Document XzoG7JM6yKqKwo340wDQ8Zqdx

524 CHAPTER 27 1965 Guide And Data' Book Heat Gain Through Outer Wall and Roof Areaj: - -i From Table 9 the temperature differential ` for'the south' wall (8-in. concrete block with 4-in. brick veneer) may be about the same as a 12-in. brick which is 6 deg.at 2:00 p.m. for a dark colored wall. From the same table, the temperature differential for the east wall (8-in. concrete block with plaster) will be 12 dee at 2:00 p.m. for a light colored wall, likewise, the tempera ture differential for the north exposed wall (8-in. concrete block phis plaster)' will be 2 deg at 2MX) pjn. 1 The party wall of 13-in. brick on the west side and part of the north ode may-be'treated as if it were an outside wall in the shade which has-a temperature differential (from -Table 9) Of2deg.- For the doors in north and east walls, estimate Us = 0.59 from' Chapter 24. The outdoor, temperature at. 2:00 p.m. is 94 F. Neglect time lag and any decrement factor!. The temperature differential ta (L'--U) m 94 -- 75 = 19 deg. From Tabled, the temperature differential-for the south door may be-considered the same as dark frame construction and estimated at 30 F. -The tabulation of the preceding values is given in the following table: Section Net Abba Sq Ft TempehaTUBB DirrsBENTIA-L F Deg* Hrt Trans mission CoErn,-CIENT ;u Heat : Flow ' ' Rate' . PEB Hour Btu: Roof South wall . . East wall North exposed wall .. West A northparty wiill Doors in north and east Twalls Door in south wall' .' 4000 405 765* 170* 1065* 70 35 52+4 = 56 - 0.34. 6+4 = 10 0.39 12+4-16 ;> 0:4S 2+4-6 0.48, 2+4-6 0.26 * .76,200 1,580 ' 5,8S0.i . 490 1,660; 19 54 ! '0:59 ` ''780 ::0.S9 ; 700' '''Total:.v'.. v------ -- 87 ,290 * Calculated (ram pea* wall area, lea faocatraliao And doom.. . * Valoea given ere corrected (or t -- (< = 1 dea-' ` Heal Gam Through Faiestration Areas: . ^Examinataon .of'Tables 11- through 17 shows that for south windows at 40*N. latitude, the Solar Heat Gain Factors at 2:00. p.m suntime are highest in December and lowest in June. Some judgment is therefore required to select . the heataim through windows.which, combined with the other loads; will result in the nmimnm total heat gain The equivalent temperature differential method for calculating roof loads is shown in the notes for Table 8 to apply for. tho months of April through August without reduc tion in hint flow..Therefore, August is selected for-the calculation* of heat gains through windows. . !- Using Tables 13{18, and 2GA, the total heat gains through the', south and north -windows were calculated as shown in the follow ing tabulation: The solar heat gains for the south windows .were faJrwn aa the product of. the Shading Coefficient and the average of the Heat Gain Factors for the three hours,-12:00 noon,-1:00 pjn., 'and, 2:00 p.m. Averaging of the solar heat, gains .for. the three hours, which is a method based on experience and judg ment, is intended to adjust the instantaneous heat gains to air conditioning loads. The solar heat gain for the north windows were calculated for 2:00 p.m. The reasons for not averaging these Heat Gain Factors is that the magnitude and variations are low, and previous hours'would not affect the results materially. The air-to-air heat gain must be added to the solar beat gain for the total lead through the windows. Location Abba Sq ft South windows North windows 60 30 Total Solas Heat Gain Btu/ (HB) (sq it) Aib to Am :Heat * Gain Btu/ (SQ FT) 67 11 11 11 Total Gain Btu/ (he) (sq ft) , Total Gain.?. Btp/" (hb) 78 4,680 22 660 5,340 Heat Gam from-Ventdation and Infiltration: l Since the desired outdoor air. rate 1275, ,cfm ts greater, than one air change per hour, it will be satisfactory for determining the ventilation component of the beat gain. .? Window infiltration can be taken as serd since the .windows are sealed. .. Door infiltration requires Borne judgment. Assume that`for each person passing through the double doors, the infiltration win be 100 cu ft of outdoor air see.Chapter 24. 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 persona per hour. Total infiltra tion will then be 40 X 100 = 4000 cfh or 67 cfm. . The design rate of entry of outdoor air is then: .V _ Q = 1275 +. 67 - 1342 cfm. - The sensible, latent, and total loads are determined from Equations 6, 7, and 8, respectively, at 2:00 p.m: ((, * 94, (,=75; W. - 0.0161, Wi ',--,0.0093).- All the air entering* the room as infiltration becomea a part of the space load." Infiltration (see Equations 6, 7, and 8): q. - 67 X 1.08 (94 - 75) - 1375 Btub, sensible. g. = 67 X 4840 (0.0161 - 0.0093) =. 2210.Btub, latent: q, - q. 4- q. - 1375 + 2210-- 3585 Btuh, total.; *` : Ventilation Air Taken .through .Coding I/nil, Which ,Becomes a Part of the Space Load (see Equations 9 and 10): qri - 1275 X 1.08.(94-75) (0*15) `- 3920 Btub/sensibie`: * gw --1275 X4840 ,(0.0161-0.0093)(0.15)-6300 Btuh, latent Ventilation Air Taken.Through. Cooling.Unit Which Does Not. ( Become a Part of the Space Load (seeEquations 11 and It) : .. g,, - 1275 X.1.08 (94-75) (1-0.15) - 22,200'Btub, sensibUt.1 g = 1275 X 4840(0.0161-^.0093) (1-0.15). -- 35,700 Btuh, latent. gi* ;- 'g.,- +'g,, + gw + ql' r 3920 + 22,200 +.6300 + 35,700 *"=* 68,120 Btuh total. ` `^ Heat.Gain from Sourccswilhin the Conditioned Space: For the occupants, use the data of Table 26 for moderately active office work, corrected for an indoor temperature of 75 F. Sensible heat*gain -- 85 X 250*-- 21,250 Btu per hr.' Latent heat'gain ='85 X 200 = 17,000 BtU'per hr.* > . ~ '*;._ Total - 38,250 Btu per hr." . ** 'j For the gain from lighting, use Equation 14 with a use factor of unity, and a special allowance factor of 1.20 for the fluoreecents and of unity for* the tungsten globes.'' **'** gw - (12,000 X 1.20 + 4000) X 3!41 = 62,700 .Btu.per^hr. . .For the/on.motor,,;use Equation .15>with a load-factor of unity,, and omit term Motor Efficiency because the motor .is hot* within the space. .{ ',g.-= 7.5 X 2544 - 19,100 Btu per hr. . ' Moisture Permeation, Miscellaneous Allowance, and' the' Load1 Lag Estimate: 1 `Moisture permeation will be-negligible, since, this a com fort job with a-good building construction. > )i There would be some beat gain in the ductwork, but this would not be great because of the short run involved. Because of the relatively high heat from the roof and the relatively hup thermal capacity for the building, practical judgment for this job would suggest that an adjustment for the load lag should be made to the load as computed for a design condition of 75 F. Because of insufficient information on this subject at the present time, no factor can be given. Total Loads and Required Air Quantity Through Conditioning Equipmentr . * "'VV':--J . The total loads are summarised in table 29.. - Compute the enthalpy difference ratiofrom Equation 21. . . K-H. _ (200,975 + 25,510)' x ^ Air-Conditioning Cooling' load 525 Table 29 Summary of Total Loads for .Example I0,;Y Load. Cocpooeaf - Senable Bfo/fr latent Bto/hr With good - distribution and diffusion, thin temperature should not produce objectionable drafts. The various calculations for the sensible, latent, and total heat loads for Example 10 are shown in Table 30. All walla, roof and doors........................... 87,290 PART II: RESIDENTIAL COOLING LOADS 5,340 infiltration 67 Cfm...................................... Ventilation air (1275 cfm X 0.15).... - 1,375. 3,920 2,210 6,300 : The acknowledged differences between heat gains and cooling loads axe of essential importance in calculating resi Occupants..*................................. ........ .21,250 lighting............................................... . - 62,700 Motor, fan...................................................... 19,100 17,000 : dential cooling load. This is largely due to the following fac tors: 200,975 25,510 1. The loads on residential cooling systems are primarily those imposed by beat flow through structural components and by air Ventilation 1275 cfm X (1-0.15)......... 22,200 , leakage or ventilation. Internal loadsj particularly those imposed 35,700' . by occupants and lights, are small in comparison to those ex- 223,175 61,210' - perienced in commercial or industrial installations. Grand total sensible arid latent'............... 284,385 2. Most residences are cooled as a single sbne, there being no means to redistribute cooling unit capacity from one area to another as loads change from one* hour of the day to another. 3. Most residential systems employ units of relatively small capacity (from about 20,000 to 60,000 Btuh) which have no From the ASHRAE Pstchboketbic Chart, (Chart I) Chap means for controlling capacity except by cycling the condensing ter 3, determine that the apparatus dew point is 53.0'F. unit. When it is remembered that cooling load is largely affected Compute the effective air quantity (Equation 22). Then, by conditions outside the house and that only a few days each season are design days, it becomes apparent that a partial load 1.08(75 - 53) X 0.85 = 9950 cfm. situation exists during most hours of the season.1 A n oversized unit which has no capacity control is detrimental to good system , (Refer to Chapter 34 for cofl selection.) . ' From note under Equation 22 the dry-bulb range wfll be' (75 -- 53) .X 0.85 -- 18.7 deg, and the dry-bulb temperature - ' of air leaving the cofl wfll he 75 -- 18.7 -- 56JJ F. The dry- bulb temperature leaving the fan (including the heat supplied tor the-fan motor) or delivered, into the.room, will be .(from Equation 24): ` *" performance under these circumstances. 4. Dehumidification is achieved only during periods of cooling unit operation, there being only very limited use of reheat or bypass systems to achieve direct control of humidity under condi tions of relatively light sensible load. Space condition control is usually limited to the use of room thermostats, essentially sensible beat actuated devices. 5. The systems in most residences are operated twenty-four .200,975 - 19,10,0, 75 58 F.' 1.08 X 9950 hours per day, thus permitting full advantage to be taken of thermal flywheel effects of structural members, and furnishings within the structure. (This accentuates the partial load effects mentioned in item 3 above.) .1 6. Equipment should be of the smallest possible capacity comp Toble; 30Summery of-Calculations fov Exdrhple-JO mensureto with good comfort performance, in order to minimi^, initial equipment and distribution system costs.' From the foregoing, it is apparent that accurate cooling load calculation i& if anything, more important for reddentialmstal- lations than for non-resideatial installations. `. 'Sensible Load *' Transmission - ''*' :"** Btu/Hr Roof 4000 sq ft X 56* X 0.34 ............ 76,200! - 8. wall 405 sq ft X IIP. X 0.34 = ........... 1,580, E. wall 765 sq ft X 16* X 0.48 =....................5,8S0 ' N. wall ex! 170sq ft X 0* X 0.48 - '' 490 " N; A W: party wall 1065 sq ft X 6* X 0.26 - 1,660 ' Floor none . Doors N. A E. 70 sq ft X.19 X.6i59 = .. . Door 8. 35 sq ft X 34 X 0.59 - ......... Transmitted Solar Radiation and Transmission S. glass 60 sq*ft X 78 -___ . .; N. glaas 30 sq ft X 22-.. ........ Internal Load : , . 780.., 700,: Infiltration67cfm X I.08 X 19 = 'H" y^tiUtion 1275 cfm X 1.08 X 19* X015 - Lighte!(12,000 X 1^0 + 4000) 3 41 - People 85 X 250 - Motor,,fan.7.5 hp X 2544 - . 1,375 : 3,920 62,700 * 21,2501 19,100. Tc+at. Sensible Space'Load. . . * 200,97 Latent Load - .... Infiltration 67 cfm X 4840 X 0.0068,--..:V. .2,210 p!?i nl?25.'rflIlX 4840 X0 W68X0.15 6,300 People 85 X.200 =......................................... 17^000 ' Total Latent Space Load..........*.* .*.. ; * * ` 25,511 Ventilation Aib Which Dobs Not Become ' -viS OF Space Load ' ......... latent 1275 cfm XX481400S-X 01.90006X8(.lX^)(.11-50):1=5):...*.71:-2-2--,-'2--0-l Gbajjd Total Load .'. 284-,3J Interpretation of Data In attempts to calculate cooling loads for residences, the equivalent temperatures of Tables 8 and 9 have been found unsuccessful when applied directly. By making use of results of studies conducted in 5 research residences at the University of Illinois,1* these equivalent temperature differences have been successfully applied to residential cooling load calcula tions and a comprehensive study of these data has resulted in the development of an all-industry residential heat gaiij calculation procedure.** Although the procedure was devel oped primarily for use by installers of residential equipment and systems, its engineering basis and examples of its .use in engineering design will be given here.' ' Design Temperatures' Residences, unlike many other structures and types, of occupancy, can be assumed.to be occupied, and usually con ditioned, for 24 hours per day, every day of the cooling season. The indoor design temperature is therefore a constant value, usually 75 F. Tfae outdoor design temperature is that shown in Table l. . . An assumption of a single indoor temperature is not a suffi cient condition' for equipment selection and system design if the design goal is occupant comfort without requiring un economic equipment capacity. The procedure is therefore based upon an assumed indoor temperature, swing, of not more than 3 deg on a design day, when the residence is con ditioned 24 hr per day, and the thermostat setting is 75 F. An -