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2nd Period Electrican > HCC > Flashcards

HCC Flashcards

1
Q

Closed Loop Control

A

uses feedback to make the control process automatic

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2
Q

Thermostat

A

temperature actuated sensor that provides feedback

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3
Q

High limit switch

A

safety device that shuts gas valve
prevents dangerously high temperature
disc type
located near top of heat exchanger
80 to 120 degrees maximum

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4
Q

Circuit voltage to ground dwelling unit

A

max 150V

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5
Q

Class 1 extra low voltage power circuit

A

30V & 1000VA

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6
Q

Class 2 low energy power circuit

A

150V & 100VA

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7
Q

24V thermostat wiring

A

LVT cable

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8
Q

Bi-metal temperature sensing device

A

operates on the principle that different metals expand and contract at different rates as temperature change

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9
Q

Strip type

A

2 strips of dissimilar metals welded together

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10
Q

Spiral type

A

wound in sprail or coil
1.5 cm by 20cm
higher sensitivity
ideal for mercury bulb switches

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11
Q

Disc type

A

2cm by 3 cm
snapping action from mechanical stress
sealed

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12
Q

Bellow type sensing

A

uses a fluid that vaporizes to move contacts
large snapping action
ideal for line voltage thermostat for unit heaters and electric heating

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13
Q

Liquid bulb type temperature sensing

A

operates by expanding and contracting volume of liquid
monitoring temperature of water and air in a pipe or tank

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14
Q

Thermocouples

A

generate voltages proportional to temperature
made of 2 dissimilar wires metals
30mV
hot junction inside metallic capsule
prove existence of open flame

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15
Q

Thermopile

A

thermocouples in series
800mVh

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16
Q

Thermistor

A

Solid State Device
resistance of semi-conductor material changes with temperature
small physical size
negative temperature coefficient
accurate

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17
Q

Resistance temperature detector

A

like thermistor
uses copper, nickel, platinum
positive temperature coeffiecint
platinum most commonly used due to high anti corrision
senses extreme temperature
greater accuracy, used for industrial settings

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18
Q

Pyrometer

A

lens focused thermocouple
measured at a distance
moving objects

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19
Q

COunter flow furnace

A

fan at the top
hot air pushed to the bottom
2 high limit switches
121 to 149 degrees maximum

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20
Q

Fan Cycling

A

fan ON is too low (49 to 60)
fan off is too high (32 to 38)
differential is to narrow (17 to 22)

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21
Q

High Limit cycling

A

fan failure

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22
Q

Thermostat contacts

A

mercury contacts
spring activated snap action exposed contacts
glass enclosed magnet and armature snap acting contacts

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23
Q

Mercury Contacts

A

mercury is tilted towards the 2 wires to complete the circuit
not for high current rating

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24
Q

Spring activated snap action exposed contacts

A

rubbing action when they close
high current switching
require maintenance

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25
Q

Glass enclosed magnet and armature snap acting contacts

A
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26
Q

Heating and cooling thermostats

A

Heating contacts close
cooling contacts open

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27
Q

Thermostat wiring

A

Red line 1
white Heating
yellow cooling
green fan

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28
Q

Anticipator

A

generates a small amount of heat to the thermostat
anticipates a rise in temperature
series for heating
parallel for cooling
adjustable for heating
fixed for cooling

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29
Q

Thermocouple power unit

A

flame proving device generates 26 to 32mV
holds armature in place for gas to flow
10 to 30 secs

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30
Q

Safety pilot switch

A

in series with main gas valve
stops gas flow

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31
Q

Safety gas valve

A

stops gas flow to main burner and pilot flame

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32
Q

Soleniod valvees

A

control flow of gas
in series with operating controllers

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33
Q

Diaphargm valves

A

turns the supply gas to main burner on or off

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34
Q

Combination gas valve

A

gas regulator, safety gas valve, power unit, main gas valve, manual has valve

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35
Q

Blower Motor

A

fractional horsepower
2 speed

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36
Q

Thermocouple test

A

Open circuit 26 to 32mV
Closed circuit 25 to 50% output
response time
turn down test ensures pilot flame ignites main burner

37
Q

Cycle of operation

A

room gets cold, thermostat contacts close
anticipator heat up
solenoid engergizes
gas valve opens
ignition
heat exchanger warms
fan on reached, blower fan turns on
room at desired temp
thermostat contacts open
soleniod drops plunger
gas valve closes
heat exchanger cools
fan off reached
rooms cools

38
Q

Step open gas valve

A

2 step gas release
reduce inital inrush of gas

39
Q

Make up air and exhaust air

A

interlocked
make up air must be pre-heated

40
Q

HRV

A

recovers heat from exhaust air

41
Q

Efficiency Ratings

A

standard 55 -72%
mid efficiency 80-83%
high efficiency 90-93%

42
Q

Combustion air components

A

combustion air blower
air prove switch
heat exchanger
primary high limit switch

43
Q

combustion air blower

A

move products of combustion
purge combustion chamber

44
Q

air proving switch

A

pressure controller NO points
creates low pressure
prevents unsafe burner operatiion

45
Q

burner assembly

A

burners
gas valve
ignitier
flame sensor
roll out limit switch

46
Q

hot surface ignition system

A

no pilot flame
silicon nitride
dont touch with bare hands

47
Q

intermittent pilot ignition system

A

ignites pilot flame

48
Q

flame sensing

A

use the flame as a conductor

49
Q

cycle of operation efficient gas heating

A

thermostat contacts close
combustion air motor purges
air prove switch closes
igntion circuit energizes
gas valve opens
igntion
flame sensor senses flame
deenergize ignition system
blower fan energizes after set temperature

50
Q

Cartridge air filtration

A

installed in return air supply
standard fiberglass
mid efficient 3 to 10 micron
high efficiency 1 micron
micro-biocide
electronic filters charges particles with positive charge
electrostatic
connected to HTG ACC COM

51
Q

humidifiers

A

standing water absorbent pads
rotating drum humidifier
rotating disc
flow thru

52
Q

zone valve transformers

A

40 VA
not loaded beyond 32 VA

53
Q

Reverse acting aquastat

A

prevents cold water from circulating the system

54
Q

cad cell

A

light sensitive
resistance drop to 300 to 1000 ohm to allow current flow

55
Q

circulating pumps

A

1 hp
single stage centrifugal pump can be oil or water lubricated
provides proper pressure
can run continuously with a bypass valve

56
Q

low water cut out

A

shuts fuel supply if water level in boiler falls below a point
float switch
combined with make water switch
24V

57
Q

Aquastats

A

react to water temperature
fail-safes

58
Q

immersion aquastat

A

gas filled bulb switching mechanisim through capilliary tube

59
Q

surface mounted aquastat

A

mounted on external pipe or heat exchanger surface
affected by ambient temperature
high limit protection
switch burner mechanism and ignition sequience off
maintain minimum working temperature

60
Q

compressor

A

compress refrigerant
in cool low pressure
out hot high pressure

61
Q

condenser

A

finned heat radiator
cooled by passing air from convection or cooling fan
cool compressed hot refrigerant vapours

62
Q

evaporator

A

finned heat absorber device
located in air stream
expose refrigerant to air stream

63
Q

refrigerant control valve

A

released controlled amounts of cooled compressed refrigerant
temperature controlled thermal electric valve
pressure controlled automatic expansion valve

64
Q

Auxillary devices

A

filter dryer
pressure control
internal pressure sensor
short cycling protection
crackcase heater

65
Q

cycle of operation

A

reciever warm high pressure
refridgerant control valve cold low pressure
evaporator coil warm low pressure
compressor hot high pressure
condensor warm high pressure

66
Q

disconnecting means

A

within sight
within 3m

67
Q

conductor lengths

A

18 AWG <35m
16AWG > 35m

68
Q

combined heating and cooling

A

evaporator coil in warm air plenum
2 speed blower motor low for heat, high for cool
cooling unit
heating/cooling thermostat
indoor fanrelay
transformer
low temp sensor

69
Q

Heat pumps

A

reversing refrigerant for both heating and cooling
4 way reversing valve
indoor and outdoor coil

70
Q

components of HVAC

A

Heating
cooling
ventiliation

71
Q

compressor lockout switch

A

when low pressure, high poressure, low temperature switch is activated

72
Q

Ventilation

A

blower (indoor blower motor)
blower motor
supply building with air
evaporator

73
Q

disconnect on rooftop units

A

within sight
within 3m

74
Q

Rooftop heating cycle

A

thermostat for heating closes
combustion blower motor energize
air pressure switch closes
spark ignition energizes
flame rod proves pilot flame, ignition circuit deenergizes
main gas valve opens
evaporator fan energizes
thermostat contacts opens
gas valve closes

75
Q

Rooftop cooling cycle

A

thermostat for cooling close
compressor and condensor start
evaporator fan energizes
thermostat contacts opens

76
Q

make up air unit

A

direct fired no heat exchanger
indirect fired with heat exchanger
exhaust fan

77
Q

2 wire thrmostat

A

simple homes
R W

78
Q

3 wire thermostat

A

R W G

79
Q

5 wire thrmostat

A

RC RH W Y G
rc rh jumpered

80
Q

7 wire thermostat

A

RH RC W1 W2 Y1 Y2 G

81
Q

HVAC control systems

A

DDC
BAS
EMS
ECS
FMS

82
Q

analog input

A

varying signal

83
Q

digital output

A

on or off

84
Q

analog output

A

0-10 V

85
Q

rooftop enclosure

A

raintight

86
Q

MAXIMUM WATTS PER METER

A
87
Q

What type of signal is used to communicate between the temperature controller and the electronic controller in a solid state switching arrangement?

A

MILIAMP

88
Q
A

2nd Period Electrican (4 decks)

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