Document 82RbwLnvRn1RqKG5Eqbbn0m2k

314 CHAPTER 13 1953 Guide. Heat Gain from Sources within the Conditioned Space: For the occupants, use the data of Table 25 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. For the gain from lighting, use Equation 15 with a use factor of unity, and a special allowance factor of 1.20 for the fluorescents and of unity for the tungsten globes. g.i = (12,000 X 1.20 + 4000) X 3.41 = 62,700 Btu per hr. For the fan motor, use Equation 16 with a load factor of unity, and omit term Motor Efficiency because the motor is not within the space. gn = 7.5 X 2544 = 19,100 Btu per hr. Moisture Permeation, Miscellaneous Allowance, and the Load-Lag Estimate: Moisture permeation will be negligible, since this is a comfort job with a good building construction. There would be some heat gain in the ductwork, but this would not. be great be-, cause of the short run involved. Practical judgment for this job_would suggest that no adjustment for load-lag need be made to the load as computed. (Refer to Fig. 4). While it is true that inside radiation forms an important part of the total heat gain, it is advisable to be conservative in recognizing the effect of the large, flat, hot roof on the comfort sensations of the occupants. Radiation from the relatively low ceiling, augmented by heat absorption from the lighting fixtures, would produce a sensation of. warmth in excess of the nominal effective temperature (see Chapter 6) estab lished by the wet-bulb and dry-bulb temperatures. Hence, it is not desirable to take advantage of every small decrease possible in the peak design load, especially since the peak occurs in mid-afternoon when everything would be rather weft warmed. Total Loads and Required Air Quantity through Conditioning Equipment: The total loads are summarized in Table 27. Compute the enthalpy difference ratio from Equation 18. h i - h. (187,515 + 30,120) X 1076 = 7770. W,-W. 30,120 Table 27. Summary of Total Loads--Example 13 Load Component Sensible Btu/hr Latent Btu/hr All walls, roof and doors.................................. Glass areas......................................................... Infiltration 67 cfm........................................... Ventilation Air (1275 cfm X 0.15)................... Lighting......................................................... Motor, fan............................................. 78,500 6,030 1,085 3,100 17,000 62,700 19,100 Space Load.................................................... 187,515 Ventilation 1275 cfm X (1-0.15).................... Totals........................................................... 17,600 205,115 Grand Total Sensible and Latent................................................... 2,300 6,570 21,250 30,120 37,230 67,350 272,465 From the A.S.H.V.E. psychrometric chart Chapter 3, determine that the appa ratus dew-point as 53.9 F. Compute the effective air quantity (Equation 19). Then, 187,515_______ Q, 1.08 (80 - 53.9) X 0.85 7830 cfm. Cooling Load 315 (Refer to Chapter 36 for coil selection.) From note under Equation 19 the dry-bulb range will be (80 -- 53.9) X 0.85 .= 22.2 deg, and the dry-bulb temperature of air leaving the coil will be 80 -- 22.2 = 57.8 F. The' dry-bulb temperature leaving the fan (including the heat supplied by the fan motor), or delivered into the room, will be (from Equation 16): 187,515 - 19,100 80 - 19.9 = 60.1 F. 1.08 X 7830 With good distribution and diffusion, this temperature should not produce objec tionable drafts. Example 13: Summary Outdoor Conditions..................... .95 DB Space Conditions......................... . .80 DB 78 WB. 65 WB 0.0169 Humidity Ratio 0.0098 Humidity Ratio Difference............................ 15 0.0071 \ - ' - Sensible Load ' Transmission Btu/Hr Roof 4000 sq ft X 53 X 0.34 =......................................... .........V 72,000 S. Wall 405 sq ft X 6 X 0.41 =........................................ 995 E. Wall 765 sq ft X 11 X 0.52 =......................................... ,............ 4,380 - N. Wall Ex. 170 sq ft X 3 X 0.52 =..................................... :........ 265 N. & W. Party Wall 1065 sq ft X 2 X 0.26 =............................... 550 Floor None Door 35 sq ft X 15 X 0.59 =................................................................ 310 All Glass and Rest of Doors =................. ....................................... 3,020 Solar Radiation S. Glass 60 sq ft X 14 =........................................................................ S. Glass (Doors) 35 sq ft X 42 =........................................................ E. Glass (Doors) 18 sq ft X 14 =........................................................ N. Glass 30 sq ft X 15 =.......................................... '........................... 840 1,470 250 450 Internal Load Infiltration 67 cfm X 1.08 X 15 =....... ....................... ............. 1,085 Ventilation 1275 cfm X 1.08 X 15 X 0.15........................................... 3,100 Lights (12,000 X 1.20 + 4000) 3.41 =................................................. 62,700 People 85 X 200 =.................................................................................. 17,000 Motor, Fan 7.5 hp X 2544 =......................................:........................ 19,100 Total Sensible Space Load....................................................... 187,515 Latent Load Infiltration 67 cfm X 4840 X 0.0071 =............................................... 2,300 Ventilation 1275 cfm X 4840 X 0.0071 X 0.15 ...................................... 6,570 People 85 X 250 =.................................................................................. 21,250 Total Latent Space Load.......................................................... Ventilation Air Which Does Not Become Part of Space Load Sensible 1275 cfm X 1.08 X 15 X (1-0.15) =................................................ Latent 1275 cfm X 4840 X 0.0071 X (1-0.15) =............................................. Grand Total Load................................................................ 30,120 17,600 37,230 272,465 LETTER SYMBOLS USED IN CHAPTER 13 = fraction of incident solar radiation absorbed, dimensionless; subscripts D, d, t refer to direct, diffuse and total, respectively. P = solar altitude, degrees. y -- wall solar azimuth, degrees. f = emissivity, dimensionless. = incident angle, degrees. h = amplitude decrement factor, dimensionless.