Document wgxZykVpRoreqZ6owdQwNOmnJ

Heating Ventilating Air Conditioning Guide 1938 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. PROBLEMS IN PRACTICE 1 What important functions of heating, ventilating, and air conditioning systems do automatic controls fulfill? Controls are applied to maintain adequate requirements for human comfort and efficiency; to maintain requirements for industrial processes; to obtain economy in operation; and to provide necessary safety measures. 2 How may temperature control be obtained in a room heated by a unit heater? With constant steam supply, the unit heater motor may be started or stopped by a thermostat, either directly or through a relay. With intermittent steam supply, opera tion of the motor by thermostat can be limited to the time that steam is available, by using a reverse-acting temperature or pressure limit switch. 3 How may temperature control be obtained in a room cooled by a selfcontained mechanical unit? The fan operation may be controlled by a manual switch, while a room thermostat in con junction with a solenoid valve may regulate the flow of the refrigerant to the coil. The thermostatic circuit might be operative only when the fans'are running; and the com pressor might be controlled by refrigerant pressure. 4 How may temperature control be obtained in a room heated by an auto matically-fired warm air furnace? A room thermostat might control the combustion unit; and a limit switch in the top of the furnace unit, when at a low setting of its control might operate the fan whenever there is a rise of temperature, and when at a high setting of its control it might shut off the combustion unit. A room humidity control operating a solenoid valve on the water supply to the humidifier, or operating a relay on the recirculating pump motor to the humidifier, may be connected in parallel with the fan motor. Humidification may be supplied only when heat is supplied and when the humidity control acts in conjunction with a time switch. 5 How may humidity be controlled in a unit humidifier for a steam or hot water heating plant? Since heat is required for evaporation, a temperature limit switch, preferably of the immersion type, may be placed in the heating supply riser to cause the unit to be in operative when heat is not available. A room humidity control will operate a solenoid valve on the water supply to the sprays. Both the solenoid valve and the humidity control may be electrically wired in parallel with a fan motor, and be subject to the temperature limit switch. 702 Chapter 38 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 and 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. 703