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COSC 326 - MEP II > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

How much percentage of total world energy does the US consume?

A

Around 25%

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2
Q

When we build a more efficient building, we use high performance glass, higher levels of insulation, better windows, etc., in order to:

A

Save Energy

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3
Q

(T/F) As a percentage of rejected energy, transportation is “better” than electricity generation

A

False

Electrical generation is about 50% rejected energy while transportation is closer to 74%. Cars are terribly inefficient!

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4
Q

(T/F) The U.S. consumes about 5% of the total world energy consumption.

A

False

The US actually has about 5% of world population but uses 25% of the world’s energy.

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5
Q

What was the cause of a huge drop in commodity prices for U.S. oil and natural gas in 2008 - 2009?

A

Financial collapse of the U.S. housing market.

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6
Q

Data for energy statistics in the U.S. are provided by:

A

EIA

Energy Information Agency

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7
Q

What type of transformer would be found at the exit of the main power plant?

A

Step-up Transformer
The voltage at the power plant is several thousand and up to 20 -30kV. However, for efficient (low current) transmission, that power “flows” better at several hundred kV.

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8
Q

The role of high-pressure steam in a Rankine Cycle power plant is to?

A

Run through a series of steam turbines that then drive a generator

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9
Q

When we hear the term “Alternating Current” (A.C.) this really describes:

A

The back-and-forth flow of Amperes in an electrical power system.

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10
Q

(T/F) ERCOT regulates the interstate transmission of power for Texas.

A

False

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11
Q

(T/F) FERC regulates the operations of the Western Interconnect, Eastern Interconnect, and the Texas Interconnect.

A

False

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12
Q

How do we get the power we need for our commercial/industrial/residential buildings?

A

From the generation station, through the step-up/step-down transformers and ultimately to the customer.

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13
Q

In a power plant, where is all the electrical power generated?

A

The generator

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14
Q

What do all major power generation facilities in the US generate (talking about energy)?

A

3 Phase and 60 Hz

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15
Q

What does ERCOT stand for?

A

Energy Reliability Council of Texas

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16
Q

Why do we use aluminum core as conductors (wires)?

A

Cost and weight

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17
Q

Most every electrical power provider transmits power out on to the electrical grid using

A

a Delta configuration

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18
Q

A typical step-down transformer serving a commercial building has the following important operational characteristic.

A

It has delta service entering as primary with wye on secondary

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19
Q

What is a common configuration for commercial construction?

A

480V phase-to-phase

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20
Q

ALL commercial and residential electrical work in the US is governed by ________ and considered as “________ ________” installations

A

NEC

“low voltage”

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21
Q

Low voltage is defined as:

A

120 - 600 Volts alternating current

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22
Q

Medium voltage systems are defined as:

A

2,400 - 69, 000 alternating current

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23
Q

Medium voltage systems are only found in:

A

Utility distribution and industrial work.

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24
Q

High voltages are defined as:

A

> 69,000

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25
Q

Why do we distribute at high voltages?

A

Efficiency

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26
Q

Why is primary power distribution at very high (usually) voltages?

A

Higher voltage allows smaller current.

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27
Q

The power factor, as used in electrical power calculations, can be considered:

A

a measure of the “efficient” use of power at the customer’s site.

28
Q

The NEC refers to the wires that carry power into and throughout a building as

A

“conductors”

More commonly out on the job site, these are referred to as “wires” or “wiring”

29
Q

What causes expansion in aluminum conductors in an electrical power system?

A

Current flowing through the aluminum conductor results in heating of the metal.

30
Q

THHN describes…

A

The type of exterior insulation on a conductor.

31
Q

What is the application equation for a single phase?

A

Watt = Volt x Amp x power factor
or
W = V x A x pf

32
Q

What is the application equation for a three phase?

A

Watt = Volt x Amp x power factor x 31/2
or
W = V x A x pf x √3

33
Q

The #14 AWG would be called:

A

14 Gauge

34
Q

4/0 is referred to as:

A

Four ought wire

35
Q

What is the most common conductor type you will find in most building construction projects?

A

THHN

36
Q

What is the second most common conductor type you will find in most building construction projects?

A

XHHW

37
Q

Basic conduction heat transfer equation

A

Q = U x A x (T outside - T inside) btu/hr

38
Q

1 BHP =

A

33,472 Bthu/hr

39
Q

What is referred to as the recovery rate?

A

How quickly the water heater responds to a given load (use of hot water)

40
Q

What identifies a forced draft boiler?

A

Forced draft boilers usually have a fan attached at the burner port that directly inject air into the combustion chamber and this promotes more complete combustion of the fuel and better heat transfer to the water in the boiler which yields improved boiler efficiency.

41
Q

Hot water piping systems in boilers have a hot water supply temperature of _______ F or higher adn after serving the heating load in the system, have a return hot water temperature of _____ F or lower.

A

180 F

160 F

42
Q

Why do we use water instead of air in HVAC systems?

A

An equivalent mass of water con “carry” a lot more energy than air

43
Q

How does water end up circulating in an HVAC sytem?

A

Pumps

44
Q

What is the primary type of pump used for water delivery?

A

Centrifugal pump

45
Q

(T/F) An end suction pump is a type of centrifugal pump.

A

True

46
Q

In end-suction centrifugal pumps, where are the maintenance issues located?

A

impellers, bearings and seals.

47
Q

What are the two types of end-suction pumps?

A

Close-coupled and frame-mounted.

48
Q

Define close-coupled pump

A

The close coupled end-suction pump is a compact version where the pump is physically attached to the body of the electric motor. They are usually physically smaller than frame mounted pumps and circulate a smaller volume of water. They can be placed in-line in piping systems.

49
Q

Define frame mounted pump

A

The frame is literally, the frame to which the electric motor and pump are attached. The motor is on the left end of the frame and the pump is on the right. The shaft that connects the motor to the pump rotates at a high RPM and is a safety hazard.

50
Q

In what type of applications are frame-mounted pumps used in?

A

Usually used in applications requiring high flow rates and with high operating pressure requirements

51
Q

Define horizontal split case (HSC) pumps

A

They are another option for applications requiring movement of large volumes of water and at low to medium operating pressures. These pumps generally have a smaller footprint compared to a frame mounted pump of similar capacity and the top of the case (split case) can easily be removed for servicing of internal components of the pump.

52
Q

Define “head” (HVAC application)

A

the height to which a pump can raise a column of water

53
Q

Why would an HVAC designer prefer to use an air-water system rather than an all-air system for a building load?

A

Can “carry” the same amount of energy in a much smaller package (water in a pipe) than in air in ductwork.

54
Q

The volute of a pump is…

A

the part of the pump where the impeller rotates and directs water flow.

the impeller is the rotating part of a pump (besides the drive shaft!) and is how a pump generates the increase in pressure for a hydronic system.

55
Q

Why is it important that the mechanical contractor align the pump/motor driveshaft?

A

Proper alignment will reduce/eliminate vibrations from the pump. Poor alignment will, very quickly, lead to pump/bearing failure! The vibrations will also have the client calling about noise complaints.

56
Q

A good type of pump to use as an in-line circulator is:

A

close-coupled

57
Q

What might be one cause of head (pressure) loss in an AHU chilled water coil?

A

Piping arrangement in coil. Piping arrangement/diameter/u-bends/number of rows… are all primary reasons for pressure (head) loss in these units.

58
Q

The water-side equation to determine the required flow in gallons per minute (gpm) would be:

A

Q = 500 x gpm x ΔT (Btu/hr)

59
Q

What is the purpose of a diffuser?

A

To provide thermal comfort for the occupants of a space or to provide proper thermal conditions for equipment in the space.

60
Q

Diffusers are defined as _________ ________ in an air distribution system that distribute conditioned air in various directions through the use of built-in deflecting vanes

A

terminal devices

61
Q

The highest velocity at this diffuser is where?

A

The center

62
Q

An exhaust system is being installed for the automatic dishwasher for the cafeteria of the new high school building project that your company is working on. The duct material for this application should be:

A

Stainless Steel (type 304)

63
Q

What are the three main descriptors for duct systems?

A
  1. Low velocity, 400 – 2,000 feet per minute (fpm),
  2. Medium velocity, 2,000 – 2,500 fpm.
  3. High velocity, 2,500 – 3,500 fpm.
64
Q

What is the most common duct material used for HVAC duct-work systems?

A

Galvanized Steel

65
Q

When is aluminum ducting used in?

A

Clean room and specialized healthcare applications.

Also used where high moisture levels would be encountered, and for special or decorative duct systems.

66
Q

When is stainless steel ducting used in?

A

Commercial exhaust and specialized duct systems. Typically applications might include kitchen/restaurant exhaust, exhaust with high moisture content, and combustion fume exhaust.

COSC 326 - MEP II (3 decks)

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