Ready Reckoner

Household energy use

The figures on household energy use I have referred to in this book come from the Australian Greenhouse office. The key figures are summarised in the table below and provide a quick way to estimate the impact of the various components employed in the average household.

More detailed figures are available at greenhouse.gov.au Note that these figures are per household, rather than per person.

Activity

percentage of household use

Tonnes CO2

Travel – domestic

23%

6

Travel – work

11%

3

Laundry/dishwasher

2%

1

Cooking

3%

1

Lights

5%

1

Waste

5%

1

Water heating

16%

4

Home heating and cooling

11%

3

Fridge Freezer

9%

3

Electronics & appliances

15%

4

Total

100%

27

 

These figures consider the energy consumption in running the home, not in building it or in the appliances that we purchase. Buying a new solar hot water service eliminates the 3 tonnes of carbon dioxide equivalent used to heat water, but greenhouse gases have been generated by manufacturing and installing the unit. These emission figures are generally assigned to industry, rather than domestic use. The article on embedded energy at the end of chapter one explains this concept in more detail. Because of this it is best to buy new appliances when old ones wear out.

Replacing an electric or gas hot water service with a solar one immediately eliminates 3 tonnes of CO2 each year. This is the easiest challenge to tackle. Reducing your driving is the next easiest thing to address, and also has an immediate effect. As well, it has the advantage of not requiring any new appliance. If you assume about 5tonnes of CO2 per car per year, you can see the value of doing without a second car. Renting cars on those occasions where you need two cars may be more cost effective as well as more energy efficient.

Replacing existing appliances with energy efficient appliances can significantly reduce energy consumption but using them less will have a much greater impact. Consider seriously whether you need new appliances at all. Some appliances – a rice cooker or bread maker, for example – may contribute to a more sustainable lifestyle as well as energy efficiency. This may offset the energy cost of producing the appliance.

Estimating specific emissions

The figures for average usage give an overview of where you might make major savings. If you want to estimate more accurately the contribution any particular appliance or activity makes to global warming – energy use, the following table is more specific. For some activities, different options offer different levels of accuracy. These remain rough estimates, based on a wide range of assumption.

Activity

Units used to calculate

kgCO2e pa

Driving

Small car

4,000 – 6,000

 

Av family car

6,000 – 8,000

 

4WD

9,000 – 12,000

 

Litres petrol per week

150

 

Dollars per week spent on fuel

180

Electricity

Avg home (2,500 kwh per quarter)

10,000

 

Kwh per quarter (non green power)

4

 

Kwh per quarter (100% green power)

0

Hot water

Avge home (electric hot water)

4,300

 

hot electric water service using offpeak 1 (per litre)

25

 

hot electric water service using offpeak 2 (per litre)

37

 

Gas hot water service (per litre)

12

 

Solar hot water electric boosted (per litre)

12

 

Solar hot water manual boost (per litre)

6

Flying

Australia (Bris – Mel)

1,000

 

Asia (return)

4,000

 

US, Europe (return)

10,000

 

Passenger kilometre

0.7

 

 

Domestic heating and cooling

Changing the way you heat and cool your home can clearly make a significant contribution. Again, a change in your habits is more effective than buying a new appliance. If you are building or renovating, however, this will be one of the most significant contributions you can make.

The table below from the Sustainable Energy Development Office of Western Australia (http://www1.sedo.energy.wa.gov.au/pages/heat_run.asp) rates the energy consumption of various approaches to heating. The figures will be slightly different for NSW, because of differences in the relative cost of different sources of energy. I have invited the NSW greenhouse office to provide similar figures for residents of Sydney.

CENTRAL HEATERS (150m² floor area)

Approximate Annual Greenhouse Gas Emissions
Central heater comparison 

SPACE HEATERS (60m² floor area)

Approximate Annual Greenhouse Gas Emissions
Room heater comparison 

PORTABLE HEATERS (30m² floor area)

Approximate Annual Greenhouse Gas Emissions
Portable heater comparisons 

  • Range for central and space heaters is from most efficient to least efficient models known to be available. This is little variation in efficiencies of portable heaters
  • The more natural gas appliances used, the lower the natural gas price and the less the heater will cost to run.
  • Note Electric heaters which use NaturalPower instead of conventional electricity will have no greenhouse gas emissions, but will cost more to run. If wood is sustainably grown the fuel is greenhouse neutral. However wood fires still cause pollution.

Measuring energy

We instinctively know what energy is. When we have a lot of energy we bounce around, energetically. When we light a fire under a kettle, the energy of the fire heats the water. If we use the steam to drive a steam engine, we can do useful work: Lifting an object, driving a train, running a factory. Work is what we do with energy.

Energy is measured in joules. One joule of energy will accelerate one kilogram of stuff by one meter per second for every second that it is applied. To hold up a kilogram of apples against the earth’s gravitational field consumes 10 joules of energy every second.

If we carry around a kilogram of apples we burn those 10 joules of energy every second. The rate at which we use energy is called power. Power is measured in watts. One watt is one joule each second. Carrying the bag of apples requires ten watts of power. Carrying the bag for one hour uses one watt hour of energy. Another way of saying that is that it used 36,000 joules or 36 kilojoules.

A 100 watt light globe, then, uses as much energy as holding up a 10 kilogram bag of apples against the earth’s gravity. Doing it for an hour uses 100watthours, or 36kilojoules.

We pay around 15c per kilowatt hour for electricity. Look at your electricity bill to get a more accurate calculation.

If your electricity bill is $300 per quarter, you are using around 2,000 kilowatt hours of electricity each quarter, that is 8,000 kilowatt hours of energy each year. This is also called 8Megawatt hours. That is equivalent to 28,800 megajoules, also known as 28.8Gigajoules.

Energy comes from burning fuel. The energy value of food is measured in Calories. To do a good day’s work, the human body needs at least 2000Calories of food each day. One Calorie is equal to 4,187 Joules. The energy in a day’s food is over 8 megajoules. The human being is not a terribly efficient machine.

The energy content of petroleum, by comparison, is enormous. One litre of fuel oil packs 40Megajoules of energy. That is the equivalent energy of five days worth of food. A barrel of oil holds about 6000 litres of fuel. When you consider that the world uses over 80 million barrels of oil each day, you can start to see the scale of the energy challenges we currently face.

The following table lists various units of energy that you will encounter, and the conversion rates between them.

 

 

cubic metre

cubic foot gas

million Btu

therm

gigajoule

kilowatt hour

cubic metre of LNG

ton of LNG

1 cubic meter gas 

1

35.3

0.036

0.36

0.038

10.54

0.00171

0.000725

1 cubic foot gas 

0.0283

1

0.00102

0.0102

0.00108

0.299

0.00005

0.00002

1-million Btu 

27.8

981

1

10

1.054

292.7

0.048

0.0192

1 therm 

2.78

98.1

0.1

1

0.105448

29.27

0.0048

0.00192

1 gigajoule 

26.3

930

0.95

9.5

1

277.5

0.045

0.018

1 kilowatt hour 

0.0949

3.3

0.003415

0.03418

0.0036

1

0.000162

0.000065

1 cubic meter LNG 

584

20 631

21.04

210.4

22.19

6,173

1

0.405

1 ton LNG 

1,379

48 690

52

520

54.8

15 222

2.47

1

1 barrel Arabian Lt. 

0.152

5 350

5.46

54.6

5.75

1 597

0.259

0.105

1 ton Arabian
Lt. 

1.111

39 218

40

400

42.2

11 708

1.9

0.769

 

Source: Energy Information Administration, Annual Energy Review 1995, DOE/EIA­0384(95) (Washington, DC, July 1996)

 

 

There are also hundreds of online conversion tools to convert instantly between any range of energy units. These examples are fairly typical

http://www.chemlink.com.au/conversions.htm

http://www.convert-me.com/en/convert/energy

http://www.unitconversion.org/unit_converter/energy.html

Energy and greenhouse gases

The biggest cause of global warming is the amount of carbon dioxide in the air.

To calculate the amount of carbon dioxide you produce I have used the following conversion factors.

Energy source

unit

CO2e

Electricity generated in NSW

kilowatt hour

1kg

 

megawatt hour

1 tonne

Petrol burned in four stroke engine

litre

2.5kg

Oil consumed by industry

barrel

15 tonnes

Steel manufacture

tonne

2.9 tonnes

Concrete production and manufacture

tonne

128 kg

Greenhouse tomatoes

kg

3kg

Paper manufacture

tonne

40kg

 

Obviously these figures are approximations that depend on a range of factors. The analysis below explains how these figures have been arrived at.

The generation of electricity produces greenhouse gas through the burning of coal and other fuel. Burning coal, for example, produces more greenhouse gas than natural gas. Hydroelectricity produces very little greenhouse gas. The actual process of capturing energy from falling water and using it to turn a turbine produces no greenhouse gas, but some emissions are created by the cars, trucks and other machines used by the hydroelectricity companies.

The amount of greenhouse gas produced by your electricity use depends on the way it is generated. In Sydney, one megawatt hour of electricity produces about 985kilograms of carbon dioxide equivalent. Throughout this book I have rounded this to one tonne of CO2 per Megawatt hour. In Tasmania, the number is closer to 30kilograms because of the predominance of hydro electricity.

Carbon dioxide is not the only greenhouse gas – other greenhouse gases also trap the sun’s energy. Methane, for example, is a more effective greenhouse gas than carbon dioxide. Methane is the active ingredient in natural gas and is a byproduct of digestion, and the decomposition of food and other rubbish.

The amount of greenhouse gas that any country, industry, or household produces is measured in tonnes (or kilograms) of Carbon Dioxide equivalent. If a process produces one tonne of carbon dioxide equivalent, it has the same effect that one tonne of carbon dioxide would.

It may be useful to know that one tonne of coal produces over three tonnes of carbon dioxide equivalent. High quality coal is basically pure carbon. If it is burned efficiently, that carbon is burned with very little pollution and is totally converted to carbon dioxide. Every carbon atom combines with two oxygen atoms to produce a molecule of carbon dioxide. Oxygen is 14% heavier than carbon, so one tonne of high quality coal produces 3.28 tonnes of carbon dioxide. Low quality coal produces a mixture of pollutants, including oxides of sulphur and nitrogen which are greenhouse gases as well as causing acid rain and other problems.

 

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