Document LJVb875bMrko3BQ5j66MvvOdg

818 CHAPTER 75 1962 Guide And Data Book heated per day, and the maximum amount which will be used in any one hour, as well as the duration of the peak load. In cases where the requirements for hot water are reason ably uniform, as in residences, apartment buildings, hotels, and the like, smaller storage capacity is required than in the case of factories, schools, and office buildings, where practi cally the entire day's usage of hot water occurs during a very short period. Correspondingly, the heating capacity must be proportionately greater with uniform usage of hot water than with intermittent usage where adequate storage be provided to carry over the momentary peak load. With inter mittent usage there may be several hours between prak de mands during which the water in the storage tank mn be brought up to temperature. As a general rule, it is desirable to have a large storage capacity in order that the Halting capacity, and consequently the size of the heater, or the load on the heating boiler, may be as small as possible. In estimating the hot water which ran be drawn from a storage tank, it should be borne in mind that only about 70 percent of the volume of the tank is available, sinra, by tbe time this quantity has been drawn off, the incoming cold water has cooled the remainder down to a point where it ran no longer be considered hot water. Where steam from the heating boiler is used to heat do mestic hot water, the computed load on the boiler should be increased by 4 sq ft EDR (equivalent direct radiation) for every gallon of water per hour heated through a 100 deg rise. The actual requirement is (100 X 8^3)/240 = 3.48 sq ft per gal heated 100 deg. The value of 4 allows for transmission losses. There are two methods in common use for estimating the hot water requirements of a building: (1) by the number of people, and (2) by the number of plumbing fixtures in stalled. Where the number of people to be served can be rea sonably estimated, the data in Table 11 may be used. Example J: Determine the heater size and storage tank ranacity tor a residence housing five people. Solution: From Table 11, 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 = 285 gal. The heater should have a storage capacity of 200 X 1/5 = 40 gal. and a heating capacity of 200 X 1/7 = 285 gal per hr. The conditions given in Example 3 may be cited as aver age. It is possible to vary the storage and heating capacity by increasing and decreasing one over the other. Such a condi tion is illustrated in Example 4. Example 4: Determine the required heater capacity for an a^rtment homsu^aX) people, if the storage tank has a eapac ity of 1000 gal. What heater capacity'will be required if the storage tank is changed to 2500 gal capacity? Solution: Assume an apartment house housing 200 people Fran the data m Table 11: Daily requirements = 200 X 40 s 8000 gal. Maximum hours demand - 8000 X 1/7 = luo n1 2Txum^4smload " 4 Wttter required for *** pS a ?000-f?L5tr^E.tank is used, hot water available from 0 iiT 7^' Water k* heated in 4 hr - . 7W ~ 3550 8*1- Heating capacity per hour -- 3880/4 = o'.* '""-e*! tunk, a 2500-g.l tank had been in- (STx07TO/<TM ',P",ty Per hoUr w<n,ld * - Table 12 may be used to determine tbe size of water heat ing 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 19. The heater or corl should have a water heating capacity equal to this prob- able maximum demand. The storage tank should have capacity equal to the probable maximum demand multiotJl by the storage capacity factor in line 20. Example s\5 illustrate tbe procedure. Example 6: Determination of heater and storage tank ^ for an apartment building from number of fixtures. 80 GO lavatories.... 30 bathtubs........ 30 showers......... 60 kitchen sinks. 15 laundry tubs. X 2 = 120 gaj per k X 20 - 600 gal per hr X 75 - 2250 gal per hr X 10 - 600 gal per hr X 20 - 300 gal per hr Possible maximum demand............. Probable maximum demand........... ,,. Heater or coil capacity.................... Storage tank capacity....................... = 3870 gal per hr -- 3870 X 0 30 " n61 gal per hr = 1161 gal per hr =. nei x 1.2S = 1450 gal Although, in private dwellings a water temperature of 140 F is reasonable for dishwashing, in public places sanitation regulations make 180 F water mandatory in the rinsing cycle. Thus the hot water requirements for food service establish ments present special problems, due to the need for two water temperatures. The lower temperature water is dis. tributed for.general use, but the 180 F water.should be con fined to the equipment requiring ii, and should be obtained by boosting the temperature at that point. It would be danger ous to distribute 180 F water for general use. The U. S. Public Health Service, the National Sanitation Foundation, and other health and .sanitation organizations have formulated rules and standards of cleanliness for com mercial food service establishments. Certain of these rules as sume that the dishes in public eating places are sufficiently free of bacteria. The National Sanitation Foundation h* published standards for the design of dishwashing inar.h?na and water heaters used by restaurants. In a restaurant, bacteria kill is usually achieved by exposing the washed dish to a rinse of 180 F water for several seconds. In addition, an ample supply of general purpose hot water, usually 140-150 F, is required for the wash cycle of dishwash ers,.as well as for persons! use, pot washing, general cleaning and other restaurant hmw In order to correctly size a water heating system it is neces sary to determine: 1. Types and sizes of dishwashers used. 2. Required quantity of general purpose hot water (manu facturers' data should be consulted to determine the '*>*! fill requirements of the wash tanks). 3. Duration of peak hot water dTn*nri period. 4. Inlet water temperature. 5. Type and capacity of existing water heating system. 6. Type of water heating system desired. The American Gas Association has published a recom mended procedure* for sizing gas-fired water heaters for res taurants. This procedure is discussed in the following para graphs. Table 13 is used to size the required heater or heaters after allowance has been made for the quantity of hot water that may be withdrawn from the storage fomk each hour. The gen eral, purpose-and 180 F water requirements are determined from Tables 14 and 15. To determine tbe quantity, in gallons per hour, of usable hot water from storage, the duration, in hours, of consecu- Table 13.... Gas Input Requirements for Heating Water* Twpvatot Cm, Deg F .0 * 60 70 SO 90 100 no Gas input Required, in Thousands of Bis per Hour IS12 18 21 24 27 30 33 24 30 36 42 48 54 60 66 36 45 54 63 72 81 90 99 100 48 60 72 84 96 108 120 132 60 75 90 105 120 135 150 ' 165 72 90 108 126 144 162 180 198 84` 105 126 147 168 189 210 231 200 96 120 144 168 192 216 240 264 108 .. 135 162 189 216 243 270 297 120 150 180 210 240 270 300 330 275 132 165 198 231 264 297 330 363 300 144 180 216 252 288 324 360 396 325 156 195 234 273 312 351 390 429 350 168 210 252 294 336 378 420 462 375 180 225 270 315 360 405 450 495 400 192 240 288 336 384 432 480 528 425 204 255 306 357 408 459 510 561 450 216 270 324 378 432 486 540 594 475 228 285 342 399 456 513 570 627 500 240 300 360. 420 480 540 600 660 525 252 315 378 441 504 567 630 693 550 . 264 330 396 462 528 594 660 726 575 276 345 414 483 552 621 690 759 600 . .288. 360 . .432 504 676 648 720 792 650 312 390 468 1 546 624 702 780 858 700 336 420 504 588 672 756 840 924 750 360 450 540 630 720 810 900 990 800 384 480 576 672 768 864 960 1056 850 900 950 1000 408 510 612 714 816 918 1020 1122 432 540 648 756 864 972 1080 1188 456 570 684 798 912 1026 1140 1254 480 600 720 840 960 1080 1200 1320 . Values extracted from Reference 1. * 8opply water piTiini --I to be SO pais. , 120 36 72 108 144 180 216 252 288 324 360 396 432 468 504 540 576 612 648 684 720 756 792 828 - 864 936 1008 1080 1152 1224 1296 1368 1440 130 39 78 117 156 195 234 273 312 351 390 429 468 507 546 585 624 663 702 741 780 819 858 897 936 1014 1092 1170 1248 1326 1404 1482 1560 140 42 84 126 168 210 252 294 336 378 420 482 504 546 588 630 672 714 756 798 840 882 924 966 1008 1092 1176 1260 1344 1428 1512 1698 1680 Table 14....Rinse Water (180 F) Requirements for Dishwashing Machines* Type and Six* of Oithwo.Aer Row Rofe, CP Hot Water taqwrraaaft, gallons par boar at 180 F Heaters With no Infernal Storogeb Heaters With Infernal Storage to Meet gpm Row Demand* Door type, 16 x 16 in. rack.............. ............................. undercounter type......... .......................... Conveyor type single tank............................................ multiple tank (dishes fiat)................. multiple tank (dishes inclined)......... Silver washera.................................................................. Utensil washer*................................................................ Make-up water requirements....... ............................ Value* extracted from Reference S. * FVrc priiiiuu at daliwmabera b emtimod to be SO pals- * Baaad oo tbe spm Sow rata. .... * Baaed oo dishwasher gppatfca at 100 percent of mechsrural rapacity. 6.94 8.67 10.4 5 6.94 5.78 4.62 7 8 2.31 416 520 - 624 300 416 347 277 420 480 139 69 87 104 70 416 347 277 45 75 139