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period 2 - sait > Principles of Automatic Heating Controls > Flashcards

Principles of Automatic Heating Controls Flashcards

1
Q

In psychometrics, what does the term “specific humidity” refer to?

A

The ratio of mass of water vapor to the mass of dry air in a given volume

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2
Q

What device is commonly used for humidification in residential and commercial settings?

A

humidifier

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3
Q

What mechanism primarily drives the flow of combustion gases in a natural draft furnace?

A

the buoyancy effect due to temperature differences

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4
Q

which of the following best describes the ventilation system in a natural draft furnaces?

A

it relies on a chimney or flue to create a natural airflow

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5
Q

What is the primary purpose of redundant gas valves in a furnace system?

A

to provide backup safety measures in case of a primary valve failure

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6
Q

What state should a high limit control be in when de-energized?

A

it should be closed, it will open on a rise in temperature

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7
Q

With the burner firing and the fan running, what voltage would you get across a closed high limit switch?

A

0 volts

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8
Q

What is the primary benefit of automatic heating and cooling controls?

A

enhance comfort and convenience

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9
Q

what device is commonly used in automatic heating and cooling systems to controls room temperature?

A

thermostat

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10
Q

how do programmable thermostats contribute to energy efficiency in buildings?

A

they automatically adjust temperature settings base on occupancy patterns

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11
Q

what is the primary function of a combination gas valve in a heating system?

A

to regulate the flow of natural gas to the burner

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12
Q

in a smart heating and cooling system, what technology features allow users to controls the temperature remotely via a smartphone or computer?

A

internet connectivity

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13
Q

What improvement associated with automatic heating and cooling control

A

indoor air quality

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14
Q

what does the psychometric chart primarily illustrate?

A

relationships between temperature, humidity and other air properties

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15
Q

what is the primary function of a thermocouple in a furnace

A

to detect the presence of a pilot flame

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16
Q

How does a thermocouple operate in a furnace

A

it generates electricity when heated, signaling the gas valve to remain open

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17
Q

What is Open Loop Feedback

A

you receive feedback within the control system (cuize control)

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17
Q

What is a closed loop system?

A

when you do not receive feedback ( foot on the gas petal)

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18
Q

What is direct acting?

A

switch that opens on rise

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19
Q

What is reverse acting?

A

a switch that closes on rise

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20
Q

Define temperature?

A

the measurement of the intensity of heat of a substance

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21
Q

Define humidity?

A

the amount of moisture present in the air

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22
Q

Define air movement

A

Measures velocity of the air moving over the occupants. Rapid air movement provides cooling through evaporation and aids comfort conditions when ambient

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23
Q

What are economizers?

A

using outside air to cool the building instead of an air conditioning compressor

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24
Q

Wire count on a 2 stage heating/2 stage cooling, fan control, and common (no battery)

A

7 (R, W1,W2,Y1, Y2, G, C)

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25
Q

How to test the High Limit Switch

A
  • block airflow
  • disconnect the motor
  • place cardboard or sheet metal in front of air filter
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26
Q

When does the fan limit open on rise and close on rise?

A

90F, 125F

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27
Q

When does the high limit open on rise and close on rise?

A

190F, 160F

28
Q

What are heat anticipators and how are they set

A

prevent the overshoot of temperature, set to current of the gas valve

29
Q

What is an ammeter multiplier

A

used when checking current draw of the gas valve with a clamp meter, wrap the wire from W to the gas coil 10 turns and put the meter through the coil

30
Q

What are the control modes for two position control or a digital control?

A

on/off

31
Q

What are the control modes for a heat/cooling anticipator?

A

timed on/off
timed with 2 positions

32
Q

Natural draft furnaces use what type of current to move heated air through the building

A

convection currents

33
Q

In a natural draft furnaces, what is known as the control agent?

A

a controlled device that meters the flow of combustible gas

34
Q

most modern gas valves are what type?

A

combination gas valves

35
Q

combination gas valves controls what (4)

A
  • control gas flow
  • regulate manifold pressure
  • regulate pilot line assembly
  • provide pilot proving
36
Q

Most redundant gas valves are

A
  • normally closed
  • low pressure drop
  • solenoid actuated valve
37
Q

Pilot gas valves are

A
  • normally closed solenoid valve that start and stop the flow of combustible gas to the pilot assembly
38
Q

what is the Seebeck effect

A
  • temperature difference between two dissimilar electrical conductors or semi conductors produce a voltage difference between two.
  • when heat is applied to one of the two conductors, heated electrons flow towards the cooler one
39
Q

Thermocouple assembly is

A

a pilot gas solenoid valve powered by the Seebeck effect

40
Q

How many mV does a thermocouple produce and what type of device is it?

A
  • produces 20 to 30 mV
  • pilot proving device
41
Q

Thermopile/powerpile produces how many mV?

A

750mv

42
Q

Refrigeration mechanics work on mV as low as _____ and as high as _________

A

25mv; 600V

43
Q

What is the purpose of the high limit controller

A
  • it interrupts the safety circuit in a furnace
  • if the heat exchanger temperature rises beyond safe temperature limits, the NC switch will open
44
Q

What is an auxiliary high limit switch?

A
  • additional high limit switch
  • for instance, on counter flow furnaces, if the fan motor fails, heat will not go to the normal place above the heat exchanger, so they put one in the blower area
45
Q

What is a fan controller?

A
  • starts and stops the supply air fan in response to the temperature of the heat exchanger
  • prevents uncomfortable cool drafts by allowing the supply fan to start only after the heat exchanger is warm
  • helps prevent cracks in the heat exchanger
46
Q

What is a combination fan & high limit ?

A
  • serves as the fan control and high limit switch
  • common on older furnaces and still used on inderect fired MUA’s
47
Q

What is a high limit control

A
  • temperature limit controller that interrupts the safety circuit in a furnace if the heat exchanger temperature rises beyond safe temperature limits
48
Q

Causes for high limit control to trip

A
  • plugged filters, dirty AC coil, loose belt, dirty fan, fan motor fail, closed fire damper
49
Q

What temperature is the fan controller set to start?

A

125F

50
Q

What temperature deviation can cause human discomfort?

A

5F (3C)

51
Q

what are the 3 basic goals you use to evaluate a good building control system

A
  • minimum deviation from normal conditions following a heating or load change
  • minimum time to restore conditions to normal following heating or cooling load change
  • minimal offset due to changes in the external environment
52
Q

what is psychmetrics

A

the study of the properties as it relates to human discomfort

53
Q

what are the 3 variables of psychometrics

A

temperature
humidity
air movement

54
Q

what temperature range are most people comfortable with?

A

72F to 75F (21.5C - 24C)

55
Q

what relative humidity range is considered comfortable?

A

30% to 60%

56
Q

what are the 3 common voltage levels that are used to actuate main gas valves

A

24vac, 120vac, 750mV DC

57
Q

what device does a high limit controller control?

A

interrupts the safety circuit in a furnace

58
Q

what are the three types of zone thermostats

A

electronic, electromechanical, thermopile

59
Q

who publishes the Canadian Electrical Code?

A

Canadian Standards Association

60
Q

how much over current protection is required for a non standard 24 volt transformer used to power a Class 2 control circuit?

A

should no exceed 100 volt amperes

61
Q

What is the usual size of a conductor in a class 2 circuit?

A

14 AWG

62
Q

What are the requirements for a disconnect switch for a 100,000 BTU furnace

A

must be accessible in an emergency and labelled accordingly

63
Q

How to calculate continuous duty motor conduct ampacity?

A

125% of motors full load current

64
Q

what is the minimum ampacity for control components that conduct power for a hermetic compressor?

A

contactors, relays and other controls must be rated for LRA of motor. If unavailable, must be rated for 6x FLA of motor compressor

65
Q

How to calculate the size of an overload protector fuse for a hermetic motor compressor?

A

1.4x RLA - overload relays
1.25 x RLA - fuses

66
Q

What is a cut in, cut out and differential switch and how to calculate?

A
  • its a compressor pressure switch that controls when the compressor starts and stops when the pressure drops back to the cut in pressure
  • for example: compressor is set to cut out at 150 psi, and set to cut back in at 75psi, the differential is 75psi
67
Q

What is a rollout/spill switch?

A

a safety cut out switch that cuts supply to the furnace when it detects higher temperatures than normal immediately outside the combustion chamber

68
Q

What is a thermister

A

resistance thermometer whose resistance is dependent on temperature.
- Negative temperature coefficient thermister is when temperature rises, resistance decreases
- positive temperature thermister coefficient is when temperature increases, resistance increases (most common and used as a fuse)
- found in digital thermometers

period 2 - sait (3 decks)

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