Document omKE2xqzjY0Oaog84Vr9QK34D

122 CHAPTER 9 1959 Guide Table 17 .... Effective Resistance of Ventilated Attics*--(Summer Condition)11 PART A. NON-REFLECTIVE SURFACES No VonHJation Natural Voa&otioo Power Ventilation* Veatdotion Air temp^ F Sol-aiH temp., F > Ventilation rate, cfm/ sq ft 0.1* 0.5 l/U Ceiling resistance, ru* 1.0 1.5 10 20 10 20 10 20 10 20 10 20 120 1.9 1.9 ' 2.8 3.4 6.3 9.3 9.6 16 11 20 80 140 1.9 1.9 2.8 3.5 6.5 10 9.8 17 12 21 160 1.9 1.9 2.8 3.6 6.7 11 10 18 13 22 120 1.9 1.9 2.5 2.8 4.6 6-7 6.1 10 6.9 13 90 140 1.9 1.9 2.6 3.1 5.2 7.9 7.6 - 12 8-6 15 160 1.9 1.9 2.7 3.4 5.8 9.0 8.5 14 10 17 120 1.9 1.9 2.2 2.3 3.3 4.4 4.0 6.0 4.1 6.9 100 140 1.9 1.9 2.4 2.7 4.2 6.1 5.8 8.7 6.5 10 160 1.9 1.9 2.6 3.2 5.0 7.6 7.2 11 8.3 13 PART B. REFLECTIVE SURFACES' 120 6.5 6.5 8.1 8.8 13 17 17 25 19 30 80 140 6.5 6.5 8.2 9.0 14 18 18 26 20 31 160 6.5 6.5 8.3 9.2 15 18 19 27 21 32 120 6.5 6.5 7.5 8.0 10 13 12 17 13 19 - 90 , 140 6.5 6.5 7.7 8.3 12 15 14 20 16 22 160 6.5 6.5 7.9 8.6 13 16 16 22 IS 25 120 6.5 6.5 7.0 7.4 8.0 10 8.5 12 .8.8 12 100 140 6.5 6.5 7.3 7.8 10 12 11 15 ' 12 16 160 6.5 6.5 7.6 8.2 11 14 13 18 15 20 The term efftcdm rtsistance i* need when there i attic ventilation. A value for do ventilation it alto included. The effective rtetitanee of the attic may be added to the rrsistarm (1/U) of the (Table IS, Part D) to obtain the effective reetstanee of the combination baaed on aol-air (Chapter U) and room temperature. These value* apply to wood frame construction with a roof deck and roofing having a conductance of 1J> Bto/(aq ft) (hr) (F dec)- t When attic ventilation meet* the requirement* of Table S in Chapter 10,0.1 cfm/aq ft may be assumed as the natural summer ventilation rate for design purpoeea. Strutaae* t/ntt, abbreviated r b one (hr) (aqft) (F deg) per Btu. Determine ceiling Amstanoe from Table* Hand 16, and correct for framing by Figure 8- Do not add tbe effect of a reflective surface facing the attic to tbe ceiling resistance from Table 16, Part D, as it b accounted for in Table 17, Part B. d Roof rarfrae temperature rather than aol-air temperature (see Chapter 13) may be used if 0.29 ia subtracted from the attic resistance ahown. Ratod on air discharging outward from attic. ( Surfaces with effective emiasmty B cf 0.0S between ceiling jotsfs being tbe attic apace. by the roof area. Values of Ur and [/* should be calculated nging a value of 2.5' (the reciprocal of one-half the air space resistance, 0.80) rather than the conductances of surfaces facing the attic, since the attic is assumed to be equivalent to an air space. If the attic contains windows, dormers, and vertical wall spaces, and if their area is small compared to that of the roof, they may be considered part of the roof area. For accuracy, the sum of the coefficients of each individual section, multi plied by its percentage of the total area, should be used as Ur. Where attic wall areas are large or where louvers or vents are used, it is preferable to estimate the attic temperature as illustrated in Chapter 12, and calculate the heat loss through the ceiling by multiplying the value of /* for the ceiling by the difference in temperature above and below the ceiling. - BASEMENT FLOOR, BASEMENT WALL, AND CONCRETE SLAB ROOR COEFFICIENTS The heat transfer through basement walls and floors to the ground is dependent on the temperature difference between the air within and that of the ground, on the material con stituting the wall or floor, and on the conductivity of the sur rounding earth. The conductivity of the earth will vary with local conditions, and is usually unknown. Tests11 at the ASHAE Research Laboratory indicate a beat flow of approxi mately 2.0 Btu per (hr) (sq ft) through an uninsulated con crete basement floor,, with a temperature difference of 20 deg between ground temperature and the air temperature 6 in. above the floor (see Table 18). For basement walls below grade only, the temperature dif ference for winter design conditions will be greater than for tiie floor. The test results indicate a unit area heat loss, at mid height of the basement wall portion below grade approxi mately twice that of the same floor area. For concrete slab floors laid in contact with the ground at grade level, testeu indicate that for small floor areas (equal to Table 18 .... Coefficients of Transmission ((/) of Concrete Basement Floors on Ground with Various Types of Finish Flooring U = 0.10* Btu per (hr) (sq ft) (Fahrenheit degree temperature difference between the ground and the air over the floor). * Since authentic date axe not available, this coefficient ia sometimes used tar concrete floor* os ground. For more recent procedure*0 refer to National Bmw tf Standard* Report BMS-IQ3. Heat Transmission Coefficients of Building Materials 123 that of a house 25 feet square) the heat loss may be calculated as proportional to the length of exposed edge rather than total area. This amounts to 0.81 Btu per (hr) (linear foot of ex posed edge) (Fahrenheit degree difference between the indoor air temperature and the average outdoor air temperature). It should be noted that this may be appreciably reduced by in sulating under the ground slab, and also along the edges be tween the floor and the abutting walls. See also sections on Basement Temperatures and Heat Loss, and on Floor Heat Loss in Basementless Houses, in Chapter 12. In most calcula tions if the perimeter toss is Uteri accurately, no other floor loss need be considered. GLASS AND DOOR COEFFICIB^TS The U values for glass sheets and hollow glass block, given in Sections A, B, and C of Table 19, have been computed by methods ind data given in an ASHVE Research Paper.* It is assumed that the surface conductance for convection loss td the air is 4.0 Btu per (hr) (sq ft) (F deg). It is also as sumed that the glass loses heat by radiation to the ground wnH to the clear sky, which together have an effective radiat ing temperature below the air temperature. It is therefore necessary to determine, by trial and error, the temperature of the outdoor glass surface such that the sum of the radiation and convection losses equals the heat conducted through the glass section, and equals the heat delivered to the glass from the heated space. This heat flow, divided by the air-to-air temperature.difference, results in a U value that is used in the usual manner. The equivalent surface conductance for -radiation and convection combined, based on air-toswface temperature difference, therefore varies from about 5.5 for single glass to about 6.6 for double glass for exactly the same environmental design conditions. Curtains, draperies, Vene tian blinds, etc., will result in lower glass surface temperatures than when the windows are not covered. It is assumed that the room air temperature equals the aver age temperature of the room surfaces seen by the glass. Special consideration should be given to those cases where the glass sees interior surfaces at temperatures differing greatly from the room air temperature, i.e., such cases as in sun rooms, greenhouses, and some panel heated rooms, or where there is an unusual amount of air motion in the vicinity of the glass. Although based on zero outdoor air, the values change only slightly with different design temperatures, being about 5 percent greater for a 30 F outdoor design temperature. In computing the Table 19 values, consideration of the de pendence of the indoor surface conductances upon tempera ture and direction of heat flow leads to surface conductances averaging about 1.50 for block and vertical glass, and about 1.80 for horizontal glass, as compared to the value of 1.46 used in computing U values given in other tables in this chapter. These values should therefore be used in estimating the temperature at which condensation on glass surfaces will occur. The application factors given in Section D of Table 19 are based upon hot box tests summarized in a research bulletin,14 and are approximate only. In practice, some variation in heat flow through windows having the same ratio of glass to sash area, may be expected because of difference in construction details and in air-space edge effects. The high conductance of aluminum and steel sash must be taken into consideration where excessive amounts of metal sash and frames are in volved. This is particularly important when they are in close proximity to radiation heat sources and are consequently subjected to high differential temperatures. Table 19 .... Coefficients of Transmission (U) of Windows, Skylights and Glass Block Walls Coefficients are expressed m Btu per (hour) (square Foot) (Fahrenheit degree difference in temperature between (be arr on the two *idei). Those for out door exposures are bored upon tbe following outdoor conditions;' 0 F air temperature, dear duos, no color radiation, ond 15 mpb outdoor wind velocity SECTION A--VERTICAL GLASS SHEETS Number of Sheets...................... One Two Three Air space, inches............... Outdoor exposure.......... Indoor exposure............. None X X 1* X 1.13 9.610.55 9.53 J.41 0.3610.34 0.75 0.50 0.46 0.45 0.38 0.33 0.32 SECTION B--HORIZONTAL GLASS SHEETS Heed Row Up Hoot Flow Down One Two One Two o!e3Air space, inches . .. None X 1 X Outdoor exposure . 1.40 0.700.66 None X X Indoor exposure.. 0.96 0.59|0.56 0.56 0.60 0.43 0.39 0.38 SECTION C--WALLS OF HOLLOW GLASS BLOCK Description Outdoor Indoor Exposure Partition SX x bXx 3J4 >n- thick.......................................... 7X x IX x 3% in. thick........................................... llX x ILX x 3% in. thick...................................... TX x ?X x 3% in. thick with glass fiber di viding the cavity............................................... llX x LlX x 3% in. thick with glass fiber dividing the cavity................................................ 0.60 0.56 0.52d 0.4S 0.44 0.46 0.44 0.40 0.38 0.36 SECTION O--APPROXIMATE APPLICATION FACTORS FOR WINDOWS--MULTIPLY FLAT GLASS U VALUES BY THESE FACTORS Window Description Single Glass Double Glass* Windows with Storm Sash1 Percent Glass* Factor Percent Glass* Factor Percent Glass* Fto, Sheets................................ 100 100 100 1.00 Wood sash...................... 80 0.90 80 0.95 80 0.90 Wood sash...................... 60 0.80 60 0.85 60 0.80 Steel sash....................... 80 1.00 80- 1.20 80 1.00* Aluminum. ................... 80 1.10 80 1.30 80 1.10 For I in. or greeter. b See Chapter IS. Tablet 14 and 14, (or rammer load. * See Chapter 13, Tables 14,14, aad 16, for summer load. d From unpublished data recommended by ASHAE Tech. Adv. Comm, on Heat Flow Through Fenestration. * Unit type double (Using (two light* or panes in oune opening). ( Use with V values for two sheet* with 1 in. air apaoe. * Rnfind on area of expoaed portion of aasb; doe* not include frame or portions of aaab concealed by frame. * For metal storm aaab or metal saah with attached storm pane.