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B10 Flashcards

1
Q

Absolute humidity

A

The mass of moisture (i.e. water vapour) present in one kilogram of an air/moisture mixture. The measurement unit for absolute humidity is kg/kg

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2
Q

Air conditioning

A

The simultaneous control of the physical and the chemical conditions of the atmosphere within a structure. This is achieved by affecting some or all of the following air conditions: temperature, humidity, motion, distribution, pressure, and filtration (dust, bacteria, odours, toxic gases, and ionization.)

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3
Q

Air diffuser

A

Air distribution outlet or grille designed to direct airflow into desired patterns.

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4
Q

Air washer

A

A mechanical device placed in an air stream to cool, clean, humidify, or dehumidify the air.

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5
Q

Air handling unit

A

A machine comprised of a fan, a filter, a heater, a cooler, and a humidifier,
used to supply conditioned air in an HVAC system.

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6
Q

Axial flow fan

A

A fan that supplies air parallel to the direction of the fan shaft.

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7
Q

Centrifugal fan

A

A fan that supplies air perpendicular to the fan shaft. Centrifugal fans are classified according to the shape and design of the fan blades: backward inclined, forward curved, backward inclined with airfoil blades, and radial blades.

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8
Q

Charged media air cleaner

A

An electrically charged fibreglass or cellulose filter mat, installed in an air stream, which efficientlv removes particulate matter.

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9
Q

Conduction

A

The transmission of heat through and by means of matter unaccompanied by any obvious motion of the matter.

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10
Q

Convection

A

Transfer of heat by means of movement or flow of a liquid or gas.

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11
Q

Damper

A

Device to control air flow

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12
Q

Dew point

A

The temperature at which air subjected to cooling becomes saturated and below which the water vapour will begin to condense out of the moist air.

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13
Q

Dry air filter

A

A matting of fine tangled fibrous material, placed across an air duct or plenum, to remove particulate from an air stream.

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14
Q

Dry bulb temperature

A

The temperature of a gas or mixture of gases indicated by an accurate thermometer when there is no latent heat flow from the thermometer.

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15
Q

Duct system

A

In HVAC systems, a collection of large interconnected ducts, fans, filters,
coils, dampers, and louvres for moving air to and from conditioned spaces.

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16
Q

Effective temperature (ET)

A

The overall effect of air temperature, humidity, and air movement on human comfort.

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17
Q

Electronic air cleaner

A

An air purification device that imparts an electrical charge to particles in an air stream causing them to collect on an oppositely charged plate

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18
Q

Evaporation

A

Term applied to the changing of a liquid to a gas. Heat is absorbed in this process.

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19
Q

Fire damper

A

A steel frame equipped with steel dampers, which fit tightly in the casing when closed. The damper is activated by the melting of a fusible link

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20
Q

Fixed louvres

A

A non-adiustable assembly of blades that direct airflow.

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21
Q

High efficiency particle air (HEPA)

A

An air filter capable of removing particles as small as 0.3 micron in diameter with 99% efficiency. They are commonly used in hospitals, laboratories, and other facilities requiring supply air nearly free of particles.

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22
Q

Humidity

A

The presence of moisture in the air

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23
Q

HVAC stands for

A

Heating, ventilation, and air conditioning

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24
Q

Makeup air

A

In an HVAC system, the fresh air supplied to an occupied space to replace stale, oxvgen depleted, and possibly smelly air in the building or system

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25
Q

Mechanical ventilation

A

The use of fans to recirculate, exhaust, and supply fresh air to occupied spaces.

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26
Q

Mixed air

A

In an HVAC system, a mixture of make-up air and return air that is to be recirculated in a building or system.

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27
Q

Natural ventilation

A

Passive ventilation achieved by permitting airflow through building openings. such as windows and doors, without the use of fans.

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28
Q

Odour absorber

A

A method of removing objectionable vapours in an air conditioning system, by exposing the air stream to activated carbon or activated potassium permanganate.

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29
Q

Opposed blade damper

A

Dampers with blades linked so that adjacent blades rotate in opposite
directions. Opposed blade arrangements are superior when modulation of airflow is required.

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30
Q

Parallel blade damper

A

Dampers consisting of two or more blades linked together in such a way
that all blades rotate in the same direction. This type is often used on mixing boxes where sets of dampers are used to direct airflows toward each other for good mixing.

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31
Q

Preheat coil

A

In an HVAC system, a device for raising the temperature of extremely cold outside air to prevent freezing of downstream equipment.

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32
Q

Relative humidity (RH)

A

The ratio of the amount of water vapour in the air to the amount water
vapour that the air can hold at a given temperature.

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33
Q

Relief Damper

A

A passive damper comprised of a series of interconnected, weighted blades that open and close simultaneously, due to differences in static pressure across the blades. Relief dampers are used to relieve excess building static pressure and prevent cold air from entering a building.

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34
Q

Return air

A

In an HVAC system, the air returning from a ventilated space, to be reheated, recooled, filtered, humidified, or exhausted.

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35
Q

What does SMACNA stand for

A

Sheet Metal and Air Conditioning Contractors’ National Association

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36
Q

Specific humidity

A

The mass of moisture (i.e. water vapour) present in one kilogram of an air/moisture mixture. The measurement unit for absolute humidity is kg/kg.

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37
Q

What is specific humidity also called

A

Absolute humidity

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38
Q

Static pressure (duct)

A

The pressure exerted by the air on duct, pipe, or vessel walls.

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39
Q

Stationary air louvres

A

Louvres used in fresh air intake openings to minimize the amount of water and snow entering an air handling system.

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40
Q

Supply air

A

In an HVAC system, conditioned air that is delivered to an occupied space.

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41
Q

Total pressure

A

The sum of static pressure and velocity pressure.

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42
Q

Tube axial fan

A

A heavy-duty propeller fan suitable for duct mounting.

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43
Q

Vane axial fan

A

A tube axial fan equipped with guide vanes located behind the fan wheel to straighten out the spiral flow of air.

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44
Q

Velocity pressure

A

The pressure caused by the impact of the air flowing through a duct or pipe.

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45
Q

Ventilation

A

An HVAC process that supplies or removes air from an occupied space.

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46
Q

Viscous

A

Thick and sticky

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47
Q

Wet bulb depression

A

The difference between the wet-bulb and dry-bulb temperatures as measured with a psychrometer, for the calculation of relative humidity.

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48
Q

What does a heating process increase?

A

Air temp

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49
Q

What does a cooling process remove

A

Heat from the air

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50
Q

What does a filtration process remove?

A

Particles from the air

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51
Q

What does a ventilation process do?

A

Remove or supply air

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52
Q

What does a humidification process control?

A

The humidity in the air

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53
Q

Heating, cooling, filtration, ventilation, and humidification are all also called?

A

Air conditioning

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54
Q

(True or false)
Each building is required to change the air in the building

A

True

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55
Q

How often does building air change?

A

Per hour

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56
Q

How is building air change measured

A

m3/hour

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57
Q

What are fans used for?

A

To supply fresh air and to exhaust air

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58
Q

Why is exhausting air important?

A

The air may contain odours, excess humidity, CO and other contaminants that may have an adverse effect on people’s health.

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59
Q

Why isn’t 100% makeup air used?

A

It is costly

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60
Q

HVAC systems usually include:(6)

A

Fans, filters,ducting, heating coils, cooling coils, and humidity control

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61
Q

HVAC systems must have a way to?

A

Distribute air and methods of controlling the flow of air entering and leaving a building.

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62
Q

What is the purpose of HVAC?

A

To improve the comfort of people occupying the building space.

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63
Q

What are the factors that influence human comfort? (4)

A

Temp, humidity, air quality and air movement.

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64
Q

What does air quality refer to?

A

Odours, particulates and other conditions that may affect human health.

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65
Q

Air movement refers to?

A

The velocity, noise, drafts and air circulation in general.

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66
Q

When does heat shock occur?

A

When differences between indoor and outdoor temps are substantial.

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67
Q

How to prevent heat shock?

A

Providing a gradual decline in temp that minimizes the steep differences between indoor and outdoor temp near entrances.

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68
Q

In hot conditions what does HVAC treat?

A

High temp and high humidity (RH)

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69
Q

In cold conditions what does HVAC treat?

A

Low temp and low humidity

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70
Q

(True or false) the thermal and atmospheric conditions in a space does not need to be controlled.

A

False
(The thermal and atmospheric conditions in a space MUST be controlled)

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71
Q

What is the key criterion for the design of HVAC systems?

A

Human health

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72
Q

What does high humidity increase the chances of?

A

Mold to form inside the building.

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73
Q

The human body is like a furnace, using food as fuel, what temperature should it be constantly kept at?

A

37°c

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74
Q

A sensitive temperature regulating mechanism allows continuous transfer of?

A

Heat by conduction, convection, radiation and evaporation.

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75
Q

What is the heating function in a HVAC system?

A

source of heat is required to ofset the beat loss to the atmosphere surrounding the building through exterior walls, the roof, floor slabs on grade, and basement walls. The heat must be, every distriaked in all areas of the building. (Aka to balance heat loss and evenly distribute it)

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76
Q

What is the cooling function in a HVAC system?

A

A source of cooling is required to offset the heat gain through the buildings exterior shell from balance hear gain solar radiation and the atmosphere surrounding the building, as well as from internal sources of heat. The cooling must be effectively distributed to ensure that comfort conditions are maintained throughout the building. (Aka balance the heat gain, and evenly distribute it)

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77
Q

What is the function of ventilation in a HVAC system?

A

Provision of outside air into the building is required to replenish the oxygen supply for the occupants . Also, outdoor air is necessary to dilute odours which which develop in the building and provide make-up air for the rooms having exhaust systems, thus maintaining an acceptable air balance in the building. (Aka to replenish O2 and make air balanced)

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78
Q

What is the function of humidification in a HVAC system?

A

When the relative humidity of the outdoor air is low, moisture must be added within the building-If low add moisture to maintain acceptable conditions for human comfort, Also, this moisture minimizes the effects of static electricity, which may be important for proper operation of sensitive equipment within the building. (Aka if low add moisture)

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79
Q

What does humidification minimize?

A

Static electricity

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80
Q

What is the disadvantages of humidification?

A

•Can create mold + Ca
•bad for sensitive equipment

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81
Q

What is the function of a dehumidifier in a HVAC system?

A

A method of removing excessive moisture from the building may be required to maintain a relative humidity acceptable to occupants and for operation of sensitive equipment. Also, in colder climates, dehumidification may be required in humid areas, such as swimming pools, to prevent structural damage during winter due to frost formation in exterior walls. (Aka if high, removes moisture)

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82
Q

What is the function of air circulation in a HVAC system?

A

Air movement is required in each space to assist in dissipation of body heat from occupants and prevents a buildup of odours which may develop in stagnant areas. (Aka prevents odour)

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83
Q

(True or false) it is possible to find exact conditions that are satisfactory for all people.

A

False

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84
Q

Is effective temperature (ET) an actual temperature?

A

No it is not an actual temperature.

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85
Q

What are the 3 combined things that effective temperature (ET) measures?

A

•dry bulb temp
•relative humidity (RE)
•air movement

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86
Q

What should the the relative humidity be kept between during summer? (%)

A

30% - 70%

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87
Q

What happens if relative humidity is above 70%?

A

Air will feel muggy and gross no matter the temperature.

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88
Q

What happens if the relative humidity is below 30%?

A

Air becomes too dry and affects nasel membranes

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89
Q

An increase in air flow increases?

A

Heat loss of the body

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90
Q

How does increased air flow increase the heat loss of the body? (3)

A

•conduction
•convection
•evaporation

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91
Q

What is a good example of cooling by increasing the air flow?

A

Use of an electric fan

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92
Q

What is the measurement of airflow that is considered to be relatively still?

A

4.6m-7.6m/min

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93
Q

What is the measurement of airflow that is considered to be a draft?

A

19.8m/min

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94
Q

If rooms are on the side of the house where the sun shines on how should they be kept?

A

Cooler

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95
Q

How should rooms on the north side or exposed to the wind be kept?

A

Warmer

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96
Q

To prevent discomfort when occupants are in a building for a short time, how should the air temperature be kept?

A

Higher

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97
Q

What % of people will not be satisfied now matter how the temperature conditions have changed?

A

2%

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98
Q

How is air mainly conditioned?

A

In a air handling unit

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99
Q

Typical air handling units may include:(6)

A

•fan
•filters
•humidifier
•heating coil
•cooling coil
(And maybe a humidifier/dehumidifier)

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100
Q

Many medium to large systems utilizing return air and mixed air may require?

A

An exhaust or return fan

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101
Q

What are exhaust/return fans used for?

A

Used to overcome friction losses

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102
Q

Noise dampening is the result of?

A

The air flowing at a high velocity

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103
Q

What are air filters required to remove from recirculated air and from outside air before introducing it into the building. (5)

A

Dust, dirt, smoke, pollen and lint.

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104
Q

Because each application is unique, what are the requirements that very in accordance?(5)

A

•geographical location
•local weather conditions
•type of occupancy
•building layout
•construction

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105
Q

What does forced air systems provide?(4)

A

Heating, filtration, circulation, and ventilation.

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106
Q

What is required to maintain satisfaction year round in larger residences located in areas with very cold winters, and super hot summers?

A

A more complex system

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107
Q

What’s an advantage of of a full recirculation (100%)?

A

Lower in operating costs

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108
Q

What’s a disadvantage of of a full recirculation (100%)?

A

Air over time becomes muggy and gross

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109
Q

What is the supply air drawn through in a fixed outdoor air percentage system?

A

Non modulating dampers

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110
Q

What percent of outdoor air do non modulating dampers permit?

A

10%-30%

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111
Q

HVAC system with fixed outside air and return air dampers are cheaper than ones using variable percentages of outdoor air because?

A

They do not use control systems to modulate the dampers.

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112
Q

(True or false) fixed outdoor air systems are not able to respond as well to weather changes.

A

True

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113
Q

What is the ratio that a variable mixed percentage air handling system will vary?

A

Makeup air : recirculated air based on climate conditions

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114
Q

(Variable mixed percentage air handling system)
On a cold winter day what will the ratio of makeup air : recirculating air be?

A

Makeup air % will be reduced, and more air will be recirculated.

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115
Q

(Variable mixed percentage air handling system)
On a hot summer day what will the ratio of makeup air : recirculating air be?

A

Higher % of makeup air, lower % of recirculating air.

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116
Q

Advantage of Variable mixed percentage air handling systems?

A

Balances human comfort while maintaining reasonable operating costs.

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117
Q

Disadvantage of Variable mixed percentage air handling systems?

A

Costly to install

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118
Q

Where are Variable mixed percentage air handling systems typically installed?

A

•residential buildings
•commercial buildings
•industrial buildings

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119
Q

Where does air first travel in HVAC unit basic with no controls?

A

It first travels through an air filter.

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120
Q

What is the most common air filter?

A

Media types

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121
Q

If the air quality requires higher filtration, what type of filter is used?

A

Electronic filter

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122
Q

How is air heated or cooled?

A

Heating coils or cooling coils.

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123
Q

What do heating coils use to heat?(3)

A

•hot water
•glycol
•steam
(Even though some are electric)

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124
Q

What do cooling coils use to cool/ dehumidify? (2)

A

•chilled water
•liquid refrigerant

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125
Q

Advantages of 100% makeup/ outdoor air handling units?

A

Air will not be muggy or contain large amounts of odours.

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126
Q

Disadvantage of 100% makeup/ outdoor air handling units?

A

Operational costs are very high because no recirculated air is used.

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127
Q

Where are 100% makeup/ outdoor air handling units used? And why?3)

A

Used where there are harmful chemicals in the air.
•garages
•operating rooms
•laboratories

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128
Q

What is pure dry air?

A

It is an invisible, odourless, tasteless mixture of gases that surround the earth.

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129
Q

What is the composition of dry air?

A

•23.2% of oxygen and 76.8% nitrogen by mass
•21% of oxygen and 79% nitrogen by volume

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130
Q

Why does completely pure and dry air not occur in nature?

A

Many contaminants are found in the air. Ex(dust, smoke, bacteria,pollen, fumes…ect)

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131
Q

Moisture in the air is not water droplets, it is?

A

Water that has been evaporated into a Vapour, which is thoroughly mixed with the air and occupies in the same space.

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132
Q

What vapour in the air is actually?

A

Low pressure, low temperature steam.

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133
Q

How can there be steam at atmospheric pressure while the temperature is well below the boiling point of water?

A

while the mixture of air and water vapour is at atmospheric pressure, the water vapour itself is not. It is actually at an extremely low pressure. It is known that the temperature at which water vaporizes gets lower when the pressure is reduced, and water will vaporize into steam even at temperatures down to 0°C, provided the is low pressure is low enough.

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134
Q

The formula for calculating relative humidity (RE) is?

A

Actual mH2O
———————- x100%=RH
Max mH2O

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135
Q

Relative humidity (RE) and temperature are inversely related, this means?

A

•When temp increases, RE decreases
•when RE increases, temp decreases

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136
Q

The amount of water air can hold depends on?

A

The temperature

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137
Q

The change in temperature changes the relative humidity, IF _______ _______ remains constant.

A

Absolute humidity

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138
Q

When is the dew point reached?

A

Water vapour contained = Max amount air will hold at a low temperature.

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139
Q

What does it mean when relative humidity is 100%

A

It is fully saturated

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140
Q

When a liquid in glass thermometer is used to measure the temperature of air, the temperature sensitive element of the thermometer (bulb) is dry, the temperature is measured with?

A

An ordinary thermometer called a dry bulb temperature.

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141
Q

is the temperature indicated by a thermometer having its bulb covered by a water-wetted wick, which is exposed to a stream of rapidly moving air is called?

A

Wet bulb temperature

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142
Q

How does the wet bulb thermometer measure temperature?

A

It measures the dry bulb temperature, and then subtracts the cooling effect of evaporation.

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143
Q

How do you maintain a constant Relative humidity?

A

Moisture must be added to the air when it’s temperature increases.

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144
Q

In winter months if the temperature is low, then the actual mass of water vapour the air can hold is?

A

Low

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145
Q

If the actual mass of water Vapour air can hold is low, it causes?

A

Air to feel very dry

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146
Q

If the actual mass of water vapour air can hold is low, and only heat is added, the relative humidity will decrease resulting in?

A

The air feeling even drier, be tough the actual mass of water vapour has not changed.

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147
Q

What is the purpose of humidification, and what is the process?

A

•The purpose of humidification is to increase the relative humidity to the air
•the process adds moisture to heated air.

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148
Q

A dry indoors can cause?

A

•Throat and nose membranes to to dry causing discomfort and cracked lips.
•it also causes a static charge to build up.

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149
Q

What is the result of having a static charge built up, due to dryness?

A

an electric shock caused by the discharge of this static electrical charge, when any metallic object, or even another person, is touched.

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150
Q

The amount of moisture that air absorbs depends on?

A

The pressure and temperature of the air.

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151
Q

(True or false) the higher the air temperature, the more moisture it can absorb. (Vise versa)

A

True

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152
Q

Why does indoor air get so dry during cold weather, even though air at the outside temperature is saturated?

A

Because when the air temperature is raised without the addition of moisture, relative humidity drops.

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153
Q

When outside air is continually drawn into a building for ventilation purposes where is it heated, and what is the result?

A

•it is heated directly in the heating system or by mixing with room air.
•the result is relative humidity drops sharply = dryness

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154
Q

From a health stand point what is the desired % of relative humidity?

A

Between 35%-50%

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155
Q

Having the relative humidity between 35%-50% in colder climates, can result in?

A

May create a condensation problem on the cooling surfaces of walls, windows and ceilings = damaging the structure.

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156
Q

What do you do to prevent condensation in colder climates?

A

Lower the relative humidity

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157
Q

(True or false) in residences with a non- ducted heating system those using steam, hot water, or electric radiant heat humidification is possible.

A

False (in residences with a non- ducted heating system those using steam, hot water, or electric radiant heat humidification is NOT POSSIBLE.

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158
Q

What are the 3 types of humidifiers used for residential purposes and warm air systems?

A

•pan
•wetted element
•atomizing

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159
Q

Pan Type Humidifier with Plates consists of _________ partially filled with water.

A

A shallow pan (or tray)

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160
Q

In Pan Type Humidifier with Plates what part of the absorbent plate is immersed in water?

A

The lower part of the absorbent plate.

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161
Q

In Pan Type Humidifier with Plates, water is drawn to the surface of the plates by?

A

Hygroscopic action

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162
Q

In Pan Type Humidifier with Plates, what does the warm air passing over the plate cause?

A

The water to evaporate and the vapour to be carried off by the air.

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163
Q

In a Pan Type Humidifier with Plates, what is used to control the water level in the tray?

A

An automatic float valve

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164
Q

In a Wetted Element Humidifier, the unit makes use of?

A

water saturated evaporation pad through which warm air is forced.

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165
Q

In a Wetted Element Humidifier, what are the two types of pads used?

A

Flat or cylindrical

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166
Q

In a Wetted Element Humidifier, how is the water supplied to the pad?

A

water is supplied to the flat pad either by gravity from a distribution pan above the pad, or by a spray.

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167
Q

In a Wetted Element Humidifier, what is used to control water supply to the pad?

A

A solenoid valve

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168
Q

In a Wetted Element Humidifier, Cylindrical pads rotate through a tray partially filled with water, the level in this tray is controlled by?

A

A Float valve

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169
Q

In a Atomizing Humidifier, what is used to break water into small particles?

A

using either a spinning disc, or cone, or a spray nozzle.

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170
Q

I’m the basic spinning type humidifier,what atomizes water into a fine mist?

A

A rapidly rostering disk

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171
Q

The basic spinning disc type humidifier is usually used as?

A

A room unit, either portable or stationary.

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172
Q

In the spray humidifier, water under pressure is forced through a nozzle that breaks the water up into?

A

A fog, which is then absorbed by air.

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173
Q

In a spray humidifier, what controls to the spray, by means of a solenoid valve?

A

A humidistat

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174
Q

Most water contains?

A

Dissolved mineral salts

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175
Q

When water evaporates in the humidifier, where do the salts stay?

A

In evaporation plates and pads.

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176
Q

What can occur when salts are built up to an extent?

A

Clogging occurs, and proper evaporation is prevented.

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177
Q

To keep humidifiers in top condition, the plate units should be cleaned by?

A

soaking them in a slightly acidic solution and then washing them in soapy water.

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178
Q

The tray or pan should also be cleaned out to remove?

A

The salt build up

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179
Q

The float and solenoid valves should be checked for?

A

Leakage

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180
Q

The nozzle of atomizing humidifiers can easily plug if?

A

Solids are present

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181
Q

What is recommended To minimize/ prevent solids plugging the nozzles in atomizing humidifiers ?

A

The use of a fine screen in a supply line.

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182
Q

What is the disadvantage of atomizing humidifiers?

A

since the water is sprayed into the air the salts in solution in the water appear as a fine white dust which settles in ducts and rooms. Regular deaning is then required to remove this dust.

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183
Q

How is water softened?

A

By ion exchange

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184
Q

The residue from ion exchange will be increased because?

A

the magnesium and calcium salts will be replaced by sodium salt.

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185
Q

What are the 3 basic types of humidifiers used for HVAC?

A

•air washers
•steam grid humidifiers
•pan type humidifier

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186
Q

What is the most versatile pieces of equipment used in HVAC systems?

A

Air washer

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187
Q

What is the main purpose of air washers?

A

the humidification of air, but in combination with humidification

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188
Q

Air washers are also used to:(4)

A

•heat
•cool
•dehumidify
•clean the air

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189
Q

Air washers consist primarily of?

A

a casing and a spray chamber, in which a bank of spray nozzles is installed.

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190
Q

Other washers have two or even three banks of sprays for?

A

Increased efficiency

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191
Q

What happens when the air flows through the spray chamber and comes in contact with the spray water?

A

The air humidity increases, but the air stream entrains some water droplets.

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192
Q

I’m air washers, what are installed at the outlet of the washer to prevent droplets of water from being carried away by the air?

A

Eliminators

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193
Q

In air washers, eliminators are designed to?

A

change the direction of the airflow several times, causing the droplets to impinge and run down the surface of the eliminators into the bottom of the tank.

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194
Q

In air washers, what washes dust particles down?

A

continuous stream of water from the flooding nozzles washes them down.

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195
Q

In air washers, Some odours are also removed by them, but are not effective in removing?

A

greasy particles, soot or tobacco smoke.

196
Q

In an air washer, the spray water collects in the bottom tank and is usually recirculated to the?

A

Sprays by a pump.

197
Q

In a air washer, the level in the tank is maintained by?

A

A float controlled makeup valve

198
Q

An air washer should be installed on?

A

the suction side of the fan where it can be maintained at a pressure slightly below that of the atmosphere in order to avoid leakage of water through the joints.

199
Q

When the air washer is used for humidification, the spray water must be heated above?

A

the dew point temperature of the entering air.

200
Q

When the air washer is used for both heating and humidification, the spray water must be heated above?

A

the dry bulb temperature of the entering air.

201
Q

When the air washer is used for both heating and humidification, the spray water must be heated above?

A

the dry bulb temperature of the entering air.

202
Q

What is achieved when the air washers uses spray water that is cooled to a temperature below the dew point temperature of the entering air?

A

Cooling and dehumidification

203
Q

What 3 methods are used to maintain the spray water at the desired temperature in air washers?

A

•Only part of the spray water is recirculated and hot or cold water is added as needed.
•The spray water is recirculated through a heat exchanger and is either heated or cooled by hot or chilled water.
•a heating or cooling coil is directly mounted in the sump of the washer.

204
Q

When steam is available, humidification can be achieved with a steam grid humidifier by?

A

Injecting steam into the supply air stream .

205
Q

Steam grid humidifiers are found where?

A

They are found where humidity is already achieved.

206
Q

Why do steam grid humidifiers use steam to inject into the supply air stream?

A

They use steam because it is already a vapour, which is easier to carry.

207
Q

Steam grid humidifiers comes complete with a drain pan to?

A

Catch the condensate droplets.

208
Q

In a steam grid humidifier, To achieve satisfactory results, the steam pressure should be in the range of?

A

35kpa-70kpa

209
Q

Why do steam grid humidifiers have to keep the steam pressure in a specific range?

A

to prevent splashing of condensate and an objectionable increase in the temperature of the supply air.

210
Q

In a steam grid humidifier, Good control of the humidity is achieved by using?

A

a steam modulating control valve, actuated by a humidistat located in the room or in the return air stream.

211
Q

In a steam grid humidifier, Good control of the humidity is achieved by using?

A

a steam modulating control valve, actuated by a humidistat located in the room or in the return air stream.

212
Q

In a steam grid humidifier, why are on/off controls not recommended?

A

Fogging, over heating, and wide fluctuations in the relative humidity would occur.
(If turned off, there would be no flow which would result in steam condensing)

213
Q

In a steam grid humidifier, what does the baffle at the entrance of the chamber knock down?

A

any condensate formed in the supply line or manifold jacket.

214
Q

In a steam grid humidifier, the condensate that collects in the drain leg, is removed by?

A

A trap.

215
Q

In a steam grid humidifier, The steam then flows upward to the control valve which regulates?

A

the supply of steam to the manifold at a pressure slightly above atmospheric.

216
Q

In a steam grid humidifier, where is the steam first directed to?

A

Downward to the re evaporating chamber.

217
Q

In a steam grid humidifier, any entrained liquid is separated by?

A

the 180° turn the steam must make before it can enter the manifold.

218
Q

In a steam grid humidifier, what is the temperature and pressure of the re-evaporating chamber that is surrounded by the steam in the separating chamber?

A

High pressure, high temperature.

219
Q

In a steam grid humidifier, the latter is referred to as?

A

Clean steam humidification.

220
Q

In a steam grid humidifier, The dry, low-pressure steam then flows into the?

A

Distribution manifold.

221
Q

In a steam grid humidifier, The dry, low-pressure steam then flows into the?

A

Distribution manifold.

222
Q

In a steam grid humidifier, the steam used can cause health problems if?

A

If it contains chemicals such as Amines.

223
Q

In a steam grid humidifier, what circulates with the steam?

A

Neutralizing and filming amines.

224
Q

In a steam grid humidifier, what is the disadvantage if steam carrying amines is used for humidification?

A

The amines can be inhaled, negatively impacting human health.

225
Q

Since steam in steam grid humidifiers can be bad for human health, humidification steam must be of?

A

High purity

226
Q

Clean steam humidification uses a heat exchanger that is supplied with?

A

High or low pressure steam as the heat source.

227
Q

In clean steam humidification, the heat will be added to?

A

Demineralize the water and cause it to boil into low pressure clean steam

228
Q

Since clean steam humidification requires a heat exchanger to be used in conjunction with the steam boiler, what is the disadvantage?

A

It is a relatively expensive method of humidification.

229
Q

In clean steam humidification, the piping or fittings that will contact the demineralized water or steam must be made of?

A

Stainless steel

230
Q

Applications for clean steam humidification are: (4)

A

•hospitals
•archives
•pharmaceutical industries
•museums

231
Q

Applications for clean steam humidification are: (4)

A

•hospitals
•archives
•pharmaceutical industries
•museums

232
Q

Why are clean steam humidifiers used for hospitals and pharmaceutical industries?

A

That want air to be as clean as possible.

233
Q

Why are clean steam humidifiers used for museums, and archives?

A

It doesn’t cause leeching, or a coating of hardness or scale on the artifacts/paintings.

234
Q

In clean steam humidifiers demineralization is?

A

Soft water that usually comes out of a deaerator.

235
Q

the pan type humidifier consists of a water pan equipped with?

A

a float valve assembly, overflow and drain connections, as well as a steam or an electric heating coil in the pan.

236
Q

In a pan type humidifier moisture is added to the airstream by?

A

Vaporizing the water in the pan

237
Q

The pan humidifier offers.

A

A broad range of capacity.

238
Q

Where are pan humidifiers usually installed?

A

inside the casing of an air handling apparatus, inside the supply air duct, or attached to the underside of a duct.

239
Q

Some pan humidifiers come equipped with a fan which allows?

A

Remote mounting

240
Q

The electrically heated pan humidifier is equipped with a low water cut-off switch to protect?

A

The heating element from early failure

241
Q

The steam heated pan humidifier offers high capacity and accurate humidity control if used with?

A

a modulating control valve and steam pressure not exceeding 103 kP2.

242
Q

What is used to vaporize the water in the pan of a pan type humidifier?

A

Heating coils

243
Q

What is used to vaporize the water in the pan of a pan type humidifier?

A

Heating coils

244
Q

What happens when all the water is evaporated from the pan in a pan type humidifier?

A

Scale forms

245
Q

What happens when less moisture evaporates from the skin?

A

Bodies feel warmer

246
Q

When less moisture evaporates, temperature set points and fuel consumption can be?

A

Reduced

247
Q

When humidifiers use water, the dumps must be kept clean to prevent?

A

Legionella Pneumophila bacteria from growing.

248
Q

The two treatments for humidifiers are?

A

Mechanical and chemical

249
Q

What is the most common method of cleaning humidifiers?

A

Mechanical cleaning

250
Q

How often does Mechanical cleaning require flushing of old water from the system, and replacing with fresh water?

A

Weekly

251
Q

What chemical treatment is used to keep humidifiers clean?

A

Regularly adding a batch of biocides to the system.

252
Q

Combining what two ways of treating humidifiers gives the best results?

A

flushing and biocide treatment

253
Q

How do you verify that a system is clean?

A

regularly scheduled swab test is performed to ensure the system is clean of bacteria.

254
Q

If a swab test is positive for bacterial growth, the system must be?

A

taken off line and drained and The entire system must be cleaned and sprayed with chemicals to kill the bacteria.

255
Q

What must be done to verify that the system can be placed back on line?

A

Another swab test.

256
Q

An air conditioning system consists of a group of components which?

A

operate together in a controlled manner to produce specific conditions of the air within a space or a building.

257
Q

What energy do Fans convert into the form of air pressure?

A

Mechanical energy into potential energy.

258
Q

What energy do Fans convert into the form of air pressure?

A

Mechanical energy into potential energy.

259
Q

The air pressure at the outlet of the fan will be greater than?

A

The air pressure at the outlets of the air handling system.

260
Q

What will the difference in air pressure cause?

A

The higher air pressure to flow to regions of lower air pressure.

261
Q

For a fan to operate there needs to be a difference in?

A

Pressures (high to low)

262
Q

The pressure in fans is usually quite small, slightly above?

A

Atmospheric pressure

263
Q

What is used to measure the small pressure?

A

Manometers

264
Q

What are the 3 types of pressure fans develop?

A

•static pressure
•velocity pressure
•total pressure

265
Q

(True or false) Each can be read separately, depending upon the way the manometer is connected to the outlet duct.

A

True

266
Q

In static pressure, the air is?

A

Not moving

267
Q

Static pressure can be read by connecting the manometer at?

A

Right angles to the ducts

268
Q

Static pressure can be read by connecting the manometer at?

A

Right angles to the ducts

269
Q

What does the static pressure overcome to be measured?

A

The resistance of ducts and filters

270
Q

Air in velocity pressure is?

A

Moving

271
Q

Air in velocity pressure is?

A

Moving

272
Q

Velocity pressure is only detected when?

A

It strikes a surface

273
Q

What is added to a duct if it has a damper (restricting the air flow)?

A

A thin metal vane

274
Q

What is added to a duct if it has a damper (restricting the air flow)?

A

A thin metal vane

275
Q

If a thin metal vane is added to the duct, what will be equal on either side of it?

A

Static pressure

276
Q

What will cause the vane to tip backwards when the damper opens?

A

The moving air striking it

277
Q

What is the sum of velocity pressure and static pressure that can be measured by connecting a manometer?

A

Total pressure

278
Q

What is the sum of velocity pressure and static pressure that can be measured by connecting a manometer?

A

Total pressure

279
Q

Total pressure remains constant throughout the duct without losses due to?

A

Friction or turbulence

280
Q

Which side of the fan can Static pressure be positive (above atmospheric) on?

A

Fan outlet side of the duct

281
Q

What side of the fan can static pressure be negative (below atmospheric) on?

A

The suction side of the fan

282
Q

As air passes, it goes through the converging section which causes?

A

The velocity pressure if the air to increase.

283
Q

Why is static pressure and velocity pressure inversely related?

A

To keep the total pressure constant, and to keep balance.

284
Q

What happens to velocity air and velocity pressures when it goes through a diverging section?

A

They will both decrease

285
Q

What is the difference between total pressure line and the static pressure line in a pressure conversion diagram?

A

Velocity pressure

286
Q

(True or false) in a steam turbine nozzle, velocity pressure and static pressure are not inversely related.

A

False
(In a steam turbine nozzle, velocity pressure and static pressure ARE inversely related.)

287
Q

The velocity increases and the pressure decreases when the cross sectional area?

A

Decreases

288
Q

What part of the duct will have losses?

A

The converging and diverging sections.

289
Q

The conversion of pressure and velocity is never 100% efficient, due to?

A

The formation of eddy currents.

290
Q

eddy currents and turbulence will not form and pressure recovery will be close to 90% if?

A

The transition is gradual enough

291
Q

In the diverging zone, the abrupt angles of the zone cause?

A

The recovery of static pressure to be poor.

292
Q

What is the result of the static pressure being poor?

A

A loss in total pressure

293
Q

What is the result if the pressure lines on a pressure conversion chart are generally sloped downward?

A

The result is pressure losses due to friction and turbulence.

294
Q

Centrifugal fans are classified according to?

A

The shape and design of the blades

295
Q

What are the 4 types of centrifugal fans?

A

•backward incline (BI)
•forward curved (FC)
•backward incline with air foil blades
•backward incline with radial blades

296
Q

What are the two types of fans?

A

•centrifugal fans
•axial flow fans

297
Q

Axial fans are not classified by their blade, they are classified according to?

A

The principles on which they are designed.

298
Q

Axial fans are not classified by their blade, they are classified according to?

A

The principles on which they are designed.

299
Q

What are the 3 general types of axial fans?

A

•propeller
•tube axial
•vane axial

300
Q

Centrifugal fans consist of?

A

a rotor or wheel having several radial blades, mounted on a shaft within the fan housing.

301
Q

What is another name for a centrifugal fan?

A

Squirrel cage

302
Q

Air enters near the axis of the wheel, flows to the circumference under the influence of?

A

the as it rotales in a centrifugal force produced by the rotation and is discharged through the outlet, located tangentially with respect to the fan wheel.

303
Q

The flow of air through the fan is caused by?

A

•The centrifugal force imparted to the air enclosed between the blades.
•The tangential velocity imparted to the air as it leaves the tips of the blades.

304
Q

Centrifugal fans:
In order to convert this velocity energy into useful static pressure?

A

The fan housing is given a scroll or volute shape, with a gradually increasing cross-sectional area in the direction of the airflow.

305
Q

Operating limits have been standardized for centrifugal fans commonly used for?

A

Heating, ventilating, and air conditioning.

306
Q

Centrifugal fans classifications are based on:(5)

A

•construction of the fan
•types of materials used
•static pressure developed
•fan speed
•outlet velocity

307
Q

What are the standard air conditions?(3)

A

•21°C
•103 kPa (76cm Hg) barometric pressure
•a density of 1.2kg/m3

308
Q

If pressure and temperature changes, it causes ____ ______ ______ to change.

A

Standard air conditions

309
Q

Any fan duty involving air or gases at other temperatures or altitudes above sea level must be corrected to standard conditions before?

A

Determining the class of fan required

310
Q

There are four types of centrifugal fans used in air conditioning systems, what attributes distinguishes one from another?

A

the shape of the blades and the way they are inclined.

311
Q

A backward inclined centrifugal fan has?

A

blades are sloped backward relative to the direction of rotation.

312
Q

The 4 shapes of a centrifugal fans blades are?

A

•backward incline
•forward curved
•backward inclined airfoil blades
•radial blade

313
Q

If the wheels rotate at the same speed, the horizontal vectors would be of equal lengths, meaning?

A

the wheels produce equal forward motion.

314
Q

What would cause the vectors to be equal length?

A

The centrifugal forces being equal but in a direction according to the inclination of the blades.

315
Q

Because the pressure produced by a fan is proportional to the resulting velocity , it is evident an Forward curved fan can operate at?

A

a much slower speed to produce a pressure equivalent to that of the backward incline fan.

316
Q

What is the rotational speed and power consumed in a backward incline fan?

A

•810r/min
•6.7kW(9hp)

317
Q

What is the rotational speed and power consumed in a forward curved fan?

A

•450r/min
•8.12kW(10.9hp)

318
Q

What is the rotational speed and power consumed in a backward incline airfoil fan?

A

•815r/min
•6.6kW(8.8hp)

319
Q

What is the rotational speed and power consumed in a backward incline airfoil fan?

A

•815r/min
•6.6kW(8.8hp)

320
Q

A backward incline fan is more efficient than?

A

Forward curved fans

321
Q

How much power to backward incline fans require to deliver a specified air amount?

A

Less power

322
Q

Higher efficiencies result in the backward inclined fans being?

A

Quieter in operation

323
Q

In sizes smaller than 600 mm (24 in.) diameter, the high speed of both types of backward inclined fans may require?

A

High speed belts, causing more noise.

324
Q

the lower speed (for the same air volume) of the forward curved design makes them?

A

More desirable for small fans.

325
Q

the backward inclined airfoil fan is more efficient than?

A

The backward inclined fan

326
Q

Why are the backward inclined airfoil fan is more efficient than backward inclined fan?

A

the aerodynamic shape of the airfoil blades permits smoother airflow through the wheel.

327
Q

What can rarely justify the higher initial cost of the airfoil fan when the system involved operates in the low pressure range (i.e. lower than 0.75 kPa (3 in.) static pressure)?

A

the magnitude of this difference in efficiency

328
Q

What characteristic of the forward curved fan is sometimes highly desirable?

A

The low rotation speed.

329
Q

The low rotational speed is particularly adapted to?

A

factory-assembled air-handling units having two or more fans on a common shaft.

330
Q

The higher speed of the backward inclined fan may require a?

A

shaft of excessively large size.

331
Q

What is another name for the radial blade fan?

A

Paddle wheel

332
Q

(True or false) the radial blade fan has a high initial cost.

A

FALSE: the radial blade fan has a LOW initial cost.

333
Q

What are the disadvantages of a radial blade fan?

A

less efficient and noisier than the other styles.

334
Q

How does it flow to the shaft In a axial flow fan?

A

Parallel

335
Q

What are the 3 types of axial fans?

A

•propeller
•tube axial fan
•vane axial

336
Q

What is a shaft mounted propeller fan driven by?

A

A motor either directly, or by a v-belt

337
Q

Where is a propeller fan often placed?

A

In a mounting ring

338
Q

What kind of capacity does a propeller fan have?

A

High air moving capacity.

339
Q

What are propeller fans unable to produce?

A

High pressures

340
Q

What is the pressure range propeller fans are usually used for?

A

0.03 to 0.06kPa
(1/8 to 1/4 in water)

341
Q

Since propeller fan can only produce low pressure it can’t be used in ducted air distributions, but it can be used in?

A

air cooled condensers, unit heaters and exhaust fan for ventilation purposes.

342
Q

The power required for a propeller fan is?

A

Lowest at maximum air delivery

343
Q

Why is the propeller fan the most economical type?

A

It produced large air movements at low pressures.

344
Q

What fan is a heavy-duty propeller fan suitable for duct mounting?

A

Tube axial fan.

345
Q

The tube axial fan will produce pressures up to?

A

0.6 or 0.75 kPa (2 ½ or 3 in. of water)

346
Q

A tube axial fan discharges the air in a spiral motion, therefore?

A

friction losses in the ducts and the system are considerably higher than with the straight airflow produced by the centrifugal fan.

347
Q

tube axial fans are seldom used in?

A

Commercial air conditioning

348
Q

Axial fans are more common in?

A

industrial air conditioning applications, where noise is less objectionable.

349
Q

Axial fans are more common in?

A

industrial air conditioning applications, where noise is less objectionable.

350
Q

Axial fans are often the logical choice for?

A

Transportation and marine applications.

351
Q

What type of fan is a tube axial fan equipped with guide vanes located behind the fan wheel to straighten out the spiral flow of air?

A

Vane axial fan

352
Q

What do Vane axial fans reduce?

A

Turbulence and friction and improved efficiency.

353
Q

Since vane dial fans are relatively noisy, when used in commercial air conditioning, it is necessary to?

A

use sound attenuators at strategic locations in the ductwork.

354
Q

Since vane dial fans are relatively noisy, when used in commercial air conditioning, it is necessary to?

A

use sound attenuators at strategic locations in the ductwork.

355
Q

Vane axial fans and tube axial fans are often used when?

A

space considerations are important.

356
Q

Vane axial fans and tube axial fans are often used when?

A

space considerations are important.

357
Q

Vane axial fans are usually mounted off the floor which can present maintenance problems because?

A

the fan bearings (and the motor in the case of direct driven fans) are mounted inside the casing.

358
Q

Vane axial fans are usually mounted off the floor which can present maintenance problems because?

A

the fan bearings (and the motor in the case of direct driven fans) are mounted inside the casing.

359
Q

What is the issue when fans usually drop in pressure?

A

Closed dampers or some other kind of blockage is likely preventing normal airflow.

360
Q

What is the issue when fans usually drop in pressure?

A

Closed dampers or some other kind of blockage is likely preventing normal airflow.

361
Q

Fan performance curves are obtained from?

A

from a series of laboratory tests conducted on a fan with various restrictions at the end of the test duct.

362
Q

Fan performance curves are obtained from?

A

from a series of laboratory tests conducted on a fan with various restrictions at the end of the test duct.

363
Q

Flows are varied between?

A

Flows are varied between full shut off(closed outlet and zero air flow) to free delivery(fully open outlet and zero fan static pressure).

364
Q

When doing a series of laboratory tests, the results are illustrated graphically by plotting?

A

Static pressure, fan power, and static efficiency against the air volume flow rate.

365
Q

When doing a series of laboratory tests, the results are illustrated graphically by plotting?

A

Static pressure, fan power, and static efficiency against the air volume flow rate.

366
Q

The purpose of fan performance curved are?

A

To allow designers to determine the correct fan selection for the system and allow operators to use the curves to help troubleshoot fan performance issues.

367
Q

In a backward incline fan curve,The power volume curve increases from?

A

shutoff, rising to a maximum, after which it decreases sharply to free delivery.

368
Q

In a backward incline fan curve, the power is measured in?

A

Horse power

369
Q

In a backward incline fan curve, when does The static efficiency curve rise from zero?

A

At shut off

370
Q

In a backward incline fan curve, when does, when does it decrease to zero?

A

At free delivery

371
Q

A non overloading fan has?

A

A relatively constant power input requirements for a given speed and will not change significantly with changing air flow conditions.

372
Q

In a forward curve fan curve, as the volume increases?

A

the static pressure curve falls off slightly.

373
Q

In a forward curved fan curve, The power requirements rise from a minimum at shutoff to?

A

A maximum at free delivery.

374
Q

In a forward curved fan curve, At constant speed, when there are changes to the airflow, the power requirements will?

A

increase causing the fan and motor to overload.

375
Q

In a forward curved fan, The normal application range for the fan is to the right of the peak of the static efficiency curve because?

A

the fan operation can be unstable when operating on the left portion of the curve.

376
Q

In a forward curved fan, The normal application range for the fan is to the right of the peak of the static efficiency curve because?

A

the fan operation can be unstable when operating on the left portion of the curve.

377
Q

The operator may check the air delivery system by measuring?

A

the fan speed and the motor amperage.

378
Q

How can a operator determine if the system is operating correctly?

A

By Comparing the actual values on the performance curves.

379
Q

Normal torque motors are used for?

A

Fan duty

380
Q

The fan motor size must be large enough to handle the maximum?

A

brake power of the fan and operate within its rated power.

381
Q

What is reserved for drive losses and reduction in line voltages?

A

normal allowable 15% overload factor

382
Q

the fan drives available are direct drives or V-belt drives unless?

A

Variable speed control is necessary.

383
Q

the fan drives available are direct drives or V-belt drives unless?

A

Variable speed control is necessary.

384
Q

Direct drives are usually used on?

A

Smaller sized air moving equipment.

385
Q

Direct drives are suitable for?

A

•Systems where the resistance can be determined accurately
•Systems where exact air quantities are not required

386
Q

What is used on most air conditioning, heating, and ventilation applications?

A

V belt drives

387
Q

In order to minimize vibration problems and premature wearing of the belts, it is important to use a matched?

A

set of belts and good quality balanced sheaves.

388
Q

when the motor size is 5.6 kW (7 ½ hp) or smaller, It is customary for the manufacturer to supply?

A

an adjustable motor sheave and a fixed pitch fan sheave.

389
Q

V belt drives are particularly useful on applications where?

A

adjustments may be required to obtain more exact air quantities.

390
Q

What motor size is the adjustable pitch motor sheave available as an optional feature on drives?

A

sizes 7.5 kW (10 hp) or larger.

391
Q

What motor size is the adjustable pitch motor sheave available as an optional feature on drives?

A

sizes 7.5 kW (10 hp) or larger.

392
Q

Guards are required for?

A

safety on all V-belt drives.

393
Q

Belt guards are?

A

fabricated of sheet metal with suitable brackets to allow for easy installation.

394
Q

The better quality belt guards have?

A

facing of expanded wire mesh to allow inspection of the belts while they are in motion.

395
Q

Better quality belt guards have two tachometer holes which permit?

A

measurement of the fan and motor speed without removal of the belt guard.

396
Q

What is required for direct drive equipment?

A

Coupling guards.

397
Q

What is required for direct drive equipment?

A

Coupling guards.

398
Q

Considerable economy in power consumption can be obtained on large air conditioning and Ventilation systems or on large industrial processes (eg. laboratory exhausts) by reducing?

A

The air volume handled by the fan during periods of partial loads, such as evenings or weekends.

399
Q

AC motors are speed-adjustable using?

A

Variable frequency drives.

400
Q

Variable frequency drives control AC motor speed and torque by controlling?

A

The motor input frequency and input.

401
Q

From the standpoint of sound level the variable frequency drives are?

A

The most efficient.

402
Q

From the standpoint of sound level the variable frequency drives are?

A

The most efficient.

403
Q

Fluid drives are used mainly on?

A

Industrial installations

404
Q

advantages of the fluid drive are?

A

the simplified starting equipment and the de-clutching feature, which relieves the driven fan of shock loading during start-up.

405
Q

What is the least expensive and least efficient control method?

A

Outlet damper control

406
Q

Outlet damper control is used on?

A

fans with constant speed motors

407
Q

Radial fans are installed in?

A

The fan inlet

408
Q

Why do Radial vanes have the vane shafts interconnected?

A

So all vanes rotate in unison and in the same direction.

409
Q

Radial vanes reduce energy consumption by?

A

controlling the amount of air spin at the fan inlet, thus controlling the static pressure and power requirement at a given speed.

410
Q

What is the main function of the duct system?

A

transmit supply and return air between the air handling apparatus and the conditioned space.

411
Q

Why will Air flowing through a duct will lose some pressure?

A

Because of friction and turbulence.

412
Q

Why will Air flowing through a duct will lose some pressure?

A

Because of friction and turbulence.

413
Q

The greater the velocity of air flowing through a duct of a given size, the greater the?

A

pressure loss.

414
Q

the power required to deliver a certain quantity of air will rise rapidly due to?

A

increased friction losses when the size of the duct is reduced.

415
Q

Why would a bigger fan be needed?

A

A bigger fan would be needed due to friction.

416
Q

What happens to a furnace if there is no return?

A

The furnace is shut down.

417
Q

What is one common way to classify duct systems?

A

By pressure and velocity

418
Q

What will change if the operating pressure or velocity of the system changes?

A

the design and operations of the system will change.

419
Q

What will change if the operating pressure or velocity of the system changes?

A

the design and operations of the system will change.

420
Q

What is the air velocity and duct static pressure of low pressure?

A

•velocity =less than 11m/s
•dsp = not exceeding 0.50 kPa (5 cm of water)

421
Q

What is the air velocity and duct static pressure of medium pressure?

A

•velocity= from 11 m/s to 25 m/s
•dsp= up to 1.50 kPa (15 cm of water)

422
Q

What is the air velocity and duct static pressure of high pressure?

A

•velocity= greater than 25 m/s
•dsp= from 1.50 kla to 2.5 kPa (25 cm of water)

423
Q

fibreglass duct is further classified for construction at pressures?

A

Below 0.50kPa

424
Q

The larger the building the larger the duct work must be to support?

A

the large volumes of air the system will move.

425
Q

What may be considered a disadvantage in large and medium sized buildings?

A

Sizing

426
Q

What does increasing the size of the ducting do to the air friction and resistance airflow?

A

It will decrease them, therefore reduce power requirements for the fan.

427
Q

Since In large buildings, the space required by the low pressure class of ductwork to move large amounts of air would be excessive, what must be used?

A

Medium and high pressure systems.

428
Q

The space saving feature of systems is partly offset by the following factors, which result from the higher static pressures and air velocities:

A

•Higher operating cost
• Higher initial cost of air handling apparatus
• Higher initial cost for special equipment required reducing the air velocity before distribution to the air space
• Special control devices
• More careful and costly fabrication and installation of ductwork
• Costly noise suppressing devices required (acoustical duct lining or sound attenuators)

429
Q

consider leaks and duct strength as functions of pressure to help?

A

Helps to operate and troubleshoot problems

430
Q

Noise, vibration, and friction losses are functions of?

A

Velocity

431
Q

To safely operate, troubleshoot, and improve overall efficiencies of HVAC systems, it is important
to:

A

• Know the system layout
• Understand the design limits of the system.
• Know the methods used for fabrication and installation.

432
Q

What are materials used in sheet metal duct?

A

galvanized or black steel, aluminum, stainless steel and copper.

433
Q

Galvanized steel is mainly used in?

A

ventilating and air conditioning systems where the normal service involves only atmospheric contaminants and localized water carryover from cooling coils, humidifiers, air washers, or outdoor air intakes.

434
Q

What is the advantage of galvanized steel?

A

It is corrosion resistant

435
Q

What is the disadvantage galvanized steel?

A

It’s costly

436
Q

What Black steel heavy gauge sheets used for?

A

kitchen exhaust ducts, for ducting protected with waterproofing mastic coatings, or for drain pans.

437
Q

Black steel has the advantage of?

A

being durable and of high strength.

438
Q

Aluminum, stainless steel, or copper is used where?

A

the cost is justified by the need for maximum resistance to moisture.

439
Q

Cement asbestos ducts are used for?

A

buried (underground) exhaust of corrosive material, such as from laboratory fume hoods.

440
Q

Cement asbestos ducts are used for?

A

buried (underground) exhaust of corrosive material, such as from laboratory fume hoods.

441
Q

Fibreglass ducts are used in ?

A

some low-pressure systems.

442
Q

Fibreglass ducts are used in ?

A

some low-pressure systems.

443
Q

Advantages of fibreglass ducts are?

A

They are very lightweight, have a low initial cost, are naturally silencing, and can be fitted on site.

444
Q

Disadvantages of fibre glass ducts are?

A

have low strength, are easily punctured, and cannot be used to handle air with high moisture levels or oil and grease, such as found in kitchen exhausts.

445
Q

Considerations for ductwork layout:

A

• The air volume delivered to each zone
• The type, number, and location of outlets and returns
• Duct routing
• Initial cost
• Operational costs

446
Q

Considerations for ductwork layout:

A

• The air volume delivered to each zone
• The type, number, and location of outlets and returns
• Duct routing
• Initial cost
• Operational costs

447
Q

Ducts are fabricated in sections fastened together with special?

A

seams, slips, and locks.

448
Q

Ducts are fabricated in sections fastened together with special?

A

seams, slips, and locks.

449
Q

What does The air handing unit condition?

A

the air entering the building.

450
Q

What does The air handling unit use to connect to the duct work, and to reduce vibration and sound transmission to the air duct?

A

A flexible connector

451
Q

Th air is distributed to the branch ducts through?

A

the main trunk.

452
Q

What happens when you go from a large duct to a smaller duct?

A

Velocity increases, pressure decreases.

453
Q

What reroutes air from the main trunk to supply air to specific zones or areas of the building.?

A

A take off

454
Q

reducers are used to compensate for the reduction of air volume in order to maintain?

A

Duct pressure and velocity

455
Q

Why does The return air duct brings air from the occupied spaces?

A

To be reconditioned in the air-handling unit.

456
Q

Why does The return air duct brings air from the occupied spaces?

A

To be reconditioned in the air-handling unit.

457
Q

Construction details are found in the?

A

Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) Standards.

458
Q

Construction details are found in?

A

Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) Standards.

459
Q

What is used to provide stiffness in Ducts of large dimensions?

A

stiffeners or be diagonally creased

460
Q

Why do Ducts of large dimensions need stiffness ?

A

To prevent vibration

461
Q

Ducts passing through non-conditioned spaces must be insulated to prevent?

A

excessive heat loss or gain and to prevent condensation.

462
Q

Ducts passing through non-conditioned spaces must be insulated to prevent?

A

excessive heat loss or gain and to prevent condensation.

463
Q

Ducts must be made as tight as possible to prevent?

A

air losses due to leakage.

464
Q

Changes in duct size should be gradual with a slope of?

A

1 in 7

465
Q

Changes in duct size should be gradual with a slope of?

A

1 in 7

466
Q

Flexible connections made of heavy canvas or neoprene coated glass fire cloth must be provided at?

A

fan discharge and suction openings.

467
Q

Mitre elbows which have legs of equal length may increase?

A

velocity.

468
Q

Mitre elbows which have legs of equal length may increase?

A

velocity.

469
Q

What should be provided with Short radius elbows?

A

Turning vanes

470
Q

What should Supply and return air branch ducts contain to permit satisfactory air gets too item
balancing?

A

Dampers

471
Q

What should be used in all branch ducts?

A

Splitters and positive lock dampers.

472
Q

What should be used in all branch ducts?

A

Splitters and positive lock dampers.

473
Q

At what temperature do Fire dampers with fusible links have to be installed in ducts, which pass through firewalls?

A

70°C

474
Q

What is used to lower installation costs and ease the install?

A

an elephant trunk style air duct in lieu of standard metal round ducts

475
Q

Factors that will affect leakage are:

A

• Static pressure
• The total length of installed duct
• The number of joints, seams, and openings
• The method used to seal openings and joints
• The quality of work

476
Q

What percent has Air leakages from ducts have been found to vary from depending on the quality of work?

A

5% to 30%

477
Q

What do The effects of air leakage in supply air ducts differ from?

A

those in the return air ducts.

478
Q

What do Air leakage from the supply duct create a loss of?

A

Cooling or heating affect

479
Q

What percent should you assume the leakage of When the entire supply air duct is outside the conditioned space?
(Absa ?)

A

10%

480
Q

The fraction of leakage can be determined by the ratio of?

A

the ratio of length outside the conditioned space to total length of supply duct.

481
Q

What does NOT need to be considered in loss calculations?

A

Losses from bare supply air ducts within the conditioned space

482
Q

What does NOT need to be considered in loss calculations?

A

Losses from bare supply air ducts within the conditioned space

483
Q

To reduce airborn noises, the metal duct must be lined with?

A

Acoustically absorbent materials

484
Q

to help withstand the erosive air velocities without deterioration, dust liners consist of?

A

flexible or semi rigid fibreglass blankets with a special surface coating
on the side facing the air stream

485
Q

In some cases what can also function as thermal insulation?

A

Liners

486
Q

In some cases what can also function as thermal insulation?

A

Liners

B10 (1 decks)

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