LHV is Lower Heating Value. It is equally applicable to heat measured in joules, calories , or British Thermal units. It recognizes that the heat of vaporization of the water vapor in the exhaust can not be usefully recovered in an internal combustion engine. HHV is higher heating value, and cools the exhaust to the intial temperature including condensing the water vapor. HHV is important from a theoretical view and may be applicable to a high efficiency furnance. LHV is the way to usefully compare alternative vehicle fuels (although HHV may be applicable to a fuel cell vehicle). kWh/km directly relates to how one's electricty is metered, and how far one wishes to go in a car. It is going to have a leg up on any other unit. Maybe I could sell kJ/km on the basis of comparing alternative forms of energy. You know and I know the two "k's" cancel each other. However, J/m is far removed from both a measure of energy (the joule is too small) and the meter just has no relation to how far one wishes to go in a car (at least to people with limited metric literacy.) I believe you have, in fact, used kJ/km in your exercise examples, walking, running, biking.
--- On Thu, 8/27/09, Pat Naughtin <[email protected]> wrote: From: Pat Naughtin <[email protected]> Subject: [USMA:45698] Re: Wh/mile vs J/km To: "U.S. Metric Association" <[email protected]> Date: Thursday, August 27, 2009, 4:19 PM Dear Stan, John and All, I have interspersed some remarks in red. --- On Thu, 8/27/09, STANLEY DOORE <[email protected]> wrote: From: STANLEY DOORE <[email protected]> Subject: [USMA:45696] Wh/mile vs J/km To: "U.S. Metric Association" <[email protected]> Date: Thursday, August 27, 2009, 7:55 AM Dear Metricators: I like the greeting! Use J/km rather than Wh/mi as some news media are beginning to use. I have added some thoughts about choice of units below. Here's a chance for USMA and others to promote and use of the SI. I agree. What do you think? Stan Doore On 2009/08/28, at 00:02 , John M. Steele wrote: I agree, although the appropriate prefix is probably kilojoule. The prefixes in both numerator and denominator are redundant, but may seem "more useful" to the average person. At the time of creating a suitable unit (note singular) it is appropriate to consider a number of issues. I can't think of any reason why the word 'seem' should be considered at all. Better considerations are questions like: 1 What is the best choice of an SI unit – in this case it is joules per metre (symbol J/m)? 2 What unit gives whole number values that will fall within the expected normal range of values – in this case it is the joule per metre (J/m)? See: http://www.metricationmatters.com/docs/WholeNumberRule.pdf 3 Which unit will give values that will mostly fall within the range 0 to 9999 – in this case it is the joule per metre (J/m)? 4 What is the simplest possible SI (or metric) unit for this purpose – in this case it is the joule per metre (J/m)? My basis for the kilojoule. Approximate specs for the Volt are 8 kWh battery (28.8 MJ) and 40 miles (64 km) on battery alone. These may be "best case" but they yield 450 kJ/km. Or 450 joule per metre (J/m) could be used. As nobody has yet developed a mindset for comparing previous values, there is absolutely no need to try to comply with supposed mindsets such as mindsets based on kilometres (especially in the USA). Gasoline and diesel mileage may be similarly expressed. Using DoE typical LHV heat values, gasoline consumption of 8L/100 km (close to current CAFE) yields 2.6 MJ/km. Or you could express this as 2600 joules per metre. (Unless, of course, you are frightened of big numbers for some reason. It is my observation and belief that most folk would prefer to think of 2600 dollars rather than 2.6 kilodollars!) (yes I know LHV heat value is redundant; it looks naked without it) To an engineer this may be true. But, for my poor agricultural mind, I had to look up LHV on Google – I am now no wiser – for some reason LHV values in calories don't do much for me! Cheers, 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 for more metrication information, contact Pat at [email protected] or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
