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528 CHAPTER 37 1959 Guide utilization over the heating season can be calculated from data. They show a variation from approximately 72 to 88 percent depending upon the type and size of system. Laboratory tests on a gas conversion burner in a heating boiler operated with on and off cycles gave about 72 percent efficiency* Other tests on coal-fired room heaters indicated,' for the hparing season, efficiencies of 65 to 75 percent, when the heat from the flue pipe was included.* A survey of. 30 residences in one locality showed a variation of 45 to 75 per cent in utilization efficiency, depending upon the condition of tiie equipment and the fuel used* Experience at the University of Illinois was used in es tablishing overall efficiencies for a tabulation of the compara tive costs of heating the same building with various fuels to be found in a publication of the Small Homes Council.'- - The effitwentyp of utilization - over the heating season shown in Table 1 are suggested as a guide. Considerable Table 1 .... Efficiency of Utilization Over the Heating Season Type of Fwel-fiwmag (Av? Efficiency, Percent Gas, designed unit......................................... Gas, conversion unit..................................... Oil, designed unit........................................... Oil, conversion unit....................................... Bituminous coal, hand-fired with controls. Bituminous coal, band-fired without con trols............................................................... Bituminous coal, stoker-fired...................... Anthracite, hana-fired with controls......... Anthracite, hand-fired without controls... Anthracite, stoker-fired................................ Coke, hand-fired with controls__ Coke, hand-fired without controls. Direct electric heating................. 76-80 60-80 65-80 60-80 60-65 40-60 60-70 60-80 50-65 60-80 60-80 50-65 100 judgment may have to be exercised in selection of appro priate Values for any given case of fuel consumption calcu lations. CALCULATED HEAT LOSS METHOD The quantity of fuel or energy required for heating may be found by the Calculated Heat Loss Method from the equa tion *-Wc where F = quantity of fuel or energy required (in the units in which C is expressed). X m average heat requirement for the period under con sideration, Btu per hour. N * number of heating hours in estimate period (for. an Oct. 1-May 1 heating season, 212 days X 24 hr *=* 5088). B = efficiency of utilization of the fuel over the period, expressed as a decimal; not the efficiency at peak.or rated load condition. C " heating value of one unit of fuel or energy. The value of X is usually found from the equation X Hit ~ Q u-u (2) where H *= calculated heat loss including infiltration loss, Btu per hour, based on t, and U t average inside temperature maintained during heating period, Fahrenheit. L, TM average outside temperature through estimate period, Fahrenheit (for U. S. cities with an Oct. 1-May 1 heat ing season--see Table 2). U ** indoor design temperature, Fahrenheit (usually 70 F). (, -- outdoor design temperature, Fahrenheit (see Table 2). so that the value of F becomes Hit - ON Bit4 - U)C (3) The calculation of X, the average heat requirement, Btu per hour, over the period under consideration is given only approximately by Equation 2, when the value of H used is the calculated maximum load, or design heating load for the building, as computed by the methods outlined in Chapters 9,11, and 12. This value is commonly used since it is usually available from the boating system design calculations. This procedure will usually lead to values of X which are too high. In the first place, the design wind speed on which such cal culations are based is usually higher than the average wind speed for the period so that infiltration losses may be over estimated. In addition there will usually be many sources of heat not taken into account in the estimation of maximum heat demand which may actually contribute to the heating and thus may decrease the fuel or energy required for heat ing without necessarily affecting the maximum heat demand. The more important sources are solar radiation, people, lights, and equipment. Improved estimates of fuel requirements will result if H ran be recalculated so as to be more representative of average conditions over the heating period rather than the maximum conditions used in ma-rimnm heating load estimation. Further improvement may be obtained at the expense of more in volved calculations by making estimates of the average heat gains, and deducting these from the calculated heat losses. There is a practical limit to the refinement in calculations which should be attempted since there will always be some factors which are only approximately known. The weather, for example, very largely determines the heat losses, but will normally be described only approximately in terms of aver age values of a limited number of weather elements. Wind speed, and sunshine will not necessarily be distributed uni formly over periods of different outdoor temperatures. In ad dition there is a limit to the accuracy of prediction of the weather elements over the period of interest which is always in the future. For these and other reasons, including such unpredictable factors as the way in which windows and doors will be opened and closed, the determination of if or of X must always be in the nature of an estimate only. Values of the average outdoor temperature, U, are re quired for the calculation of X by means of Equation 2. Such values for the period October 1 to May 1 are given for U. S. cities in Table 2. The assumption of an Oct. 1-May I heating season is reasonably accurate in the well-populated New York-Chicago zone but heating may be required over a longer period for points as far north as Minneapolis, and over a shorter period south of Washington, D. C. Conse quently values taken from Table 2 may have to be adjusted (Text continued on p. 634.) Estimating Fuel Consumption for Space Heating 529 Table 2 .... Average Monthly, and Yearly vegreeDayifcH Giles in the-United States and Canada*- (Base 65 F) Stale Station Anniston.............. A Birmingham........A Montgomery...,. A Montgomery....... C Vor. No. of Avg. Soo- Winter Mr Aug. sapt. Tamp.6 52.3 51.8 58.9 56.4 0 0 17 0 (j 13 0 (1 0 000 000 000 Od. Nov. fee. ten. F*b. Mar. Apr. May June Yaetfy Total 118 438 614 614 485 381 12S 25 123 396 598 623 491 378 128 30 W 219 3/6 416 304 222 47 0 23 198 357 412 290 209 40 0 69 304 491 517 388 288 80 0 56 267 458 483 360 26b 66 0 0 2820 0 2780 0 1612 0 1529 0 2137 a 1954 Flagstaff............... A Phoenix................A Phoenix................ C Yuma....................A 35.9 59.5 57.7 62.5 49 78 243 0U0 000 000 586 876 1135 1231 1014 949 687 465 212 7525 22 223 400 474 309 196 74 0 (J 1698 13 182 360 425 275 176 62 0 (] 1492 0 105 259 318 167 88 14 0 0 951 BentonviUe............. 06/07-40/41 35 Fort Smith.......... A Little Rock..........A 1 1 38 216 516 810 879 716 519 247 86 7 4036 0 0 9 131 435 6SM 775 571 415 127 24 c 3188 0 0 10 no 405 654 719 543 401 122 18 0 2982 Calif.. - Eureka................. C Independence......... Los Angeles......... A Los Angeles......... C Needles................... Point Reyes........... Red Bluff............. A S&cramento......... A Sacramento......... C San Diego............A San Francisco___A San Francisco___C San Jose............... C 98/99-40/41 17/18-38/39 98/99-40/41 43 22 43 49.3 59.3 52.9 53.0 54.2 53.5 267 248 264 00 0 0 0 28 31 22 56 0 fl 17 0 (1 0 36U 336 263 000 0 0 22 0 0 17 11 7 24 144 136 101 189 177 110 7 11 26 335 411 508 552 465 493 432 375 282 4632 86 345 580 629 400 304 145 43 0 2532 216 512 778 799 619 477 267 120 IS 3834 87 200 301 378 305 273 185 121 66 2015 41 140 253 32S 244 212. 17* 63 19 1451 19 217 416 447 243 124 26 3 C 1495 282 317 425 467 406 437 413 415 363 4474 59 319 564 617 423 336 177 51 C 2546 98 357 595 642 428 345 222 103 7 2822 75 321 567 614 403 317 196 85 5 2600 52 147 255 317 247 223 151 97 43 1574 174 318 4X7 530 398 37i 32/ 264 164 3421 128 237 406 462 336 317 279 248 18C 3069 9/ 270 450 487 342 308 229 137 46 2410 Colo.. .. Denver................. A Denver................. C Durango.................. Grand Junction. .A Leadvilla................. Pueblo...................A 04/05-40/41 07/08-40/41 37 34 37.0 37.9 39.9 5 11 120 0 5 103 26 37 201 (1 l 36 280 332 509 0 0 74 425 771 1032 2125 924 843 385 711 1042 854 797 535 861 12U4 1271 1002 859 333 792 1132 1271 924 735 841 1139 1413 1470 1285 1245 383 771 1051 1104 865 775 525 286 65 6132 492 266 6t 5673 615 394 139 7143 402 145 23 5796 99(1 74(1 434 10678 456 203 27 5709 Conn... Hartford...............A New Haven......... A 0 14 101 384 699 1082 1178 1050 871 528 201 31 6139 0 18 93 363 663 1026 1113 1005 865 567 261 52 6026 D. C.. . Washington......... A Washington......... C 43.4 0 0 37 237 519 837 893 781 619 323 87 0 4333 0 0 32 231 510 831 884 770 606 314 80 0 4258 Fla....... Apalachicola....... C Jacksonville........ A Jacksonville........ C Key West............. A Key West............. C Miami.-................. A Miami................... C Pensacola............. C Tampa..................A 60.9 0 0 0 60.6 (J l 0 62.0 0 c 0 72.5 0 c 0 73.1 . c 0 0 (1 0 71.4 0 c 0 59.7 0 c 0 000 17 154 304 352 263 184 33 0 0 1307 16 148 m 331 247 161 23 t ( 1243 11 129 276 303 226 154 14 C C 1113 l (1 22 34 25 f C c ( 89 C C 12 V 24 1 C t ( 77 C 8 52 66 48 12 c c ( 178 c 5 4f 57 48 15 0 c ( 173 li 177 334 -383 275 2(E 45 t ( 1435 0 60 163 201 148 102 0 0 0 674 Ga........ Atlanta................. A Atlanta................. C Augusta............... A Macon................... A Savannah............. A Thomasville... 05/06-40/41 36 56.7 0 0 8 no 393 614 632 512 404 133 20 0 2826 (j ( 8 107 387 611 632 515 392 135 24 ( 2811 0 c 0 54 282 494 521 412 m 62 l ( 2238 0 c 0 6S 28C 481 497 391 275 62 C ( 2049 0 c 0 3i 225 412 424 33C m i ( 1710 0 0 2 48 208 361 359 299 178 52 5 1 1513 Idaho.. Boise.....................A Lewiston.............. A- Pocatello..............A 39.8 35.0 ft0 0 135 389 762 1054 1169 868 719 453 249 92 5890 0 ( 133 40( 747 961 106C 815 66c 40? 222 5483 0 0 283 487 873 1184 1333 1022 880 561 317 13b 6976 111..:... Chicago................ A Peoria...................A Springfield........... A Springfield........... C 35.1 37.3 37.7 39.8 0 0 90 (J 11 86 0 6 83 c c 66 350 765 1147 1243 1053 868 507 229 58 6310 339 759 1122 124C 1023 823 435 192 41 6087 315 722 1066 116f 95S 769 404 171 32 5693 259 666 ion 1116 907 713 35C 127 14 5225 * Di (or United State* aties from a pubUatioo of the United States Weather Bureau. Jfo4Uy Normal Ttmptrctvm, PneipiUticn and Dtfr* Dor*. ISM, are for the period 1931 to 1950 inclusive. Tboee United States cities tot which yean are fives is Column S are not listed is the above publication and the data are those which wen computed by the United States Weather Bureau in 1940 and 1947 in accordance with the requirements of the National Joint Committee on Weather Statistics.. Data for airport stations, A, aad dty stations, C, are both given wkr* available. * Data for Canadian cities were computed by the Meteorological Division, Department of Transport from normal monthly mean temperatures, adjusted for the sum mer months by a method described by H. C. 8. Thom, The Rational Relationship between Heating Degree Days and Temperature, Itentilf Weottar flraww Vnl. 83, No. 1, January 1951. * For period October to Anril. inclusive.