Obviously, there may be alternatives to my viewpoint, but I felt the SI rating was incidental to the conversation when the real issue is that the label is completely wrong and contributes to the confusing of power and energy.
Of course, the BTU is as poorly and multiply defined as the calorie. Pick a BTU, pick any BTU! However, I would hazard a professional SWAG that the rating relates to a fuel rating and an API method, therefore BTU60, the value at 15.5555 °C (60 °F), which is 1054.68 J/BTU. Of course 1 h = 3600 s, so 15000 BTU/h x 1054.68 J/BTU x 1 h/3600 s = about 4400 W (4394.5 W if you like "decimal dust"). Any other BTU would only change the result slightly. For practical accuracy just multiply the BTU/h value by 0.293 to get watts (in your head, even 0.3 would suffice) ________________________________ From: "[email protected]" <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Wed, June 9, 2010 9:07:13 AM Subject: [USMA:47590] Re: One unit only John, Although you may be forgiven(?) for quoting Jim's non-SI value, you too do not include the power of the gas grill in watts. What is it? Why burden the readers to convert to SI? Gene p.s. I do have highest regard for the postings of both of you relative to postings by other subscribers in spite of this rare deviation from SI. ---- Original message ---- >Date: Tue, 8 Jun 2010 18:59:49 -0700 (PDT) >From: "John M. Steele" <[email protected]> >Subject: [USMA:47581] Re: One unit only >To: "U.S. Metric Association" <[email protected]> >Cc: "U.S. Metric Association" <[email protected]> > > Jim, > > I agree with glassy-eyed and wobbly kneed, but this > is the ROOT of all energy vs power confusion. > > Just ask, "So, after the grill has consumed 15000 > BTU, it dies? That seems like a lot of money for a > grill with a one hour life." > > I'm afraid it is up to the engineers to be > persistent PITAs on this matter. Proud to serve. :) > > ------------------------------------------------ > > From: James R. Frysinger <[email protected]> > To: [email protected] > Cc: U.S. Metric Association <[email protected]> > Sent: Tue, June 8, 2010 9:47:38 PM > Subject: Re: [USMA:47579] Re: One unit only > John, your last paragraph can be exemplified with > the ratings that one sees posted for gas grills. > They are usually rated as being, for example, "15 > 000 BTU". What is meant, though, is "15 000 Btu/h" > -- where I have fixed the error in the symbol and > have added the divisor. The former is an energy > value; the latter is a power value (the rate at > which chemical energy is converted to thermal > energy). > > Caution: Experience has shown that if I try to > discuss this with the sales staff, they get > glassy-eyed and start to look wobbly in the knees. > > Jim > > John M. Steele wrote: > > 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. > >...
