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Rage against BTU's
4

Rage against BTU's

Rage against BTU's

(OP)
When I began working in the HVAC field, I became alarmed at the many terms used to measure heat production/absorption. I quickly caught on that BTU actually means Btu/hr (even in printed publications!)  This much I can handle, kind of like the police officer saying you were "15 miles" over the speed limit - everyone knows what is implied.

Then I found in my Mechanical Engineering Reference Manual the following footnote:

"In the United States, various confusing and ambiguous abbreviations for units of heat absorption have been used, including kB, kBtu, kBH, kB/hr, and MBH (or MBh) (1000 Btus per hour); and, mB, MB, mBtu, MBtu, MMBH, and MB/hr (1,000,000 Btus per hour).  In some particularly unfortunate cases, "MB" is used to mean 1000 Btus (no hour rate), and "MMB" is used to mean 1,000,000 Btus (no hour rate).  The actual meaning often has to be determined from the context."

I cannot get over the absurdity.  How did we get to this point?  Shouldn't engineers have developed a clearer standard by now?

I know, I know, we should just use Joules & Watts.  Is anyone else bothered by this?

RE: Rage against BTU's

Yes, sometimes I feel that there are so many pounds of pressure in my head, that my skull will explode!

RE: Rage against BTU's

(OP)
It's like having ten yards of dirt dumped on you!

RE: Rage against BTU's

microns - as a unit of pressure (vacuum).

Ton - as a unit of energy (12,000 BTU/hr)

RE: Rage against BTU's

a micron is 1/1000 of a millimeter


TTFN

RE: Rage against BTU's

"Shouldn't engineers have developed a clearer standard by now?"  Not only have we not developed a clearer standard, we're still developing junk.  

Ever hear of the "Therm".  This psuedo-unit started showing up on utility bills and in gas-sales contracts a few years ago and has taken the gas industry by storm.  A Therm is (to quote a contract I saw a while back) "that volume of gas which, at STP of 14.73 psia and 72F, would provide energy equivilant to 100 BTU".  On your natural gas bill they don't define it, but they assume some heating value (depends on the utility but it is commonly 1050 MBTU/SCF) pressure and temperature and use their old volume flow meters.  My energy usage jumped 7% the month my utility instituted this change and has been 5-10% higher ever since (even though one of my children has left home and I have replaced a very clogged water heater with an on-demand unit).

I especially like the defination of STP that the contract had.  See, as a profession we just don't get any smarter.

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The Plural of "anecdote" is not "data"

RE: Rage against BTU's

Ton is actually TR (Tons of Refrigeration). Another interesing Italian unit is frig/hr (kcal/hr).

RE: Rage against BTU's

IRstuff,

I know that a micron is 1/1000 of a millimeter.  However it is a commonly used term in the HVAC industry as a measure of vacuum.  Should be microns of Mercury, but nobody uses the "of Mercury" part.

RE: Rage against BTU's

(OP)
zdas, you are right about the "Therm".  I once called the gas company to get a rate quote and he gave me the price per Therm.  
"Excuse me, what's a therm?"
"Let me get back to you on that"

I think the junk units are not being created by engineers, but by marketing professionals.  The problem is there aren't enough people out there who can recognize and protest a smoke & mirrors device to blur a rate hike.

RE: Rage against BTU's

"A therm? Why, that's what your thermometer measures! Duh, sir."

Hg

RE: Rage against BTU's

I think it all gets back to laziness.  Many people say "3000 pound concrete" for "3000 psi concrete", which takes a little more effort to say.

DaveAtkins

RE: Rage against BTU's

Sute, but since mmHg is usually abbreviated to mm anyway, micron is consistent with that, aside from the fact that micrometer is the preferred term.

From a purely pragmatic perspective, it's moot, since there's hardly any physical meaning to 1 micrometer of mercury.


TTFN

RE: Rage against BTU's

No different from any other height of a column of some liquid for measurement of pressure.

RE: Rage against BTU's

A term that has popped up repeatedly in the thermo forum is "head in feet" - usually when someone is pumping something other than water and wants to know if they need to take into account the different densities.  I even had someone "correct" me when I pointed out that it was "feet of water" and was actually a pressure unit.

It's not so much that the units are invalid, it's just that people (engineers included) aren't using them correctly.

Patricia Lougheed

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RE: Rage against BTU's

3
This may be a rant, but I don't know how any self-respecting engineer could use inch-pound units.  SI is the only self-contained system that links all engineering fields.  There are no standards for use of inch-pound units.  All inch-pound units have no real meaning by themselves - they are derived from SI units, which are self-consistent and defined by actual constants (e.g. cesium atom transitions, light velocity).

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Rage against BTU's

Yeah, it's a rant and a bit rude...

Our servo designer uses inch-pound units and can probably design his way around just about any other servo designer or your choosing, in inch-pounds or meter-Newtons.  Engineering expertise and self-respect is hardly defined by the unit system one uses.

And given that there are rather precise conversions between inches and meters and between pounds and kilograms, the physicality of the units is quite irrelevant.  Moreover, with a decent math package, conversions are completely transparent.

Finally, the definitions of the meter and second are by CONVENTION only and redefined at will:

Quote:

On October 20, the meter was redefined again. The definition states that the meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. The speed of light is

c = 299,792,458 m/s

The second is determined to an uncertainty, U = 1 part in 10E14 by the Cesium clock. The General Conference made the iodine stabilized Helium-Neon laser a recommended radiation for realizing the meter at this time. The wavelength of this laser is

?HeNe = 632.99139822 nm

with an estimated relative standard uncertainty (U) of ± 2.5 x 10­11.

In all of these changes in definition, the goal was not only to improve the precision of the definition, but also to change its actual length as little as possible.
from http://www.mel.nist.gov/div821/museum/timeline.htm

Quote:

This process is repeated many times while the microwave signal in the cavity is tuned to different frequencies. Eventually, a microwave frequency is found that alters the states of most of the cesium atoms and maximizes their fluorescence. This frequency is the natural resonance frequency of the cesium atom (9,192,631,770 Hz), or the frequency used to define the second.
from http://www.boulder.nist.gov/timefreq/cesium/fountain.htm
These definitions were chosen to match the platinum meterstick standard in Paris and its incorporation into the standard definition of the speed of light.  There is no physical "meter" or "second" in nature.  We arbitrarily chose these definitions.  "9,192,631,770 Hz" is hardly a natural standard.


TTFN

RE: Rage against BTU's

IRstuff,

I agree it was rude to use the word could in my first sentence.  I think I should have used "prefer", because I truly think inch-pound units make no sense and I think most educated people like engineers would agree.  Perhaps that is a leap, but so be it.

My point was not to denigrate any person.  I can use inch-pound units as needed, and a good design that uses inch-pound units proves the talent of the designer since there are complications associated with inch-pound units.

There may be precise conversions between systems, but these are misused frequently due to lack of attention to significant digits, among other things.  I think reliance on math packages has caused a great deal of problems relating to this issue.  I think another disaster from NASA is likely due to units and software problems.

I never said the SI units were "natural", but they are self-consistent and constant within the accuracy and precision needed for nearly all applications.  The SI is being improved constantly, for example, the greater precision of atomic clocks leading to a more precise second, which will lead to more accuracy with the meter and so on.  The same cannot be said for inch-pound units.

Regards,

Cory

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RE: Rage against BTU's

The standards are essentially irrelevant, since neither I nor you (presumably) own a Cesium clock.

The meter is converted at 39.37 in/m, which is accurate to 2 ppm.  This conversion factor has changed less often than the definition of the meter itself.  

The second is the same Cesium-based second.  Inaccuracy and sloppiness is a function of the quality of the engineer.  The meter itself is already accurate to 0.01ppm, so any additional accuracy is irrelevant to almost everyone except the guys at NIST.

As for the Mars Explorer, the error was not a units problem, but a human communication problem, coupled with inattentiveness to obvious (in hindsight) navigation errors during the mission as well as lack of due diligence in design verification.

Usage of common SI unit base is no guarantee from elimination from screwup.  The Hubble was designed using a common unit base, but someone used the wrong test lens.  Focal lengths are often expressed in meters, cm, mm.  Plenty of room for confusion if you're not paying attention or doing the sanity checks that you need to do.

I don't really want to belabor the point, but the British Beagle was presumably designed using the metric system and was lost in space anyway.




TTFN

RE: Rage against BTU's

I guess I may be a purist.  If I am designing a spacecraft that will measure physical phenomena of the universe with ultra-precision, why would I use inch-pounds to design and manufacture the craft's components and SI for the software calculations onboard the craft?

I didn't mention NASA because of Mars Explorer.  I have a strong belief that NASA's (and its contractor's) use of inch-pound units will bring problems in the future.

Human error will exist with either system.  I think if the systems are examined logically and with human behavior removed, there is no reason to use inch-pound units instead of SI.

Regards,

Cory

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RE: Rage against BTU's

I agree that with all else being equal, SI is preferrable.  Nuff said about that...

I disagree with "reliance on math packages" as being the root cause of engineering problems.  As usual, lack of diligence, competence, training, etc. are the real culprits.  Problems today cannot be solved with pencil and paper or slide rule or even trusty HP-15Cs.  You HAVE TO rely on your software, but you have a fundamental duty to verify its performance.  

I place great reliance on Mathcad because I've used for over 10 years and it completely solves the unit conversion problem, which is why I have absolutely no qualms about getting a requirement document with mixed SI and English units.  The quantities and their units go in and the correct answer comes out.  In fact, version 12 will include my all-time favorite units; furlongs and fortnights, so rates can even be expressed as furlongs/fortnight.  I've been waiting since junior year in high school to have this opportunity.  Obviously, Mathcad is not nearly close to perfect, but for many tasks, it's completely unsurpassed.

As for engineers in general, a quick perusal of the postings on the site will readily prove my point.  We are graduating engineers who are incapable of reverse-engineering trivial algebra problems, let alone understand basic concepts of heat transfer.  These guys are going to screw up regardless of their unit system.  I'd worry about those guys designing critical systems that will affect my life before I'd worry about the final transition to SI in the US.


TTFN

RE: Rage against BTU's

BTW, when speaking of pressures measured in torr, it is self understood that they refer to mm Hg at 0oC.

RE: Rage against BTU's

I think it is important to distinguish between "metric" units and "SI" units. By all means correct me if I am wrong, but I don't believe that even the most metricated of countries measure their road speed in metres per second.

I find that the difficulty in conversion between the imperial and metric units is not the multiplying factor; rather it is the change of base from 12 to 10 (or 60 to 10 in hours-minutes-seconds) where one is most likely to make a mistake.  That is why I steer clear of imperial wherever possible.

BTW
(1) What on earth made the SI "they" think that using the word "kilogram" for the base unit of mass was a good idea? Anyone have a suggestion as to what word should replace it?

(2) I understand that many hydro engineers still use the unit "hectare feet" to describe reservoir volume: A non-SI metric unit multiplied by an imperial one!

M

--
Dr Michael F Platten

RE: Rage against BTU's

While there is a historical distinction between "metric" and SI, at this point in time, SI is the internationl standard for the metric system, so they are interchange in normal usage.


TTFN

RE: Rage against BTU's

Note that the BIPM site lists "centi" as a valid prefix, and they oughta know. Why does the notion persist that centimeters aren't valid SI units? Okay, hours and minutes strictly speaking aren't (although they are offically accepted for use with the SI), but centimeters?? I've seen this raised not only in one of these fora but on reference sites about the SI.

Hg

RE: Rage against BTU's

The detail that drew me to this particular thread was my misunderstanding of the subject from the title; I thought that this was a diatribe against the use of an apostrophe when forming a plural noun, as in "BTU's"

The difficulty with abbreviations is to affect some distinction between the base abbreviation and its (not it's) plural form.  I thought I'd see some advice or suggestions regarding this "problem".  Uppercase/lowercase is as clear a distinction as possible, but (of course) many abbreviations are not all uppercase letters.  I know that starting a new thread is better, but I'm trying not to take myself too seriously.

However, at the risk of taking myself too seriously, I'll also offer these comments to comments on this thread:
1) feet of head = (ft * lbf) / (lbm); specific enthalpy, in good old irrational US units.
It is not necessarily, depending upon the context, feet of water column as a designation of pressure.
2) I know that "fora" is the plural of "forum".  Does anybody use fora, aquaria, or stadia in everyday speech?  I cannot unselfconsciously bring myself to do so.

RE: Rage against BTU's

I know that "fora" is the plural of "forum".  Does anybody use fora, aquaria, or stadia in everyday speech?  I cannot unselfconsciously bring myself to do so.

I use "fora" and "stadia" but not "aquaria".  I also say "concerti" and "radii".  On the other hand I'm part of the new wave that sees "data" as a mass noun like "water" and therefore singular.

Regarding the apostrophe issue, SI doesn't endorse the use of their abbreviations as standalone nouns, so plurals wouldn't come up under that system.

Hg, language dork

RE: Rage against BTU's

IRStuff,

RE: Your delight in the furlong and the fortnight:

On another one of these forums (sorry, fora!), I found a link to a site which introduced me to a couple of wonderful units:

attoparsec (approximately = 3.1 cm)
microfortnight (= 1.2096 sec)

Both are perfectly good "human scale" units. The only thing missing is a complementary mass unit. I propose to use the yottaEarth (1E-24 times the mass of the earth, or approximately equal to 6.65 kg). Using these base units, it should be possible to derive consistent units for all the other engineering terms e.g. density in yottaEarths per cubic attoparsec, velocity in attoparsecs per microfortnight, and so on.)

Henceforth, I am going to do all of my calculations in these units.

RE: Rage against BTU's

JulianHardy,

Nice! Just to get at Cory sometimes, I use the units of Calories for torque...

Best regards,

Matthew Ian Loew


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RE: Rage against BTU's

HgTx,

I know this is OT (it wasn't me that started it!), but "Fora" realy grates on me. I would always say "Forums" and with some justification; my dictionary (Concise Oxford English) lists the plural of "forum" as "forums" except for the special case of where "forum" has its original meaning, i.e. the market place in a roman city. Other dictionaries may disagree.

M

--
Dr Michael F Platten

RE: Rage against BTU's

mloew,

Is that a calorie in the original sense or a kilocalorie?  Another example of ludicrous non-SI units.

Cheers.

Cory

RE: Rage against BTU's

Here's another US use of a metric"imperial" unit:

Ksi = 1000psi... commonly used when discussing stresses or tensile strength of materials.

Nick
I love materials science!

RE: Rage against BTU's

Actually, this form of abbreviated terminology is rampant elsewhere.  

My local station talks about "traffic; every 10 minutes."  

But, I don't want traffic, I want traffic information.


TTFN

RE: Rage against BTU's

MikeyP: I never said it was wrong to use the English plurals. "Fora" is not THE plural of "forum", but it is still A plural.

English inflections on loan words are pretty much always fine (I'm reluctant to say "always" because someone will come up with an exception). So it's wrong to say that "forums" is wrong, as some pedants would, but that doesn't mean "fora" is wrong too.

I picked up "fora" the same way I picked up "radii", "children", "indices", and "geese"--by hearing it used as an irregular plural. It's a valid linguistic process.

(On the other hand, "octopi" is just completely wrong either way, dammit. But "Kleenices" and "Vaxen" are gems.)

Hg

RE: Rage against BTU's

You're right HgTX, It's not wrong. It just grates on me for some reason.

M

--
Dr Michael F Platten

RE: Rage against BTU's

Ramblings......

Reliance on software - I did all my undergraduate work on a slide rule, and got a good feel for "how big" or where the decimal should be.  People with software don't usually develop that intuitive feel.  I notice that I've lost it lately, it takes a lot of thought.

How about working with "CHU" - Centigrade heat units, the amount of heat to raise the temperature of one pound of water by on degree Centigrade....

http://www.sizes.com/units/index.htm
has lots of units and systems, from antedeluvian times, and across the world.

I've never like the plural of computer mouse being mice.  They should be mouses.  Did you know that a Mickey is a unit of a computer mouse's movement?


Larry

RE: Rage against BTU's

" raise the temperature of one pound of water by on degree Centigrade"

There's a real bastard unit.

The metric folks already have the calorie.  Heat required to raise one gram of water one degree Centigrade.

The also have the Calorie.  Heat required to raise one kilogram of water one degree Centigrade.

Yup, the case of the first letter in the word changes the meaning by three orders of magnitude.  Who dreamed that one up?

RE: Rage against BTU's

Can someone please tell me conversion of "frig/hr" to "Kcal/hr"?

RE: Rage against BTU's

From http://www.sizes.com/units/frigorie.htm, and quoted:

"frigorie

A unit of energy?? used in refrigeration, 1 kilocalorie15. (CIPM 1950) approximately 4.1855 joules. But 1000 cal15 per hour , about 1.16264 watt."


Can't find "frig" though.

Larry

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