Document n4Jr41nOVGbm22VYwavvXZyw

628 CHAPTER 29 1951 Guide Central Systems for Air Conditioning 629 spaces that are otherwise usable should be charged against the system as an The location of the complete apparatus, assembly, including the dehumi- operating cost. . difier, will be dependent on the type of building, spaces available, structural, In general, the apparatus should be arranged to have straight line air characteristics, etc. The type of conditioner used may. limit the location flow. Each change in direction increases air resistance and, in addition, under certain conditions. Where cooling coils employing chilled water' or elbows and offsets may cause eddy currents resulting in stratification. brine as the cooling agent are used, there are few limitations with regard The usual order of equipment location, beginning at the outside air intake, to location other than those of pumping power, working pressures, piping is: weather hood of louvers, outside air dampers, return air connection, costs, etc. Where spray dehumidifiers are used, very definite limitations filters, tempering coils,, cooling coils or sprays, by-pass connection with or present themselves, and these may require certain extraneous equipment without reheaters, reheaters, fan and distributing ducts. .. to make the system workable. If several spray type dehumidifiers are Screens at the intake prevent the entry of large foreign matter, birds, located on different levels, thus involving different water pressures, a surge etc. A hood or louver at the outside air intake prevents the entry of rain or storage tank, to which the return water from each dehumidifier can be and snow. Since in most climates there are many days during which use taken, is required. Should the water level in the pan of the dehumidifiers of 100 percent outside air unheated or uncooled may be economical, the be low in relation to that of the surge tank, return water pumps will be areas of all air-passing and treating apparatus should be large enough for required, and these pumps will have to be operated until the water-supply such a volume, and the exhaust or spent air equipment should be capable lines are drained in order to prevent flooding of the lower dehumidifiers. of discharging "out of doors, all of the air admitted. Where spray dehumidifiers are on the same level, equalizing lines between The by-pass connection normally connects the return air duct system the pans-may be required if a storage tank is not provided. It is exceeds with the apparatus casing between the conditioner and the supply fan. ingly important that water-tight drained floors be provided under all Usually the by-pass opening is sized to handle about 50 percent of the fan overhead cooling systems, since water condensed out of the air generally capacity where a variable by-pass is used, though extreme load variations will be present and may damage the interior finish of the rooms below the may require a larger size. It is at times good design to locate a reheating apparatus. coil in the by-pass connection to permit using some by-pass air when heat-' All of the various pieces of equipment from the outdoor air intake through ing is required. Since the relatively high resistance of the cooling coil or the fan usually are connected together by sheet metal casings. Frequently, spray is to be balanced by the heating coil and by-pass connection, enough the building structure or specially constructed walls or partitions may be heating surface can be provided to raise the temperature of the by-pass used to form a portion of the casing. In any case the casing or connection- air to the point where the mixture of by-passed air and conditioned air must be sufficiently sturdy for the required duty. Sheet metal work must will have the required temperature. When a variable by-pass is used, a be well braced not only to prevent vibration under pulsations in air flow, damper working in opposition to'the by-pass damper should be placed but also to withstand the abuse of normal usage. Casings should be across the face of the dehumidifier, for unless the resistances of the two are braced wherever access doors are installed, and all large panels should be carefully balanced at all operating points, the proper mixtures of air. will adequately reinforced by structural steel. not be obtained. Outside air that has not been dehumidified should not be by-passed around a cooling coil or spray dehumidifier if accurate control Accessibility for Service of- the delivered relative humidity is desired. Where the by-pass is made a part of the dehumidifier or conditioner and is located on the top or side of it, the return air connection should be arranged so that stratification of return air is insured, baffles being provided to accomplish this purpose if necessary. Where return air and by-pass air connections are taken off a. return duct system, it may be necessary to install a back-draft damper between the return air connection and the by-pass connection. When the, by-pass damper is at maximum opening it may be much easier for outside, air to pass through the return damper, into the return duct connection and through the by-pass, than for return air to pass through the by-pass con nection into the fan. Air tends to take the path of least resistance and, if the dehumidifier resistance is high, and if the return duct resistances are' Each apparatus layout should be made with accessibility in mind. Where cooling convectors are used, space for removing and repairing or replacing them should be provided; Adequate space should be provided for the servicing and replacement of eliminators. Whether these accom pany sprays or wetted coils, filters must be so located that the proper cleaning, replacement or routine servicing can be accomplished without difficulty. Free access to the bearings of all moving machinery is a neces sity. Provision should, be made for the complete removal and replace ment of any parts of the apparatus that are subject to wear, deterioration or damage, whether they be filter, fanwheel, motor, pump impeller, or heat transfer surface. low, this situation is apt to occur. A recirculating air fan, instead of a back-draft damper, may be required for this case, if the failure of return au DESIGN PROCEDURE to reach the dehumidifier of conditioner is a serious matter under reduced load conditions. The customary design procedure is outlined herewith. For simplifica tion the procedure is set up on the basis of a year-round system. For j* il LOCATION OF APPARATUS In general, the outside air intake, preheaters, and return air connections precede the conditioner, while the by-pass, reheaters and fan follow it. systems designed only for winter or for summer, the unrelated parts may be omitted. 4 In the case of a blow-through system, where the fan is located ahead of , 1. Selection of design conditions (inside and outside). - the conditioner, the leakage of air at the conditioner is outward, instead of a. Summer. inward, And may be accompanied by water leakage. m b. Winter.