Sizing water meters 2

[Siteplanman]

As a site engineer, I often use rule of thumb to size water meters. It is based on building sizes & uses. For instance, smaller retail shops often require a 3/4" or 1" domestic water meter. A restaurant or larger anchor may need a 2" meter. This rule of thumb works well when there are time constraints; more time (& money) would allow me to run hydraulic models on all water distribution systems. My question is: does anyone have a rule of thumb for master meters that will serve larger developments (say a major anchor, a dozen small shops, a couple of restaurants)?

 

[BobPE]

There are no rules of thumb for sizing water meters, they are size on flow and flow alone. There are plenty of books out there that allow you to properly estimate flow and size meters based upon that calculation.

If you are using rules of thumb, it is costing you unknow amounts of revenue becaue of poor meter efficiencies.

Sorry for the harsh truth, but you are not the only one that has sized meters that way and I find it sommon practice and I always try to inform people.

BobPE

 

[KRSServices]

i have found that in sizing of water meters, you have to be aware of flow and demands. Residential serivces (3/4&quot typically have a 5/8" meter. That not a rule of thumb, but a fact. Most meters fail in favour of the user (reading low) so the type of meter to be used is important. Here are some rules of thumb, which work fine, but are not definitive.

1) Typically, the meter size (nominal diameter) is one size smaller than the service pipe.

2) turbine meters versus positive displacement have weaknesses and strengths depending on the condidtions of service.

3) For users with varying flow rates, compound meters work well because low and high flow rates can then be measured with equal accuracy.

4) Guard the meter against tampering by regular visual inspections rather than exclusive remote reading. That is probably one of the singlemost pieces of advice that I can provide.

5) Schlumberger, Ford, Census, and others all have ample liturature on meter compatibility and suitability for a variety of applications. KRS Services

http://www.krs-services.com

 

[BobPE]

KRSS:

Please explain to me how you came up with the understanding that typically meters are on pipe size smaller that the service? All my engineering books tell me that pipe size has absolutely nothing to do with meter size, and as an engineer, I agree with them.

A lot of people have no clue how to specify a meter and that is how that rule of thumb came about.

If in doubt, there is a manual on water meters for the lay person published by AWWA.

BobPE

 

[KRSServices]

Y'know, I knew BobPE that you could not resist asking me that! Every water meter ever installed for me, through which every ststem were designed by professional engineers or specified by City Utility engineers have all applied that rule. City of Edmonton, Calgary, Whitehorse, Grand Prairie, Toronto, Burnaby, New Westminster, etc. all have specified diameters for their water meter connections. Truly, I have no idea where it comes from, although when I apply that rule to the flow hydraulics, velocities of water nominally increase at lower flows through smaller diameters.

Now you have my curiousity, check your domestic water meter. I'll wager that if you have a 3/4" service line, your inside diameter of the meter will be 5/8". Likewise on the office building, the inside diameter of the meter will be less than the ID of the service pipe. I'll bet you a coffee and donut on that one. KRS Services

http://www.krs-services.com

 

[BobPE]

I take you challange KRS:

I do know about my office building since the owner asked me for help to look at a problem.

I am in a 37 floor building of various occupancy. There are 2 services, one dedicated 12 dedicated fire which is metered, one 10 inch domestic service. Now by rule of thumb, a 10 or 8 inch meter would work. This building has a bank of several metere ranging from a 12 inch compound meter to a 1 inch meter. Now the meters are all owned by the water company, designed by an engineering firm they retained. Why would this be?

My house meter is a 5/8", not based upon the line diameter, but rather the idea that in my regeion, there are 2.8 people per home, 100 gal per person, per day with a residential di-urnal curve. The means that the flow range of the meter is well suited to capture the actual flow to the home at best 80 percent of the time. This means that I get 20 percent free water during a typical day since this meter was not desingned by an engineer, and that's ok with me. My neighbor has the same size line, but a 1 inch meter. Why is that. He applied for a pool permit, this means that the a 5/8" meter would not capture a high revenue flow since it would be pegged off its efficiency curve during large volume pool filling. Now the trade off is that low flow leaks which are usually not cought by meters will increase in volume before detection, but large flows will be captured whre revenue is much more profitable. Now, my neighborhood being similar to many working class neighborhoods, there is also a home with a 1.5 inch service and a 5/8" meter. Why is that? Well, his engineer worked with the water company and realized that headloss at his elevation through a long service would be the limiting factor in design. Now,by rule of thumb that should be a 1 inch meter? No way, the water company when presented with this information specified a 5/8 meter based upon flow in the home not rule of thumb. I told him to request a 1 or 1.5 inch meter, the 1.5 was rented out as a commercial so the base charge was higher, the 1 inch was categorized as a residential at the same rental fee as a 5/8 inch. The 1 inch would have gave him roughly 40 percent free water without high demands like a pool. The water company engineer said no way, 5/8 inch. Why is this, he was on a vengance to reduce unaccounted for water in the system.

Maybe I souldn't be commenting on this, because I get paid good money by water comapnies to study their unaccounted for water from an engineering prespective. My meter analysis typically save 5 to 10 percent off the base system unaccounted for water. So maybe rule of thumb is the way to go....That will give me work to do for many a year to come....

BobPE

 

[KRSServices]

Thank you BobPE, as usual you eloquently illutrated my point for me, in many more words than I could have imagined. Now let me provide an additional perspective, from the water utility's point of view.

Water meters are a tool utilized for revenue recovery. You see there is really only one number that really concerns water utilities and that is the total volume of water treated in a given time period. Water meters, as a total number measure about 75% to 85% of the total water recovered in a system. Water meters can be sized utilizing hydraulic equations each and every time. Factor in the cost of that engineering, and the price of the meter installation just went up for the municipality. Now, statistically compare those calculations on say a 100,000 services and you'll find that statistically, they fit within the so called "rule of thumb", but now the municipality has just incurred those engineering costs, necessary or not.

Bob, since I am obviously conversing with an experienced individual in water flow analysis and water systems, I totally agree with your reply, in a theoretical world. But you know full well, as I do, that the meters in any given system if they were 100% accurate, would only account for about 70% to 80% of the total treated water produced at the plant. Leakage, fire fighting, flushing, water breaks account for the remaining water. Every measured unit of water will have a rate attached that accounts for the losses, in addition to other costs.

The Utility you referred to in your example has chosen to hire an experienced and competant engineer to review service applications to determine the appropriate meter for a given service. That's cool, because it is very likely that they have realized a potential cost savings within the context of their established water rates, as you wrote about. In the big picture, did the cost of implemantation of the re-sizing program, complete with retro-fitting of meters on older systems, including engineering costs, really save much money? How long is it going to take for that utility to realize a payback for the cost of the retro fit. Did they even begin retrofitting, or are they merely realizing that there is a potential for additional revenues from this point forward, and therefore the Utility engineer reviews applications?

For every rule of thumb, there are going to be anomalies, just as those you described, but in the big picture, the did the "free" or unaccounted water really make a resounding impact on the utility's overall annual budget once implemented? Or was it a small percentage. I've been there, done that. I know the cost to retrofit systems, old plumbing, etc. I also know that in all cases (my instances only) the cost to implement a program was not worth it in terms of dollars and political fallout. I have managed larger towns and know of very large cities that utilize a flat rate system (no meters) for water utility recovery. They are water hogs, but are happy water hogs. I also have worked with cities and towns that have implemented stringent metering and water conservation programs due to growth and the high cost of treatment.

The bottom line here is that you are correct, with water metering, a "rule of thumb" should never replace sound engineering, but on the other hand one must balance the rationale of undertaking the engineering when the outcome is well within the statistical average. Average residential, average outcome. Complex user, variable flows, compound meter - sized by the utility or developer's engineer. I can also produce reams of data sheets illustrating the smaller meter size relative to commercial/industrial service size. I can also produce several Utility specs where within a flow range and line size, a meter size is prescribed, and it is usually smaller! Those are my observattions, and they will be identical to other communities across North America The utility is satisfied and the customer grumbles about water rates. Nuff said. KRS Services

http://www.krs-services.com

 

[dicksewerrat]

Now that you guys are done, I will give you some real facts from a municipal engr. Water meters are sized according to the size of the hole drilled into the water main for the individual property water supply line. What is called a 3/4 supply line has a 5/8 inch hole in the main. It is just that the 3/4 line connects to the 3/4 corporation cock. The meter nipple for the 5/8 meter is a 1/2 x 3/4 brass fitting which has the same internal diameter as the hole in the main. This size meter has the lowest cost minimum bill as set by 'politicians' nominally called 'City Elders'. The connection is made with a 1/2 x 3/4 reducing street ell into the gate valve on the stret side of the supply line. It is connected on the other side by the same thing or a 1/2 x 3/4 ips to sweat copper fitting. As the number of fixture units go up so does the meter size. 3/4 meter is connected by 3/4 x 1 fittings. 1" by 1 1/4 x 1 fitiings.

 

[RWF7437]

What a heated discussion this turned out to be !

The AWWA Manual is probably the best guide for sizing water service lines and meters. The trick of course is to be able to estimate the demands closely which is necessarily part guess work. Some water suppliers size meters and some don't just because they don't want the liability if they badly under or over size.

Water meters are the cash registers of the system and large meters especially should be sized carefully and calibrated frequently because the errors they may entail represent a large proportion of the revenue stream.

Just my thoughts, and experience, on this. I've never been, until now, so emotional about water meters. Think I'm talking to too many engineers.

Good luck,

 

[boo1]

My local water dept sizes our single family homes meters. They use the the one size down method.

 

[Brad0313]

Get a copy of American Water Works Association (AWWA) M-22. It will show you how to determine the DFU's and size the meter.

 

[gibfrog]

Here in southwest Florida is how I design meters sizes -

1) I count all the fixtures by fixture units and total them. This data is suplied by the owner or architect.

2) I look on municiality supplied AWWA charts/tables, what meter size for my number of fixture units and what peak gpm to expect at 30 psig.

3) I will not size any line under 1", even for a 5/8" domestic meter or a standard minimum 3/4" commercial meter.

4) I usually size my line atleast one size larger than my meter, 5/8",3/4" meters = 1" line min (may be 1.5" if long run), 1" meter = 1.5" line min, 1.5" meter = 2" line min, etc... I do not make the line size too big to worry about stagnant water, but I do worry about excessive head losses. I also know that the number of fixtures I design for is lowballed by the owner/contractor due to water capacity fees based upon meter size and water impact fees for anticipated usage, so a larger service line may be necessary. I now place the number of fixture units supplied by the owner on my utility plan just to cover my butt. (I also check to see what size line the architect has called out for.)

Best of luck.......



Clifford H Laubstein
FL PE 58662

 

[erikfinley]

See Volume 12, Number 7, (July 1986) "OpFlow" (A monthly AWWA publication). "Sizing and Selecting Modern Water Meters"