Document 0JMdn1yYr0ewokGv9kQZz9wRM

American Society of Heating and Ventilating Engineers Guide, 1937 Fig. 4. Typical Layout for Down-Feed System House Tankf ------------------------------------------------ ----------------------------------------------------- ------------------------- _z: 197 4* 255 5* 197 4" ,f t 8th. 4 W.C.-F. V. 2U.-F.V. 3 Lav. 215 4- 6W.C.-F.V. 4 Lav. 122 3"j 1 S. S. ^ 166 2" 7th. 4W.C.-F.V. 2U.-F.V. 3 Lav. 211 ^a`F V- 2 1 S.& . 4W.C.-F.V. 145 2 2U.-F.V. 6th. ^ 3 Lav. 196 2f 6WC.-F.V. 12Q t 1 S.S. . 117 2 '5th. ] ^ 4W.C.-F.V. 2U.-F.V. 3 Lav. 180 2" fW.C.-F.V. 4 Lav. 120 2" ias. 25 T 4th. 10 Lav. . 4 W. C. - F. v! 160 2 2U.-F.V. j 3 Lav. . 3W.C.-F.V. 119 2 1 Lav. , > is.a 11 f 3rd. 1S.S. 130 _ 2 4W.C.-F.V. 2U.-F.V. | 3 Lav. 90 2* 2-Lav. 8 " 2nd. 1S. S. 98 .. lj 2W.C.-F.V. 1U.-F.V. 1 Lav. 89 if 3W.C.-F.V. 1 Lav. 44 1st (1) .1 S. S. 45 1W.C.-F.V. (2) 4 i 1 S. S. (3) and, with this drop, the sizes according to the chart (Fig. 3) are 6 in., 5 in., and 4 in., reS5E3tlbely' 100^ the run !s reduced to 200 ft instead of 600 ft, the allowable drop will be------- 200------- = 2.7 lb per 100 ft. This gives 5 in., 4 in., and 3 in., respectively, for the flows of 400, 200, and 100 gpra. From Example 3 it is evident that, while the down-feed system possesses certain economies in size for the riser portion, it is quite likely to involve large distribution main sizes, especially when the tank is not elevated to a considerable degree. SIZING A PIPING SYSTEM . Example 4 Fig. 4 shows a typical layout with three risers extending eight stories and with the fixtures noted on each floor. First this will be solved for a down-feed arrange ment assuming that the level of the water in the house tank is 30 ft above the fixtures on the top floor, that the length of run from the tank to the farthest fixture is 200 ft, equiva lent length of fittings 100 ft, and the pressure required at the fixture is 7 lb. 654 Chapter 35--Water Supply Piping and Water Heating Table 5. Typical Calculation of Pipe Sizes on Down-Feed Riser with 1 Flush Valve Water-Closets and Urinals (Riser No. 1. Fig. 4) Floor of Bldg. 1st 4th 5th 0LL Fixtures on Floor 1 s. s. IS. s. 1 s. s. 10 Lav. 4 W. C. 2 U. 3 Lav. 4 W. C. 2 U. 3 Lav. Gpm PER Fixture 4 4 4 3 45 30 3 45 30 3 Maximum Gpm ON Floor Maximum Gpm ON Riser Probable Use (per cent) Probable Demand Riser Gpm Allowable Drop Lb per 100 Ft 4 4 100 4 30 4 8 100 8 30 4 12 92 11 30 30 42 58 25 30 180 60 9 249 291 40 117 30 180 60 9 249 540 27 145 30 4 W. C. 2 U. 3 Lav. 45 30 3 180 60 9 249 789 21 166 30 4 W. C. 2 U. 3 Lav. 45 30 3 180 GO 9 249 1038 19 197 2 Pipe Size In. % H % 1 2 2 2 4 The 30-ft head is equal to a static pressure of 0.43 X 30 or 12.9 lb per square inch and to maintain a pressure of 7 lb at the highest fixtures the drop allowable in pressure is 12.9 - 7.0 lb or 5.9 lb. As the total equivalent run is 300 ft, this is a drop per 100 ft of 1.97 lb, or practically 2 lb. Therefore, all risers and mains from the top floor back to the tank must be sized on the basis of a drop of 2 lb per 100 ft. Tables 5,6,7 and 8 show the schedule for Risers Nos. 1, 2 and 3 with the maximum possible flow taken from Table 1, the percentage of use at the peak taken from Fig. 1, and the maximum probable flow at the peak worked out for each portion of the riser, the riser sizes being taken from Table 2 as far as possible and from Fig. 3 where the amounts exceed the values given in this table; a drop of 30 lb per 100 ft is used except on the riser from the top floor back to the tank where 2 lb per 100 ft is the allowable limit. The reduction in pipe size which would occur if flush tank water-closets were used on the top floor and only 3 lb pressure used on the fixtures is given in Tables 9 and 10. This illustrates why flush tank closets so frequently are substituted on the uppermost floor when a house tank is the source of water pressure. If it is now assumed that Riser No. 1 is to be fed from the bottom and the minimum street pressure is 75 lb with the top fixture of the riser 80 ft above the main, the problem would be solved by determining the maximum rate of flow in each portion of the riser as shown in Table 11 and then finding the allowable drop which can be used per 100 ft. The 80 ft of riser height will use up 0.43 lb X 80 = 34.4 lb and the pressure at the top of the required 15 lb will make the total reduction 49.4 lb, leaving a balance of 25.6 lb which may be used up in friction. If the distance from the .street main to the bottom of the riser, which will be assumed to be the farthest one on the horizontal line, is 100 ft, and u the fittings are sufficient to add another 100 ft, as well as the 80 ft of vertical distance up the riser, the total equivalent run will be 280 ft, which will be taken as an even 300 ft. 655