Principles of Automatic Heating and Cooling Controls

Question 1

How can we think of the idea of heat?

Answer 1

energy in transit from a high-temperature object to a lower temperature object

Question 2

Define temperature

Answer 2

a measurement of an object’s thermal intensity

Question 3

Cold is the _____ _____ of heat

Answer 3

relative lack

Question 4

The quantity of heat cannot be _____, but must be _____

Answer 4

measured, calculated

Question 5

What is the metric unit of measurement for energy?

Answer 5

joules

Question 6

what is the metric unit of measurement for power?

Answer 6

watts

Question 7

what is the imperial unit of measurement for energy?

Answer 7

btu

Question 8

what is the imperial unit of measurement for power?

Answer 8

btuh

Question 9

What does Btu stand for?

Answer 9

british thermal units

Question 10

How many calories are in one btu?

Answer 10

250

Question 11

How many joules are in one btu?

Answer 11

1055

Question 12

What is a British thermal unit?

Answer 12

the quantity of heat required to raise the temperature of one pound of water, one degree Fahrenheit

Question 13

What are three ways that heat is transfered from one object to another?

Answer 13

conduction, convection, radiation

Question 14

Define conduction

Answer 14

the method by which heat is transfered through solids

Question 15

Define convection

Answer 15

the method by which heat is transfered in fluids such as air or water

Question 16

Define radiation

Answer 16

the method which heat is transfered by electromagnetic wave motion

Question 17

Does heat always transfer from a high temperature object to a lower temperature object?

Answer 17

yes

Question 18

What does human comfort depend on?

Answer 18

temperature, humidity, air movement and radiation

Question 19

What is the average temperature that is comfortable for most people?

Answer 19

20 degrees celsius

Question 20

What is the percentage of humidity in the air that is comfortable for most people?

Answer 20

40% at 20 degrees Celsius

Question 21

Name the main reasons for using an automatic control system

Answer 21

comfort, safety, economy and convenience

Question 22

Describe a basic heating cycle in a room step by step

Answer 22

1) thermostat closes
2) gas valve opens
3) burner ignites
4) plenum warms
5) fan switch closes
6) blower starts

Question 23

Describe a basic cooling cycle in a room step by step

Answer 23

1) thermostat opens
2) gas valve closes
3) burner stops
5) plenum cools
6) fan switch opens
7) blower stops

Question 24

What are the basic components of a forced-air heating system?

Answer 24

Main burners, fan or blow, load devices, controlling devices, heat exchanger, flue or stack

Question 25

What is the purpose of the main burner?

Answer 25

burn the fuel to heat the inside surface of the heat exchanger

Question 26

What is the purpose of the fan or blower?

Answer 26

to draw clean air from the house return air vents and blow this air over the outside surfaces of the heat exchangers

Question 27

What is the purpose of load devices such as gas valves, relays, motors, igniters, etc?

Answer 27

They respond according to the feedback they receive from the controlling devices

Question 28

What do controlling devices do?

Answer 28

They are sensing devices that provide feedback to a load device and tell it what to do

Question 29

What are some examples of controlling devices?

Answer 29

thermostats, humidistats, limit switches, pressure switches, flame rods, sail switches, etc

Question 30

What is the purpose of the heat exchanger?

Answer 30

Heat is conducted through the heat exchanger walls to warm the clean air circulated by the blower

Question 31

What is the purpose of the flue or stack?

Answer 31

it is a pipe that carries gasses from the burning fuel out of the heat exchanger to the chimney

Question 32

Is there feedback in a closed loop system?

Answer 32

yes

Question 33

What is a device that reacts to changes in a variable condition?

Answer 33

a controlling device

Question 34

What does a limit or safety device do?

Answer 34

detects dangerous conditions in the system

Question 35

Is the control circuit for a residential heating system an example of a closed loop or open loop control system?

Answer 35

closed

Question 36

In a domestic gas furnace, the fan motor starts when:

Answer 36

the air in the plenum warms up to a pre-set temprature

Question 37

Can the fan motor keep running after the main burner shuts off?

Answer 37

yes

Question 38

What do schematic diagrams show?

Answer 38

the logic operation of components

Question 39

If you wanted to find the relative position of components in a heating system and the wiring between them, what kind of diagram would you look at?

Answer 39

wiring diagram

Question 40

A schematic diagram is drawn with power _____ and ____ heat

Answer 40

off, no

Question 41

What kind of device is a relay coil?

Answer 41

load device

Question 42

A pressure switch is an example of what kind of device?

Answer 42

controlling