What's the Difference Between HP and BHP?

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I gave you a GA.

I wish to add just a couple of things to the Drawbar HP statement. It is also used in agriculture for farm tractors. Along those lines there is also a HP rating for the power available at the power take off (PTO) and on the really old ones at the flat belt drive. The ratings at each point is almost always different.

Thanks for the comprehensive answer, I was wondering about ps and was planning on trying to look it up. I was going to start the search with pound seconds, silly me.

The most GAs I've ever seen, good work.

In my industry, air movement - HVAC, Hp is the rating for the motor that you will need for moving air under the operating conditions for flow (ACFM) and static pressure. The BHp is the Hp that the motor would pull if it was operated with that same flow and SP equated back to a 70F air temperature.

The difference really matters when you have a fan moving high temperature air with a given flow (ACFM or actual ft3/min) and a given static pressure (Inches W.C. for most HVAC applications).

Let's say you had a fan designed to pull air through a system and that fan, under normal conditions pulled air at 500F from an oven with a given density. When that fan is operating normally, it requires a motor with a given amount of Hp.

Now let's say that the system has cooled down to room temperature and you go to start this system up and the system is sitting at 70F. The problem with this is that fans are constant volume devices so the fan will try to pull the same volume of air. However, at 70F the air is much more dense than it would be at 500F. Therefore, in terms of volume the fan would try to move the same amount of air, but in terms of mass, it would be moving much more air - almost double.

Assuming ambient pressure and altitude:

Density at 500F .041 lb/ft3

Density at 70F .075 lb/ft3

As you can see, it's close to double the density at 70F that it is at 500F, so the fan is trying to move twice the mass, resulting in a much higher work load and Hp.

For motor rating in my industry, you select a fan and motor with a given operating Hp then if you need cold start capability you would actually size the motor based on the BHp rating, not the Hp rating. This is because the fan is set up to run at a constant speed based on the sheave ratio (belt/gear ratio), it will attempt to run at the same speed and deliver the same volume of air, but this will overload the motor and cause the motor to trip out on overload or possibly even burn up depending on other factors.

Since this results in much larger motors and excess power consumption, a cheaper solution in today's world is the use of a current limiting VFD (variable frequency drive) which will slow down the motor to pull only the amount of current programmed into the VFD and prevent overload, thus allowing air movement in the system although at a lower flow rate. As the system heats up and the density lowers, then the VFD would allow more flow, eventually getting to full speed when the density is low enough to prevent current limiting.

I'm not sure if this answers your question, but feel free to redirect me or ask me further questions if this is the direction you are looking.

By your answer and what you will see as my answer, it appears the Brake Horsepower has different meanings in different industries. In your industry it is as you have described. In the auto industry it has been described further in other posts.

I am in the pump industry. In that industry, BHP is a calculated number that is derived from the Laws of Affinity. By using the Affinity formulae, the horsepower for a particular set of pump characteristics can be ascertained. This is differentiated from the Nameplate Horsepower (the horsepower shown on the nameplate of the driving motor).

For instance, the motor nameplate may indicate that the motor is a 5 HP motor. However, the conditions of service for which the pump is being applied may be 250 GPM @ 45' TDH. By the Affinity laws, that condition would exert a BHP of 4.37 if the pump efficiency is taken to be 65% (as shown on the manufacturer's published curves). Of course, what that would indicate is that the 5 HP motor is large enough to operate the pump at the design conditions.

That is a cursory definition of BHP. There are other factors that would impact the use of the 5 HP motor in the example above, but the primary difference between BHP and HP, at least as it applies to the pump industry, is that BHP indicates the ACTUAL HP a pump would require at a particular set of conditions, while HP alone usually indicates the nameplate HP of the motor driving the pump.

Exactly the same in HVAC.

BHP describes the motor HP and Torque required for system function at the given loads. Those loads are based upon the cfm x static pressure/6356 x efficiency and the density of product air /standard air.

All of which come back to the fan - Laws of Affinity.

HP to a motor is specific power production to a normal load.

BHP to a motor is power required to perform a factored load.

If the normal HP is close to the factored (calculated requirements) HP then a standard motor will work.

People use 'brake horsepower', in reference to to a car's total power because it is the power seen at the brakes, in other words, the power that the brakes can attempt to dissipate, which is the amount of power available to accelerate the car. A manufacturer may say that their motor generates '500 horsepower', but due to mechanical losses between the crankshaft and the tyres, you may only obtain 420 brake horsepower.

Regards,

dave

thanks for the correction Ken, much appreciated.

dave

1.HP is generally reffered to as a unit measure of linear power and is equale to 745W. 2. BHP is a unit measure of TOURQE and is related to dynamometer power measurments system.

In design considerations in most of our project, HP is the input power of a motor that electrical trade should consider while the BHP is the power output of the motor that mechanical/ hydraulic trades consider since the main concern of electrical trade is the power consumption and the power are the main concern is the output.

Hope you find this in order.

If you still have question that you think I can help, don't hesitate to email me at bennegregsiman@yahoo.com or bsiman@meinhardt.com.ph

Regards,

Benn

Hi ! Regards from USAC Guatemala. "Hp" stands for the total power that a machine can generate, no matter it's a boiler, an internal combustion engine or an electric motor. Some of the energy that the machine generates gets lost in many ways (heat, vibrations, friction losses etc.) so the nominal Hp stands for this loses and for the power available to be used. "BHp" stands for the power the machines deliver to an virtual axis, wether it has one or not, so if you put a power meassuring brake to the machine's axis, BHp, will stand for the energy or power used to stop the axis from turning. In synthesis, Hp = BHp + losses. Hope this gives you a little help.

Rgds.

Nestor Antonio Gomez R.

Mech. Ind. Eng.

USAC / Guatemala

Guest,

I do not think this is right. When you indicate the rating in HP (horse-power) for an electric motor, it means the output power (mechanical power at the shaft = torque x rotational speed), so it does not include any losses (mechanical or other).

The term BHP (break-horse-power) is the power output at a certain moment. For example, you have a motor whose rating is 10 HP (the nominal ( full load, 100% load) output power is 10 HP ( 7.46 kW)) and the application needs only 8 HP (5.97 kW), the 8 HP are "labeled" as 8 BHP. That would mean that the 10 HP rated motor is loaded up at only 80%. The input power (electrical power in this situation) includes all losses, etc.

This earlier CR4 discussion covered the topic pretty well, including accurate conceptions as well as misconceptions.

1 hp = 735watt

1 bhp = 753watt

1 IHP = 735watt

There are 2 types of hp related to enjine that is

IHP and BHP

IHP is nothing but the actual power that is generated inside the enjine.

all the generated power is not delivered to the wheel some power is lost inside the enjine by friction so the power that is delivered to the wheel to move the vehicle is called bhp

IHP= bhp +(the power lost by friction)

After your third post, I suppose we might be "getting your point", if it were correct. Repeatedly posting the same information is discouraged here and in most other forums.

Your implication that the conversion factor from hp to watts changes with the measurement technique is not correct. There is not a fixed the relationship between IHP and BHP that your figures 753/735 would imply. The difference between the two (essentially the effect of internal engine friction) depends upon many engine features (piston ring tension, number of rings, bearing type, oil type and viscosity, etc.)

The standard conversion from hp to watts is 745.7 (usually rounded to 746) watts per hp.

Re

all the generated power is not delivered to the wheel some power is lost inside the enjine by friction so the power that is delivered to the wheel to move the vehicle is called bhp

To avoid confusion, this should read

All the generated power is not delivered to the flywheel. Some power is lost inside the engine by friction, so the power that is delivered from the flywheel to the transmission is called bhp.

The power delivered to the vehicle's wheels is refered to as wheel hp (or sometimes road hp) and is less than engine bhp, because of transmission and tire losses.