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PE 4B > Unit 9 Compression, Absorption, Refrigeration > Flashcards

Unit 9 Compression, Absorption, Refrigeration Flashcards

1
Q

Refrigeration is the artificial production of

A

Cold, using mechanical means

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2
Q

First Fundamental principle of refrigeration

A

A substance must absorb or reject latent heat in order to change state

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3
Q

When latent heat is added to a liquid

A

It evaporates

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4
Q

When latent heat is removed from a gas

A

It condenses

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5
Q

What happens when an ice cube tray is placed into a freezer

A

First, the refrigerant removes sensible heat from the water, and then it removes latent heat of fusion

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6
Q

The evaporation of a liquid can lower a body’s temperature by the extraction of sensible heat, and the evaporation process can cause a change in state if;

A

The liquid evaporation occurs at a low enough temperature

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7
Q

The second fundamental principle of refrigeration

A

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

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8
Q

Saturation temperature

A

The temperature at which a substance is heat saturated, and additional heat causes a change in state, but no temperature change.

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9
Q

saturation temperature depends on

A

The pressure applied

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10
Q

Saturation pressure

A

The pressure applied to the boiling liquid surface when saturation temperature is reached

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11
Q

Third principle of refrigeration

A

For every saturation pressure, there is one corresponding saturation temperature

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12
Q

ASHRAE

A

American Society of heating, refrigeration and air conditioning engineers

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13
Q

The fourth principle of refrigeration

A

One of the physical properties of every pure liquid is a characteristic set of saturation pressures and temperatures

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14
Q

A physical property of every pure liquid is a set of

A

Saturation pressures and temperatures

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15
Q

Refrigerant

A

A liquid that is capable of boiling at low temperature

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16
Q

The temperature of a refrigerant can be controlled by

A

Varying the pressure in the vessel

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17
Q

The refrigerated space

A

Inside an insulated room

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18
Q

Refrigerated medium

A

The substance being cooled

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19
Q

The evaporator in a refrigeration system is in physical contact with

A

The refrigerated medium, so that heat May transfer to the refrigerant

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20
Q

A back pressure regulator, in the form of a throttling valve installed at the evaporator Outlet

A

By adjusting the valve, refrigerant Vapor flow can be adjusted, which changes the saturation pressure and saturation temperature in the vessel.

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21
Q

Vacuum pump at the evaporator Outlet

A

The vacuum pump can withdraw refrigerant Vapor faster than the rate at which it boils. So, the vacuum pump can lower the evaporator pressure to below atmospheric pressure

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22
Q

Liquid receiver

A

Reservoir of refrigerant to supply liquid to the evaporator. Continuously fed to replace the refrigerant boiled in the evaporator. Used in larger refrigeration systems

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23
Q

Metering device

A

Installed between the liquid receiver and the evaporator, to control refrigerant flow.

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24
Q

If too much refrigerant enters the evaporator

A

Both vapour and unboiled liquid will leave the evaporator. The liquid will damage the compressor

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25
Q

If the evaporator is fed to little refrigerant

A

The evaporator will starve or run dry. Heat flow to the evaporator will be reduced due to insufficient boiling liquid

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26
Q

Refrigerant Vapor must be

A

Recovered and reused

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27
Q

The refrigerant Vapor that leaves the evaporator is;

A

Compressed, and then cooled in a heat exchanger (the condenser). In the condenser, The Vapor gives off latent heat to a coolant or cooling medium and returns to its liquid state. The liquefied refrigerant then flows from the condenser to the liquid receiver until it’s reused in the evaporator

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28
Q

To get refrigerant Vapor to release its latent heat

A

The Vapor must be hotter than the cooling medium

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29
Q

Most condensers use a relatively warm cooling medium

A

Between 0 and 40 degrees Celsius

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30
Q

A compressor draws refrigerant vapour at a low pressure and discharges it at

A

A higher pressure and also raises the refrigerant Vapor temperature.

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31
Q

After the pressurized, high temperature vapour leaves the compressor

A

It enters the condenser, transfers heat to the surrounding coolant, and condenses. The liquid refrigerant drains to the receiver, and eventually returns to the evaporator, where the cycle repeats.

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32
Q

5 mandatory components in a refrigeration system

A

Refrigerant

evaporator

refrigerant metering device (control valve, orifice or capillary tube)

Condenser

Compressor

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33
Q

Optional components for a refrigeration system

A

liquid receiver

Condenser cooling fan

Evaporator fan

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34
Q

Metering device Inlet

A

Condenser Outlet

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35
Q

Evaporator Inlet

A

Metering device Outlet

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36
Q

Compressor Inlet

A

Evaporator Outlet

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37
Q

Condenser Inlet

A

Compressor Outlet

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38
Q

Energy is consumed in order to compress refrigerant. The energy consumed by the compressor results in

A

An increase in enthalpy, pressure and temperature

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39
Q

In the condenser, the refrigerant first gives off

A

The energy added by the compressor. Then, the saturated refrigerant Vapor gives off the latent heat it absorbed in the evaporator, condensing back to saturated liquid.

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40
Q

Batch process

A

A discrete mass of refrigerant circulates through the system, and repeatedly undergoes thermodynamic processes

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41
Q

Constant flow cycle

A

When the heat transfer is continuous in a refrigeration cycle

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42
Q

Subcooled

A

Cooled to below its saturation temperature

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43
Q

Thermostatic expansion valve

A

Small bulb located at the evaporator Outlet, monitors evaporator superheat and controls the opening of the metering device.

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44
Q

Due to length of the pipe, internal roughness of the pipe and bends in the evaporator and condenser, the pressure of the refrigerant;

A

Drops from the metering device Outlet to the compressor Inlet, and from the condenser Inlet to the metering device Inlet

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45
Q

In both the high and low sides, pressures drop in;

A

The direction of refrigerant flow

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46
Q

The evaporator pressure drop reduces;

A

The compressor suction pressure, increasing the pressure ratio and making the compressor work harder

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47
Q

Internal combustion engines are compared according to

Boilers are compared according to

Refrigeration plants are compared according to

A

Kilowatt output

Horsepower

Tonnes of refrigeration

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48
Q

Evaporator capacity (evaporator tonnage)

A

Cooling capacity of the evaporator. Expressed in tonnes of refrigeration

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49
Q

The evaporator transfers less Heat than;

A

The condenser, because it does not need to handle the energy added to the refrigerant by the compressor. Therefore, evaporators often have smaller capacity than condensers

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50
Q

Condenser capacity

A

The heat rejection capability of the condenser. Must have greater heat transfer capability then the evaporator

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51
Q

Net refrigerating effect (NRE)

A

Heat absorbed per kilogram of refrigerant circulated through the evaporator (kj/kg)

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52
Q

Flash gas

A

The portion of refrigerant that evaporates.

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53
Q

Flashing occurs because

A

The liquid has higher enthalpy in the high side then it can have on the low side. This excess enthalpy is converted to latent heat in the evaporator, producing flash gas.

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54
Q

_____ reduces the amount of flash gas produced

A

Subcooling

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55
Q

The refrigerant that flashes into vapour

A

Will not take part in the actual Refrigeration process. Only the remaining liquid water absorbs heat from the surrounding medium for evaporation.

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56
Q

NRE is considerably less when

A

The liquid refrigerant entering the evaporator is at a temperature higher than the boiling point in the evaporator.

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57
Q

The amount of liquid that may flash into vapour can be as high as

A

30%

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58
Q

Coefficient of performance (COP)

A

The ratio of the amount of heat absorbed from the refrigerated medium by the evaporator, to the amount of energy used to drive the compressor.

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59
Q

A higher COP means

A

A more effective refrigeration system

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60
Q

COP formula

A

NRE/Compressor power in Kw

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61
Q

Pressure ratio

A

Absolute compressor discharge pressure/Absolute suction pressure

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62
Q

Refrigerants are categorized according to

A

Flammability and toxicity, then placed in a safety group.

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63
Q

Refrigerants are also classified according to

A

Their impact on the environment, chemical Origins, and operating temperature suitability

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64
Q

ASHRAE denotes refrigerants with the capital

A

“R” followed by a dash and a number

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65
Q

There are over ____ ASHRAE designated refrigerants and refrigerant blends

A

300

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66
Q

Leaks are inevitable. Leaking refrigerant may have considerable environmental impact on

A

The Earth’s ozone layer and on global warming

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67
Q

Refrigerants that contain chlorine

A

May have ozone-depleting potential (ODP).

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68
Q

Unlike combustion equipment, refrigeration systems do not produce

A

CO2 (carbon dioxide)

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69
Q

Global warming potential (GWP)

A

Refrigerants rated according to their global warming potential.

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70
Q

Natural refrigerants

A

Refrigerants that occur naturally in the environment.

EX; ammonia, water, carbon dioxide

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71
Q

Ammonia natural refrigerant

A

Desirable since it is an energy efficient refrigerant with zero ODP and zero GWP

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72
Q

Many refrigerants begin as hydrocarbon compounds, but are

A

Chemically modified to achieve certain physical properties

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73
Q

CFC’s

A

Chlorinated fluorocarbons. Because they are chlorinated, they have high ODP.

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74
Q

R-11 and R-12 refrigerants

A

Phased out chlorinated fluorocarbons, they have high ODP.

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75
Q

Halocarbons

A

Includes; CFC, HFC, HCFC

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76
Q

Thermodynamic properties are

A

The physical properties that directly affect the movement of heat

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77
Q

Examples of thermodynamic properties

6

A

Pressure, temperature, volume, density, enthalpy and entropy

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78
Q

Refrigerants with low evaporator pressure

A

Air May leak into the refrigeration circuit, therefore are purgers must be installed to continuously remove air from the system

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79
Q

Refrigerants operating pressures vary with temperature

A

Important, since it determines the strength of the equipment required, cost of construction, and operator Staffing requirements

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80
Q

When choosing a refrigerant it should have a

A

Low condensing pressure. As well, evaporators should preferably operate above atmospheric pressure to prevent air and moisture infiltration, which causes operational problems

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81
Q

Refrigerants with lower specific volume

A

The refrigeration compressor system can have a smaller displacement compressor, as well suction lines can be made smaller in diameter.

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82
Q

Refrigerant liquid density informs designers

A

About how heavy liquid lines will be. This helps determine the size of control valves and piping.

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83
Q

The NRE is the heat absorbed

A

In the evaporator, under standard operating conditions

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84
Q

Latent heat of evaporation formula

HFG=

A

HG-HF

Enthalpy of saturated vapour - Enthalpy of saturated liquid

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85
Q

6 important physical properties of refrigerants

A

Miscibility, leakage tendency, odour, toxicity, formability/explosiveness, moisture reaction

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86
Q

Miscibility

A

Refers to when two or more liquids are soluble in all proportions

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87
Q

Refrigerants come in contact with Lube oil in the

A

Compressor crankcase, cylinder walls and screws. Refrigerants carry some of this oil into other parts of the system

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88
Q

Miscibility is dependant on

A

The type of refrigerant and the type of lube oil

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89
Q

Lube oils are categorized as

A

Conventional mineral-based oils and synthetic polyester oils

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90
Q

Ammonia is not

A

Miscible with Lube oil

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91
Q

Oil miscible refrigerants dilute

A

Compressor crankcase oil, lowering its viscosity and lubricating ability

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92
Q

When non-miscible refrigerants are used

A

Oil tends to build up in the evaporator and condenser, reducing system capacity.

May need oil separators and oil return systems

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93
Q

Ammonia systems require oil

A

Separators and oil return systems. These remove oil from the piping and other low points in the system, and return the oil to the compressor

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94
Q

Refrigerants that have greater molecular mass, have larger molecules and are less likely

A

To escape through tiny openings (leaks)

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95
Q

4 Leakage tendency factors

A

Operating pressure, viscosity, density, and chemical effects on seals and gaskets

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96
Q

At high temperatures, refrigerants are capable of absorbing greater amounts of

A

Moisture than at low temperatures. When a warm moisture saturated refrigerant is cooled to a lower temperature, it will produce free water

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97
Q

Moisture in the refrigerant should be avoided for 3 reasons

A

May cause ice to form between valve and valve seat of metering device

May cause acid formation, resulting in corrosion

Water combining with ammonia

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98
Q

Ammonia combines with water to form

A

Ammonium hydroxide, which is highly corrosive to copper and alloys. Ammonia systems must never use components made of copper or copper alloys

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99
Q

By decreasing the pressure exerted on a refrigerant

A

It’s boiling point decreases, and it will absorb latent heat of evaporation from its surroundings. After evaporating, the refrigerant is pressurized and returns to its liquid state by discarding latent heat

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100
Q

Closed cycle refrigeration system

A

Vapour from the evaporator is collected continuously. The vapour is compressed, condensed, and returned to the evaporator so the same refrigerant is used over and over

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101
Q

Two classes of closed-cycle refrigerating systems

A

Compression system and absorption system

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102
Q

Closed cycle compression refrigeration system principal parts
5

A

Evaporator

Compressor

Condenser

Metering device (liquid refrigerant control/regulating valve)

Liquid receiver

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103
Q

Closed cycle compression system two sections;

A

High-side and low-side, divided by the centre line

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104
Q

Closed cycle Compression High side

A

Contains refrigerant at high pressure and temperature. Refrigerant leaving the compressor is high pressure superheated gas. Refrigerant in the condenser is both liquid and gas. In the condenser, refrigerant is at saturation temperature and pressure. Refrigerant leaving the condenser is high pressure, high temperature liquid. Refrigerant entering metering device is high pressure and temperature, but subcooled by a few degrees.

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105
Q

Closed cycle compression low side

A

Contains refrigerant at low pressure and temperature. Refrigerant leaving metering device is low pressure saturated liquid and Flash gas. Refrigerant in the evaporator is both liquid and gas, at saturation pressure and temperature. Refrigerant leaving the evaporator is low pressure, low temperature gas. Refrigerant entering the compressor is low pressure and temperature, but superheated to an extent

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106
Q

Closed cycle compression low side system

Includes all equipment Downstream of the metering device including;

A

The evaporator, suction side of compressor, all interconnected tubing and piping

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107
Q

Closed cycle compression

Design pressure of low side is determined by the;

A

Temperature requirements for the cooled medium

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108
Q

Closed cycle compression

The high side consist of;

A

Compressor discharge, condenser, liquid receiver, piping Upstream side of the metering device, connected tubing and piping

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109
Q

Closed cycle compression

High side design pressure is determined by;

A

Required condensing temperature of the refrigerant vapour, which depends on the temperature of the available condensing medium

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110
Q

Direct system- direct expansion systems or DX

A

The evaporator surface is in direct contact with the material or space being refrigerated.

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111
Q

Household refrigerators and air-conditioners are examples of

A

Direct systems

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112
Q

Evaporators used in DX systems

A

Are called; DX coils

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113
Q

Indirect system

A

Liquid, such as brine, glycol or water is cooled by the refrigerant and then circulated by means of a pump to the material or space being refrigerated.

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114
Q

Advantages of indirect systems

A

Hazardous refrigerants can be used to cool brine. They are also cost-saving, most of the system is filled with chilled water or brine, Which is far less costly. Chilled water or brine transfers heat from occupied space, reducing the amount of refrigerant required

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115
Q

Chillers

A

Evaporators used to cool water or brine

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116
Q

Packaged refrigeration unit advantages

A

Components designed to match each other for greatest operating efficiency. Compact since its on a single skid, less space requirements needed. Installed easily and quickly. Factory tested and manufacturer takes full responsibility for design and performance.

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117
Q

Economizer installed between a condenser and chiller

Serves 3 purposes;

A

Produces flash gas to cool the compressor motor

Increases the net refrigerating effect (NRE) of the evaporator

Reduces power consumption of the compressor

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118
Q

When evaporator flash gas is reduced

A

Net refrigerating effect increases, which increases the cooling capacity of the system

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119
Q

Compression system with economizer installed in between the condenser and chiller

Only the refrigerant Vapor produced by the evaporator goes through

A

2 compression stages

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120
Q

Economizer provides an _________ effect for the compressor

A

Intercooling.

The cool vapour from the intermediate chamber cools the first stage compressor discharge gas, reducing power required for compression in the second stage

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121
Q

Refrigeration compressors are cooled without

A

Fins

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122
Q

Refrigeration compressors are designed specially to prevent or inhibit

A

Refrigerant leakage

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123
Q

Refrigeration compressor three main functions

A

Draws refrigerant gas from the evaporator as it’s produced.

Raises the refrigerant gas pressure so refrigerant can flow from the high side to the low side

Raises the saturation temperature of the gas to above the temperature of the condensing medium

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124
Q

Three types of refrigeration compressors

A

Reciprocating, rotary, centrifugal

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125
Q

Reciprocating compressors

A

A piston travels back and forth in a cylinder, drawing in and compressing the vapour

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126
Q

Rotary compressors

A

Use helical rotors or an eccentric rotor with vanes to compress the vapour

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127
Q

Centrifugal compressors

A

Rapidly revolving impellers to draw in the vapour and discharge at high velocity by centrifugal force. High velocity, low pressure vapour is converted to low velocity, high pressure vapour before it leaves the compressor

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128
Q

Compressor safety head

A

Entire head lifts when the pressure in the cylinder becomes too high, due to liquid refrigerant in the cylinder. Lifting action allows liquid to pass into the discharge line without doing serious damage

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129
Q

Rotary compressors in compound refrigeration systems

A

The compressor is called a booster. Produces very low evaporator pressure for deep freeze applications

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130
Q

Helical rotor compressor design is primarily in

A

Medium and high capacity Refrigeration

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131
Q

New compressors must be able to efficiently operate over

A

A pressure range, rather than a single evaporator or condenser pressure

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132
Q

Heat exchange results in one process fluid

A

Gaining Heat and the other losing Heat

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133
Q

Two main heat exchangers used in a refrigeration system

A

Evaporator and condenser

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134
Q

Evaporator is the part of the refrigeration system in which

A

Liquid refrigerant is vaporized by the absorption of heat from the medium to be cooled

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135
Q

Three types of evaporators

A

Direct expansion “or dry” evaporator

Flooded evaporator

Liquid recirculating (or liquid overfeed) evaporator

They differ in the method of refrigerant circulation

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136
Q

Dry evaporator (direct expansion)

A

Expansion valve admits only enough liquid refrigerant to maintain desired temperature. Amount of liquid refrigerant entering, balances the amount of refrigerant Vapor leaving, with no recirculation. Evaporator only contains a small amount of liquid refrigerant at any time

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137
Q

Flooded evaporator

A

Kept almost completely filled with liquid refrigerant regardless of load demand. Respond rapidly to changes in load as refrigerant has already gone through a pressure reduction and is awaiting exposure to heat.

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138
Q

________ has a higher heat transfer rate than the dry evaporator

A

Flooded evaporator

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139
Q

Flooded evaporator is applicable for

A

Pasteurization processes where on Startup, fluid must not pass through without being cooled.

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140
Q

Flooded evaporator disadvantages

A

Requires a relatively large refrigerant charge and is bulky

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141
Q

Liquid recirculating evaporator (liquid overfeed)

A

Used in overfeed refrigeration systems. Has a constant flow of liquid refrigerant regardless of load demand. Has a pump that feeds around three times the amount of liquid then the evaporator requires.

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142
Q

Critical element of the liquid recirculating evaporator

A

The low pressure receiver. Separates liquid and Vapor returning from the evaporators, so that the vapour can be re compressed or condensed. Without it, liquid would enter and damage the compressor

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143
Q

Low pressure receiver is also called

A

A surge drum or accumulator

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144
Q

Recirculating evaporator advantages

A

Higher heat transfer since it is completely wetted with liquid. Respond rapidly to changes in load as refrigerant has already gone through a pressure reduction and is awaiting exposure to heat.

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145
Q

Liquid recirculating evaporator is applicable for

A

Quick freeze and loads that swing from almost no load to full load quickly.

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146
Q

Liquid recirculating evaporator disadvantages

A

Requires a relatively large and costly refrigerant charge

Needs additional equipment such as surge drum, pumps, level controller. Adds to initial cost

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147
Q

Classes of evaporators according to their Construction

4

A

Bare tube, plate surface, finned tube, Shell & tube

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148
Q

Bare tube evaporator

A

Single coil bent in various shapes, or various coils placed in parallel and connected to Common headers. Steel or copper tubing. Used in any type of evaporator

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149
Q

Bare tube evaporators can be used where

A

Temperature is maintained below 1°C, such as coolers and freezers. Can be submerged in liquid

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150
Q

Plate surface evaporator

A

Uses a coil and two plates. Can be used individually or in Banks. Usually used as a direct expansion evaporator

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151
Q

Plate surface evaporator is widely used in

A

Refrigerators, freezers, display cases and Locker plants because it can be easily cleaned with manual scraping.

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152
Q

Finned tube evaporator

A

Bare tube evaporator coil with fins attached. Used as a direct expansion evaporator.

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153
Q

Finned tube evaporator is the most widely used in

A

Air conditioning applications. Also used in walk-in coolers and display cases

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154
Q

Shell & tube evaporator

A

Cylindrical steel Shelf with multiple straight bare tubes in parallel. Used for almost any type of liquid cooling application.

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155
Q

Function of the refrigeration condenser

A

Removes heat from compressed refrigerant Vapor until it changes to liquid. The condenser must remove both the heat absorbed in the evaporator by The Vapor, and the heat of compression added by the compressor

156
Q

Three types of condensers

A

Air-cooled, water cooled, evaporative

157
Q

Air-cooled condensers

A

Uses air to remove heat from refrigerant vapour. Cooling air is circulated by fans or blowers. Commonly mounted Outdoors on a roof location

158
Q

Air-cooled condenser disadvantages

A

Cooling load increases in hot weather, condenser capacity is reduced as temperature difference between cooling medium and refrigerant decreases.

159
Q

Air-cooled condenser advantages

A

Do not require cooling water or water treatment chemicals, and do not breed harmful bacteria. Preferred when environmental considerations are of importance

160
Q

Water cooled condensers

A

Use cooling water to remove heat from refrigerant vapour

161
Q

Three types of water cooled condensers

A

Double tube, shell and coil, Shell and tube

162
Q

Double tube condenser

A

Water flows through inner tube, while refrigerant flows in the opposite direction. Lowest efficiency. Sometimes used as a booster condenser

163
Q

Shell and coil condenser

A

Very efficient and compact, easily adaptable to packaged Refrigeration units. Difficult to clean. Repair costs may increase when leaks develop

164
Q

Shell & tube condenser

A

Number of straight tubes fastened in the tube sheets. Has water boxes to direct the cooling water through two or more passes.

165
Q

Shell in tube condenser is used in

A

Ammonia installations, as well as medium and large-sized air conditioning installations using other types of refrigerants.

166
Q

Evaporative condensers

A

Uses air and water to provide Cooling in order to condense the refrigerant vapour.

167
Q

Evaporative condensers are favoured in locations where

A

It is necessary to conserve water. 80 to 90% in water consumption savings

168
Q

Evaporative condensers may be located either

A

Indoors or Outdoors.

Indoors requires Ducts Which are connected to the outside.

In Outdoors, care should be taken to prevent freezing of water during cold weather. Can be done by using a heating coil in the sump of the condenser

169
Q

Cooling towers used with water cooled condensers to

A

Limit water consumption

170
Q

Three types of refrigeration system controls

A

Operating controls (system capacity)

Actuated or secondary controls

Limiting and safety controls

171
Q

Operating controls

A

Start or stop the compressor, or regulate its capacity when the process conditions approach or deviate from set points

172
Q

Actuated or secondary controls

A

Either indirectly control the changes in operation called for from the primary controls, or regulate the cycle during operation

173
Q

Limiting and safety controls

A

Protects the system against operation Beyond the limits it was designed for

174
Q

Human machine interfaces (HMI’s)

A

Allows operator to receive operational data and alarms on a screens, and ability to make changes to set point. Allows a unit to be stand alone

175
Q

Refrigeration plant cooling capacity must always equal

A

The cooling load

176
Q

If a refrigeration plant operates at full capacity when the load is low ______

If a refrigeration system operates at low capacity when the cooling load is high ______

A

The temperature of the refrigerated medium will drop below set point

The temperature of the refrigerated medium will rise above set point

177
Q

Compresser capacity can be adjusted by

A

Cycling it on and off, regulated with multi-stage control and fully modulated

178
Q

Compressor Control Systems respond to

3

A

Temperature, pressure and humidity

179
Q

A suction pressure actuated control cannot be used with

A

An automatic expansion valve, or a capillary tube

180
Q

Chilled water flow switch

A

Installed in chilled water Outlet line, protects the chiller from freezing due to lack of water flow. Opens compressor motor circuit when water flow drops below the safe minimum flow. Prevents compressor from starting if flow is not established

181
Q

Motor demand limiter

A

Most centrifugal Chillers have this, limits the maximum current flow to the compressor Drive motor. Overrides the water temperature sensor if the motor load reaches the maximum amperage setting.

182
Q

Motor demand limiter

One of the most common and useful purposes it serves

A

Limit the current flow when the machine is first started. Prevents low temperature trips on Startup

183
Q

Instead of demand limiters, some chillers use

A

Soft loading strategies on Startup. PLC control strategy that brings the chilled water loop temperature from its start value to its set point in a controlled manner. Prevents Chiller from going to full capacity during the pull down period

184
Q

Restart inhibit

A

Keeps compressors from short cycling or restarting in a short period of time. Allows motor to cool off for 10 or more minutes

185
Q

In the condenser, non condensable gases

A

Occupy space, impede heat transfer, and raise condenser pressure

186
Q

Chiller low limit thermostat

A

Immersed in the water at the coldest point of the chiller, to prevent freezing. Opens the control Circuit of the compressor several degrees above the freezing point

187
Q

Refrigeration compressor crankcase and oil sumps are both under

A

Low side pressure

188
Q

many compressors pump down

A

The low side before they cycle off. Reduces low side pressure to just above atmospheric

189
Q

Net Lube oil pressure

A

The difference between the oil pump supply pressure and the crankcase pressure

190
Q

Flow switches are operated by the force exerted on

A

A flexible vane immersed in a flowing fluid

191
Q

Flow switches are used in;

A

Chilled water lines, cooling water lines and air ducts

192
Q

Flow switches are often used as

A

Safety lockout switches if the fluid flow becomes insufficient or ceases. Can also be used to close flow indicator circuits

193
Q

When compressor Lube oil is cool

A

It dissolves more refrigerant than when it is hot. Dissolved refrigerant dilutes Lube oil, which causes excessive bearing wear. When the compressor starts, refrigerant in the oil vaporizes, forming bubbles. When lube pump draws bubbles, it may lose its prime and starve bearings of oil

194
Q

Refrigeration system pressures and temperatures must remain constant while the system is in operation. For this to occur

A

The amount of refrigerant fed to the evaporator must always equal the amount of refrigerant circulated by the compressor

195
Q

As cooling load increases, refrigerant flow must

A

Increase

196
Q

Flow of refrigerant through the compressor is controlled by;

Flow of refrigerant through the evaporator is regulated with;

A

Various capacity control methods, including on off cycling and unloading

A metering device

197
Q

If too much refrigerant enters the evaporator

A

The cooling load will not be able to vaporize all of the refrigerant. Remaining liquid will enter the compressor suction line and destroy the compressor

198
Q

Metering devices include;

3

A

Capillary tubes, fixed orifices, expansion valves and float valves

199
Q

Manual expansion valves are

A

Seldom used in modern refrigeration systems. Occasionally used in bypass lines around automatic control valves or defrosting system

200
Q

Automatic expansion valve (AEV)

A

Pressure regulating, maintains constant pressure in the evaporator whenever the compressor is running regardless of load. Automatically shuts off liquid flow when compressor stops

201
Q

When temperature of the refrigerated space or medium drops below set point, a thermostat stops the compressor and

A

The expansion valve stays open and allows liquid to enter the evaporator. Liquid continues to vaporize, causing the evaporator pressure to increase.

202
Q

AEV’s are used on;

A

Small refrigerating units, such as refrigerators and freezers.

203
Q

Thermostatic expansion valve (TEV)

A

Most widely used metering device. Similar to automatic expansion valve, but features thermal power element.

204
Q

The thermostatic expansion valve adjusts the amount;

A

Of liquid admitted to the evaporator so that, under all load conditions, nearly the entire evaporator surface is used to transfer heat to the evaporating liquid refrigerant. Ensures no liquid leaves the evaporator with the vapour. Vapor leaving the evaporator must be superheated

205
Q

To compensate for a large evaporator pressure drop, a thermal expansion valve may be equipped with

A

An equalizing line

206
Q

In a flooded evaporator, the low pressure float valve is used to

A

Maintain a constant level of liquid refrigerant. Installed in the low side of the system

207
Q

High pressure float valve

A

Liquid level operated control valve, located on the high side. The amount of refrigerant charge in a system with a high pressure float valve is critical

208
Q

Capillary tube

A

Simplest of all metering devices. Fixed length of tubing with a small inside diameter. Create considerable pressure drop along its length, restricting the flow of liquid from the condenser to the evaporator and maintains pressure difference between the high-side and low-side.

209
Q

Capillary tubes are limited to

A

Small refrigeration units, since it is small and not very sensitive to load changes. Used in refrigerators, freezers and air conditioners

210
Q

Evaporator capacity can be controlled by using

A

Sectional evaporators or evaporator dampers

211
Q

Sectional evaporators

A

Divided into two or more sections, each with a flow control valve. Sections of the evaporator can be shut off as cooling load decreases.

212
Q

Evaporator dampers

A

Uses a face damper to vary the quantity of air passing over the evaporator coils and controlled by a positioner.

213
Q

Evaporator face damper disadvantage

A

Air flow varies with cooling load. In HVAC, reduction in air flow caused when the dampers closed reduces ventilation air to unacceptable levels

214
Q

Evaporator face and bypass damper

A

Dampers connected to same damper Drive. Regardless of damper position, quantity of air passing through the ducts remains constant

215
Q

Methods used to control compressor capacity

2

A

Intermittent operation and continuous operation with reduced output

216
Q

Intermittent operation

A

Compressor is stopped when the desired low temperature of the substance is reached, and started up when the temperature rises to a certain level.

217
Q

Intermittent operation is only used

A

On small systems with fairly constant loads, as the most power is consumed on Startup

218
Q

In larger systems, the compressor operates continuously but

A

At reduced capacity

219
Q

Capacity of reciprocating compressors is reduced by

4

A

Cylinder unloading, cylinder bypass, Hot Gas bypass, variable speed Drive

220
Q

Cylinder unloading

A

Method of capacity reduction that deactivates one or more cylinders in sequence, based on the cooling load

221
Q

Cylinder unloaders work by

A

Keeping the intake valves of one or more cylinders in the open position, preventing the compression of vapour drawn in during the suction stroke

222
Q

Cylinder bypass

A

Bypasses the discharge from one or more cylinders back to the suction side of the compressor

223
Q

Hot Gas bypass

A

Capacity control. Has a normally closed solenoid valve located in the bypass line. When energized, some hot high pressure gas is allowed to go directly into the suction line

224
Q

Hot Gas bypass disadvantages

A

Little or no reduction in power consumption when bypass line is open. Compressor overheating can occur.

225
Q

Hot Gas bypass is used only on

A

Small compressors. Often used in conjunction with other types of capacity control

226
Q

Centrifugal compressor capacity control

3

A

Speed control, suction throttling, variable Inlet guide vanes

227
Q

Suction throttling

A

Uses a butterfly damper installed at the inlet to a centrifugal compressor.

228
Q

Suction throttling is not economical because

A

The input power to the compressor does not decrease by the same amount as the capacity. Has been replaced by variable Inlet guide vanes

229
Q

Variable Inlet guide vanes

A

Vanes are linked so they operate together. Operated by a Rack & Gear Arrangement attached to a piston.

230
Q

Variable Inlet guide vanes efficiency

A

Very efficient, compared to suction throttling. Reduces compressor power consumption

231
Q

Pressure gauges are rarely installed on

A

Low capacity commercial refrigeration systems

232
Q

Accumulator

A

Simple liquid trap located in the compressor suction line. Collects and holds liquid so that it does not enter the compressor

233
Q

Accumulators must not be insulated

A

So heat may be absorbed through the accumulator wall.the heat vaporizes the trapped liquid and returns it to the compressor suction. If insulated, liquid refrigerant could accumulate and eventually become entrained in the compressor suction

234
Q

Oil separator

A

Separates oil that leaves the compressor with the high pressure vapour, and returns it to the compressor crankcase. Maintains oil level in the crankcase and reduces the need for oil addition

235
Q

Oil separator should be installed in

A

The discharge line between the compressor and the condenser

236
Q

Refrigerating systems using oil miscible refrigerants use

A

Oil separating devices in the compressor discharge line

237
Q

Suction strainer

A

Installed in compressor suction lines to keep impurities from entering compressors, which could damage them.

238
Q

Filter drier

A

Removes moisture, particulate and scale from liquid refrigerant. Installed in the liquid refrigerant line ahead of the expansion valve

239
Q

Moisture in a refrigeration system can cause the following problems
2

A

Ice buildup in metering device.

Acid formation resulting in, corrosion, sludge, deterioration of motor insulation

240
Q

Sightglass and moisture indicators

A

Small housing, with one or two lenses installed in liquid refrigerant line to observe liquid flow.

Vapor appears in the liquid line when the system contains insufficient refrigerant, causing the pressure drop in the liquid line to the metering device to increase. Vapor bubbles also show if the flow in the liquid line is restricted

241
Q

Economizers are used for three reasons

A

Reduce the temperature of liquid refrigerant

Prevent flashing of the liquid due to the pressure drop that occurs as refrigerant flows through the liquid line

Increase the temperature of the vapour passing through the economizer

242
Q

If liquid passes through the evaporator, the economizer will

A

Evaporated before it reaches the compressor suction. Prevents liquid slugging in the compressor

243
Q

Distributor

A

Placed in the liquid line directly Downstream from the expansion valve, and ensures each evaporator coil is fed refrigerant equally. Used when a large direct expansion evaporator has more than one refrigerant circuit

244
Q

Vibration absorber

A

transmission of vibration and noise is prevented, by connecting the piping to the main components of the refrigeration system using vibration absorbers

245
Q

Vibration absorber should be located

A

As close as possible to the compressor for maximum effect

246
Q

Ammonia steel pipe should be

A

Type S (seamless)

or

Type E (Electric resistance welded)

247
Q

Horizontal refrigeration lines should slope

A

Downward in the direction of refrigerant flow, minimum slope of 4.2mm per metre.

248
Q

As an added precaution against leakage along valve stem

A

Packed valves may be equipped with a valve cap that covers and seals the valve stem. Cap must be removed before valve can be operated

249
Q

Liquid receiver gauge glass

A

Installed in Vapor space and the liquid space. Usually a reflex glass, since it makes clear liquids appear as black

250
Q

Purge valve

A

Used to vent non-condensable gases from the system

251
Q

Charging valve

A

Used to charge the system with refrigerant

252
Q

Two most common pressure relief devices in refrigeration systems

A

Fusible plug and spring loaded relief valve

253
Q

Fusible plugs

A

Device containing an alloy that melts at a specified temperature to relieve pressure. When plug melts entire refrigerant charge escapes. New plug and new refrigerant charge are required to resume operation

254
Q

Fusible plugs are used

A

In smaller systems, and only to protect smaller volume components. Located above or below the liquid refrigerant level, except on the low side. Primarily used to protect from explosion in case of fire.

255
Q

Refrigeration safety valves do not have

A

Manual try leavers or exposed Springs. Refrigerant must be contained within the system. Valves must be replaced every 5 years

256
Q

Emergency discharge system consists of

3

A

Pipe in connection to the top of a receiver or vessel where refrigerant is stored

Emergency discharge valve, outside of the building

Diffuser, located at high elevation to spread the refrigerant Vapor over a large area

257
Q

After a refrigeration system is installed, repaired, or modified, the entire system must be

A

Thoroughly inspected for leaks

258
Q

__________ must not be used for system pressure testing

A

Oxygen and flammable gases. An explosion could result. Nitrogen gas is commonly used for leak testing

259
Q

Positive pressure pneumatic testing

A

Inert gases, such as dry nitrogen or carbon dioxide, are used as the testing medium. Gas supplied from high-pressure cylinders, connected through a pressure-reducing valve to the high or low side pressure of the system

260
Q

Before a pressure test

A

Piping joints must be uninsulated, welded joints unpainted and free of rust, dirt, oil. Fields test should be witnessed by jurisdictional inspector

261
Q

For pressure testing, valve lineup must permit the

A

High and low pressure sides of the system to be initially tested together, at the same pressure

262
Q

Fluids that are not to be used for leak testing an ammonia refrigeration system
4

A

Oxygen or combustible gas mixtures

Carbon dioxide

Halogen refrigerants

Water or Water Solutions

263
Q

Refrigeration system pressure test

System must be held under pressure until;

A

Proven tight with no more than 1% loss in pressure, after accounting temperature change.

264
Q

For safety, and to prevent over pressurization of the system, the pressure testing cylinder must have;
5

A

Shut off valve, bleed valve, pressure regulator, adjustable pressure relief valve, calibrated cylinder and line pressure gauges

265
Q

Pneumatic pressure applied to a refrigeration piping system under test shall not exceed

A

130% of the design pressure of any system component

266
Q

If no further leaks are discovered during the pressure test, the system may be left pressurized for

A

About 24hrs

267
Q

Detecting leaks in a system that operates below atmospheric is

A

More difficult. Leakage of air in the system will cause The Purge unit to cycle more than usual, resulting in a loss of refrigerant because it’s impossible to totally separate air from the refrigerant during purging

268
Q

To test a sub atmospheric pressure refrigeration system for leaks, it is necessary to

A

Shut down the compressor and Break Free the vacuum by pressurizing system with dry nitrogen.

269
Q

Leak Detectors used to find leaks

5

A

Electronic Leak Detectors, litmus paper, phenolphthalein paper, sulfur candles, soap and water

270
Q

Two most common Leak Detection methods

A

Soap and water test and electronic leak detector

271
Q

Electronic leak detector

A

Draws vapour through a tube with a sniffer at the end. Sniffer is placed in areas where a leak is suspected. Measures electrical resistance of vapour sample. When a sample contains refrigerant, the change in resistance causes the detector to react

272
Q

Sniffers are available to detect

A

Ammonia, HFC’s, HCFS’s

273
Q

Litmus paper detector

A

Change in colour in the presence of an acid or base.

274
Q

Red litmus paper turns ______ in the presence of ammonia

A

Blue

275
Q

Phenolphthalein paper

A

Used when a more sensitive test for ammonia is required. White papers which change to red when exposed to a solution with a pH greater than 8.3

276
Q

Sulphur candle test

A

Can detect ammonia leaks. When the flame from The sulphur candle comes in contact with leaking ammonia, thick white smoke is created

277
Q

Sulphur dioxide formed when a Sulphur candle is burned is an

A

Irritating and toxic gas. Only done and well-ventilated areas

278
Q

Soap and water leak test

A

Brush the solution on the area where leak is suspected. Bubbles will appear if there is a leak

279
Q

Copper plating

A

Acids remove Copper from heat exchanger surfaces and redeposit it at points of high temperature, such as bearings and compressor exhaust valves

280
Q

To prevent copper plating, large temporary dryers are installed

A

As liquid refrigerant passes through the drying agent, any existing moisture is absorbed

281
Q

Before charging an empty refrigerating system, the entire system is

A

Put under a very high vacuum (5000 microns or 0.67kpa absolute) with a special vacuum pump. System compressor must not be used since it is not designed for this and could be damaged.

282
Q

After the vacuum is obtained,

A

The vacuum is broken by admitting dry nitrogen gas. The gas is then evacuated from the system buy the pump to once again produce a high vacuum. Second vacuum removes the last traces of moisture from the system. If pressure does not increase, it is free of leaks and moisture

283
Q

Before system charging is done

A

System drying and evacuating is done prior

284
Q

Only ____________ should attempt to charge refrigeration systems

A

Technically qualified persons, trained and certified in the handling of refrigerant

285
Q

Initial refrigerant charge is added to

A

The high pressure side of the system. A dehydrator should be installed in the line between the refrigerant drum and the liquid charging valve.

286
Q

King valve is also called

A

Also called the liquid line shut off valve.

287
Q

In preparation for charging the system, the liquid line shut off valve is

A

Closed at the receiver Outlet

288
Q

If the refrigeration system uses ammonia, the vacuum is broken

A

Gas and not liquid

289
Q

In small refrigeration systems, Frost formation on the compressor suction line indicates

A

Overcharging. This causes high suction and discharge pressures, and hi compressor power consumption.

290
Q

Refrigeration compressors are internally lubricated by

A

Hand pumps and pressure rated hoses with quick connectors

291
Q

Refrigeration compressors have _______ to show crankcase oil level

A

Bullseye gauge glasses. Normal oil level is about 1/2 the glass. If oil is low, first try to return Lube oil from the oil separators back to the crankcase

292
Q

Oil separators that do not automatically drain to the crankcase, may drain to

A

oil pots.

293
Q

Oil pots

A

Small pressure vessels left open to the system to gather oil.

294
Q

When a refrigeration system is shut down for a prolonged of time, it should be

A

Pump down and all refrigerant should be stored in the liquid receiver. This prevents unnecessary strain on the low pressure side of equipment and loss of refrigerant while system is shut down

295
Q

Direct expansion evaporator, it is essential that the evaporator be pumped down

A

Every time the compressor is shut down to make sure all refrigerant is removed from the evaporator. Prevents liquid slugging and compressor damage on Startup

296
Q

When shutting down compressor

A

Never pump down below 7 kPa to 14 kPa since a slight positive pressure is needed to prevent air from being drawn in through minor leakes on compressor shaft seal.

297
Q

Non condensable gases must be removed from the system either by

A

Manual or automatic purging.

298
Q

Purge connections are made at the

A

Highest point of the condenser and receiver, since this is where gases tend to collect

299
Q

Purgers

A

Refrigerate the mixture of refrigerant and non-condensable gases. The resulting liquid returns to the receiver. The non-condensable gases are vented to the atmosphere.

300
Q

The condenser and receiver should be purged

A

Separately

301
Q

Purger chilling coil

A

Causes vapour to condense and separate from the gas mixture, since non-condensable gases that enters the purger may carry a considerable amount of refrigerant vapour

302
Q

Whenever non condensable gases are released through the relief valve,

A

A small amount of refrigerant is always discharged with the gases. Refrigerant losses increase with size of installation

303
Q

Air-cooled condensers should not be cleaned with

A

Pressure washers, the high pressure water will bend the cooling fins and restrict airflow. Bent cooling fins can be straightened with a special comb

304
Q

Absorption systems require

4

A

A condenser, liquid receiver, expansion valve, evaporator

A compressor is not required

305
Q

Absorption system function 1

Absorber

A

A low pressure absorber containing a liquid (the absorbent), that withdraws the refrigerant vapour from the evaporator

306
Q

Absorption system function 2

Generator

A

A high-pressure generator that contains and heats up a concentrated absorbent / refrigerant solution. This drives the refrigerant Vapor out of solution and raises its vapour pressure

307
Q

Absorption system function 3

Heat source

A

A heat source that adds energy to the system

308
Q

Absorption system function 4

Pump

A

Pump that moves the concentrated solution from the low pressure absorber to the high pressure generator

309
Q

Many absorption systems are designed to use waste

A

Heat from boiler flue gas or gas turbine exhaust.

310
Q

Absorption system generator may be used for

A

Steam or hot water boiler needs to be kept in operation

311
Q

Electrical energy used by an absorption system is

A

Less than a similar capacity compression refrigeration system. Because pumps in an absorption system require less power than a refrigeration compressor. Also, smaller emergency generators can be installed

312
Q

Absorption system refrigerants

A

Use only natural refrigerants, like ammonia and water. Reduces contribution to global warming if a leak occurs, and by reducing electricity consumption and production of greenhouse gases

313
Q

In an absorption system, carry over from the evaporator

A

Will not cause damage. Permits continuous operation of the absorption system without changing set points or continuously monitoring of loading. Slugging and evaporator freezing are not a problem

314
Q

Absorption systems require more _________ then compression systems

A

Cooling water. Since the absorption condenser must reject the heat added in the generator plus the heat absorbed in the evaporator, which is way more than the heat of compression added by compressor

315
Q

More equipment and piping are needed for

A

An absorption system.

316
Q

Absorption systems are very ________ in operation

A

Quiet. Well-suited for concert Halls, theatres and other applications where noise of a compression system would affect human comfort.

317
Q

Water is used as the liquid absorbent in the ammonia absorption systems because

A

It has the ability to absorb ammonia Vapors in large quantities, and at a rate equal to the rate of vapour production in the evaporator

318
Q

Ammonia absorption system;

When the low temperature, low pressure vapour is discharged from the evaporator to the absorber

A

It dissolves into a spray of water. Rapid absorption of ammonia occurs by the absorber which maintains the low pressure in the evaporator. Forms a solution of refrigerant vapour and water which forms a concentrated aqueous solution, called strong aqua.

319
Q

Ammonia absorption system;

A pump transfers the strong aqua from the low-pressure absorber to the high-pressure generator.

A

In the generator, a heat source, raises the temperature of the strong aqua. This boils off the ammonia absorbed by the water in the absorber, producing high pressure, high temperature ammonia vapour. Water left in the generator is called week Aqua, which flows back to the absorber

320
Q

Absorption system high side

A

Consists of the generator and condenser

321
Q

Absorption system low side

A

Consists of the evaporator and the absorber

322
Q

Ammonia absorption systems are used in

A

Cold Storage, food processing, or other applications where extremely low temperature cooling is needed. Can be cooled in the -30°C range, which lithium bromide systems cannot.

323
Q

Ammonia absorption systems are seldom used in

A

Air conditioning purposes because of the toxic properties.

324
Q

Lithium bromide absorption systems are more suitable for

A

HVAC use

325
Q

Lithium bromide absorption systems

A

Large-capacity packaged water chillers, used in HVAC service. Use water as a refrigerant, and lithium bromide solution as the absorbent.

326
Q

Lithium bromide absorption system;

When water is the refrigerant, to lower the saturation temperature to a temperature useful for cooling

A

The system must operate under an extremely high vacuum

327
Q

Since very low temperatures are not required for air conditioning purposes, lithium bromide absorption systems maintain an evaporator temperature of

A

4°C to 7°C

327
Q

Two factors lithium bromide absorption units are based on

A

Lithium bromide has the ability to readily absorb water vapour

Water boils at low temperatures when under a high vacuum

328
Q

Lithium bromide absorption system

Generator is also called

A

A concentrator

329
Q

Absorption units are all built on the Hermetic principle, because

A

Air infiltration must be prevented. Parts of the units which are under vacuum or a completely seal welded.

330
Q

Crystallization

A

When a saturated solution is cooled, it will not be able to hold the same amount of salt in solution. Some salt will precipitate out of the solution

331
Q

Crystallization occurs when the temperature of a solution is

A

Lowered so far that it’s salt concentration exceeds the maximum concentration the solution can hold at that lower temperature.

332
Q

Crystallization of a solution is a problem in

A

Lithium bromide systems. When it occurs, the precipitated salt can restrict or block circulation

333
Q

Lithium bromide absorption system

The Vapor pressures, depends on the temperature and concentration of

A

The solution in each section

334
Q

The solution in the absorber is not in equilibrium since

A

More molecules of water vapour are absorbed than leave the solution. The solution becomes increasingly dilute

335
Q

Two reasons for mixing dilute and concentrated Solutions together to form an intermediate solution

A

If the concentrated solution is sprayed directly on absorber cooling coils, it’s temperature would drop below that required to keep the salt in solution, and salt crystals would precipitate. Dilution prevents this

A higher solution flow rate is required in the absorber than in the concentrator. Some recirculation of the dilute solution is required to obtain this higher rate

336
Q

Before a lithium bromide absorption system is shut down, it must go through

A

A dilution cycle. During the cycle to dilute and concentrated Solutions are mixed so that crystallization is prevented when the temperature drops during the shutdown.

337
Q

Crystallization is of particular concern when

A

A power failure occurs and the unit cannot operate through its normal dilution cycle

338
Q

Heat exchanger bypass

A

Pipe that leads from the concentrator to the absorber

339
Q

The purpose of the heat exchanger bypass is to;

2

A

Limits the level of the solution in the concentrator by bypassing it’s solution directly back to the absorber

The bypass conducts the full flow of hot concentrated solution directly back to the absorber, in case the regular return through the heat exchanger is blocked by crystallization

340
Q

The lower loop of the bypass tube is filled with solution at all times. This forms

A

A loop seal between the high and low pressure side of the system

341
Q

The concentrator, absorber, and evaporator circulating pumps used on an absorption unit are of the ______

A

Hermetic type, to prevent infiltration of air in this High vacuum unit.

342
Q

Most common cause of non condensable gases in absorption systems

A

An air leak somewhere in the unit. There are always some non condensable gases in an absorption unit

343
Q

Non condensable gases has the following effects on absorption units
3

A

Reduced capacity and higher chilled water Outlet temperature

Crystallization

Corrosion

344
Q

Purge chamber

A

Basically a small absorber.

345
Q

Octyl alcohol charge

A

Wetting agent that helps the lithium bromide solution absorb water vapour, increasing the efficiency of the system. Should be added to the system

346
Q

Log sheets

A

Best way to spot gradual changes in performance of the absorption unit.

347
Q

The degree of Hazard in a refrigeration system depends on

5

A

Toxicity or flammability of refrigerant

Amount of refrigerant in system

Building occupancy class

Leakage probability of the system

Internal pressure of refrigeration system

348
Q

Refrigeration safety limit controls set at to not more than

A

90% of the system high side design pressure

349
Q

Safety valves installed on compressors usually discharge to

A

The low side of the system. So that when pressure is relieved, refrigerant is contained within the system

350
Q

3-way safety valve

A

Places only one valve in service at a time. Allows one valve to be isolated so it can be tested, recertified, serviced or replaced.

351
Q

CSA B-52 requires overpressure protection for lengths of pipe that contain liquid refrigerant

A

And can be isolated. Because, if a section of pipe is isolated and the temperature increases, hydrostatic liquid expansion May over pressurized pipe and fittings

352
Q

Size of water tank needed to absorb ammonia charge

A

Tank must be large enough to contain the water and ammonia without overflowing. Tank must be kept warm so water does not freeze.

353
Q

The owner of a refrigeration system must provide

A

Directions for operating system, precautions in case of breakdown or leakage. Instructions in a conspicuous location near as practical to the compressor

354
Q

Anything moist attracts and dissolves ammonia, forming

A

Highly corrosive ammonium hydroxide. Exposure to ammonia, will damaged eye tissue, mucous membranes, and skin. If inhaled, damages the lungs

355
Q

When ammonia is released to the atmosphere,

A

It dissolves readily in atmospheric moisture, forming a dense, caustic White Cloud. Never enter a cloud of ammonia.

356
Q

At atmospheric pressure, ammonia boils at _____

It also has a very high ________

A

-33°C

Latent heat of evaporation. Even a small amount sprayed on skin or eyes can cause frostbite and chemical burns

357
Q

Those exposed to ammonia regularly may have a reduced ability to detect it by smell. Therefore,

A

The nose should not be used to assess ammonia concentrations.

358
Q

Personal protective equipment should be used when there’s a possibility of ____ exposure to ammonia

A

50ppm

359
Q

Before hot work is performed on refrigerant lines

A

Must be purged using inert gas to reduce combustion and toxicity hazards. Must be leak detected after work is completed

360
Q

Refrigerant cylinders must be stored

A

A safe distance from an open flame or hot surface. Handled with care, because of potential of frostbite due to escaping liquid refrigerant

361
Q

Any routine maintenance activity that may create a discharge of refrigerant,

A

Should be performed with the aid of a buddy. But he should have water source available and means of signalling for emergency assistance.

362
Q

If the operator draining oil is overcome by fumes or must abandon the work station due to emergency,

A

The drain could be left open causing a deadly release of refrigerant. A self-closing emergency stop valve, Deadman valve, could be used.

363
Q

According to the International Institute of ammonia Refrigeration (IIAR), ammonia piping labels must have;

A

The word “ammonia” in Black letters on an orange background. An arrow indicates direction of refrigerant flow. Label also has several colour bands.

364
Q

One band shows the refrigerant _____

Another band indicates weather the piping is ___

A

State:
Yellow=liquid
Blue=vapour
Both bands=liquid and vapour

High side or low side:
Red=high pressure
Green=low pressure

365
Q

Valves should be identified with;

A

A permanent tag that will not fade or fall off.

Include; valve number, fluid, and State

366
Q

Employers must provide, and ensure that

A

Workers wear, appropriate personal protective equipment. Impervious clothing, gloves, Splash proof goggles, face shield

367
Q

If a refrigerant leak occurs and there’s no way to identify potential for workers or facility occupants exposed to respiratory hazard, the leak must be considered

A

LDLH and appropriate emergency response taken

368
Q

According to OSHA, the PEL for ammonia is a Time weighted average of

A

50 PPM

369
Q

Persons trapped in an ammonia leak should

A

Breathe as little as possible and open their eyes only when necessary. Some protection is possible with a wet cloth covering the nose and mouth. Remain close to the door, since ammonia Vapor Rises. Then proceeded to source of ventilation air by traveling against the airflow

370
Q

Persons exposed to ammonia should be

A

Removed to a warm, fume free location, placed in a reclining position with Head and Shoulders elevated. Keep warm with blankets

371
Q

If liquid ammonia contacts a person’s skin

A

Brought to a safety shower and the affected area flooded with water for 15 minutes. If no shower available, body parts immersed in relatively warm water, victim’s clothing may be frozen to the skin.

372
Q

If ammonia enter the nose or throat but victim can still swallow

A

Drink large quantities of water

373
Q

If eyes made contact with ammonia

A

Wash with clean water for at least 30 minutes. Eyelids must remain open

374
Q

Workers in refrigeration plant should not wear

A

Contact lenses

375
Q

Ammonia Refrigeration plants require an E2 plan if the total amount of refrigerant on-site equals

A

4.5 tonnes

376
Q

When using a Deadman valve, never

A

Prop open the spring loaded handle. Propping it open renders it ineffective

377
Q

The secondary refrigerant is often called the

A

Brine system. Describes the secondary refrigerant, which includes salts and glycols.

378
Q

The use of a brine system prevents the main refrigerant, which may be hazardous, from

A

Circulating in public areas. Also allows refrigeration system to use multiple evaporators providing brine at different temperatures

379
Q

Salinity test

A

Common brine System test. Uses a hydrometer to test the concentration of the brine

380
Q

Ammonia refrigeration systems require regular testing of

A

The brine for any levels of ammonia. Presence of ammonia in the brine indicates a leak in the primary refrigerant piping and must be dealt with.

381
Q

At least once per year, a sample of the secondary refrigerant should be

A

Drawn and sent out to a qualified lab facility for a complete analysis

382
Q

Testing the specific gravity and freezing point of brine indicates

A

The strength, concentration, of the brine.

383
Q

The secondary Refrigeration side of the system is the

A

Pump and piping that will move the brine to the area being cooled

384
Q

When liquid evaporates it _________

When liquid condenses it ________

A

Absorbs heat

Releases heat

385
Q

Ammonia is explosive in concentrations of

A

15 to 28% volume in air

PE 4B (8 decks)

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