Unit 47 Test and Quiz
True
A reciprocating compressor cannot be unloaded to 0 pumping capacity True or False
reduced-voltage start.
An autotransformer start is commonly referred to as a part-winding start. full-winding start. wye-delta start. reduced-voltage start.
10 tons, 15 tons, and 25 tons
Which of the following represents the most complete and accurate list of possible system capacities for a chilled-water system that is equipped with one 10-ton and one 15-ton scroll compressor? 10 tons, 15 tons, and 25 tons 10 tons and 15 tons 0 tons and 25 tons 15 tons and 25 tons
They require field-installed water lines.
Which of the following statements is true regarding package-type chillers? They require field-installed refrigerant lines. They require field-installed water lines. They require field-installed refrigerant and water lines. They require no field-installed lines whatsoever.
5F°
A chiller barrel that has three passes will most likely operate with a design approach temperature of about 1F° . 5F° . 9F° . 13F° .
Centrifugal
All low-pressure chillers use which type of compressor? Reciprocating Scroll Rotary Centrifugal
prerotational guide vanes.
Capacity control on a centrifugal compressor is accomplished by the slide vanes. check valves. prerotational guide vanes. postrotational guide vanes.
True
The rotary screw compressor is capable of handling large volumes of refrigerant with few moving parts True or False
salt.
Lithium-bromide, Li-Br, is best characterized as a salt. sand. sugar. soil.
A
The building heat adds about ____________ degrees F to the water supplied by the chiller A. 10 B. 5 C. 20 D. 15
number of cycles per second of the power supplied to the system's motors.
A variable frequency drive (VFD) is used to vary the voltage supplied to the system's motors. resistance of the system's motors. number of cycles per second of the power supplied to the system's motors. amperage draw of the system's motors.
constant suction.
All of the following methods can be used to control the capacity of a reciprocating compressor except suction valve lifting. blocked suction. variable frequency drive (VFD). constant suction.
rate at which heat is supplied to the concentrator.
Capacity control on an absorption system is typically accomplished by varying the speed of the condenser water circulator pump. speed of the chilled water circulator pump. pressure setting on the system's rupture disc. rate at which heat is supplied to the concentrator.
secondary refrigerant.
Chilled water, when circulated throughout a building to provide comfort cooling, is referred to as a primary refrigerant. secondary refrigerant. bypass refrigerant. reciprocal refrigerant.
water is less expensive than refrigerant.
Circulating water throughout a building to provide comfort cooling is desirable from an economic standpoint because water is lighter than refrigerant. water is less expensive than refrigerant. the design chilled water temperature is lower than the design boiling temperature of the refrigerant. water does not require the use of a pump to move it through the system.
suction-cooled compressors.
Compressors that are cooled with refrigerant that leaves the evaporator are referred to as liquid-cooled compressors. suction-cooled compressors. vapor-cooled compressors. discharge-cooled compressors.
direct-expansion evaporators.
Evaporators that operate with an established amount of superheat are referred to as low-side float evaporators. high-side float evaporators. flooded evaporators. direct-expansion evaporators.
95F°
For an approach temperature of 10F° , what is the temperature of the water leaving a condenser if the condenser saturation pressure is 344 psig for an R-410A system? 75F° 85F° 95F° 105F°
1%
For each 1F° of added subcooling, the efficiency of a system will increase by approximately 1%. 3%. 5%. 7%.
Fan-like action
How does a centrifugal compressor create the pressure differential needed to move refrigerant through the system? Nesting scrolls Suction and discharge valves Rotating vanes Fan-like action
High suction pressure and high discharge pressure
If a low-pressure chiller has a low-side leak, which of the following will most likely result? High head pressure and low suction pressure Low head pressure and high suction pressure Low suction pressure and low discharge pressure High suction pressure and high discharge pressure
Rust can form.
If air is present in an absorption chilled water appliance, which of the following will most likely occur? Rust can form. The Li-Br solution will become more diluted. The Li-Br solution will become more concentrated. System operating pressure will drop.
surge
If the compression ratio on a centrifugal compressor rises too high, the compressor will stop pumping and make a loud sound commonly referred to as a purge. splurge. merge. surge.
Heat
Instead of using a compressor, an absorption air-conditioning chiller uses which of the following as its driving force? Heat Electricity Oil Air
air being pulled into the system.
Low-side system leaks in a low-pressure chiller will often result in system refrigerant leaking from the system. water being pulled into the system. air being pulled into the system. nitrogen leaking out of the system.
three-phase, fractional horsepower motors.
Oil pumps used in conjunction with centrifugal compressors typically use three-phase, fractional horsepower motors. single-phase, fractional horsepower motors. three-phase, multi-horsepower motors. single-phase, multi-horsepower motors.
A
One type of chilled-water system that utilizes scroll compressors is the __________________ chiller A. reverse-cycle B. vapor compression C. parallel flow D. flooded evaporator
slide valve on the compressor's suction side.
The capacity of a chiller operating with a rotary screw compressor is most likely controlled by a slide valve on the compressor's suction side. slide valve on the compressor's discharge side. check valve on the compressor's suction side. check valve on the compressor's discharge side.
D
The colder the water that is circulated in a chiller, ___________________ A. the less efficient the chiller will be B. the larger the terminals and piping are required to be C. the more freeze protection is required throughout the system D. the smaller the terminals and piping are required to be
10F°
The design temperature difference between the chilled water supplied to the building and the water returning to the system from the building is 10F° . 15F° . 20F° . 25F° .
pressure transducers and thermistors to control the operation of a stepper motor.
The electronic expansion valve relies on pressure transducers and thermistors to control the operation of a stepper motor. the difference between the system's high and low pressure to control the valve. the difference between the condenser and evaporator outlet temperatures to control the valve. pressure transducers to maintain the desired evaporator saturation pressure.
D
The evaporator of a chiller is also referred to as the _____________________ A. water box B. indoor coil C. outdoor coil D. chiller barrel
is constant as long as the pressure drop across the orifice remains the same.
The flow through an orifice metering device is constant under all operating conditions. increases as the pressure drop across the orifice decreases. decreases as the pressure drop across the orifice increases. is constant as long as the pressure drop across the orifice remains the same.
hydrometer.
The instrument used to measure the specific gravity of absorption chiller solutions is the psychrometer. refractometer. anemometer. hydrometer.
A
Two common ways that unloading is accomplished are ___________________. A. suction-valve-lift and blocked suction B. piston actuated and thermostatic C. blocked suction and blocked discharge D. gas bypass and cylinder bypass
Partitions
What component is incorporated into the marine water boxes to direct water through a shell-and-tube heat exchanger? Partitions Abscissions Diverters Converters
6F°
What is the approach temperature for an R-410A chilled-water system that produces 43F° water when it operates with an evaporator saturation pressure of 112 psig? 4F° 6F° 8F° 10F°
volute.
The outer portion or shell of the compressor used on low-pressure chillers is called the baffle. volute. nozzle. suction.
chiller barrel
The portion of a chilled water system that cools the water that is used to cool the building is referred to as the chiller barrel. shell- and-tube condenser. shell and coil condenser. cooling tower.
remove air from a low-pressure chiller.
The purge unit is designed to remove water from a low-pressure chiller. remove air from a low-pressure chiller. introduce water to a low-pressure chiller. introduce air to a low-pressure chiller.
is greater than the rate of heat exchange between two gases as well as greater than the rate of heat exchange between a gas and a liquid.
The rate of heat exchange between two liquids is greater than the rate of heat exchange between two gases, but less than the rate of heat exchange between a gas and a liquid. is less than the rate of heat exchange between two gases, but greater than the rate of heat exchange between a gas and a liquid. is greater than the rate of heat exchange between two gases as well as greater than the rate of heat exchange between a gas and a liquid. is less than the rate of heat exchange between two gases as well as less than the rate of heat exchange between a gas and a liquid.
15 psig.
The rupture disc on a low-pressure chiller typically releases pressure at 0 psig. 5 psig. 10 psig. 15 psig.
prevent backward refrigerant flow when the system compressor cycles off.
The scroll compressor is equipped with an internal check valve to maintain the system's high-side pressure above a preset minimum level. prevent backward refrigerant flow when the system compressor cycles off. maintain the system's low-side pressure below a preset maximum level. prevent system superheat from rising above its design set point.
weak solution.
The solution that is pumped into the concentrator in an absorption chiller is referred to as the strong solution. concentrated solution. weak solution. absorbed solution.
strong solution.
The solution that leaves the concentrator in an absorption chiller is referred to as the absorbed solution. strong solution. weak solution. diluted solution.
8F° and 12F°
The superheat maintained by a thermostatic expansion valve is typically between 0F° and 4F° . 4F° and 8F° . 8F° and 12F° . 12F° and 16F° .
C
The two classification of compression cycle chillers are _______________________. A. industrial and commercial B. water and glycol C. high-pressure and low-pressure D. high-temperature and low-temperature
high-side float and the low-side float.
The two float-type metering devices are the liquid float and the vapor float. high-side float and the low-side float. liquid float and the low-side float. vapor float and the low-side float.
B
The typical condensing temperature for a chilled-water system equipped with a water-cooled condenser is about ____________ degrees F A. 115 B. 105 C. 95 D. 125
105
The typical condensing temperature for the refrigerant in a water-cooled chilled water system is 85F° . 95F° . 105F° . 115F° .
1.29%
What is the voltage imbalance on a three-phase power supply if the voltage readings are: L1-L2: 466 V, L1-L3: 470 V, and L2-L3: 459 V? 1.29% 1.83% 2.15% 2.85%
The machine will stop cooling and the solution will crystallize.
What will occur if the strong solution in an absorption chiller becomes too strong? The machine will stop cooling and the solution will evaporate. The machine will cool excessively as the solution evaporates. The machine will stop cooling and the solution will crystallize. The machine will cool excessively as the solution crystallizes.
B
When water is cooled and circulated throughout the building to air-heat exchange coils, the water is referred to as a (n) A. refrigerant B. secondary refrigerant C. antifreeze D. expandable refrigerant
A larger drive gear and a smaller driven gear
Which of the following best describes a two-gear drive assembly on a centrifugal compressor? A larger drive gear and a smaller driven gear A larger driven gear and a smaller drive gear Two same-size gears in an oil-filled reservoir Two same-size gears in a glycol-filled reservoir
Babbitt construction with a steel sleeve
Which of the following best describes the bearings on a centrifugal compressor? Steel construction with a babbitt sleeve Babbitt construction with a steel sleeve Copper construction with a steel sleeve Steel construction with a copper sleeve
The chiller has a critical refrigerant charge.
Which of the following is true regarding a high-pressure chiller equipped with an orifice metering device? The chiller has a critical refrigerant charge. The chiller operates with R-410A as its refrigerant. The chiller operates with 10F° of superheat. The chiller operates with a reciprocating compressor.
60% Li-Br, 40% distilled water
Which of the following most closely represents the concentration of Li-Br in an absorption system? 50% Li-Br, 50% tap water 60% Li-Br, 40% distilled water 40% Li-Br, 60% tap water 40% Li-Br, 60% distilled water
Pitting occurs when electricity arcs as starter contacts open and close.
Which of the following statements is true regarding "pitted" contactor and starter contacts? Pitting occurs when a system is off for a prolonged period of time. A voltage reading of 0 volts will be measured across a set of closed, severely pitted contacts. Pitting occurs when electricity arcs as starter contacts open and close. Pitting contacts can be sanded smooth to restore the integrity of the contacts.
The compressor would have to pump over 2400ft3 of water vapor for each pound of water circulated through the system.
Why is water not used as a primary refrigerant in a vapor-compression refrigeration system? The water would freeze at the required temperature for cooling. The compressor would have to pump over 2400ft3 of water vapor for each pound of water circulated through the system. The pressures acting on the water would be much higher than those in traditional vapor-compression refrigeration systems. Water, when mixed with refrigerant oil, creates substances that pose a danger to the stratospheric ozone layer.
wye configuration and then transitions to a delta configuration.
With a wye-delta or star-delta configuration, the motor starts as a wye configuration and then transitions to a star configuration. wye configuration and then transitions to a delta configuration. delta configuration and then transitions to a wye configuration. delta configuration and then transitions to a star configuration.
