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American Society of Heating and Ventilating Engineers Guide, 1937'" 1 tion equipment^ and suitable controls. Generally, however, a central station air conditioning system is designed for year-round service: This means that properly sized heaters and humidifiers, with their respective controls, must be added. With few exceptions, systems designed to meet summer capacity requirements will have ample capacity for winter and intermediate season conditioning. -------- quarter 10--Central Systems for Cooling and Dehumidifying ding upon apparatus space and other design conditions. Still d ther arrangement of equipment will result if the dehumidified air fan Trvers the conditioned air to several other fans rather than to the con"r.1 ed space directly. These booster fan equipments may use part by"`7. ajr as illustrated in Fig. 3 or 100 per cent dehumidified air and piheaters. The main apparatus, in either case, may or may not have a by-pass connection, depending on load conditions and other design factors. The systems illustrated in Figs. 1 and 2 may be converted into the rface cooling type by merely replacing the dehumidifiers with surface moling coils which use cold water or direct expansion of refrigerant to \TMomplish the required cooling and dehumidifying. The coils may also be installed within the spray chamber, either in series with the sprays or below them. DEHUMIDIFIERS Information on spray type dehumidifiers is given in Chapter 12. Surface cooling type dehumidifiers generally consist of extended-surface Motor i1 #5 Fig. 3. Central Dehumidifying Plant and Local Recirculating Fans coils within which the water or refrigerant is circulated or the refrigerant A common arrangement of a central station spray type system for is expanded. The air to. be cooled and dehumidified is drawn or blown cooling and dehumidifying is illustrated in Fig. 1. The plant may be over the coils. This system is generally comparatively low in initial cost designed to condition 100 per cent outside air, 100 per cent return air, ora and has low operating costs. Some localities have refrigeration codes mixture of outside-and return air. Further, part of the air returned from which restrict the use, in comfort conditioning applications, of refrigerants the conditioned space may be by-passed1 around the conditioner as acting by direct expansion in coils exposed to the air stream. Therefore, illustrated in Fig. 2. The reheater may be installed in the fan inlet local codes should be consulted by the designer before he plans a system chamber as shown, in the by-pass air duct, or in the fan discharge duct, e-: employing, direct-expansion methods. Close humidity control cannot be maintained during the- cooling season by the surface cooling type qf ^Patents exist covering the use of the by-pass for cooling and dehumidifying systems. equipment. Winter humidification may be accomplished by use of 186