Power Engineering Book 2 Part 2 > Unit 4 > Flashcards

Unit 4 Flashcards

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1
Q

What is the first fundamental principle of refrigeration?

A

A substance must absorb or reject latent heat to change state

Adding latent heat to a liquid makes it evaporate; removing latent heat from a gas makes it condense.

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2
Q

What happens when a refrigerant continually draws heat away from a body of water?

A

Its temperature drops, and its state changes from liquid to solid

This involves removing sensible heat and then latent heat of fusion.

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3
Q

What is the effect of pressure on a boiling liquid?

A

The pressure determines the temperature at which the liquid boils

For example, at higher pressures, water boils at higher temperatures.

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4
Q

What is the saturation temperature?

A

The temperature at which a pure liquid is heat-saturated

Additional heat causes a change in state but no change in temperature.

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5
Q

For every saturation pressure, there is one corresponding __________.

A

saturation temperature

This relationship is crucial in understanding refrigeration principles.

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6
Q

What is the second fundamental principle of refrigeration?

A

The pressure exerted on the surface of a boiling liquid determines the temperature at which it boils

This principle explains why boiling points vary with altitude.

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7
Q

What is the ASHRAE designation for water as a refrigerant?

A

Refrigerant 718 or R-718

Water must be boiled in a deep vacuum to work as a refrigerant.

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8
Q

What are the four principles of mechanical refrigeration?

A
  • A substance must absorb latent heat to change state
  • The pressure on a boiling liquid affects its temperature
  • For every saturation pressure, there is a corresponding saturation temperature
  • Every pure liquid has a characteristic set of saturation pressures and temperatures

These principles are fundamental to understanding refrigeration systems.

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9
Q

In a refrigeration system, what is the evaporator responsible for?

A

Boiling the refrigerant

The evaporator is in contact with the refrigerated medium, allowing heat transfer.

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10
Q

What happens to the temperature of a refrigerant when the pressure in the vessel is varied?

A

The temperature can be controlled

This principle is crucial for the operation of refrigeration systems.

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11
Q

What is a limitation of a simple refrigerator regarding temperature control?

A

No means of controlling the temperature

The refrigerant can only boil at atmospheric pressure.

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12
Q

What happens to the refrigerant vapour in a simple refrigerator?

A

Vents directly to the atmosphere

This can waste refrigerant and contaminate the environment.

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13
Q

What device is used to address the issue of temperature control in refrigeration systems?

A

Backpressure regulator

It adjusts the saturation pressure and temperature in the vessel.

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14
Q

What happens if the vent valve is closed in the evaporator?

A

Evaporator pressure increases

This continues until the saturation temperature equals the refrigerated space temperature.

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15
Q

What device can be installed at the evaporator outlet to achieve low pressure?

A

Vacuum pump

It withdraws refrigerant vapour faster than it boils.

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16
Q

What are the four principles mentioned for creating cold temperatures in refrigeration?

A
  • Refrigerant evaporation
  • Temperature control
  • Pressure regulation
  • Use of vacuum pumps

These principles are essential for practical refrigeration systems.

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17
Q

What is the first requirement for an actual refrigeration system to run continuously?

A

A continual feed of vaporized refrigerant to replace the refrigerant boiled in the evaporator

The rate of replacement must match the rate of evaporation.

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18
Q

What is the purpose of a metering device in a refrigeration system?

A

To control the refrigerant flow between the liquid receiver and the evaporator

It prevents too much refrigerant from entering the evaporator, which can cause damage.

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19
Q

What happens if there is not enough refrigerant in the evaporator?

A

The evaporator will run dry, reducing heat flow and refrigerating effect

Insufficient boiling liquid affects the system’s efficiency.

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20
Q

What is the role of the condenser in a refrigeration system?

A

To cool the refrigerant vapor and return it to its liquid state

The vapor gives off latent heat to a coolant in the condenser.

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21
Q

What must the temperature of the refrigerant vapor be in relation to the cooling medium for condensation to occur?

A

Higher than the temperature of the cooling medium (typically higher than 40°C)

This ensures effective heat transfer and condensation.

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22
Q

What does the compressor do in a refrigeration system?

A

Draws refrigerant vapor at low pressure and discharges it at higher pressure

It raises the temperature and pressure of the refrigerant vapor.

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23
Q

What are the mandatory components of a refrigeration system?(5)

A
  • Refrigerant
  • Evaporator
  • Refrigerant metering device
  • Condenser
  • Compressor

These components are essential for the system’s operation.

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24
Q

What are some optional components in a refrigeration system?(3)

A
  • Liquid receiver
  • Condenser cooling fan
  • Evaporator fan

These components can enhance system efficiency and performance.

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25
What is the **mechanical energy** of compression converted to in a refrigeration system?(2)
* Potential energy * Internal energy (vapor temperature) ## Footnote This conversion is essential for raising the refrigerant vapor temperature.
26
What is the **capacity of a refrigeration system**?
The rate at which it removes heat from the refrigerating medium ## Footnote In the SI system, refrigeration capacity is expressed in various units including kJ/h, kJ/min, kJ/s, or kW.
27
What is the **Net Refrigerating Effect**?
The amount of heat absorbed by the refrigerant in the evaporator ## Footnote It can be expressed in kg of refrigerant or as the heat removal rate in kJ/sec.
28
Define **Coefficient of Performance (COP)**.
The ratio of the amount of heat absorbed from the refrigerating medium by the evaporator to the amount of energy used to drive the compressor ## Footnote A higher COP indicates a more effective system.
29
How is the **Compression Ratio** calculated?
Clearance volume plus piston displacement divided by clearance volume ## Footnote This relates to the volume above the top dead center and the volume between top and bottom dead centers.
30
What is the **Pressure Ratio**?
The compressor cylinder discharge pressure divided by the suction pressure ## Footnote Absolute pressures must be used; it is often confused with compression ratio.
31
What are **thermodynamic properties of refrigerants**?(6)
* Boiling points * Condensing points * Absolute pressure * Volume * Density * Enthalpy ## Footnote These properties are essential for solving capacity and performance problems and are found in refrigeration tables.
32
What is the **importance** of knowing the **chemical and physical properties** of refrigerants?
To compare refrigerants and ensure the appropriate one is used for specific applications ## Footnote Proper identification of refrigerants is crucial for their effective use in various systems.
33
Refrigerants are categorized according to their **flammability** and **toxicity** and then placed in a _______.
safety group ## Footnote This classification helps in assessing the risks associated with different refrigerants.
34
List the three additional classifications of refrigerants according to their properties.
* Impact on the environment * Chemical origins * Operating temperature suitability ## Footnote These classifications help in selecting the right refrigerant for specific applications.
35
What does **ASHRAE** stand for in the context of refrigerant identification?
American Society of Heating, Refrigerating and Air-Conditioning Engineers ## Footnote ASHRAE provides standards and guidelines for refrigerant classification and identification.
36
What are the various ways to identify refrigerants? (4)
* ASHRAE designation * Chemical formula * Chemical name * Trade name ## Footnote These identifiers are essential for proper refrigerant usage and safety.
37
What temperature range is suitable for **High Temperature** refrigerants?
Evaporator Temperature Above 0°C ## Footnote High temperature refrigerants are used in large scale low-pressure chillers.
38
What temperature range is suitable for **Low to Very Low Temperature** refrigerants?
Evaporator Temperature Below -25°C ## Footnote These refrigerants are used in applications like cold storage and ice-making.
39
According to **ASHRAE Standard 34**, how many groups are refrigerants classified into?
Eight groups ## Footnote This classification is based on toxicity and flammability.
40
What is the environmental impact of leaking refrigerants?
Considerable impact on the Earth's ozone layer and global warming ## Footnote Leaks are inevitable in refrigeration systems.
41
What does **Ozone Depleting Potential (ODP)** refer to in refrigerants?
The potential of refrigerants to deplete the ozone layer ## Footnote Refrigerants containing chlorine, such as R-11 and R-12, have high ODP and are being phased out.
42
Name two **phased-out refrigerants** due to high ODP.
* R-11 * R-12 ## Footnote These refrigerants are no longer produced due to their harmful effects on the ozone layer.
43
What does **Global Warming Potential (GWP)** measure in refrigerants?
The potential of refrigerants to contribute to global warming ## Footnote Refrigerants with high GWP, like R-12, are being phased out.
44
What are **natural refrigerants**?(3)
* R-717 (ammonia) * R-744 (CO2) * R-718 (water) ## Footnote Natural refrigerants have less environmental impact and are energy efficient.
45
What are the **ideal properties** of a refrigerant?(9)
* High latent heat capacity * Low boiling point * Low condensing pressure * Inoffensive odor * Non-toxic * Non-corrosive * Non-flammable * Low vapor specific volume * Low liquid density ## Footnote No single refrigerant meets all these criteria, so selection involves compromise.
46
Fill in the blank: Refrigerants should have a **_______** nature to be suitable for use.
non-toxic ## Footnote This property ensures safety in refrigeration systems.
47
What are the **standard conditions** for comparing refrigerants?(2)
* Evaporator temperature: -15°C * Condenser temperature: +30°C ## Footnote These conditions affect the performance and properties of refrigerants.
48
What is the **importance of low condensing pressure** when choosing a refrigerant?
Prevents air and moisture infiltration ## Footnote Low condensing pressure reduces operational problems in refrigeration systems.
49
What does **h_f** represent in refrigeration tables?
Enthalpy of saturated liquid ## Footnote This property is crucial for calculating refrigerant performance.
50
What does **h_g** represent in refrigeration tables?
Enthalpy of saturated vapour ## Footnote Understanding this helps in evaluating the efficiency of refrigerants.
51
What does **h_fg** represent in refrigeration tables?
Latent heat of evaporation ## Footnote It is calculated as hg minus hf, indicating the energy required for phase change.
52
What are the **important physical properties** of refrigerants?(6)
* Miscibility * Leakage tendency * Odour * Toxicity * Flammability/explosiveness * Moisture reaction ## Footnote These properties are essential for understanding the behavior and safety of refrigerants.
53
Define **miscibility** in the context of refrigerants.
How soluble two or more liquids are when mixed together ## Footnote Some refrigerants are entirely miscible with lube oil, while others may be partially miscible or not miscible at all.
54
Which refrigerant is **not miscible** with lube oil?
Ammonia (R-717) ## Footnote Ammonia's incompatibility with lube oil affects its performance in refrigeration systems.
55
What effect does **oil-miscible refrigerants** have on compressor crankcase oil?
Dilutes compressor crankcase oil, lowering viscosity ## Footnote This dilution can impact the lubricating ability of the oil.
56
What is the **effect of refrigerants** on lubricating oil?(3)
* Incompatible with mineral oil (for some) * Miscible with Polyolester oil * Moderately miscible with mineral oils (for some) ## Footnote The type of refrigerant determines its compatibility with different types of lube oil.
57
What is the **odour** of R-717 (Ammonia)?
Strong and pungent ## Footnote The distinct odour of ammonia can serve as a warning for leaks.
58
What happens when refrigerants carry oil into the **condenser and evaporator**?
Coats heat transfer surfaces, reducing capacity ## Footnote An insulating coating can hinder the efficiency of heat exchange.
59
What is the **leakage tendency** of refrigerants?
Refers to the propensity of refrigerants to escape from the system ## Footnote Leakage can lead to environmental and safety issues.
60
Fill in the blank: The **mass of refrigerant** circulated per tonne of refrigeration is determined using _______.
refrigeration tables ## Footnote These tables provide essential data for calculating refrigeration system performance.
61
What happens when **oil-miscible refrigerants** are used?(2)
* Dissolve most of the oil in components * Return oil to the compressor ## Footnote This avoids problems with heat exchange.
62
What is the consequence of using **non-miscible refrigerants**?(3)
* Oil builds up in the evaporator * Reduces system capacity * Blocks evaporator tubing ## Footnote Ammonia systems require oil separators and oil return systems to manage oil.
63
What is the role of **oil separators** in ammonia refrigeration systems?(2)
* Remove oil from low points in the system * Return oil to the compressor ## Footnote Oil separators are installed on the compressor discharge piping.
64
The **miscibility** of refrigerants affects what aspects of a refrigeration system?(3)
* Need for oil separators * Size of piping * Refrigerant velocity ## Footnote Proper refrigerant velocity prevents oil from settling in evaporator tubing.
65
What does a **slight odour** in halocarbon refrigerants indicate?
* Easier detection of small leaks ## Footnote A strong, pungent smell from ammonia can induce panic in public spaces if detected.
66
Which refrigerant is known to support combustion?
Ammonia ## Footnote Ammonia is explosive in concentrations between 15% and 28% by volume in air.
67
What happens to chlorofluorocarbon refrigerants when exposed to a flame?(2)
* React and decompose * Produce highly toxic products ## Footnote Ample ventilation should be provided when using an open flame for leak detection.
68
What can happen if a substantial leak of refrigerant occurs?(2)
* Displaces air * Accumulates in low-lying areas ## Footnote Proper ventilation is essential to prevent asphyxiation.
69
What factors determine the **leakage tendency** of a refrigerant?(4)
* Operating pressure * Viscosity * Density * Chemical effects on seals and gaskets ## Footnote The molecular mass also affects the ability to escape through tiny openings.
70
What are the three reasons why **moisture** in refrigerants should be avoided?
* Causes ice formation in metering devices * Can lead to acid formation and corrosion * Ammonia combines with water to form corrosive hydroxide ## Footnote Moisture can deteriorate motor insulation in hermetic compressors.
71
What is the **principle** on which most refrigeration systems operate?
Closed-cycle, compression refrigeration principle ## Footnote This principle involves the continuous collection and reuse of vapor from the evaporator.
72
What are the two classes of **closed-cycle refrigerating systems**?
* Compression system * Absorption system ## Footnote This chapter focuses only on the compression system.
73
Name the two types of **refrigeration systems** discussed in the chapter.
* Direct Refrigeration System * Indirect Refrigeration System ## Footnote Power engineers must understand the differences between these systems.
74
List the **five principal parts** of a simple closed-cycle compression refrigeration system.
* Evaporator * Compressor * Condenser * Liquid refrigerant control or regulating valve * Liquid receiver ## Footnote All these components are essential for the operation of a mechanical compression system.
75
What happens to the **high-pressure, high-temperature liquid refrigerant** as it passes through the regulating valve into the evaporator?
It flashes into vapor ## Footnote This occurs because the pressure in the evaporator is kept low, lowering the boiling point of the liquid.
76
What does the **low-pressure, low-temperature liquid/vapor mixture** do in the evaporator?
Absorbs heat from the surrounding medium ## Footnote By absorbing heat, the refrigerant evaporates completely by the end of the evaporator.
77
To condense the vapor back to a liquid, what must be removed from the refrigerant?
Latent heat absorbed in the evaporator ## Footnote A condensing medium, such as air or water, is used to absorb this heat.
78
What is the function of the **compressor** in a compression refrigeration system?
To raise the pressure and temperature of the refrigerant vapour ## Footnote The compressor draws low pressure and temperature vapour from the evaporator and compresses it.
79
In a compression refrigeration system, the **low-pressure side** includes which components?(3)
* Evaporator * Suction of the compressor * Interconnected tubing and piping ## Footnote The pressure on this side is determined by the evaporation temperature required for proper refrigeration effect.
80
What happens to the refrigerant vapour in the **condenser**?
It gives up sensible heat and latent heat of condensation ## Footnote The heat given up by the vapour is carried away by the condensing medium.
81
The **high-pressure side** of the system consists of which components?(5)
* Compressor discharge * Condenser * Receiver * Upstream side of the regulating valve * Connected tubing and piping ## Footnote The pressure on the high side is determined by the required condensing temperature of the refrigerant vapour.
82
What is the state of the refrigerant vapour after it is compressed by the compressor?
Superheated vapour ## Footnote The work done on the vapour during compression increases its temperature above the saturation temperature.
83
Fill in the blank: The heat removed from the refrigerant by the **condensing medium** is equal to the heat added to the refrigerant in the **________** plus the work done on the refrigerant by the compressor.
evaporator ## Footnote This represents the basic energy flow in the compression refrigeration system.
84
What must happen to the **temperature** of the vapour leaving the evaporator for effective heat transfer to the condensing medium?
It must be raised above the temperature of the condensing medium ## Footnote This is achieved by the compressor.
85
What is the role of the **liquid receiver** in a compression refrigeration system?
To store the condensed refrigerant before it flows to the evaporator ## Footnote The liquid receiver holds the refrigerant at a saturation temperature corresponding to the discharge pressure of the compressor.
86
What is a **direct refrigeration system**?
A system where the **evaporator** is in direct contact with the material or space being refrigerated ## Footnote Direct refrigeration systems are often called **direct expansion systems**.
87
What characterizes an **indirect refrigeration system**?
A system where a **liquid** (such as brine or water) is cooled by the refrigerant and then circulated to the space being refrigerated ## Footnote The cold brine absorbs heat from the space and circulates back to be cooled again.
88
In an indirect refrigeration system, what is typically used as the heat transfer medium?
Water ## Footnote Water is cooled in a chiller by evaporation coils and circulated through cooling coils.
89
What is the typical temperature range for **chilled water** in indirect refrigeration systems?
Kept at or above **5°C (41°F)** ## Footnote This prevents freezing while cooling the air.
90
What is the freezing point of the brine solution used in skating rinks?
Can be subjected to temperatures as low as **-50°C (-58°F)** ## Footnote The brine is usually a solution of **calcium chloride**.
91
What is the relationship between **compression refrigeration system temperatures** and **pressures**?
Understanding temperature and pressure readings is crucial for determining system operation ## Footnote The operator must know what the readings should be for the low and high sides and how they change with operating conditions.
92
What does the **low side pressure** of a refrigeration system depend on?(2)
* Application of the system * Type of evaporation used ## Footnote The low side pressure is influenced by the temperature required for the medium to be cooled.
93
What is the typical range for **evaporation temperature** in refrigeration systems?
* Between 5°C (9°F) and 10°C (8°F) lower than that of the cooled medium ## Footnote This ensures sufficient heat transfer from the medium to the liquid refrigerant.
94
What happens to **humidity** in relation to the temperature differential (TD) of the coil?(2)
* Higher TD: Greater moisture removed * Lower TD: Higher space or process humidity ## Footnote Humidity control is as important as temperature in refrigeration processes.
95
What does the **high side pressure** correspond to in a refrigeration system?
The condensing temperature of the refrigerant vapor ## Footnote This temperature depends on the cooling medium and the type and size of the condenser.
96
How does the **condensing temperature** of the vapor relate to the cooling medium?
It has to be higher than that of the cooling medium ## Footnote For example, the refrigerant temperature in a water-cooled condenser will be approximately 11°C (20°F) higher than the cooling water.
97
What are the **main components** of a refrigerating plant?(7)
* Compressor * Evaporator * Condenser * Flow control valve * Liquid receiver * Auxiliary equipment * Controls ## Footnote These components can be ordered and installed separately but are often found in factory-assembled, packaged units.
98
The **function of the economizer** in a refrigeration system is to:(2)
* Control the flow of liquid refrigerant * Reduce pressure and temperature in stages ## Footnote It is installed between the condenser and chiller (evaporator).
99
What happens to the liquid refrigerant when it passes from the upper chamber to the lower chamber of the economizer?(2)
* Part of the liquid flashes into vapor * Remaining liquid cools down to a lower temperature ## Footnote This process helps in cooling the liquid refrigerant before it enters the evaporator.
100
The economizer provides an **intercooling effect** for which component?
Compressor ## Footnote The cool vapor from the intermediate chamber cools the first stage compressor discharge gas.
101
What is the **advantage** of having less flash vapor produced in the economizer system?(2)
* Increased refrigerating effect per system * Reduced power requirement for compression ## Footnote This is due to the multi-stage pressure reduction process.
102
What causes a gradual pressure drop through each side of the refrigeration system?
Friction in the evaporator, condenser, and piping ## Footnote This is an important consideration in actual systems.
103
List the **advantages** of a **packaged refrigeration unit**.(5)
* Components designed for greatest operating efficiency * Compact design with all components on a single frame * Equipped with auxiliary equipment like gauges and controls * Easy and quick installation * Factory assembled with manufacturer responsibility for design and performance ## Footnote These advantages contribute to the effectiveness and efficiency of refrigeration systems.
104
What is the **function of the compressor** in a refrigeration system?(4)
* Draw low-temperature vapour from the evaporator * Raise the pressure and temperature of the vapour * Maintain low pressure in the evaporator for liquid refrigerant to boil * Maintain high pressure of refrigerant vapour entering the condenser ## Footnote The compressor is considered the heart of the refrigeration system.
105
Name the **three main classifications** of compressors.
* Reciprocating compressors * Rotary compressors * Centrifugal compressors ## Footnote Each type has distinct mechanisms for compressing vapour.
106
Describe the operation of a **reciprocating compressor**.(4)
* Piston travels back and forth in a cylinder * Draws in and compresses the vapour * Driven by a connecting rod attached to a rotating crank * Suction and discharge valves control gas flow ## Footnote The piston creates a vacuum during the down stroke and compresses gas during the up stroke.
107
In a reciprocating compressor, what happens during the **down stroke** of the piston?(3)
* Creates vacuum in the cylinder * Pressure in suction line forces suction valve open * Discharge valve remains closed ## Footnote This allows the compressor to draw in low-pressure vapour.
108
During the **up stroke** of the piston in a reciprocating compressor, what occurs?(3)
* Pressure in the cylinder raises discharge valve * Gas flows into discharge pipe * Suction valve remains closed ## Footnote This process compresses the vapour and prepares it for discharge.
109
What is the role of the **suction and discharge valves** in a reciprocating compressor?
* Control the flow of gas into and out of the cylinder ## Footnote These valves open and close based on pressure changes during the piston strokes.
110
Fill in the blank: The **high velocity low-pressure vapour** is converted to _______ before it leaves the centrifugal compressor.
low velocity high-pressure vapour ## Footnote This conversion is achieved through the use of rapidly revolving impellers.
111
What are the **three types** of reciprocating compressors?
* Open * Hermetic * Serviceable or Semi-Hermetic ## Footnote Each type has distinct features regarding design and serviceability.
112
In an **open compressor**, what extends outside the crankcase?
Crankshaft ## Footnote A sealing arrangement is required to prevent refrigerant escape.
113
What drives a **hermetic compressor**?
Electric motor directly connected to the crankshaft ## Footnote The compressor and motor are mounted within the same housing.
114
What is a key feature of **serviceable or semi-hermetic compressors**?
Cylinder heads, end, and bottom plates can be removed for servicing ## Footnote This allows for internal mechanism maintenance.
115
How are reciprocating compressors identified by their **cylinder arrangement**?(6)
* Vertical * Horizontal * 45° inclined * V-type * W-type * Radial ## Footnote These arrangements affect the compressor's design and application.
116
List the **main parts** of a refrigerant compressor.(6)
* Compressor body * Crankshaft * Pistons and connecting rods * Suction and discharge valves * Safety head * Compressor bearings ## Footnote Each part plays a crucial role in the compressor's operation.
117
What construction types can the **compressor body** have?(2)
* One-piece * Two-piece ## Footnote One-piece has crankcase and cylinders cast in one block, while two-piece parts are cast separately.
118
What type of crankshaft is often used in **small capacity compressors**?
Eccentric type ## Footnote Larger compressors typically use a conventional type crankshaft.
119
What type of pistons are usually found in refrigeration compressors?
Automotive or trunk type ## Footnote Pistons are fitted with piston rings to prevent vapor escape.
120
What is the function of the **lower piston ring**?
Distributes lubricating oil evenly over the cylinder wall ## Footnote It also allows excess oil to return to the crankcase.
121
What connects the **pistons** to the **connecting rods**?
Piston or wrist pins made of case-hardened steel ## Footnote The connection can vary in design, affecting movement.
122
What are the **two commonly used types** of basic compressor valves?
* Flexible reed valves * Disc valves ## Footnote These valves are essential for the operation of refrigeration compressors.
123
What is the purpose of a **safety head** in compressors?
To prevent damage from hydraulic pressure caused by trapped liquid ## Footnote The safety head lifts when cylinder pressure becomes too high, allowing liquid to pass into the discharge line.
124
What happens to the **valve assembly** in compressors when excessive pressure occurs?
It lifts to allow escape of compressed vapor and trapped liquid ## Footnote This prevents damage to the compressor.
125
What materials are commonly used for **compressor bearings**?(2)
* Bronze for smaller compressors * Steel or bronze backed babbitt for larger compressors ## Footnote Ball and tapered roller bearings are used to a limited extent.
126
What are the two lubrication systems used for compressor bearings?
* Splash system * Pressure system ## Footnote The splash system relies on oil storage in the crankcase, while the pressure system uses a gear pump to deliver oil.
127
What is the function of the **diaphragm valve** in compressors?
Covers a series of ports and flexes upward with gas pressure ## Footnote This allows for proper gas flow in the compressor.
128
What is the role of **spring tension** in flexible reed valves?
Keeps the valve closed until vapor pressure exceeds it ## Footnote This mechanism ensures proper operation of the valve.
129
What is the **primary motion** used in rotary compressors for compression?
Rotary motion ## Footnote Unlike piston-type compressors that use reciprocating motion.
130
Name the **different designs** of rotary compressors.(3)
* Stationary single-blade * Rotating sliding vane * Helical rotor or screw ## Footnote These designs vary in their construction and operation.
131
The **stationary single-blade rotary compressor** is widely used for what type of refrigeration?
Low capacity refrigeration ## Footnote It features a rotor or roller within a cylinder.
132
In the stationary single-blade rotary compressor, what prevents back flow of high-pressure vapour?
Check valve or reed valve ## Footnote This is crucial when the compressor is not running.
133
During the operation of a stationary single-blade rotary compressor, what happens in **Position a**?
The housing fills with low-pressure vapour ## Footnote The rotor has moved past the suction port.
134
In **Position b** of the stationary single-blade rotary compressor, what is happening?
The vapour is being compressed ## Footnote The increasing cylinder volume behind the rotor draws vapour from the evaporator.
135
What occurs in **Position c** of the stationary single-blade rotary compressor?
Vapour reaches condenser pressure and is displaced through the discharge ## Footnote Suction continues behind the rotor.
136
What is the design of the **rotating sliding vane compressor** characterized by?
Cylindrical rotor with radial slots for sliding vanes ## Footnote The rotor is mounted eccentrically in the cylinder.
137
How do the **vanes** in a rotating sliding vane compressor maintain a good seal?
Due to centrifugal force ## Footnote The edges of the vanes are held firmly against the wall.
138
What happens to the refrigerant vapour in the rotating sliding vane compressor as it moves through the cylinder?
It is compressed ## Footnote The vapour is trapped between the vanes and pushed toward decreasing volume.
139
In the rotating sliding vane compressor, where is the **compressed vapour** forced into?
Discharge ports in the cylinder wall ## Footnote A reed or check valve is used for this process.
140
What type of **compressor design** is used for medium and high-capacity refrigeration?
Helical Rotor (or Screw) Design ## Footnote This design features specially shaped helically grooved rotors.
141
In a **screw compressor**, how many helical lobes does the male (driving) rotor typically have?
Four ## Footnote The male rotor has four helical lobes along its length.
142
What is the primary function of the **screw compressor** in a refrigeration system?
To compress vapor ## Footnote The compressor traps vapor and forces it axially along the rotors, reducing the space occupied by the vapor.
143
What is critical about the **direction of rotation** in rotary compressors?
It must be correct to avoid damage ## Footnote Operation in reverse direction can cause immediate damage to a screw type design.
144
What device is often included in **screw compressors** to ensure proper rotation?
Phase sequence control ## Footnote This control checks the phase configuration of the power supply to the compressor.
145
What is the typical configuration of the **motor and compressor** in a refrigeration system?
Combined in a single casing ## Footnote This forms a hermetic unit for efficiency.
146
In a **centrifugal compressor**, how is the vapour compressed?
By giving it high velocity through a rapidly rotating impeller ## Footnote The high-velocity vapour then travels through specially shaped passages where velocity is converted to pressure.
147
What is the main component of a **centrifugal compressor**?
A bladed wheel or impeller ## Footnote The impeller rotates at high speed within a casing.
148
What is the advantage of a **centrifugal compressor** over other types?
Simplicity of operation ## Footnote There are no valves, pistons, or cylinders, leading to minimal maintenance.
149
What type of compressors can **centrifugal compressors** be designed as?(2)
* Open type compressors * Hermetic type compressors ## Footnote Open type has a shaft extending through housing, while hermetic type has the compressor and motor sealed in one housing.
150
What are compressors with more than one impeller called?
Multistage compressors ## Footnote They are distinguished by the number of pressure stages supplied, such as two-stage, three-stage, etc.
151
Fill in the blank: The **kinetic energy** of low-pressure, high-velocity vapour is transformed into _______ in a centrifugal compressor.
potential energy ## Footnote This transformation occurs as the vapour travels through specially shaped passages.
152
What happens to the vapour after it leaves the **impeller** in a centrifugal compressor?
It flows through a volute-shaped casing or a nozzle-shaped channel (diffuser) ## Footnote This process converts the velocity of the vapour into pressure.
153
Why is a **centrifugal compressor** operated at high speed?
To increase pumping efficiency ## Footnote It can be directly coupled to an electric motor or other high-speed driver.
154
What is the primary function of **compressor seals** in refrigeration compressors?
Prevent refrigerant and oil leakage ## Footnote Seals also prevent moisture and air from entering the compressor.
155
What are the two main types of **shaft seals** used on open type compressors?
* Stationary seals * Rotating seals ## Footnote These seals are used to connect the compressor and motor.
156
What type of seal is primarily used on **large capacity ammonia compressors** operating at low speeds?
Packing Gland Seal ## Footnote This seal uses semi-metallic packing impregnated with graphite.
157
How does a **Packing Gland Seal** create a tight seal?
By compressing packing material with tightened bolts ## Footnote The packing is made of semi-metallic material impregnated with graphite.
158
What component is placed between two sets of packing in a **Packing Gland Seal**?
Lantern ring ## Footnote The lantern ring provides pressurized oil lubrication to the shaft and packing.
159
What is a **Bellows Seal** in refrigeration compressors?
A metallic bellows soldered to a ring that bears against the shaft ## Footnote It prevents leakage and is fastened to a flange held against the housing.
160
What does the **diaphragm** in a **Diaphragm Seal** do?
Maintains constant pressure between the seal nose and the rotating collar ## Footnote It reduces friction using oil from the lubrication system.
161
What is the role of the **seal gasket** in a Bellows Seal?
Prevents leakage ## Footnote The gasket is tightly held against the housing by a cover plate.
162
What are the **advantages** of using **mechanical seals** in compressors?(3)
* Reduced wear on rotating shafts * Prevent leakage along the shaft * Greater initial cost for long run gain ## Footnote Mechanical seals are preferred over packing glands for their efficiency.
163
In a **rotating mechanical seal**, what are the two flat sealing surfaces called?(2)
* Sealing ring * Mating ring ## Footnote The sealing ring rotates with the shaft while the mating ring is stationary.
164
What prevents leakage between the casing and the **mating ring** in a mechanical seal?
O-ring gaskets ## Footnote O-rings also prevent leakage between the shaft and the sealing ring.
165
What is the **capacity** of a refrigeration compressor dependent on?(5)
* Cylinder bore * Length of stroke * Number of cylinders * Number of revolutions per minute * Volumetric efficiency ## Footnote These factors determine the volume of refrigerant that can be circulated.
166
What is **piston displacement** in a refrigeration compressor?
The volume of refrigerant circulated through all cylinders per unit of time ## Footnote It is typically rated in cubic metres per minute or hour.
167
How can **piston displacement** be calculated?
Using the formula: V = A × L × N × R ## Footnote Where V is volume, A is cross-sectional area, L is length of stroke, N is number of cylinders, and R is revolutions per minute.
168
What is **volumetric efficiency**?
The ratio of actual mass of refrigerant to theoretical mass ## Footnote It indicates how effectively the compressor fills with refrigerant.
169
What are the two main reasons for the **reduction in mass** of refrigerant entering the cylinder?
* Warmer cylinder walls * Pressure drop through suction valves ## Footnote These factors prevent the cylinder from filling completely with vapour.
170
What is the **clearance** between the piston and the cylinder head in reciprocating compressors?
0.4 mm to 0.8 mm ## Footnote This clearance affects the mass of vapour in the cylinder.
171
An increase in the **pressure ratio** will result in higher discharge temperatures and larger _______.
power consumption ## Footnote Higher temperatures can accelerate chemical reactions in materials like lubricating oil.
172
What is the effect of higher temperatures on maintenance costs?
Higher maintenance costs ## Footnote This is due to accelerated chemical reactions of materials such as lubricating oil and oxygen.
173
What are the **two types of heat exchangers** used in a refrigeration system?
* Evaporator * Condenser ## Footnote The purpose of heat exchange is to remove heat from a process.
174
What is the primary function of a **heat exchanger**?
To transfer heat from one fluid to another without mixing the fluids ## Footnote Heat exchange refers to both the gain and loss of heat.
175
What are the **two basic types** of evaporators based on their operation?
* Dry/Direct Expansion * Flooded ## Footnote These types differ in how they manage the refrigerant flow and heat absorption.
176
In a **dry/direct expansion evaporator**, how is the liquid refrigerant managed?
The amount of liquid refrigerant is controlled to maintain the required superheat in the vapor leaving the coil ## Footnote There is no recirculation of liquid or gas in this type.
177
What characterizes a **flooded evaporator**?
It is kept almost completely filled with liquid refrigerant regardless of load demand ## Footnote This type has a higher heat transfer efficiency but requires a larger refrigerant charge.
178
How many classes can evaporators be divided into based on their **construction**?
Four classes ## Footnote The classification is based on the design and materials used in construction.
179
What is a **bare tube evaporator**?
It consists of a single coil or multiple coils placed in parallel, constructed of steel pipe or copper tubing ## Footnote It can function as either a direct expansion or flooded evaporator.
180
What is the **application** of **bare tube evaporators**?(3)
* Maintained space temperature below 1°C * Used in coolers and freezers * Submerged in liquids to be cooled ## Footnote Frost accumulation cannot be readily prevented in these applications.
181
Describe the **manufacturing methods** for a **plate surface evaporator**.(2)
* Two flat steel plates embossed to form a serpentine coil * Regular coil attached between two plates ## Footnote This evaporator can be formed into various shapes and is used singly or in banks.
182
List the **applications** of the **plate surface evaporator**.(4)
* Refrigerators * Freezers * Display cases * Locker plants ## Footnote It can be easily cleaned and defrosted without interrupting the cooling process.
183
What is the purpose of **fins** in a **finned tube evaporator**?
To increase heat exchange surface area ## Footnote Fins are attached to the bare tube evaporator coil by crimping or bonding.
184
What happens when the refrigerant in the **finned tube evaporator** is below freezing?(3)
* Moisture condenses on fins and tubes * Freezes, reducing openings between fins * Can plug off openings unless defrost method is employed ## Footnote Defrost methods include electric elements or hot refrigerant from the compressor.
185
What is the fin spacing used for a **low-temperature finned evaporator** compared to a **medium-temperature evaporator**?(2)
* Low-temperature: Wider spacing * Medium-temperature: Closer spacing ## Footnote Wider spacing allows longer refrigeration periods between defrost cycles.
186
How does air flow over the **evaporator** in applications requiring low air velocities?
By natural convection ## Footnote In other applications, fans are used to increase air flow and cooling capacity.
187
What is the most widely used evaporator in **air conditioning applications**?
Finned tube evaporator with forced air circulation ## Footnote The air is forced between the fins, giving up its heat to the vaporizing refrigerant.
188
What is the role of the **refrigerant distributor** in a fin tube evaporator?
To provide even refrigerant flow to each of the evaporator circuits ## Footnote Larger evaporators may require splitting into sections to prevent excessive pressure drops.
189
What is the design approach for larger **evaporators** to manage pressure drops?
Multiple coils in parallel with one another ## Footnote This design replaces one large coil to improve efficiency.
190
What type of **evaporator** consists of a cylindrical steel shell with straight bare tubes arranged in parallel?
Shell and Tube Evaporator ## Footnote It is used for almost any type of liquid chilling application.
191
In a **direct-expansion evaporator**, where is the liquid refrigerant admitted?
In the lower tubes ## Footnote The refrigerant evaporates by absorbing heat from the liquid surrounding the tubes.
192
What is the role of **baffles** in a shell and tube evaporator?
To force the liquid to follow a tortuous path across the tubes ## Footnote This helps in reducing the temperature of the liquid as it exits.
193
In a **flooded evaporator**, how is the level of liquid refrigerant maintained?
By a float-controlled valve ## Footnote At least seventy-five percent of the tubes must be submerged at all times.
194
What is the purpose of a **surge drum** in a flooded evaporator?
To separate liquid from vapor before it enters the suction line ## Footnote The drum is connected to the evaporator by large diameter pipes.
195
In the second method of separating liquid from vapor in a flooded evaporator, what is used to aid in this process?
Chevron shaped eliminator plates ## Footnote These plates help in separating the liquid from the vapor effectively.
196
What happens to the liquid refrigerant carried over with the vapor in the surge drum?
It drops out of the gas flow ## Footnote This occurs due to the change in direction and the length of gas travel.
197
In a flooded evaporator, how are the tubes arranged?
In a single or multi-pass configuration ## Footnote The shell is filled with liquid refrigerant surrounding the tubes.
198
What is the primary function of a **refrigeration condenser**?
To cool superheated refrigerant vapour until it condenses to a liquid and becomes subcooled ## Footnote The condenser removes both latent and sensible heat absorbed in the evaporator, along with heat of compression added by the compressor.
199
What are the **three general types** of condensers?
* Air-cooled * Water-cooled * Evaporative ## Footnote The condenser capacity is typically 15% to 20% larger than the evaporator.
200
How does an **air-cooled condenser** operate?
It uses air to remove heat from the refrigerant vapour flowing through finned tubes ## Footnote Cooling air is circulated around the tubes by fans or blowers.
201
What must be provided for an **indoor-mounted remote air-cooled condenser**?
An adequate supply of ventilation air ## Footnote For larger units, ducts must be used to carry ventilation air to avoid excessive air movement and indoor temperature rise.
202
What is the main disadvantage of **large indoor condensers**?
They require extensive space-consuming ductwork ## Footnote Therefore, they are usually mounted outdoors.
203
What type of fan is commonly used in **outdoor air-cooled condensers**?
Belt-driven propeller fan or direct drive fans ## Footnote Fans are used to force or draw air through the condenser.
204
What are the **three basic designs** of water-cooled condensers?
* Double tube * Shell and coil * Shell and tube ## Footnote These designs are used to remove heat from the refrigerant vapour using cooling water.
205
Describe a **double tube condenser**.
A small tube contained concentrically within a larger tube ## Footnote Cooling water flows through the inner tube while refrigerant flows in the opposite direction in the space between the tubes.
206
What is a key operational requirement for a **double tube condenser**?
Water flow must be controlled based on the refrigeration system condensing pressure ## Footnote This is accomplished through a water regulating valve.
207
What is the main advantage of a **shell and coil condenser**?
It is very efficient and compact ## Footnote This makes it easily adaptable to packaged refrigeration units.
208
What is a disadvantage of the **shell and coil condenser**?
Difficult to clean and costly to replace if leaks develop ## Footnote Tubes can be cleaned with an acid solution.
209
What is the main function of a **shell and tube condenser**?
To condense refrigerant vapour by cooling it with water ## Footnote The hot refrigerant vapour enters the top and condenses on the cool outer surface of the tubes.
210
What type of refrigerants are **shell and tube condensers** used for?(2)
* Ammonia installations * Medium and large air conditioning installations ## Footnote This type of condenser is widely used due to its high cooling efficiency.
211
What are the advantages of a **horizontal shell and tube condenser**?(4)
* High cooling efficiency * Reasonable cost * Easy to clean * Low maintenance costs ## Footnote These features make it a popular choice in various installations.
212
What is the primary cooling method used in **evaporative condensers**?
Uses both air and water to cool and condense refrigerant vapour ## Footnote This method enhances the efficiency of the condensation process.
213
In an **evaporative condenser**, where does the hot refrigerant vapour enter?
At the top of the condenser ## Footnote The refrigerant liquid leaves at the bottom and flows to a receiver.
214
What components are included in the **evaporative condenser** setup?(4)
* Condensing coils * Fan * Cooling water spray nozzles * Air eliminators ## Footnote These components work together to facilitate the cooling and condensation process.
215
Fill in the blank: The **shell and tube condenser** consists of a welded steel shell containing a number of __________.
straight tubes ## Footnote These tubes are fastened in the tube sheets which close the shell.
216
What is the purpose of **water** in the operation of evaporative condensers?(3)
* Cools and condenses refrigerant vapour * Absorbs heat from refrigerant * Evaporates to aid in reducing water temperature ## Footnote Water is sprayed over tubes and absorbs both sensible and latent heat.
217
What percentage of water consumption can evaporative condensers save compared to conventional water-cooled condensers?
* 80% to 90% ## Footnote This significant reduction is due to the evaporation of spray water.
218
What is used to maintain a constant water level in the condenser sump?
Float valve ## Footnote This device compensates for the evaporation of water.
219
What should be done to prevent freezing of water in the condenser during cold weather?(2)
* Place a heating coil in the sump * Drain the condenser sump to an indoor tank ## Footnote These methods help keep the water temperature above freezing.
220
What is the role of the **liquid refrigerant receiver** in the evaporative condenser?
Provides subcooling of the liquid refrigerant ## Footnote This increases the refrigerating effect before the refrigerant is supplied to the evaporator.
221
What can cause a serious reduction in the rate of heat transfer in condensers?(3)
* Dirty cooling water * Coating of oil on refrigerant-side surfaces * Scale accumulation on waterside surfaces ## Footnote These factors can significantly reduce the efficiency of the refrigeration system.
222
What is the recommended action if non-condensable gases are present in the condenser?
Remove and replace refrigerant ## Footnote Non-condensables reduce condenser capacity and increase compressor discharge pressures.
223
What maintenance action should be taken for condenser tubes or coils?(2)
* Inspect surfaces frequently * Clean when deposits are discernible ## Footnote Regular maintenance is essential for efficient operation.
224
How can the interior surfaces of shell and coil condensers be cleaned?(2)
* Circulate an acid or chemical solution * Use mechanical cleaners or brushes ## Footnote Cleaning requires advice from a qualified chemist or manufacturer.
225
What is the purpose of **pressure gauges** in refrigeration systems?
Indicate conditions inside the refrigeration system, including pressures in the evaporator and condenser ## Footnote They also show corresponding evaporator and condenser saturation temperatures.
226
How many **pressure gauges** are typically used in a refrigeration system?
At least two ## Footnote One connected to the high-pressure side and one to the low-pressure side.
227
What do **suction strainers** do in refrigeration systems?
Remove foreign matter and water from the refrigerant ## Footnote They help ensure safe and efficient operation of the equipment.
228
What is required when a **pressure gauge** is permanently installed on the high side of a refrigeration system according to CSA Standard B52-09?
Must be constructed for not less than 1.2 times the design pressure ## Footnote This ensures safety and reliability.
229
What is the purpose of **pulsation dampeners** on pressure gauges?
Prevent flickering of the pointers due to pulsations in pressure ## Footnote This provides a more stable reading.
230
What does the **oil pressure gauge** measure in a refrigeration system?
Oil pressure differential ## Footnote Found by subtracting the compressor suction pressure from the oil pressure on the gauge.
231
Fill in the blank: **Driers** in refrigeration systems are used to remove _______ from the refrigerant.
foreign matter and water ## Footnote This is essential for the efficient operation of the system.
232
What is the purpose of an **accumulator** in refrigeration systems?
Collects liquid refrigerant to prevent damage to the compressor ## Footnote It ensures that liquid does not leave the evaporator and allows for the return of system oil.
233
How does an **accumulator** return oil to the system?
Through a small bleed hole at the bottom ## Footnote The oil is drawn into the pipe due to a venturi effect.
234
What is the consequence of trapping oil in the **accumulator**?
Causes the compressor lubricant level to drop ## Footnote This can lead to insufficient lubrication for the compressor.
235
What happens to refrigerant vapor in the **oil separator**?
It is forced to spin, causing oil droplets to collect on the walls ## Footnote Centrifugal force aids in the separation of oil from vapor.
236
What is the purpose of the **sight glass** in an oil separator?
Allows determination of the oil level ## Footnote It helps in monitoring the oil accumulation in the separator.
237
What type of refrigerants require **oil separating devices**?
Oil-miscible refrigerants, such as Freons ## Footnote These devices are used in the compressor discharge line.
238
What is the function of an **automatic float trap**?
Allows collected oil to return to the compressor crankcase ## Footnote It opens the drain valve when sufficient oil has accumulated.
239
To prevent **Freon** from condensing with the oil, where should the trap be placed?
Close to the compressor and protected against cold air drafts ## Footnote This ensures the trap remains hotter than the condensing temperature.
240
What is a potential issue if too much oil leaves the **compressor**?
Increased compressor discharge pressure and power consumption ## Footnote This can lead to inefficiencies in the refrigeration system.
241
What is the main function of a **suction strainer** in a refrigeration system?
To remove particles of foreign matter from the refrigerant vapour before it enters the compressor ## Footnote This prevents damage to compressor parts and ensures proper seating of compressor valves.
242
What is a **strainer-drier** used for in a refrigeration system?(3)
* Removal of moisture from the liquid refrigerant * Prevention of ice buildup in the expansion valve * Prevention of acid formation and corrosion ## Footnote It contains a desiccant that absorbs moisture and functions as a strainer to filter out foreign particles.
243
What materials can a **desiccant** in a strainer-drier be made from?(3)
* Silica-gel * Activated alumina * Calcium sulfate ## Footnote These materials remove moisture either by absorption or chemical change.
244
What does a **sight glass** in a refrigeration system indicate?(3)
* Liquid flow * Insufficient refrigerant * Presence of vapour bubbles ## Footnote It helps observe the liquid refrigerant line and diagnose system issues.
245
What are the two advantages of using a **heat exchanger** in a refrigeration system?
* Reduces temperature of liquid refrigerant * Prevents liquid slugging in the compressor ## Footnote This increases the refrigeration effect and efficiency of the system.
246
Fill in the blank: A **heat exchanger** transfers heat from the relatively warm liquid refrigerant to the cold _______ being drawn from the evaporator.
vapour ## Footnote This process enhances the efficiency of the refrigeration cycle.
247
What happens when the liquid refrigerant passes through the **expansion valve**?
It experiences a pressure drop, which can cause flashing of the liquid ## Footnote This is mitigated by the heat exchanger.
248
Where should the sight glass be installed to indicate if the refrigerant contains any flash vapour?
Before the expansion valve ## Footnote This placement helps in diagnosing issues related to refrigerant flow.
249
What is the purpose of a **heat exchanger** in refrigeration systems?
To facilitate heat transfer between refrigerant and other fluids ## Footnote Illustrated in Figure 7(a) for small and medium capacity refrigeration.
250
In low capacity systems, how is the **capillary tube** typically connected for liquid refrigerant control?
Soldered to the **suction line** ## Footnote This allows heat transfer to take place, as shown in Figure 8.
251
What is the function of a **distributor** in a direct-expansion evaporator?
To evenly distribute liquid refrigerant to all circuits ## Footnote Illustrated in Figure 9 and Figure 10.
252
What is a **vibration absorber** used for in refrigeration systems?
To prevent transmission of vibration and noise ## Footnote Typically connected to main components via flexible elements, as shown in Figure 11.
253
What is the role of the **thermal bulb** in a refrigeration system?
To sense temperature changes and control refrigerant flow ## Footnote Typically part of the expansion valve setup.
254
What components are typically involved in a **refrigeration system** that can cause vibration or noise?(3)
* Compressor * Evaporator * Condenser ## Footnote These components are connected through rigid piping.
255
Where must **vibration absorbers** be placed in relation to the compressor crankshaft?
In parallel with the compressor crankshaft ## Footnote This placement allows the compressor to rock without putting excessive stress on the piping.
256
What happens if a **vibration absorber** is placed perpendicular to the crankshaft?
It can cause premature failure ## Footnote The absorber would be stretched or compressed, leading to potential issues.
257
What materials are suitable for refrigerant lines up to 100 mm in outside diameter for all refrigerants except ammonia?(2)
* Copper * Steel ## Footnote Steel is preferred for larger piping, and wrought iron may be used for its corrosion resistance.
258
What should be done to minimize corrosion in refrigerant piping?
Keep all piping clean ## Footnote This is crucial for maintaining the integrity of the refrigeration system.
259
What are the types of **joints** for refrigerant piping?(4)
* Flanged * Flared * Welded * Brazed ## Footnote The type of joint depends on the piping size and application.
260
What is the most commonly used method for joining iron and steel piping?
Welding ## Footnote This method provides strong and reliable connections in refrigeration systems.
261
What materials should never be used for tubing in an **ammonia refrigerating system**?(2)
* Copper * Copper alloys (e.g., brass) ## Footnote These materials are susceptible to damage from ammonia.
262
What is the purpose of **manual stop valves** in a refrigeration system?
To isolate parts of the system ## Footnote They are designed to prevent the escape of refrigerant to the atmosphere.
263
What feature does the **diaphragm type valve** have to prevent refrigerant escape?
A back seat ## Footnote This feature prevents refrigerant from escaping along the valve stem when fully open.
264
What is an added precaution against leakage along the valve stem in many packed valves?
A valve cap that covers and seals the valve stem ## Footnote The cap must be removed before the valve can be operated.
265
What is the purpose of the **gauge glass** in a refrigeration receiver?
To see the level of liquid present in the receiver ## Footnote The amount of liquid is indicative of the efficiency of the system.
266
What happens to the **steel balls** in the safety-type gauge glass fitting during glass breakage?
They move up their inclined planes to rest against the ball seats ## Footnote This action prevents leakage of refrigerant.
267
What is the function of the **unseating spindle** in the gauge glass system?
To allow the liquid to find its level in the gauge glass after replacement ## Footnote It is used after the glass has been replaced.
268
What type of glass is used to indicate level when most refrigerants are clear?
Reflex glass ## Footnote Reflex glass uses prismatic action to display clear liquids.
269
How does **reflex glass** indicate the level of clear liquids?
Uses prismatic action to display liquids with a dark or black color ## Footnote This helps in visualizing the level of clear refrigerants.
270
What is another common method of indicating receiver level besides gauge glass?
Using multiple sight glasses ## Footnote These can be reflex designs or use brightly colored flotation balls.
271
If one sight glass has a ball at the top and another has a ball at the bottom, where is the liquid level?
Between the two glasses ## Footnote This indicates the liquid level in the receiver vessel.
272
What is the purpose of a **charging valve** in a refrigeration system?
To charge the system with refrigerant ## Footnote The open ends of these valves are usually capped to prevent escape of refrigerant.
273
Name two common **pressure relief devices** used in refrigeration systems.
* Fusible plug * Spring-loaded relief valve ## Footnote These devices help prevent dangerous pressure levels in the system.
274
What does a **fusible plug relief device** do?
Releases refrigerant by melting at a specific temperature ## Footnote This prevents dangerous pressure buildup by sensing temperature.
275
What is the requirement for **positive displacement compressors** according to the Code?
Must be equipped with a pressure relief device of adequate size and pressure setting ## Footnote This device prevents rupture of the compressor.
276
Fill in the blank: The **emergency discharge line** shall be connected directly to the top of the _______ or other vessel.
receiver ## Footnote This setup is crucial for safe refrigerant discharge in emergencies.
277
What color should the **emergency valve** box be painted according to the B52-05 Mechanical Refrigeration Code?
Bright red ## Footnote This color helps in identifying the emergency valve quickly.
278
What is the purpose of the **manually operated emergency valve**?
To safely discharge refrigerant in an emergency ## Footnote It must be tamper-proof and accessible only to authorized personnel.
279
What is the primary function of **cooling towers**?
To lower the temperature of the cooling water ## Footnote Cooling towers accomplish this through heat transfer and evaporation.
280
What percentage of water typically evaporates in a cooling tower during the cooling process?
About 5% ## Footnote The evaporation process draws heat from the remaining water.
281
List the methods used to enhance **air circulation** in a cooling tower.(4)
* Fans * Convection currents * Natural wind currents * Induction effects from the water sprays ## Footnote These methods improve evaporation by increasing air contact with water.
282
What are the alternatives to recycling cooling water through a cooling tower?(2)
* Once-through system with water from a stream or lake * Cooling pond or natural water body ## Footnote These alternatives are used when cooling towers are not feasible.
283
Cooling towers are commonly used when cooling water is _______ or expensive.
scarce ## Footnote They are also used when a temperature within 4 - 6°C of the ambient wet bulb temperature is required.
284
What are the **basic components** of a cooling tower?(6)
* Inlet water distributing box or sprays * Packing or fill * Air moving equipment * Inlet air louvres * Drift eliminators * Cooled water basin ## Footnote These components work together to facilitate the cooling process.
285
The rate of heat transfer in a cooling tower depends on the **relative velocity** of what two elements?
* Air * Water ## Footnote The interaction between air and water is crucial for effective cooling.
286
What factors determine the **rate of cooling** in a cooling tower?(4)
* Relative velocity of air and water * Area of water surface in contact with air * Length of contact time between air and water * Difference between inlet water temperature and inlet air wet bulb temperature ## Footnote These factors influence the efficiency of the cooling process.
287
What are the two subcategories of **natural draft cooling towers**?
* Atmospheric towers * Chimney towers ## Footnote Chimney towers are mainly used in large generating stations.
288
In what conditions do **atmospheric towers** operate effectively?
In locations with relatively constant winds and large open spaces ## Footnote The operation of atmospheric towers depends on atmospheric conditions.
289
What is the maximum height of a **chimney tower**?
Up to 90 m (300 ft) ## Footnote Chimney towers can have base diameters up to 60 m (200 ft) and sizes up to 25,000 mpl (882,200 f3/h).
290
What is the primary function of the **louvres** in atmospheric towers?
To allow air to flow across the tower by natural currents ## Footnote The sides of atmospheric towers are louvred.
291
How does water enhance the process of **evaporation and cooling** in cooling towers?
Fine particles of water come in close contact with air currents ## Footnote This occurs as water falls from a perforated overhead flume or spray nozzles.
292
What should be included in a **monthly inspection schedule** for cooling towers?(3)
* Cleaning the louvres, piping, and nozzles * Cleaning the water basin and checking for leaks * Cleaning the suction screen and checking float control valve operation ## Footnote This ensures continuous, effective operation of the tower.
293
What could cause **high discharge water temperature** from the tower?(4)
* High wet bulb air temperature * High concentration of solids in the water * Restriction of airflow through the tower * Poor water break-up due to worn or dirty nozzles ## Footnote These factors can lead to operational problems in cooling towers.
294
What might cause a **reduction in water flow** in cooling towers?(3)
* Restrictions created by algae * Scale * Dirt ## Footnote These restrictions can affect the efficiency of the cooling tower.
295
What can cause a **tower basin or sump to overflow**?(3)
* Clogged sump screen * Restriction in the water outlet piping * Leaking float control valve ## Footnote These issues can lead to operational inefficiencies.
296
What can lead to **excessive water drift** in cooling towers?(3)
* Excessive wind velocity * Broken or missing louvres * Excessive water pressure in the nozzles ## Footnote These factors can negatively impact the cooling process.
297
What are the **two classes** of mechanical draft cooling towers?
* Forced draft cooling towers * Induced draft cooling towers ## Footnote These classes differ in their airflow direction and fan placement.
298
In a **counterflow** cooling tower, the airflow is in what direction relative to the falling water?
Opposite direction ## Footnote This design enhances heat transfer efficiency.
299
What is the airflow direction in a **crossflow** cooling tower?
Horizontal in the filled portion ## Footnote This design contrasts with counterflow towers.
300
What are the **advantages** of a counterflow tower compared to a crossflow tower?(4)
* Occupies less floor space * Taller for a given capacity * Lower fan power requirement * Lower energy costs ## Footnote These factors make counterflow towers more efficient in certain applications.
301
What must all mechanical cooling towers ensure regarding **discharge air**?(2)
* Diffuses freely without recirculating through the tower * Air intakes are not restricted ## Footnote Proper air flow is crucial for effective operation.
302
Where should cooling towers be located in relation to the **refrigeration systems** they serve?
As near as possible ## Footnote They should never be located below the systems to prevent drainage issues.
303
In a **forced draft cooling tower**, where is the fan located?
At the base of the tower ## Footnote This design allows for low-velocity air movement through the packing.
304
What materials are used to cover the structural framing of a **forced draft cooling tower**?(3)
* Aluminum * Galvanized steel * Seamless plastic panels ## Footnote These materials help protect the structure while allowing airflow.
305
What is the role of **drift eliminators** in a cooling tower?
Remove water entrained in the air ## Footnote They are located at the outlet of the packed sections.
306
What is the primary function of the **fans** in an induced draft cooling tower?
Draw air upwards against the downward flow of water ## Footnote This design maximizes heat transfer efficiency.
307
In an induced draft cooling tower, where is the **distribution system** located?
Just under the drift eliminators ## Footnote This positioning helps in effective water distribution.
308
What type of cooling tower requires **large electric motors** due to the tortuous path that the air takes?
Counterflow induced draft tower ## Footnote This type of tower has a longer travel path for air with less resistance.
309
What are the components illustrated in a **counterflow induced draft tower**?(5)
* Drift Eliminators * Wire-Mesh * Fan Guard * Handrails * Fibreglass Reinforced Plastic ## Footnote These components are essential for the operation of the cooling tower.
310
In a counterflow induced draft tower, where are the **fans** located?
At the top ## Footnote The fans draw air through cells or packing connected to a suction chamber.
311
What is the purpose of the **distribution system** in a cooling tower?
To cascade water in small drops over the packing ## Footnote This process enhances the cooling effect by maximizing air and water contact.
312
What is a newer type of induced draft cooling tower that consists of a **venturi-shaped chamber**?
Venturi Tower ## Footnote This design includes a spray manifold and a sump, eliminating the need for fill or fans.
313
What type of airflow does a **crossflow tower** provide?
Horizontal airflow ## Footnote Water falls through the packing while air flows horizontally.
314
What happens to the water in a **venturi tower** during the cooling process?(4)
* Injected at the narrow end by spray nozzles * Induces large airflow * Heat transfer occurs by evaporation * Remaining water drops in temperature ## Footnote The cooled water then falls into the sump for circulation.
315
What are the advantages of the **venturi cooling tower**?(4)
* Quiet operation * No moving parts * Elimination of electrical connections * Reduced maintenance requirements ## Footnote These features contribute to its efficiency and reliability.
316
How often should the **fan motor** be lubricated in a mechanical draft cooling tower?
Every three months, or as specified by the manufacturer ## Footnote Use the recommended lubricant for maintenance.
317
What should be checked **monthly** in a mechanical draft cooling tower?(2)
* All tower bolts * Float valve ## Footnote Regular checks help ensure proper operation.
318
On **V-belt driven fans**, what maintenance should be performed monthly?(2)
* Lubricate the fan shaft * Check the tension on the belt ## Footnote This maintenance is crucial for fan performance.
319
How often should the **interior of the tower** be inspected?
Annually ## Footnote This inspection should coincide with cleaning and repainting corroding exterior metal surfaces.
320
When should **fan blades** be cleaned and painted?
Annually, and inspected for cracks ## Footnote Regular maintenance helps prevent operational issues.
321
What should be done if **scaling or algae formation** is evident in a cooling tower?
Consult a water treatment specialist ## Footnote This ensures proper treatment and maintenance.
322
What action should be taken if ice forms on the **fill** of a cooling tower?
Action must be taken to ensure the operation of the heat transfer surface ## Footnote Ice formation can threaten the tower's functionality.
323
What is the purpose of a **bypass line** in cold climate operation of cooling towers?
To direct flow to the water basin beneath the tower instead of over the fill ## Footnote This helps manage water flow during startup and normal operation in cold weather.
324
What may be required if **severe ice formation** occurs on louvres?
Fans may need to be reversed for a period of time ## Footnote This helps to melt ice by changing the pattern of falling water.
325
What is used to prevent the **water basin** from freezing when the tower is shut down?(2)
* Thermostatically controlled electric heaters * Steam coils ## Footnote These methods help maintain water temperature in cold conditions.
326
What method allows water to drain continuously from the tower basin to an **indoor storage tank**?
Tank or dry basin method ## Footnote This method prevents freezing in the basin.
327
What is the purpose of a **bypass line** from the tower supply line during cold weather?
To drain the supply line and regulate the cooling water temperature ## Footnote This helps manage water flow and temperature in freezing environments.
328
What is the primary purpose of an **air conditioning system**?
To maintain space conditions that are satisfactory for the comfort of the occupants ## Footnote The requirements for system performance vary according to the type and location of each building.
329
List the **functional components** of air conditioning systems.(6)
* Heating * Cooling * Ventilation * Humidification * Dehumidification * Air Circulation ## Footnote Each component plays a crucial role in maintaining indoor air quality and comfort.
330
What is the function of **heating** in an air conditioning system?
To offset heat loss to the atmosphere through exterior walls, roof, and floor slabs ## Footnote Heat must be effectively distributed to all rooms and zones.
331
What does **cooling** in an air conditioning system offset?
Heat gain through the building exterior from solar radiation, surrounding atmosphere, and internal sources ## Footnote Cooling must be effectively distributed to maintain comfortable conditions.
332
What is the purpose of **ventilation** in air conditioning systems?
To replenish oxygen supply, dilute odors, and provide makeup air for washroom exhaust systems ## Footnote This helps maintain an acceptable air balance in the building.
333
When is **humidification** necessary in an air conditioning system?
When the relative humidity of outdoor air is low ## Footnote It maintains acceptable conditions for human comfort and minimizes static electricity.
334
What is the role of **dehumidification** in air conditioning?
To remove excessive moisture to maintain acceptable relative humidity ## Footnote It is especially important in cold climates to prevent structural damage due to frost formation.
335
What is the importance of **air circulation** in a building?
To assist in dissipation of latent heat and prevent odor buildup in stagnant areas ## Footnote Proper air movement is essential for maintaining indoor air quality.
336
What is the purpose of **air filters** in air conditioning systems?(5)
* Remove contaminants such as dust * Remove dirt * Remove smoke * Remove pollen * Remove lint ## Footnote Air filters clean the recirculated air before it is introduced into the building.
337
List the **basic requirements** to achieve satisfactory conditions in a building's air conditioning system.(5)
* Geographical location * Local weather conditions * Type of occupancy * Building layout * Construction ## Footnote These factors influence the design and complexity of the air conditioning system needed.
338
What type of air conditioning system provides heating, air filtration, air circulation, and ventilation?
Forced air system ## Footnote This system is suitable for larger residences in areas with extreme weather conditions.
339
What are the **three main categories** of air conditioning systems?
* Unitary Systems * Central Systems * Combined Systems ## Footnote These categories reflect the different methods of conditioning air in buildings.
340
What is a **Unitary System** in air conditioning?
Each individual room or zone is provided with a self-contained air conditioning unit ## Footnote This system maintains desired environmental conditions independently for each space.
341
In a **Central System**, where is the air conditioned?
In an air handling unit located in a central mechanical room ## Footnote The conditioned air is distributed through supply ductwork to all rooms and zones.
342
What does a **Combined System** typically provide?(3)
* Ventilation * Cooling * Heating (via supplementary equipment) ## Footnote This system allows for superior zone temperature control but is more complex and costly.
343
What are the main components of an **air handling unit**?(5)
* Fan * Filters * Humidifier * Source of heating and cooling * Motorized dampers for airflow control ## Footnote These components work together to condition the air in a building.
344
What type of fan is commonly used in large central air handling units?
Centrifugal fans ## Footnote These fans are used for their efficiency in moving large volumes of air.
345
Fill in the blank: A simple cooling only unit would consist of a fan, filter, and _______.
cooling coil ## Footnote This basic setup is sufficient for cooling applications.
346
What are the **four different arrangements** of air handling units?(4)
* Full recirculation * 100% outside air * Makeup air systems * Mixed air system ## Footnote Each arrangement serves different purposes and is designed for specific applications.
347
In the **full recirculation** arrangement, what percentage of outside air is typically drawn in?
10% ## Footnote This arrangement is commonly used with a forced air furnace to provide ventilation.
348
What is a **makeup air system** used for?(2) buildings
* Kitchens * Parking garages ## Footnote These systems ensure that negative pressure does not develop in buildings where large quantities of outside air are required.
349
As outdoor temperature increases above **12.5°C (55°F)**, what becomes necessary for cooling?
Mechanical cooling ## Footnote This is required to reduce the air temperature when operating on full outdoor air.
350
What happens when the outdoor temperature exceeds **24°C (75°F)** return air temperature?
It is more energy efficient to operate on recirculation ## Footnote The dampers adjust to a 10% or 15% minimum outside air position.
351
What is the purpose of **motorized relief air dampers** in mixed air systems?
To allow return air to be exhausted from the building ## Footnote This is necessary when the unit is operating on full outdoor air.
352
What is **free cooling** in the context of air handling units?
Achieving desired supply air temperature without mechanical cooling ## Footnote This results in significant energy savings compared to systems without this feature.
353
What is a **unitary air conditioning system**?
A self-contained, packaged system providing air conditioning for a specific area ## Footnote It typically requires little or no ductwork and is controlled by a thermostat.
354
What are the main components of a **window air conditioner**?(6)
* Supply air plenum * Low efficiency air filter * Evaporator coil * Condenser compartment * Compressor * Condenser fan ## Footnote Designed to supply conditioned air directly to the space without ductwork.
355
What type of air conditioning unit is typically **floor mounted** and may include auxiliary heating coils?
Packaged Air Conditioner ## Footnote These units can handle larger areas than window air conditioners.
356
What is a key feature of **process cooling units** for computer rooms?(4)
* Higher air volume handling * High efficiency cooling coils * Dual refrigeration circuits * Capacity humidifiers ## Footnote These units maintain fine control of environmental conditions in computer rooms.
357
What is the purpose of **electric reheat coils** in sophisticated air conditioning units?
To provide dehumidification while maintaining space temperature ## Footnote They operate in conjunction with the refrigeration system.
358
What is a **unit ventilator** designed for?
Individual room temperature control in buildings with many zones ## Footnote Commonly used in hotels and includes a filter, fan, and heating/cooling coil.
359
How does a **unit ventilator** operate?(3)
* Draws room air * Mixes with outdoor air * Filters and blows air through coils ## Footnote Coils are connected to a piping system for chilled or hot water.
360
What device controls **room temperature** in air conditioning systems?(2)
* Space thermostat * Return air thermostat ## Footnote These thermostats operate a control valve in the water supply to the coil.
361
What is required for each **cooling coil** in air conditioning systems?
Condensate drain piping ## Footnote Installation of condensate drain piping may be difficult.
362
What are the potential issues with **outdoor air intake** during winter?
Freezing problems ## Footnote This is particularly a concern in colder climates.
363
What type of air handling units are used for larger applications from **2.7 to 68 tonnes**?
Rooftop Units ## Footnote These units have a weatherproof casing enclosure for exposed installations.
364
Name the components that a **rooftop unit** may consist of.(6)
* Plenum section * Filter section * Supply fan * Heating section * Cooling coils * Humidifier ## Footnote There is flexibility in the selection of components.
365
What is used in heating and cooling coils where outdoor temperatures can drop below **freezing**?
Glycol ## Footnote Glycol is essential for preventing freezing in coils.
366
What type of buildings are **rooftop units** well suited for?(7)
* Single zone commercial buildings * Warehouses * Light manufacturing plants * Recreational facilities * Gymnasiums * Office buildings * Schools ## Footnote Must be designed to prevent noise transmission into occupied spaces.
367
What is the main characteristic of **central air conditioning systems**?
All major equipment components are located in a central mechanical room ## Footnote This setup satisfies heating and cooling requirements in each zone.
368
What is the most common **central system** used in residences?
Forced air furnace ## Footnote This system provides conditioned air ducted to each room in the house.
369
What additional features can be added to a **forced air furnace**?(3)
* High efficiency electronic air filters * Water humidifiers * Split-system, direct expansion cooling coil ## Footnote These features help maintain satisfactory environmental conditions year-round.
370
What is the primary control mechanism for a **single zone air conditioning system**?
Wall mounted room thermostat ## Footnote The thermostat cycles the heating/cooling fan to maintain space conditions.
371
What is a **manual override switch** used for in an air conditioning system?
Continuous fan operation ## Footnote Allows for constant air circulation within the space if desired.
372
What type of buildings is a **single zone air conditioning system** particularly well suited for?(5)
* Wood frame construction * Retail buildings * Food stores * Restaurants * Offices ## Footnote This system utilizes spaces between floor joists for return airflow.
373
What are the drawbacks of a **single zone air conditioning system**?(2)
* Noisy operation * Limitation of single zone temperature control ## Footnote Supply air registers are typically installed at floor level below windows.
374
What features can modern **residential furnaces** include?(3)
* Multi-speed blowers * Two-stage gas heating * Condensing heating sections ## Footnote Condensing gas furnaces extract additional heat through the absorption of latent heat.
375
What is the most energy efficient motor type for residential furnaces today?
Electronically commutated motor (ECM) ## Footnote ECMs are brushless DC designs and can be up to 200% more efficient than common multi-speed motors.
376
What is the main characteristic of a **single zone, constant air volume system**?
Air handling unit located in a mechanical room ## Footnote This system is suitable for single zone applications like gymnasiums and retail spaces.
377
What does the **Terminal Reheat System - Low Velocity** allow for?
Multizone temperature control ## Footnote It maintains a constant supply air discharge temperature and distributes conditioned air through low velocity ductwork.
378
What is a significant drawback of the **Terminal Reheat System - Low Velocity**?
Very high energy consumption ## Footnote It was widely used before the escalation of energy costs in the 1970s.
379
What is the purpose of the **terminal reheat box** in the **Terminal Reheat System - High Velocity**?
Reduce airflow to low velocity ## Footnote It maintains a constant supply air volume despite air pressure fluctuations.
380
What is a benefit of the **Terminal Reheat System - High Velocity**?
Reduced ductwork costs and building space requirements ## Footnote It is suitable for large buildings and retrofit projects with limited space for ductwork.
381
What is a potential maintenance issue with the **Terminal Reheat System - High Velocity**?
Increased noise and vibration ## Footnote This is associated with high velocity operation and the addition of pressure regulating controls.
382
What is a **Multizone System** in air conditioning?
A constant volume system with mixed air dampers, filters, humidifier, and fan ## Footnote It includes cooling coils and heating coils arranged in hot and cold decks.
383
What is the function of **zone mixing dampers** in a Multizone System?
To modulate the mixture of hot and cold air to satisfy space conditions ## Footnote Each pair of dampers is connected by a separate duct to each zone.
384
What is a **Dual Duct System** in air conditioning?
A system where hot and cold air are supplied separately and mixed in each zone ## Footnote It includes filters, humidifier, fan, hot deck, and cold deck discharge compartments.
385
In a Dual Duct System, how is the **supply air temperature** maintained?
By modulating the supply air temperature through a room thermostat ## Footnote This maintains space conditions in each zone.
386
What is the purpose of **pressure regulator devices** in a Dual Duct System?
To adjust for fluctuations in duct static pressures and maintain constant airflow ## Footnote This is important due to the high velocity design of the system.
387
What type of buildings commonly use the **Dual Duct System**?(4)
* Larger office buildings * Commercial buildings * Institutional buildings * Medical buildings ## Footnote It provides good control of space conditions and can handle many more zones than a Multizone System.
388
What is a key design consideration for **Dual Duct Systems** to minimize noise transmission?
Installation of silencers and acoustic insulation in mixing boxes ## Footnote This is crucial due to the high velocity design of the system.
389
What are the **advantages** of central air systems compared to unitary systems?(4)
* Easier to operate and maintain * Better control of noise and vibration * Higher operating efficiencies for high load requirements * Lower initial cost per unit output ## Footnote Central systems are typically used in larger buildings.
390
What is a key **advantage** of central air systems regarding maintenance?
Major components are in a mechanical room ## Footnote This allows inspection without disrupting occupied areas.
391
What is a disadvantage of central air systems related to **space requirements**?
Requires building space for mechanical rooms and ductwork ## Footnote The cost of this ductwork can also be significant.
392
What can happen if a key component of a central air system **breaks down**?
Shutdown of the air conditioning system for the entire building ## Footnote This highlights the risk associated with central systems.
Power Engineering Book 2 Part 2
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