HP versus Brake Horsepower 3

[Lead Engineer]

I seem to be the only one in my company that believes that BHP is the power available to the system before losses due to appurtenances, e.g. a belt drive for a fan. For simplicity sake,(I may not be using an accurate analogy) I suggest that the BHP is the NEMA or nominal horsepower. For example, Greenheck on their cut sheets for fans shows the "Operating Power" then below in the section that tells you the motor size 10 hp or 5 hp . . .
I talked to an EE friend of mine and he told me that he checked a couple of other sources and he was not sure that he agreed with me.
These are a couple of websites that I used in my discussion;

http://www.wisegeek.org/what-is-brake-horsepower.htm

http://www.differencebetween.net/tehcnology/difference-between-hp-and-bhp/

Seems pretty clear to me.
The term BHP comes from the early days of measurement where they actually would apply a brake to the output shaft and calculate HP from the force on the brake.
I could always not be accurate, or the other case is that the term depends on context of usage . . .

 

[IRstuff]

Maybe you should post an example

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Lead Engineer]

IRstuff, that is a good idea, see attached screen shot as an example.

 

[georgeverghese]

Process engineers use the term Absorbed Power to indicate the power absorbed by a fluid (a liquid in a pump or gas in a compressor or the air induced through a fan) as opposed to Driver Rated Power (or driver ISO power in the case of a gas turbine or gas engine).

 

[Lead Engineer]

Thank you all for all of your suggestions on how to explain my situation to other engineers in the company. I will take what has been posted and think about how to have that discussion.

 

[Compositepro]

Lead Engineer, the screen shot you provided contains some words and numbers taken out of context. I, as an experienced engineer, can't even provide a decent guess as to what the numbers mean. It is possible that some engineer who is familiar with the catalog might give some insight, but those terms and numbers mean nothing out of context and it is pointless to argue about it with anyone. Those terms musts be defined somewhere in the catalog. Realize that catalogs are often put together by non-technical people. You need to know enough to know when you do not have enough information.

 

[Lead Engineer]

Now you are getting it, you can see the problem I am dealing with. The people that I am speaking with are not experts in this area, one is from power plant support engineering, the other is a "rain-maker" for a company.

 

[LittleInch]

Lead Engineer - yr post of 6 Mar 21:25 I think got it just about right.

As said before forget the Brake bit and just think about where it is and what it is.

So in your thinking HP would be motor rated shaft power in hp or kW
and BHP would be fan or equipment required or absorbed shaft power or maybe inlet shaft power.

however I'm with composite pro - that little snippet you sent makes no sense.
The 263 (BHP) I would have taken as motor rated shaft output power, but what 300/36 is I have no idea. I thought for a moment it was electrical power and amps, but I was way off.

Incidentally you do need about 250A for a motor of this size and voltage so you're going to have cables the size of your arm going into it....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MintJulep]

This should contain your answer
AMCA Publication 211-13 Certified Ratings Program - Product Rating Manual for Fan Air Performance

This may be simpler.
Greenheck Fan Fundamentals

 

[enginesrus]

The term Brake goes back to the prony brake that was used to measure rotating shaft torque.
That torque is converted to HP which is a time based measurement, that really has little to do with horses, and was based on an arbitrary figure that was standardized.

 

[LittleInch]

engines rUs.

On the contrary, the term horsepower was originally derived by James Watt in order to properly compare his steam driven engines for removing water from a mine and that of horses.

I know wiki sometimes isn't super accurate, but there are a lot of references here.

https://en.wikipedia.org/wiki/Horsepower

Now they might well have come up with a standardized "horse", but it was actually based on a long term power of a horse or set of horses doing work which could be measured (lifting water a set distance in a set time).

As it says peak power of a horse could be up to 10+ hp, but over a long period of time it settles out at around 1hp as we know it today ( 746 W)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[enginesrus]

Maybe so but the number is still an arbitrary number that was decided on.

 

[RodRico]

Like others, I read "brake" to mean "as measured on a brake dynometer." This differentiates it from calculations of power output which are less certain even when incorporating the best available modeling software. That being said, there's no assurance whether the full compliment of accessories and heat transfer systems is in place during the measurement, so I prefer "at the rear wheel," a figure few marketing folks would approve for publication.

 

[Tmoose]

Over the last several years snowblower manufacturers seem to have abandoned mentioning the HP of their machines, choosing instead to list engine displacement in ccs or (gross) torque per J1940. Displacement in ccs will be 130 to over 400. Since the torque is measured at somewhere between 3000 and 3600 rpm, the governed rpm of most lawn and garden equipment, it is 5252/3600 or numerically about 50% larger than the HP. Additionally "torque" has become a buzzword when talking (bragging??) about cars, trucks and motorcycles.

Since the power is usually so nicely matched to the machine, the user is satisfied, so as a practical matter, whether 4, 6 or 8 HP is available does not matter very much. Like legend says Rolls Royce rated their cars' power as "sufficient." I imagine Marketing is also made happy, since a Larger number of something per dollar can only help make the initial sale.

 

[drawoh]

Tmoose,

An old co-worker of mine was boasting about his new Camaro[ ]Z28. He told me that he never ran the engine over 3000RPM, and I suggested he trade the vehicle in for a mini-van. He assured me that it is torque that makes you accelerate.

Good Newtonian physics. No comprehension of what a transmission does.

--
JHG

 

[CWB1]

Power is largely overrated anymore. Marketing and emissions requirements for both outdoor power equipment and vehicles have combined to give us what we have today - great big power numbers at rarely used engine speeds and disappointing amounts of torque in the useful range.

 

[RodRico]

drawoh,

They're related via HP = Torque * RPM/5252 (or Torque = HP * 5252/RPM) and largely equivalent given the proper transmission.

Remember the wheels on an auto, propellers, etc. are typically only turning a couple thousand RPM at most, let's say 2,000 for now. An engine that's turning at 8,000 RPM with 100 lb-ft torque is producing 152 HP and will use a 4:1 gear ratio yielding 400 lb-ft torque at 2,000 RPM. In contrast, an engine running at 4,000 RPM with 200 lb-ft of is also producing 152 HP but will use a 2:1 ratio. The real difference is more subtle.

Friction losses in an engine increase with RPM, and it becomes very difficult to maintain volumetric efficiency (thus yielding a less than flat torque curve). The differences impacting efficiency explain why the world's most efficient piston engines tend to be slow turning marine engines like the Warsilla 31 (

https://www.wartsila.com/twentyfour7/energy/wartsila-31-the-most-efficient-engine-in-the-world).

Furthermore, though a race driver or a well programmed nine-speed automatic transmission with tight ratios and lock-up capability can keep a high RPM engine with peaky torque at the right RPM, the average driver of a manual transmission typically finds the process difficult and inconvenient in comparison to driving a slower speed engine with a lot of torque.

Rod

 

[Tmoose]

I think "torQuE" is a little more accurately "low end POWER."

 

[drawoh]

CWB1,

People in North America (older people anyway) are used to the old Detroit iron, slow revving, high displacement V8s. This makes it difficult for them to drive the newer, smaller engines that develop power at higher speeds. My understanding is that Europeans rev their engines much more than Americans do.

--
JHG

 

[drawoh]

RodRico,

My little anecdote is funny only if you understand torque, rotation speed and power. Everybody here seems to. I hate explaining jokes.

What we are discussing here is official terminology. Some standard, somewhere, defines the term BHP. It is likely that another standard, somewhere else, also defines the term BHP. It is very likely that the two definitions are not identical, even if the second B stands for "Brake", and not perhaps for "Bob".

--
JHG

 

[LittleInch]

drawoh,

It probably has more to do with the fact that the majority of cars in Europe are or until very recently were, manual drive and how much you revved before changing gear is up to you, not some sort of dumb automatic 3 speed box.

Cost of fuel and tax made smaller engines much more used and in many you had to know how to use the full rev range in order to get the bloody things to go....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.