Talk:Energy efficiency

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[edit] References and refrigeration

• It would be good to have a reference or two or three to the international standard & text books that define energy efficiency.
• As mentioned on Talk:Emergy#HOWEVER according to Ohta, the definion of energy efficiency sometimes has an unreasonable result with reference to refrigerators, where η becomes negative and the efficiency of heat pump exceeds 100% (Ibid.). Is energy efficiency of refrigerators >100% when energy efficiency is defined as it is in this article? Sholto Maud 01:45, 30 December 2005 (UTC)
• it would be good to have refrances to where energy efficiency can exceed 100% (outside newtonian physics of course)

[edit] The Definition given here is to narrow, and that is misleading

It is often mistakenly thought that "efficiency" is the synonomous with the efficiency factor. That is only true, if both quantities on the right hand side of the definition

efficiency = benefit / effort (that is the general definition)

have the dimension of "energy" or "power". But very often the benefit has nothing to do with energy. For example, the benefit can be a mileage (unit "miles"). The effort e.g. is the fuel needed (unit "gallons") and the efficiency of this service will be given by

mileage / (fuel consumption)

with the unit "miles/gallon". In Europe the inverse value

effort coefficient = 1/efficiency

is established: the specific fuel requirement in (liter fuel)/(100 km). Such values characterising the efficiency are not "efficiency factors" - they are values with a dimension. It is not possible to introduce an efficiency factor instead of these quantities. Looking at most services produced by the use of energy you will find, that they do not have the dimension of energy.

That sound like an academic question? No, not at all. This is a key insight.

Let us look at an example: The efficiency factors of heating boilers can not be increased to more than 100% (law of energy conservation) and contemporary values already are in the range of 90%. But: the efficiency of the total service "heating" (to be measured by the area heated with a given amount of fuel) can be increased almost without any limit - by better insulation and heat recovery. If you only look at the efficiency factor, there will not be a noteworthy potential for energy saving for heating. But if we have a broader look at the service and realise, that the so called "heating demand" can be reduced to values near to zero (by insulation and heat recovery), we will understand that there is a huge potential for better efficiency. This has been demonstrated by the multitude of Passive Houses which have already been built and are occupied.

But it is not only true for heating, it is quite similar with many other applications of energy: At the end of the supply chain, the final use is made out of the energy supplied. At this end there are the major potentials for an increased efficiency: And it is not a few percents which can be saved; it is the major part - in most cases.

WF 2006-11-08 Reference: Dr. Wolfgang Feist, Source: http://www.passivhaustagung.de/Passive_House_E/efficiency_factor.html

[edit] Clean-up Redirect

I agree that the content is too narrow. The article Energy conversion efficiency is more complete, and refers readers to the more specific terms and equations (e.g., Thermal efficiency). As such, I will 'boldly' redirect to it. 129.237.114.171 19:28, 21 November 2006 (UTC)

If the goal is to broaden the content of this article, then I would argue against redirecting it to energy conversion efficiency. Although the energy conversion efficiency article is indeed a more information-packed article than this one, its intended focus is limited to the efficiency of energy conversion machines whereas this article has a broader focus intended to cover the efficiency of all sorts of processes, not just those whose end purpose is to convert energy from one form to another. (As an example, consider the efficiency of a resistor; a resistor does not fall under the category of an energy conversion device, yet it is still appropriate to calculate its efficiency through use of the Work / energy formula.) I have removed the redirect for this reason, but I will watch for further discussion on this issue. Riick 03:51, 27 February 2007 (UTC)