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262 CHAPTER 12 1957 Guide outdoor air supply equals or exceeds the amount of natural infiltration which would occur without ventilation, the natural infiltration may be neglected. 9. The sum of the heat losses by transmisions (Item 6) through the outside walls and glass, as well as through any cold floors, ceilings or roof plus the heat equivalent (Item 7) of the cold air entering by infiltration, or required to replace mechanical exhaust, represents the total heat loss equivalent for any building. . 10. In buildings which have a reasonably steady internal heat release of appre ciable magnitude from sources other than the heating system, a computation of tnis heat release under design conditions should be made for deduction from the total of the heat losses computed in items 1-9. This is especially important for heating sys tems of high initial cost or those for which a demand charge is based on installed capacity. DESIGN OUTDOOR WEATHER CONDITIONS There are no hard and fast rules for selecting the design outdoor weather conditions to be used for a given locality or type of building or heating system, and the selection is to some extent a matter of judgment and experience. The appropriate design temperature in a given locality may vary with heat capacity and degree of insulation of a particular structure, the amount of protection from the wind, the length of time that nightly minimum tempera tures persist, whether the particular building is being used day and night, and perhaps other factors. For heating systems that depend primarily on electrical energy as a source of heat it will often be desirable, for economic reasons, to make a more careful analysis of the factors that affect design weather conditions than would otherwise be justified. The outside design temperature seldom is taken as the lowest tempera ture, or even the lowest daily mean temperature ever recorded in a given locality. Such temperatures rarely recur in successive years. Likewise the wind direction and velocity occurring at the time of design outside tempera ture may be different from the average velocity and prevailing direction during the winter. The A.S.H.AiE. Technical Advisory Committee on Weather Design Conditions has recommended the adoption for heating load calculations of an outside design temperature which is equalled or exceeded during 97\ percent of the hours in December, January, February and March. Complete design temperature data based on this formula are not available, but Col umn 8, Table 1, lists this recommended design temperature based on airport station readings for the period indicated, generally the five years, 19351939. In most cases these stations are outside of the city and these data apply primarily to rural areas. In general the use of the airport data for buildings within an adjacent city will not make an appreciable difference in design load. Because of the limited data available in Column 8 of Table 1, design temperatures in common use are listed in Column 10 for the United States. Many of those values were furnished by A.S.H.A.E. members, the re mainder were taken from an ACRMA Bulletin,1 manufacturers' publica tions, and other sources,2 and a few were estimated. The map in Fig. 1 shows isotherms of outdoor winter design temperature which are based on the values in Column 10 of Table 1 with some modifica tions where other data indicated that Column 8 furnishes a more reasonable design temperature. These isotherms have also been modified slightly in accordance with the elevations of the various cities. The isotherms are drawn on 10 deg temperature intervals, in most cases, and are so placed that interpolation between isotherms will provide the proper design temper ature for cities between the isotherms. Thus, a city located half-way be- Heating Load 263 Table 1. Winter Climatic Conditions* State Cod. 2 Station1* Con. 3 Col. 4 tEviolaen0 Period Recoofrd^** n Col. 5 Low- TEe8mTp. ROeNc ord'1 Col. 6 Aver aAgne nual TMeminp..* Col. 7 Ava. Win ter Temp. DCeosli.g8n DryoTBneuTmlAbpC. B9a7s*%is* Col. 9 VDWeelsin.igdant Temp.1* Col. 10 DDerstig-n TBeumlbp. in CoMMpN F *F "F F Mph *F AWVvienold.. DFJaeencb....1 Mph Ala... Anniston............ O Birmingham....... ..G 733 711 Birmingham...... ..A 615 Mobile................. ..G 143 Mobile................. ..A 219 Montgomery...... ..G 293 Montgomery__ A 226 Aril.... Flagstaff............ ..G 6957 Kingman............ ..A 3473 Phoenix.............. ..G 1122 1893-1947 1893-1945 1939-1947 1872-1947 1940-1947 1872-1947 1938-1944 1899-1947 1935-1939* 1895-1947 Phoenix.............. ..A 1112 1937-1947 Tucson................ ..C Up to 1946 Tucson................ ..A 2561 1935-I939d Winslow.............. ..C 4853 Up to 1946 Winslow.............. ..A 4899 1932-1947 Yuma................. C 146 1876-1946* Ark.,,. Fort Smith......... ..C 545 1882-1945 Fort Smith......... ..A 463 1945-1947 Little Rock........ ..C 451 Little Rock........ ..A 282 Cal.... Bakersfield......... ..A 499 1879-1942 1942-1947 1937-1946* Burbank............. ..A 740 1931-1947 Daggett ......... ..A 1925 1935-1939* Eureka................ C. 115 1886-1947 Fresno................. ..G 387 1887-1939 Fresno................. ..A 281 1939-1947 Dm Angeles........ ..G 534 1877-1947 Oakland.............. ..A 21 1929-1947 Red Bluff........... ..G 341 1877-1934 Red Bluff........... ..A 346 Reddinsr. ....... A 579 bacrampTitn ..G 116 1944-1947 1935-1939* 1877-1947 Col... Conn.. DC... Fla... Ga... Idaho.. Sacramento........ A Ban Diem........... .0 Ban Diero........ A Ban Frnnrnsm c Ban Jrnp ..o Williams ..A Denver ..C Denver. ..A Grand Junction. C Pueblo.. ..C Pueblo.. ..A Hartford ..G Hartford ..A New Haven....... ..C New Haven... ..A Washington........ ..G Washington ..A Apalachicola G Jacksonville ..C Jacksonville... ..A gey West......... .C Key West........ Miami A Mj&mi Pensacola... Pensacola Tampa... ..O .A TamDa Titusville Atlanta Augusta .. Augusta.. Macon Macon A Savannah Savannah.. Boise....... Boise <j A G 22 90 34 164 100e 124 5398 5379 4587 4770 4810 229 20 180 17 128 20 23 104 29 23 48 253 13 67 113 111 12 52 1020 195 424 408 432 115 56 2818 1938-1947 1871-1940 1939-1947 1875-1947 Up to 1946 1935-1939* 1871-1947 1934-1947 1889-1945* 1889-1938* 1939-1947 1905-1940 1940-1947 1872-1946* 1943-1947 1871-1947 1935-1939* 1922-1947 1871-1947 1938-1947 1871-1947 1939-1947 1896-1947 1940-1947 1879-1947 1943-1947 1890-1940* 1941-1946 1935-1939* 1878-1945* 1871-1946* 1939-1947 1899-1947 1939-1947 1871-1945 1939-1947 1864- 939* Burlev Idaho Fails piston. in-... Pocatello Pocatello.. ............ 4150 A 4744 763 C 4522 4467 1935-1939* 1935-1939* 1900-1944 1899-1947 1938-1947 Chicago 601 Up to'Vote Bluk BPaoea indicate data not yet completed. -10 -10 -10 -1 13 -5 9 -25 8 16 21 6 19 -19 -18 22 -15 7 -12 7 19 21 20 17 23 28 23 17 25 17 17 22 25 34 27 22 -29 -30 -21 -27 -26 -18 -24 -15 -4 -15 18 10 16 41 42 27 28 7 20 * 19 31 -8 3 10 7 8 16 -28 -35 -18 -23 -28 -23 12 22 18 19 -15 26 -1 27 6 10 25 29 26 37 28 37 37 -11 -2 . -1 -1 29 38 35 23 32 12 22 1 -12 52.3 53.8 51.8 58.9 56.4 35.9 59.5 57.7 57.2 57.2 43.6 43.5 62.5 50.4 51.6 55.5 57.5 49.3 53.8 59.3 51.9 53.9 52.9 53.0 58.2 54.2 53.5 39.0 37.0 39.9 41.1 36.4 38.4 43.4 60.9 62.0 60.6 73.1 72.5 71.4 59.7 66.0 51.3 54.2 54.7 58.5 56.7 40.3 36.9 42.7 37.1 35.0 21 7.4 30 8.5 22 8.6 31 5.6 30 6.3 6 7.5 21 33 35 27 8.5 32 4.5 36 7.5 32 7.1 43 5.8 29 8.3 6 8.8 2 6.4 4 8.3 11 8.1 14 7.4 31 7.0 45 7.3 38 6.5 22 10.2 29 7.7 2 8.8 -7 7.6 6 7.2 10 8.0 15 9.9 10 7.5 -10 7.7 25 5.4 25 5.2 -10 30 10 8.3 fi 8.3 25 30 25 35 6.4 30 6.1 30 35 35 25 -10 -15 -20 0 0 0 25 25 45 35 20 30 7.2 6.3 7.5 7.5 4.4 7.9 8.7 9.4 7.8 8.4 9.0 10.6 10.1 10.9 8.6 10 11.7 10 6.5 15 6.7 20 9.5 -10 9.1 5 4.1 -5 8.9 -10 12.0