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Energy Systems - The Laws of Energy
This page: 1st Law of Energy Efficiency | 2nd Law of Energy Efficiency | Net Useful Energy

1st Law of Energy Efficiency (%)

=
useful energy (work) output
X 100
total energy (work) input

For many of us the initial cost often makes the extras seem beyond our budget but what this 1st law is stating is that we should not look at the initial cost but the total cost of the lifetime of that device or living creature.

When you move into that new dream home of yours you often find incandescent lights have been fitted throughout the house unless you specified differently. The cost of buying the globe and the light fitting are basically very cheap. To fit a flurolescent globe is dearer and to fit a flurolescent globe and light fitting dearer still. What most of us do not consider is the total cost of using that globe to illuminate our home each night.

If you could compare two identical homes, built next door to each other, one fitted with incandescent lights the other with fluorscent lights and the two families have similar home needs, requiring roughly the same number of hours of electricity each week, then when their electricity bills arrive for the same period you will you notice a difference.

Incandescent globes are cheaper to buy but give out less light (illumination 5%) and create more heat than fluroescent globes (illumination 22%). This means that your electricity bill for the incandescent owner included heating the air around the light globe to the tune of 95% of the cost. This heat is not warming any individual but warming in most cases air around the ceiling and over time will cause the insulation (probably plastic) around the light fitiing to become brittle requiring replacement eventually. The fluroescent light on the other hand only heats the air around the light using 78% of the power used to light the room.

These figures can be improved upon with new technology but the message is the same. Initial costs might be higher if you have fitted more efficient lights or devices but will use less power and be cheaper in the long term. Think about it!

If we use less power then we are lengthening our use by date on our power supply.

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2nd Law of Energy Efficiency (%)

=
minimum amount of useful energy (work)
X 100
actual amount of useful energy (work) needed to perform task

Applying the 2nd law to energy that we have used, gives us a truer indication of how much energy we actually used to gain an output and how much we wasted in achieving that output. Statistics show that the majoritory of people in developed countries only efficiently use 10 to 15% of all energy they pay for.

The following table based on data from the American Institute of Physics, Efficient Use of Energy (New York: American Institute of Physics, 1975), pp.49-50. illustrates this fact .
source: http://www.nesh.ca/jameskay/www.fes.uwaterloo.ca/u/jjkay/pubs/exergy/index.html

Use

Estimated First Law Efficiency (%)

Estimated Second Law Efficiency (%)

Space Heating

 
  • Furnaces

60

6

 
  • Heat pump

270

9

Water Heating

 
  • Electric

75

1 - 2
 
  • Gas

50

3

 
  • Air Conditioning

200

5

Industrial

 
  • Process Steam

80

25

 
  • Direct Heat
40
20
 

 

Additional information can be found at the following links:
Standford University - http://gcep.stanford.edu/research/factsheets/systems_analysis.html .
Winnipeg University's http://theory.uwinnipeg.ca/mod_tech/node80.html

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Net Useful Energy

=.
Total useful
energy
   minus  
Useful energy to find, prepare, upgrade and deliver the energy in a useful form
  minus  
useful energy lost and wasted

Possibly the easiest way to explain net useful energy is to compare it to net profit of a business where what you outlay to gain an income is deducted from your income to show what monies above all costs you recouped in your dealing(s).

In terms of energy, we the custodians of the world are currently using annually more of natures fossil fuels than nature can provide. Sometime between the year 2020 and 2060 it is estimated by some that all current known resources of fossil fuel in the world will be exhausted. If we compared this fact to the net profit analogy above, in simple terms the world would be bankrupt with no reserves of any type of fossil fuel.

What is important for all of us is how we develop and use what remaining fossil fuel we have left to allow the world to go beyond these dates. Using 9 units of fossil fuel to gain 10 units of non renewable energy is poor judgement. What the world needs is positive, economical foresighted development. Are you up to it?

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Please Note

The above information might not be as accurate for Australia as it should be with mining corporations and governments amending rules and regulations from time to time. The content has been based on data collated from various sources dating back as far as 1980 and will not necessarily reflect the thinking of every metalurgist, chemists, geologist or those concerned with climate change. No paper will please everyone and debate is good if based on facts and not solely on theories. We encourage dialogue and all suggestions that can improve on the information given. Improvements can be sent to info@energy.edu.au.

The base for many of the ideas used in this and other charts can be found in:
G. Tyler Miller Jr "Living in the Environment", Wadsworth Publishing Company, California 1979, p272 under the penship of Howard T Odum, Professor of Environmental Engineering Sciences at the University of Florida.

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