Document zQL0R42zgxGpEJjqZNYox5MV3

658 CHAPTER 47 1959 Guide tafe floor aroo --1000 tq ft. Window* on om ode only--240 q ft. Hoof timtsaudea factor*. U; roof--0J5, wail--0.25, glen--M3. No MEUmfiea. Hoof goto* boxed on artificial fighting of 2.3 wotf* por sq ft of floor area. Occupants, 35. So4or tnfonaty and incidence of 45 dog N. fofflwdo, Oocooiber I. Window* chatted by reaction fcfindx. Since the romidorofloo if cooiinfl, a room tmperofare of 75 F, instead of Am 72 F diown m Table 1, was mod n the oboe* chart*. Net cooftng requirement far the oufli exposure approodbe* ttaf of fbe north exposure oo o doy whoa the Ay bat a hoary doed cover. fig. 1.... Typical Net Heating and Cooling Requirements of Classrooms Installation cost is a prime consideration in design. It should be considered in relation to the overall cost of school operation. The cost of maintenance is reflected in man hours required to provide proper operation and reasonable life of the equipment. Proper location, access, and working space for the equipment are reflected in reduced operator or custodian time. Some systems require more frequent attention, overhaul, or replacement than others. Operating costs may be held to a minimum by: (1) selection of the proper fuels for system requirements based on fuel eco nomics in a particular area; (2) providing flexibility for operation of sections of systems according to use; (3) provision of adequate automatic temperature control and system control. Periods of use contemplated for the entire school building, or sections of it, due to summer school, or community use of an auditorium throughout the summer or during spring and fall months (in a region where these are mild) may influence a decision to include air-conditioning systems. DESIGN CONSIDERATIONS Design for the required indoor environment for learning must be made in consideration of the heat losses, heat gains, and air movements; ventilation means and ventilation rates; space temperature requirements; variability of occupant density; independent operation of various spaces; practi cability of cooling; means of cooling (if it is to be included in the design); and automatic control of the environment. A typical illustration of heat losses and heat gains in classrooms is presented in Fig. 1, applicable for sun effect to about 45 deg north latitude and design temperature for heating of 0 F. For the classrooms shown and based on the construction and conditions described in the footnote, heat gains in the classroom with north exposure equal the heat losses at 32 F. In the south classroom, practically no heatingis required after the room is occupied and lighted. Ac cordingly, heat is required in the south classroom only for warm-up. Cooling is required in north classrooms at out door temperatures above 32 F and, in south classrooms, at all temperatures above 0 F. Conditions shown for the north classroom would apply to a south classroom when the sky is fully overcast. fig. 2.... Natural Air Currents'in Classrooms Natural air movements or air currents prevailing in the space must be taken into account in design. Fig. 2 illustrates two conditions: the first having windows located along one ride, the second having windows for cross-lighting. Measured conditions are shown for classrooms of the first type. It is significant, as will be noted in these illustrations, that, even though the room temperature at the control point may be at the desired level, uncomfortable conditions could be expected for the students in the first or second rows paralleling the windows. Direct radiation installed at the glass exposures cannot be fully effective in wanning the descending currents of cold air unless it extends the full length of the windows, is located close to the window sill, and is in operation whenever the outdoor temperature is low enough to cause these downdrafts. Ventilation means and rates are largely fixed by state and municipal codes and vary considerably with type and intended use of any building. Applicable ventilating systems are shown in Table 1. Natural ventilating systems are those relying on opening of windows to admit and exhaust air. Mechanical supply or exhaust systems are those using fans to supply or exhaust air. Natural ventilating systems are not suitable for spaces such as gymnasiums, auditoriums, cafeterias, and meeting rooms, because of size or density of occupancy; nor for laboratories, large toilet rooms, locker rooms, or kitchens in which intense odors are common; nor in shower rooms where high vapor concentrations are likely to occur. It is not possible to obtain consistently good room conditions in classrooms by means of any ventilating system that depends on openable windows for introduction of air. This is the case with each of the natural ventilation systems shown in Table 1. The problems are due to the following factors: 1. At low outdoor temperatures, the windows are kept closed, resulting in high odor intensities. 2. As outdoor temperatures rise, up to temperatures of 60 F, uncontrolled, uncontrollable, and variable drafts will occur in the occupied aone. Typical conditions are shown in Fig. 3. 3. Frequent adjustment of window openings by the in structor, with consequent distraction from t^ar-hing duties, will be necessary to provide adequate ventilation without excessive drafts and to maintain proper room temperature. 4. Manual readjustment of window openings is an erratic -method of controlling ventilating 5. The advantages of saving time and obtaining greater ac curacy of temperature control are lost. School Systems 659 Spec* Table 1.... Applicable Ventilating Systems and Room Temperatures Haioraf Natural with Notwo/ with Mechanical Supply MaJumfcqf Supply, Gravity Exhaust Atechonicat Exhaust and Exhaust Gravity Exhaust Boom loop F 4. Kitchen 8. Locker Rooms 12. Showers No* No No No No No Yes No No If Code* Yesd No No* No No No II Code*-- No Yes Yes* No* If Code* Yes* No No* No No No If Code* If Code* Yes Yes* No* If Code* Yes4 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes 72 Yes 60-70 Yes No Yes 65-72 Yes 72 Yes No 75-80 No 72 Yes 65-70 No 70 No 75-80 to See tart. b If pernitted by code. * Unless rooms are interior. * If rooms sie small sad have opensMe windows. Temperature requirements of various spaces depend on occupancy, function, degree of activity, and type of clothing. Values generally accepted are listed in Table 1. In meeting spaces such as auditoriums, cafeterias, gym nasiums, and the like, the variability of occupant density may warrant the use of separate units or systems for the several spaces in order to permit their individual operation without operating the entire school system. It may be practicable to counteract the net heat gains shown in Fig. 1 or some of them by cooling with ventilation air or other means besides refrigeration. This would require the use of mechanical air supply with sufficient cooling capacity at a 55 F outdoor air temperature to offset the net heat gains. If the amount of air required results in an excessive cost of the mechanical system, a study should be made of means of reducing the various cooling load sources, particularly the solar load. When outdoor tem peratures are in excess of 65 F, windows with ample opening - to produce rapid changes of air in the space, are necessary to maintain comfortable conditions, unless cooling by re frigeration is installed. When the outdoor temperature is above 65 F, relatively high velocity air movement in the space is not objectionable from the standpoint of comfort. Even under the most favorable conditions, ventilation sys tems eannot maintain comfort when the outdoor tempera ture exceeds 72 F. DESIGN OF THE MECHANICAL PLANT Heating, ventilating, and cooling loads are computed ac cording to the procedures given in Chapters 9, 11, 12, and 13. The performance requirements of the various parts of the system, whether combined or operating separately, according to use, are then established, with due considera tion being given to the method of control and operation of the entire school project. Heating requirements should be determined for design conditions and. for warm-up periods, the heaviest warm-up load being that which occurs after a weekend shutdown when the outdoor temperature is at de sign value. The load applicable during occupancy, considering net heating and .cooling loads, is determined and evaluated as shown in Fig. 1. If planned use of the building extends through the summer, cooling design dry-bulb temperatures used are those established by the ASHAE Technical Advisory Committee on Weather Design Conditions which are shown in Column 6 of Table 2, Chapter 13, and referred to as "TAC 2Yt% Basis." Design temperatures in common use, both dry- and wet-bulb, may also be found in the same table in Columns 7 and 8. For detailed analysis of frequency of occurrence of extreme conditions by months, reference may be rnnrfa to Region Climate Analyses and Design Data, published in 1951 by the American Institute of Architects. These analyses are available for all United States areas. The requirements of each of the mechanical systems in corporated in a school plant are as follows: 1. An adequate warm-up rate for heating, the ability to raise room temperatures to required conditions shown in Table 1 within an acceptable interval of time when the out door temperature is at design value. Usually, warm-up re quirements after a weekend shutdown axe used as a basis. 2. Maintenance of indoor design temperature when cooling is required. Considering the heat gains shown in Fig. 1, a typical analysis of ability to provide cooling with outdoor air is shown in Fig. 4. 3. Uniformity of air motion, discussed - under Criteria for Design. Generally this requirement is satisfied by a system providing constant air flow, with proper distribution of the air supplied. 4. Uniformity of temperature of supply air, discuraed under Criteria for Design. 6. Introduction of ventilation air, according to applicable codes; otherwise on a rational basis, as discussed in Chapter 6 for quantity and Chapter 20 for distribution. 6. Interception of deflection of window drafts in rooms having extensive fenestration, such as classrooms. (See Fig. 2.) 7. Acceptable noise levels which will depend on location of the school and on the equipment provided. TYPES OF VENTILATING SYSTEMS Any ventilating system provides air circulation and thus includes means of supply and exhaust. Ventilation systems may be classified by the type of supply (window or mechan ical) or exhaust (window, gravity, or mechanical). Air Supply Methods Windows are generally of double bung type or consist of metal architectural sections, the bottom section being ar ranged to swing inward to deflect air upward and the top section to swing outward from a hinge at its top or center. If double bung windows are used, a deflecting device, gen erally of glass, to prevent interference with light transmis sion, is provided at the bottom to deflect incoming currents upward, as illustrated in Fig. 3, and thereby prevent them from blowing directly on room occupants at desk level. Since windows require manual opening, proper control of air currents cannot be provided. ..Mechanical air supply is generally provided by a central I