Document M4ExNOX67OvVw5qEyq63DQOw7

218 CHAPTER 10 1952 Guide represent current engineering practice. Some tests of infiltration through swinging and revolving doors have been reported:4 The data -in Table 3 are indicative of what might be expected in this connection, but it should Be noted that Table 3 is based on a no-wind condition, and therefore not directly applicable to heating design. Air Change Method The amount of air leakage may be estimated by assuming a certain num ber of air changes per hour for each room, the number of changes as sumed being dependent upon the type, use, and location of. the room, as indicated in Table 4. Where it is not possible to determine or pre-determine with accuracy the width of crack or clearance of windows, or where other sources of air leakage cannot readily be evaluated, as is often the case, the use of the air change method may be justified.* The values in Table 4 may be used with reasonable accuracy for resi dences, and are the requirements for each room. The total infiltration allowance for the entire building should be one-half the sum of the infil- Table 4. Aik Changes Taking Place under Average Conditions in Residences, Exclusive op Air Provided for Ventilation* Kind or Room or Building Number of Air Changes taking Place per Hour Rooms, 1 side exposed. Rooms, 2 sides exposed!__ Rooms, 3 sides exposed.__ Rooms, 4 sides exposed:___ i iM 2 2 Kind of Room or Building Rooms with no windows or outside doors___ Entrance Halls Reception Halls.. ........ Bath Rooms__ _ ......... Number of Air Changes taking Place per Hour MtoH 2 to 3 2 2 less than i air change. tration allowances of the individual rooms, since whatever air enters-on the windward side, generally leaves the building on the leeward side, and the infiltration requirements therefore do not exist simultaneously on all sides, or in all rooms. An allowance of one air change per hour for all sources of air leakage for the entire volume may be considered average for a well constructed residence. The air leakage, due to opening and closing of doors in vestibules, is sometimes based on the air change method, even though the air leakage estimates for other rooms are based on the crack method. Except for vestibules and reception halls, it is not advisable to attempt to apply the air change method to factories and industrial and commercial buildings, because .of wide variations in the type and percentage of fenestration which is- the principal source of- air leakage in such buildings. INFILTRATION DUE TO TEMPERATURE DIFFERENCE .The- air exchange due to temperature difference, inside to outside, is a chimney effect, causing,air. to enter through openings at lower levels, and to leave at higher levels.8 Although it is. not appreciable-in low buildings, this loss should be considered in tail, single story buildings with openings near the ground level and near the ceiling! Also in tall, multi-story, build ings it may be a considerable item, unless the sealing between various floors and rooms is quite perfect. -' : . In tall buildings, temperature difference or chimney effect will-produce Infiltration and Ventilation 219 a head that will add to the effect of the wind at lower levels, and subtract from it at higher levels. On the other hand, the wind velocity at lower levels may be somewhat abated by surrounding obstructions. Further more, the chimney effect is reduced in multi-story buildings by the partial isolation of floors, thereby preventing free upward movement, so that wind and temperature difference may seldom cooperate to the fullest extent! Making the assumption that the neutral zone7 is located at mid-height of a building, and that the temperature difference is 70 deg, Equations 1 and 2 may be used to determine an equivalent wind velocity to be used in connection with Tables 1 and 2, that will allow for both wind velocity and temperature difference: V. = Vv* - i;75o (1) where . Ve:= Vv + 1.756 (2) Ve = equivalent wind velocity to be used in conjunction with Tables 1 and 2, miles per hour. V = wind velocity upon which infiltration would be determined if temperature difference were disregarded, miles per hour. a = distance of windows under consideration from mid-height of building if above mid-height, feet.' b = distance if below mid-height, feet. The coefficient 1.75 allows for about one-half the temperature difference head. For buildings of unusual height, Equation 1 would indicate negative infiltration at the highest stories, which condition may, at times, actually exist. Sealing of Vertical Openings In tall, multi-story buildings, every effort should be made to seal off vertical openings, such as stair-wells and elevator shafts, from the remainder of the building. Stair-wells should be equipped with self-closing doors, and, in exceptionally high buildings, should be closed off into sections of not over 10 floors each. Plaster cracks ' should be filled. Elevator en closures should be tight, and solid doors should be used. If the sealing of the vertical openings is made effective, no allowance need be made for the chimney effect. Instead, the greater wind move ment at the greater heights makes it advisable to install additional heating surface on the upper floors above the level of neighboring buildings, this additional surface being increased as the height is increased. One arbi trary rule is to increase the heating surface on floors above neighboring' buildings by an amount ranging from 5 per cent to 20 per cent. This extra heating surface is required only on the windward side and on windy days, and hence, automatic temperature control is especially desirable with such installations. In stair-wells that are open through many floor levels, although closed off from the remainder of each floor by doors and partitions, the strati fication of air makes it advisable to increase the amount of heating surface at the lower levels, and to decrease the amount at higher levels. One rule is to calculate the heating surface of the entire stair-well in the usual way, and to place 50 per cent of this in the bottom third; the normal amount in the middle third, and the balance in the top third.