Water Meter Sizing - avoiding $5K expense?

[fortop]

I am planning a remodeling project which will add 2 shower equipped bathrooms (3/4 baths). Based on the Uniform Plumbing Code meter sizing table 6-6, I can get by with a 1" building supply and a 3/4" meter (based on total fixture unit load and maximum allowable developed length.) Water pressure at my house is high - 87#.

My problem is that I have a 5/8" meter with 3/4" couplings, with a 3/4" city service line, and a 1" copper building supply from the meter to the building, but our city does not install 3/4" meters - only 5/8" meter then the next size is 1" meter. To go up to a 1" meter the city wants about an additional $5000 charge up front (covers the cost of adding a 1" city service line from the main to the new 1" meter, breaking/replacing the pavement, capital cost for the system, etc.)

Two questions:
1) Is a 5/8" meter really a "nominal" 3/4" meter in the Uniform Plumbing Code chart (since I see no 5/8" meter listed there)?
2) Is there somewhere I can get the mathematical formula that UPC uses to make the chart, and possibly demonstrate to the city that I would have enough volume/pressure with a 5/8" meter and 1" building supply line and my big 87# pressure - still meeting UPC requirements?
(I would imagine that the formula would take into account friction loss on the pipe over a given distance, city pressure, fitting friction loss, etc. Even with an actual 5/8" "restriction" at the water meter, I would think that the additional volume in a 1" building service and main trunk line would compensate for the 1/8" loss at the meter (3/4" - 5/8" = 1/8" less). I could even increase the size of the trunk line inside the building to 1 1/2" or so to add additional volume in the system. I'll bet 100' or so of 1 1/2" of PEX would not cost $5000.

Thanks

 

[Bob NH]

Meters come in 5/8", 3/4", 1", and larger.

My catalog gives the following ratings for various brands of meters. The ratings are by size of meter; max continuous flow; and maximum intermittent flow.

5/8"; 10 GPM; 20 GPM
3/4"; 15 GPM; 30 GPM
1"; 25 GPM; 50 GPM

With your high pressure, I would put in up to 1" line where I could without greatly added cost.

If you have a problem you could prevent rapid pressure changes by putting a 40 gallon bladder tank off a tee in the incoming line.

 

[Sponsor]

 

[fortop]

Thanks for the information. Any idea why UPC table does not reference 5/8" meters? Or, where I can get the calculations for a 5/8" meter in UPC?
That looks like the only way I can avoid the expense of installing a 1" meter.

The question is actually: 3/4" city service tap + 5/8" meter +1" building supply = how many fixture units allowed over what developed length?

I already have a 1 inch line from the meter to the house, and will use at least that size for the main trunk in the house. The city says UPC requires no more than 85# maximum pressure, so I will use a pressure regulator to get it at least to that level, and probably adjust it to much lower until I have just satisfactory pressure at all outlets.

 

[Terry]

https://terrylove.com/watersize.htm

The one inch meter greatly increases volume of water.
However, your pressure is pretty high.
You will be getting a lot of water though the 1" main at that pressure.
I would consider using a 1-1/4" pressure reducer at the home, to drop it below 70 PSI and have the main branch 1-1/4 until you can split it some.
Your local inspector may be able to cut you some slack with the high pressure main.

 

[BAPlumber]

I'd ask the city if the existing 5/8 meter was adequate for the building prior to the remodel. if so, how did they make that determination.

 

[Toolaholic]

I have a question. Are You intending on using ALL these fixtures at ONCE ??

Save the 5 K

 

[fortop]

Terry, thanks for the feedback. I agree that the excess pressure should compensate for the smaller water meter diameter, but I need some math/logic to back me up with the city plans reviewer and don't know where to get the physics information the UPC used in developing their chart. I think my problem is actually too much water flow, but I don't know how to prove that.

BAPlumber - Thanks, that was my thought too. In the past, the city did not get concerned with water meter size for normal residential installations - everybody got a 5/8" meter unless it was a larger multi-family residence. This year they started using the UPC table to size water meters for remodeling plans, based on fixture unit load, etc., so this is where I am now. I need to find a way to demonstrate that my situation complies with UPC even though it does not specifically show up on the chart. I suggested just allowing me to install a 1" meter at my expense to satisfy the chart, but the city water department says that would require a 1" city service line from the main - so I am back to square one.

Apparently, logic does not to apply here. If I shut off a garden hose attached to a hose bibb by using the spray nozzle on the end of the hose, rather than the hose bibb valve, the hose will explode or the nozzle will blow apart within 20-30 minutes. Even a heavy duty hose will blow. So, I know I have too much water flow and can't see spending $5k to get even more water flow I don't need.

 

[fortop]

toolaholic - Another good logical point - nobody would ever open every fixture at full bore at once. However, that doesn't show up on the UPC chart, so that logic apparently does not apply. I wish you were doing my plan review.

 

[fortop]

How would this logic work?

5/8" vs. 3/4" meter means 33% "shortage" in water volume (10 GPM vs. 15 GPM). 5 GPM/15 GPM = 33%.

87# PSI (city service) vs. 61# PSI ("Over 60 PSI" Pressure Range in UPC chart)
means 42% "overage" in pressure (26 PSI/61 PSI = 42.6%).

So, 42% overage in pressure makes up for 33% shortage in volume - correct?

(This assumes that the UPC formula give equal weight to volume and pressure in the calculation.)

 

[Phil H2]

The logic doesn't work. The relationship between flowrate and pressure loss is not linear. I do not know what process is used to develop the tables in the code. Two common ways of estimating pressure loss in pipes are the Hazen-Williams equation and the Darcy-Weisbach equation. You will find tons of links if you search the internet using either pair of names as keywords. The Darcy Weisbach equation is more accurate in more situations. But. it requires calculating the Reynolds number and using a Moody diagrams to determine a friction factor. You also need details about the pressure drop in the meter. The meter manufacture usually publishes data about pressure drop at different flowrates or give a K factor (or other coefficient) for calculating the pressure drop through the meter. Any easier method than calculations is to use tables or charts for pressure loss in pipes.

But, I don't know if calculating equivalent pressure loss will help you with the building inspector.

 

[Bob NH]

This is probably a revenue issue with the municipality.

You could test the situation by putting a pressure gauge on a faucet while you draw water from another faucet at a particular flow rate. You can get a gauge that connects to a hose connection.

Try turning on 3 showers and see if you maintain 50 psi on an outdoor faucet near where the water enters the house. You may have to run a supplemental faucet to get a flow that is consistent with your proposed expansion.

Run the test and go to the inspector once you have the answers. Then try to negotiate with the inspector about how much flow you need and how much pressure. You will of course have the answer so when he comes to verify the result you know that you will pass.

Hazen-Williams and Darch-Weisbach never had to convince a building inspector. I'm a civil engineer and those calculations are the last place that I would go to solve your problem.

One test beats 20 analyses and 4 tables.

 

[fortop]

Bob NH and Phil H2 - thanks for the great information.

I think our inspectors are fixated on the UPC charts, since that is the only tool they are given to work with per local ordnance. That's why I was hoping to use the source data from the charts to calculate the values for my particular situation.

I have the property gutted now, with just a hose bibb in the front and rear of the house. I just put a gauge on the front hose bibb and it registered about 90# without anything running. I opened the rear hose bibb full bore and the gauge dropped to 70#. (The front hose bibb and rear hose bibb are currently connected with a 1" diameter PVC pipe.)

Since you have an engineering background, how would this sound in ballpark terms - just taking a guess?:

3/4" city service + 5/8" meter + 1" copper building service with total developed length of 150' - with 87# city pressure - head (difference in elevation) is 7.5') total fixture units is 38.

I'm guessing that I would not go down below 40# pressure in any case. (I suppose I could fabricate a manifold with multiple hose bibbs to replace the current single hose bibb at the rear to simulate a 38 fixture unit load?)

I know I have way too much water flow now, and adding 2 shower baths won't reduce pressure to a unacceptable level. Adding a new 1" meter and 1" city service line will just make my high pressure problem worse, not better, and cost me an additional $5k to boot. (I know the inspectors will tell me to just install a pressure reducer to compensate for the extra unnecessary pressure I was required to create.)