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210 CHAPTER 16 1962 Guide And Data Book with due consideration being given to the method of control and operation of the entire school project. Heating require ments should be determined for design conditions and for warm-up periods, the heaviest warm-up load being that which occurs after a weekend shut down when the outdoor tempera ture is at design value. The load applicable during occupancy, considering net hpftting 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 theASHRAE. Technical Com mittee on Weather Data which are shown in Column 4 of Table 2, Chapter 26 of the 1961 Guide And Data Book. De- - sign wet-bulb temperatures may also be found in the same table in Column 6. For detailed analysis of frequency of occur rence of extreme conditions by months, reference may be made 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 beating, 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 are used as a basis. 2. Maintenance of indoor design temperature when cooling is required. Considering the heat gains shown in FIs. 1, a typical analysis of ability to provide cooling with outdoor sir is shown in Fig. 4. 3. Uniformity of air motion, discussed under Criteria for Design. CeaeiaUy 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, discussed under Criteria for Design. 5. Introduction of ventilation air, according to applicable codes; otherwise on a rational basis, as discussed in the 1961 Gums And Data Book, Chapter 8 for quantity and Chapter 11 for distribution. 6. Interception or 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 an<l 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 Window are generally of double hung type or consist of metal architectural sections, the bottom section being ar ranged to swing inward to deflect air upward and the top wowth exposwe ________ south exposure z! 5 O O 20 |I f At Ljs <'2s' 'A ro AX 0 JP 20 30 40 50 60 70 n 0 1 0 20 3O 40 SO 60 7075 OUTOOOfl TCMCftATURE -F Bouc Cooling ntqinrvoonfr Aoorr in Fig. t. A * Hot hoed Qdo with voof* otjoa sir cotiftoUot of room hapwdiw of 75 F. 8, C, and O Hot hoof 525, )000, oai 1500 cb, roepoc- tivofy. codroOod to 55 f. minimum. Cooitng dr lefflprofare wO bo higher or outdoor oh fomporeforo rtM* 06000 55 7. Fig. A... Typical Coaling Capacities, Using Outdoor Air section to swing outward from a hinge at its top or center. If double hung 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 and since wind effects on the opening are constantly changing, proper control of air currents cannot be provided. Mechanical air supply is generally provided by a central duct system, the air being delivered through wall grilles or ceiling diffusers, or by self-contained units within the rooms, such as unit ventilators and unit conditioners located at the outside walls.'Grilles are generally located most con veniently at the inride or corridor wall. They must be of the deflecting type, deflecting upward in consideration of the drop in the air stream when air is introduced at lower than room temperature. Diffusers are generally located in ceilings of rooms in a pattern to provide proper air dis tribution. In location of both wall grilles and diffusers, it is important that the air-delivery path be free of obstruc tions, which might be light fixtures and crossbeams; since presence of obstacles will result in uncontrollable and turbulent currents of air extending into the occupied zone and causing drafts. Grilles and diffusers are generally se lected to provide a terminal velocity of 50 fpm at ap proximately one-fourth the distance from an opposite wall or other obstacle to air flow. Exhaust Methods Window*, when used for exhaust, are opened at the top to taka advantage of natural rise in the warm air to be exhausted. Windows are not fully effective for exhaust purposes, except in completely still weather. Typical con ditions shown in Fig. 3, indicate that, if windows are on the windward ride, air is introduced rather than exhausted. Gravity exhaust ventilation 13 obtained through exhaust grilles in the ceiling (or in a wall away from the windows) connected to roof ventilators. Air is exhausted by wind effect and chimney effect due to differential pressure re sulting from thermal head. This type of exhaust is used in conjunction with air supply obtained by admitting air at the windows. Satisfactory air changes can be obtained by this method within limits shown in Fig. 3, if the roof ventilators are adequately large. However, room conditions cannot be fully acceptable, since objectionable cold drafts are certain to occur in cold weather. Control of conditions> depends on manual adjustment of window openings, a method that is reasonably satisfactory only in mild climates, but is not recommended where the design temperature is lower than 30 F. Gravity exhaust ventilation may be used in combination with mechanical air supply systems. In mechanical exhaust systems' the roof ventilators de scribed in preceding paragraph on gravity exhaust ventila tion are replaced with motor-driven exhaust fans. If this system is used in conjunction with window supply of air, it should be remembered that when windows are closed, replacement air is draws from the corridor or the ventila tion rate is greatly reduced. At such times, negative pres sures will prevail in the building, with adverse effects on incinerators, hooded equipment, and other local exhaust and fuel-firing equipment. TYPES OF HEATING AND COOLING SYSTEMS Systems may be classified according to methods of heat ing and cooling. Each may be combined with means for School Atr Conditioning 211 ventilation in various ways. Only a few states have specific requirements with respect to types of systems. Accordingly, except in these states, engineers and administrators of school construction are free to analyze and choose kinds of sys tems. The possible combinations of such systems are ex tremely numerous. A discussion of those encountered most often will follow. pirect Radiation This type of heating includes cast-iron radiators, castiron or nonferrous convectors, and continuous finned-pipe elements in connection with steam or water heat ing systems (see Chapters 6 and 8 in this volume acd Chapter 46 in the 1961 Guide And Data Book). The radiation must extend the full length of the outside or window walls and the full width of high windows used in cross-lighted designs illus trated in Fig. 2. Control is obtained by manual valves, by individual automatic control valves for each room, or by an automatic valve or valves controlling zones of the system, according to exposure. Direct radiation may be used with natural ventilation, natural ventilation with gravity exhaust, and natural ven tilation with mechanical exhaust. It is designed for the warm-up load and to provide a warm curtain of rising air to mix with the incoming cold air to temper it. However, it is inadequate for this purpose, because heating require ments are satisfied at relatively low outdoor temperatures as soon as classrooms are occupied and lighted, as illustrated in Fig. 1. The system requires the teacher to adjust open ings' for ventilation. Installation costs can be relatively low. Panel Heating Floor panel beating is adaptable to the slab-on-ground type and to the open-corridor type of school, particularly in the warmer riimutet Design data are given in Chapter 10, Panel Heating, which also describes features of panel heating control systems. (See also Chapter 13 of the 1961 Guide And Data Book.) The floor system lends itself well to individual room control, although zone control, including sev eral rooms of the same exposure in the same zone, is practi cable. Floor panel beating systems are adaptable in areas havingdesigntemperatures down to 0 F. Since the requirement for hating is materially reduced when the spaces are oc cupied and lighted, as illustrated in Fig. 1, the panels should be constructed to have minimum rroLon and thus minimum storage effect. This is accomplished by nring a slab, only sufficiently thick to enclose the tubing or piping, underbid -by a slab of insulating concrete. Even with light concrete panels, there is enough storage effect to cause overheating after warm-up and to make it difficult to follow rapidly changing loads. Any of the types of ventilating systems already discussed may be combined with panel heating systems. However, the panel heating system cannot be effective in combating the natural condition of downdrafts &t the windows. The panel system is well adapted for use in primary classrooms with slab-on-ground floor construction, where students spend much time on the floor. Central Indirect Air Systems In these systems, air is supplied for ventilation and beatn>8- At a central point or points, outdoor ventilation air *ud recirculation air is mixed and heated by automatically controlled steam or hot water coils. Gravity or mechanical e*k*ust is coordinated with the air supply system. The central system can be arranged to recirculate air from Window oils to intercept the flow of uncontrolled cold window drafts into the classroom. Such returns are fully effective only if the openings are located in the window sills; if located below the rills, the natural air currents will not be intercepted. There are many variations of the system, which may include features of central systems described in Chapter 1. Air supply may be controlled by zones of similar occupancy and: identical orientation. In dividually controlled booster or reheat coils may be located within ducts leading to each of the spaces. Individual room control may also be provided by a double duct system, equipped with mbring dampers for each room located within a short distance ahead of the supply grilles or diffusers serving the room. Means of cooling can be included. Split Systems The central indirect air systems may be combined with direct radiation or convection units described in the pre vious section, Direct Radiation.. In this combination, air may be supplied by the ventilating system at constant temperature, usually 55 F, when the outdoor temperature is less than 55 F. In this case direct radiation may be de signed to take care of the building heat loss. In order to prevent window drafts, the temperature of the ventilation air should be controlled to require operation of the direct radiation when the outdoor temperature is below 55 F. The direct radiation is controlled by automatic valves operated by a room thermostat for the individual room and essentially provides reheat as required. These systems have wide flexi bility but are usually higher in first cost than central in direct systems. Central Direct-Bred Air Systems These systems are forced circulation warm air furnace systems. They may be arranged for single or double duct air distribution, as discussed under Central Indirect Air Systems. This type of system is further discussed in Chapter. 5, Warm Air Heating. They are usually installed with zone controls and arranged to permit use of any desired proportion of outdoor air during periods of space occupancy. Mechanical cooling may be obtained by installation of cooling coils in the main supply ducts. Unit Ventilators Unit ventilators are used in classrooms to provide heat ing, controlled ventilation, and cooling, using outdoor air as the cooling medium. Auditorium unit ventilators areused in large rooms such as auditoriums, gymnasiums, and large lecture rooms. Classroom unit ventilators are often combined with matching storage cabinets or may be com bined with ducts extending the full length of the windows and arranged either to discharge air upward along the window rilla or withdraw air at the window rill* and thereby prevent downdrafts from the windows. In order to effect ively intercept natural downdrafts, the return grille must be located with the top of the unit at the level of the win dow sill. Classroom unit ventilators may also be combined with extended finned-pipe, radiation at the window rills to combat cold window downdrafts. Electrical unit ven tilators are also available. Unit ventilators using hot prater for beating and chilled water for cooling are used for school buildings where year-round use is contemplated or where warm fall or spring seasons warrant the installation of airconditioning equipment. These units and their controls are described in Chapter 45 of the 1961 Guide And Data Book. The noise level of the unit ventilators under the operating conditions of the installation should be considered. ThS3 systems have a high degree of flexibility.