INTERNETWATER SUPPLY SIZING

Copyright © 2005 RsLogical, inc.All Rights Reserved

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SIZING THE WATER DISTRIBUTION SYSTEM

Water distribution systems that are sized properly will not onlyprovide water in sufficient volume for the fixtures to operate, but alsoreduce the chance for water hammer to occur in the system.Velocities exceeding 8 feet per second in the piping will causeerosion and water hammer.

This training booklet will help you to understand how to size thewater supply system using the Pressure Available For UniformLoss method. To do this you will need to have a copy of the WIplumbing code and in particular Comm. 82.40. Tables 82.40-1WATER SUPPLY FIXTURE UNITS FOR NONPUBLIC USEFIXTURES and 82.40-3 CONVERSION OF WATER SUPPLYFIXTURE UNITS TO GALLONS PER MINUTE will be used.

Pages 4 and 5 illustrate a first floor plan and basement plan of atypical ranch style home. There are 1-1/2 baths in this dwelling.Page 11 contains an isometric drawing of the water supply systemwith the sfu loads and pipe diameters. Cold water lines areillustrated with a bolder line than the hot water lines for easieridentification. Several points along the piping are lassoed withnumbered tags. The numbers in those tags are the sfu load in thatsection of pipe.

The first valve after the water service enters the building is theBuilding Control Valve. In the case of an interior pressure tank, theBuilding Control Valve is the first valve downstream of the tank.Building Control Valves shall be installed within 3 feet of developedlength of where a water service first enters a building and within 3feet of developed length downstream of an interior pressure tank.

Another point of interest is the tee in the cold water line that connectsthe water heater to the cold water supply. It is pointed out in theisometric drawing on page 11. This tee is commonly referred to asthe Transition Tee. Sections of cold water pipe from the Transition

Tee back upstream to the Building control valve are assigned sfu’s ina different manner than other parts of the system. That is becausethese sections of pipe supply all the hot water sfu’s in the system andthe cold water sfu’s to any fixture downstream of the section of pipeyou are assigning the load to. This will be explained in greater detaillater.

Completing a Water Calculation Worksheet

Page 9 illustrates the completed water calculation worksheet. Usingthe Total sfu from Table 82.40-1, add the total sfu’s from eachfixture and appliance in the dwelling. Find Table 82.40-1 on page 6.

1 - Automatic Clothes Washer = 1.0 hot 1.0 cold 1.5 total1 - Dishwashing Machine = 1.0 hot 0.0 cold 1.0 total2 – Hose Bibbs – ½” = 0.0 hot 6.0 cold 6.0 total1 – Kitchen Sink = 1.0 hot 1.0 cold 1.5 total1 - Laundry Tray = 1.0 hot 1.0 cold 1.5 total1 - Lavatory = 0.5 hot 0.5 cold 1.0 total1 - Water Closet = 0.0 hot 2.0 cold 2.0 total1 - Bathroom Group, W/BT = 2.0 hot 3.5 cold 4.0 total

Totals sfu’s 6.5 hot 15.0 cold 18.5 total

Note the total sfu’s is 18.5. In order to find the pressure loss in psigin the water service and water meter if supplied, those sfu’s must firstbe converted into gallons per minute. Table 82.40-3 on page 6 isprovided to do this conversion. Notice the line between 10 and 20sfu’s in the table. 18.5 sfu’s is not shown so you must interpolate thegpm. These are flush tank type water closets.

10 sfu’s = 8 gpm and 20 sfu’s = 14 gpm. The difference between 20and 10 is 10 and the difference between 14 and 8 is 6. You mustdivide the difference of 6 by 10 to find how much to add for every 1fixture unit over 10 sfu’s. Dividing 6 by 10 results in .6 for every 1

2fixture unit over 10. There are 8.5 sfu’s over 10 so multiply .6 by

8.5. .6 X 8.5 = 5.1 That means you add 5.1 gpm to 8 gpm and comeup with a conversion of 13.1 gpm demand of the building.

On the top of the water calculation worksheet there is a boxed inarea. Inside the box is the information required to find the loss in theservice and the pressure available at the building control valve.

There are other factors that affect the pressure at the building controlvalve. Difference in elevation, (6 ft), Length of the service, (70 ft.)and the low pressure at the connection to the water main or exteriorpressure tank, (48 psig)

Pressure loss in the water service

Now that you know the gpm demand of the building, the pressureloss in psig within the service can be determined by using one of thegraphs in the Appendix of the code. This sample is going to useGraph A- 82.40 (7)-6 PEX Tubing ASTM F876. Find that graphon page 7 of this booklet. The flow rate is located along and up theleft side of the graph. The pressure loss due to friction (psig/100 ft ofpipe) is displayed along the bottom of the graph.

By following the graph line located at 13.1 across the graph until itintersects with the 1” pipe size line you will find a circle. Lookingdown the graph you will see that it is just over 10 psig/100 ft.Actually it is 10.3 psig loss per 100 ft. of pipe. There is not a total of100 ft in the service though. It is 70 ft in length. Therefore youmultiply 10.3 by .70 and the result is 7.2 psig loss in the service.That loss is entered on line 7. Then subtract it from the pressure inthe water main (48) leaving 40.8 psig.

Next is the pressure loss or gain from the elevation differencebetween the main and the building control valve. 6ft X .434 = 2.6psig loss on line 8. Subtract line 8 from line 7 subtotal and line 9 is38.2. Transfer 38.2 down to line B.

This sample has a 5/8 water meter installed. Page 8 has GraphA-82.40(7)-1 illustrated with the graph line extending up from 13.1gpm circled at the intersection of the graph line of a 5/8 meter. Thatloss is 6.4 psig and is entered on line C. subtotal of the worksheet.Subtracted from line B. the pressure available is 31.8 on line C.subtotal.

The tub valve is a pressure balance valve, which requires 20 psig tooperate so that is the controlling fixture. Subtracted from 31.8 theremainder is 11.8 psig on line D. subtotal.

The next step is the difference in elevation from the building controlvalve to the controlling fixture, which is 12 ft. Multiplied 12 by .434and there is pressure loss of 5.2 psig from the elevation difference.That now leaves 6.6 psig on line E. subtotal.

There is no device creating an addition loss to the controlling fixturetherefore 6.6 is transferred down to G. subtotal.

Determine Line G. by taking a measuring tape and measuring alongthe piping starting at the building control valve all the way to thecontrolling fixture. Include the fittings and into and out of the waterheater if the controlling fixture is not a cold only fixture.

This sample is 76 ft for the developed length and equals 114 whenmultiplied by 1.5. The A value in this sample is rounded up to 6.

Assigning Water Supply Fixture Units

In the sample used in this booklet there are 6.5 hot sfu’s. Assign thesfu’s to the hot water piping first.

To the left of the water heater there are 2 sfu’s. Those 2 units comefrom 1 hot unit of the Kitchen Sink and 1 hot unit of the DishwashingMachine. To the right of the water heater there are 4.5 sfu’s. 2 fromthe Bathroom Group, 1 from the Laundry Tray, 1 from the AutomaticClothes Washer and .5 from the Lavatory in the powder room.

3Now that you know there are 6.5 sfu’s on the hot water, you can

determine the sfu’s on the cold water line that supplies the waterheater. Starting at the water heater, you must assign the unitsbackwards or upstream to the building control valve. That cold waterline on the upstream side of the Transition Tee not only supplies allthe hot water units, it also supplies the cold water past the waterheater. But only the balance of the total sfu of the fixture is addedfrom fixtures past the heater. In other words, the kitchen sink with atotal of 1.5 sfu’s has 1 sfu already included from the hot and youonly add .5 from the cold.

Notice that there are 4 sfu’s on the cold water line to the left of theheater or past it. 3 sfu’s come from the ½ inch hose bibb and 1 sfufrom the cold of the kitchen sink. Remember now that pipe is pastthe Transition Tee so it only supplies the cold water to those fixtures.This may confuse you because to the right of the heater or upstreamof the Transition Tee, the pipe supplies 10 sfu’s. You can’t add the4 cold units past the heater to the 6.5 hot units to determine the loadupstream of the Transition Tee because the total of the Kitchen Sinkis 1.5 not 2. Therefore you have 6.5 from the hot, 3 from the hosebibb and .5 or the balance of the total of the Kitchen sink.

The rest of the cold sfu’s from fixtures that connect to the cold lineback to the building control valve are added in the same manner.Hose bibbs do not have hot sfu, so the total value is added. The coldbranches that come off the cold to the water heater are assigned thefull value of the cold because they only serve the cold to thosefixtures.

The sample drawing on the next page is an example of a waterdistribution system in a 1-½ bath ranch home. There are 18.5 totalwater supply fixture units. Count them yourself by using Table82.40-1 (Nonpublic Use Fixtures). Notice that there are 6.5 hotsfu’s. That is the sfu you start with at the transition tee to the heater.

There is a Dishwasher, Kitchen Sink and ½” Hose Bibb on the coldpast the water heater. You do not add the full value of the cold sfu tothe 6.5 hot sfu to determine the load on the upstream side ofTransition tee. Remember that fixtures other than lavatories have atotal that is less than the hot and cold sfu combined. That’s becausethe faucet port will not allow the full flow of both the hot and cold.But if either one is used alone you will get the full sfu flow. So youdo not add 4 + 6.5 to find the load on the upstream side of theTransition tee. You only add the full 3 sfu from the Hose Bibb(because there is no hot) and the .5 sfu that is the balance of thekitchen sink total. Remember that 1 sfu is already on the upstreamside of the Transition tee from the hot of the Sink. Therefore 10 sfuis the load on the point.

Notice that the tag with 5.5 is the full load of the cold sfu’s becausethat cold line does not serve the water heater. Tags with 13, 15.5 and18.5 are lassoed around the cold water line that serve the waterheater. Therefore only the balance of the total sfu’s less all the hotsfu’s from fixtures served by that pipe is added to the total hot sfu’sto determine the load in the tagged section.

The last step is to size the distribution piping by using the tablesprovided in Comm.82.40. This sample home is going to use CPVCTubing ASTM D2846 for the distribution piping so Table 82.40-8has been included on page 10.

A dark line is provided under the pressure available for uniform lossin the first column and stretches across the table. These are FT orflush tank fixtures in the system, which means the maximum load onthe sections of each size of pipe shall not exceed the sfu’s listed justabove the dark line. 7.0 are the maximum sfu’s for 3/4 inch diameterpipe and 15.5 is the maximum sfu’s for 1 inch diameter piping.

The pipe diameters required at the changes are shown on theisometric plan on page 11.

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Sizing the Water Supply

Exercise 1

Copyright © 2005 RsLogical, Inc.All Rights Reserved

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Sizing the water supply

Exercise 1

Contents

Page no:

13 Instructions14 1st Floor plan of exercise house15 Basement plan of exercise house16 Isometric drawing of the water distribution system17 Tables 82.40-1 and 82.40-318 Water Calculation Worksheet19 Water Calculation Worksheet20 Graph 82.40(7)-7; PE Copper Tube Size21 Graph 82.40(7)-1; Water Meters22 Table 82.40-8; CPVC tubing ASTM D2846

InstructionsThis is Exercise 1 of the Internet Water Supply Sizing course. Inside this packet are the tables, graphs, drawings and worksheets you will need tocomplete this exercise. Fill out the water calculation worksheet from the information below. Label the sfu’s and sizes at the tags of this exercise.When Exercise 1 and Exercise 2 have been completed, log onto your course at rslogical.com and complete the 101 questions there.

Use the following information to complete the water calculation worksheet:

Low pressure at the water main; 50 psig;Water service from the main to the lot line is 1-1/4 inch PE copper tube size 35 ft in lengthWater service from the lot line to the building control valve is 1-inch PE copper tube size 75 ft in length;Difference in elevation between the main and the building control valve; 5 ft;3/4 Water meter;Pressure required at the controlling fixture, pressure balance tub valve; 20psigElevation from the building control valve to the controlling fixture; 12 ftDeveloped length from the building control valve to the controlling fixture; 80 ftWater distribution material is CPVC Tubing ASTM D2846

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Sizing the Water Supply

Exercise 2Copyright © 2005 RsLogical, Inc.

All Rights Reserved

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Exercise 1 was a refresher in water distribution sizing for a small ranch type dwelling unit that could well be located in a municipal setting. Inoutlaying areas water softeners are commonly installed and result in lower operating pressure. The following pages describe an alternate approvalof a conversion table of SFU’s to GPM. It applies to single-family dwellings or single dwelling units in multi-family buildings. This new tablehas greatly reduced the GPM load created by SFU’s. But it can apply only to sizing the water softener and finding the pressure loss throughit. Table 82.40-3 must still be used to find the GPM demand of the building and the in all other lines of the water calculation worksheet.

If a dwelling has more than 40 SFU’s in the water distribution system, the table does not apply. The table also will not apply when the demand ofany fixture exceeds the GPM listed in the new table. Be careful when using this table as there are many tub and shower faucets which demand agreater than average supply of water and pressure. When adding up the total SFU’s, hose bibbs are not included in the load because the softenerdoes not serve them.

The letter of approval issued by the department is displayed on the next few pages of this packet. Note the 6 stipulations that are included in thisapproval. Stipulation 6 states that the GPM flow rate used to find the pressure loss from the softener shall not be less than any faucet or fixturerequirement as stated by the manufacturer. That will apply to many body showers and roman tub type fillers.

For this exercise, all the fixtures except the 2 outside hose bibbs are to be included in the calculations. A sample calculation to find the pressureloss from a softener is displayed on page 27. This exercise will use the same manufacturer’s table as displayed on page 27. There is an additionalworksheet on page 28. Page 29 displays the piping plan from exercise 1 with modifications for the water softener. After you have finished thenew water calculations and determine a new “A” value, assign SFU’s and sizes to the drawing on page 29. The developed distance is going to begreater now because the piping goes through the water softener on the way to the controlling fixture.

When exercise 1 and exercise 2 are both completed, log onto rslogical and enter your answers.

Use this information to complete the Water Calculation Worksheet

The new developed distance from the building control valve to the controlling fixture is 100 ft. Fill out the worksheet supplied on page 28. You can start with the same number from exercise 1 on line E. subtotal. Use the drawing supplied on page 29 and maximum load table 82.40-8 from exercise 1 to assign SFU’s and sizes to the drawing. After completing both exercise 1 and exercise 2, log onto rslogical.com and enter your answers.

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GPM 800 1200 1600 22504 5.2 4.5 4.0 3.55 6.5 5.7 5.2 4.86 7.5 6.5 6.0 5.87 8.4 7.5 6.5 6.28 9.5 8.4 7,2 6.89 10.1 9.5 8.4 7.510 10.8 9.8 9.1 8.411 12.5 10.5 9.8 9.1

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