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Page 5 of 9

Chapter 5

Water Heating

Introduction

Heating water consumes the second greatest amount of energy in the average household (after heating and cooling). Understanding your water consumption habits is therefore a key component of any energy-saving strategy. Knowing what the right system for your home is can greatly reduce your energy consumption, and minimise water wastage.

Energy-efficient habits

The most effective measure you can take to curb your home’s need for water heating is to use less hot water! Ultimately, the less water your system must heat up, the less energy your water heater consumes. There are various concrete measures you can take to help reduce your hot water consumption.

  • Have shorter showers - make sure your hot showers don’t run for more than a couple of minutes.
  • Shower at a slightly cooler temperature - dilute your shower with a little less hot water.
  • Turn off water heating systems when you are away if you have a tank.
  • Use cold water in your washing machine - when washing clothes, make sure you use cold water. Performing hot washes is inefficient and mostly unnecessary (see section 6).
A softly lit kitchen with a speckled black stone tap. Water falls from the tap nozzle while a single indigo flower sits perched in a clear glass bottle beside the sink.

A diagram depicts a large showerhead with a long stream of water with the text 20 litres per minute. Next to this is a smaller more efficient showerhead with a smaller stream falling from it and reads 7 litres per minute.

Audit

Check your shower

  • Install water efficient shower heads: Water efficient shower heads gives the same experience as normal showers but uses a lower water flow. Standard shower heads have a flow rate of more than 20L per minute, while efficient ones use as little as 7L. Water efficiency translates to energy efficiency when using hot water.
  • Fix leaks and drips: leaks from hot water taps will slowly consume hot water, causing your system to heat up more often.

Is your hot water system healthy and efficient?

  • Insulate tank: An insulated tank will be able to maintain the temperature of the heated water for longer. This means the system won’t have to heat up as often to maintain hot water for the home.
  • Insulate pipes: Pipes delivering hot water loses heat to the environment. By insulating pipes, water will be delivered hotter, thus requiring less hot water when performing activities such as showering.
  • Install heat traps: Heat traps prevent unwanted movement of hot water out of the tank. In newer water heating systems, heat traps are already built in. Normally, hot water rises by natural convection up the intake pipe, where cold water normally comes through. Heat trap prevents this with a simple looping design, stopping hot water from rising out of the tank.
  • Plan for the future: You’re probably not in the market for a hot water system if the one you’ve got is fairly new and working without issues. But in the event that your system breaks down and you need an upgrade ASAP, be sure that you’re informed to make the right decision.

Types of hot water systems

Normally, homeowners only upgrade their water heating system after their old one breaks down. Plan for the future so when the time comes to get a new system, you know the type that is most appropriate for you.

Understanding the different types of water heating will allow you to be smarter about your energy efficiency. Choose the right system based on:

  • Your hot water demand profile – For example, do people all use hot water at the same time (e.g. in the morning) or is use spread out throughout the day or split between morning and evening?
  • Available energy sources – Apart from electricity, do you have access to solar and gas?
  • Energy efficiency - Hot water systems have Energy Star ratings just like other devices; try to choose one that strikes a balance between out-of-pocket price and long-term running costs.
  • Your climate – Some systems aren’t suitable in certain climates (e.g. solar thermal systems and heat pumps - see below) .
  • Your budget – A lower price tag does not always mean lower costs in the long run; keep in mind operating and maintenance costs.
Instantaneous (continuous flow)

Electric/Gas Systems

Continuous flow systems heat up water as it flows in, meaning they are not affected by the heat loss from the storage of hot water. These systems use electricity or gas to heat up water as it passes through the pipe, so you can’t run out of hot water unless the source of electricity or gas is cut off.

The unit itself is small and discrete compared to storage systems. Depending on the number of the hot water outlets in the home, you will need to get the appropriately sized system;, otherwise you might not have sufficient hot water.

Older systems take a couple of seconds before the hot water reaches the outlet, but newer systems have designs that allow water to come out instantly hot. Some systems also allow you to set the water temperature so it doesn’t require dilution with cold water due to being overheated - nor does it come out too cold.

A diagram of water being heated instantaneously within the pipe as it travels to the tap and basin. Below a storage tank is depicted heating the water and storing while waiting for the tap to be turned on.
Storage Systems

Storage systems come in the form of a unit and a storage tank. The unit heats up the water and stores it until it needs to be used. These systems suffer from standby heat loss, but can readily provide hot water and meet greater demand when needed.

Keep in mind that tanks need consistent maintenance, as they can suffer from corrosion and ‘scaling’, which is the build-up of mineral deposits from water with high mineral content.

Electric vs Gas Systems

Compared to continuous systems, storage systems using gas or electricity consume more energy, as they must continuously reheat the water after the heat is lost from the tank.This translates into more operational costs down the track. This can be minimized with better insulated tanks and pipes, and more efficient systems.

Electric systems take around 1 to 2 hours to heat up hot water, depending on the system. Gas systems take about half this time. Electric systems may be subject to different electricity rates. Some electricity retailers offer cheaper rates if they are able to control when the system will turn on. This usually means that your tank will be set to run during the night, when there is less stress on the grid. These ‘off-peak’ systems generally require larger tanks, as the hot water has to last through the whole day.

Heat pump

Heat pumps work in the same way as a refrigerator, but in the opposite direction, so that heat is extracted from the air and put back inside. The system comes with a compressor unit and a tank, but these can usually be combined; they also often have a booster systems in case the temperature is too cold or demand is high.

These systems are very efficient when compared to electrical/gas storage systems, but require an ideal climate and well-ventilated spot. Heat pumps don’t generally work well in cold regions, instead running best in moderate climates. They can also be situated near compressors of air conditioners to make use of the warm air being expelled out of the home.

This system is a good alternative when solar isn’t suitable for your house, and the only energy source available is electricity.

Solar thermal

Solar thermal hot water comes with the solar unit and a booster element. Water is heated using solar energy during the day and hot water is maintained by the element during periods of less sunshine, or when the water temperature is not quite warm enough. The system runs better in sunny locations, and may not operate effectively or at all in some colder and less sunny climates. A well-run system will pay for itself over the long run, as running costs are comparatively low, despite the more expensive upfront cost.

Heating water with solar PV

Solar PV systems can be retrofitted or installed new with a device called a hot water diverter, which effectively channels ‘excess’ solar electricity (i.e. solar output in excess of household demand) into the element of a hot water tank. In doing so, a hot water diverter can improve the returns on not only the hot water system but also the solar PV system. Sophisticated diverter units (or regular hot water units coupled with a smart energy management system) may also be capable of taking advantage of cheaper, off-peak or controlled load rates in addition to solar energy.

In the next chapter, learn about reducing energy consumption in other aspects of your household.

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