1
Q
What are the four main components of the refrigeration cycle?
A
- Compressor
- Condenser
- Refrigeration metering devices
- Evaporator
These components work together to facilitate the refrigeration process.
2
Q
The refrigeration metering device controls the flow of liquid refrigerant from the _______ side of the system.
A
high-pressure
This device is crucial for regulating the refrigerant flow to the evaporator.
3
Q
What is the purpose of capacity control in refrigeration systems?(function)
A
To reduce the capacity of the refrigeration system to match the equipment capacity
This ensures that the system operates efficiently during varying load conditions.
4
Q
List the methods that a building operator should be familiar with regarding refrigeration systems.(3)
A
- Methods used to control compressor output
- Forces which control thermal expansion valves
- Disadvantages associated with evaporator capacity control
Understanding these methods is essential for effective system management.
5
Q
What is the role of expansion valves in the compression refrigeration cycle?
A
To maintain the desired temperature of the cooled medium by controlling the flow of liquid refrigerant
Proper operation of expansion valves is critical for system efficiency.
6
Q
Name the six basic types of metering or flow control devices.
A
- Hand-operated expansion valve
- Automatic expansion valve (constant pressure)
- Thermostatic expansion valve
- Low-pressure float valve
- High-pressure float valve
- Capillary tube
These devices vary in operation and application within refrigeration systems.
7
Q
What material is a hand-operated expansion valve typically made of?
A
Brass
This material is commonly used for its durability and resistance to corrosion.
8
Q
What type of valve is equipped with a tapered valve stem and a matching tapered valve seat?
A
Hand operated expansion valve
This type of valve is used for throttling service and allows for precise adjustments.
9
Q
The automatic expansion valve maintains a constant _______ during compressor operation.
A
evaporator pressure
It automatically shuts off liquid flow when the compressor stops.
10
Q
What are the two forces that balance each other in an automatic expansion valve?
A
- Spring force
- Evaporator pressure
These forces determine the opening of the valve to allow liquid refrigerant flow.
11
Q
What is the primary function of the thermostatic expansion valve?
A
To control refrigerant flow based on temperature changes
It uses a thermal element connected to a temperature-sensing bulb.
12
Q
The thermal power element of a thermostatic expansion valve consists of a bellows or diaphragm chamber connected to a _______.
A
temperature-sensing bulb
This bulb is usually filled with the same refrigerant used in the system.
13
Q
What happens to the refrigerant in the thermal bulb of a thermostatic expansion valve when the temperature changes?
A
The pressure of the refrigerant changes
This change in pressure affects the operation of the expansion valve.
14
Q
What is a disadvantage of using automatic expansion valves in refrigeration systems?
A
They can allow unvaporized refrigerant to carry over into the compressor
This can cause damage to the compressor.
15
Q
The thermostatic expansion valve is designed to ensure that refrigerant _______ completely in the coil.
A
vaporizes
This prevents issues with unvaporized refrigerant entering the compressor.
16
Q
What is the role of the spring in an automatic expansion valve?
A
Exert a downward force on the diaphragm
This force is counteracted by the evaporator pressure to control the valve opening.
17
Q
In a system with two constant pressure valves, what can cause the thermostat to call for the compressor to operate continuously?
A
Higher cooling load near the thermostat
This can lead to imbalances in refrigerant flow between interconnected cooling coils.
18
Q
What is the purpose of the thermostatic expansion valve?
A
Adjusts the amount of liquid admitted to the evaporator
Ensures a high percentage of the surface is used for heat absorption while preventing liquid from leaving the evaporator with the vapor.
19
Q
At what temperature does the vapour typically leave the evaporator superheated?
A
5°C to 6°C
This is necessary to ensure that no liquid refrigerant exits the evaporator.
20
Q
What three forces control the operation of the expansion valve?
A
- Force exerted by the thermal element (opens the valve)
- Evaporator pressure (closes the valve)
- Spring pressure (closes the valve)
The interaction of these forces determines the valve’s opening and closing.
21
Q
What happens when there is an insufficient amount of liquid refrigerant admitted to the evaporator?
A
Superheat of the vapor rises, increasing pressure in the thermal element
This action opens the valve more, allowing more liquid refrigerant to enter the evaporator.
22
Q
What is the function of the equalizing line in a thermal expansion valve?
A
Connects the underside of the diaphragm with the outlet of the evaporator
Compensates for pressure drops to maintain sufficient valve opening.
23
Q
In a flooded evaporator, what is the role of the low-pressure float valve?
A
Maintains a constant refrigerant level
Regulates the flow of liquid into the evaporator based on the liquid level.
24
Q
Where is the float ball located in a low-pressure float valve system?
A
In the low-pressure side of the system
It responds to the liquid level in the evaporator.
25
What is the purpose of the **bypass line** with a hand-operated expansion valve?
Provides cooling if the pump fails
## Footnote
Allows refrigerant to bypass the pump and continue cooling.
26
What is the **saturation temperature** corresponding to the evaporator pressure at -7°C?
142 kPa
## Footnote
This is the pressure at which the refrigerant changes from liquid to vapor.
27
What occurs when the **pressure drop** across the evaporator is large?
Causes a reduction in temperature and pressure near the evaporator outlet
## Footnote
This leads to reduced valve opening and efficiency.
28
What method of **refrigerant level control** uses a low-pressure float switch and a solenoid valve?
A system that controls the operation of a solenoid valve in the refrigerant supply line
## Footnote
This method is used in large flooded evaporators.
29
What does the **high-pressure float valve** allow in a refrigeration system?
It allows liquid refrigerant to flow into the evaporator at the same rate as refrigerant vapor is condensed
## Footnote
This valve is critical for maintaining the refrigerant charge in the system.
30
What is the function of a **capillary tube** in a refrigeration system?
It creates a considerable pressure drop along its length to control the flow of liquid from the condenser to the evaporator
## Footnote
The capillary tube has a very small inside diameter, resulting in high resistance.
31
In what type of equipment is the **capillary tube** commonly used?(2)
* Domestic freezers
* Room air conditioners
## Footnote
It is suitable for small refrigerating equipment with fairly constant loads.
32
What is the critical aspect of the **amount of refrigerant charge** in a system with a high-pressure float valve?
It must be maintained to prevent liquid carryover or starvation of the evaporator
## Footnote
This balance is essential for the proper functioning of the refrigeration system.
33
What is the purpose of **capacity control** in a refrigeration system?
To maintain desired temperature and humidity during peak loading periods
## Footnote
Capacity control ensures the system can handle the highest load experienced throughout the year.
34
What must the rated capacity of a refrigeration system be in relation to the highest load?
Slightly higher
## Footnote
This design consideration is crucial for effective operation.
35
Name the two methods for controlling the capacity of an **evaporator**.
* Sectional evaporators
* Evaporator dampers
## Footnote
These methods help match the evaporator capacity to the building load.
36
What is a common application for controlling evaporator capacity?
Using **sectional evaporators**
## Footnote
Sectional evaporators can be made inoperative as the cooling load decreases.
37
What happens to the solenoid valve in a sectional evaporator when the cooling load decreases?
Closes to make section A inoperative
## Footnote
This allows for proportional reduction in cooling capacity.
38
What is the function of a **face damper** in an evaporator?
To vary the quantity of air passing over the evaporator coils
## Footnote
This damper increases air resistance as it closes.
39
What is the disadvantage of using a face damper for capacity control?
Reduces air volume to the space
## Footnote
This can lead to inadequate cooling in some situations.
40
What is the purpose of a **bypass damper** in conjunction with a face damper?
To maintain constant air quantity through the duct
## Footnote
The bypass damper opens as the face damper closes.
41
What is necessary for effective **compressor capacity control**?
Simultaneous control of the compressor output
## Footnote
Changes in evaporator load require adjustments in compressor operation.
42
What drives refrigerating compressors in most applications?
Electric motors
## Footnote
This is typical except in industrial applications.
43
List the methods used to control **compressor output**.(7)
* Intermittent operation
* Compressor unloader
* Cylinder bypass
* Hot gas bypass
* Compressor speed control
* Suction throttling
* Variable inlet guide vanes
## Footnote
These methods help regulate the compressor's capacity to match the load.
44
What is the purpose of **intermittent operation** in refrigeration systems?
To stop the compressor when the desired low temperature is reached and restart it when the temperature rises
## Footnote
This method is typically used in low-capacity refrigeration systems with moderate loads.
45
In larger refrigeration systems, why is **frequent starting and stopping** undesirable?
It can put undesirable stresses on the motor and switchgear and cause severe power fluctuations
## Footnote
Continuous operation is preferred to avoid these issues.
46
What is a **compressor unloader**?
A device that reduces the output of the compressor by keeping the intake valves of one or more cylinders open
## Footnote
This prevents the compression of vapor during the suction stroke.
47
How does a **solenoid valve** function in a refrigeration system?
It opens or closes based on electrical current, controlling the flow of refrigerant
## Footnote
When energized, it draws an iron core upward, opening the valve port.
48
What happens when the **suction pressure** falls to a preset value in a refrigeration system?
A pressure switch energizes a solenoid, admitting condenser pressure to the unloader piston
## Footnote
This moves the piston downward, holding the suction valves in the open position.
49
What is the **suction cut-off** method?
A method that blocks the inlet to the cylinder to prevent overheating of the refrigerant and compressor parts
## Footnote
This method is used for cylinder unloading.
50
What is the benefit of starting a compressor in an **unloaded condition**?
It reduces the starting current of the electric motor
## Footnote
This is important for capacity control in multi-cylinder continuous operating compressors.
51
What is one method of controlling the capacity of **reciprocating compressors**?
By bypassing discharge from one or more cylinders back to the suction side of the compressor
## Footnote
This allows for better management of the compressor's output.
52
What is the role of the **unloader piston** in a refrigeration system?
To depress the suction valves and hold them in the open position when the compressor is unloaded
## Footnote
This allows vapor to be drawn into the cylinder without compression.
53
What is the purpose of the **de-superheating expansion valve**?
To provide vapour cooling
## Footnote
It helps prevent compressor motor and component overheating.
54
What happens when the **suction pressure** increases to the cut-out pressure?
The pressure switch de-energizes the solenoid to close the bypass line
## Footnote
This action prevents overheating of the compressor motor.
55
What is the function of the **hot gas bypass** in capacity control?
Allows some hot gas to go directly into the suction line
## Footnote
It is used when a reduction of compressor capacity is required.
56
What are the **methods** of controlling the speed of a compressor?(4)
* Temperature-sensing device
* Variable speed electric motor
* Hydraulic coupling
* Variable-frequency drive (VFD)
## Footnote
These methods help adjust the compressor speed according to load demand.
57
What is **suction throttling** accomplished by?
A butterfly damper installed at the inlet to a centrifugal compressor
## Footnote
It can be adapted to automatic control but is not economical.
58
What do **variable inlet guide vanes** do in centrifugal compressors?
They adjust the airflow to optimize compressor performance
## Footnote
Pneumatic or electric operators position the vanes based on air or oil pressure.
59
What safety feature prevents the compressor from starting unless the vanes are closed?
A vane switch
## Footnote
This ensures safe operation of the compressor.
60
As the **vanes** move towards the closed position, what happens to the refrigerant vapour?
It swirls or spins in the same direction as the compressor impeller
## Footnote
This action reduces the power required by the compressor.
61
What do modern centrifugal compressors typically combine for maximum efficiency?(2)
* Motor control
* Vane control
## Footnote
Both systems work together to optimize performance under varying load conditions.
62
What are the **three distinct classes** of refrigeration controls?
* Operating or primary controls
* Actuating or secondary controls
* Limiting and safety controls
## Footnote
Each class serves a specific function in the operation and safety of refrigeration systems.
63
What is the function of **operating or primary controls** in refrigeration systems?
Start or stop the compressor or regulate its output based on changes in temperature, pressure, or humidity
## Footnote
These controls ensure the system operates within desired limits.
64
What do **actuating or secondary controls** do in refrigeration systems?
Indirectly control changes called for by primary controls or regulate the cycle during operation
## Footnote
They support the primary controls in maintaining system efficiency.
65
What is the purpose of **limiting and safety controls**?
Protect the system against operation beyond its designed limits
## Footnote
These controls are essential for preventing damage to the refrigeration system.
66
Name the types of **operating controls** for refrigeration systems.(3)
* Temperature
* Pressure
* Humidity
## Footnote
These controls are crucial for maintaining the desired conditions in refrigeration systems.
67
What are the two types of **temperature-actuated controls**?
* Direct type
* Indirect type
## Footnote
Direct type operates in the space to be cooled, while indirect type uses a fluid-filled bulb connected to the control.
68
How does a **bimetallic thermostat** operate?
Bends when subjected to temperature changes, closing or opening an electrical circuit
## Footnote
This bending action is used to start or stop a compressor.
69
What are the methods by which **thermostats** may be operated?(5)
* Movement of a bimetallic element
* Expansion of a fluid (liquid or gas)
* Vapour pressure of a volatile fluid
* Electrical resistance
* Electronic signals
## Footnote
The first three produce mechanical effects, while the last two produce electrical signals.
70
What is the primary function of a **thermostat** in refrigeration systems?
Controls the power supply to small compressor motors
## Footnote
Larger motors are controlled by a thermostat that actuates a magnetic motor starter or contactor.
71
What is the difference between a **motor starter** and a **contactor**?
* Motor starter: Equipped with external overload devices for motor protection
* Contactor: Not equipped with overload devices
## Footnote
Motor starters are used for larger motors, while contactors are used for smaller applications.
72
What does the **unloader actuator** do in a compressor?
Controls temperature fluctuations in the cooled medium
## Footnote
It is actuated by the thermostat or pressure switch.
73
What components are included in a **thermostatic controller**?(3)
* Bulb
* Tube
* Bellows filled with liquid, gas, or saturated mixture
## Footnote
These components respond to temperature changes.
74
What happens to the **pressure of the confined fluid** in a thermostatic controller when the temperature of the bulb increases?
Pressure increases, causing the bellows to expand
## Footnote
This movement affects the primary beam and electrical contacts.
75
What is the **cut-in point** in a thermostatic controller?
The temperature at which the electrical contacts close
## Footnote
This occurs when the armature is attracted to the permanent magnet.
76
What is the **cut-out point** in a thermostatic controller?
The temperature at which the electrical contacts snap apart
## Footnote
This occurs at a lower temperature than the cut-in point.
77
What is the **temperature differential** in a thermostatic controller?
The difference in temperature between the cut-in and cut-out points
## Footnote
It is adjustable using the differential adjustment feature.
78
What does the **range adjustment** in a thermostatic controller do?
Sets the temperature level at which the cut-in occurs
## Footnote
The range could vary, affecting when the compressor activates.
79
In a refrigeration system, what is the role of **temperature actuating devices**?
Control the operation of the compressor
## Footnote
They are used in conjunction with refrigerant flow controls.
80
What is the purpose of a **pressure-actuated control** in refrigeration systems?
To start and stop the compressor based on suction pressure
## Footnote
It maintains the evaporator temperature within close limits over varying load conditions.
81
What happens when the **pressure rises** due to an increase in evaporator temperature?
The contacts in the pressure control close, referred to as the **cut-in pressure**
## Footnote
This initiates the compressor operation to cool the space.
82
What is the **cut-out** condition for a pressure-actuated control?
When the temperature of the space is cooled down to the desired low value
## Footnote
For example, 2°C in a 2°C - 5°C range.
83
What is the most common choice for controlling refrigerated space temperature?
A **non-equalizing thermostatic expansion valve**
## Footnote
It senses the pressure within the evaporator.
84
What is the function of a **humidistat** in air conditioning systems?
To control refrigerant flow to the evaporator for lowering humidity
## Footnote
It condenses moisture on the cold surfaces of the evaporator.
85
What is a **dehumidistat**?
A humidistat used specifically for controlling dehumidification
## Footnote
It operates similarly to a standard humidistat.
86
What type of element is often used in a **humidistat** to sense humidity?
A **hygroscopic element**
## Footnote
Historically, human hair was used, but synthetic materials are now common.
87
How does a **humidistat** control humidity levels?
By activating a switch for on-off control or a potentiometer for modulating control
## Footnote
It adjusts the operation of the humidifier based on humidity levels.
88
What is the role of an **electrolytic hygrometer cell** in humidity control?
To measure moisture content and control humidity
## Footnote
It uses a desiccant to absorb moisture and measures the resulting electrical current.
89
What must be ensured for **humidistats** to function properly?
They should be kept dust free and have covers that permit free air circulation
## Footnote
This is essential for accurate humidity measurement.
90
What is the purpose of the **refrigerant flow control** in a refrigeration system?
To regulate the amount of liquid refrigerant flowing into the evaporator
## Footnote
It is one of the most important secondary controls in a refrigerating system.
91
What type of valve is typically used to control refrigerant flow in refrigeration systems?
Solenoid Valve
## Footnote
The solenoid valve is electromagnetically operated and is usually located in the liquid refrigerant line ahead of the thermostatic expansion valve.
92
When does the **solenoid valve** close in a refrigeration system?
When the desired refrigerating space temperature is reached
## Footnote
The thermostatic control device breaks the electrical circuit, releasing the plunger and closing the valve.
93
What ensures positive closing of the **solenoid valve** when the electrical circuit is interrupted?
A breakaway pin under spring pressure
## Footnote
This mechanism assures that the valve closes completely.
94
In a multi-evaporator system, how is the flow of liquid refrigerant controlled for each evaporator?
By a separate solenoid valve for each evaporator
## Footnote
Each zone's temperature is controlled independently by a thermostat.
95
What is the function of the **condenser cooling water regulating valve**?
To automatically regulate the flow of cooling water to the condenser
## Footnote
It opens when the compressor is in operation and shuts off when the compressor stops.
96
What causes the **condenser cooling water regulating valve** to open?
High side pressure on the discharge side of the compressor
## Footnote
This pressure acts on the bellows to open the valve against spring force.
97
What happens to the **condenser cooling water regulating valve** when the compressor stops?
The valve closes due to spring tension overcoming the bellows force
## Footnote
This stops the flow of cooling water to the condenser.
98
How is the pressure at which the condenser is maintained adjusted?
By adjusting the spring tension
## Footnote
This adjustment affects how the valve responds to changes in cooling load.
99
What is the purpose of an **evaporator pressure regulating valve**?
Prevents low pressure and temperature conditions in the evaporator
## Footnote
Low evaporator pressure can cause frosting of coils or freeze-ups in water chillers.
100
What happens when the **pressure in the evaporator increases**?
Pressure under the seat disk increases, affecting the bellows
## Footnote
This action regulates the flow of refrigerant.
101
In direct-expansion evaporators, what signals the closure of the **solenoid valve**?
Thermostat or humidistat
## Footnote
This occurs when the temperature or humidity of the cooled space is sufficiently lowered.
102
What is the function of a **bypass valve** in the refrigeration cycle?
Opens when the solenoid valve closes to allow pump out completion
## Footnote
It remains open until the compressor shuts off.
103
What is the role of **evaporator pressure regulator valves** in systems with multiple evaporators?
Maintain different evaporator temperatures
## Footnote
They allow for temperature control in cold storage applications.
104
What does a **suction pressure regulating valve** do?
Limits suction pressure at the compressor inlet to a preset maximum
## Footnote
Protects the compressor from overload when evaporator pressure rises.
105
What is the consequence of **failing to pump out** the remaining refrigerant in the evaporator?
Could result in liquid slugging or high suction pressure
## Footnote
This occurs when the compressor is restarted.
106
What are the **typical refrigeration system safety shutdown devices**?(4)
* High-Pressure Safety Cutout
* Low Pressure Cut-off
* Low Limit Thermostat
* Oil Pressure Failure Switch
## Footnote
These devices guard against abnormal conditions in a refrigeration system.
107
The **High-Pressure Safety Cutout** prevents pressure from building up to a dangerous level due to what two main causes?
* Insufficient cooling of high-pressure vapor
* Presence of non-condensables in the system
## Footnote
CSA B52 Mechanical Refrigeration Code mandates pressure-limiting devices for systems operating above atmospheric pressure.
108
What is the purpose of the **Low Pressure Cut-off** in a refrigeration system?
To protect the system against lower than normal suction pressure
## Footnote
It can occur if the compressor fails to stop at its cutout pressure or if the evaporator ices up excessively.
109
The **Low Limit Thermostat** is used to prevent damage to equipment by breaking the control circuit of the compressor at what condition?
When the temperature drops below the minimum setting
## Footnote
This is crucial in water chilling systems to prevent freezing.
110
What does the **Oil Pressure Failure Switch** do in a refrigeration compressor?
Shuts down the compressor when oil pressure drops below a safe minimum limit
## Footnote
This is necessary to prevent extensive damage to the compressor.
111
The **oil pressure failure switch** operates based on the pressure differential between which two points?
* Oil pump discharge
* Suction pressure
## Footnote
This ensures that the compressor operates safely under the correct oil pressure conditions.
112
Fill in the blank: The **timed switch** in the oil pressure failure switch allows the compressor to operate for about ________ to establish the required oil pressure differential.
two minutes
## Footnote
If the pressure differential is not established within this time, the compressor shuts off.
113
What happens if the oil pressure differential does not build to the cut-in point within the preset time in the oil pressure failure switch?
The compressor stops
## Footnote
The timer switch contacts open, preventing further operation until manually reset.
114
What happens if the **oil pump discharge pressure** drops below the cut-in point during compressor operation?
The crankcase or suction pressure closes the differential pressure switch, energizing the heater circuit, causing the timer switch to stop the compressor
## Footnote
This process is crucial for protecting the compressor from damage due to low oil pressure.
115
What does the **high motor temperature cutout** do?
Stops the compressor if there is a loss of motor cooling or motor overload due to malfunction of the operating controls
## Footnote
Similar to the high oil temperature cutout, it protects the compressor from overheating.
116
How does **motor overload protection** work?
Uses a current transformer with a resistor in the motor control circuit to detect increased current flow
## Footnote
This change in voltage is amplified to operate relays controlling the refrigeration system.
117
What happens if the **vane controller** fails?
The relay will operate solenoid valves to override and force the pneumatic actuator on the vanes to the closed position
## Footnote
This ensures the system can still function even if the controller fails.
118
What does the **low oil sump temperature protection** switch do?
Prevents the compressor from starting if the oil heater fails to heat the lubricant to preset temperature
## Footnote
This is important to separate any refrigerant dissolved in the oil from the lubricant.
119
What is the function of **flow switches** in refrigeration systems?
Used as safety lockout switches for the refrigerating system if flow slows or ceases
## Footnote
They can also close flow indicator circuits and operate based on the force exerted on a flexible vane.
120
What does the **high oil temperature cutout** do?
Shuts down a compressor when the lubricating oil temperature becomes too high
## Footnote
This can occur due to loss of water in the oil cooler or bearing failure.
121
What is a **thermistor**?
An electronic component whose electrical resistance varies quickly and substantially in response to changes in temperature
## Footnote
It reacts faster than a thermostat and is used when reaction speed is important.
122
What is the maximum number of starts allowed for large centrifugal or screw compressors in an hour?
Usually three
## Footnote
This limit is due to the stress placed on the motor during the start phase.
123
What must be thoroughly inspected for leaks after a **refrigerating system** is installed?
The entire system
## Footnote
Federal law requires that the origin of a leak must be found and repaired before more refrigerant may be added.
124
What is the consequence of **moisture** in a refrigeration system?
Serious operating problems
## Footnote
Moisture may be removed through temporary driers, but sometimes the system requires draining, drying, and recharging.
125
What must be done if a refrigeration system contains **non-condensable gases**?
The system must be purged
## Footnote
Purging must be accomplished by closely following a sequence of operations.
126
What type of gases should not be used for **pressure testing** a refrigeration system?
Oxygen or any flammable gas
## Footnote
Using these gases can result in an explosion.
127
What is the recommended test medium for **positive pressure testing**?
Dry nitrogen
## Footnote
Inert gases like dry nitrogen or carbon dioxide are used as testing mediums.
128
What must be done after the system is pressurized for a minimum of **2 hours**?
The system must be pressure tested without loss of pressure
## Footnote
This is a requirement as per CSA B52.
129
What is the first step in the **positive pressure testing** procedure?
Remove controls and relief valves which may be damaged by the test pressure
## Footnote
This ensures that sensitive components are not harmed during testing.
130
What should be done to isolate the **compressor** during pressure testing?
Shut the discharge and suction valves
## Footnote
This prevents pressure from affecting the compressor during the test.
131
What is the purpose of the **hand expansion valve** during the testing process?
To ensure it is open at the inlet to the evaporator
## Footnote
Most expansion devices cannot be opened as the system pressure will cause them to close.
132
What should be tested for leaks if the **pressure does not drop noticeably**?
All pipe joints in the system
## Footnote
Small leaks can be detected by brushing a soap solution around each joint, indicated by the formation of bubbles.
133
What method is used to **depressurize** the system after testing for leaks?
Releasing the gas to the atmosphere
## Footnote
The soap solution should be washed off after the test to prevent dirt accumulation.
134
What device picks up the frequency generated by gas leaving the system through a small hole?
Ultrasonic detector
## Footnote
This device is an alternate method to leak testing when using nitrogen.
135
How long should the system be left **pressurized** after the pressure test?
About 14 hours
## Footnote
The nitrogen or carbon dioxide bottle must be disconnected if the system is left unattended.
136
What should be done if the **system pressure** has not changed after the pressure test?
Gas is bled off from the high and low sides of the system
## Footnote
Any controls or relief devices previously removed for the pressure test are re-installed.
137
What is the first step in testing a **sub-atmospheric pressure refrigerant system** for leaks?
Shut down the compressor and break the vacuum
## Footnote
This is done by pressurizing the system with dry nitrogen.
138
What should be connected to the **charging valve** during sub-atmospheric pressure testing?
Nitrogen cylinder
## Footnote
The charging valve should be opened fully after connecting.
139
What should be observed on the **evaporator and condenser gauges** during testing?
Pressures
## Footnote
Close the nitrogen shutoff valve when both gauges read an adequate positive pressure.
140
What should be used to test all joints during sub-atmospheric pressure testing?
Electronic or halide leak detector
## Footnote
This is used when the system contains a nitrogen and refrigerant mixture.
141
What is the purpose of the **purge system** after leak repairs?
To release noncondensable gas used to elevate system pressure
## Footnote
If the purge system uses chilled water, a supply of cold potable water is required.
142
What are some common **leak detection methods** besides the soap test?(5)
* Halide torch
* Electronic leak detector
* Litmus paper
* Phenolphthalein paper
* Sulfur candle
## Footnote
These methods are used to test for leaks during normal operation.
143
What does an **electronic leak detector** measure?
Electrical resistance of the vapor sample
## Footnote
It indicates the presence of refrigerant either on a meter or by activating a light or buzzer.
144
What color does **red litmus paper** turn when exposed to ammonia?
Blue
## Footnote
This indicates a basic solution due to the presence of ammonium hydroxide.
145
What does **phenolphthalein paper** indicate when it turns red?
A pH greater than 8.3
## Footnote
This includes ammonium hydroxide solutions.
146
What is created when a **sulfur candle** comes in contact with leaking ammonia?
Thick white smoke
## Footnote
Caution: The dioxide formed is toxic and should only be used in well-ventilated locations.
147
What causes serious operating problems in a **refrigerating system**?
Moisture or water vapour
## Footnote
Moisture can cause icing at the expansion valve and form acids that react with oil.
148
What is the process called when acids remove copper from heat exchanger surfaces?
Copper plating
## Footnote
This occurs when acids redeposit copper at high-temperature points.
149
What should be installed in the system to absorb moisture during operation?
Temporary driers
## Footnote
These driers adsorb any moisture present in the refrigerant.
150
Before charging an empty refrigerating system, what must be done to the system?
Put under a very high vacuum
## Footnote
A special vacuum pump is used for this purpose.
151
What temperature should the surrounding air be for effective evacuation of the system?
20°C (68°F) or higher
## Footnote
This temperature is necessary for proper moisture evaporation.
152
What indicates that the system is free of leaks and moisture after evacuation?
No increase in pressure on the gauges
## Footnote
This confirms that the system is ready to be charged with refrigerant.
153
What can happen if a system is not adequately evacuated before being charged?
Air remains as a noncondensable
## Footnote
This can cause high compressor discharge pressures and temperatures.
154
What should be checked before proceeding with the actual **charging process**?(4)
* All components ready for operation
* Valves opened where necessary
* Controls adjusted to required settings
* Sequence of controls and interlocks tested
## Footnote
Ensuring readiness is crucial for safe operation.
155
Where is the initial refrigerant charge given in the system?
High-pressure side
## Footnote
The refrigerant drum is connected to the liquid charging valve.
156
What safety equipment must be used when handling refrigerants?
Goggles
## Footnote
Goggles protect the eyes from injury caused by freezing moisture.
157
What is the first step in preparation for charging a refrigeration system?
Check that the liquid line shutoff valve is closed
## Footnote
This is crucial to prevent refrigerant loss during charging.
158
Fill in the blank: The refrigerant container is inverted so only ______ will pass through the charging line.
liquid
## Footnote
This ensures that only liquid refrigerant enters the system.
159
What happens once the pressure starts rising above atmospheric pressure during charging?
The compressor starts
## Footnote
This indicates that the system is in normal operation.
160
What must the evaporator have during the charging operation?
A source of heat energy
## Footnote
This is necessary to vaporize the refrigerant as it passes through the system.
161
What is the purpose of **charging** in a refrigeration system?
To ensure the system has received the required amount of refrigerant
## Footnote
Charging should continue until the system has settled down to normal.
162
What does a **sight glass** indicate in a refrigeration system?
The flow of refrigerant
## Footnote
If bubbles appear in the sight glass, it may indicate overcharging.
163
What problems can **overcharging** a refrigeration system cause?(4)
* High suction and discharge pressures
* High compressor power consumption
* Liquid refrigerant forced into the compressor
* Frost formation on the suction line
## Footnote
Overcharging can lead to significant operational issues.
164
What is the effect of **noncondensable gases** in a refrigeration system?
They cause high-side pressure to rise above the condensing temperature pressure
## Footnote
This can lead to increased power consumption and reduced compressor capacity.
165
What are the main components of a **purge system** in refrigeration?(4)
* Purge condensing unit
* Purge tank
* Liquid return line
* Filter drier
## Footnote
The purge system is essential for removing noncondensables without venting refrigerant to the atmosphere.
166
Fill in the blank: Noncondensable gases consist mainly of _______ that may have leaked into the system.
air
## Footnote
They can enter due to improper operating or maintenance procedures.
167
What happens when the **suction temperature** in the purge tank begins to fall?
The purge control initiates a pump-out cycle
## Footnote
This occurs when the amount of noncondensables limits the condensing surface in the tank.
168
What is the role of the **pump-out compressor** in the purge system?
To remove noncondensables from the purge tank
## Footnote
It discharges them through the carbon tank and out through the exhaust solenoid valve.
169
What should be done if the system appears to have **lost refrigerant**?
Conduct leak checking
## Footnote
It is illegal to add refrigerant without determining the leak origin.
170
What is the consequence of **high temperatures** in a refrigeration system?
They are detrimental to compressor valves and lubrication
## Footnote
High temperatures accompany higher pressures, which are undesirable.
171
What is the purpose of the **carbon tank** in the purge unit?
To capture the refrigerant through an adsorption process
## Footnote
The carbon tank is part of the purge unit that helps in managing refrigerant vapors.
172
What happens when the **purge controller** operates the small pump-out compressor?
The refrigeration system of the purge unit is shut down
## Footnote
This is part of the sequence of operation for managing refrigerant vapors.
173
What is energized in the carbon tank to aid in the **regeneration** process?
A small heater
## Footnote
The heater helps cause the refrigerant vapor to return to the chiller.
174
During the operation of the purge unit, what is drawn into the **purge tank**?
Refrigerant vapor from the chiller
## Footnote
This occurs through the condensing process.
175
What indicates that the **noncondensables** have been removed from the purge unit?
The temperature of the refrigerant suction line rises
## Footnote
This triggers the stopping of the small pump-out compressor.
176
What does the purge unit controller initiate based on the hours of the **pump-out compressor**?
A regeneration cycle
## Footnote
This cycle involves shutting down the purge system refrigeration unit.
177
What is the purpose of the **purge unit**?
To remove noncondensables that may enter the low pressure side of the system
## Footnote
It separates refrigerant vapor from noncondensables.
178
What must be done when the oil level in the **crankcase** becomes low?
Oil must be added
## Footnote
This is crucial for the proper operation of the refrigeration compressor.
179
What is the **conventional method** of adding oil to a compressor?
Pouring it through a fill opening
## Footnote
This method cannot be used when the system is pressurized.
180
What is an alternate method for adding oil if a special pump is not available?
Using the compressor suction to draw oil into the crankcase
## Footnote
This method requires careful management of the suction valve.
181
What should be ensured when adding oil to the system?
The proper oil type is used
## Footnote
Oil types depend on the refrigerant type and operating temperature.
182
What should never be allowed when using a hose to add oil to the crankcase?
The end of the hose should not come above the surface of the oil
## Footnote
This prevents air from being pulled into the system.
183
What should be done after completing the job of adding oil?
Wipe up any oil spills
## Footnote
This is important for safety and cleanliness.
184
What must be taken care of to avoid introducing **contaminants** into the machine?
Ensure no dirt, water, nitrogen, or dust enters
## Footnote
Contaminants can severely affect the operation of the refrigeration system.
185
What is the **first step** in the procedure for adding oil to a compressor?
Obtain a container of the correct oil
## Footnote
This step is crucial to ensure the right type of oil is used in the compressor.
186
What should be connected to the **discharge side** of a hand pump when adding oil?
A rubber hose
## Footnote
This connection allows for the transfer of oil from the container to the compressor.
187
Before tightening the rubber hose connection to the fill valve, what should be done?
Place the suction of the pump into the oil container and prime the suction line
## Footnote
Priming the suction line ensures that the pump can effectively draw oil.
188
What is the purpose of tightly connecting the rubber hose to the fill line?
To prevent air entering the system
## Footnote
Air in the system can cause operational issues and affect performance.
189
What should be done after the oil charge is complete?
Close the fill valve and disconnect the rubber hose
## Footnote
This ensures that the system is sealed and prevents any leaks.
190
What is the first step in **draining oil** from the compressor?
Pump down the compressor until the pressure in the crankcase equals atmospheric pressure
## Footnote
This step is necessary to safely drain the oil without pressure buildup.
191
What should be done to the compressor before draining oil?
Shut off and isolate the compressor, and lock it out
## Footnote
Locking out the compressor ensures safety during maintenance.
192
How can oil be drained from the compressor?(2)
* Opening the drain valve
* Removing the drain plug
## Footnote
Both methods allow for the removal of excess oil from the system.
193
What caution should be exercised when removing drain plugs?
Crankcase pressure may blow out oil and refrigerant vapor
## Footnote
This can create a hazardous situation if not handled carefully.
194
What should an operator do **prior to the startup and shutdown** of a refrigeration system?(3)
* Follow a series of steps
* Consult the manufacturer's operation manual
* Maintain the refrigeration system in good, efficient running order
## Footnote
These steps are crucial for ensuring the system operates effectively.
195
What is the purpose of **safety devices** in centrifugal compressor water chilling systems?(2)
* Protect systems against abnormal conditions during startup
* Protect systems during operation
## Footnote
Operators should be able to list and describe these safety devices.
196
Why is it important to have a **regular operational maintenance schedule** for refrigeration systems?(2)
* To ensure appropriate maintenance
* To keep the system running efficiently
## Footnote
A logbook should be maintained to record the maintenance performed on each system.
197
What does the **CSA, B52 Mechanical Refrigeration Code** contain?(3)
* Instructions regarding signs on refrigerating systems
* Charging/discharging of refrigerants
* Owner's responsibilities
## Footnote
Building operators should be familiar with the contents of this code.
198
What are the **general guidelines** for starting a reciprocating or rotary compressor refrigerating system?(5)
* Consult the manufacturer's operation manual
* Familiarize with the entire refrigeration system
* Check power availability to circuit breakers and pumps
* Check high- and low-pressure cutout switches
* Check operation of interlocks
## Footnote
These guidelines apply to both new systems and those that have been shut down for maintenance.
199
Before starting the compressor, what should be checked regarding **shutoff valves**?(2)
* Open shutoff valves in cooling water supply and return lines
* Open water supply valve to evaporative condenser sump
## Footnote
Ensure that the system is ready for operation.
200
What should be checked regarding the **oil level** in the compressor?
It should be at or above the center of the sight glass
## Footnote
Proper oil levels are crucial for compressor operation.
201
When starting smaller capacity compressors, what valves should be opened?
* Open suction and discharge valves
## Footnote
For larger compressors, only the discharge valve should be opened initially.
202
What should be done with the **solenoid valve** in the liquid line before starting the compressor?
It should be closed under normal system conditions
## Footnote
This is part of the startup procedure.
203
What should be ensured if the compressor is equipped with an **oil sump heater**?(2)
* It is energized
* Oil temperature is high enough to drive off refrigerant
## Footnote
This step is important for preventing refrigerant contamination.
204
What is the first step in starting the **compressor**?
Check controls for proper operation and reset if necessary
## Footnote
This ensures that all systems are functioning correctly before starting the compressor.
205
When checking the **liquid refrigerant sight glass**, what indicates that refrigerant may need to be added?
Bubbles
## Footnote
Bubbles in the sight glass suggest that the refrigerant level is low.
206
What should be checked after the compressor has run for about **15 to 20 minutes**?
Oil level in the crankcase
## Footnote
If pressure lubricated, check the oil pressure as well.
207
What is the purpose of closing the **liquid line shutoff** or 'king' valve during shutdown?
To stop the flow of refrigerant to the evaporator
## Footnote
This is a critical step to ensure the system is safely shut down.
208
What pressure should the compressor suction gauge indicate before stopping the compressor during shutdown?
14 kPa (2 psi)
## Footnote
This pressure is necessary to prevent air from being drawn in through leaks.
209
What should be done if the system is equipped with an **evaporative condenser** during shutdown?(3)
* Close the makeup water supply
* Drain the water
* Flush the condenser
## Footnote
These steps help maintain the condenser's integrity.
210
What should be checked before starting the **centrifugal compressor**?(3)
* Oil levels in the compressor, pumps, motors, and gear boxes
* Refrigerant level
* Water level in the cooling tower
## Footnote
These checks ensure that all components are ready for operation.
211
What is the purpose of the **purging unit** before starting the compressor?
To remove any air that may have entered the system
## Footnote
This step is crucial for the proper functioning of the refrigeration system.
212
How long should the **oil pump** operate before starting the compressor?
10 minutes
## Footnote
This ensures that the oil temperature reaches the required minimum.
213
What happens to the **inlet damper or vanes** during the starting sequence?
They are held in the closed position
## Footnote
This reduces starting torque and current draw.
214
What should be monitored for the first **30 minutes** after the compressor starts?(3)
* Oil and refrigerant levels
* Operating temperatures
* Any unusual sounds
## Footnote
Continuous monitoring helps ensure the system operates safely and efficiently.
215
What is generally advised to do after a prolonged shutdown of a **compression refrigeration system**?
Start operating at a reduced capacity for several hours
## Footnote
This prevents the compressor motor from cutting out on overload until the temperature is within the operational range.
216
How is an **automatically controlled refrigerating system** stopped?
Initiate the stop sequence through the facility control system or local panel
## Footnote
If auxiliary equipment is not electrically interlocked, each piece must be stopped separately after the compressor shutdown.
217
What should be done if the system is to be shut down for an **extended period of time**?(3)
* Close all valves
* Open main circuit breakers
* Drain water from cooling tower and lines if exposed to freezing temperatures
## Footnote
Follow any other precautions recommended in the manufacturer's operation and maintenance manual.
218
List the **safety shutdown devices** specific to centrifugal compressors.(6)
* Chilled Water Low Temperature Cutout and Recycle Switch
* Chilled Water Flow Switch
* Vane Closed Switch
* Low Oil Pressure Cutout Switch
* Condenser High Pressure Cutout
* Refrigerant Low Temperature Cutout
## Footnote
These devices protect the system against abnormal conditions during startup and operation.
219
What does the **Chilled Water Low Temperature Cutout and Recycle Switch** do?
Shuts down the compressor if the temperature drops approximately 2.5°C - 3°C (5°F - 6°F) below the setpoint
## Footnote
It restarts the compressor when the temperature rises approximately 3°C (5°F) above the cutout point.
220
What is the function of the **Chilled Water Flow Switch**?
Opens the compressor motor circuit when water flow drops below the safe minimum
## Footnote
It also prevents the compressor from starting if flow has not been established.
221
What does the **Vane Closed Switch** do in a centrifugal compressor?
Allows the compressor to only be started under a no-load condition
## Footnote
This switch is closed when the vanes are in the closed position.
222
What does the **Low Oil Pressure Cutout Switch** prevent?
Compressor operation when oil pressure is below a safe minimum value
## Footnote
This is a critical safety measure to protect the compressor.
223
What does the **Condenser High Pressure Cutout** do?
Shuts down the compressor when condenser pressure reaches an excessively high value
## Footnote
This switch must be manually reset before the compressor can be started again.
224
What is the purpose of the **Refrigerant Low Temperature Cutout**?
Senses refrigerant temperature and shuts down the compressor if it drops below the setting
## Footnote
This prevents freezing of the water in the system.
225
What is the purpose of a **Motor Demand Limiter** in refrigeration systems?
Limits maximum current flow to the compressor motor
## Footnote
It overrides the water temperature controller to prevent high electrical demand at startup.
226
What happens if no restriction is placed on the current flow during **startup**?
The motor draws maximum current until the water temperature reaches the controller setpoint
## Footnote
This can lead to high electrical demand and potential overload of the compressor motor.
227
How can the **Motor Demand Limiter** be adjusted to manage electrical demand?(2)
* Set to 40% initially
* Gradually increase to 60%, 80%, and 100%
## Footnote
This gradual increase helps minimize maximum electrical demand and reduces the risk of motor damage.
228
What is recommended for the **routine operation** of refrigeration systems?
Establish a regular operational routine and record observations
## Footnote
Regular checks help prevent unnoticed adverse conditions that can lead to breakdowns.
229
What should be included in the **daily logs** for refrigeration systems?(3)
* Temperatures
* Pressures
* Observations of system operation
## Footnote
These records are essential for indicating changes in system performance.
230
What do **national and local codes** govern regarding refrigeration systems?(5)
* Installation by qualified personnel
* Inspection by authorities
* Installation of safety devices
* Proper design and materials
* Compliance with electrical and piping codes
## Footnote
These codes ensure safe installation and uniform performance of refrigeration systems.
231
What must be posted conspicuously on refrigeration systems with a capacity exceeding **125 kW**?(3)
* Instructions for emergency shutdown
* Contact information for service
* Regulatory authority contact information
## Footnote
This ensures that critical information is readily available in case of emergencies.
232
What is the importance of following **manufacturer instructions** for refrigerating equipment?
Ensures reliable operation and proper care of the equipment
## Footnote
Neglecting these instructions can lead to breakdowns and costly repairs.
233
What is a **preventive maintenance program** for refrigeration systems?
A program that includes regular checks and maintenance to ensure system reliability
## Footnote
It helps in identifying potential issues before they lead to failures.
234
What is **preventive maintenance (PM)** in the context of compression refrigeration systems?
A system of regularly scheduled inspections, lubrications, adjustments, minor part replacements, and minor repairs
## Footnote
PM is necessary to keep the refrigerating plant and equipment in good operating condition.
235
List the **benefits** of a good preventive maintenance program.(10)
* More dependable service from the equipment
* Increased operating efficiency and reduced energy consumption
* Elimination or reduction of major breakdown repairs
* Reduction of overall maintenance costs
* Efficient scheduling of maintenance operations
* Reduced spare parts inventory required
* Control of labour and material cost
* Better means of identifying causes of breakdowns
* Extended life expectancy of plant and equipment
* Accumulation of history records for each piece of equipment
## Footnote
These benefits contribute to the reliability and efficiency of refrigeration systems.
236
What should be checked during **weekly maintenance** of a compression refrigeration system?(7)
* Operation of compressor lubrication
* Lubricating oil pressure
* Vane seal oiler on centrifugal compressors
* Shaft seals for excessive oil leakage
* Frequency of purge pump operation
* Condition of air filters
* Screen at the pump inlet and spray nozzles on evaporative condensers
## Footnote
Weekly checks ensure the system operates efficiently and identifies potential issues early.
237
What is the recommended **oil discharge pressure** for lubrication in a compression refrigeration system?
140 to 245 kPa (20 - 35 psi) above the suction pressure
## Footnote
This pressure range is crucial for proper lubrication system function.
238
During **monthly maintenance**, what should be lubricated?
All fan and motor bearings
## Footnote
Lubrication should follow the manufacturer's recommendations and avoid over greasing.
239
What should be checked during **semi-annual maintenance** of a compression refrigeration system?(3)
* Operation of pumps and condition of couplings
* Condition of stands, supports, and vibration isolators on cooling towers
* Operation of safety controls
## Footnote
These checks help ensure the reliability and safety of the refrigeration system.
240
What is included in the **annual maintenance** of a compression refrigeration system?(7)
* Service motors on compressor and pump
* Check condition of stands, supports, guards, insulation, and vibration absorbers
* Drain the condensing system and clean scale or sludge formation
* Flush pumps and sump tank
* Replace worn fan belts
* Check condition of electrical starters and contactors
* Check and clean condenser heat transfer surfaces
## Footnote
Annual maintenance is crucial for long-term performance and reliability.
Power Engineering Book 2 Part 2
flashcards
Decks in class (4)
# Cards
