Pat, I'm sorry but I must go back to your statement to Stan, " It seems really odd to me that engineers, who > probably know much better, are using a power unit > when they are referring to energy."
In the instance you cite, you are talking about energy over a time period, and energy divided by time is power. Annual energy usage has a dimension of power, whether you use power units (watts) or explicitly describe the energy and the time period. Stan is at least technically correct in using watts. I have some misgivings about average power vs peak power if the situation is not fully explained. Power and energy have exactly the same relationship between them as velocity and distance. If either is described fully as a time function, I can derive the other. Since I am retired, I drive much less. Pardon the miles, but they are unfortunately the units on my odometer. I am only driving 4000 - 4500 miles per year. As there are 8760 hours in a common year, my average speed is circa 0.5 MPH. That, of course is completely useless as a description of my driving which is normally at 25 - 75 MPH, plus many hours with the ignition is off. My miles per annum is a speed (just not terrible useful). 0.5 MPH or 4400 miles/annum encodes the same information. In the same sense 1600 PJ/annum and 50.7 GW encode the same information. As I don't know how evenly the 1600 PJ of coal is burnt over the year, the utility of average power may be debatable but it is technically correct. When energy usage over a period is described, the period is so intimately attached to the energy that it would be better to drop both units than only one. I do understand that you meant petajoules per annum, but I believe that omitting the per annum has lead to some of the confusion that has existed here in various notes about energy vs. power. It must be completely explicit, or at least that is my view on the matter. ________________________________ From: Pat Naughtin <[email protected]> To: [email protected] Cc: U.S. Metric Association <[email protected]> Sent: Tue, June 8, 2010 8:43:21 PM Subject: Re: [USMA:47574] Re: One unit only On 2010/06/09, at 10:11 , John M. Steele wrote: > >Or in a given heap of coal. I of course agree with that, and believe I >already referenced that situation, if only by that example. However, Pat is >describing an annual energy usage as though it was a one time use and energy >was never used again. The specific example in Pat's pdf file is the 1600 PJ >of black coal. Pat is using the joule (with prefix) to refer to an annual >energy use, but omitting the unit "per year". It is terribly important >whether that time period is a day, year, or decade. Thus, the figure is >REALLY an average power, which he is disguising as an energy and saying the >engineers are confused. That 1600 PJ is used in one particular calendar year, >and the next year, a roughly comparable amount is probably used. >> >>It is not practical to talk about a discrete amount of energy a nation uses >>because it KEEPS using it, and so the total energy used is a monotonically >>increasing function (like my electric meter or gas meter). I can only >>describe the amount used over a period of time (such as a billing period in >>the case of those meters). I can describe the energy and the time period, or >>I can recognize that energy/time = (average) power over the time period. >> > Dear John, With respect it appears that you misread my example. The text surrounding the list referred to the year 2001-2002 so the year was clear in the original quote from the Australian Bureau of Statistics – my error was in not transferring this reference to the year in my translated paragraph – you will see the context if you re-read the whole of the surrounding text.. All that was being compared was the amount of energy used in that single year. To remind you, the original reference was at http://www.metricationmatters.com/docs/AWordAboutGlobalWarming.pdf but be quick if you want to confirm my mistake because I will emend it soon. Cheers, Pat Naughtin Author of the ebook, Metrication Leaders Guide, see http://metricationmatters.com/MetricationLeadersGuideInfo.html Hear Pat speak at: http://www.youtube.com/watch?v=_lshRAPvPZY PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com/ to subscribe. On 2010/06/09, at 10:11 , John M. Steele wrote: Or in a given heap of coal. I of course agree with that, and believe I already referenced that situation, if only by that example. However, Pat is describing an annual energy usage as though it was a one time use and energy was never used again. The specific example in Pat's pdf file is the 1600 PJ of black coal. Pat is using the joule (with prefix) to refer to an annual energy use, but omitting the unit "per year". It is terribly important whether that time period is a day, year, or decade. Thus, the figure is REALLY an average power, which he is disguising as an energy and saying the engineers are confused. That 1600 PJ is used in one particular calendar year, and the next year, a roughly comparable amount is probably used. > >It is not practical to talk about a discrete amount of energy a nation uses >because it KEEPS using it, and so the total energy used is a monotonically >increasing function (like my electric meter or gas meter). I can only >describe the amount used over a period of time (such as a billing period in >the case of those meters). I can describe the energy and the time period, or >I can recognize that energy/time = (average) power over the time period. > > > > ________________________________ From: "[email protected]" <[email protected]> >To: U.S. Metric Association <[email protected]> >Sent: Tue, June 8, 2010 7:31:28 PM >Subject: [USMA:47572] Re: One unit only > > >There are discrete amounts of energy, *independent of time*. >i.e. independent of power. Examples: > >1. Work required to lift a mass m, a height h, in a gravitational field g, >where g can be g(h) W = m g h (symbols in italics) > >2. Energy of a photon; E = h f (f = nu) > >3. Kinetic energy of a moving object at constant speed; > KE = 1/2 m v^2 > >etc. etc. >---- Original message ---- >>Date: Mon, 7 Jun 2010 03:35:43 -0700 (PDT) >>From: "John M. Steele" <[email protected]> >>Subject: [USMA:47532] Re: One unit only >>To: "U.S. Metric Association" <[email protected]> >> >> Well, they are different, but "distinct and >> separate" might be an overstatement. Formally, >> energy is the integral of power with respect to >> time, power is the derivative of energy with respect >> to time, mathematically. It is not possible to talk >> about the energy used by a nation because it keeps >> using more, you can only talk about the energy used >> over some period of time such as a year. >> Energy/time is power, whether you express it as >> watts or joules per year. Joules per year suffers >> from the same issue as the kilowatt-hour. By >> introducing a non-SI unit of time, the coherence of >> the SI is lost. Also the term year lacks precision, >> common, leap, Julian, Gregorian, etc.? Of course, >> these energy per annum figures are estimates >> compiled by summing numerous sources and making >> estimates for any missing data. They probably do >> not have the precision for the issue of "which year" >> to matter. Do we see a curious spike every 4 years? >> >> As an engineer, the only misgiving that I have using >> watts in this sense is that it is only a measure of >> the annual average power. The times and magnitudes >> of peak power, and also the base power requirements >> (the valleys) are important. Using watts in this >> average sense is technically correct, but it may >> create a false expectation that only this amount >> needs to be available on an instantaneous basis; >> that expectation is wrong. If the use of exajoules >> per annum helps legislators avoid that >> misunderstanding, I, as an engineer, am quite >> capable of dividing by 31.5 Ms. >> >> ------------------------------------------------ >> >> From: Pat Naughtin >> <[email protected]> >> To: U.S. Metric Association <[email protected]> >> Cc: U.S. Metric Association <[email protected]>; >> gmail aaj <[email protected]> >> Sent: Mon, June 7, 2010 12:36:46 AM >> Subject: [USMA:47525] Re: One unit only >> Dear Stan, >> It seems really odd to me that engineers, who >> probably know much better, are using a power unit >> when they are referring to energy. >> As far as I know power and energy were clearly >> distinguished as two quite separate and distinct >> physical realities late in the 1700s or early in the >> 1800s (I would like to have an exact date but this >> is the best I can do at present). >> As you know the unit for energy in the International >> System of Units (SI) is the joule (symbol J) and the >> unit for power in SI is the watt (symbol W). It >> makes no sense at all to me to pretend you are >> talking about energy when you are trying to describe >> it with the SI unit for power. >> You will recall that I am really concerned about >> this issue because until journalists and politicians >> are able to comprehend the nature of energy and how >> to measure it, we have no chance that they might >> begin to comprehend issues such as 'global warming', >> 'climate change', or 'the end of oil' as these are, >> in essence energy issues, and not power issues. >> My approach is to use the SI unit, joule, only, and >> to use it with an appropriate prefix to give whole >> number amounts. See the short article at >> http://www.metricationmatters.com/docs/AWordAboutGlobalWarming.pdf >> for an example of how I use the energy unit, joule. >> Cheers, >> >> Pat Naughtin >> On 2010/06/07, at 10:17 , Stanislav Jakuba wrote: >> >> I am attaching an energy article that is >> distinguished for using only one unit, the watt >> (W), throughout. That units was selected as it is >> both familiar everywhere, incl. in the US, and >> shorter than others that one could select to >> express the average energy usage. The watt (as >> GW) is the only unit need for these kinds of >> global statistics, and using it exclusively >> enables immediate comparisons. >> >> >> >> I do not mean to start a debate about the opinions >> expressed in the treatise, although I will >> certainly read all. Instead, I do hope to >> "persuade" everybody in the energy business to >> settle on this unit for any kind of energy usage, >> i.e.power, anywhere in the world instead of >> the plethora of units common in energy related >> statistics. On the scale of countries, only one >> prefix also, the G, suffices. >> >> >> >> Stan Jakuba >> >> >> >> <Pacific Gas & E.3USMA.doc> >> >> >> Pat Naughtin >> Author of the ebook, Metrication Leaders Guide, that >> you can obtain >> from http://metricationmatters.com/MetricationLeadersGuideInfo.html >> PO Box 305 Belmont 3216, >> Geelong, Australia >> Phone: 61 3 5241 2008 >> Metric system consultant, writer, and speaker, Pat >> Naughtin, has helped thousands of people and >> hundreds of companies upgrade to the modern metric >> system smoothly, quickly, and so economically that >> they now save thousands each year when buying, >> processing, or selling for their businesses. Pat >> provides services and resources for many different >> trades, crafts, and professions for commercial, >> industrial and government metrication leaders in >> Asia, Europe, and in the USA. Pat's clients include >> the Australian Government, Google, NASA, NIST, and >> the metric associations of Canada, the UK, and the >> USA. See http://www.metricationmatters.com/ to >> subscribe. > >
