Reed,

I took your class on July 17. Great Job! Your personal experiences and understanding really helps to bring boiler codes to life, making them easier to remember. I live in So. MN and was wondering if you will ever add some online classes on boiler operations. These would not have to be just for testing but for better understanding of boiler operations and maintenance.

I  am trying to figure the horsepower of our boilers. We have two Kewanee Type C 7l76 Series 4X boilers. Ther are connected to a common header. One has a  modulating burner with max input of 1,824,000 btu, the second has a two stage burner with max input of 1,820,000 btu. On the affidavid it says to divide the total btu input 3,644,000 by 67,000 for 54.39 total horse power.

In class we learned that 1 horsepower is equal to 34,478 btu. I realize I need to account for efficiency loss and if we have an efficiency of 80 percent on high fire I still have 2,915,200 btu. and using the 34,478 but/hp I have 84.55 hp, I know there would still be a loss in conduction and radiation but that should be minimal, so what is the real hp of these boilers?

Thanks for the help!

Roger

We are definitely planning online versions of our courses, so keep checking the site.

Do you know the square feet of heating surface for your boilers?

-Reed

Roger,

Sorry for the delay on this.  I've been swamped.  Using the 67,000 btu/hr = 1 Hp will work fine for your application, but if you want to calculate the heating surface you are certainly on the right track the way you are going about it.  I would use:

tube length  X  tube circumference

+

area of both tube sheets (end plates)

-

tube holes/openings

+

the area of the pressure vessel exposed to the firebox

I think this is a rough estimation of what you are describing, although you used a little bit different terminology.  The only flaw I can see is "inside tank circumference".  I think you are talking about the area of the tube sheet times the length of the pressure vessel, but I'm not sure.  Either way, the only part of the pressure vessel that would be considered heating surface would be the portion exposed to the flame, which is probably just the part on the bottom.

Now, 67,000.  I'm not sure where this number comes from exactly, but it is the number to use.  The "1 Hp = 10 square feet of heating surface" calculation has been used for more than 130 years (since 1876) as a rough estimate of boiler horsepower.  It has never been very accurate (even in the beginning) because different boilers have different efficiencies, etc.

Today, a typical boiler (as I've seen them) will have 2 or 3 times the horsepower calculated by heating surface.  The state uses this number for simplicity's sake.  This works fine because the number just has to be in the ball park relative to other boilers.  An exact calculation isn't necessary.

1 horsepower = 34,478 btu/hour  (remember to include the "/hour" - btu is energy, btu/hour and horsepower are power measurements).

I don't know why Minnesota uses 67,000 btu/hour, but I'll bet it gives an answer closer to 10 sq ft = 1 Hp than the 34,478 number does.

I would guess the square foot calculation will result in a lower horsepower number than the btu calculation, but you are free to use either since the nameplates don't list the square feet.

I hope this helps.

Regards,

Reed

great response,

i wonder how many other boiler operators are asking these great question and doing the numbers