Boiler rated at 789 MBTUh, gas burner pulling 581 MBTUh

JohnNY

A client has a boiler with a ratings plate calling for 789 MBTUh at 2,008 sq. ft. of steam.

I clocked the gas meter at 581 MBTUh.



Now, I'm asking what affect this downfiring has on the production of steam in terms of the actual output versus the square foot rating.

Is it a simple calculation of 240 BTUs per square foot of steam? I don't think it's ever that cut and dry. (After all: 789,000 divided by 240 = 3287.5)



What I'm not going to mention is the fact that the boiler is installed in a building where my EDR calculations came up with a demand of 507 square feet.

('cause if I mention that, you'll all get sidetracked)

Steamhead

Well, it's oversized for sure

but I'd want to see the combustion test results. If they're OK and the boiler makes steam in 10 minutes or so from a cold start, I think you're OK. 

JohnNY

Right, but...

...I'm looking for a way to calculate how many square feet of steam it's producing at the reduced input.



Hi, Steamhead.

Mike Kusiak_2

Input rate vs output

First start with the BTU input of 789 MBTU. Assuming an efficiency of 80%, 789 x .8 gives you a gross output of 631 MBTU. 631000 BTU divided by 240BTU/Sq Ft =  2630 Sq Ft Gross Steam. Now if you divide by the 1.33 pickup and piping factor, you get a Net Steam rating of 1977 which is pretty close (maybe the actual efficiency is higher than the assumed 80%).



So if your actual input is 581 MBTU, the actual steam rating is 581/789 x 2008 Sq ft = 1478 Sq Ft Net. Still much larger than your EDR of 507.



Why is the actual firing rate so low, even though it looks like its working in your favor?

JohnNY

I don't know....

...but I'm guessing someone's had a go at this building's problems before.



Perhaps the installing contractor.



Thanks for the help. This is an evaluation that's not going to be received well.