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Commercial Refrigeration > Units 21, 22,
The process of removing heat from a place where it is not wanted and transferring that heat to a place where it makes little or no difference is known as ____. - Answer refrigeration The household refrigerator fresh-food compartment is a good example of ____ refrigeration. - Answer medium-temperature The household refrigerator fresh-food compartment typically ranges from ____. - Answer 28 to 40°F Low-temperature food storage applications generally start at ____. - Answer 0°F High-temperature refrigeration applications will normally provide box temperatures of ____. - Answer 47 to 60°F A refrigeration system designed for the storage of flowers or candy is considered a ____ type. - Answer high temperature The ____ in a refrigeration system is responsible for absorbing heat into the system from whatever medium is to be cooled. - Answer evaporator The boiling temperature and its relationship to the system exist in the ____. - Answer evaporator
A typical evaporator operating temperature in an air-conditioning system is ____. - Answer 40°F The ____ of the liquid refrigerant determines the coil operating temperature. - Answer boiling temperature If an evaporator has a pressure drop of 10 psig and the low side pressure is 15 psig, what is the pressure at the inlet of the evaporator? - Answer 25 psig Evaporators that are operated full of liquid and are equipped with a device to keep the liquid refrigerant from passing to the compressor are known as ____. - Answer flooded evaporators A direct expansion-type evaporator is also called a ____. - Answer dry-type evaporator ____ is the best method of checking to see when a refrigerant coil has a proper level of refrigerant. - Answer Superheat A typical superheat for an evaporator operating under normal conditions would be ____. - Answer 8 to 12°F If the application requires a coil design to operate below freezing, there must be provision for ____. - Answer defrost The refrigeration evaporator is a component that absorbs heat from the conditioned space into the refrigeration system. - Answer true The film factor is a relationship between the medium giving up heat and the heat-exchange surface. - Answer true A stamped plate evaporator usually does not use a fan to move air across it. - Answer true The capacity (tonnage) of the heat exchanger can vary with its height and depth. - Answer true
A normally operating water-cooled condenser is operating with a 10° differential between water in and water out. If scale forms on the water tubes and the entering water is 85°F, which of the following is possible? - Answer both a and b are correct. Mineral deposits in the water portion of a water-cooled condenser act as ____. - Answer an insulator In a water-cooled condenser with dirty condenser tubes, the temperature difference between the refrigerant and the leaving water will be ____ when the tubes are clean. - Answer greater than The water circuit in shell and coil and coil-type tube-in-a-tube condensers must be cleaned ____. - Answer chemically The shell-and-tube condenser is cleaned ____. - Answer with a brush after removing the end caps In a water-cooled condenser, a regulating valve is used to control the ____. - Answer refrigerant condensing temperature What can be used to maintain the head pressure of a system with a water-cooled condenser? - Answer water regulating valve A normally operating water-cooled condenser is operating with a 10° differential between water in and water out. If the amount of 85°F water going through the condenser is reduced, which of the following is a possible temperature of the water leaving the condenser? - Answer 105°F If an R-12 refrigeration system has its air-cooled condensing unit on a 100°F roof and the condenser outlet temperature (refrigerant) is 115°F, with how much subcooling is the condenser operating? - Answer 15°F Condensing temperatures in an air-cooled condensing unit can be reduced by ____. - Answer all of the above An air-cooled condenser that is operating in a climate that has four distinct seasons must ____. - Answer have some type of head pressure control
Which of the following can be used to maintain the head pressure of a system with an air-cooled condenser? - Answer all of the above A water regulating valve helps to maintain a system's head pressure by modulating the flow of refrigerant through the condenser. - Answer false The desired water flow through a condenser connected to a recirculating water system is 3 gallons per minute. - Answer true When the evaporative condenser is used in colder climates, freeze protection must be provided in winter. - Answer true If the spring pressure of a water regulating valve is increased, the system head pressure will also increase. - Answer true One large problem designer's face when designing air-cooled refrigeration and air conditioning equipment is a changing ambient from the changing seasons. - Answer true High head pressures from low ambients can cause insufficient refrigerant flow rates through metering devices, which in turn starve evaporators. - Answer false Low suction pressures, iced coils, short-cycling, and inefficient cooling can also result from low head pressures. - Answer true Hard starting may also occur in a low ambient condition causing low head pressures. - Answer true The heat in the vicinity of the discharge gas has a tendency to cause any minerals in the water to deposit onto the ____________________. - Answer tube-surface In a water-cooled condenser, the leaving water temperature is normally ____________________°F lower than the condensing temperature of the refrigerant. - Answer 10
Rotary compressors have pistons that rotate inside the cylinders. - Answer false The rotary screw compressor uses an open motor instead of the hermetic design. - Answer true The sight glass on a semi-hermetic compressor is used to allow light to enter the crankcase to keep the oil warm. - Answer false The shell of a hermetic type reciprocating compressor is generally considered to be on the low pressure side of the system. - Answer true The hermetic reciprocating compressor motor is essentially made of the same materials as an open type compressor motor. - Answer false A bolted together motor-compressor assembly is sometimes referred to as a semi-hermetic type. - Answer true Mufflers are used in many fully hermetic compressors to muffle compressor pulsation noise. - Answer true The higher the rpm of a compressor, the higher the pumping efficiency. - Answer false Scroll compressors are becoming popular because they can handle liquid floodback without compressor damage. - Answer true The scroll compressor is one type of reciprocating compressor. - Answer false SEER is calculated based on the total amount of cooling (in BTU's) the system will provide over the entire season, divided by the total number Watt-Hours it will consume. - Answer true Because a scroll compressor's has fewer moving parts, it operates much quieter than other compressor designs and technologies. - Answer true
Excessive heat and pressure on the oil in a compressor can cause oil to break down and cause the formation of carbon and acid. - Answer true The compression ratio for an R-22 compressor operating with 68.5 psig suction pressure and 260 psig heat pressure is 3.3 to 1. - Answer true The type of compressor that is driven by a belt is the ____________________ compressor. - Answer open-drive A compressor that has the motor and compressor in one housing that is welded together is called a(n) full hermetic type. - Answer true A compressor that has the motor and compressor in a housing that is bolted together is called a(n) ____________________ type. - Answer semi-hermetic The space at the top of the cylinder when the piston reaches the top of its stroke is called ____________________. - Answer clearance-volume A temperature operated disc is a bimetallic disc that senses compressor discharge temperature and opens at 270 degrees F. - Answer true The Internal Pressure Relief valve opens at approximately 400 +/- 50 psi differential between high and low side pressures for R-22, and 500 to 625 psi differential for R-410A. - Answer true The thermostatic expansion valve regulates refrigerant flow to the evaporator based on - Answer suction-line superheat. The capillary tube is A type of - Answer metering device. The TXV sensing bulb is mounted - Answer on the suction line between the evaporator and compressor.
What type of TXV can handle large varying head pressures, widely varying evaporator loads and very low liquid-line temperatures? - Answer Balanced-port Which type of valve uses A control board, transistors, thermistors, and A stepper motor controlled by an algorithm? - Answer Electronic expansion valve The difference between the superheat set point of an electronic expansion valve and the actual super heat is called a(n) - Answer error. The terms "offset" and "error" are one and the same. - Answer true
