Document zodD4rkGeG7YXdXKrOkr92Ykz

196 CHAPTER 15 1962 Guide And Data Book Table 7 .... Comparison of Internal Loads $q ft Hoor/Perzoo.......................... 20 " 60 60 Warn* /Sq F Cfm par Sq Ft or Tons per 1000 Sq Ft 100 3 15 T.D. cfm/M ft ^ 1.23 0.93 0.82 0.78 0.75 Total Totis/iGGu oq ft 4.17 3.0 2.72 2.58 2.34 6 20* T.D. cfm/sq ft 1.40 1.16 1.08 1.05 1.03 Total Tons/1000 sq ft 5.0 3.83 3.55 3.41 3.17 9 22* T. D. cfm/sq ft 1.68 1.47 1.38 1.36 1.34 Total Tons/1000 sq ft 5.73 4.60 4.32 4.18 3.94 12 25* T.D. cfm/sq ft 1.85 1.67 1.60 1.58 1.56 Total Tons/1000 sq ft 6.67 5.50 5.22 5.08 4.85 15 25* T.D. cfm/sq ft 2.22 2.04 1.98 1.95 1.92 Total Tons/1000 sq ft 7.5 6.33 6.05 5.90 5.66 * Liberated in coodiliooed space. An important load, frequently overlooked in apartment buildings, is heat gain from piping for hot water services. Occupancy will vary considerably. In accounting or other sections where clerical work is done, the maximum density is approximately one person per 50 sq ft of floor area. Where there are private offices, density may be as little as one per son per 200 sq ft. The most serious cases, however, are the occasional waiting rooms, conference rooms, or directors' rooms where the occupancy may be as high as one person per -20 sq ft Ventilation Requirements There has been much variation in the rate at which outdoor air has been introduced for ventilation, a term that may make-up for exhaust, smoke-removal, odor-control, pres surization (against inleakage), etc. Past designs were some times based on cfm per expected occupant (an acceptable basis for cafeterias and other short-time use), sometimes on a stated percentage of total air circulated, and frequently on cfm per square foot of floor (the usual present baas for office buildings). Standards have improved as air-conditioning uses grew; 10 years ago, 0.25 cfm per sq ft would have been as well-accepted as a. present rate 50 percent higher. Now 0.35 to 0.45 cfm per sq ft may be considered as good present day practice. As it happens, this corresponds quite well with the quantities of primary air required, typically, for the opera tion of many modem induction air-conditioning units and corresponds also with the 65 cfm, plus or minus, required to Table .3 .... Proportional Distribution of Cooling Load in Relation to Percentage of Glass in Sunlit Facade4,b Gfou in Facade % 25 ' 50 75 People, Lights & Office Equipment % 36 27 22 Window Heat Input (max.) % 26 43 53 Conditioning Outdoor Air % 23 17 14 Conduction through Walls %32 1 Miscellaneous - % 12 11 10 Total % 100 100 .100.. * With driwo Venetian biindz. b For peak eooiiag dwnzod. pressurize a typical hotel room which has interior bathroom exhaust. An important economy consideration for interior zones with all-air conditioning, and also for peripheral zones with double-duct systems, is to arrange for increasing the propor tion of outdoor air, up to 100 percent of the total circulated, whenever this will afford sufficient cooling without the use of refrigeration. This is frequently the case in spring and fall. An example will demonstrate toe large effects, even on in terior zone demands, caused by heavy concentrations either of population, or of lighting (or other electric) heat sources. The tabulation presented is based on the following reasonable assumptions: 1. Minimum desirable total air supply 2. Sensible heat per person (average) 3. Latent heat per person (average) 4. Desirable outdoor air 5. Outdoor air to be at least 6. Outdoor air conditioning 7. Desirable temperature difference be tween maintained and entering air tem peratures (for economical refrigeration) (75Foutdoorand 64F indoorwet-bulb) 8. Maximum permissible temperature dif ference 0.75 cfm/sq ft 200 Btub 200 Btub 0-4 cfm/sq ft 10.0 cfm/peraon 40 Btuh/cfm 20 F deg, or less 25 deg Table 2 shows some interesting comparisons between in ternal loads, excluding solar loads. COOUNG LOAD DISTRIBUTION The proportion* of total cooling demand chargeable to dif ferent factors will be instructive. An evaluation may be based on any desired set of assumptions. The following are for an office building: Floor ares Electric heat Outdoor air Outdoor air conditioning Glass in facades (with good Inside Venetian blinds, or equivalent) 100 sq ft/person 6 watts/sq ft 0.4 cfm/sq ft 40 Btuh/cfm 25, 50, and 75% - On these assumptions, people and lights will give out per square foot of floor about 22.5 Btuh of sensible heat, and 2-5 Btuh of latent heat. Conditioning of outdoor air brought in for ventilation and pressurizing will absorb about 16 Btuh of total heat per square foot floor. For the peripheral zone di rectly exposed to sunshine (assumed to extend 14 ft inward) the heat through glass will approximate 20, 40, or 60 Btub per sq ft of floor, for the three glass-percentages stated, re spectively. With average walls, wall conduction will approximate 3, 2, or 1 percent of the total in the 3 cases. Miscellaneous allow ances (for fan-heat, duct heat pick-up, and safety factors) will approximate not over 12 percent of the total. For a sunlit facade (with blinds drawn),, the load analysis is given in Table 3 for conditions of 25, 50, and 75 percent glass in facade. Table 3 deals only with peak cooling demand. As window solar heat loads grow larger, toe type of sir-handling scheme that will be most economical may also change. Public Building Air Conditioning 197 INSTALLATION COSTS The installation costs of air-conditioning buildings of the multiroom type fall under three main heads: 1. Central Refrigerating Plant. A reasonable preseaV-dsy cost figure would be 6450 to 6500 per ton of refrigeration. 2. floor "Work or Distributing Systems, 'lms includes fans and drives, cooling and heating coils and connections, under-window units (where used), ducts, filters, outlets, automatic controls, exhaust ventilation, pipe connections (also thermal and acoustic Basis for Cost Analysis For a multistory office building, under typical metropolitan conditions, an attempt to analyze the cost of installation has been based on the following four schema, as affected by relative proportion of sensible heat load from windows: t. A double-duct all-air system, with controlled reiving boxes under windows for peripheral zones, plus a single-duct system with cone reheat for inside zones. IJ. Metal radiant and acoustic ccilinpt for cooling and hooting Upheral zones, plus a single-duct system for all parts of the r, zoned by floors, and by peripheral and interior zones. Iff. Fan-coil unite under windows for peripheral zones, plus a single-duct system with zone reheat for interior zones. IV. Induction mite under windows for peripheral zones, plus the aingle-duct system for interior zones. In all but the Scheme I, piping is separately zoned for each major facade, and an average of one thermostat,to each two units. Estimated costs are shown in Tables 4, 5, and 6 for a tall building, about 300 X 80 ft in plan with principal exposures north and south. Peripheral zone areas would amount to about 10,000 and the interior zone areas to about 8000 net sq ft per floor (for the four systems Schemes I, II, III, and IV considered). Table 4____Estimated Cost for Air Conditioning Systems Schemes I, II, HI and IV--25% Glass Scheme i II ` at IV Per Floor Pericherai AC Tons Ducted (BAR) Cfm Central Plant Cost 6 Peripheral AC System Interior AC System Cost 6 Electric, Plumbing, & Miscel. 6 Cost per Sq Ft 6 43 26 60,000 31,000 40 28 32,000 30,000 43,000 43,000 12,000 12,000 13,000. 9,000 99,000 94,000 5.50 . 6.22. 40 26,000 30,000 40,000 12,000 16,500 98,500 5.48 40 27,000 43,500 12,000 10,000 95,500 SoU 4--Double-Duet CFM iwefadea 100% rcM Seek mud 60% ktf^toet "act "r*ritif SfU B--All Awfad CFif figures include appropriate i tnj n air zyetetaa. Sou C--Rariinat Ceiling ecats have been crtdtud vita v*lua of teou*tie ceiling, that might be added to other schemes. S*4 l)--Scheme in (under "MJac.") Includes drainage and electric coo- Bectjou* fm nr.tta m --Onii encloesres are included under Miscellaneous in Schemes I, SoU F--With moderate-sized windows, it is usually economical to run pn- *q{ofr.end owrmdsry water ptoieg vertically at outside walla, dose to uiuta, veT large windows this is usually impossible--and. couacqugntly extra cost at horizontal crors-oms in Qn saeh cases) becomes an added cost fzetor. ATWs G--It aunt be naderstood that these values will vary with diSesent jrtioni sad orientations of bnikiingi. as well as with locality, type, and t>". they should be considered comparative, only. Table 5 .... Estimated Cost for Air Conditioning Systems Schemer I, If, III end IV--50% Cfcrn Scftens I II ill IV p-_ cn-__- Peripheral AC Tons Interior AC Tons Ducted (SAR) am Central Plant Cost 6 Peripheral AC System Cost 6 Interior AC System Cost 6 Electric, Plumbing, & Miscel. . 6' 57 26 75,000 36,000 51,000 12,000 16,000 52 26 45,000 34,000 51,000 12,000 10,000 52 26 26,000 34,000 42,000 12,000 17,500 52 26 29,000 34,000 45,500 12,000 11,000 Overall Cost Cost per Sq Ft 8 114,000 107,000 105,500 102,500 8 6.35 5.95 5.86 5.70 See footnotes undw Table 4. Owning and Operating Cost The estimated costa presented refer to initial costs only, but annual owning or operating costs will vary in a some what parallel maimer: 1. Operating labor will be a fairly definite quantity for a given building. 2. Fixed charges will of course bear a definite ratio to invest^ menu 3. For a riven location and climate, operating costs for re frigeration (itself)' will be in proportion to horns of use and tonnage--not mavirrmm installed tons, but average tons in use. 4. Operating costs for cooling towers, filters, pumps, etc., will be about in proportion to capacity of plant and hours of use. 5. Operating costs for fans will be in proportion to cfm, fan static pressures, and hours of use; a double-duct system, for example; with its relatively high pressures and much greater cfm of ducted air will use considerably more power than an in duction system. Radiant ceiling systems, generally, will be lowest in electric consumption. The foregoing analysis was worked out primarily for office Toble 6 .... Estimated Cost far Air Conditioning Systems Schemes I. U. IU ead tV--7S% Clan Scheme 1 11 m IV Per Floor Peripheral AC Tons Interior AC Tons Ducted (SAR) am Central Plant Cost 8 Peripheral AC System Cost 8 Interior AC System Cost 8 Electric, Plumbing, A MisceL 8 74 26 91,000 44,000 59,000 12,000 17,000 68 26 53,000 41,000 55,000 12,000 12,000 68 26,000 41,000 59,000 12,000 18,000 68 31,000 41,000 60;000 12,000 127000 Overall Cost Coet per Sq Ft 8 132,000 120,000 120,000 115,000 .8 7.35 6.68 6.68 6.38 See footnotes under Table 4.