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956 CHAPTER 50 1949 Guide gallon of water heated 100 F. The value of 4 allows for transmission losses, etc. . There are two ways in common use of estimating the hot water require ments of a building; first, by the number of people and second, by the num ber of plumbing fixtures, installed. Where the number of people to be served or can be reasonably estimated, the data in Table 5 may be used. Example S. From Table 5, a residence housing five people would have a daily requirement of 5 X 40 = 200 gal per day', and a maximum hourly demand of 200 X 1/7 = 28.5 gal. The heater should nave a.storage capacity of 200 X 1/5 =?= 40 gal and a heating capacity of 200 X 1/7 = 28.5 gal per hour. ; The conditions given in Example 2 may be cited as average. It is pos sible to vaiy the storage and heating capacity by increasing and decreasing one over the other. Such a condition is' illustrated in Example 3. Examples. Assume an apartment house housing 200 people. From the data in Table 5: Daily requirements = 200 X 40 = 8000 gal. Maximum hours demand = 8000 X 1/7 = 1140 gal. Duration of peak load = 4 hr. Water required for 4-hr peak = 4 X 1140 = 4560. If a 1000 gal storage tank is used, hot water available from the tank = 1000 X 6.75 = 750. Water to be heated in 4 hr = 4560 - 750 = 3710 gal. Heating capacity per hour = 3710/4 = 930 gal: . If instead of a 1000 gal tank, a 2500 gal tank had been installed, the required heating capacity per -hour wou.ld..be4--5-6-0--------(-2-5j0-0---X---0--.-7-5--) = b/l gal. Table 6 may be used to determine the size of water heating equipment from the number of fixtures. To obtain the probable maximum demand multiply the total quantity for the fixtures by the Demand Factor in line 11. The heater or coil should have a water heating capacity equal to this probable maximum demand. The storage tank should have a capacity equal to the probable maximum demand multiplied by the storage capacity factor in line 12. Example 4 will illustrate the procedure. Example 4. Determination of heater and storage tank size for an apartment building from number of fixtures. 60 lavatories.................. " .\ X 2 = 120 gal per hour 30 bath tubs.......................................... X 20 = 600 gal per hour .30 showers....................... .X 75 - 2250 gal per hour ' 60 kitchen sinks.r.. X 10 " 600 gal per hour 15 laundry tubal....... ...................... X 20 - 300 gal per hour ' Possible maximum'demand............ .. ` 3870 gal per hour Probable maximum demand.......... .... '== 3870 X -0.30 ** 1161 gal per hour Heater or coil capacity: -- ---- --..... = 1161 gal per hour Storage, tank capacity.........'.....C... = 1161 X 1.25 = 1450 gal METHODS OF HEATING WATER .Hot water may be'heated,either by the direct combustion of fuel, by an intermediate carrier such as steam or hot water, or by . electrically heated surfaces. The simplest, method is to have .the. fire onrone side of a metal barrier and water on the other. In such, a method if the :water surfaces of heat transfer are small, and if the water, carries a heavy proportion of precipitable salts, the water passages may soon clog and then bum out. A familiar example of such trouble is the water back of the firebox in the kitchen stove or the pipe coil inserted into the firebox of a warm air. furnace .Water Services 957 or small boiler. The critical water temperature, at which the, lime, mag nesia, etc., collect on hot surfaces, varies with the character.and proportions of the solids, but generally such deposits are not a serious trouble with water temperatures lower than 140 F. Coal-burning, direct-fired water heaters may be constructed of cored cast-iron sections or of steel. In some cases the external appearance of the cast-iron sections is the same as in heating boilers, but internally the cpres are changed to enable the sections to withstand; the city water pres sure. In small capacity water heaters, efficiency is not considered so important as low first cost and ability to maintain a fire at a low. rate of combustion, mid consequently such heaters are generally built with a dry section or fire-brick, lining at the base of the fire-pot to prevent too much Chilling of the fuel. While mud and scale will eventually clog the water ways of any direct-fired heater, increased life may be obtained by pro- Table 6. Hot Water Demand per Fixture for Various Ttpes of Buildings Gallons of waler per hour per fixture, calculated at a final temperature of 140F Apart* KBNT Hocsb Club Gym Honasium PITAL Hotel Indus* TRIAL Plant OlTICE Private Build* Rssi- School IKG ' DKNCB Y3L C.A. 1. Basins, private hvatcry__ 2 2. Basin?, public lavatory____ 4 i. Bathtubs- ' 20 A niiihumfttwT* 15 5. Foot basins___ A TTtfi4>>n ninlr 3 10 7. Laundry;etationary tube__ 20 8. Paotrycnk- 5 9. Shawm------------- 75. 10. Slop ask. 20 11. TVmnH fnfttw___ 0.30 12. Storage capacity factor*__ 1.25 22 66 20 30 50-150 TM,, 3 12 20 28.. 10 -- 150 225 20 0^0 . 0.40 , 0.90 1.00 2242 6 S 12 6 20 20 30 ' -- 50-150 50-200 20-100 -- 3 3 12 20 .' 20 20 28 ..28 -- -- 10 10 -- .75 75 225 -- 20 30 20 . 15 0.25 0.25 a40 0.30 0.60 0.S0 1.00 2.00 2 20 15 3 10 20 5 75., 150.30 0.70 22 15 8 -- 30 20-100 20-100 3 12 10 20 . .... 28 10 10 225 ,. 225 20' 20 0.40 0.40 1.00 1.00 * Ratio of storage.tank capacity to probable mRy-imnm demand per hour.' viding a three-way, cock in the return line between the heater and the bottom of the storage tank, so that water can be blown through the heater or the'tank separately at full line, pressure to clean out loose sediment. Clean-oiit openings in the bottom of the heater are advantageous if used by operators of water heaters for periodic cleaning out of sediment'. Oil-burning, direct-fired water heaters usually are of steel and operate with higher flame temperature and better efficiency than commensurate sized coal-burning heaters. They have the same tendency as coal boilers to to lime up, and the water passages should be large in cross-section and.accessible for periodic cleaning. : Gas-burning, direct-fired water heaters may be;of the instantaneous or storage type. Instantaneous heaters are generally constructed of spiral water tubes of copper around which the products of combustion circulate upward, from high capacity burners. Storagertype heaters may include in one unit, an insulated storage tank, a conabusion chamber, flues, burner