Midterm 2

Question 1

CAV

Answer 1

Constant Air Volume
Air-flow Constant, Temp changes

Question 2

VAV

Answer 2

Variable Air Volume
Air-flow changes, Temp constant

Question 3

What is a zone in AHU terms?

Answer 3

Space for which temp is controlled by a single thermostat

Question 4

Why split a building into multiple zones?

Answer 4

Different cooling & heating loads
Different ventilation reqs
Different control reqs

Question 5

What is control in HVAC equipment terms?

Answer 5

Signal to equipment to adjust components

Question 6

What is automation in HVAC equipment terms?

Answer 6

reaction w/o operator input

Question 7

How does a residential thermostat work?

Answer 7

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

Question 8

Does “single zone CAV” have changing temperature?

Answer 8

Yes

Question 9

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

Answer 9

Humidity Control

Question 10

What are the four Refrigeration cycles?

Answer 10

Vapor compression cycle
Absorption refrigeration cycle
Evaporative cooling
Coefficient of performance

Question 11

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

Answer 11

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

Question 12

What is KCL?

Answer 12

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

Question 13

What is KVL?

Answer 13

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

Question 14

What is ohm’s law?

Answer 14

V=IR

Question 15

Draw a Temp/time phase change diagram.

Question 16

Draw a temp/enthalpy phase change diagram.

Question 17

Draw an AHU diagram.

Question 18

What are the thermodynamic characteristics of refrigerants?

Answer 18

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

Question 19

What are physical and/or chemical characteristics of refrigerants?

Answer 19

Good heat transfer
Low water solubility
Not reactive

Question 20

What are the safety concerns around refrigerants?

Answer 20

Flammability
Toxicity
Irritability

Question 21

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

Answer 21

Ozone depletion
Global warming

Question 22

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

Question 23

Draw evaporative cooling diagram.

Question 24

What is the equation for coefficient of performance?

Answer 24

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

Question 25

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

Answer 25

2.5 - 7

Question 26

What is the typical COP range for an absorption cycle?

Answer 26

0.5 - 1

Question 27

Electricity can convert to:

Answer 27

Mechanical energy Light Heat

Question 28

What are some things electricity can be used to power?

Answer 28

Lighting AC Transportation Production equipment

Question 29

Charge is a ________ of matter

Answer 29

Property

Question 30

Voltage is also known as

Answer 30

Potential

Question 31

Def'n of energy:

Answer 31

Discomfort caused by a local accumulation / deficit of e-

Question 32

What are the units of voltage?

Answer 32

Joule / Coulomb

Question 33

Ground def'n

Answer 33

electrically neutral place (zero voltage / potential)

Question 34

Conductivity def'n

Answer 34

the ability of e- to travel freely

Question 35

Current def'n

Answer 35

Flow rate of q

Question 36

Voltage and current are:

Answer 36

proportional

Question 37

What is the conductance or conductivity equation?

Answer 37

G = 1 / R

Question 38

Power def'n

Answer 38

Rate at which energy is used

Question 39

Power equation:

Answer 39

P = V I

Question 40

Draw power triangle, explain components.

Question 41

What is impedance?

Answer 41

Property accounting for resistance and reactance

Question 42

In an inductive circuit, current ______ voltage

Answer 42

Lags

Question 43

In a capacitative circuit, current _______ voltage

Answer 43

Leads

Question 44

What is reactive power?

Answer 44

Component of AC that does not do useful work

Question 45

What is apparent power?

Answer 45

product of voltage and current

Question 46

What is working power?

Answer 46

component of AC that performs useful work

Question 47

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

Answer 47

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

Question 48

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

Answer 48

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

Question 49

With direct current, current flows in:

Answer 49

one direction

Question 50

With alternating current, current flows in:

Answer 50

multiple directions, reverses rapidly

Question 51

What's the use of AC?

Answer 51

Can effectively raise voltage

Question 52

What do resistors do?

Answer 52

Convert electricity into heat

Question 53

Properties of capacitors:

Answer 53

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

Question 54

Properties of Inductors

Answer 54

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

Question 55

Units of Capacitance?

Answer 55

Farads

Question 56

Units of Inductance?

Answer 56

Henrys

Question 57

Capacitors in parallel and series:

Answer 57

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

Question 58

Inductors in parallel and series:

Answer 58

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

Question 59

Equation for the power triangle:

Answer 59

S^2 = Q^2 + P^2

Question 60

Equation for Reactive power:

Answer 60

Q = V x I sin(theta)

Question 61

Equation for Working power:

Answer 61

P = V x I cos(theta)

Question 62

Apparent power formula:

Answer 62

S = V x I