Lost Water Revenue 1" vs. 5/8" Meter

[Weismueller]

I am drafting a rule to cover Single Family Residential Fire Sprinkler installations. The underlying intent is to make it as easy and cost-free as possible for the residential owner, while minimizing the water utility's added expense. In this system, the standard meter size installed for single family residences is 5/8-inch, with a 3/4-inch service line. The water utility wants there to be one metered service line that Ts after the meter, providing water for both domestic and fire protection systems. In order to achieve the required flow for the sprinkler installation, it will sometimes be necessary to install a 1-inch meter and service line when a 5/8 meter would otherwise be sufficient.

I am trying to put an approximate cost figure on the additional volume of low flow rate water that would pass uncounted through the 1" vs. the 5/8" meter. This would be a cost shouldered by the water utility unless it were--somehow--included in the customer charges.

Performance curves for the meters in question demonstrate the lower sensitivity of the 1", which has 99% accuracy at about 1.25 gpm, and the 5/8", which has 99% at 0.5 gpm. However, the overall average uncounted water impact for a single family residence is not easy to arrive at.

 

[coloeng]

Have you looked into the possibility of the water provider using a 3/4" meter instead of the 1" meter. That is what our system recently did for exactly the same reason, more residential fire sprinkler systems being required by the fire departments. In our case it wasn't the potential for unaccounted for water so much as the tap fee for a 1" was 1-1/2 times that of a 5/8" and the developers were trying to save a few bucks.

 

[bimr]

Are you misreading the curves? All of these meters have the same accuracy.


ACCURACY 100% ± 1.5% of actual thruput

http://www.sensus.com/Module/Catalog/File?id=22

 

[cvg]

all of these types of meters have poor accuracy at low flows. See the attached for Neptune meters which indicates low flows at 95% accuracy. However, these are very low flows which are unlikely regardless of how much you oversize your meters. I doubt the utility will see much loss of revenue because of the meters very poor accuracty at 3/8 gallon per minute.

 

[dicksewerrat]

They are losing 10-20% through leakage. and they probably have a minimum charge for the larger meter. So they ar probably ahead of the game. Look at min charge for the 5/8" and 1 " meters. then look at the actaukl charge per gal or whatever unit they use and compare. They may also be getting a larger minimum sewage bill

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[dicksewerrat]

Of course the homeowner won't be using the shower and laundry facilities if the house is on fire.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[bimr]

I misread the accuracy, What is guaranteed is 100% ± 1.5% of actual thruput.

So the overall accuracy is guaranteed no matter what the size of the meter.

That makes sense because .5 gpm * 12 hours * 5% error is only 18 gallons.

At the other end of the scale, 30 gpm * 12 hours * .5% accuracy is 108 gallons.

It makes more sense to have higher accuracy at the higher flows, because the lost water at the low flows will tend to be inconsequential.

I agree with CVG in that the loss of revenue is insignificant. However, you may want to consider specifying the meter with the best guaranteed accuracy.

 

[Weismueller]

Thanks. Every response was helpful.

The utility has visions of cumulative loses due to tiny leaks out of customer taps and toilets--0.25 gpm leaking for a billing quarter means the utility paid to treat and pump out almost 33,000 gallons and got nothing in return.

But, I agree, the loss will most often be inconsequential; meters can be sized to reduce the problem, and the minimum charge is a convenient vehicle for balancing losses.

 

[cvg]

sizing a meter properly does not eliminate a leak, nor will it result in significantly better measurement of the leaking flow. None of the meters are more than 90 - 95% accurate in the 0.25 gpm range. Even if your meter measures to 90% accuracy at 0.25 gpm (and measures low not high), it will still measure 0.225 gpm. Only 10% of your 33,000 gallons (just 3,300 gallons) is not measured or paid for.

 

[PEDARRIN2]

Since most utilities charge you a tap fee based upon the meter size, have you accounted for the extra cost of the tap fee for a 1" meter vs. 5/8"?

 

[Weismueller]

Good error-spotting CVG.

They charge the same for all taps--the actual cost of labor and materials, if utility personnel actually perform the tap. A larger diameter tap may take longer, of course.

 

[stookeyfpe]

Why would one require a 1-inch meter for dwelling fire sprinklers? The total hydraulic demand for one- and two-family dwellings is only about 20 GPM. In my community the cost difference between a 5/8-inch, 3/4-inch and 1-inch meter is pretty significant because of CIP fees.

I understand the post is about meter accuracy but I'm questioning why such a larger meter is being sought? If it appears I am robbing or derailing your post I apologize.

 

[Weismueller]

Perfectly good question, stookeyfpe. A rep from the state fire marshal's office gave me a general opinion from experience that at least a 1" was necessary to supply fire flow requirements. He wasn't addressing the specific utility in question (or even the specific installation--Uponor-type multi-use, or dedicated lines). I recognize that hydraulics will determine, for each dwelling, what's required. My hope was that, if a 1-inch was required, and if the uncounted water difference between a 5/8 and a 1-inch meter wasn't significant (or could be quanitified) then the utility could decide to offer 1-inch meters at the same recurring cost (after initial purchase) as 5/8, if the meter was feeding a single-family dwelling with a sprinkler system. This would likely increase the number of sprinklered dwellings, and therefore the safety of people and their property.

 

[stookeyfpe]

Your state FM is confused. A residential sprinkler system does not require a 1 inch meter. You can easily supply the hydraulic demand for a residential demand for dwelling sprinkler system using a 5/8 inch meter. See International Residential Code (2009 ed.) section P2904.