Understanding a gas meter tag...

john p_2

Had a new 50kw NG generator being installed but first the utility co. insisted on a service upgrade. The building is a two story bar, bar w/kitchen on the first floor and small apt. on the second and standby generator on the roof for a wireless carrier's equipment in a shelter.
Generator operating pressure 7 - 11 In W.C. and max flow rate at 769120 BTU/HR

Pipe run from new meter in the basement to the generator is all 2" and approximately 100' in length. Generator was being commissioned and includes a load bank test which failed about mid way through.

I am waiting for the report from the outfit conducting the load bank test (mainly to see static pressure before the meter) but am confused how this could happen when a load study was conducted, utility co. gets the load study info and decides on the meter to install.

My question is - might it be as simple as an incorrect meter has been installed? If not, since generator will run but not under full load, rather than installing a gas booster pump can the gas pipe be removed and reinstalled with 3" pipe?

Interesting that there are no regulators installed anywhere in the piping - before the meter, after the meter or at the generator. I will attach a photo of the meter and tag...the tag, if somebody could explain how to read these tags, would be very helpful, thanks in advance.

Paul48

Would the only thing running off that meter be the generator? If not, what else?

Robert O'Brien

Paul48 said:

Would the only thing running off that meter be the generator? If not, what else?

That was my question

Mike

What is final connection like at the generator? Found out the hard way. Must bring full size gas line, right to the flex line. Full size, full port gas cock. At initial start we were suckling the gas out of the meter. With only a couple of smaller nipples. No service regulater, could mean lower gas pressure, 6 1/2in, best to get the 11in.

john p_2

Hatterasguy - you said the meter is sufficient. It can deliver 1040 CFH and you have a max flow of 769 CFH from the generator BUT I have 769,120 - the generator at full load NOT 769.

Yes, the generator is the only appliance fed by that meter.

Mike - see attached pic of the gas pipe reduced from 2" - not positive of the size it is reduced to, I will get that tomorrow.

SWEI

Hatterasguy said:

It can deliver 1040 CFH

1040 CFH Nominal.

Utilities often specify meters using 3:1 or 4:1 service factors.

Zman

Your meter and pipe sizing looks appropriate.
The next step is going to be to check the gas pressures before and after the meter and at the generator. Static and under load is what you need to know.
It is always a good idea to install some extra tees for this purpose. I your case, it does not looks like you have test ports.

john p_2

That's funny I don't see test ports....

ChrisJ

john p said:

That's funny I don't see test ports....

Zman said he didn't see any either and that you should install some extra tees when doing a job for this purpose.

john p_2

Ohh, misunderstood.

Mike

Looks like 11/4 to 1in connection. I had a similar size unit, and about the same lenght of pipe run. We were to get elevated gas pressure, and the boss said to run 2in wardflex or 2 1/2 black pipe! Way oversized! Ran the black pipe, reduced to 11/4 about 5ft from the unit for gas regulater. By the way, we got 1 pound out of the meter. Set the regulater for 11in, started the generator, pressure dropped to 1in,unit locks out on low pressure. Get a larger capacity regulater, get the unit running, but not at full load. We get the factory start up tech, we had paid for it. He said move the regulater back 10 ft, and bring the 2 1/2 all the way to the flex hose. It ran like a champ. Engine started on first crank. Tech said it needs more gas to start, then to run. The additional 2 1/2 was more like a storage tank. Said if it doesn't start on first or second crank it's usually starving for fuel. We'very since, run full size pipe right to the flexible line, and not had any problems.

Mike

Forgot to mention, Zman is right. You got to have pressure ports!

john p_2

I'm being told this section of Brooklyn has low pressure gas. What I find hard to believe is ....before starting the job the utility made us upgrade the service....would like to know exactly what we got for upgrading the service! Curious why there are zero test ports between street & meter. Important to know generator started no issue....when load bank got to 19kw it failed the load bank test.

Tim McElwain

Mike is correct you need to have plenty of gas avialble when the generator first fires up I usually increase the manifold size right at the unit to one pipe size larger than the supply pipe to the unit. The problem becomes a pressure problem only because there is not enough volume to handle the initial surge.

Harvey Ramer

Kind of repeating what others said.
The equivalent length of the smaller diameter piping at the generator is probably close to 5'. Entirely to much pressure drop. The flex line should come out of the connection port on the genset directly into the branch port of (in your case) a 2"X 2" (by flex line size) tee. The run of the tee should be vertical with a drip leg out the bottom. Out of the top, going up, you should have a 2" union and then a 2" gas valve with a test port. From there back to the meter.

Unlike heat load calcs, gas line sizing charts don't afford any wiggle room. All depends what kind of appliance you are dealing with, it pays to err on the side of caution.

Paul48

They witnessed a gas pressure problem, or are assuming it?

Harvey Ramer

If they didn't, they are lucky.

john p_2

Paul48 - I don't understand what you are asking....who witnessed what?

john p_2

A load bank test was performed that failed when the generator output hit about 19kw.....it started and ran up until that.

Paul48

I'm asking if they saw the gas pressure drop off at the generator.

john p_2

Yes, I belive they saw it drop to 7^ WC

Paul48

And the operating pressure for the generator is 7-11 in W.C.

john p_2

Yes

john p_2

I will attach below an email I received about the load bank test from the outfit that did the load bank test - this may help.

The gas line on this building is a very low pressure line. My technician is only getting 7inches WC when 32kW is applied to the generator. If he adds any additional kW on the gen, the gas pressure drops below 7in which is not recommended per generator manufacturer. He cannot continue the load bank with such low gas pressure, as it will cause damage to the generator.



Right now, the unit can support the current building load which is 19kW, however…. The air conditioner units are NOT on. Once the summer hits and the A/C units are on, the kW will be much higher. If the kW is higher than 32kW this generator will not run due to such low gas pressure coming in off the street. The solution would be to install a booster pump.



At this point, my technician cannot finish the load bank as the unit can’t handle a full 50kW via the load bank. Please let me know how you wish to proceed.



Thank you,

Paul48

OK......It went below the operating range.

john p_2

I'm confused & frustrated with the utility...no test ports between meter and street so I do not know the pressure coming into the building. Also, they (utility) required a service upgrade be done prior to the generator being installed but I still have a generator installed that can't pass a load bank test.

Paul48

Have you contacted the utility?

Zman

I agree with the guys that are saying that the flex line is creating a restriction.
It is also very likely that the pressure from the gas company is either low now or may drop in the future and create a problem.
You should absolutely have a tee installed so that you can properly troubleshoot this problem and future problems.

Mike

The flex line comes with unit. Should be on the horizontal run out of the unit.

jimmac

John,when you submit your load letter/calc to the utility did you specify that you needed elevated pressure?Your load letter that you sent in to NATGrid would ask you total load.But it is up to you to tell them you need an elevated pressure.They will upgrade the service diameter of the new main,but does not mean it goes High Pressure. Standard pressure is no more than a 1/4 lb. and they do not guarentee any more than that. All the roof top gens ,that I have installed required HP or elevated pressure.And after "SANDY" it has been a few.So in other words your existing gas pressure will always drop below 7" on a standard Low Pressure service.

john p_2

Don't /can't get to deep into it but I didn't submit it , that's not my responsibility. But thanks for the info, I was not aware that the elevated pressure requirement needed to be mentioned. Generac does offer a low pressure gen but this isn't one at this location. Still not getting answer to my question....they required a service upgrade but I'm still not sure what that entails....new piping w/o access ports!?!? Lol

jimmac

The meter may have "pete plugs" little brass valve for pressure readings (quite a few of the AL1000 have it ) behind it on the top portion of it.The meter was supposed to be plumbed in with purge tees by the contractor ,not the utility.IN NYC both utilities responsibility as far as piping concerns ends at the head of service valve.Everything else is on you the contractor. The service upgrade is a new gas main (service) brought into the building. This will increase the diameter of the pipe or the available capacity into the property.Was this done or your unsure of it.?

RLuck

It sounds like you only specified a load not a delivery pressure. Depending on the utility you might only be guaranteed 5-7 "wc. Sounds like you are tied into a "utilization pressure system" so the can't give you the 11" required at this time. A communication error sounds like it was made.

RJ_4

Heat content in a cubic foot of gas. 950 to 1050 btus. per cubic ft depending on ?

john p_2

RJ....What??!!

RJ_4

Natural gas has a heat content of 1010 btus per cubic ft at sea level. In Denver it is 840 and in elevations above 8000 ft. can be as low as 740 btus/cubic ft. That's why you should make sure the gas meter to the bldg. your working on has the right size meter. Some times additional heating equip is added to bldgs. without upgrading the meter.

EBEBRATT-Ed

Don't know what the procedures are in your area but this is a utility engineering issue. If they (the utility) were given the proper information concerning the generator's specifications then it is up to them to say yes or no.

In Massachusetts you have to submit specifications to the gas utility before installing. They then provide you a "letter of availability" that they can provide gas at a certain cfh and pressure.

You won't be happy with the cost of a gas booster. Very pricy

Mark Eatherton

RJ said:

Natural gas has a heat content of 1010 btus per cubic ft at sea level. In Denver it is 840 and in elevations above 8000 ft. can be as low as 740 btus/cubic ft. That's why you should make sure the gas meter to the bldg. your working on has the right size meter. Some times additional heating equip is added to bldgs. without upgrading the meter.

Don't let our flaky BTU content throw you. It is artificially low. It's good to know and understand altitudinal deration requirements, and knowing the caloric content of the gas is critical to getting the equipment optimized, but the low BTU content is Denver is actually 1,050 gas that has been intentionally diluted to the 830 level. The local utility does this so that if someone drags an appliance to Denver from Sea level, it is automatically derated and will lessen the chances of generating excess CO. There are many places in the mountains, one called The Ranch, which is west of Vail Colorado that has full caloric content gas at 1,050. This gas comes from the western slope and is not diluted.

Manufacturers do not understand our derated gas. Only well practiced contractors do. They all assume we have hot (1050) gas at hand and assume the normal values of deration. If one does that, their appliance will be undersized by about 20%.

Proceed with caution...

ME

ChrisJ

Mark Eatherton said:

RJ said:

Natural gas has a heat content of 1010 btus per cubic ft at sea level. In Denver it is 840 and in elevations above 8000 ft. can be as low as 740 btus/cubic ft. That's why you should make sure the gas meter to the bldg. your working on has the right size meter. Some times additional heating equip is added to bldgs. without upgrading the meter.

Don't let our flaky BTU content throw you. It is artificially low. It's good to know and understand altitudinal deration requirements, and knowing the caloric content of the gas is critical to getting the equipment optimized, but the low BTU content is Denver is actually 1,050 gas that has been intentionally diluted to the 830 level. The local utility does this so that if someone drags an appliance to Denver from Sea level, it is automatically derated and will lessen the chances of generating excess CO. There are many places in the mountains, one called The Ranch, which is west of Vail Colorado that has full caloric content gas at 1,050. This gas comes from the western slope and is not diluted.

Manufacturers do not understand our derated gas. Only well practiced contractors do. They all assume we have hot (1050) gas at hand and assume the normal values of deration. If one does that, their appliance will be undersized by about 20%.

Proceed with caution...

ME

I don't blame them.
Not only is it a bad rule as all appliances need to be setup properly for their location, but apparently the rule is flaky too. Some places have it derated, but others don't. I can't see that ever causing confusion or a problem.

RJ_4

Good article to read is Altitude Effects Sizing Natural Gas Piping by David R Olson www.imshvac.com.

Mark Eatherton

Funny, I know Dave Olson. He now works for Peter C DeAngelis of PCD Engineering in Louisville CO. Great guy and very knowledgeable.

ME