Chat with AIExam 21: The Cooling System
The evaporator in a commercial installation normally consists of a ____ coil, through which the building air is circulated by a motor-driven fan.
(75) 
VerifiedC
Where was the initial demand for hermetic compressors and what were the implications of this?
(85) VerifiedThe initial demand for hermetic compressors was for use on residential-type refrigerators. Therefore, most of the hermetic compressors were constructed for single-phase service. In other words, it was necessary to provide auxiliary winding and starting devices for the compressor installation. Because the refrigerant gas surrounded and filled the motor cavity, it was necessary to remove the centrifugal switch commonly provided to disconnect the starting winding at approximately 85 percent of the full speed. The switch was removed because any arcing in the presence of the refrigerant gas caused the formation of an acid from the hydrocarbons in the gas. This acid attacked and etched the finished surfaces of the shafts, bearings, and valves. The acid also carbonized the organic material used to insulate the motor winding and caused the eventual breakdown of the insulation. To overcome the problem of the switch, the relatively heavy magnetic winding of a relay was connected in series with the main motor winding. The initial heavy inrush of current caused the relay to lift a magnetic core and energize the starting winding. As the motor speed increased, the main winding current decreased and allowed the relay to remove the starting or auxiliary winding from the circuit.
____ compressors are usually used in large installations.
(66) VerifiedB
What does NEC 440.14 require of the disconnecting means in terms of location, access, installation, and mount?
(85) ____ is a method of removing energy in the form of heat from an object.
(68) Air-cooled condensers use ____ to drive air across the condensing coil.
(84) The compressor serves as a pump to draw the expanded refrigerant gas from the evaporator, boosts the ____ of the gas, and sends it to the condenser.
(69) Overload protection of the internal components is covered in the ____ Standards.
(86) The ampere rating of the disconnecting means for HVAC equipment must be at least ____ percent of the sum of all the individual loads within the equipment.
(74) One option for protecting a motor-compressor from overloads and failure to start is to use a time-delay fuse or inverse-time circuit breaker rated at not more than ____ percent of the rated load current.
(78) Under what conditions is "Branch-Circuit Selection Current" marked on a hermetic refrigerant motor-compressor?
(72) The cooling system for the drugstore and bakery in the chapter example is a ____ system with the compressor and condenser located on the ground adjacent to the building and the evaporator located in an air-handling unit in the basement.
(89) In most instances, the rated load-current (RLA)is at least equal to ____ percent of the hermetic refrigerant motor-compressor's maximum continuous current (MCC).
(73) Can you cool your kitchen by leaving the refrigerator open? Explain why or why not.
(80) The hermetic compressor consists of a motor-compressor completely sealed in a gastight, ____ casing.
(78) The ____ component of the refrigerant cycle raises the energy level of the refrigerant so that it can be condensed readily to a liquid.
(86) Air-conditioning and refrigeration equipment is required by NEC 440.4(A)and (B)to be marked with a ____ marked with the maker's name, the rating in volts, frequency and number of phases, and other information.
(68) The tremendous popularity of mechanical refrigeration for household use in the 1930s and 1940s stimulated the development of a new series of nonexplosive and nontoxic refrigerants known as ____ of the halogen family.
(73) NEC 110.9 states that equipment intended to interrupt current at ____ levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that is available at the line terminals of the equipment.
(79) 
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