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3rd Year Refrig Sait 2019 > Tyson class > Flashcards

Tyson class Flashcards

1
Q

Dry bulb temp

A

Temp of air

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2
Q

Wet bulb temp

A

Temperature of the air measured with a glass bulb covered with a wet cloth

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3
Q

Relative humidity

A

Actual amount of moisture in the air compared to the total or maximum moisture the air can hold

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4
Q

Grains of moisture

A

Unit of measure used to determine the amount of moisture in the air

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5
Q

Dew point temp

A

Temperature at which moisture condenses on a surface

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6
Q

How many grains of moisture in 1 LB of water

A

7000

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7
Q

Mass flow rate unit

A

LB/hr

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8
Q

Enthalpy unit of measure

A

Btu/Lb

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9
Q

BTU capacity formula

A

Mass Flow Rate X delta H (change in enthalpy)

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10
Q

Mass flow rate formula

A

Cfm x Specific Density x 60

= lb/hr

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11
Q

Q sensible formula

A

1.08 x cfm x delta T

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12
Q

Air heat capacity formula

A

Mass Flow Rate x delta H
= BTU/H

Or

4.5 x cfm x delta H

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13
Q

Economizer open% formula

A

Return air - mixed air
—————
Return air - outside air

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14
Q

Coil bypass factor formula

A

Leaving air - coil temp
____________
Entering air - coil temp

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15
Q

Sensible heat factor formula

A

Sensible heat quantity
____________
Total heat quantity

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16
Q

What is more dense, dry air or moist air

A

Dry air

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17
Q

Where is the vapor barrier placed

A

On warmest wall

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18
Q

Total pressure formula

A

Static + velocity

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19
Q

Pitot tube ports give what measurements on the side and bottom

A

Side port is static

Bottom port is total

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20
Q

Velocity (ft/min) formula

A

4005 x (square root of velocity pressure)

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21
Q

Cross sectional area of round duct

A

3.14 x (radius squared)

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22
Q

Total external static pressure formula (furnaces)

A

Supply static just before coil - return static right after filter

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23
Q

CFM fan laws

A

RPM 2/RPM1 = CFM2/CFM1

Double RPM -= double CFM

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24
Q

Static pressure fan laws

A

(RPM2/RPM1)squares = SP2/SP1

Double RPM = 4 x static

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25
Q

HP fan laws

A

(RPM2/RPM1)cubed = HP2/HP1

Double RPM = 8 x HP

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26
Q

Fan driver and sheave relationship

A

RPM driver x diameter of driver (motor)

RPM driven x diameter driven (fan)

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27
Q

2 main main fan classifications

A

Propeller and axial

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28
Q

3 main centrifugal fan types

A

1) Forward curve
2) Backward inclined
3) Radial or straight blade

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29
Q

Forward curve fan application

A

Furnace or small to medium RTU

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30
Q

Pros of forward curve fan (3)

A

Low speed
Quiet
Light inexpensive construction

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31
Q

Cons of forward curve fan

A

High HP requirements at near free delivery

32
Q

Pros of Backward inclined fan

A

Non overloading when wide open

33
Q

Backward inclined fan application

A

Industrial and commercial ventilation

34
Q

Advantages of radial blade fan (2)

A

Ideal for high static pressure

Ideal for areas with high dust content

35
Q

Disadvantages of radial blade fans (3)

A

Noisy
Low volume means larger size to do the job
Lower Efficiency

36
Q

Most efficient fan?

A

Air foil (backward curved) 90%

37
Q

What position does a non conventional reversing valve go to in a deenergized state

A

Fail to heat

38
Q

pressure required to move slide valve on 4 way valve

A

75-100 psi

39
Q

Define Heat Pump Balance Point

A

Lowest possible outdoor temperature at which the Heat Pump can satisfy the needs of the building.
Below balance point requires auxiliary heating

40
Q

Define unitary equipment

A

Any unit that comes completely assembled from the factory (RTU)

41
Q

Where are the metering devices typically located on a ductless split system

A

Outdoors at the unit

42
Q

What special precautions must be taken with the liquid line when installing ductless split systems

A

Must be insulated

43
Q

What is the minimum SEER rating on residential split systems

44
Q

Velocity required on AC system

A

400 cfm/ton

45
Q

Low ambient control setting

46
Q

Unitary equipment

Ideal SST, SDT, system super heat and subcooling

A

SST = 40F
SDT = 105F
System superheat = 20-30
Sub cooling = 10F

47
Q

Face velocity

A

400-500 ft/min

48
Q

What does PTAC stand for, give 1 example

A

Packaged Terminal Air Conditioner

Heat pumps

49
Q

Give 3 forms of CAPACITY control

A

Condensor fan cycling
Hot gas bypass
Compressor unloading

50
Q

Give 3 forms of HEAD PRESSURE control

A

Condensor fan cycling
Condensor flooding
Damper control

51
Q

Unit clearances from edges

A

B-52 says 10 ft

B-149 cas code says 6 ft

52
Q

Velocity required for heat

A

450 ft/min

53
Q

Average delta T for cooling

54
Q

What is the difference between a direct and indirect cooling system

A

Direct system cools the medium (air) directly (residential ac)
Indirect cools water and water cools the medium (chilled water system)

55
Q

What is EER and how is it calculated

A

Energy Efficiency Ratio

Output energy (BTU/hr)
—————
Input electrical energy (watt/ hr)

56
Q

What is ASHRAE ideal temp for comfort and efficiency

57
Q

What parts make up a headmaster and what is it used for

A

ORI (open on rise of inlet) and ORD (open on rise of differential)
Used to maintain head pressure during low ambient conditions

58
Q

What is a timed low pressure bypass timer, why is it used

A

Timed contacts that bypass the low pressure control for 3-5 min to allow head pressure to to rise to normal conditions without tripping during low ambient conditions

59
Q

Economizer mixed air temperature setting

60
Q

2 types of dampers

Which is better for mixing

A

Parallel and opposed blade

Opposed give better mixing but promote stratification (layers of different temperature air)

61
Q

Why are VFDs often used with VAV boxes

A

When dampers close at VAV boxes, static pressure increases. VFDs reduce fan speed to keep static pressures low

62
Q

Biggest advantage of RTU

A

Reduced cost of rental space

63
Q

What is the pressure setting for a DPRV (discharge pressure regulating valve)

A

Pressure equivalent to 34F

eg. R-22 @ 34F = 60 psi

64
Q

Heat pump defrost coil engages at what temp?

A

40-42F (to maintain a safety TD of 10)

65
Q

What are the symptoms of faulty compressor valves

A

Higher than normal suction pressure, lower than normal discharge pressure, lower amp draw

66
Q

Typical AC supply temp

67
Q

AHRI test condition temperatures for Return air and Ambient

A

80F return air

95F ambient

68
Q

What type of fan is used on a window AC

69
Q

What fan is used for high velocity with low static pressure

70
Q

Define radiation

A

Transfer of energy in the form of waves through space

71
Q

Calgary summer and winter design temp

A

84F summer

-24F winter

72
Q

Define thermal mass

A

Ability of an object to store heat

73
Q

Define Thermal Lag

A

The time it takes for heat to pass through an object

74
Q

Define flywheel effect

A

A building constructed with materials with a high thermal mass to provide inertia or resistance to temperature fluctuations

75
Q

Describe thermal mass used for heating

A

Concrete exposed to sun to help heat in winter

76
Q

Describe thermal mass used for limited summer time over heating

A

Mass shielded from solar gain but exposed to occupants. Heat is absorbed throughout the day and then released overnight to assist HVAC system

77
Q

What is the air velocity of the draft produced when walking past someone

3rd Year Refrig Sait 2019 (5 decks)

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