Document bajaddL5m7wyj3mJoYYo2V5ng

308 CHAPTER 13 1958-Guide Table 11. Summer Coefficients of Heat Transmission U of Flat Roofs Covered With Built-Up Roofing* Btu per (hour) (square fool) (F deg difference between the air on the two sides) Insulation on Top op Deck (Covered With Built- Up Roofing) Type op Roof Deck Ceiling not shown Thickness of Roof Deck (Inches) No Ceiling-- Underside of Roof Exposed Furred Ceiling with Air Space, Metal Lath and Plaster No In sula* tion Insulating Boardd Thickness, In. i 1 u2 No In sula- tion Insulating Board1* Thickness, In. i1 2 Flat Metal Roof Deck 4 Ply Felt Roof Ditto + 4 in* Slag 0.73 0.35 0.23 0.17 0.13 0.40 0.25 0.18 0.14 0.12 0.54 0.30 0.20 0.16 0.13 0.34 0.22 0.16 0.13 0.11 Precast Cement Tile ------ -5. = Concrete ----- -------------- idt&Sgwfif 1 -- 4 Ply Felt Roof li Ditto + 4 in* Slag 1 0.67 0.33 0.22 0.17 0.13 0.38, 0:24 0.18 0.14 0.12 0.50 0.28 0.20 0.15 0.12 0.32 0.21 0.17 0.13 0.11 4 Ply Felt Roof 2 4 6 Ditto 2 4 + 4 in. Slag 6 0.65 0.33 0.22 0.16 0.13 0.37 0.24 0.18 0.14 0.12 0.59 0.31 0.21 0.16 0.13 0.36 0.23 0.17 0.13 0.12 0.54 0.30 0.20 0.16 0.13 0.33 0.22 0.17 0.13 0.11 0.49 0.28 0.20 0.15 0.12 0.31 0.21 0.16 0.13 0.11 0.46 0.87 0.19 0.15 0.12 0.30 0.21 0.16 0.13 0.11 0.42 0.26 0.19 0.14 0.12 0.29 0.20 0.16 0.13 0.10 Gypsum and Wood Fiberb 4 Ply on 4' Gypsum Board Felt Roof 21 31 ^ Ditto 21 + i m. Slag 31 0.34 0.23 0.17 0.13 0.12 0.25 0.18 0.14 0.12 0.097 0.28 0.20 0.15 0.12 0.11 0.21 0.16 0.13 0.11 0.094 0.29 0.20 0.16 0.13 0.11 0.22 0.16 0.13 0.11 0.093 0.25 0.18 0.14 0.12 0.10 0.19 0.15 0.13 0.10 0.090 Wood0 ____V--- n / /____ 4 Ply Felt Roof Ditto + S' I 1 0.43 0.26 0.19 0.15 0.12 0.29 0.20 0.15 0.13 0.11 H 0.33 0.22 0.17 0.13 0.11 0.24 0.18 0.14 0.12 0.097 2 0.29 0.20 0.16 0.13 0.11 0.22 0.16 0.13 0.11 0.094 3 0.22 0.16 0.13 0.11 0.09 0.17 0.13 0.12 0.10 0.085 1 0.35 0.23 0.17 0.14 0.11 0.25 0.18 0.14 0.12 0.10 u 0.29 0.20 0.15 0.12 0.1C 0.21 0.17 0.13 0.11 0.093 2 0.26 0.19 0.14 0.12 0.1C 0.20 0.15 0.13 0.1C 0.090 3 0.20 0.15 0.12 0.10 0.09 0.16 0.13 0.11 0.09 0.081 a The summer coefficients are considered temporary, and have been calculated with an outdoor wind velocity of 8 mph. For.summer an inside surface conductance of 1.2 has been used instead of the regular 1.65 value. In all of these roofs a 4 ply felt roof been assumed f in. thick, thermal conductivity = 1.33. Pitch and slag have been assumed as an additional thickness of $ in. which hag been assigned thermal con ductivity = 1.0. In both cases thermal conductivity refers to one inch thickness. b 874 percent gypsum, 124 percent wood fiber. Thickness indicated includes 4 in. gypsum board. This is a poured roof. c Nominal thickness of wood is specified, but actual thickness was used in calculations. d If corkboard insulation is used, the coefficient U may be decreased 10 percent. A method of determining heat flow rates, when structure is not given in Tables 9 or 10, is illustrated in Example 7. Example 7: A 4 in. stone concrete roof covered with an average depth of 4 in. cin der concrete (A = 4.9) on which is placed a f in. thick felt roof with $ in. pitch and slag surface, is exposed to the sun. The location is the central part of the United States. Cooling Load 309 Design temperatures arc: outdoor 95 F; daily range 20 deg; indoor temperature 80 F. Find the heat flow rate at 2:00 p.m. for a day in July. Solution: For the purpose of selecting the equivalent temperature differential, this construction is assumed to be equal approximately to an uninsulated 6 in. concrete roof, for which the equivalent temperature is found to be 38 deg in the 2:00 p.m. column of Table 9. Calculate the overall heat transmission coefficient U (see Equa tion 3 of Chapter 9) of the roof as follows: XJ =---------------:--------1------- :---------------= 0.33. _L 4 4 -375 | 0 50 , 1 1.2 + 12 + 4.9 + 1.33 + 1.00 + 4.0 The heat flow rate is then 38 X 0.33 equals 12.5 Btu per (hr) (sq ft). OUTDOOR GLASS INDOOR SOLAR RADIATION REFLECTED 1 SOLAR RADIATION RADIATION EXCHANGE BETWEEN GLASS AND SURROUNDINGS TCONVECTION EXCHANGE BETWEEN GLASS AND SURROUNDINGS \ V----- TRANSMITTED SOLAR RADIATION ABSORBED ENERGY DUE TO THE HEAT CAPACITY OF THE GLASS CONVECTION AND RADIATION EXCHANGE BETWEEN CLASS AND INDOORS --A. Fig. 2. Instantaneous Heat-Balance for a Glass or Glass Block Section TABLES FOR CALCULATING SOLAR HEAT GAIN THROUGH GLASS AREAS Basic Principles In order to set forth the principles involved in calculating heat flow through glass areas, the general instantaneous heat-balance relation will be presented. It will be shown schematically in Fig. 2. The net heat gam for the indoor space is the result of several contributing factors. The following observations concerning the behavior of glass with respect to radiant energy will lead to a better understanding of the.heat-balance relation. ,, Glass transmits, in varying degrees, radiation having wave lengths between au and 4.75 microns. The percentage of each wave length transmitted is dependent upon the chemical and physical characteristics of the glass, and upon the angle of cidence of the radiant energy. Of the energy not transmitted, part is absorbed and part reflected. 2. Glass is opaque to radiant energy emitted from sources below 450 F. two pf6?6 the abve-principles, it is convenient to group radiant energy into classifications, solar radiant energy and low-temperature radiant energy. The complete heat-balance for a glass section can be expressed for a unit time interval as follows: Total heat flow, 1 Transmitted, through glass sectionJ " solar radiation ]Heat flow by convective and radiative exchanges at (2a) the indoor surface mi ft h! *2TM term right side of Equation 2a can also be expressed by neat balance equation as follows: