Document JJkgGpE7RwrkBxrgY613mzNa

312 CHAPTER 13 1954 Guide of Equation 18 may be solved by ;trial and error by substituting values of ft, and W, corresponding to assumed apparatus dew-point temperatures. 5. Compute the required air quantity from thedelation Qri = (Space sensible load) Space \ / Apparatus \ ^ ( Coil \ (19) K1.08 dry-bulb/ \ dew-point j I by-pass ) \ factor / The magnitude of Qr is substantially the quantity, cfm, of cooled and dehumidified air fbr which the distribution system must be designed. The numerical factor' 1.08 is derived from the product 1 cfm X 60 min X 0.244 X ''O' 00923V': ' . '" '* (1-----1)62 / = assuming an average supplyairdew-pointof-55 F; iSince standard air density (0.075) includes the weight of the water vapor, it is desirable to reduce it to the basis of dry air by the last factor where 0.00923 = humidityratio of; air. at 55 F dew-point, and 0.62 = ratio of density of water vapor to dry air at same temperatureand pressure.. Refer to Chapter 36 for coil Selection) , ! ! j - Note that the product [(space dry-bulb) -- (apparatus dew-point)] X (coil by- -j pass factor) is equal to the dry.bulb range through which the conditioned air is cooled.* Hence; in rare instances whenthecondition line of the process may not intersect the. saturation line; any other convenient reference temperature on the condition line if may be used instead, provided that the coil by-pass factor is specified accordingly op the proper basis;*' " '; ' ,!l: 0. MINIMUM ENTERING AIR TEMPERATURE Due consideration must be given to the temperature of .the air entering) ,4- the conditioned space in order to prevent objectionable drafts. With qeil-vv'; ing type diffusers or wall grilles with a high aspect ratio (see Chapter 31), many engineers consider 20 deg as the maximum difference for good* design [p under average conditions. This difference can only be exceeded with ex-a-p: tremely high ceiling outlets or wall grilles. Thus, if 8Q`F dry-bulb is to be maintained in a space with average ceiling height, the:minimum delivered*, air temperature would be limited to about 60 F dry-bulb temperature. If the latent heat load is relatively high, it is often necessary to circulate morejji air with a higher delivered dry-bulb temperature in order to produce a->f thermodynamic balance. If the dry-bulb temperature of the air supplied^),; to the space is known, the required air quantity can be calcuated frbnhiv the formula, 'fe " q` 1.08 (b - b) t,or the supply temperature can be determined as follows, (>& i.o8 x EXAMPLE--COOLING LOAD CALCULATION (21) 'll* .lit? An effective means of summarizing the calculation procedure will be thefc use of an illustrative example. While condensed calculation forms ai^ commonly employed for work of this nature, an outline will be used' hereisg in order to facilitate explanatory comments: l!1- Ex,ample IS: A one-story office building Fig. 6 is located in an eastern state nearjjQjjti deg latitude. The adjoining buildings on the north and west are not conditioned,jg! Cooling Load air temperature, at--a--n-y---tim..e..moifmtheemdiasyk.nown to be'substantially equal to the,o utdoor South wall construction: 8 in. concrete block, 4 in. brick veneer, 4 in. plaster on walls. (Table 9, Chapter 9, No. 92B, t/= 0!41-.) East wall and outside.nortk.wsl! construction^ in; concrete block, painted white, in. piaster on walls., (Table 8, Chapter 9, No, 82B;!U = 0.52:);i' **-: * West wall and adjoining north party 'Wall'construction': 13 in. solid brick) no plaster: : i,>! 1.65, 5 + 1:65 or' ^- 0.263: Use U = 0.26. Roof construction:>24 in. flat roof deck Of 2 mV gypsiiin'fiber concrete' oh.gypsum board surfaced with'built-up roofing. (Table l'l','f/!=* 0.34/or summer.) Floor construction: 4 in. concrete on ground. Window: 3 ft x 5 ft, non-opening type, with medium colored Venetian blinds,for windows on south wall. Approximately 4 in. `reveal on all windows. ADJOINING 0tlILDING :' . 13 BRICK PARTY WALL ' W GENERAL * OFFICE IO'-o* CEILING FLAT ROOF eo-o gCONCRETE BLOCK-gVASTro PARKING LOT, 5*X 7 Fig. 6. Plan of One-Story Office Building Front doors: Two 2 ft-6 in. x 7 ft (glass panels). Side doors: Two 2 ft-6 in. x 7 ft G glass panels). Rear doors: Two 2 ft-6 in. x 7 ft (wood panels). ., Outside design conditions: Maximum dry-bulb 95 F, wet-bulb 78 F; Wo = 0.016. ffis vapor ,, Indoor p,d--eersilgbnudcrryoynaadiiirirtt;i;ioohAnnesss==': ID44)r11rv:y.3-3V-88biuBuBHlttbuu, gtpoepr'lbwdert-ybauilrb. 65 F ;Wj ,! . ' , 0.0098 lb vapor per imbddrryvaaWir; .Ai, - 2--9.9-5 Btu per lb.dry air.. - Occupancy: 85 office workers. Lights: 12,000 watts, fluorescent; 4000 watts tungsten. Fan motor: 7} hp. . Assume that cooling coil has a by-pass factor of 0.15, i.e., that 15 percent of th r Passes through the coil without contacting the coil surface. Conditioning equipment to be located in adjoining structure to north. th F'nd: Total, sensible) and latent maximum cooling loads and required air quantitj mugh conditioning equipment. Tntial necessaFrryo=m 8T5aXble153,=th1e27r5eccofmmmore7n6d,e5d00vceunftti)lapteior nhrr.ate. is 15 cfin per. person