Principles of Automatic Heating and Cooling Controls

Question 1

What is heat?

Answer 1

A form of energy arising from the random motion of molecules.

Energy in transit from a warmer object to a cooler object.

Question 2

What is cold?

Answer 2

The relative lack of heat.

Question 3

What is the unit used to measure the amount of energy to raise 1 pound of water 1 degree farenheit?

Answer 3

1 British thermal unit (Btu)

Question 4

What does one calorie represent?

Answer 4

The amount of energy required to raise 1 gram of water 1 degree Celsius at a pressure of 1 Atmosphere.

Question 5

Can heat be measured?

Answer 5

No. It must be calculated.

Question 6

How is a heating system rated?

Answer 6

By it’s rate of energy input.

Question 7

What are the typical ratings of a standard single dwelling heating unit?

Answer 7

100 000 Btu or 29.3 kW.

Question 8

How is a cooling system rated?

Answer 8

By the rate of energy output.

Question 9

What are the typical ratings of a standard single dwelling Cooling system?

Answer 9

7.5 tonne*cal/h or 2.5 tons

Question 10

What are the three methods of heat transfer, and how is it achieved?

Answer 10

Conduction - Heat transfer through solids, molecules pass on energy to surrounding molecules.
Convection - Fluids expand when heated and therefore generate currents through the fluid mass, generating heat.
Radiation - Transfer of energy by electromagnetic wave motion.

Question 11

Would heat ever transfer from a cold object to a warmer one?

Answer 11

No.

Question 12

Is the rate of heat transfer dependent on the temperature differential between two entities?

Answer 12

Yes, the wider the differential, the faster the transfer.

Question 13

What is human comfort dependent on?

Answer 13

H-umidity (40%)
A-ir movement (Fast air is cold)
R-adiation (Cold objects steal heat)
T-emperature (20*)

Question 14

When only some conditons are met for basic human comfort, what is the condition of feeling cold in these circumstances named?

Answer 14

COLD 20.

Question 15

Why do we use automatic controls?

Answer 15

S-afety
E-conomy
C-omfort
C-onvenience

Question 16

What is a closed loop control system?

Answer 16

One which uses feedback to make the control process automatic.

Question 17

How does the air get heated in a basic forced air heating system?

Answer 17

By convection of air in the plenum through radiation of the heat exchanger filled with hot gas.

Question 18

Where is a filter typically located on a basic forced air heating system?

Answer 18

Before the fan at the cold air return, so that dust does not burn on the heat exchanger or clog the fan.

Question 19

There are three generally used power supplies on basic forced air heating systems, what range are they?

Answer 19

120v AC (Power cct.)
24v AC (Control cct.)
26-32mV DC (Flame proving cct.)

Question 20

How does a thermostat work?

Answer 20

Ambient temperature operates a thermal sensing device which opens or closes a set of contacts. The temperature at which it operates may be set.

Question 21

How does a fan control switch look on a schematic diagram?

Answer 21

A normally open temperature actuated switch. (square lightning bolt pattern)

Question 22

How does a High limit switch look on a schematic diagram?

Answer 22

A normally closed temperature actuated switch. (square lightning bolt pattern)

Question 23

How does an exhaust prove switch look on a schematic diagram?

Answer 23

A normally open pressure actuated switch. (half circle pattern)

Question 24

How does a Hot surface igniter look on a schematic diagram?

Answer 24

Like the top of a castle wall, or a square resistor.

Question 25

Must gas fired heating equipment be on it’s own branch circuit?

Answer 25

Yes in mostly all cases.

Question 26

How far must electrical equipment be from gas relief devices?

Answer 26

1m for natural gas.

3m for propane.

Question 27

What type of class 2 cable may you use for heating controls?

Answer 27

LVT (Low- Voltage thermostat) Cable.