Document ppjvGZDJBKpedyxVNporK2Mx7

298 CHAPTER 12 1950 Guide 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 + 67 = 1342 cfm. The sensible, latent and total loads are determined from Equations 13,14 and 15, respectively, at 3:00 pan. (Table 13) = 95, ft = 80, W',, = 0.0169, W, = 0.0098. All the air entering the room as infiltration becomes a part of the space load. Infiltration: g, = 67 X 1.08 (95--80) = 1085 Btuh, sensible. q. = 67 X 4840 (0.0169-0.0098) = 2300 Btuh, latent. ? = 3. + 9. = 1085 + 2300 = 3385 Btuh, total. - Ventilation Air Taken through Cooling Unit Which Does Not Become a Part of the Space Load: q. - 1275 X 1.08 (95-80) - 20,700.Btuh, sensible. q. -= 1275 X 4840 (0.0169-0.0098) = 43,800 Btuh, latent. q% = 9. + 9. = 20,700 + 43,800 = 64,500 Btuh, total. Heat Gain from Sources within the Conditioned Space: For the occupants, use the data, of Table 24 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 16 with a use factor of unity, and a special allowance factor of 1.20 for the fluorescents and of unity for the tungsten globes. q* (12,000 X 120 + 4000) X 3.41 = 62,700 Btu per hr. For the fan motor, use Equation 17 with a load factor of unity, and omit term Motor Efficiency because the motor is not within the space. i = 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. 6). 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 a4vantage of every small decrease possible 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 Table 26. Compute the specific enthalpy of the water difference room air and supply air, from Equation 19. (183,945 + 23,550) . 9* 1 23,650 X 1076 - 9480. Cooling load 299 Table 26. Summaby or Total Loads--Example 11 Load Cohfokxmt 8eX8IBLK Btu/Hr Latent Btu/hr 78,500 5,560 1,085 17,000 . 62,700 19,100 183,945 20,700 204,645 2;300 21,250 23,550 43,800 : 67,350 271,995 From the Goff diagram, determine that the apparatus dew-point is 54.3 F (refer to Chapters 3 and 29). In computing the effective air quantity, assume a coil efficiency of 85,per cent. 'Then, 183,945 Q, 1.08(80 - 54.3) X 0.85 7810 cfm. (Refer to Chapter 35 for coil selection and efficiency.) From note under Equation 20 the dry-bulb range will be (80--64.3) X 0.85 == 21.8 deg, and the dry-bulb temperature of air leaving the coil will be 80 --21.8 = 58.2 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 22): 183,945 - 19,100 <4 1.08 X 7810 80 - 19.5 60.5 F. With good distribution and diffusion, this temperatureshould not produce objec tionable drafts. Example 11: Summaby Outdoor Conditions............... ..95DB Space Conditions-- ...............80 DB 78 WB 65 WB 0.0169 Humidity Ratio 0.0098 Humidity Ratio Dipfebence......................... 15 .0.0071 SensiblbLoad Transmission Btu/Hr < Roof 4000 sq ft X 53" X 0.34 =............................................................ 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 soft X 3 X 0.52 --................... ....................... 265 N. & W. Party Wall 1065 sq ft X 2 X 0.26 -.................................. Floor None 550 ~ Door 35 sq ft X 16 X 0J -.......... ..................................... .......... 810.. . ,. All Glass 160 sq ft X 15 X 1.04 -........................................................ 2,510 Solar Radiation S. Glass 60 sq ft X 0.46 X 0.74 X 42 =.............................................. S. Glass (Doors) 35 sq ft X 1.0 X 42 =.................... E. Glass (Doors) 18 sq ft X 15 -.............. N. Glass 30 sq ft X 15 =............................ 860 1,470 270 450 , a Internal Load Infiltration 67 cfm X 1.08 X 15* =........................ ....... ......... . 1,085 Lights (12,000 X 1.20 + 4000) 3.41 -...:........ ...................... . 62,700 People 85 X 200 =................................../............................ ................... 17,000 , Motor, Fan 7JS hp X 2544 =........................................ ...................... 19,100 ! Total Sensible Space Load............................................................. 183,915