Hot water systems supply heated or cooled water for domestic use. They can be powered by gas, electricity, solar energy or reclaimed heat. They operate either continuously or intermittently (on demand). Continuous flow systems only heat the water when a tap is turned on, so they do not suffer from the heat loss associated with storage tanks. They are a popular option in new homes as they are energy efficient and compact. Gas models can run on natural gas, LPG bottled gas or electricity and can have an electronic ignition or pilot flame.
Domestic hot water systems are the most common type of hot water system found in Australian homes. They are available in a wide range of sizes and styles to suit most needs, including gas continuous flow systems. They can be supplied by either mains pressure or a tankless system. Electric systems can be used to provide DHW during the cheaper ‘off-peak’ times at night, and can be powered by either an inverter or a fixed electric element. The energy efficiency of an electric system can be improved by choosing a model with high thermal efficiency and a large capacity storage tank, as well as insulating the tank to minimise heat loss.
Solar hot water systems rely on the sun’s radiation to raise the temperature of the water. The 2 main types are flat plate and evacuated tube collectors. Solar systems require a good level of insulation to reduce heat loss from the back and sides of the collectors, as well as to the tank. A good quality, high-efficiency system will also be able to generate hot water for most of the year.
The operation of a hot water system is affected by the method of replenishing it with fresh water, in particular the way water is brought into the system and out of it. The methods employed may lead to thermal stratification and entropy generation in the heating system, and damage to the system pipes due to corrosion. Specialists should be consulted about treatment of the water, in order to minimise these effects.
The most effective way to conserve energy in a hot water system is to reduce demand. This can be achieved by reducing the amount of water used, for example by only running washing machines and dishwashers when full. Using economy cycles or half loads can also save energy, as will turning off the hot water system when not in use. It is also advisable to insulate hot water pipes and the hot water tank, as this can significantly reduce heat losses. In addition, a hot water tank should be set at no higher than 60degC to prevent the growth of bacteria such as Legionella. If you are going on holiday, turn the hot water system off before you leave and make sure that it is re-set to this temperature upon your return. This will help to protect you and your family from potentially dangerous diseases.
source https://flowlinkplumbing.wordpress.com/2025/05/16/energy-efficient-hot-water-systems-5/
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