Author Topic: Possibly stupid question about natural gas  (Read 1590 times)

Offline a10t2

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Possibly stupid question about natural gas
« on: September 26, 2014, 06:20:38 PM »
This seems like a straightforward question but google is failing me.

Our natural gas supply line is 3/4" steel at 0.5 psi (14" WC). Looking at the code tables, that's ~200 cfh, or ~200,000 BTU/hr given a 30 foot pipe run. Only about half of what we want/need.

But all the burners and appliances specify a 6" or 7" WC. Would the 3/4" pipe be able to supply ~400 cfh at the lower pressure (give or take, assuming an ideal gas)? Could it be as simple as teeing off the line, or would we have to put in a 0.25 psi regulator, or two?

Edit: Got my stupid backward non-metric units mixed up.
« Last Edit: September 26, 2014, 06:26:17 PM by a10t2 »
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Offline kramerog

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Re: Possibly stupid question about natural gas
« Reply #1 on: September 26, 2014, 08:49:51 PM »
It sounds like you need a larger pipe, maybe 1.25", to provide the flowrate.  I don't have a flow table handy to give you accurate sizing information.

You might need a pressure regulator at the discharge end of your pipe for code/safety purposes.  Having said that most if not all consumer appliances have their own regulators so that pressure fluctuations don't affect the size of flames.  Many burners don't really care about pressure, all they care about is flow rate.    Is it possible that the specs are nominal?  Are you concerned about being up to code?

Offline kramerog

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Re: Possibly stupid question about natural gas
« Reply #2 on: September 26, 2014, 10:09:43 PM »
Engineering toolbox says that you with a 6" pressure drop you can get 406 cfh.  You have 7" available (14"-7").  You need to figure out how many and what kinds of fittings you are going to use and then factor that into the pressure drop calculations as you only have 1" water column to overcome their pressure drops. 

In comparison with a 1" pipe, you can get 446 cfh with only 1" of pressure drop. 1" pipe would be a much better choice.

http://www.engineeringtoolbox.com/natural-gas-pipe-calculator-d_1042.html

Offline a10t2

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Re: Possibly stupid question about natural gas
« Reply #3 on: September 26, 2014, 11:24:58 PM »
I'm still waiting to hear back from the utility, but I *think* we're maxed out at 3/4", since it's a 3/4" main. If that's the case we'll just have to go electric for the other appliances.

I'm pretty sure my original thinking was off, anyway. The water column given is gauge pressure, so the actual pressure drop from a 7" WC would be about 0.25/(10.5+0.5), or ~2%. Which is why the code tables neglect pressures below 2 psig.
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Offline majorvices

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Re: Possibly stupid question about natural gas
« Reply #4 on: September 27, 2014, 12:25:14 AM »
Hang on .... I'm texting my HVAC guy my password so he can answer your question. ;)

We have 1" pipe in our brewery and had to upgrade our meter at the street but I imagine the supply line is bigger than 3/4". But its best to leave it to the pros for that stuff, IMHO.

Offline a10t2

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Re: Possibly stupid question about natural gas
« Reply #5 on: September 27, 2014, 01:15:08 AM »
But its best to leave it to the pros for that stuff, IMHO.

Agreed. I definitely won't be doing any gas work myself. Just trying to educate myself so that I can communicate it to the contractor.
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Offline kramerog

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Re: Possibly stupid question about natural gas
« Reply #6 on: September 27, 2014, 04:15:32 AM »
I'm still waiting to hear back from the utility, but I *think* we're maxed out at 3/4", since it's a 3/4" main. If that's the case we'll just have to go electric for the other appliances.

I'm pretty sure my original thinking was off, anyway. The water column given is gauge pressure, so the actual pressure drop from a 7" WC would be about 0.25/(10.5+0.5), or ~2%. Which is why the code tables neglect pressures below 2 psig.

I suspect that you could get the flow you want because the pressure is quite a bit higher upsteam of the meter.  You would just need a wider pipe than what is going into the meter.  Anyway the utility should know.


Offline anthony

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Re: Possibly stupid question about natural gas
« Reply #7 on: September 28, 2014, 08:06:28 PM »
We have 2 inch pipe to our brewing area which supplies a total of 920k BTU. We had to have our meter upgraded as well.

Offline a10t2

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Re: Possibly stupid question about natural gas
« Reply #8 on: October 08, 2014, 10:16:05 PM »
This freaking process is unbelievable… The utility won't give us an estimate on running new gas and electric without plans drawn up by a licensed architect, the architect can't do the drawings without knowing which service(s) each piece of equipment will use, and I can't make an educated decision on that without knowing what it will cost to run the services. ::)

It's a good thing I don't have to worry about losing my hair over this…
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Offline majorvices

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Re: Possibly stupid question about natural gas
« Reply #9 on: October 09, 2014, 01:17:18 AM »
This freaking process is unbelievable… The utility won't give us an estimate on running new gas and electric without plans drawn up by a licensed architect, the architect can't do the drawings without knowing which service(s) each piece of equipment will use, and I can't make an educated decision on that without knowing what it will cost to run the services. ::)

It's a good thing I don't have to worry about losing my hair over this…

You need a new architect. The best thing about an architect is that they either have a relationship with the city inspectors or know what to do to circumvent inspection problems. And they need to guarantee their work qualifies for city inspection.

Offline jtoots

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Re: Possibly stupid question about natural gas
« Reply #10 on: October 09, 2014, 04:32:09 PM »
You need a new architect.

Agreed... A good architect will put all those pieces together for you, and if they need to hire external consultants they'll do so.  Coordinating all the equipment with respective specialists is part of what you hire them to do.

Offline Joe Sr.

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Re: Possibly stupid question about natural gas
« Reply #11 on: October 09, 2014, 04:50:22 PM »
This freaking process is unbelievable… The utility won't give us an estimate on running new gas and electric without plans drawn up by a licensed architect, the architect can't do the drawings without knowing which service(s) each piece of equipment will use, and I can't make an educated decision on that without knowing what it will cost to run the services. ::)

It's a good thing I don't have to worry about losing my hair over this…

IME, the utility shouldn't need drawings but they will need load calcs and/or a list of your equipment.  We typically start out with what we want and if the cost of service is too much, we back down from there.  I'm generally dealing with electric service, but I believe the same iterative process works with gas service.  What you intend to use will drive the size of the service.  On bigger buildings, that may change the entry point for the gas or water line depending on which adjacent street has the main that can provide the size of service we need.

Regardless, you should give the architect your ideal list of equipment.  He can calculate the gas service you need and/or pass that list on to the utility to do so.  The utility can tell you if what you need is available at that location.  If not, or if too expensive, alter your plans.

My final piece of advice on utilities, based on experience, is that ideally you want to stay within the parameters of the service that they already have available.  Second best is to stay within what they are REQUIRED to provide to new users.  Sometimes existing facilities don't match current requirements. 

If they need to bring new service it is #1 expensive and #2 puts you at the mercy of their scheduling.  Utilities are not known for keeping to schedule nor for staying within budget.
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