# Principles of Automatic Heating and Cooling Controls Flashcards

1
Q

What is heat?

A

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

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

2
Q

What is cold?

A

The relative lack of heat.

3
Q

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

A

1 British thermal unit (Btu)

4
Q

What does one calorie represent?

A

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

5
Q

Can heat be measured?

A

No. It must be calculated.

6
Q

How is a heating system rated?

A

By it’s rate of energy input.

7
Q

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

A

100 000 Btu or 29.3 kW.

8
Q

How is a cooling system rated?

A

By the rate of energy output.

9
Q

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

A

7.5 tonne*cal/h or 2.5 tons

10
Q

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

A

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.

11
Q

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

A

No.

12
Q

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

A

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

13
Q

What is human comfort dependent on?

A

H-umidity (40%)
A-ir movement (Fast air is cold)
T-emperature (20*)

14
Q

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

A

COLD 20.

15
Q

Why do we use automatic controls?

A

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

16
Q

What is a closed loop control system?

A

One which uses feedback to make the control process automatic.

17
Q

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

A

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

18
Q

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

A

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

19
Q

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

A
```120v AC (Power cct.)
24v AC (Control cct.)
26-32mV DC (Flame proving cct.)```
20
Q

How does a thermostat work?

A

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

21
Q

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

A

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

22
Q

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

A

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

23
Q

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

A

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

24
Q

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

A

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

25
Q

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

A

Yes in mostly all cases.

26
Q

How far must electrical equipment be from gas relief devices?

A

1m for natural gas.

3m for propane.

27
Q

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

A

LVT (Low- Voltage thermostat) Cable.