Gas CFT

Way too much pseudo-precision, for one thing.

MMBTU ≠ Cubic meters/28.17385

Cubic meters/28.17385 is a volume, and MMBTU is a unit of heat.

Yes sir, i know, but don’t get why they use 28.17385 and why not 35.3147 ?

What we really have here is a fruit salad of units.

Over here you told the forum “Secondly if my GCV= 1010.92 BTU/SCF then what is in MJ/KG , how to convert it”

So you are starting with M³ of gas with calorific value in BTU/Cubic Ft, and you want a result in MJ per kilogram. Is that about the end game here?

I have just 2 questions, 1, BTU/SCF to MJ/KG

secondly 28.17385 and why not 35.3147 ?

Probably make more money that way.......I don't know.

How doe it affect you ?

Please define TLAs before using them. On the assumption of some usual meanings:

A1) The density needs to be in that calculation somewhere in order to make the dimensions match.

A2) -

Why is it impossible to ask the <...they...>?

..."The amount of energy of natural gas can be converted from Btu per cubic feet to Joules per cubic meter. If 1 Btu equals 1055.1 J and 1 ft³ equals 0.028316 m³, then 1000 Btu/ft³ multiplied by 1055.1 J and divided by 0.028316 m³ equals 37 MJ/m³, which is the average energy content of natural gas."...

https://hypertextbook.com/facts/2002/JanyTran.shtml

1 M³ = 35.3147 ft³ this is a volume measurement....

http://www.processassociates.com/process/property/hc_gas.htm

MMBTU= Cubic meters/28.17385 = CFT * GCV/1000

Should be "MMBTU=Cubic meters / 28.1735 * CFT * GCV/1000"

https://www.scribd.com/document/359617168/Gas-Bill-August-2017

yes, this is , but question is why 28.17385 and why not 35.3147 ?

Understanding a gas bill is harder than rocket science...

Their number is very close but not exactly what we get:

Here is the example:

https://www.scribd.com/document/363228647/ebill-1

Measured QTY = 13 cubic meters

GCV is Gross Caloric Value in BTUs / SCM = 1020.8 BTUs / cu ft at STP

Using their formula:

CM=13, GCV=1020.8, MMBTU = millions of BTUs

MMBTU = (CM/28.17385)*(GCV/1000)=0.471019 million BTUs

Our formula:

MMBTU = 13 meters*35.3147 cu ft/meter *1020.8 BTU/cu ft = 468640.1466 BTUs or 0.468640 million BTUs

I don't know why they are not exactly the same.

Yes, that is the problem you get me ..

Ah, I see this trouble has been discussed here before:

https://cr4.globalspec.com/thread/119474/Gas-Consumption-Calculation

The review of your three previous threads explains a lot.

But I didn’t get the answer, did you get it ?

Post deleted.

[sigh]

[unsubscribe]

Ok, now please just forget other things, my only pending question is why 28.17385 instead of 35.3147 ?

thanks sir.

Note that you multiply by 35.3147 and divide by 28.17385. The reason the two methods almost come up with the same answer is 35.3147 x 28.17385 = 990.982. That and the factor of 1000 in the formula give you 990982, close to the millions of BTUs which the answer MMBTU is given in (<1% error). (See #9)

The thermal value GCV (gross calorific value) is 1020.8 in both cases, so calorific value has no bearing.

The question should be: "why 28.17385 and not (1000/35.3147) = 28.3168, (< 1% error)".

My guess is it has to do with the temperature calibration of the gas meter (and they hid it here so you wouldn't find it.)

Haha,

some one told me it because of gas density hidden 28.17385/35.3147= 0.7977

Having looked at this, and the earlier thread, 28.17385/35.3147 = 0.798. Depending on the assumptions made about temperature and pressure correction, this is close to the gas density, kg/m³. I don't think gas density should come into it, the CV is stated on a volume basis. I think the calculation overcharges you by about 25%.

I would get all the facts lined up, and have a discussion with the supplier. If I'm right, you might even get a rebate for past overcharging. Good luck!

Please ignore my #24! I got it all wrong, I was mixing up tops and bottoms of fractions . I trust Rixter's explanation has answered your question.

Agree with your 1st sentence!

I don't follow

Our formula:

MMBTU = 13 meters*35.3147 cu ft/meter *1020.8 BTU/cu ft = 468640.1466 BTUs or 0.468640 million BTUs

Why is the 35.3147 on the top line? Using the OP's formula but putting 35.3147 in place of 28.17385 I get 0.376 MMBTU. Did I misunderstand your calculation?

Did I misunderstand your calculation?

Calculate the BTUs in 13 cubic meters of gas:

13 m³ x 35.3147 ft³/m³ x1020.8 BTU/ft³ = 468640 BTU

Units of m³ and ft³ cancel leaving BTUs.

MMBTU = millions of BTUs

CM = gas volume, 13 m³

GCV = gross caloric value, 1020.8 BTUs/ft³

The gas people divide by the mysterious constant "28.17385" with no units attached (see #19) and the answer is in millions of BTUs (MMBTU), so there has to be a divide by 1,000,000 in there somewhere.

There is a divide by 1000 and the other factor of 1000 comes from dividing by 28.17385 instead of multiplying by 35.3147. The 28.17385 should be the number of cubic meters in 1000 cubic feet, 28.3168. But the 28.17385 is off by about 1% (in their favor).

28.3168 m³ = 1000 ft³

Their formula (with units) should be:

MMBTU (BTU x 10⁶) = (CM m³ / (28.3168 m³/1000 ft³) ) * GCV (BTU/ft³)/1000

OK thanks. I was way screwed up there.

Just one more comment on this - can check their 28.17385 figure by equating the MMBTU from the 2 formulas. It comes to 1000/35.3147(ft³/m³) = 28.31682, vs their 28.17385. The difference isn't to do with correction of gas GCV for actual temperature and pressure, as that would apply to both formulas so cancels (along with m³ and GCV). Perhaps they use a slightly different figure for ft in a meter.

there are two possible heat output from burning natural gas, for instance.

One is the net value of heat after producing water in combustion, related to the hydrogen content in the fuel, abbreviated LHV, the value of the burning before accounting for the water produced is called HHV higher heat value.

Perhaps that is the difference?

see https://www.clarke-energy.com/2013/heating-value/

No. Read your Clarke Energy link again.

I find it ironic that USA suppliers sell natural gas measured as British Thermal Units, but in the U.K. natural gas is measured and charged in Therms.

Definition of therm is 100,000 btuH, gas bills in US mostly use therms since I started looking around 1985...

In the UK gas is measured in m3 and charged per kWh. I guess charge per kWh is to give a direct comparison with electricity.