Document ybQm3nkE9p56oeQDd2MJZzkY4

292 CHAPTER IS *1948 Guide an ^1'xa7JlP^e 71. A one-story office. building;.Fig. :7 is located m an eastern state near* 40 deg latitude. The adjoining buildings on the north, and west are not conditioned and the air temperature within them is known to be substantially equal to the outdoor air temperature at any time of the day. South wall construction: 8 in. concrete block. 4 in. brick veneer, k? in. plaster on walls. (Table 8, Chapter 6,_No. 92B, U = 0.41.) East wall and outside north wall construction: 8 in. concrete block, 14 iti. plaster on walls. (Table 7, Chapter 6, No. 82B, U = 0.52.) West wall and adjoining north party wall construction: 13 in. solid brick, no plasters . -w = xk + IT + TB5 r' J/ = 0*263* Use; U ~ ;26- Roof"construction: 2^ in. flat roof deck of 2 in. gypsum fiber concrete on gypsum, board surfaced with built-up roofing. (Table 14, Chapter 6,- No. 6A, U ^ 0.38.) Floor construction: 4 in; concrete on ground. r -'ii ' Window: 3 ft x 5 ft, non-opening type, with Venetian.blinds for those on'south wall. Approximately 4 in. reveal on all windows. . Front doors: Two 2 ft-6 in. x 7 ft (glass panels). Side doors: Two 2 ft-6 in. x 7 ft (}/2 glass panels). Reardoors: Two 2 ft-6 in. x 7 ft (glass panels). Outside design conditions: Sol-air temperature cycle corresponding to New York City, Table10, this chapter; maximum dry-bulb 95 F, wet-bulb 78 F; W0 -- 0.0169 lbs vapor per IB dry. air; Ao = 41.38 Btu per lb dry air. * Indoor design conditions:" Dry-bulb 80 F, wet-bulb.65 F; W\ = 0.0098 lbs vapor per lb dry air; h\ = 29.95 Btu per lb dry air. Occupancy: 85 office workers. i . Lights: 12,000 watts fluorescent, 4,000 watts tungsten. Fa.n motor:' 7)^ hp. , Conditioning equipment to be located in adjoining structure to north. Required: Total, sensible;, and latent maximum cooling, loads and required air quantity through conditioning equipment. Solution. From Table 4 the recommended ventilation rate is 15 cfm per person. rTotat necessary = 85 -X 15 1275 cfm or 76,5Q0-cu ft per hr. Check: Room volume is 40,000 cu ft = 1.91 air changes per hr.. r* . Cooling Load 293. Estimated Timeof Maximum Cooling Load. For this job, judgment indicates-that the greatest single contribution to the cooling 1 load will be from the roof. Hence, the time of the maximum cooling load will be the . time of the maximum heat gain through the roof. In some cases, there would be no clear-cut evidence of this nature and,consequently it.would be necessary to estimate the load for several successive times and then to select the maximum. From Table 12, estimate the roof time lag as 2 hours. From Table 13, take the time of the maximum rate of heat entry as 1:00 p. m. The estimated time of maximuminterior heat gain follows as 3:00 p. m. (This may be slightly different than 3:00 p. m. civil time.) Heat Gain Through Outer Wall and Roof Areas. -.The first step is to determine values of tp using Tables 10 and 12 and Fig. 4 as follows: tm (24 hr average) is read directly, from Table 10. -: The time lag is approximated from Table, 12 for exterior.walls. South wall: Estimate 4 in. common brick as 2.3 hr, 8 in. concrete block and % in. plaster (equivalent to 6 in; of solid concrete) as 3.8 hr, plus 1 hr for heavy construction = approximately 7 hrs. East wall and exposed North wall: Estimate 8 in. concrete block and in. plaster as 3.8, plus 1 hr = approximately 5 hrs. The time of maximum rate of heat entry is entered in the next column as the time* earlier than 3:00 p. m. by the amount of the time \a.g'. tc* is read from Table 10. Factor X is read from Fig. 4, and tp is calculated from Equation 10. The tabulation of the values obtained is given in the following table. Section Roof (light const.)........... South wall........................ East wall........................... Exposed north, wall. .1-- tm F 106.4 90.7 92.3. 88.5. For (&//of 0.25. Time Lao Hr 2 7 5 5 Time op Max. Heat Entry . 1 p. m. 8 a. m. 10 a. m. 10 a. m. F 154 86 114 . 92 . Factor X 0.91 0.30 0.35 0.50 F' 150 89 100 90 . Next, for an indoor temperature ft -- 80 F, the rates of heat gain may be calculated and tabulated. Section Roof......................... ............. -- South wall................................ East wall...... ........................... Exposed north wall................. Net Area Sq Ft 4000 405s 765a 1703 u Btu/(Hr) . (Sq Ft) (F Deg) 0.38 0.41 0.52 0.52 , (*p -- <0 F Dec . 70 9 20 10 Total............ 'Q Btu Per Hr 106,400 1,490 7,950 880 116,720 "Calculated from gross .wall area less windows and doors. Determine Heat Gain Through Parly Wall and Inside Door Areas. For the door, estimate U = 0.59, from Chapter 6, Table 9, No. 5A; Space tempera ture at 3:00 p. m. is, from Table 10, 94 deg'F. Neglect the time lag for the'door and take (<p -- ti) = 94 -- 80 = 14 F deg. The party wall will be treated as if it were an outside wall in the shade, which cor responds to (b/fo) = 0 in Table 10. From Table 12, time lag = 9.5 hr, >. -- 0.23. l0 .= 84.8 + 0.23 (76 - 84.8) = 82.8 F.