Document ybmv87ywmGK5DzLO8xE4kKRoX

338 CHAPTER 13 1958 Guide / perature differential for the north exposed wall (8 in. concrete block plus plaster) will be 3 deg at 3:00 p.m. (by interpolation) for a light wall. The party wall of 13 in. brick on the west side and part of the north side may be treated as if it were an outside wall in the shade which has a temperature differential (from Table 10) of 2 deg. For the door in north wall estimate U -- 0.59 from Chapter 9. The outdoor temperature at 3:00 p.m. is 95 F. Neglect time lag and any decrement factor. The temperature differential is (Ip -- U) = 95 -- 80 = 15 deg. The tabulation of the pre ceding values at 3:Q0 p.m. is given in the following table: Section Net Area Sq Ft Temperature Differential F Deg Heat Transmission Coefficient (U) Heat Flow Rate per Hour Btu Roof South Wall East Wall North Exposed Wall West & North Party Wall Door in North Wall 4000 405* 765* 170* 1085* 35 53 6 11 3 2 15 0.34 0.41 0.52 0.52 0.26 0.59 72,000 995 4,380 265 550 310 78,500 * Calculated from gross wall area, less windows and doors. Heat Gain Through Glass Areas In computing the load for 3:00 p.m., only the south windows and doors will be exposed to direct sunlight. Tables 12 and 13 will give the total heat gain from the glass areas. The window reveals will shade the south windows; the fraction of the window area receiving direct radiation is obtained from Equation 5 by substituting values as follows: n = s/l = 4/60; r, = 4/36; 0 = 45.5 deg, tan 0 = 1.02 y -- 74 deg, tan y = 3.487, cos y = 0.276 - - 4 (S) -1+ (a) ^ - * The Bouth doors will be considered entirely sunlit. The outdoor air temperature is 95 F at 3:00 p.m. From Table 25 the inside Venetian blind factor is 0.65. The instantaneous heat gains due to transmitted direct and diffuse solar radiation, and from convection ana radiation gain, are found in Tables 12 and 13 as listed below for the south facing doors and windows, the north facing windows and the J glass doors-in the east wall. The gain through the solid portion of the east doors may be approximated by use of Fig. 3, since the wood panels have little heat capacity. From Table 4 the diffuse radiation value is taken as 18 Btu per (hr)(sq ft) from which U, + aJJ{m is found to be 98.2 for a = 0.7 and /m, = 4.0. From Fig. 3, 7 = 22.0 Btu per (hr) (sq ft). These heat gains are itemised in the following table. Location South Doors East Doors/Glass \Wood North Windows Total Area So Ft 60 35 18 18 30 Frac tion Sunlit 0.462 1.00 -- -- -- Shads Factor 0.65 -- -- -- -- Trans Solar Gain Btu/ (hr) (sq st) Cobb Cony from 75F to and Rad 80F Gain Btu/ Indoor Temper (hr) ature (sqft) Btu/(hb) (sq ft) Total Gain Btu/ (hr) (sqft) 13 19 _ 42 19 -- 14 17 -- -- 22 -- 15 17 32 61 31 22 32 Total Gain Btu/hs 1920 2135 560 960 5970 .Cooling Load 339 In some jobs it would be desirable to increase (or decrease) the instantaneous radi ation heat gain by a load-lag factor. .The reason for not doing so in this case is that the solar gain is of a low magnitude, and reference to the table indicates that 0.8 of the previous hour would not affect the results materially. Heat Gain from Ventilation and Infiltration: Since the desired outdoor air rate 1275 cfm is greater than one air change per hour, it will be satisfactory for determining the ventilation component of the heat gain. Window infiltration can be taken as negligible since the windows do not open. Door infiltration requires some judgment. Assume that for each person passing through the double doors, the infiltration will be 100 cu ft of outdoor air, see Chapter 10, Table 3. Assume that the outside doors will be used at the rate of 10 persons per hour and the inside doors at the rate of 30 persons per hour. Total infiltration will then be 40 X 100 = 4000 cfh or 67 cfm. The design rate of entry of outside air is then: Q = 1275 -f 67 = 1342 cfm. The sensible, latent and total loads are determined from Equations 7, 8, and 9, respectively, at 3:00 p.m. (Table 8) to = 95, t, = 80, Wo = 0.0168, W, = 0.0098. All the air entering the room as infiltration becomes a part of the space load. Infiltration (see Equations 7, 8, and 9): 7. = 67 X 1.08 (95-80) = 1085 Btuh, sensible. 7. = 67 X 4840 (0.0168-0.0098) = 2270 Btuh, latent. 7t = ?. + 7. = 1085 + 2300 = 3385 Btuh, total. Ventilation Air Taken through Cooling Unit Which Becomes a Part of the Space Load (see Equations 10 and 11): 7.i = 1275 X 1.08 (95-80) (0.15) = 3,100 Btuh, sensible. ?i = 1275 X 4840 (0.0168-0.0098) (0.15) = 6,480 Btuh, latent. Ventilation Air Taken through Cooling Unit Which Does Not Become a Part of the bpace Load (see Equations 12 and 13): 7.* = 1275 X 1.08 (95-80) (1-0.15) = 17,600 Btuh, sensible. 7* = 1275 X 4840 (0.0168-0.0098) (1-0.15) = 36,715 Btuh, latent. 9* = 7.i + ?,, + 7Ci + 9ex = 3100 + 17,600 + 6480 + 36,715 = 63,895 Btuh total. Heal Gain from Sources within the Conditioned Space: For the occupants, use the data of Table 27 for moderately active office work. Sensible heat gain = 85 X 200 = 17,000 Btu per hr. Latent heat gain = 85 X 250 = 21,250 Btu per hr. Total = 38,250 Btu per hr. allowni^16 r a'D ^rom lighting, use Equation 15 with a use factor of unity, and a special ce factor of 1.20 for the fluorescents and of unity for the tungsten globes. 9.i = (12,000 X 1.20 + 4000) X 3.41 = 62,700 Btu per hr.