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Heating Ventilating Air Conditioning Guide 1938 Table 6. Typical Calculation of Pipe Sizes on Down-Feed Riser with Flush Valve Water-Closets and Urinals (Riser No. S. Fig. 4)' Floor of Bldg. 1st 2nd - Fixtures on Floor 1 W. C. 2 W. C. 1 U. - 1 Lav. Gfm PER Fixture 45 Maximum Gpm on Floor 45 Maximum Gpm ON Riser 45 Probable Use per CENT) Probable Demand Riser Gfm 100 45 Allowable Drop Lb per 100 Ft 30 45 90 30 30 33 123 168 58 98 30 3rd 4 W. C. 2 U. 3 Lav. 45 30 3 180 60 9 249 417 31 130 30 4th 4 W. C. 2 U. 3 Lav. 45 30 3 180 60 9 249 666 24 160 30 5th 6 W. C. 4 Lav. 45 3 270 12 282 948 19 180 30 6th 6 W. C. 4 Lav. 45 3 270 12 282 1230 16 196 30 7th 6 W. C. 4 Lav. 45 3 270 12 282 1512 14 211 30 8th 6W.C. 4 Lav. 45 3 270 12 282 1794 12 215 2 Pipe Size In. 1H IX 2 2 2 2X 2X 4 Then the allowable drop per 100 ft will be --= 8.5 lb and the sizes shown in Fig. 5 are based on this amount of drop. Of course the other risers will have the same maximum flows at the bottom as they -formerly had at the top, namely 215 and 122 gal, respectively, for Risers Nos. 2 and 3.; Combining these maximum flows in the same man ner as pursued in the down-feed system it is seen that the maximum flow between Riser No. 2 and Riser No. 3 is 255 gpm, and between Riser No. 3 and the street main, 282 gpm which at a drop of 8.5 lb gives the main sizes indicated. It will be noted that in determin ing the maximum flow in an up-feed riser it is necessary to begin at the top floor and work-down instead of beginning at the bottom floor and working up as was done in the down-feed sizing. - SIZING UP-FEED AND DOWN-FEED HOT WATER SYSTEMS Hot water supply systems, when of the circulating type, have a few differences to be considered although the same general principles of sizing apply to these lines as to the cold water lines. Owing to .the fact that there are no flush valves on the hot water piping and also because many plumbing fixtures have no hot water connections, the sizes of the hot water piping in general will be considerably less than the cold water piping in the same building. On the other hand it is almost invariably 794 Chapter 43. Water Supply Piping and Water Heating Table 7. Typical Calculation of Pipe Sizes on Down-Feed Riser with Flush Valve Water-Closets and Urinals (Riser No. S. Fig. 4) Floor op Bldg. Fixtures on Floor 1st 2nd 1 S. S. 3 W. C. 1 Lav. 3rd 2 Lav. 4th 3 W. C. 1 Lav. 1 S. S. 5th . 6th 7th 8th 1 S. S. 1 S. S. 1 S. S. 1 S. S. Gpm PER Fixture 4 45 3 3 45 3 4 4. 4 4/ 4 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 30 135 3 138 142 63 89 30 6 148 61 90 30 135 3 4 142 290 41 119 30 4 294 . 41 120 30 4 298 40 120 30 4 302 40 121 30 4 306 40 122 2- Pipe Size In. X. IX ix 2 2 2 2 3 required that a gravity circulation be kept up in such hot water lines and this often has a considerable influence on the size. There'are three methods of arranging circulation lines, as follows: 1. By using the,plain up-feed with a returncarried back from the top of.the riser and paralleling it. ' ' ." ' ` 2. By carrying a supply riser up in one location thus supplying fixtures on up-feed, then-crossing over at the top and coming down past, another collection of fixtures and supplying these by a down-feed. 3. By carrying all of the water to the top of the building and dropping risers wherever needed, feeding all hot water on a down-feed system. .. Table 8." Size of Distribution Main for Down-Feed Systems (See Fig. 4)' Riser No. 1 2 3 Maximum ` Gpm Riser 1038 1794 306 Maximum Gpm Main 1038 2832 3138 ' Probable Use (per cent) 18 9 9 1 Probable Gpm 187 255 282 . Allowable Drop Lb per 100 Ft ' Size op ' Main In. 24 24 25 In the first instance the up-feed riser may be sized for the same pressure, drop as used for the cold water riser and, from the top of the riser just below the top fixture connection, a return circulation line may be carried back to the main return line in the basement and connected through a check valve, set on a 45-deg angle, and a gate valve; these return circu lation lines should never be less than % in., and on the farther half of the risers, not less than 1 in. to favor circulation in the far end. Typical top and bottom connections for such risers are shown in Fig.; 6. 795