Heating And Cooling Systems 030203a

Question 1

What is temperature a measure of?

Answer 1

An object’s thermal energy.

Question 2

What is a BTU (British thermal unit) defined as?

Answer 2

The approximate quantity of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.

Question 3

Heat is transferred from one object to another by 3 different ways. What are they?

Answer 3

Conduction.

Convection.

Radiation.

Question 4

The method by which heat is transferred through solids is known as what?

Answer 4

Conduction

Question 5

Method by which heat is transferred through fluids such as air or water is known as?

Answer 5

Convection.

Question 6

Heat transfer by electromagnetic wave motion is known as?

Answer 6

Radiation.

Question 7

What four variables are human comfort dependent on?

Answer 7

Temperature.

Humidity.

Air movement.

Radiation.

Question 8

What is the term Cold 20 referring to?

Answer 8

When a temperature is set to 20 degrees Celsius but the room still feels cold due to the other variables like air movement, humidity or radiation.

Question 9

What is one BTU (British thermal unit) equivalent to?

Answer 9

250 calories or 1055 joules.

Question 10

What is one calorie defined as?

Answer 10

The amount of heat required to raise the temperature of 1 gram of water by 1 degrees Celsius at atmospheric pressure.

Question 11

What are the four main reasons for using automatic controls?

Answer 11

Comfort, safety, economy and convenience.

Question 12

How would heat be defined?

Answer 12

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

Heat always transfers from hotter to cooler.

Question 13

How is cold defined?

Answer 13

The relative lack of heat.

Question 14

What are the three types of bimetal temperature sensing devices?

Answer 14

Strip type. (Two strips of dissimilar metals)

Spiral type. (Bimetal strip in the shape of a spiral. Ideal for activating mercury bulb switches.)

Disc type. (Suitable for larger ampacity loads. Also suitable for monitoring the temperature of moving air.)

Question 15

What are all the types of temperature sensing devices?

Answer 15

Bimetal.
Bellows.
Liquid bulb.
Thermocouple.
Thermopile.
Thermistor.
Resistance Temperature Detector. (RTD).
Pyrometer.

Question 16

What are liquid bulb temperature sensing devices really good for?

Answer 16

Monitoring the temperature of water and air in a pipe or tank.

Question 17

What are thermocouples and how much voltage do they generally generate?

Answer 17

Temperature sensor that generates a small voltage in proportion to temperature.

Typically generate a voltage between 26-32 millivolts DC.

Question 18

What is the device called that has many thermocouples connected in series?

Answer 18

Thermopile or powerpiles.

Voltage can reach as high as 800 mV DC.

Question 19

What is the a thermistor?

Answer 19

A solid state device in which the resistance of the semiconductor material changes in response to changes in temperature.

Question 20

What type of temperature sensing device has a negative temperature coefficient?

Answer 20

Thermistors.

As temperature goes up, resistance goes down.

Question 21

What is the most common type of metal used in resistance temperature detectors and why?

Answer 21

Platinum.

Chemically stable metal that resists corrosion and oxidation in hostile environments. Has a very high melting point.

Question 22

What temperatures can pyrometers measure?

Answer 22

As high as 4000 degrees Celsius.

Suitable for measuring the temperature in industrial kilns and metal refining furnaces.

Question 23

What temperature sensing devices are considered as solid-state?

Answer 23

Thermistors.
Resistive temperature devices (RTDs).
Thermocouples.
Thermopiles.

Question 24

Which temperature sensing device uses the expansion and contraction of ether?

Answer 24

Bellows type.

Question 25

What are the three types of contacts in a thermostat?

Answer 25

Mercury contacts.

Spring-activated, snap-action exposed contacts.

Glass-enclosed magnet and armature snap-acting contacts.

Question 26

What component of a thermostat can increase the sensitivity of thermostats?

Answer 26

Anticipators

Question 27

What are the thermostat wiring terminals and what is each terminal meant for?

Answer 27

Source - R, Rh, Rc

Heating - W

Cooling - Y

Fan - G

Common - C

Question 28

What are some types of heating systems?

Answer 28

Resistive.

Forced Air.

Hydronic.

Heat pump.

Question 29

What is the most common type of electric heating system and what is an example of it?

Answer 29

Resistive heating.

Electric baseboard heating.

Question 30

What type of heating unit can be either passive or forced air?

Answer 30

Resistive heating.

Question 31

Which device can provide both cooling and heating?

Answer 31

Heat pumps.

Question 32

Which method of heat transfer does a hydronic heating system utilize?

Answer 32

Convection.

Question 33

What are thermocouples most often used for?

Answer 33

To prove the existence of a flame.

Used in hot water tanks, furnaces or gas fireplaces.

Question 34

What are the advantages and disadvantages of thermocouples?

Answer 34

Advantages - simple, durable construction and relatively low cost.

Disadvantages - Slow response time.

Question 35

What is the expected mV output of a thermocouple when doing a closed circuit test?

Answer 35

25% to 50% of the open circuit mV output.

7.5mV to 15 mV.

Question 36

What are the tests that you should perform on a thermocouple?

Answer 36

Open-circuit test. (26 to 32 mV)
Closed-circuit test (7.5 to 15 mV)
Response time test.
Dropout point test.
Turn down test (performed by a gas fitter.)

Question 37

How do you convert Celsius to Fahrenheit?

Answer 37

Temperature x 1.8 + 32