Cost Advisor

Energy efficient water heating solutions

February 12, 2014

Energy efficient water heating installations

The following fuels can be used to heat water:

  • electricity
  • gas
  • solid fuel, and
  • solar

Electricity and gas

Electricity can heat water with dose to 100 per cent efficiency, bot gas appliances lose some heat to atmosphere as part of the combustion process. However, modern gas appliances can be as much as 95 per cent efficient.

When comparing energy sources to heat water, the overall energy consumption must be considered. Between electricity generation and the electricity consumed to heat water, a lot of energy is lost. Most of this loss occurs when electricity is generated by burning fossil fuels (the conversion process is very inefficient) and energy is lost in die transmission and distribution process.

Burning gas to heat water produces less greenhouse gas emissions than electricity. However; gas systems may not be as efficient at converting energy into hot water.  However, gas compares favourably to electricity when considering overall carbon emissions. Gas burners are more powerful than electric heaters so will heat water a lot faster!

in New Zealand there is a growing trend to reduce solid fuel heating from fires and wood burners, particularly in areas that experience problems with smog. In terms of efficiency, pellet wood burners can be up to 88 per cent efficient.

Solar water heating

In New Zealand, solar radiation is an abundant energy source, and many homes are exposed annually to 20 to 30 times more energy from the sun than they use in electricity or gas. Standard solar water heating systems can produce around 75 per cent of a household’s water heating in summer, and between 25 and 45 per cent in winter. Solar water heaters function well From Invercargill to the far north, although the solar contribution varies depending on location and the time of year.

Solar water systems have many benefits, including providing reliable hot water in times of electricity shortages (as long as the hot water system doesn’t use a pump), lower electricity
costs, and an increasing awareness of a renewable energy resource. The environmental benefits are significant. If each household in New Zealand had its own solar water heater, carbon dioxide emissions from electricity generation would be reduced by about 2 million tonnes per year. If commercial and industrial Operations installed solar water heaters, the environmental benefit would be greater still.

Heat pump water heating

Heat pump water heaters provide a form of indirect solar water heating. The sun heats the air around the home each day, and a heat pump water heater shifrs some of this heat from the outside air into hot water. These systems can
be two to three times more energy efficient than conventional electric resistance water heaters. Heat pump water heaters can also be effective in situations where solar water heating is not suitable, such as:

• houses that don’t get direct sun during the day, or
• houses where it would be particularly expensive to install a solar hot water system.

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