Document 6b2YOaQNmaMLkgG993eK2GrLR

250 CHAPTER 12 1956 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 siim 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 healing 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.A.E. 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,' 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 W 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 251 Table 1. Winter Climatic Conditions* Col. 2 Station1* Col. 3 Col. 4 Ele vaTIONv Period Record** FT Col. 5 Low est Temp, on Rec ord*1 Col. 6 Col. 7 Col. 8 Col. 9 Col. IoIcol. 11 Aver- Design Design %aoe An nual Min. Temp. Avo. Win ter , Temp.' DRYr Bulb Temp. onTAC 974 Wind Vel. at Design Temp.11 DryBulb Temp. in Common "F Basis* *F Mph Use* F Avg. Wind Vel. Dec. Jan.. Feb.j ..C 733 1893-1947 Ark.. Cal... Birmingham Birmingham Mobile......... Mobile............... Montgomery__ Montgomery___ Flagstaff......... Kingman............ Phoenix............. Phoenix......... Tucson.............. Tucson................ Winslow.............. Winslow.............. Yuma.................. Fort Smith.. Fort Smith........ Little Rock....... Little Rock....... Burbank. Daggett . ..C 711 A 615 C 293 .A 226 C 4853 .A 4899 .C 146 C 545 .A 463 C 451 .A 282 .A 499 ."A 740 A 1925 1893-1945 1939-1947 1872-1947 1940-1947 1872-1947 1938-1944 1899-1947 1935-1939* 1895-1947 1937-1947 Up to 1946 1935-1939** Up to 1946 1932-1947 1876-1946* 1882-1945 1945-1947 1879-1942 1942-1947 1937-1946* 1931-1947 1935-1939* -10 -10 -1 13 -5 9 -25 8 16 21 6 19 -19 -18 22 -15 7 --12' 7 19 21 Eureka... Fresno.... Ljob Angel Oakland.. C 115 1886-1947 C 387 1887-1939 A 281 1939-1947 C 534 1877-1947 A 21 1929-1947 C 341 1877-1934 20 17 23 28 23 17 Sacramento.. Sacramento.. A 346 A 579 C 116 A 22 1944-1947 1935-1939* 1877-1947 1938-1947 25 17 17 22 C 90 1871-1940 A 34 1939-1947 25 34 C 164 1875-1947 27 C 100e Up to 1946 Col... A 124 Denver.............. C 5398 Denver.................. A 5379 1935-1939* 1871-1947 1934-1947 Grand Junction. C 4587 1889-1945* C 4770 1889-1938* Conn. A 4810 1939-1947 C 229 1905-1940 A 20 1940-1947 D.C.. C 180 1872-1946* i 17 1943-1947 -15 -4 C 128 1871-1947 -15 Ha... \ 20 1935-1939* 3 23 1922-1947 18 : 104 1871-1947 10 K 29 1938-1947 16 3 23 1871-1947 41 i 48 1939-1947 42 3 253 1896-1947 27 Pensacola.. Pensacola.. Tampa... Tampa,. i 13 " 67 i 113 ? 111 i 12 1940-1947 1879-1947 1943-1947 1890-1940* 1941-1946 28 7 20 19 3r Ga... 52 1935-1939* 1020 1878-1945* -8 195 1871-1946* 3 424 1939-1947 10 408 899-1947 7 432 939-1947 8 Idaho.. Savannah .......... a Boise. .;............ r Boise............ ......... * Burley... .........^ Idaho Falls.... ^ * . a Lewiston............ `' r* Pocatello........ Pocatiio........ c. Cairo q Chicago............. 115 871-1945 56 939-1947 2818 864- 939* 2849 939-1947 4150 935-1939* 4744 935-1939* 763 900-1944 4522 899-1947 4467 938-1947 319 ] 572-1947 601 (Up to 1946 8 16 --28 --13 -35 --18 --23 -28 --23 --16 - Blank 8pacea indicate data not yet completed. 52.3 53.8 51.6 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 54.2 53.5 39.0 37.0 .9 41.1 36.4. 43.4 60.9 62.0 60.6 73.1 72.5 71.4 59.7 51.3 54.2 54.7 58.5 56.7 40.3 39.8 36.9 42.7 37.1 35.0 46.4 37.6 5 10 8.0 7.4 15 9.9 10 7.5 -10 8.6 25 7.7 5.4 25 5.2 -10 30 6.7 10 8.3 5 8.3 25 7.5 7.1 6.4 8.3 6.5 10.2 4.5 8.8 7.6 30 7.3 25 5.4 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 0 9.8 -10 12.0