Document 91NnyqXQ5d1gaXV3D6EBBnr87

HEATINC VENTILATING AIR CONDITIONING GUIDE 1940 Refrigeration, by Well Water When well water is available in sufficient quantities at low temperatures during the cooling season, it may be pumped directly to air washers or cooling coils. Control is usually effected through control valves on the water supply to the cooling unit actuated by temperature or humidity controllers, or both, located either at the outlet of the conditioner or in the conditioned space. INDUSTRIAL PROCESSES There are many industrial processes requiring automatic temperature and humidity regulation. The control equipment operates on the same principles that have been described, but it is often especially designed for each particular process. Each installation, or the installation for each process, is likely to be a problem peculiar-to that process. 668 Chapter 39 MOTORS AND CONTROLS Direct Current Motors, Alternating. Current Motors for Single Phase and Polyphase, Special /Applications, Classification of Motors, Manual Control, Automatic Control, Pilot Controls, Direct Current Motor Control, Squirrel Cage Motor Control, Multispeed Motor Control, Slip Ring Motor Control, Single Phase Motor Control THE electric motor, available in many different types suitable for various services, is now the most widely used form of prime mover. The equipment for starting, controlling and protecting these motors varies with the type and with the functions it is desired to attain. . Motors used for heating, ventilating arid air conditioning applications may be divided into two general classifications as follows: ' 1. For use with direct current. 2. For use with alternating current. DIRECT CURRENT MOTORS There are three types of direct current motors available: 1. Shunt Wound. 2. Compound Wound. 3. Series Wound. Shunt Wound motors being suitable for application to fans, centrifugal pumps, or similar equipment where the amount of starting torque required is relatively small, are used for the majority of applications in the field of heating, ventilating and air conditioning. They may be used on recipro cating pumps and compressors, if started under unloaded conditions. Compound Wound motors are required for application to compressors, stokers, reciprocating pumps when started under loaded conditions, and also when applied to similar equipment where high starting torque is required. Whenever frequent starting makes high starting and accelerat ing torque desirable, or where sudden changes of load are encountered, compound wound motors are used. Series Wound motors find only limited application in a few special cases and are available in only a limited range of sizes. 669