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Discuss Pressure loss on gas pipe (BS 6891 pipe sizing) in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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Hi,
I'm doing my ACS and have an issue with pressure loss calculations!!
sample question : "what would the pressure loss per meter be on copper tube of 15mm feeding a 12kw (gross) gas hotplate"
I can't for the life of me get the correct answer.....
I nett the hotplate 10.81kw divide that by 9.7 to get 1.11M3/h I then use the pipe length table which shows 15mm 1.3M3/h is maximum length of 12meters.
That means (i think) in 12meters of 15mm copper the loss is 1mb, so if i divide 1 by 12 it gives me 0.0833mb drop per meter ??
but the answer is 0.1042mb

I look forward to your help.....
 
Hold on. You say you have given the answer at the end??? I haven’t checked it though. So it could be wrong. You having us on here?
 
12 kw gross

10.90 kw net

15mm at 10 m with 1 mbar drop 1.1 m3/h

1.1 divided by 10 = 0.11 mbar drop
 
Hi,
I'm doing my ACS and have an issue with pressure loss calculations!!
sample question : "what would the pressure loss per meter be on copper tube of 15mm feeding a 12kw (gross) gas hotplate"
I can't for the life of me get the correct answer...
I nett the hotplate 10.81kw divide that by 9.7 to get 1.11M3/h I then use the pipe length table which shows 15mm 1.3M3/h is maximum length of 12meters.
That means (i think) in 12meters of 15mm copper the loss is 1mb, so if i divide 1 by 12 it gives me 0.0833mb drop per meter ??
but the answer is 0.1042mb

I look forward to your help...

you need to divide 1.3 by 12 not 1 = 0.1083 m bar
 
where does the 1.3 come from?

1.3 m3/h at a max length of 12m

So you have 12 m of copper and at the end of it you can pass / pull off 1.3m3/h with your 1 mbar pressure loss

Eg the capacity of the pipe at 12m
 
1.3 m3/h at a max length of 12m

So you have 12 m of copper and at the end of it you can pass / pull off 1.3m3/h with your 1 mbar pressure loss

Eg the capacity of the pipe at 12m
I thought the maximum lengths on the table were equivalent to 1mb drop?
 
I thought the maximum lengths on the table were equivalent to 1mb drop?

this will confuse you now :D

To estimate pressure loss across a pipe leg

(mbar) = (328785 ÷ dia + 7558) x m3/h x m3/h ÷ dia ÷ dia ÷ dia ÷ dia ÷ dia x Length

so

328785 divided by the dia of the pipe (15mm) plus 7558 = 29477

29477 x 1.3 x 1.3 = 49816.13

49816.13 divided by the dia of the tube 5 times then times by the length

49816.13 ÷ dia ÷ dia ÷ dia ÷ dia ÷ dia x 1 = 0.065 mbar per m of 15mm
 

Attachments

  • PipeSizingComm.pdf
    188.9 KB · Views: 21
this one might be better
 

Attachments

  • Domestic Gas Planning And Sizing.pdf
    86.1 KB · Views: 985
Has the site changed shaun? Been having trouble opening attachments like this.

No computer normally opens them fine phones can be a bit hit and miss
 
if i do the question on my Anton app it comes out at 0.1042
exactly as the question states!! I'm glad its not just me but won't help me for the exam :(
 
It’s all aprox especially when your working by the m
 
Go back to your tutor and ask them to do a lesson on it
 
i get that BUT the answers are 0.1414 0.2296 0.1042 0.0719 so you could choose at least 2 of those answers and maybe even 3 and be aprox (as you say) and fail :( its annoying

Hmm. I'd convert 12kW gross flow by dividing by 10.76, giving 1.12 m^3/hr, which everybody seems to be happy with. According to Table 1, here:

https://copperplumbing.org.uk/sites...achments/domestic-gas-planning-and-sizing.pdf

1.1 m^3 / hr gives a pressure drop of 1 mbar along 15m of 15mm/0.7mm tube, i.e. a drop of 0.067 mbar/m, which is very close to SaunCorbs's value in post #9.

However, if one uses the more sophisticated formula and calculator here:

Natural Gas - Pipe Sizing Calculator

with 13.6mm (id) for the pipe, 1.063 mmH2O (0.1042 mbar) for the pressure drop, and 1m for the pipe length, and 0.6 for the specific gravity of the gas you get a flow rate of 1.13 m^3 / hr, which is close enough to make me think that it is this formula that has been used to set the test and calculate the model answer.
 
Last edited:
Just to update you (if interested). I hadn't been on my gas course since doing the preliminary exams over 2 years ago (due to personal reasons) as I have now got my head back into the books to get this done as soon as i can, it seems a few things have changed. There are now new pipe sizing tables in the updated NIC/EIC books, which I have just purchased....... So in simple terms the question answer is.....
12kw gross = 1.11M3h go to table 5.5 using flow rate 1.25M3h shows 0.1042mb/m drop........
seems i was over thinking it!
Thanks for everyone that helped.
 
I personally use these to do pipesizing calcs.
 

Attachments

  • Pipe Sizing Chart 1 (2 files merged).pdf
    237.3 KB · Views: 173

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