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Worksheets141 mid term review/ final part 1
Total questions: 47
Worksheet time: 24mins
Thermostatic expansion valves are the only metering devices used in high pressure chillers.
True
False
To unload a reciprocating compressor, hot gas bypass across the cylinder is the best method.
True
False
When referring to evaporators, the terms "direct expansion" and "dry type" can be used interchangeably.
True
False
High pressure chillers use either air- or water-cooled condensers.
True
False
Low pressure chillers use either air- or water-cooled condensers.
True
False
Lithium bromide is ideal for use in absorption systems because it is non-corrosive.
True
False
Electronic starters are much smaller than conventional starters.
True
False
The evaporator of a chiller can be used to absorb heat from ____.
water
a solution of water and polyethylene glycol
the refrigerant
both a and b
A benefit of operating a compressor unloaded is ____.
reduced energy costs
reduced compression ratios
increased cooling
both a and b
A reciprocating compressor with six cylinders, three banks of two cylinders each, can have its capacity reduced by unloading to ____% of full capacity.
12.5
25
33-1/3
50
When a chiller using a low-pressure refrigerant is operating, the low pressure side of the system ____.
always shows a positive pressure
is always in a vacuum
contains a mixture of oil and air
rejects oxygen and moisture
Two basic categories of chillers are the ____.
compression cycle and absorption
purge and absorption
absorption and lithium bromide
purge and lithium bromide
Direct expansion evaporators have ____.
expansion joints between sections of the evaporator
an established superheat at the outlet of the evaporator
subcooling at the outlet of the evaporator
an established superheat at the inlet of the evaporator
A purge unit ____.
helps to provide subcooling in the condenser
helps to provide superheat in the suction line
relieves non-condensable gases from the system to the atmosphere
provides capacity control
A centrifugal compressor uses ____ for capacity control.
guide vanes
block vanes
guide blocks
control vanes
Speeds up to ____ rpm are used in centrifugal compressors.
15,000
20,000
25,000
30,000
The compressors used in low pressure chillers are the ____ type.
reciprocating
scroll
screw
centrifugal
The condenser water pump is the device that moves the water through the condenser and cooling tower circuit.
True
False
A well-designed and installed cooling tower requires only a minimum of maintenance.
True
False
Distilled water is added to the cooling tower to make up for water lost during blowdown.
True
False
If vortexing occurs, it is an indication that there is not enough air in the tower.
True
False
Spray ponds on rooftops have made a comeback in the last few years because they cool the roof and reduce the solar load on the structure.
True
False
Natural draft towers and spray ponds are designed to produce a difference in water and air temperatures of ____°F.
3
5
7
10
A new chemical-free water purification technology is used in cooling towers to ____.
avoid vortexing
balance the water flow
eliminate scale
All of the above.
When sizing a cooling tower, the tower is sized to handle the cooling load of the conditioned area plus about ____% for heat of compression.
0
15
25
35
Two methods used to aid the evaporation rate of water in a forced or induced draft tower are ____.
vortexing and cavitation
spray pond and prevailing wind
float type valve and by-pass valve
splash and wetted-surface (or fill)
The heat that the cooling tower must reject from the water in the chiller is the cooling load of the conditioned area plus the heat of ____.
absorption
compression
vortexing
cavitation
If the blower on a cooling tower breaks down on a hot day, the ____.
approach temperature will increase
water supplied to the condensers will be warmer
efficiency of the tower will increase
Both a and b.
Cooling towers are designed to reduce the entering water temperature to within ____°F of the air's wet-bulb temperature.
3
7
14
35
The purpose of the cooling tower bypass valve is to ____.
route debris away from the tower sump
prevent cavitation at the pump
provide makeup water to the tower sump
help maintain the correct water temperature to the condenser
The term ____ refers to the process of cooling the circulating condenser water by evaporating the tower water.
cyclic
adiabatic
isothermal
polytropic
Technician "A" says that a cooling tower can reduce the temperature of the water supplied to the condensers to a temperature equal to, but not less than, the wet-bulb temperature of the ambient air. Technician "B" says that a cooling tower's approach temperature is the temperature of the water returning from the water cooled condensers. Which of the following statements is correct?
Technician "A" is correct. Technician "B" is correct.
Technician "A" is correct. Technician "B" is incorrect.
Technician "A" is incorrect. Technician "B" is correct.
Technician "A" is incorrect. Technician "B" is incorrect.
Two types of shaft seals used for centrifugal pumps are ____.
stuffing box and mechanical types
stuffing box and splash types
ceramic and splash types
ceramic and bellows types
If the purge unit on a chiller is operating very frequently, the system may have a leak.
True
False
After chemically cleaning a condenser, it is extremely important to make sure that the chemicals are neutralized or the tubes may be damaged.
True
False
The operation of chillers involves starting, running, and stopping the system’s components in an orderly manner.
True
False
Low-pressure chillers operate in a vacuum and will stay in a vacuum if the equipment room is not warm enough to keep the refrigerant warm.
True
False
If an absorption chiller makes an "ice-crackling" sound, it is an indication that no condenser water is flowing.
True
False
The first step in starting a chilled-water system is to ____.
activate the compressor unloading system
establish the chilled-water flow
activate the condenser heat removal system
start the compressor operation sequence
Chillers manufactured in the last few years all have ____ controls.
electronic
hydraulic
pneumatic
pressure-based
A typical chilled water system is designed to operate with a leaving water temperature of ____°F.
35
40
45
50
There should be a ____ test point at the inlet and outlet of any water heat exchanger, chiller, or condenser.
temperature
pressure
vapor
moisture
Reciprocating chillers have crankcase heaters to ____.
preheat the chilled water for better efficiency
prevent refrigerant migration to the crankcase
preheat the compressor bearings for longer wear
minimize condenser subcooling
Water-cooled chillers must have water treatment to ____.
increase the pH content of the water in the sump
decrease the pH content of the water in the sump
prevent minerals and algae from forming in the water circuit
help preheat the water in the condenser water circuit
Centrifugal chillers range in size from ____ tons for a single chiller.
10 to 50
10 to 80
50 to 500
100 to 10,000
What may happen if a lithium-bromide absorption system is started with the cooling water too cold?
High head pressure in the system.
Low head pressure in the absorber.
Removal of system load, compressor cylinders will unload.
Crystallization occurs.
When a water-cooled chiller is operating normally, it can usually be left unattended, except for which component?
The condenser.
The evaporator.
The metering device.
The cooling tower.
