Document YDm3KdEx4RLqJvE3re748jQd0

338 CHAPTER 13 1957 Guide Ventilation Air Taken through Cooling Unit Which Does Not Become a Part of the Space Load (see Equations 12 and 13): 5,, = 1275 X 1.08 (95-80) (1-0.15) = 17,600 Btuh, sensible. g,, - 1275 X 4840 (0.0169-0.0098) (1-0.15) = 37,230 Btuh, latent. at = 9.1 + s.x + g.i + 9.* = 3100 + 17600 + 6570 + 37230 = 64,500 Btuh total. Beat 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. 9,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. 5,, = 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 iB 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 possiule in the peak design load, especially since the peak occurs in mid-afternoon when everything would be rather well warmed. Total Loads and Required Air Quantity through Conditioning Equipment: The total loads are summarized in the following table: Summary of Total Loads--Example 13 Load Component Sensible Bto/hr Latent Bta/hr 78,500 6,030 1,085 3,100 17,000 62,700 19,100 187,515 17,600 205,115 Grand Total Sensible and Latent...................................................... 2!300 6,570 21,250 30,120 __ 37,230 67,350 272,465 Compute the enthalpy difference ratio from Equation 18. hi - h. (187,455 + 30,120) Wi-W, 30,120 X 1076 = 7770. Cooling Load 339 From the A,S.H,A.E. psychrometric chart.Chapter 3, .determine that the appa ratus dew-point as 53.9 F. Compute the effective air quantity (Equation 19). Then, Qn = 187,455 1.08 (80 - 53.9) X 0.85 = 7830 cfm. (Refer to Chapter 35 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 (frond Equation 16): t. 187,455 - 19,100 1.08 X 7830 80 - 19.9 = 60.1 F. With good distribution and diffusion, this temperature should not produce objec tionable drafts. The various calculations for the sensible, latent, and total heat loads for Example 13 may be summarized as follows: . Example 13: Summary Outdoor Conditions................... ....... 95 DB Space Conditions............................... 80 DB 78 WB 65 WB Difference............................. 15 0.0169 Humidity Ratio 0.0098 Humidity Ratio 0.0071 Sensible Load Transmission Roof 4000 sq ft X 53 X 0.34 =........................... S. Wall 405 sq ft X 6 X 0.41 .. ........................... E. Wall 765 sq ft X 11 X 0.52 =....................... N. Wall Ex. 170 sq ft X 3 X 0.52 =....... - N. & W. Party Wall 1065 sq ft X 2 X 0.26 =. Floor None Door 35 sq ft X 15 X 0.59 =............................... All Glass and Rest of Doors =......... .......... Solar Radiation S. Glass 60 sq ft X 13 ................................. S. Glass (Doors) 35 sq ft X 42 = -.'---E. Glass (Doors) 18 sq ft X 14 =........ N. Glass 30 sq ft X 15 =................-............ Interned Load Infiltration 67 cfm X 1.08 X 15 ........... Ventilation 1275 cfm X 1.08 X 15 X 0.15.. Lights (12,000 X 1.20 + 4000) 3.41 =......... People 85 X 200 ................................ ............. Motor, Fan 7.5 hp X 2544 =......................... Total Sensible Space Load............................................. ............... Btu/Hr 72,000 995 4,380 265 550 310 3,020 780 1,470 250 450 1,085 3,100 62,700 17,000 19,100 187,455 Latent Load WWtmion 67 cfm X 4840 X 0.0071 =............. .................. ... 2,300 People 85 X1225705 c--fm.....X....4..8..4..0....X....0....0..0..7..1....X. 0....1...5....................................................................................:. 261,5,27500 - Total Latent Space Load........................ 30,120 Sw!Jli'ation Aib Which Does Not Become Part of Space Load Law .l?75 Cfm X 1.08 X 15 X (1-0.15) =................................................ 1275 Cfm X 4840 X 0.0071 X (1-0.15) =.................................................. --__ Grand Total Load....... ............................................ ------------- - -- - - ---- --.--------------------------------- it. 17,600 37,230 272,405