion, which needs to be replaced every few years. Warranties offered for tanks typically range from five to ten years.
Continuous flow water heaters Continuous flow or instantaneous systems heat only the water required and do not use a storage tank, so do not suffer the heat/energy losses of storage systems. They can operate on natural gas, LPG or electricity. Gas models are available with either electronic ignition or a pilot flame. They can be mounted externally or internally if suitable ventilation is available. Because continuous flow systems heat the water as it is used, they cannot run out of hot water. Continuous flow water heaters can be fitted with sophisticated temperature controls, including controls that allow the user to set the desired water temperature at the point of use (e.g. in the shower).
Water is not overheated and hot water does not need to be diluted with cold water to achieve a suitable temperature, thus saving energy and reducing the risk of burns or scalding. Types of hot water service The main types of water heaters on the Australian market are: heat pump gas (natural or LPG)
— storage or instantaneous solar
— electric or gas (natural or LPG) boosted electric
— storage or instantaneous.
Heat pumps Air-sourced heat pumps are an efficient type of water heater that extracts heat from the environment (air, water or ground) to heat water. Electricity is not used directly to heat water (unless the heat pump is fitted with an electric boost element); it runs the compressor and thus its use is much less than for traditional resistive electric systems and of similar efficiency to an electrically boosted solar system. The pumps operate like a refrigerator but in reverse. Ambient air is used to heat a refrigerant, which converts to a gas. The gas is then compressed, expelling heat, which is transferred to the water. The refrigerant is expanded back to a liquid and the cycle repeats.
Solar hot water systems Solar hot water systems
Use roof mounted solar collectors to absorb energy from the sun to heat water which flows to a storage tank.
There are various system options available, allowing choice of: boosting options gas (natural or LPG) electric collector types flat plate panels evacuated tube collectors system configuration thermosiphon integrated systems split systems split systems. Solar HWSs are storage systems and, depending on your climate, can provide up to 90% of your hot water for free, and without greenhouse gas emissions using the sun’s energy (DCCEE 2010).
They cost more to buy and install than conventional HWSs but can save energy and reduce bills. Rebates and incentives are offered around Australia to reduce the up-front cost of solar units (see www.yourenergysavings.gov.au/rebates). The time required to break even (the payback period) depends on the climate, type of system installed, hot water use and energy tariff applied.
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