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170 CHAPTER 12 1962 Guide And Data Book these data. They show a variation from approximately 70 to 90 percent depending upon the type and sire of system, laboratory tests on a gas conversion burner in a hw.tmg boifer operated with on and off cycles gave about 72 percent efficiency.* Other tests on coal-fired room heaters indicated, for the heating 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 utilisation efficiency, depending upon the condition of the equipment and the fuel used.* Experience at the University of Illinois was uqed 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 efficiencies of utilization over the halting ymsop shown in Table 1 are suggested as a guide. Considerable Table 1 .... Efficiency of Utilization Over the Heating Season (Residential Systems) Type of Fvet-Burahtg Uait Oil, dfsiimpH unit Oil, conversion unit.......... Bituminous coal, hand-fired with controls.. Anthracite, hand-fired with rontmla Efficiency, Percent 70-80 65-80 50-65 50-70 60-80 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 XN ` EC (1) where F " quantity of fuel or energy required Cm the units in which C is expressed). X -- average heat requirement for the period under con sideration, Btu per hour. N -- number of beating hours in estimate period (for an Oct. 1-May 1 heating season, 212 days X 24 hr = 5088). E efficiency of utilisation 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 tha equation Hit - Q 4-C (2) where H ~ calculated heat lose including infiltration loss, Btu per hour, baaed on t, and U- t = average inside temperature maintained during period, Fahrenheit. < = average outside temperature through estimate period, Fahrenheit (for U. S. cities with an Oct. 1 -May 1 heat- mg season--see Table 2). Id = indoor design temperature, Fahrenheit (usually 70 F) U -- outdoor design temperature, Fahrenheit (see Table 1 Chapter 25 of the 1961 Guide And Data Boos). ' so that the value of F becomes Hit - t,)N E{U - t.)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 23,24, and 25 of the 1961 Guide And Data Book. This value is commonly used since it is usually available from the hating 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 calculations are based is usually higher than the average wind speed for the period so that in filtration losses may be overestimated. 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 heating without necessarily affecting the maximum heat demand. The more importantsources are solar radiation, people, lights, and equipment. Improved estimates of fuel requirements will result if H can be recalculated so as to be more representative of avenge conditions over the heating period rather than the maximum conditions used in maTinuirn 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 |nss^ There is a practical limit to the refinement in calculations which should be attempted since there will alw&yB be some factors which are only approximately known. The weather, for example, very largely determines the heat loses, 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 dosed, the determination of H 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 I are given for U. S. cities in Table 2. The assumption of an Oct. 1-May 1 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 appropriately. When data on degree days are available these may be used in the calculation of average outdoor tempera ture for use in Equation 2 or 3. (See definition of degree day, Chapter 63 of the 1961 Guide And Data Book.) It may be noted that a portion of Equation 3, (t--t^N will, when divided by 24, correspond exactly to the degree days for the period, provided that {=65 F, the nqn>1 basis for calculating degree days (see discussion of degree days in Estimating Fuel Consumption or Energy for Space Heating 171 Table 2 .... Average Monthly and Yearly Degree Days for Gties in the United States and Canada*-b- (Base 65 F) Slots Staffed Ala.---- Anniston..............A Birmingham........ A Mobile.. ............. A Mobile..................C Montgomery....... A Montgomery........C Yam No- of Arg. Soo- Winter lamp.* Mr ** Sepf. 52.3 51.8 58.9 56.4 0 0 17 0 0 13 000 000 0 0. 0 0u0 Ocf. Nov. Dec. Jon. Feb. Mar. Apr. May hm 118 438 614 614 485 381 128 25 123 396 598 623 491 378 uw 30 28 219 376 416 304 222 47 0 23 198 357 412 m 209 4(1 0 69 304 491 517 388 288 80 0 55 267 458 483 360 265 66 0 0 0 0 0 0 0 foorfy Total 2820 2780 1612 1529 2137 1954 Flagstaff...............A Phoenix................A Phoenix................C Yuma................... A 35.9 59.5 57.7 62.5 49 78 243 0U0 000 000 588 876 1135 1231 1014 949 687 465 212 7525 22 223 4on 474 30S 196 74 0 0 1698 13 182 360 425 275 175 62 0 0 1492 0 105 259 318 167 88 14 0 0 951 Aik.... Bentonvilie............. 06/07-40/41 35 Fort Smith.......... A Little Rock..........A 1 1 38 216 516 810 879 716 519 247 86 7 4036 u 0 9 131 435 698 V75 571 418 127 24 0 3188 0 0 10 110 405 654 719 543 401 122 18 0 2982 Calif..-* Eureka................. C Fresno.................. A Independence......... Los Angeles......... A Los Angeles......... C Needles................... Point Reyes........... Red Bluff............. A Sacramento......... 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 S3.0 54.2 53.5 267 248 264 (J 0 0 0 (1 28 31 22 56 0 0 17 000 350 336 263 0U0 0 0 22 u (J 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 68U 629 40(1 304 145 43 <] 2532 216 512 778 799 619 477 767 120 1H 3834 87 200 301 378 305 273 185 121 6 2015 41 1411 253 328 244 212 129 68 19 1451 19 217 416 447 2 124 2e ? 0 1495 282 317 425 467 40H 43*/ 41? 415 363 4474 59 319 564 617 423 33(1 177 51 G 2546 98 357 595 642 42* 348 222 103 7 2822 75 321 567 614 4IK 31/ 19C 85 5 2600 52 147 255 317 247 223 151 97 43 1574 174 318 487 530 39? 37H 327 264 164 3421 128 237 406 462 336 317 279 24f 1SG 3069 97 270 450 487 342 308 229 137 46 2410 Colo.... Denver.................A Denver................. C Durango.................. Grand Junction. .A Leadvtile................. Pueblo.................. A 04/05-40/41 07/06-40/41 37 34 37.0 37.9 39.9 5 11 120 G 5 103 25 37 201 C (1 36 28U 332 509 0 0 74 425 771 um 1125 924 843 385 711 958 1042, 854 797 535 861 1204 1271 1002 859 333 792, 1132 1271 924 73f 841 1139 1413 1470 1285 1245 383 771 1051 1104 865 775 525 286 65^ 6132 492 26t 61 5673 615 394 139 7143 402 145 23 5796 99G 74G 434 10678 456 203 27 5709 New Haven......... A 0 14 101 384 699 1082 1178 mm 871 S28 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........ C Kev West.............A Key West.............C Miami...................A Wmmi. . . . . . . . . . . . . . . . . . . . 4J . Pensacola............. C Tampa................. A 60.9 60.6 62.0 72.5 73.1 71.4 59.7 000 rG0 c00 GQ0 GC0 GG0 GC0 GG0 000 17 154 304 352 263 184 33 0 0 1307 16 14f 309 331 247 16? 2J ( c 1243 11 129 276 303 226 154 14 C G 1113 C l 22 34 25 f t C G 89 C C 18 2 24 7 C C Q 77 C f 52 5? 4f 12 C t C 178 C 5 48 67 4i 15 C C C 173 If 177 XU 383 275 20? 45 t l 1435 0 60 163 201 148 102 0 0 0 674 Ga...... Atlanta.................A Atlanta.................G Augusta............... A Macon...................A Savannah........ . .A 1'homasviUe........... 05/06-40/41 36 56.7 0 0 8 110 393 614 63? 512 404 133 20 0 2826 Q 0 8 103 387 611 632 515 392 135 24 G 2811 C c 0 5i 282 4W 521 412 30? 6V ( c 2138 G G 0 63 2St 4H1 497 391 2/5 62 C G 2049 C C 0 3f 225 412 424 use 23? 4? ( l 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 0 0 135 389 762 1054 T169 868 719 453 249 92 5S90 c C 133 406 747 961 106C 815 66? 40? 222 5483 0 0 183 487 873 1184 1333 1022 880 61 317 136 6976 BI......... Chicago................A Peoria................A Springfield........... A Springfield........... C 35.1 37.3 37.7 39.8 0 0 90 11 86 c 6 83 ( ( 56 350 765 1147 1243 1053 888 507 229 58 6310 33S 754 112? mr 10V* 82? 435 192 41 6087 315 72? 1066 1166 95f 769 404 171 32 5693 251 661 1017 1116 907 712 351 127 14 225 * far United States ritae Erotn e publication at the United States Weather Bureau, UenUdf Normal Ttmpmbtrte, Pncipitetien end Dfree Dor*. er* tot tfapwiod 19X1 to IftSO mchaiTC. Tboac United States cities (or which years ire gives in Colama l ere oct listed la the shore publication sod the date are those which *en computed by the United States Weather Bureau in 1M6 and 1947 in accordance with the requirements of the National Joint Committee on Weather Statistics. Deta tm airport stations. A, and ritystations, C, are both given where arailable. ^t* tor Canadian i-iti-- SBtimmpnW Mrt--wplngwwl nivisiwm IVfwrtTTM-nt rd Trsnfert (wm mwm! ninthly rwn tnffllHTltims. f *fljnrtr1 fffT *h~------ taw months by a method deeerihed by H. C. 8. Thom. The Rational Relationship between ***-*"! Decree Days and Temperature, MeatUp Weather Baker?, VoL Q, No. 1, January USA * Par period October to April, inclusive.