Document kDm2g1ZEyZ51RevBqg1XMN5kE

f3do CHAPTER 13 1954 Guide ;ciCnt to warrant farther consideration: Tig. 4 offers a simplified schematic 'illustration'showing how the radiative part of the instantaneous heat gain 'is first absorbed bysolid objects, and is hot encountered by the conditioning & equipment as a cooling load until some later time, when it finally appears * in' the5 air stream entering the-equipinen;i While it is true-that some lag also is inherent in convective heat transfer and the time required to change the air in the conditioned space, this is usually of the order of a few minutes to perhaps half an hour. Heat storage in the interior furnishings and ; .structure increases according to the proportion of the instantaneous heat gain which is in the form of radiation, and also as the thermal capacitance of the objects and materials involved is increased. Constituents of the total instantaneous heat gain which have appreciable radiation components include those due to glass areas, exposed walls and roofs, lighting, appliances, and people. No comprehensive data, are presently available, for use in design load estimates to evaluate the interior load-lag effect, but several investigators1?' i4 , 28 . 29. so jjaVe made a' study of the problem and have-presented many . useful data. Tables 9,10, .13,14,18,20, and 21 are all based on instantane- ous rates of heat transfer. Hence, practical judgment and experience offer, the only basis of procedure. Until the needed data become available, it is recommended that the non-continuous load be averaged over two or three hours during the time of maximum load, when determining the total instantaneous cooling load where a large portion of the heat gain is radiant.' This suggestion applies only to conditions near the time of maximum heat gain, as the heat stored within the structure would necessarily appear in the cooling load eventually; but if it appears at a time when the gain fromx outside is relatively low, the equipment will be able to maintain satisfactory conditions within the range of maximum capacity, , LOAD FROM INTERIOR PARTITIONS, CEILINGS, AND FLOORS Whenever a conditioned space is adjacent to another space in whicb-a different temperature prevails, the transfer of heat through the separating structural section must be considered. Calculations are made according to the relation: | q= (7iAi(fb -- <i) Btu per hour. . .,(6) where Ui = coefficient of overall heat transfer between the adjacent and the conjfi; tioned space, Btu per (hour) (square foot) (Fahrenheit degree). A i = area of separating section concerned, square feet, fb = air temperature in adjacent space, Fahrenheit degrees.' t , = air. temperature in conditioned space, Fahrenheit degrees. ' lit Magnitudes of Eli may be obtained from Chapter 9: The-temperature fb may have any value over a considerable range, according to conditio?^ in the adjacent space. The temperature in a kitchen or boiler room may K? as much as 15 to .50 deg above the outdoor air .temperature. ,It is recoffl*' mended5 that actual temperatures be'measured in adjoining spaces wherever, practicable. Where nothing is known, except that the adjacent space is. conventional.construction and contains no heat sources,.it is recommend#1, that the difference (fi, -- fi) he taken as the difference between the 0 door air and conditioned-space design dry-bulb temperatures minus 5 deg- Cooling Load . 301 In some cases it may be that the air ,temperature, in the adjacent-space will correspond closely to the outdoor/air temperature at all times.1 Under these latter conditions, the heat gain; through, the partition will be periodic in nature, and the value, of a shaded wall should be used .from Table -10. For floors directly, in contact with the ground,1 or over. an Underground basement that is neither ventilated nor warmed, the heat transfer1 may be neglected for cooling-load estimates. * LOAD FROM OUTSIDE AIR, VENTILATION AND INFILTRATION Ventilation. Data for determining the necessary ventilation1 rate have been presented previously in. this-, chapter, i Ventilation required is pri marily dependent upon the number .of, occupants and upon the materials and apparatus within the space which may. give, off odors.: For spaces having ceding heights 10,ft or,less, the total requirement should be checked against the volume, and in no case should the ventilation air rate, be less Fig. 4. Origin of the Difference Between the. Magnitudes of the Instan taneous Heat Gain.and Instantaneous Cooling Load; The radiation absorbed by the interior furnishings and structure reaches-the conditioning equipment after a considerable delay in time. than one air change per hour. In spaces having ceilings higher than 10 ft where the occupant load is iow, a check calculation can be.made against the volume of the space below an assumed 10-ft ceiling. . . Infiltration must never be counted upon to provide ventilation, because on still days there will be little or no infiltration. Infiltration. The principles of infiltration calculations have been dis cussed in Chapters 11 and 12, with emphasis on the heating season. For the cooling season, infiltration calculations are usually limited to doors and windows. To compute cooling-load infiltration for windows by the crack method, use the data of Table 2, Chapter 11, for a wind velocity of 10 mph. Note that for double-hung windows the length of crack is three times the width plus twice the height; while for metal-sash windows the crack length is the total perimeter of the movable or ventilating sections. In calculating window infiltration for an entire structure, it is not necessary to consider the total crack length on all sides of the building, for the wind would not act simultaneously on all sides at once. In no case, however, should less than half of the total crack length be figured. A knowledge of the pre vailing wind direction will aid judgment in this consideration. Cooling-load infiltration for doors51 may be obtained from Table 3, Chapter 11. For conditions other than those covered, the notes appended to the table will provide a basis for estimates.1 The tabulated data may also he used as the basis of estimates for interior doors between an air-condi- ned and a non-air-conditioned space. ... Infiltration load must be included whenever the new air introduced