Document 10Lb9qqrDvk9Qdmodmok9ZLKo

258 CHAPTER 12 1954 Guide 2. Wind increases materially the infiltration of cold air through the cracks around doors and windows, and even through the building materials themselves (see Tables 1 and 2, Chapter 11). : Theoretically, as a basis for design, the most unfavorable combination of temperature and wind velocity should be chosen. It is entirely possible that a building might require more heat on a windy day with a moderately low outside temperature, than on a quiet day with a much lower outside temperature. However, the combination of wind and temperature, which is the worst, would differ with different buildings, because wind velocity has a greater effect on buildings which have relatively high infiltration losses. It would be possible to compute the heating load for a building for several different combinations of temperature and wind velocity which records show to have occurred, and to select the worst combination, but designers generally do not feel that such a degree of refinement is justified. Therefore, since Table 1 lists the maximum wind velocity occurring &.' during the coldest 2\% of the winter hours for each locality, this value . should be the basis for estimating infiltration losses. When using the air j: change method it will not be necessary to consider the wind velocities. V Designers employing the crack method generally use values corresponding :k to a 15-mile wind. The effect of the wind velocity on the transmission,:; coefficient can be evaluated from Table 21 of Chapter 9. Exposure Factors Many designers use empirical exposure factors to increase the calculated, heat loss of rooms or spaces on the side or sides of the building exposed to; the prevailing winds. However, the use of exposure factors is unneces-^ sary when the Guide method of calculating heat losses is used. Therefore, :; exposure factors may be regarded as factors of safety for the rooms or spaces; exposed to the prevailing winds, to allow for additional capacity for these: rooms or spaces, or to balance the radiation, particularly in the case of; multi-story buildings. Tall buildings may have severe infiltration hen| losses, induced by their stack effect (see Chapter 11), which will required: special consideration. Although the exposure allowance frequently is as-A sumed to be 15 percent, the actual allowance to be made, if any, must to|v a large extent be a matter of experience and judgment of the designer/!' since there are at present no authentic test data available from which rules^ could be developed for the many conditions encountered in practice. -V AUXILIARY HEAT SOURCES | The heat supplied by persons, lights, motors and machinery alway?l should be ascertained in the case of theaters, assembly halls, and industrial; plants, but allowances for such heat sources must be made only after carefulconsideration of all local conditions. In many cases, these heat source|should not affect the size of the heating plant at all, although they may have; a marked effect on the operation and control of the system. In general' where audiences are present, the heating system must have sufficient^ capacity to bring the building to the stipulated inside temperature before; the audience arrives. In industrial plants, quite a different conditioj; exists, and heat sources, if always available during occupancy, may `W; substituted for a portion of the heating installation. In no case should tn,.;j actual heating installation (exclusive of heat sources) be reduced b that required to maintain at least 40 F in the building. Heating Load Electric Motors and Machinery 259 Motors and the machinery which they drive, if both are located in. the room, convert all of the electrical energy supplied into heat. This heat is retained in the room if the, product manufactured is, not removed until its temperature is the same as, the room temperature. V : If'power is transmitted to the machinery from the ^outside, then only the heat equivalent of the brake horsepower supplied is used. In some' mills this is the chief source of heating, and it is frequently sufficient to overheat the building even in zero weather;, thus requiring cooling by ventilation the year 'round. Table 7 shows the heat output equivalent Table 7. Heat Equivalents of Various Sources* Machinery (Motor in room) = Motor Hp/efficiency x 2544 Btu/hr. Machinery (Motor outside room) = Motor Hp x 2544 Btu/hr. Electric Lights = Kilowatts x 3413 Btu/hr. Gas (Producer = 150) (Manufactured = 535) (Natural = 1000) Btu/cu ft. * Additional values are given in Chapter 13, Table26. of various sources of heat in a factory. For information concerning the heat supplied by persons, refer to data given in Chapter 6, and also Table 25, Chapter 13. For appliances see Table 26, Chapter 13. INTERMITTENTLY HEATED BUILDINGS In the case of intermittently heated buildings additional heat is required for raising the temperature of the air, the building materials and the ma terial contents of the building to the specified inside temperature. The rate at which this additional heat must be supplied depends upon the heat capacity of the structure and its material contents, and upon the time in which these are to be heated.16 This additional heat may be computed and allowed for as conditions re quire, but inasmuch as the heating system proportioned for taking care of the heat losses will usually have a capacity about . 100 percent greater than that required for average winter weather, and inasmuch as most buildings may either be continuously heated or have more time allowed for heating up during the few minimum temperature days, no allowance usually is made, except in the size of boilers or furnaces. For churches, auditoriums and other intermittently heated buildings, additional capacity should be provided. RESIDENCE HEAT LOSS PROBLEMS The following Examples 6 and 7 will illustrate the procedure for calcu.'"6 the heat loss of a residence, uninsulated and insulated, in accordance yith the recommendations given in this chapter. vicir;' Calculate the heat loss of the residence shown in Fig. 2 located in the w;n Chicago. From Table 4, design outdoor conditions are --10 F and 12 mph Unhpt loside temperature from Table 2 is assumed to be 70 F. The attic is baseme * Assume ground temperature to be 50 F (see Fig. 3, Chapter 35) under losses h i Sarage floors and 32 F adjoining basement walls. Estimate infiltration 8ideredD^ u a'r cl'anBe method. No wall, ceiling or roof insulation is to be con- a >n this problem, but all first and second floor windows, except in the garage,