Document N2LqVBmBeB2QVzM0RJv37w97w

262 CHAPTER 12 1958 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 transmissions (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 this 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 oh 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 T, fists this recommended design temperature based on airport y station readings for the period indicated, generally the five years, 1935- ;ib 1939.". 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 -y design load. ;V 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: -V-< mainder were taken from an ACRMA Bulletin,1 manufacturers' publica- iy: tions, and other sources,2 and a few were estimated. The map in Fig. 1 shows isotherms of outdoor winter design temperature y>, which are based on the values in Column 10 of Table 1 with some modifica- j,yy tions where other data indicated that Column 8 furnishes a more reasonable yy; 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- 0'-: ature for cities between the isotherms. Thus, a city located half-way be- Heating Load 263 ----------Col. 1 State Col. 2 Station1* Table 1. Winter. Climatic Conditions* - EleVATION FT Period Record** Col. 5 Col. 6 Col. 7 Col. 8 Col. 9 Col. 10 Col. 11 Low-y B8T : ON RecOBD Aver age NT7AL Min.Temp. Avg. Win- Tkmp.' Design Design DbtBulb Temp. dnTAC 97*% Wind Vel. at Design Temp.1* DrtBulb Temp. in Common Basis* Use* A vg. Wind Vel. Dec. Jan.. Feb.j F F F F Mph *F Mph Ala.... 0 733 .0 711 .A 615 1893-1947 1893-1945 1939-1947 -10 -10 -10 .O 143 1872-1947 -1 .A 210 1940-1947 13 C 293 1872-1947 -5 A 226 Aria.... C 6957 Kingman............ A 3473 .0 1122 1938-1944 1899-1947 1935-1939* 1895-1947 9 -25 8 16 .A 1112 1937-1947 21 C Jp to 1946 6 A 2561 1935-1939d \ 19 .C 4853 Jp to 1946 -19 .A 4899 1932-1947 -18 c 146 1876-1946* 22 Ark..., .c 545 1882-1945 .A 463 1945-1947 -15 7 Little Rock........ C 451 1879-1942 -12 Little Rock........ .A 282 1942-1947 7 Cal.... .A 499 1937-1946* .19 Burbank............. ..A 740 1931-1947 21 Daggett ............ ..A 1925 1935-1939* Eureka................ C 115 1886-1947 20 Fresno................. ..C 387 1887-1939 17 Fresno................. A 281 1939-1947 23 Los Angeles........ ..O 534 1877-1947 28 Oakland.............. .-.A 21 1929-1947 23 Red Bluff........... ..C 341* 1877-1934 17 Red Bluff........... ..A 346 1944-1947 25 Redding.............. A 579 1935-1939* 17 Sacramento........ ..C 116 1877-1947 17 Sacramento........ ..A 22 1938-1947 22 San Diego........... ..C 90 1871-1940 25 San Diego........... ..A 34 1939-1947 34 San Francisco... . C 164 1875-1947 27 San Jose.............. ..C 100 Up to 1946 22 Williams.............. ..A 124 Col.... Denver................ ..G 5398 Denver.............. A 5379 1935-1939* 1871-1947 1934-1947 -29 -30 Grand Junction. ..C 4587 1889-1945* -21 Pueblo................. ..O 4770 1889-1938* -27 Conn.. Pueblo............... ..A 4810 Hartford........... .0 229 1939-1947 1905-1940 -26 -18 D.C... Fla.... Hartford......... A New Haven___ ..C New Haven... ..A Washington....... ..C Washington...... ..A Apalachicola.... . t: Jacksonville___ ..o Jacksonville ..A Key West.......... ..C Key West.......... ..A 20 180 17 128 20 23 104 29 23 48 1940-1947 1872-1946* 1943-1947 1871-1947 1935-1939* 1922-1947 1871-1947 1938-1947 1871-1947 1939-1947 -24 -16 -4 -15 18 10 16 41 42 253 Miami.......... ..A 13 Pensacola.......... ..L 67 1940-1947 1879-1947 27 28 7 Tampa....... C 113 20 Ga__ ui.. Titusville Atlanta 52 1020 Augusta......... Macon....... r Macon.... a Savannah r Savannah a Boise.......... r Boise......... a Burley........... a Idaho Falls Lewiston. a r 4744 Pocatello.. r Pocatello___ Cairo....... a ......... r 1 4467 1938-1947 Chicago... :| 6oic Up to 1946 8 8 -18 -23 -23 apaces indicate data not yet completed. 52.3 12 53:8 51.8 22 58.9 18 56.4 19 -15 35.9 26 -1 27. 6' > 10 59.5 57.7 57.2 57.2 43.6 .43.5 62:5 50.4 51.6 25 55:5 57.5 29 49.3 26 53.8 37- 59.3 51.9 53.9 52.9 28 53.0 37 58.2 37 54.2 53.5 -11 -2 39.0 37.0 39.9 41.1 36.4 * -1 38.4 -1 43.4 60.9 29 62.0 60.6 73.1 72.5 38 71.4 35 23 59.7 66.0 12 51.3 54.2 54.7 22 58.5 56.7 -8 42.7 35.0 37.6 21 7.4 30 8.6 22 8.6 31 5.6 30 6.3 6 7.5 21 6.6 33 5.6 35 4.9 27 8.5 32 4.5 36 7.5 32 7.1 43 5.8 29 8.3 0 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 8.8 7.6 5 10 15 10 -10 25 25 -10 30 10 5 25 8.0 9.9 . 7.5 7.7 5.4 5.2 6.7 8.3 8.3 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 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 6.5 15 6.7 20 9.5 -10 9.1 0 7.2 10 -10 12.0