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Building Science > Principles of Energy > Flashcards

Principles of Energy Flashcards

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1
Q

What is energy?

A

A measurable quantity of heat, work, or light

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2
Q

What are the only two significant sources of energy?

A

Sun, nuclear material

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3
Q

What’s potential energy?

A

Stored energy

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4
Q

What’s kinetic energy?

A

Energy in transition or motion changing from one type of energy to another

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5
Q

Doing work requires two things:

A

Converting potential energy to kinetic, Transporting the energy to where its needed

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6
Q

What’s the easiest form of energy to move?

A

Electricity

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7
Q

What’s the most difficult form of energy to move?

A

Mechanical energy because of huge losses due to friction

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8
Q

What’s the first law of thermodynamics?

A

Energy is neither created nor destroyed

Energy transfers and changes forms

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9
Q

What’s the second law of thermodynamics?

A

In any system, heat always moves from high temperature to low temperature, unless there is some other external source of energy

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10
Q

What’s temperature?

A

A measure of the kinetic energy, or molecular movement, within an object

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11
Q

What is heat?

A

The flow of thermal energy between two objects whenever there is a temperature difference between them

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12
Q

What is enthalpy?

A

The internal heat of an object, measured in BTUs per pound

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13
Q

What’s a BTU?

A

A measurement of heat. 1 BTU = the heat required to raise 1 pound of water 1 degree F.

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14
Q

What’s specific heat?

A

Number of BTU’s that one pound of any material will absorb for each degree F of temperature change.

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15
Q

What’s the specific heat of water?

A

1 BTU/lb?/degreeF

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16
Q

What is sensible heat?

A

Heat that causes a temperature change

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17
Q

What is latent heat?

A

Heat that causes a change of state

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18
Q

What type of heat can transfer more energy?

A

Latent heat

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19
Q

Describe steam heating.

A

Water is vaporized (absorbs latent heat)

Steam is condensed (releases latent heat)

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20
Q

Describe air conditioning.

A

Refrigerant is vaporized (absorbs LH)

Refrigerant is condensed (releases latent heat)

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21
Q

What is power?

A

The rate at which work is done or energy is released, measuring the capacity to do work. Measured in Watts, HP, BTUH

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22
Q

What is energy?

A

The amount of work that gets done in a given timeframe. Energy has a time component.

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23
Q

Energy =

A

Power x Time

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24
Q

Heat, electricity, and fluids flow when 2 things occur:

A

An open path allows their flow
There is a pressure difference.
Heat: path = molecules, pressure = temp difference
Electricity: path = wires, pressure = voltage
Water: path = pipe, pressure = height difference

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25
Q

Fluids flow from…

A

high pressure to low pressure

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26
Q

When pressure equalizes, flow will ______.

A

stop

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27
Q

What are three types of flow paths?

A

Conductor - allows rapid flow
Resistor - flow occurs slowly
Barrier - flow is stopped or negligible

28
Q

Heat flows in what three ways?

A

Conduction, convection, radiation

29
Q

What is conduction?

A

Heat flow through solids, between adjacent molecules of objects in contact with one another

30
Q

Conductance, or K-value, measures what?

A

The rate of heat transfer through materials

31
Q

What is convection?

A

The transfer of heat through moving fluid (typically air or water)

32
Q

What is radiation?

A

The transfer of heat through space from one object to another

33
Q

All types of radiant energy are categorized by what?

A

The electromagnetic spectrum

34
Q

Solar energy consists of…

A 
UV (5%)
Visible light (46%)
Infrared heat (49%)
35
Q

When solar radiation strikes an object, 1 of 3 things occurs:

A

Reflectance, absorbance, or transmittance

36
Q

What are the only common substances that reflect both solar and infrared radiation?

A

Polished aluminum, steel, tin, silver, nickel

37
Q

What’s the only common material that transmits most solar radiation?

A

Glass

38
Q

Glass creates a greenhouse effect because it…

A

transmits solar radiation but absorbs earthly infrared

39
Q

Emittance or Emissivity measures…

A

a material’s characteristic ability to emit radiant energy. Emittance of 1 is a theoretically perfect emitter. Most materials have emittances of 85% to 95%.

40
Q

What are Low-E coatings?

A

Metallic coatings that are placed on glass in order to reduce solar transmittance by reflecting most radiation and to reduce the flow of radiant heat from outside to inside (or opposite depending on climate) by decreasing the emissivity of the glass.

41
Q

What is comfort?

A

Being in thermal equilibrium with the environment without having to sweat or shiver.

42
Q

What conditions determine outdoor comfort?

A

Temperature, humidity, solar radiation, precipitation, wind

43
Q

ASHRAE 55 defines the factors of indoor comfort:

A

Air temp, radiant temp, relative humidity, air movement (metabolic rate, clothing - uncontrolled)

44
Q

What’s the primary factor in indoor comfort?

A

Air temperature

45
Q

What are ASHRAE’s indoor design temperatures?

A

70 degrees F in winter

75 in summer

46
Q

What is ASHRAE’s heating balance point temperature?

A

65 degrees F - the outdoor temp above which no heating is needed to maintain 70 indoors. Sun and heat sources make up difference. Heat gain and heat loss are in balance.

47
Q

What’s a Heating degree-day?

A

A unit to describe how long the temp is below 65 degrees and are thus used to determine the intensity of a heating season.

48
Q

How do you calculate HDDs?

A
  1. Calculate avg temp
  2. Subtract it from balance point (65)
    Answer is the HDD for that day. The HDD From every day are added together to obtain the yearly HDD total.
49
Q

What’s the cooling balance point?

A

The outdoor temp below which no indoor cooling is needed to maintain 75 indoors. The default is 65 degrees.

50
Q

What’s a cooling degree-day?

A

A unit to describe how long the temp is above 65 and are thus used to determine the intensity of a cooling season.

51
Q

How are CDDs calculated?

A
  1. Calculate avg temp
  2. Subtract it from the balance point and remove negative
    Number gives CDD for that day.
52
Q

Why are CDDs less reliable than HDDs as a predictor of cooling costs?

A

Cooling is more complicated due to other factors of summer comfort: relative humidity, solar gain or shade, internal loads

53
Q

Homes with poor insulation, air leaks, and single-pane windows will have ______ interior surfaces.

A

colder

54
Q

Well-insulated and air-sealed homes maintain _____ interior surfaces, contributing to better comfort.

A

warmer

55
Q

Relative humidity is determined by 2 things:

A

Absolute amount of water vapor in the air

Temperature of the air

56
Q

_____ air can hold more moisture than _______ air.

A

Warmer, colder

57
Q

As air cools, its relative humidity _______.

A

increases

58
Q

100% relative humidity indicates that the air is at its ________, or is completely saturated with water. Rain (or condensation) will occur.

A

dew point

59
Q

Dew points above ___ degrees are considered uncomfortable.

A

68 degrees F

60
Q

Does humidity affect heat flow?

A

No, there is no energy advantage to inside humidity in winter.

61
Q

Indoor relative humidity guidelines:

A
62
Q

In summer, ceiling fans are only effective if:

A

You can feel the moving air

The thermostat is turned up considerably

63
Q

What is psychrometrics?

A

The science of air and its properties related to buildings and comfort

64
Q

A psychrometric chart is used to understand human comfort and the energy required to produce it. Each state point on the chart has values for:

A 
Dry bulb temp
Wet bulb or dew point temp
Enthalpy
Relative humidity
Absolute humidity
65
Q

What is enthalpy?

A

The total energy of the air measured in BTU/lb. Enthalpy is sensible heat + latent heat.

66
Q

What is relative humidity?

A

The ratio, in percent, between the actual water vapor in the air vs what the air can hold at that temperature.

67
Q

What is absolute humidity?

A

The actual amount of water in air, measured in grains of water vapor per pound of dry air.

Building Science (5 decks)

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