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HVAC II > HVAC II Final Review > Flashcards

HVAC II Final Review Flashcards

1
Q

What is Approach Temperature?

A

Delta T between evaporator coil temp and chiller water leaving temperature

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2
Q

What is the purpose of an Expansion Tank?

A

Located above boiler to give space for air initially trapped in system and for expanded water when heated

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3
Q

What type of pump is used for a circulator?

A

Centrifugal Pumps

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4
Q

What are the advantages of a HEPA Filter?

A

Very high-eff (0.3um and lower), remove 99.99%

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5
Q

How is a Purge Unit connected to a system?

A

It is connected to the top of the condenser to collect and remove the air

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6
Q

What is Ventilation?

A

Process of supplying and removing air by natural or mechanical means to and from a space

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7
Q

Where is a Balancing Valve installed on a heating terminal unit?

A

Installed on the return side of each heating unit

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8
Q

What are the types of Cooling Tower Air Flow?

A

Cross-Flow (air in thru side, pulls air out thru top) and Counter-Flow (air in thru btm, up thru top)

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9
Q

What is the purpose of the Load Limiter?

A

To sense the motor amperage and partially close the guide vanes to limit the compressor amperage to the full-load value

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10
Q

How is capacity control done on a Rotary Screw Compressor?

A

Slide valve that blocks suction gas before entering. Typically by differential pressure in the system

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11
Q

What does a normal gas flame look like?

A

Blue with slight orange tips

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12
Q

What are the types of Fan Switches?

A

Temperature (in the air stream near Heat Ex) and Timer (non-adjustable)

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13
Q

What is the delta T between condenser refrig temp and ambient temp for a High Eff system?

A

20 degrees F

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14
Q

How does a Thermocouple work?

A

Two dissimilar metals welded at one end (hot junction). When heated, generates small V (15mV loaded (connected to coil) 30mV unloaded (w/o coil). Voltage travels to cold junction at gas valve

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15
Q

What is the ideal delta T between the evap refrig coil temp and the air entering the evap coil?

A

10-20 degrees F

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16
Q

What is the purpose of Guide Vanes?

A

At entrance of impeller eye to allow or reduce flow by pneumatic or electronic motors to open or close vanes. Also, guide refrig to impeller eye.

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17
Q

What is the condition of refrig entering the compressor?

A

Superheated Vapor

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18
Q

What should the delta T be between the condenser coil and the ambient air in a standard efficiency system?

A

30 degrees F

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19
Q

What conditions cause Centrifugal Compressors to surge?

A

Too high head pressure or evaporator pressure too low that the compressor can’t overcome the pressure difference

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20
Q

Why do we use Crank Case Heaters?

A

To prevent refrigeration migration and to vaporize refrig that migrated to the compressor

21
Q

Name the types of Evaporator Defrost methods:

A

Random or Off-Cycle, Planned (forcing comp off for short periods), Hot Gas, Electric

22
Q

What is the purpose of a Gas Regulator?

A

Drops NG to usuable pressure (3.5” WC) and meters constant flow

23
Q

Name the types of Low Ambient Head Pressure Control:

A
  1. fan cycling using pressure control 2. fan speed control 3. air volume control using shutters and fan cycling 4. condenser flooding devices
24
Q

Describe a flame with Primary Air Restriction:

A

Yellow

25
Q

What is a Sling Psychrometer used for?

A

To obtain Wet-bulb and Dry-bulb temperatures

26
Q

What are the basic furnace styles?

A

Horizontal, Uplow, Downflow, Low Boy, Multipoise

27
Q

What is the minimum slope of horizontal flue pipe?

A

1/4” per foot

28
Q

STUDY P/T CHARTS

A

Study it

29
Q

What is the purpose of a Draft Diverter?

A

Prevent pilot blowout and main burner flame from being altered

30
Q

What are the characteristics of Pictoral Drawings?

A

Shows location of each component as it actually appears to the person installing or servicing equipment

31
Q

Under what conditions are people at rest most comfortable?

A

75 degrees F, 50% Humidity

32
Q

Define Humidity:

A

Moisture in the air

33
Q

Define Dew Point:

A

The exact temperature at which moisture begins to form

34
Q

If we know two point on Psychrometric Chart, how many conditions can be determined?

A

Dry/Wet Bulb give 5 (dew point, total heat (enthalpy), moisture content, RH, specific volume of air)

35
Q

Which is Heavier, NG or air?

A

Air 1.00, NG 0.60 specific gravity

36
Q

Name the types of burners:

A

Drilled Port, Slotted Port, Ribbon Burner, Single Port (inshot or upshot)

37
Q

What is the normal pressure of a NG Furnace?

A

3.5” WC (1psi = 27.7” WC)

38
Q

Where is the High Side Float at in the system (Floats are only on Chiller units)?

A

In Liquid Line entering the evaporator

39
Q

What happens to down stream temperature if there is a restriction in the Liquid Line?

A

Pressure will drop, temp will drop, capacity will drop (becomes vapor sooner)

40
Q

How close can cooling tower water be cooled to the Wet Bulb Temp?

A

Within 7 degrees of Wet-Bulb Temperature

41
Q

What material is used to make Electric Heat Elements?

A

Nichrome (Nickel-Chromium)

42
Q

What is the purpose of Auxilary Heat in a Heat Pump System?

A

Supplimental heat, emergency heat

43
Q

How does a Limit Switch function in an electric heating system?

A

Shuts off unit if high temperature occurs

44
Q

In what units is gas pressure measured?

A

inches WC

45
Q

Where is the Oriface in a gas system?

A

Spud

46
Q

Name the two basic chiller types:

A

Compression Cycle Chiller (Compression AC sys) and Absorption Chiller (sodium solution)

47
Q

How is flue gas removed from a conventional furnace?

A

Natural Draft

48
Q

To what is the Rupture Disc attached?

A

On evaporator section or suction line, breaks at 15psig

49
Q

How does a Limit Switch function on a Hydronic Boiler?

A

Shuts off unit if high temperature occurs. Immersed into boiler water or placed in a dry well into boiler. Home and light commercial low pressure at less than 30 psig set for 200 degrees F off

HVAC II (3 decks)

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