I got your points entirely, Jim. My point is that readers who know *only* SI (a real possibility, at least in the future) will not understand or accept "BTUs" which can be avoided entirely.
It is easy to express *all your points* using only the unit name watt or the quantity name power without the awkward constructions you illustrate below. Gene. ---- Original message ---- >Date: Wed, 09 Jun 2010 09:02:04 -0500 >From: "James R. Frysinger" <[email protected]> >Subject: [USMA:47601] Re: One unit only >To: "U.S. Metric Association" <[email protected]> > > >Gene, > >The non-SI units in my posting reflected the situation I was reporting. >To have converted those to SI units for you would have obscured the >point I was making. It would have been nonsensical to say, "Gas grills >are rated in non-SI units, for example 4500 W." Also, the number I used >in the value "15 000 BTU" was a somewhat typical number that I pulled >out of my head. > >I wonder if you didn't miss my point entirely. Two of them actually: >1. Gas heaters are rated in non-SI units which makes comparison to >electric heaters non-trivial. >2. Gas grills and heaters are labeled improperly in energy units instead >of power units due to the omission of the divisor unit of time. The >phrase "per hour" is "understood", the manufacturers would say but in >fact it is NOT understood by the public. > >Jim > >[email protected] wrote: >> 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. >>> >... >> >> >> >> > >-- >James R. Frysinger >632 Stony Point Mountain Road >Doyle, TN 38559-3030 > >(C) 931.212.0267 >(H) 931.657.3107 >(F) 931.657.3108 >
