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Diversity factor for gas pipe sizing

I have neer seen any charts where there is a diversity factor for gas pipe sizing.  Any resources for this?   I have alot of gas piping to size that feed many smaller loads that are unlikely to all be running at once, so just totally up the load if everything is running doesn't make sense.
The Steam Whisperer (Formerly Boilerpro)

Chicago's Steam Heating Expert





Noisy Radiators are a Cry for Help

Comments

  • furnacefigher15
    furnacefigher15 Member Posts: 514
    edited January 2012
    It may not make sense

    To run it all at once, but there are times that it will. Gas pipe sizing is critical, and it ought not be undercut to shave a few bucks on the job.



    When labor is added in to a job, the difference between 20 feet of 1 inch and 20 feet of 2 inch is very minimal.



    What kind of loads are you speaking of?
  • lchmb
    lchmb Member Posts: 2,997
    on top of

    I would much rather have to large a pipe than to small. I not only add the total load of the building I add 25% to it to make room for future expansion. They alway's say "this will be all". Til next year when they want to add a bunch of appliances....
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    Diversity refers to

    different loads which typically do not fire at the same time such as a pool heater for summer use to heat the pool and the boiler or furnace for winter heating. If there is the possibility of even those two running at the same time (indoor pool) then it is not a diversity factor. This can sometimes be different on commercial applications, I would have to know what the actual application is that you are referring to? This can get tricky sometimes as people change the way they do things and then we have problems.



    Years ago when we had a lot of gas AC and separate gas heating these could be diversified loads.
  • Diversity

    The particular application I am looking at is a building full of gas stove/ovens and possibly dryers.  It is extremely unlikely that all of this equipment would be firing at the same time.   If the gas supplier had to size the gas mains in a city for all the connected equipment to be firing at the same time I suspect the mains would be several  times larger.   Diversity factors are used to size electrical circuits, power lines, water lines, sewer lines, sewerage treatment plants, etc.   To size only to the max load, would mean, as an example, that every single electrical outlet in a home would need its own 20A circuit.  Diversity factors allow 16 outlets on a single ciruit as good design practice.  I just have never seen any information on these factors for gas.
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert





    Noisy Radiators are a Cry for Help
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    What about the possibility

    on a given Saturday AM with everyone cooking, taking showers , heat calling and drying the clothes that you threw into the washing machine Friday night. That is my take on this however Ted Lemoff P.E. in the Handbook for NFPA 54 National Fuel Gas Code does not agree with my take on this. I will post his comments in a separate posting.



    The truth is National Grid will only now days on low pressure gas guarantee you 5" W.C. pressure to the equipment, it used to be 7 to 10 " W.C.



    It is not a factor on high pressure areas as they deliver 50 to 100 pounds pressure and that can handle just about any load a neighborhood should offer.



    Are these systems on single meters to each unit? If so then the sizing is only related to each unit and you do not have to worry about diversity as the utility has to size the feed to handle the full load.



    If I were you I would sit down with the engineering division of your local utility and get their protocol on your question.To the best of my knowledge their is no diversity charts or tables only pipe sizing tables in the code book.
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    From the Code Book

    Under NFPA 54/ANSI Z223.1 National Fuel Gas Code Section 5.4.2 Maximum Gas Demand the following taken from the Handbook on the code by Theodore C. Lemoff P.E.

     

     

    5.4.2.2 The total connected hourly load shall be used as the basis for piping sizing, assuming all appliances are operating at full capacity simultaneously. 



     

     

    Exception: Sizing shall be permitted to be based upon established load diversity factors.

     

     



    Diversity of load, addressed in the exception to 5.4.2.2, is the reduction of load per unit in piping serving multiple units. Diversity of load is important in buildings such as apartment buildings, where many apartments are served by common supply piping and there are many gas ranges, water heaters, and furnaces or boilers on a single gas supply system. The reduction of pipe sizing of the supply system where a diversity of load exists assumes that appliances will not operate simultaneously. It is reasonable to assume that all occupants will not take showers at the same time, that they all will not operate cooking appliances at the same time, and that all furnaces will not operate simultaneously because of the cyclical nature of their operation. Gas suppliers may provide load diversity factors applicable to their service areas.

     



     

    5.4.3* Sizing Methods



     

    Gas piping shall be sized in accordance with one of the following:

     



    (1) Pipe sizing tables or sizing equations in Chapter 6

    (2) Other approved engineering methods acceptable to the authority having jurisdiction

    (3) Sizing tables included in a listed piping system manufacturer's installation instructions



     

    A.5.4.3 Gas Piping Size. The gas-carrying capacities for different sizes and lengths of iron pipe, or equivalent rigid pipe, and semi rigid tubing are shown in the capacity tables in Chapter 6.



     

     

    Table 6.2(a) through Table 6.2(t) indicate approximate capacities for single runs of piping. If the specific gravity of the gas is other than 0.60, correction factors should be applied. Correction factors for use with these tables are given in Table C.3.4.



     

     

    For any gas piping system, for special appliances, or for conditions other than those covered by the capacity tables in Chapter 6, such as longer runs, greater gas demands, or greater pressure drops, the size of each gas piping system should be determined by the pipe sizing equations in Section 6.4 or by standard engineering methods acceptable to the authority having jurisdiction.



     

     

    A suggested procedure for using the Chapter 6 tables to size a gas piping system is illustrated in Annex C.

     
  • metering

    We are removing the individual meters and placing all the load on the single building meter.  From what I've seen even the gas company piping feeds to the meters are sized with diversity factors, because when you add up all the loads, there is no way the gas companies mains within the building could handle the loads.
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert





    Noisy Radiators are a Cry for Help
  • don_9
    don_9 Member Posts: 395
    High pressure

    Why not just pipe in a high pressure loop around the building and come off the loop to where the meter are now and install a regulator.Take advantage of the piping thats already there.

    Off topic.Went to a home that had a gas-pac that was rusted so bad i sold them a new one.Installed the new one had 7 inch of pressure coming in.With all other appliance running it would drop down to 2 inch would run with a high 02 and low stack temps.IT had a two pound distribution system thru out the home with a low pressure reg and meter from the gas company.

    What puzzle me was the home was six years old and the guy claims he never had a issue...other then very high gas bills in the winter.It had three furnaces a,gas water heater and two gas fire places,along with a gas dryer.All pipe in from a manifold to each appliance with 3/8 copper and 2lb regs.From the meter to the manifold was fed with 1/2 copper.
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Copper?

    Sounds like propane piping
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Diversity

    "Diversity

    The particular application I am looking at is a building full of gas stove/ovens and possibly dryers. It is extremely unlikely that all of this equipment would be firing at the same time. If the gas supplier had to size the gas mains in a city for all the connected equipment to be firing at the same time I suspect the mains would be several times larger. Diversity factors are used to size electrical circuits, power lines, water lines, sewer lines, sewerage treatment plants, etc. To size only to the max load, would mean, as an example, that every single electrical outlet in a home would need its own 20A circuit. Diversity factors allow 16 outlets on a single ciruit as good design practice. I just have never seen any information on these factors for gas."





    When a gas service is undersized, there is nothing to prevent equipment from being turned on during a low gas situation (exception certain burners with low pressure safeties)



    I also have never heard of a building owner wanting to reclaim gas meters from tenants, usually they want to get rid of the gas bills and give them to the tenants.



    If I were asked to do the job you are quoting, I would size to have it all on at once, because there will be times that it is, and if it doesn't work, who messed it up?



    It's been my experience with apartments, especially the ones that have the gas bill included in the rent, they take longer showers, preheat the shower 10 minutes before getting in, crank the heat, and regulate temperature by opening windows, run laundry all day, and cook at home a lot.
  • These are condos....

    With a central heating plant and domestic water heating.

      With the recent advent of cities like Chicago and I believe New York requiring prosepective tenants to be told what it costs to heat the apartment, the days of inefficient, individual heating units for every tenant are probably numbered, as central plants are almost always more efficient when properly managed. 
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert





    Noisy Radiators are a Cry for Help
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    Dave here

    is the answer I got from a code official:



    Leave the existing outlets from the meters sized as they are assuming they were sized correctly when connected to meters, calculate full load for system and size main line at 50% of the full load taking into consideration length of run using the longest length method. That is not in writing anywhere (it should be) but this individual has used this for years and it has worked.



    If the service coming into the building is low pressure less than 1/2 pound then use 75% instead of 50%. In that case it may be better to see if the utility will run a high pressure line.



    You could also look into using a 2 pound or 5 pound system (if your utility can provide that) for your main pipe and reduce with a pounds to inches Maxitrol for the system piping.
  • Thanks Tim

    I asked several people from my local gas supplier and they just kept saying talk to your engineer.  They could REALLY, REALLY use alot of your training here!
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert





    Noisy Radiators are a Cry for Help
  • SWEI
    SWEI Member Posts: 7,356
    longest length method

    Works pretty well on most residential and light commercial when no particular branch is  radically long.



    Came across one recently which required  some alternative calcs (with the PE's blessing, of course) on a single apartment at the far end of the top floor of a commercial job.  Adding this single 40k appliance using the standard method would have increased the main sizing from 4" (with headroom) to 6", which made absolutely zero sense to either of us - yet that is what the 'official' answer would have been.
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