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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
Glass enclosed magnet and armature snap acting contacts
26
Heating and cooling thermostats
Heating contacts close cooling contacts open
27
Thermostat wiring
Red line 1 white Heating yellow cooling green fan
28
Anticipator
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
29
Thermocouple power unit
flame proving device generates 26 to 32mV holds armature in place for gas to flow 10 to 30 secs
30
Safety pilot switch
in series with main gas valve stops gas flow
31
Safety gas valve
stops gas flow to main burner and pilot flame
32
Soleniod valvees
control flow of gas in series with operating controllers
33
Diaphargm valves
turns the supply gas to main burner on or off
34
Combination gas valve
gas regulator, safety gas valve, power unit, main gas valve, manual has valve
35
Blower Motor
fractional horsepower 2 speed
36
Thermocouple test
Open circuit 26 to 32mV Closed circuit 25 to 50% output response time turn down test ensures pilot flame ignites main burner
37
Cycle of operation
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
Step open gas valve
2 step gas release reduce inital inrush of gas
39
Make up air and exhaust air
interlocked make up air must be pre-heated
40
HRV
recovers heat from exhaust air
41
Efficiency Ratings
standard 55 -72% mid efficiency 80-83% high efficiency 90-93%
42
Combustion air components
combustion air blower air prove switch heat exchanger primary high limit switch
43
combustion air blower
move products of combustion purge combustion chamber
44
air proving switch
pressure controller NO points creates low pressure prevents unsafe burner operatiion
45
burner assembly
burners gas valve ignitier flame sensor roll out limit switch
46
hot surface ignition system
no pilot flame silicon nitride dont touch with bare hands
47
intermittent pilot ignition system
ignites pilot flame
48
flame sensing
use the flame as a conductor
49
cycle of operation efficient gas heating
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
Cartridge air filtration
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
humidifiers
standing water absorbent pads rotating drum humidifier rotating disc flow thru
52
zone valve transformers
40 VA not loaded beyond 32 VA
53
Reverse acting aquastat
prevents cold water from circulating the system
54
cad cell
light sensitive resistance drop to 300 to 1000 ohm to allow current flow
55
circulating pumps
1 hp single stage centrifugal pump can be oil or water lubricated provides proper pressure can run continuously with a bypass valve
56
low water cut out
shuts fuel supply if water level in boiler falls below a point float switch combined with make water switch 24V
57
Aquastats
react to water temperature fail-safes
58
immersion aquastat
gas filled bulb switching mechanisim through capilliary tube
59
surface mounted aquastat
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
compressor
compress refrigerant in cool low pressure out hot high pressure
61
condenser
finned heat radiator cooled by passing air from convection or cooling fan cool compressed hot refrigerant vapours
62
evaporator
finned heat absorber device located in air stream expose refrigerant to air stream
63
refrigerant control valve
released controlled amounts of cooled compressed refrigerant temperature controlled thermal electric valve pressure controlled automatic expansion valve
64
Auxillary devices
filter dryer pressure control internal pressure sensor short cycling protection crackcase heater
65
cycle of operation
reciever warm high pressure refridgerant control valve cold low pressure evaporator coil warm low pressure compressor hot high pressure condensor warm high pressure
66
disconnecting means
within sight within 3m
67
conductor lengths
18 AWG <35m 16AWG > 35m
68
combined heating and cooling
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
Heat pumps
reversing refrigerant for both heating and cooling 4 way reversing valve indoor and outdoor coil
70
components of HVAC
Heating cooling ventiliation
71
compressor lockout switch
when low pressure, high poressure, low temperature switch is activated
72
Ventilation
blower (indoor blower motor) blower motor supply building with air evaporator
73
disconnect on rooftop units
within sight within 3m
74
Rooftop heating cycle
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
Rooftop cooling cycle
thermostat for cooling close compressor and condensor start evaporator fan energizes thermostat contacts opens
76
make up air unit
direct fired no heat exchanger indirect fired with heat exchanger exhaust fan
77
2 wire thrmostat
simple homes R W
78
3 wire thermostat
R W G
79
5 wire thrmostat
RC RH W Y G rc rh jumpered
80
7 wire thermostat
RH RC W1 W2 Y1 Y2 G
81
HVAC control systems
DDC BAS EMS ECS FMS
82
analog input
varying signal
83
digital output
on or off
84
analog output
0-10 V
85
rooftop enclosure
raintight
86
MAXIMUM WATTS PER METER
87
What type of signal is used to communicate between the temperature controller and the electronic controller in a solid state switching arrangement?
MILIAMP
88

2nd Period Electrican (4 decks)

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