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896 CHAPTER SO 2946 Guide. negligible. Due to the fact that the no sun period includes the night period when little or no hot water is ued, an available storage, of 50' per cent of the average daily usage is considered adequate. Since about 25 per. cent of stored hot water cannot be drawn out of a storage tank before the incoming cold water reduces the temperature of ail of the water in the tank to an unsatisfactory point for usage, the equation for calculating the storage capacity of the tank becomes: where S Q X 0.50 0.75 = 0.666(2 (4) ~ storage capacity of tank, gallons. Q = average daily usage, gallons. Thus for a family of four persons using an average of 40 gal of hot water per person per day the size of the tank would be 4 persons x 40 gal x 0.666 or 106 gal, and the nearest standard size of tank to this theoretical capacity would be used. The tank should be well insulated to prevent undue loss of heat during the 16-hour period when the coil is inoperative, Fig. 5. Solar Heater Tank Connections . Fig. 6. Solar Heating Coil Inclination and it should be located as high as possible in the building (under the peak of the roof if such exists) so as to secure a maximum circulation head from the coil. The hot water supply to the hpuse, as shown in Fig.. 5, is located at the top of the tank, which serves to vent the air from the tank ' through the hot water faucets as fast as it accumulates. The coil should be of the return-bend type, square or slightly rec- ' tangular in form, and should have the pipes running east and west, with the coil on the south side of the building where it can receive the full sun effect' all day long without shadows from the building itself or from adjacent obstructions such as trees or other structures. The coil should be placed as low as possible in relation to the storage tank level, such as on ' a porch roof, the roof of a one-story extension or, if necessary, even on the ground. Both the coil and the circulation lines should be designed to facilitate the circulation flow as much as possible using long radius copper fittings or recessed galvanized iron fittings to match the materials of the coil, circulation lines and tank. The coil should be inclined as shown in Fig., 6 so that the north 'end is raised above the south end to secure an angle with the horizontal of about 53 deg. This will result in the inlet Hot Water Supply 897 end of the coil being on the south side (or bottom) and the outlet end being on the north side (or top). This will satisfy conditions along the 30 deg N latitude which includes the portions of Florida and Southern California where these heaters are most frequently used. The hot box is usually constructed of wood on the four sides and bottom, and is insulated. Over the top of the box glass sash are placed and the box should be constructed as near air-tight as possible. The interior surfaces should be painted white to reflect the heat while the coil should be' painted black to absorb the heat. . The box need not be deeper than necessary to house the coil and to protect it from the weather. The addition of a light gage copper plate on the bottom of the box to which the pipe of. the coif is soldered, for good metallic contact, will add Table 4. Suggested Solar Heater Design Data1 B*bht> on Rats or 30 Gal I Based or Rate or 40 Gal psb Day fbb Person jj feb Dat fbb Pbbsor Ho. of Occupants in Residence......... 1 2 3 4 5 6 7 81 1 2 3 4 5 6 . 7 8 Hot Water Used at Night, gal per 15 15 15 15 15 15 15 15 20 20 20 20 20 20 20 20 Hot Water Used at Night, gal total__ 15 30 45 60 75 90 105 120 20 40 60 80 100 120 140 160 RetainedIn Tank, 25 per cent, gpL.__ 4 8 11 15 19 23 27 30 6 10 15 20 25 30 35 40 Tank Capacity Required, gal....... . 20 40 59 75 94 113 130 150 25 50 75 100 125 150 175 200 Hot Water Used During Day, gal___ 15 . 30 45 60 75 90 105 120 20 40 60 80 100 120 140 160 Total Water to be Heated: 35 70 104 135 169 203 235 270 45 90 135 180 225 270 315 360 Gal per hour......................... ........ 4.5 9 13 17 21 26 29 34 6 12 17 23 28 34 39 45 Copper Coil Required: 25 50 75 100 121 145 168 192 32 64 96 128 160 192 224 256 Equivalent length 1 in. eoQ. ft....... 100 200 300 400 484 580 664 768 128 256 384 512 640 768 896 1024 Box Sise: 25 50 75 100 121 145 168 192 32 64 96 128 160 192 224 256 ns4 6 7 8 ' 9 10 10 11 A 6 8 S 1C 11 12 12 6 8 11 12J> 13.5 14.5 16.5 8 10 12 14 16 18 IS 21 a Sun Effect and the Design of Solar Heaters, by H. L. Alt (A.S.H.V.E. Transactions, VoI. 41, 1935, p. 131). to the amount of heat received by the coil due to the fact that this plate will receive all of the sun rays which fail to directly strike the coil. The heat from this source is transmitted to the coil through the plate instead of by heating the air surrounding the coil and from which only part of the heat enters the coil, the balance being transmitted through the glass sash: Design data given in Table 4 may be used with some judgment in selecting the size of-solar heater coil and box for a particular application. These data are based on consumptions of 30 and 40 gal of hot water per day per person. FRICTION LOSS IN WATER SUPPLY PIPING Fig. 7, showing friction loss in fairly rough pipe, has been reproduced from Fig. 4 of Building Materials and Structures Report BMS 79, Water Distributing Systems for Buildings, by Roy B. Hunter, National Bureau of Standards. ' For friction loss in tubing, as well as in smooth and rough pipe the reader is referred to Figs. 2, 3 and 5 in. the same publication.