Document DMMDN5x5vaRe9j6n9oMNEKGQN

American Society of Heating and Ventilating Engineers Guide, 1935 Chapter 6--Air Leakage CRACK USED FOR COMPUTATIONS In no case, should the amount of crack used for computation be than half of the total crack in the outside walls of the room. Thus, ;T room with one exposed wall, take all the crack; with two exposed take the watl having the most crack; and with three or four exposed take the wall having the most crack; but in no case take less than half fS total crack. For a building having no partitions, whatever wind enta* through the cracks on the windward side must leave through the cracfcB on the leeward side. Therefore, take one-half the total crack for puting each side and end of the building. . -Theamount-ofair-leakage is.sometimes roughly. estimated by assumiJ a certain number of air changes per hour for each room, the number ,f changes assumed being dependent upon the type, use and location of room, as indicated in Table 3. This method may be used to advantage j a check on the calculations made in the more exact manner. Table 3. Air Changes Taking Place under Average Conditions ExcLusni of Air Provided for Ventilation Kind of Room ob Building Number of Air Chajuj, Taking Puca per Houb Rooms, 1 side exposed............................................ Rooms, 2 sides exposed-- ................................... Rooms, 3 sides exposed. Rooms, 4 sides exposed....... ................................... Rooms with no windows or outside doors--........ Entrance Halls............................................. Reception Halls...................................... Living Rooms.......................... Dining Rooms.......................................... Bath Rooms....... ................................ ' Drue Stores. ...... ...... .. _ Clothing Stores_______ __ ..._______ Churches. Factories, I.nfts, etc. 1 \a 2 2- A to A 2 to 3 2 1 to 2 i to 2 2 2 to 3 1 A to 3 1 !. ; \ r MULTI-STORY BUILDINGS In tall buildings, infiltration may be considerably influenced by tem perature difference or chimney effect which will operate to produce 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 Iowa 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 preventing free upward movement, so that wind ad temperature difference may seldom cooperate to the fullest extent Making the rough assumption that the neutral zone is located at mid-; 'Influence of Stack Eflect on the Heat Loss in Tall Buildings, by Axel Marin (A.S.H V.E. Jomol] Section, Healing, Piping and Air Conditioning, August, 1934, p. 349). 1 126 height of a building, and that the temperature difference is 70 F the following formulae may be used to determine an equivalent wind velocity vtoelboeciutyseadnidn cteomnnpeecrtaiotunrewidthiffTeraebnleces:1 and 2 that will allow for both winad Me. VM* - 1.75 Wlterc Me = equivalent wind velocity to be used in conjunction with Tables 1 and 2. M = wind velocity upon which infiltration would be determined if tem- perature difference were disregarded. o = difisatbaonvceemoifdw-hiendigohwt.s under consideration.from mid-height of bmlding6 b = distance il below mid-height. 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, although probably no greater wind velocities should be figured at such extremely high levels'. Sealing of Vertical Openings4 In tall, multi-story buildings, every effort should be made to seal off vertical openings such as stair-wells and elevator shafts from the re mainder 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 enclosures 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 high altitudes 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 arbitrary 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. Heating Surface for Stair-Wells4 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 even to the point of omitting all heating surface on the top several floor levels. One rule is to calculate the heating surface of the entire stair-well in the usual * Velocities Near a Building and Their Effect on Heat Loss, by F. C. Houghten. J. L. Blackshaw, ana Carl Gutberlet (A..S.H.V.E. journal Section, Heating, Piping and Air Conditioning, September. 1934). `See Flue Action in Tali Buildings, by H. L. Alt (Heating, Piping and Air Conditioning, May, 1932).. 127