Electric Storage and Instantaneous Water Heaters
25% of energy use in homes for water heating
33% of energy use in homes for water heating
52% of this is electric water heating
77% of this is electric water heating
Source: Consultation RIS ESWH 2013
Electric Storage Water Heaters
An Electric Storage Water Heater (ESWH) consists of an insulated storage tank, usually cylindrical, where hot water is kept ready to be used.
The water is stored at a pre-set temperature typically 60-80°C. The water is heated in the storage tank by one or more electric resistance elements.
ESWHs heat water the same way electric kettle heats water, but, unlike the kettle, an ESWHs keeps the water hot.
Over time, the water temperature decreases through heat losses from the storage tank and from hot water draw-offs (usage). This results in the tank being refilled with cold water which in turn lowers the overall temperature of water in the tank.
Instantaneous Electric Water Heaters
Instantaneous heaters, where water is heated on demand and not stored are also available, but are less common.
Instantaneous or continuous flow water heaters are designed to deliver a steady stream of heated water for a bath, sink or shower. Each time a tap is turned on, water is heated instantly by electricity and then flows to the outlet.
An Instantaneous electric water heater typically requires high power inputs, particularly if more than one unit is running at once. In some cases three phase power is required, in others single phase power is adequate.
Check with your supplier, retailer or tradesman about power requirements for your house and to help properly size your appliance.
Storage tanks are not component parts for these units, as such they are not subjected to tank heat loss requirements.
Solar and Heat Pump Water heaters
Electric resistive elements can also be key components of Solar Water Heaters and Heat Pump Water Heaters where they provide “boosting” when the water temperature is low, with solar radiation (solar) or ambient air temperature (heat pump) providing the primary energy source.
For water heaters operating on a continuous electric tariff the electric elements are turned on when the water temperature drops below the thermostat set point. The thermostat will turn on the electric elements periodically throughout the day and night, to maintain the water in the storage tank at the required temperature. The number of times and the length of time the elements operate will vary with the size, location and number of elements as well as hot water draw-off behaviour and the heat loss characteristics of the storage tank.
Some ESWHs are not operated on a continuous electric tariff but instead operate on some form of restricted tariff, such as off peak tariffs or ripple control tariffs. Often larger tanks are used to ensure that users on restricted tariffs do not run out of water before the system can reheat the water.
Restricted tariffs are used when an electricity supplier wishes to control the electricity demand of electric hot water systems on their network. Such tariffs are a type of load management system that allows the electricity supplier to switch off a set of appliances, in this case water heaters, during periods of peak electricity demand. This is often referred to as “ripple control” in New Zealand, where the majority of ESWHs are controlled. In Australia, approximately 25% of homes use a form of continuous tariff for electric water heating.
The choice for the household or business of which electricity tariff structure to use depends primarily on the level of hot water service required, the price difference of the types of tariff(s) being offered and the number of hours the tariff(s) cover. For some more specific information about tariffs, look at the factsheet – Water heaters – electricity costs and tariffs.
Is your product regulated?
Find out which GEMS determination or regulatory standard applies to your product
All products covered by energy efficiency regulations must meet certain requirements before they can be supplied or sold in Australia or New Zealand.
Depending on the product, this may include Minimum Energy Performance Standards (MEPS), energy rating label requirements or both. There are specific requirements relevant to Australia and New Zealand.
Regulation for electric storage water heaters
The existing MEPS for electric storage water heaters have been in place since 1999 in Australia and 2002 in New Zealand that regulate heat loss from water tanks for these systems. At present there are multiple standards (5) and test methods which cover these regulated systems.
The Electric Storage Water Heaters (ESWH) product profile developed in 2012 and the Consultation Regulatory Impact Statement released in 2014 have more information on the market of hot water heaters and examine the scope to increase the minimum energy efficiency standards of storage water heaters as well as investigate the current exemption in place which excludes electric boosted storage tanks for solar and heat pump water heaters from MEPS requirements. The presentation given at stakeholder consultation meetings in Australia and New Zealand (20-22 January 2014) summarises some key issues in the consultation Regulatory Impact Statement.
To find out the Minimum Energy Performance Standards (MEPS) for electric water heaters, check the relevant Australian GEMS determination (link is external) or the New Zealand regulations (link is external).