Document 8VbmpM5Y0Z7k57bQ3q75LzBLB

ISO Chapter 7 1945 Guide depend upon whether products of combustion are vented to a flue, whether they escape into the space to be conditioned, or whether appliances are hooded allowing part^of the heat to escape through a stack. There are no generally accepted ^ata available on tie effects of venting and shield ing heating applianceiLbut it is believed that, when they are properly hooded with a positive fan exhaust system through the hood, 50 per cent of the heat will be carried away and 50 per cent dissipated in the space to be conditioned. Where latent as well as sensible heat is given Table 11. Permeability of Various Materials to Water Vapor Material . Plaster base and plaster, ^ in.. ........................................................ Paint film Brick masonry, 4 in.. ......................................... ........................................ Permeability Grains per Sq Ft per Hr per Inch Hg Group 1 14.7 2.9 49.1 4.9 3.4 12.5 1.1 Foil-surfaced reflective insulation, double-faced...................................... Roll roofing--smooth, 40 to 65 Ib/roll 108 sq ft......................................... Duplex or laminated papers, 30-30-30................................................ l........... 1. Plaster,, fiberboard or gypsum lath. .. ......... Insulating lath and sheathing, board type:............... ................ .................. Insulating sheathing, surface-coated^...................... ....... ._____ ____ Group 2^ 0.08 to 0.13 0.13 to 0.17 1.37 to 2.58 11.00 3.68 to 3.84 1.15 19.73 to 20.57 2.67 to 2.74 25.68 to 34.27 3.03 to 4.36 6.19 29.07 ^Calculating Vapor and Heat Transfer Through Walls, by L. G. Miller (Heating and Ventilating 35. No. 11. 56 November, 1938). bHow to Overcome Condensation in Building Walls and Attics, by L. V. Teesdale (Heating and Venti lating, Vol. 36. No. 4, April, 1939). off,. it is usually safe to assume that all latent heat will be removed by a properly designed and operated vent or hood. Moisture Through Walls In some applications walls of the conditioned space may be in contact with other spaces which have in them a higher water vapor pressure than that in the conditioned space. It is known that water vapor will flow through the building materials in proportion to the vapor, pressure dif ference on the two sides of the material. The total amount of water vapor transmitted is dependent on the permeability which is usqally expressed in grains of moisture per square foot per hour per inch of mercury vapor pressure difference. The values for permeability in Table 11 are quoted from a publication of the National Bureau of Standards'3. The water vapor entering the conditioned space must be added to the latent cooling load. MMoisture Condensation in Building Walls, by Harold W. Woolley (/. S. Department of Commerce, National Bureau of Standards, Building Materials and Structures Report BMS63). - f $ V V i k H i Cooling Load 151 Vapor barriers, to be effective in reducing entrance of moisture, must seal completely the walls, ceilings, and floors, that are exposed to space having excessive vapor pressure and all doors must have gaskets applied to them to make the barrier effective. ILLUSTRATION From the foregoing discussion it is obvious that the determination of the maximum cooling load is rather complicated by reason of the variable nature of contributing load components. An illustrative example will explain the method presented in the foregoing text. Alternative proce dures for calculating cooling loads have been devised by various writers. One of the most recent, intended particularly for residential installations, is given in Bulletin No. 18 of the American Gas Association. Store room ^ E Ceiling height, 12-*CT ? 1C* ^ 1' 1' 8'x6' 14'x6' 14'x6' Fig. 4. Plan Diagram of Clothing Store 14'x6' Example 1. Determine cooling load requirements for a clothing store illustrated in Fig. 4 and located in Pittsburgh, Pa., Latitude 40 deg. This is a one-story building located on a comer and it faces south and west. Assume building on east and north sides conditioned. Wall construction, 8 in. concrete block, 4 in. brick veneer, plaster on walls, V = 0.33 (Table 7, Chapter 4, No. 93 B). Roof construction, 2 in. concrete,-in. insulating board, metal lath and plaster Ceiling, U = 0.26 (Table 14, Chapter 4, No. 14 B). Floor, maple flooring on yellow pine, no ceiling below, U = 0.34 (Table 10, Chapter 4, No. 1-N). Partition, wood lath and plaster on both sides of studding, U = 0.34 (Table 8, Chapter 4, No. 3 B). Windows, provided with awnings., Front doors, 2 ft 6 in. x 7 ft (glass paneled). Side door, 3 ft x 7 ft (glass paneled), U = 1.13 (Table 17 A, Chapter 4). Occupancy, 10 clerks, 40 patrons. Lights,.4200 w. Outside design conditions, dry-bulb 95 F; wet-bulb 75 F. Inside design conditions, dry-bulb 80 F; wet-bulb 67 F.