Wrong gas meter?

Nick W

I am beginning to suspect my local gas utility -- Xcel Energy -- put a 2.5-psi meter on my 0.25-psi system almost 11 years ago. Has anyone ever heard of such an error?



My recently replaced boiler was burning 19% more gas than it should, based on the orifices that the manufacturer's tag says were installed 45 years ago. I had always assumed the unlabeled orifices had been changed or drilled.



My old boiler burned 19% more gas than my neighbor's identical boiler. I had always assumed it had been derated for the 5,570-foot altitude by the installer.



My new boiler is burning 19% more gas than indicated by the clearly labeled orifices. It has 6 #49 orifices and burns 93 cu ft/hr according to the meter. Manifold pressure is 3.5 in. wc. Pressure into the gas valve is 6.25 in. wc.



Big refund maybe?

Nick W

Xcel Energy says

they will come out and check the meter within a week or two. Such prompt service!



Someone at Xcel once told me they have no program for scheduled maintenance or replacement of gas meters. Some meters in my neighborhood appear not to have been touched in 50 years or more. A neighbor's meter had so many cracks in the bellows that it would move only intermittently when a 40,000 Btu water heater was on. Lucky them! Is this they way most other gas utilities operate?

Unknown

the way most other gas utilities operate?

NOT mine,,, yes there is "scheduled maintenance" in my area. Usually they change the meters every 10 yrs or so,, and if you complain to them they`ll do-it sooner.

Do you have an outside meter?,,, perhaps it is slightly leaking on the outlet side,,, of which you`re paying for.  

Slimpickins

it's not the meter

I don't believe there is a separate meter for both pressures, it's the regulator before that meter determines your pressure. If you do have a 2.5 psi system you'd have individual regulators at each appliance dropping it down to 6-7 w.c.. I don't see how this would cause you to use more gas than the neighbors. Before having Xcel come out I'd have a HVAC service company come out to do a combustion analyst. With 3.5 w.c. manifold pressure, it may be running a little rich at 5500' 

Unknown

it's not the meter

How would you know??

Do some soap testing yourself, and see where things may be going on your side.



Some people don`t know much. :-)

Slimpickins

I know plenty

But don't know it all. I didn't say the meter wasn't possibly leaking gas and besides, real professionals don't use soap bubbles, we carry electronic gas sniffers. 

bob_46

Firing rate

Nick, at 5500 ' nat gas has 832 btu/cu.ft. you are burning 93 cu.ft. per hour so your input is 77,376 btu/hr what is the input rating on the mfg. plate?



The amount of gas needed to heat a house is a function of the heat loss and the efficiency

of the boiler.

Nick W

Bob

You are very close. The gas here had an average Wobbe index of 1,250 at standard conditions last year. The gas quality engineer at Xcel told me this is close to their high limit. The HHV works out to be 815 Btus/cu ft at my altitude; the Wobbe index at this altitude would be 1018. The PUC allows the Wobbe to vary by +/- 4%. Apparently the Wobbe is higher during cold weather because Xcel lacks adequate capacity to add enough air to the gas during periods of high demand.



My question is this: How much Wobbe 1250 gas should a #49 orifice pass at 5,570 feet? My understanding is it should pass 13 cu ft/hr; so six of them should pass 78 cu ft/hr. If this is correct, my meter is reporting 19% too much. The standard orifices for this boiler are #47's. The 49's are specified for altitudes of 4,000 ft to 6,000 ft and gas with a more typical HHV than we have here.



The boiler's input rating is 105,000.

Tim McElwain

Nick these are some figures for you

to look at. Let me try and calculate for you at 1250 BTU's and I will post it.



Let me do some calculations. I combined the info you posted on the Wall along with what you sent me by e-mail.

 

I do have some questions however:

 

1. What does the rating plate on the boiler say is the correct input?

2. I take it you have six burners with a #49 orifice is that correct?

3. Is the meter a temperature compensated meter and is it indoors or outdoors?

4. What other equipment do you have burning gas?

5. Do you know how to clock a meter?

6. Meters usually run slow rather than fast do you think yours is running fast?

7. What is the make and number of the meter and how much gas will it pass?

 

At sea level with gas at .6 Specific gravity and 3.5" W.C. and a BTU content of 1050 BTU's per cubic foot a 49 drill size should give 16,500 BTU's per orifice times 6 burners = 99,000 BTU's what your boiler would be burning at sea level.

 

At between 5,000 to 6,000 feet with Specific gravity of .6 and 3.5" W.C. and a BTU content of 850 BTU's  a 49 drill size should give 13,000 times 6 burners = 78,000 BTU's.

 

Now if the boiler came with a 49 Drill size based on my charts it should have been changed to a #51 Drill size which at 850 BTU's and specific gravity of .6 and 3.5" W.C. would be 11,000 BTU's per orifice times 6 burners = 66,000 BTU's

 

Hope this helps.

 

Tim McElwain

Nick at

1,250 BTU's per cubic foot with a 49 drill size at 3.5" W.C. specific gravity of .6 it would be 19,600 per orifice times 6 burners = 117,600



Now let me ask you a question is the boiler heating the house adequately? Has a heat loss been done recently on the house?

Nick W

The gas here has only 815 Btus/cu ft at this altitude.

Surprise! Xcel installed a new meter yesterday. It reads 4.5% less than the old one. I now realize Xcel's engineer mislead me about calculating the local Wobbe index. I have now been able to reconcile measured output, calculated input and input per the meter.



The new boiler will heat the house, but my wife will go ballistic in the middle of January and February when it won't make enough hot water for her long showers. The boiler is putting out 59,000 Btuh. This is only 56% of its rated input of 105,000 Btuh.



The heating load at -5° F is 41,000 Btuh. Design temperature according to the city's website is +1° F. I did this heat-load calculation with Wrightsoft and blower door data.



Our incoming water temperature this winter ran right at 40° F at its lowest.