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Building Environmental Systems > Midterm 2 > Flashcards

Midterm 2 Flashcards

1
Q

CAV

A

Constant Air Volume
Air-flow Constant, Temp changes

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2
Q

VAV

A

Variable Air Volume
Air-flow changes, Temp constant

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3
Q

What is a zone in AHU terms?

A

Space for which temp is controlled by a single thermostat

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4
Q

Why split a building into multiple zones?

A

Different cooling & heating loads
Different ventilation reqs
Different control reqs

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5
Q

What is control in HVAC equipment terms?

A

Signal to equipment to adjust components

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6
Q

What is automation in HVAC equipment terms?

A

reaction w/o operator input

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7
Q

How does a residential thermostat work?

A
  • Calculates difference b/w actual & required temp.
  • Measures temp. continuously & turns equipment on and off to meet required
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8
Q

Does “single zone CAV” have changing temperature?

A

Yes

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9
Q

What’s the difference b/w “single zone CAV” and single zone reheat CAV”?

A

Humidity Control

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10
Q

What are the four Refrigeration cycles?

A

Vapor compression cycle
Absorption refrigeration cycle
Evaporative cooling
Coefficient of performance

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11
Q

What is the difference between control differential and operating differential on a thermostat chart?

A

Control differential = zone where AC is on
Operating differential = includes peaks and troughs

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12
Q

What is KCL?

A

Kirchhoff’s Current Law
Sum of currents into a node = sum of currents leaving

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13
Q

What is KVL?

A

Kirchhoff’s Voltage Law
Sum of voltages around a loop = 0

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14
Q

What is ohm’s law?

A

V=IR

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15
Q

Draw a Temp/time phase change diagram.

A
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16
Q

Draw a temp/enthalpy phase change diagram.

A
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17
Q

Draw an AHU diagram.

A
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18
Q

What are the thermodynamic characteristics of refrigerants?

A

High latent enthalpy of vaporization
Low freezing T
Low condensing P
Positive evaporating P

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19
Q

What are physical and/or chemical characteristics of refrigerants?

A

Good heat transfer
Low water solubility
Not reactive

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20
Q

What are the safety concerns around refrigerants?

A

Flammability
Toxicity
Irritability

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21
Q

What are the potential negative effects of refrigerants on the environment?

A

Ozone depletion
Global warming

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22
Q

Draw vapor compression cycle, both as a T-s diagram and a diagram with components.

A
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23
Q

Draw evaporative cooling diagram.

A
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24
Q

What is the equation for coefficient of performance?

A

Qevaporator / Qcompressor
(h1 - h4) / (h2 - h1)

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25
Q

What is the typical COP range for a vapor compression cycle?

A

2.5 - 7

26
Q

What is the typical COP range for an absorption cycle?

A

0.5 - 1

27
Q

Electricity can convert to:

A

Mechanical energy
Light
Heat

28
Q

What are some things electricity can be used to power?

A

Lighting
AC
Transportation
Production equipment

29
Q

Charge is a ________ of matter

A

Property

30
Q

Voltage is also known as

A

Potential

31
Q

Def’n of energy:

A

Discomfort caused by a local accumulation / deficit of e-

32
Q

What are the units of voltage?

A

Joule / Coulomb

33
Q

Ground def’n

A

electrically neutral place (zero voltage / potential)

34
Q

Conductivity def’n

A

the ability of e- to travel freely

35
Q

Current def’n

A

Flow rate of q

36
Q

Voltage and current are:

A

proportional

37
Q

What is the conductance or conductivity equation?

A

G = 1 / R

38
Q

Power def’n

A

Rate at which energy is used

39
Q

Power equation:

A

P = V I

40
Q

Draw power triangle, explain components.

A
41
Q

What is impedance?

A

Property accounting for resistance and reactance

42
Q

In an inductive circuit, current ______ voltage

A

Lags

43
Q

In a capacitative circuit, current _______ voltage

A

Leads

44
Q

What is reactive power?

A

Component of AC that does not do useful work

45
Q

What is apparent power?

A

product of voltage and current

46
Q

What is working power?

A

component of AC that performs useful work

47
Q

What are the four types of dependent (controlled) sources?

A

Voltage controlled voltage source
Current controlled voltage source
Voltage controlled current source
Current controlled current source

48
Q

When it comes to controlled sources, how can you tell what is the input and what is the output?

A

Inside tells the output (arrow = current, + - = voltage), and outside tells the input (i = current, v = voltage)

49
Q

With direct current, current flows in:

A

one direction

50
Q

With alternating current, current flows in:

A

multiple directions, reverses rapidly

51
Q

What’s the use of AC?

A

Can effectively raise voltage

52
Q

What do resistors do?

A

Convert electricity into heat

53
Q

Properties of capacitors:

A

Store energy in electric field
Transmit AC of higher frequency
Resist change in Voltage
Cause AC to lead voltage

54
Q

Properties of Inductors

A

Store energy in magnetic field
Transmit current of lower frequency
Resist change in Current
Cause AC to lag voltage

55
Q

Units of Capacitance?

A

Farads

56
Q

Units of Inductance?

A

Henrys

57
Q

Capacitors in parallel and series:

A

Parallel = + + +
Series = 1/( 1/x + 1/x ….)

58
Q

Inductors in parallel and series:

A

Parallel = 1/( 1/x + 1/x ….)
Series = + + +

59
Q

Equation for the power triangle:

A

S^2 = Q^2 + P^2

60
Q

Equation for Reactive power:

A

Q = V x I sin(theta)

61
Q

Equation for Working power:

A

P = V x I cos(theta)

62
Q

Apparent power formula:

A

S = V x I

Building Environmental Systems (2 decks)

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