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962 CHAPTER 50 1949-Guide SOLAR WATER HEATERS Solar heaters utilize, the energy of the sun for heating hot water. The successful operation of such heaters requires the availability of sunshine practically every day in the year, which has limited their use to Florida and the southern portions of California. When supplemented with some other means of gas, coal, or oil water heating, solar heaters may be used in climates where sunshine may be more or less intermittent. They have been used in summer homes as far .north as Chicago. When properly installed and proportioned, solar water heaters render satisfactory, service especially in climates where the outside temperatures are high and ex tremely hot water is not necessarily desirable. Such installations consist essentially of a storage tank, heating coil, and hot box. The coil is installed in the hot box'and is arranged to circulate water to'and from the storage tank. The advantage in the use of this type of heater is the fact that it requires no fuel. The same materials should be used for the coil,- circula tion, lines, and tank. A, copper coil is more efficient in absorbing heat in the box; but galvanized iron of steel may be substituted, depending on the local water conditions, cost, and other considerations. The'storage tank must be able to store sufficient heated water for the . night period of about 16 hr when the coil is'not functioning or is; operating under such-poor sun conditions as to make its heating effect negligible. Due to the fact that the no sun period includes the night period when little or no hot water is used; 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 all of the water in the tank to an unsatisfactory point for usage, the equation for calculating the storage capacity of the -tank becomes: v . , .. . .. , Q X 0.50 =a666Q (2) where ' ; K' 5 = storage capacity of tank, gallons. - Q = average daily usage, gallpus- Water Services 963 Thus for a family of. four persons usihg;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, 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 house, as shown.in Fig. 11, 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 rectangular in form, and should have the. pipes running east and west, with the coil on Table 8. Suggested Solar Heater Design Data* Design Item Based on Rate on 30 Gal FEB DAT PEB PSBSON Based on Rats of 40 Gal peb Dat peb Pebson No- of Oceapanta ln Residence^___ 1 2 . .3 4 6 6 7 .8 . 1 ': 2 3 4 5 6 7 8 HopteWrsoante---r Used--a--t Ni--ght, g--al p_e.r 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 m 120 V 20 40 60 80 100 120 140 .160 Retained in Tank. 25 per cent, gal-- 4 8 11 15 19 23 27 .80 6 10 ' 15 20 25 SO 35 40 Tank Capacity Required, gaL--;___ ; 20 40 - 59 75 - 94 113 130 150 25 50 75 IM 125 150 175 .200 Hot Water Used During Day, gal--. 15 30 45 60 75 90 105 120 f 20 40 60 80 100 120 140 160 Total Water to be Heated: Gal per 6 hr period____ Gal per hour.--. _ 35 70 104 135 169 203 235 .270 45 90 135 160 225 270 315 360 -- 15 9 '13 -17 21 26 29 : 34 6 12 17 23 28 34 39 46 Copper Co2 Required: ' Surface area, oq ft __________ --' 25 50 75 200 W 145 268 192 32 64 96 123 160 192 224 256 Equivalent length 1 in. coll, ft.--,. 100 200 300 400 484 580 664 768 128 256 384 612 640 768 896 1024 Box Sixe: Area, eq ft_ Width, ft. Length, ft. . _ -- 25 4 6 50 .86 > 75 7 11 100 .8 12.5 121 9 13.5 14in5 14.5 168 10 . m 11 16.5 17.5 82 4 .8 '64 ; 6 10 96 128 160 192 224 256 8 9 10 11 12 12 12 14 16 18 19 . 21 8 Sun Effect and the Design of Solar Heaters, by H. L. Alt (A.S.H.V.E. Transactions, Vol. 41, 1935, p-131). 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 ob structions 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 circula tion 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: 12 so that the north end is raised above the south end to secure an angle with the hori zontal of about 53 deg. This will result in the inlet 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,