Allegheny County, PA Article XVI Sizing Building Water Supply Distribution System

§ 860-181 General.

A. The following sections outline a procedure for the sizing of the water supply piping. The design procedure is based on the minimum pressure available from the street main or individual source of supply the head changes in the system due to friction and elevation, the volume rates of flow required for satisfactory operation of the fixtures, and the probability of simultaneous use.

B. The procedure outline is intended to serve as a guide and does not preclude an engineering design deviating from such procedure which would accomplish the results sought in this article of the Code.

§ 860-182 Total daily water requirements.

A. Basic needs. The calculation of total daily requirements for water may be used on the unit quantities shown in Tables 860-182A, "Design Criteria for Daily Water Requirements Based on Building Occupancy," and 860-182A(1), "Daily Water Requirements for Common Farm Animals." The total daily water requirement does not constitute the peak or simultaneous water requirement of the supply and shall not be used in sizing water distribution systems. The total of the daily water requirements shall be used only to determine whether the source of the water supply is sufficient to provide the water requirements of people, animals, irrigation, and other water using facilities served. The rate of flow and pressures at which the total daily water requirements shall be delivered shall be determined as prescribed hereinafter.

	Table 860-182A Design Criteria for Daily Water Requirements Based on Building Occupancy
	Type of Occupancy	Minimum Quantity of water per person per day in gallons (or as indicated)
	Small dwellings or cottages with seasonal occupancy	50
	Single family dwellings	75
	Multiple family dwellings (apartment)	60
	Rooming houses	40
	Boarding houses	50
	Additional kitchen usage for nonresident boarders	10
	Hotels without private baths	50
	Hotels with private baths (2 persons per room)	60
	Restaurants (toilet and kitchen usage per person)	7 to 10
	Restaurant (kitchen usage per meal served)	2 1/2 to 3
	Additional for bars and cocktail lounges	2
	Tourist camps or trailer parks with central bathhouse	35
	Tourist camps or mobile home parks with individual bath units	50
	Resort camps (night and day) with limited plumbing	50
	Luxury camps	100 to 500
	Work or construction camps (semi-permanent)	50
	Camp (with complete plumbing)	45 (Ind. w.s.)
	Camp (with flush toilets — no showers)	25 (Ind. w.s.)
	Day Camps (no meal served)	15
	Day Schools, without cafeterias, gymnasiums, or showers	15
	Day School with cafeterias, but no gymnasiums or showers	20
	Day Schools with cafeterias, gymnasiums and showers	25
	Boarding schools	75 to 100
	Day workers at schools and office (per shift)	15
	Hospitals	150 to 250
	Institutions other than hospitals (per bed)	75 to 125
	Factories (gallons per person per shift, exclusive of industrial wastes)	15 to 35
	Picnic parks (toilet usage only)	5
	Picnic parks with bathhouse, showers and flush toilets)	10
	Swimming pools and bathhouses	10
	Luxury residences and estates	100 to 150
	Country clubs (per resident member)	100
	Country club (per non-resident member)	25
	Motels (per bed space)	40
	Motels with bath, toilet, and kitchen range	50
	Drive-in theaters (per car space)	5
	Movie theaters (per auditorium seat)	5
	Airports (per passenger)	3 to 5
	Self-service laundries (gallons per wash, i.e. per customer)	50
	Stores (per toilet room)	400
	Service station (per vehicle serviced)	10

	Table 860-182A(1) Daily Requirements for Common Farm Animals
	Animal	Minimum daily water requirements in gallons
	Horse, mule or steer	12
	Dairy cow (drinking only)	15
	Dairy cow (drinking and dairy servicing)	35
	Sheep	2
	Hog	4
	Chicken (100)	4
	Turkeys (100)	7

B. Calculating total daily requirements. Total daily requirements should be calculated by multiplying the unit daily requirement by the total number of persons in the occupancy involved. See Example 1 below. To this figure must be added any special use quantity, such as lawn watering, industrial requirement, etc.

C. Special requirements. The total daily amount of any special requirement shall be added to the figure obtained under Subsection B and Table 860-177G, "Minimum Flow Pressure and Flow Rates," gives special use quantities for some conditions. While the quantity of special use water shall be computed on the rates given in Table 860-177G, the total amount shall be figured for appropriate periods and conditions of use. See Example 2.

(1) Example: Assume there is a hospital outside the limits of a community. The hospital has 300 beds. In addition, the hospital supplies its own dairy products and has a farm with 40 head of cattle. In Table 860-182A, the daily water requirement per hospital bed is taken as 250 gallons per bed. From Table 860-182A(1), the water requirement per head of cattle is taken as 35 gallons per animal. Therefore, the total daily requirement is 300 by 250 plus 40 by 35 or 76,400 gallons.

(2) Example: It is assumed that at the hospital cited in Table 860-182A, there is a lawn sprinkling system operating from 12 sillcocks three hours each day. From Table 860-177G, it is seen that each sillcock requires 300 gallons per hour. Therefore, the total special use water will equal 12 by 900 or 10,800 gallons. This amount is added to that obtained in Example 1. The total quantity required is, therefore, 76,400 plus 10,800 or 87,200 gallons per day.

§ 860-183 Determination of peak demand.

A. Estimating water supply demand. In determining the size of water supply distribution piping, the maximum momentary volume rate of flow of water shall first be determined. This is the supply demand which is based on the numbers and kinds of fixtures installed, on the rates of flow required by the different kinds of fixtures, and on the probable simultaneous operation of the various fixtures. The total daily requirements do not enter into the determination. In computing supply demand, use shall be made of Table 860-183A, "Supply Fixture Unit Values for Various Plumbing Fixtures."

	Table 860-183A Supply Fixture Unit Values for Various Plumbing Fixtures
	Type of Supply Fixture
	Fixture or Group1	Supply Control	Hot	Cold	Unit Values Total2
	Bathroom group	Flush valve	3	6	7
	Bathroom group	Flush tank	3	4.5	6
	Bathtub	Faucet	1.5	1.5	2
	Combination fixture	Faucet	2	2	3
	Kitchen sink	Faucet	1.5	1.5	2
	Laundry tray	Faucet	2	2	3
	Lavatory	Faucet	1.5	1.5	2
	Pedestal urinal	Flush valve	-	10	10
	Restaurant sink	Faucet	3	3	5
	Service sink	Faucet	1.5	1.5	2
	Shower head	Mixing valve	3	3	5
	Stall or wall urinal	Flush valve	-	5	5
	Stall or wall urinal	Flush tank	-	3	3
	Water closet	Flush valve	-	10	10
	Water closet	Flush tank	-	5	5

	Notes:
	1.	For fixtures not listed, factors may be assumed by comparing the fixture to a listed one using water in similar quantities and at similar rates.
	2.	For fixtures with both hot and cold water supplies, the weights for maximum separate demands may be taken as 3/4 of the total supply fixture unit value.

B. Calculation of demand. When the water supply fixture units are used to estimate the supply demand, the supply fixture unit values as given in Table 860-183A shall be used in conjunction with Table 860-183B, "Supply Demand for Various Loads in Supply Fixture Units."[1]

	Table 860-183B Supply Demand for Various Loads in Supply Fixture Units
	Load Supply fixture units	Flush valve water closets predominate (curve 1) gpm	Tank water closets predominate (curve 2) gpm
	5	22	4
	10	27	8
	20	35	14
	30	42	20
	40	46	24
	50	51	28
	60	54	32
	88	64	40
	124	74	48
	160	81	56
	236	98	72
	300	108	85
	400	127	106
	470	135	118
	500	143	124
	600	157	143
	660	162	152
	700	170	161
	800	183	178
	850	189	185
	900	197	195
	1,000	208	208
	1,060	216	216
	1,280	243	243
	1,510	270	270
	1,990	324	324
	2,480	378	378
	2,900	432	432

(1) The estimated demand load in gallons per minute for fixtures used intermittently on any water supply pipe shall be obtained by multiplying the total number of each kind of fixture, supplied through that pipe by its Supply Fixture unit value from Table 860-183A adding the products, then referring to the appropriate columns of Table 860-183B or using the figure, select the Demand in GPM. Examples given below.[2]

[2] Editor's Note: The examples are on file in the Health Department.

(2) The additional load of any continuously flowing outlets such as hose outlets shall be computed separately and added to the total demand of intermittently used fixtures. See Example 2. below.

(a) Assume a water line serving a public washroom in which are three flushometer pedestal urinals, six flushometer closets and six lavatories with hot and cold water. First prepare a tabulation as shown:

Name of Plumbing Fixture	Number on system (or section1)	Supply fixture unit value per fixture Table 860-183A			Total supply fixture units
		Hot	Cold	Total	Hot	Cold	Total
Pedestal Urinal
Flush Valve	3		10	10		30	30
Flushometer Closet	6		10	10		60	60
Lavatory	6	1.5	1.5	2	9	9	12
Total					9	99	102
Supply demand in GPM					7	67	68

[1] See Subsection C. Referring to Table 860-183A for these fixtures, it is found that the total demand in supply fixtures units for hot was nine s.f.u., for cold was 99 s.f.u., and a total demand of 102 s.f.u. By using Figure Table 860-183B curve number 2, it is determined that the supply demand in GPM for hot water is 7, and by using the same figure but curve 1, it is determined that the demand for cold water in GPM is 67 and the total demand in GPM is 68. This break-down is used in order to size the hot water supply branch, the cold water supply branch and the building service line.

[2] Assume an apartment building (private type occupancy) having 200 bathrooms groups with flushometer closets and 200 kitchen sinks. The apartment lawn has installed in it a sprinkler system operating from seven sillcocks. What is the demand flow for which the water service to the apartment must be designed? The intermittent use fixtures are figured as in Example 1. to have a demand of 326 GPM.

Name of Fixture	Number on system	Supply fixture unit value per fixture Table 860-183A	Total supply fixture units
		Hot	Cold	Total	Hot	Cold	Total
Bathroom group	200	3	6	8	600	1,200	1,600
Kitchen sink	200	1.5	1.5	2	300	300	400
Total					900	1,500	2,000
Demand in GPM (Table 860-183B)					195	270	326

[3] The lawn sprinkler system outlets have a demand of five GPM each (Table 860-177G). The total sprinkler system demand is, therefore, 35 GPM. This is added to the total demand (326) of the intermittently used fixture making a total water demand of 361 GPM. This total figure would then be used in determine the size of the building service pipe. The 35 GPM demand figure would also be added to the cold water demand figure of 270 giving total cold water demand of 305 GPM and this figure would be used in sizing the cold water distribution piping.

[1] Editor's Note: A figure representing a graphical representative to this table is on file in the Health Department.

C. Selection of pipe size.

(1) Pipe sizes may be selected according to the following water pipe sizing procedure except that in no case shall a pipe size be less than shown in Table 860-177A nor in the case of water service lines, less than specified in § 860-176A.

(a) The water pipe sizing procedure is based on a system of pressure requirements and losses, the sum of which must not exceed the minimum pressure available at the street main or other source of supply.

(2) These pressures are expressed as follows:

(a) Pressure required at fixture to produce adequate flow — See Table 860-177G.

(b) Static pressure loss — This is computed at 0.43 psi per ft. of pipe rise or drop and is added or subtracted respectively.

(c) Loss through water meter — Pressure or friction losses for various size meters are shown in Table or Figure 860-183C(1).

(d) Loss through taps in water main — Losses for various size taps as Shown in Table 860-183C(3).

(e) Losses through special devices such as filters, water softeners, backflow preventers, etc. — These must be obtained from the manufacturer, or estimated and added to the total.

(f) Loss through fittings and valves — Losses for these devices are computed by converting the fittings or valves to equivalent straight sections of pipe and adding this length to the total for the pipe section being considered. Table 860-183C(2) shows equivalent lengths of pipe for fittings and valves.

(g) Loss due to pipe friction — This loss may be readily computed when (a) the pipe size, (b) its length and (c) the flow through the pipe are known. When these three factors are known, the friction loss can be determined from either Table 860-183C(4) to (7) or the figures.[3] The table and the figure used depends on the type of pipe used. An example of this sizing procedure is given in the following section.

Table 860-183C(1) Loss of Pressure Through Disk-type Meters in Pounds per Square Inch (psi)
	Size of Meter
Gallons per minute	5/8	3/4	1"	1"	2"	3"	4"	6"
4	1.0
5	1.6
6	2.2
7	3.0	1.1
8	4.0	1.4
9	5.0	1.7
10	6.1	2.1
15	14	5.0	2.0
20	-	8.8	3.5	1.0
30	-	19	8.0	2.3
40	-	-	14	4.0	1.6
50	-	-	22	6.2	2.4
60	-	-	-	9.0	3.6
70	-	-	-	12	4.9	1.3
80	-	-	-	16	6.2	1.7
90	-	-	-	20	8.0	2.0
100	-	-	-	-	10	2.5	1.0
120	-	-	-	-	14	3.7	1.30
140	-	-	-	-	20	5.1	2.0
160	-	-	-	-	-	6.2	2.4
180	-	-	-	-	-	8.1	3.3
200	-	-	-	-	-	10	4.0	1.0
250	-	-	-	-	-	16	6.1	1.7
300	-	-	-	-	-	23	9.0	2.3
350	-	-	-	-	-	-	13.0	3.0
400	-	-	-	-	-	-	16.0	4.0
500	-	-	-	-	-	-	25.0	6.1
600	-	-	-	-	-	-	-	9.0
700	-	-	-	-	-	-	-	13
800	-	-	-	-	-	-	-	16
900	-	-	-	-	-	-	-	20

Table 860-183C(2) Allowance in Equivalent length of pipe for Friction Loss in Valves and Threaded Fittings
Diameter of fitting (inches)	90° Std. ell, feet	45° Std. ell, feet	90° side tee, feet	Coupling or straight run of tee, feet	Gate Valve, Feet	Gate Valve, Feet	Angle Valve, Feet
3.8	1	0.6	1.5	0.3	0.2	8	4
1/2	2	1.2	3	0.6	0.4	15	8
3/4	2.5	1.5	4	0.8	0.5	20	12
1	3	1.8	5	0.9	0.6	25	15
1 1/4	4	2.4	6	1.2	0.8	35	18
1 1/2	5	3	7	1.5	1.0	45	22
2	7	4	10	2	1.3	55	28
2 1/2	8	5	12	2.5	1.6	65	34
3	10	6	15	3	2	80	40
3 1/2	12	7	18	3.6	2.4	100	50
4	14	8	21	4.0	2.7	125	55
5	17	10	25	5	3.3	140	70
6	20	12	30	6	4	165	80

Table 860-183C(3) Loss of Pressure Through Taps and Tees in Pounds per Square Inch (psi)
	Size of Tap or Tee
Gallons per minute	5/8"	3/4"	1"	1 1/4"	1 1/2"	2"	3"
10	1.35	0.64	0.18	0.08
20	5.38	2.54	0.77	0.31	0.14
30	12.1	5.72	1.62	0.69	0.33	0.10
40	-	10.2	3.07	1.23	0.58	0.18
50	-	15.9	4.49	1.92	0.91	0.28
60	-	-	6.46	2.76	1.31	0.40
70	-	-	8.79	3.76	1.78	0.55	0.10
80	-	-	11.5	4.90	2.32	0.72	0.13
90	-	-	14.5	6.21	2.94	0.91	0.16
100	-	-	17.94	7.67	3.63	1.12	0.21
120	-	-	25.8	11.0	5.23	1.61	0.30
140	-	-	35.2	15.0	7.12	2.20	0.41
150	-	-		17.2	8.16	2.52	0.47
160	-	-	-	19.6	9.30	2.92	0.54
180	-	-	-	24.8	11.8	3.62	0.68
200	-	-	-	30.7	14.5	4.48	0.84
225	-	-	-	38.8	18.4	5.67	1.06
250	-	-	-	47.9	22.7	7.00	1.31
275	-	-	-	-	27.4	7.70	1.59
300	-	-	-	-	32.6	10.1	1.88

	Table 860-183C(4) Pressure Loss of Water in Pounds per Square inch per 100 Feet of Fairly Smooth Pipe.
	For convenience this table is developed from the accompanying figure.[4]

	Table 860-183C(5) Pressure Loss of Water in Pounds per Square Inch per 100 Feet of Fairly Rough Pipe.
	For convenience this table is developed from the accompanying figure.[5]

	Table 860-183C(6) Pressure Loss of Water in Pounds per Square Inch per 100 Feet of Rough Pipe.
	For convenience this Table is developed from the accompanying figure.[6]

	Table 1503.3G. Pressure Loss of Water in Pounds per Square Inch per 100 Feet of Smooth Pipe.
	For convenience, this table is developed from the accompanying figure.[7]

[3] Editor's Note: The figures are on file in the Health Department.

[4] Editor's Note: The table and figure are on file in the Health Department.

[5] Editor's Note: The table and figure are on file in the Health Department.

[6] Editor's Note: The table and figure are on file in the Health Department.

[7] Editor's Note: The table and figure are on file in the Health Department.

(3) Example: What size copper water pipe, service and distribution will be required to serve a two story factory building having on each floor, back to back two toilet rooms each equipped with four flushometer closets, two flushometer pedestal urinals and four lavatories with hot and cold water?

(a) The highest fixture is 21 feet above the street main which is tapped with a two inch corporation cock at which point the minimum pressure is 55 psi

(b) In the building basement a two inch meter and three inch reduced pressure zone backflow preventer with a maximum pressure drop of nine psi are to be installed. The system is shown by the following diagram. To be determined are the pipe sizes for the service main, and the cold and the hot water distribution pipes.

(c) A tabular arrangement such as shown following should first be constructed. The steps to be followed in solving the problem are indicated by the table itself as they are in sequence, Columns 1 through 8 and lines a through 1.

(d) Recommended tabular arrangement for use in solving pipe sizing problems:

		Line		Lbs. Per square inch — psi
		a.	Minimum pressure available at main	55.00
		b.	Highest pressure required at a fixture (Table 860-177G)	15.00
		c.	Meter loss — 2" meter [Table 860-183C(1)]	11.00
	Service & Water	d.	Tap in main-loss 2" tap [Table 860-183C(1)]	1.29
	Distribution	e.	Static head loss 21 x .043 psi	9.03
	Piping	f.	Special fixture loss — backflow preventer	9.00
		g.	Special fixture loss — filter	0.00
		h.	Special fixture loss — other	0.00
		i.	Total overall losses and requirements, sum of lines b through h	45.32
		j.	Pressure available to overcome pipe friction, lines a minus sum of lines both	9.68

1	2	3	4	5	6	7	8
Pipe Section	Gal per minute through section (determine as in Section 1503.2)	Length of section (ft)	Trial pipe size (in)	Equivalent length of fittings & valves Table 1503.3B (ft)	Total equivalent length Col 3 & 5 100'	Friction loss, per 100' of trial size pipe Table 1503.3G	Friction loss in equivalent length Col 6 x Col 7 psi
1	2	3	4	5	6	7	8
AB	104	54	2 1/2	12.3	0.67	3.0	2.00
BC	102	8	2 1/2	8	0.16	2.8	0.45
CF	76	150	2 1/2	1.6	1.52	1.7	2.58
CD	76	13	2 1/2	8	0.21	1.7	0.36
DE	76	150	2 1/2	1.6	1.52	1.7	2.58

	k.	Total pipe friction losses (cold) 7.97 psi	7.97
	l.	Difference line j minus line k	1.71

1	2	3	4	5	6	7	8
	Hot Water Distribution Piping
AB'	104	54	2 1/2	12.8	0.67	3.1	2.00
B'C'	16	8	2	15.3	0.23	1.2	0.28
C'F'	9	150	2	1.3	1.51	0.8	1.21
C'D'	9	13	1 1/2	5	0.18	3.2	0.58
D'E'	9	150	1 1/2	1.0	1.51	3.2	4.84

	k.	Total pipe friction losses (hot) 8.85 psi	8.91
	l.	Difference line j minus line k	0.77

[1] Step 1.

[a] Column 1 — Divide the system into sections breaking at major changes in elevation or where branches lead to fixture groups. After point (B) (See sketch) separate consideration will be given to the hot and cold water piping in Column 1 of the tabular arrangement.

[b] Column 3 — According to the method given in § 860-183 determine the GPM of flow to be expected in each section of the system. These flows range from 28 to 107 GPM.

[2] Step 2.

[a] Line a — Enter the minimum pressure available at the main source of supply. This is 55 psi.

[b] Line b — Determine from Table 860-177G the highest pressure required for the fixtures on the system. Which is 15 psi to operate a flushometer valve.

[c] Line c — Select from Table 860-183C(1) the pressure loss for the meter size given or assumed. The total water flow from the main through the service as determined in Step 1 will serve to aid in the meter selected.

[d] Line d — Select from Table 860-183C(3) and enter the pressure loss for the tap size given or assumed.

[e] Line e — Determine the difference in elevation between the main or source of supply and the highest fixture on the system and multiply this figure, expressed in feet, by 0.43 psi. Enter the resulting psi product on Line e.

[f] Line f, g, h — The pressure losses through filters, backflow preventers or other special fixtures must be obtained from the manufacturer or estimated and entered on these lines.

[3] Step 3. Line i — The sum of (line b through h) the pressure requirements and losses which affect the overall systems is entered on this line.

[4] Step 4. Line J — Subtract line i from line a. This gives the pressure which remains available for overcoming friction losses in the system. This figure is a guide to the pipe size which is chosen for each section as the total friction losses through all the sections should not exceed this value.

[5] Step 5. Column 3 — Enter the length of each section.

[6] Step 6. Column 4 — Select a trial pipe size. A rule of thumb is that size will become progressively smaller as the system extends farther from the main or source of supply.

[7] Step 7. Column 5 — Select from Table 860-183C(2) the equivalent lengths for the trial pipe size of fittings and valves on the section. Enter the sum for each section in Column 5. (The number of fittings to be used in the installation of this piping must be an engineering estimate)

[8] Step 8. Column 6 — Add the figures from Column 3 and Column 5, and enter in Column 6. Express the sum in 100's or feet.

[9] Step 9. Column 7 — Select from Table 860-183C(7) the friction loss per 100 feet of pipe for the GPM flow in a section (column 2) and the trial pipe size (column 4).

[10] Step 10. Column 8 — Multiply the figures in Columns 6 and 7 for each section and enter in Column 8.

[11] Step 11. Line k — Enter the sum of the values in Column 8.

[12] Step 12. Line l — Subtract line k from line j.

[13] The result should always be a positive or plus figure. If it is not, it is necessary to repeat the operation utilizing Columns 4, 5, 7 and 8 until a balance or near balance is obtained. If the difference between lines j and k is positive and large, it is an indication that the pipe sizes are too large and may, therefore, be reduced thus saving materials. In such a case the operations utilizing Columns 4, 5, 7 and 8 should again be repeated.

[14] Answer. The final figures entered in Column 4 become the design pipe size for the respective sections. Repeating this operation a second time using the same sketch but considering the demand for hot water, it is possible to size the hot water distribution piping. This has been worked up as a part of the overall problem in the tabular arrangement used for sizing the service and cold water distribution piping. It should be noted that consideration must be given the pressure losses from the street main to the water heater (section AB) determining the hot water pipe sizes.