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5th Class PWR ENG > Heating Systems > Flashcards

Heating Systems Flashcards

(95 cards)

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1
Q

What is a radiator?

A

-Radiators use steam or hot water to heat up a space and takes up a large surface area
-Newer units use steel
- 3 types of radiators
-Floor type
-Window type
-Wall hung

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2
Q

What is a convector?

A

-Hot water and/or steam flows through copper or steel pipes
-attached to pipes are fins that help with heat transfer

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3
Q

Why are Radiators and convectors placed against outside walls, under windows?

A

-Rising warm air from these units will mix with cold air coming down from the surface above
-This will prevent cold drafts on the floors and provide more even temperatures throughout the room

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4
Q

What is a unit heater and how is it used?

A

-A unit heater uses a blower or fan to force the air through the heating coils INSTEAD of using natural circulation (This provides a large heating output for a fairly small unit)

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5
Q

what are types of unit heaters?

A

Cabinet heaters
-typically used for hard to heat areas
Vertical discharge unit heater
-ceiling mounted unit that helps with vertical air discharge
Horizontal discharge unit heater
-help heat large spaces such as warehouses

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6
Q

What is a unit ventilator?

A

-unit ventilators are a cabinet type unit heater that contain a standard heating coil, a blower or fan, air filters , several dampers, and a outside air inlet

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7
Q

what is a radiator valve and how is it used?

A

-A radiator valve manually controls the flow of steam
-used with a globe valve

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8
Q

what is a radiator trap used for?

A

-as steam in the radiator gives up its heat to the room, it condensates to water, which must be removed instintaly. The radiator trap allows condensed steam or water to be discharged

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9
Q

Explain what a condensate receiver and pump is used for?

A

-Condensate drains by gravity to the condensate receiver
-the pump then pushes the water from the receiver to the steam boiler as needed
(pump can be controlled with a float switch

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10
Q

what are 2 major function of the vacuum pump?

A
  1. it creates and maintains a vacuum in the return piping so the that backpressure is reduced and the condensate flows more easily to the condensate tank
  2. it returns the condensate back to the boiler
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11
Q

Packed radiator valves have a _____________________ diaphragm that completely seals off the valve body to prevent steam from leaking out around the valve stem?
a)copper
b)bronze
c)lead
d)steel

A

b)bronze

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12
Q

What are the types of piping arrangements for steam heating systems?

A

-One-pipe gravity return system
-two-pipe gravity return system
-two-pipe gravity steam system with steam traps
-two pipe return trap system
-hartford loop
-two-pipe condensate pump system
-two-pipe vacuum return system
-two-pipe with variable vacuum system

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13
Q

What is a one-pipe gravity return system?

A

-A one-pipe gravity return system in steam heating utilizes a single pipe for both steam supply to radiators and the return of condensate back to the boiler, relying on gravity to return the condensed water. This setup means each radiator is connected to the same pipe, with steam entering at the top and condensate exiting at the bottom.

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14
Q

what is a two-pipe gravity return system?

A

-A two-pipe gravity return system in steam heating utilizes two separate pipes: a supply pipe for steam and a return pipe for condensate, relying on gravity to return the condensate to the boiler

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15
Q

What is two-pipe gravity steam system with steam traps?

A

-A two-pipe gravity steam system utilizes separate pipes for steam supply and condensate return, with steam traps at low points in the system to drain condensate and prevent steam from entering the return line.

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16
Q

what is a two-pipe return trap system?

A

-A two-pipe return trap system utilizes two separate pipes for steam supply and condensate return to a boiler. A trap, typically a temperature-activated valve, is installed at the end of each radiator to prevent steam from entering the return line, ensuring only condensate and air return.
-the boiler will be placed well below the lowest radiator or convector

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17
Q

what is a hartford loop?

A

-A Hartford Loop is a specific piping configuration in steam boiler systems designed to prevent the boiler from losing water in case of a failure in the return line. It does this by ensuring that the return line is connected to the boiler below the lowest waterline

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18
Q

what is a two-pipe condensate pump system?

A

-A two-pipe condensate pump system uses two separate pipes: one for delivering steam to heating units and another for returning condensate to the boiler. This setup is particularly useful when gravity alone isn’t sufficient to return the condensate, and a pump is needed to assist the flow. The pump collects condensate in a receiver and then forces it back to the boiler

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19
Q

What is a two pipe vacuum return system?

A

-A two-pipe vacuum return system in steam heating is a type of system that uses a vacuum pump to draw condensate from the heating units back to the boiler, while also removing air from the system. This system relies on a vacuum in the return piping to efficiently collect and return condensate, ensuring quick heating and efficient steam distribution.

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20
Q

what is a two-pipe with variable vacuum system ?

A

-A two-pipe, variable vacuum system, often associated with steam heating, uses two pipes to distribute steam for heating and return condensate to the boiler. This system utilizes a vacuum pump to maintain a negative pressure in the return line, facilitating quick heating and efficient steam distribution. The “variable” refers to the system’s ability to adjust the pressure to match the heat demand, optimizing energy usage and maintaining steady temperatures.

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21
Q

describe a series loop system?

A

-A series loop system is a hydronic (water-based) heating system where a single pipe loop directly connects all heat emitters (like radiators or baseboards) to the heat source (boiler). The water flows sequentially through each emitter, losing heat as it goes, and then returns to the boiler. This is the simplest and most cost-effective type of hydronic system, but it has limitations in temperature and flow regulation at individual units.

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22
Q

describe a one pipe-system?

A

-A one-pipe heating system uses a single pipe that serves as both the supply and return for hot water, meaning it’s connected to the boiler and then circulates back. This design means the temperature of the water decreases as it flows through the system, from the boiler to the furthest radiator.

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23
Q

what is a two-pipe direct return system ?

A

-A two-pipe direct return system is a hydronic heating or cooling system where hot or chilled water is circulated through a network of pipes, with each heat emitter (like a radiator or fan coil) connected to a supply and return main, directly returning to the central source. The water travels along the shortest possible path back to the source, meaning the closest emitter has the shortest return path, while the furthest emitter has the longest.

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24
Q

what is a two-pipe reverse return system?

A

-A two-pipe reverse return system distributes heat equally to all radiators or terminal units by routing water to the farthest unit first and returning it from the nearest unit. This configuration aims to equalize the hydraulic resistance throughout the system, ensuring each unit receives the same amount of hot water.

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25
What is a multi-zone system?
-A multi-zone heating system divides a home into separate temperature-controlled areas, each with its own thermostat. This allows for independent temperature control in each zone, offering greater comfort and potential energy savings.
26
What are some advantages of hot water heating?
a)The temperature of the supply water can be varied in relation to the changing outdoor temperature more readily than steam temperature can vary b)A hot water boiler is smaller and more compact than a steam boiler of the same output, since no boiler steam space is required -in addition pipe size is smaller in a hot water boiler c)The piping pitch or slope is not as critical in a forced circulation hot water system d)maintenance cost are typically less in a hot water systems.
27
What are some disadvantages of hot water heating?
a)When hot water systems are used in a multi story building and the boiler has to be located in the basement, the boiler must be designed to withstand high pressures due to the high head of water in the system b)in a hot water system considerable power is required tp circulate the water c)There is a greater danger of damaging due to freezing in hot water systems. it should contain glycol/water mix d)More damage will result if there is a leak e)Hot water heating systems must be piped in a fashion to prevent air pockets in the piping. Main branches are graded
28
What are some advantages of radiant heating system?
a) more even heat distribution throughout room b) more comfort for building built in concrete slabs without a crawl space c) heating elements are out of sight and do not interfere with decorations
29
What are some disadvantages of a radiant heating system ?
a) The panels are fairly slow in heating up and cooling down due to their size and cause problems maintaining a steady room temperature b) any leak is a costly repair c) changes in the heating system are difficult to make
30
How far down should heating coils in a snow melting system go?
5 cm (2 in)
31
What are the types of accessories are used in a hot water heating system?
-Diverter fittings -air vents -air seperators -flow control valves -balancing valves and fittings -riser stop valves -pressure reducing valves -circulating pumps -expansion valves -steam or hot water converters
32
What are thermostats, humidity controllers and pressure controlled used for?
For regulating heating systems
33
How do electric controls provide control for heating systems?
1) by starting and stoping a flow of electric current 2) by varying the voltage and current between the controller and controlled device
34
What voltage doe electric controls usually use?
either... 1) common line voltage, 120 or 240 volts OR 2) extra low voltage, 12 or 24 volts
35
What are the advantages for using electricity for control purposes?
1) readily available 2) the wiring is usually simple and easy to install 3) the signals received from sensing elements can be used to produce more than one electro-mechanical output 4) single controller/actuator combinations are possible, without the need for a main air source (which is required for pneumatic controls)
36
Define actuator
A device used to position dampers and control valves
37
Define contact arrangement
The electric switch configuration of a relay, controller, contractor motor starter, limit switch, or other control device.
38
Describe normally open (NO) and normally closed (NC) contacts in electric control circuits.
NO: contacts that complete circuits when a relay is energized NC: contacts that complete electric circuits when a relay is de-generized
39
Define control valve in electric control circuits
A device used to control the flow of fluid or gas such as water, air, or steam
40
Define controller
A device that reacts to pressure, temperature, or humidity to provide two-position, floating, or proportioning control of an actuator or relay
41
Define damper
A device used to control the flow of air in a duct or through a wall louvre
42
Define line voltage
The normal electric supply voltage
43
Define linkage
A device that connects an actuator to a damper or control valve
44
Define extra low voltage
Wiring or electric devices using 30 volts or less
45
Define relay
A device consisting of a solenoid coil, which operates load carrying contacts when the coil is energized
46
Define transformer
Optimus prime and bumblebee jk. A device used to change AC voltage from one value to another
47
T/F: The thermostat is one of the most important controls on a heating system
True
48
What is the function of a thermostat?
To maintain the temperature of a heated space or substance at the desired level, by regulating the heat supply.
49
What are the different types of thermostats?
- bimetal - remote bulb - immersion (aqua stat) - duct - modulating - multi-position
50
Describe how a bimetal thermostat functions.
- has a bimetal sensing element that reacts to changing room temperatures - operates on a two-position electric switch, which opens and closes the circuit to the controlled device (which regulates the heat supply)
51
What are the parts of a bimetal thermostat?
- sensing element made of a strip with two laters of different metals that expand at different rates when heated - one strip is stationary the other can move --> the movement of the free end is used to operate an electric switch
52
What will happen to a bimetal thermostat when the room temperature is below the setting of the thermostat?
The strip is straight and the contacts of the switch are closed --> this energizes the controlled device on the heat supply.
53
What will happen to a bimetal thermostat when the room temperature is getting warmer & reaches the setting of the thermostat?
As room temperature increases... - metals of the bimetal strip will expand at different rates and cause the strip to bend As room temperature reaches the thermostat setting... - at this point, the metal strip will have bent so far that the contacts of the switch open and de-energize the controlled device so that the heat supply is stopped
54
What will happen to a bimetal thermostat when the temperature drops again after having reached the setting of the thermostat?
The bimetal strip will cool down, straighten out, and the contacts close again.
55
What helps the contact open and close in a bimetal thermostat?
A spring helps the contact 'snap' open or closed --> this prevents arcing and chattering of the controlled device
56
T/F: The range in temperature between opening and closing of the contacts should be quite large.
False! The range should be quite SMALL in order to avoid large differences in room temperate
57
What will happen to the free end movement if the bimetal strip is lengthened?
The free end movement will increase, and the contacts will open and close within a smaller temperature range.
58
What is the function of a heat anticipator?
It gives the thermostat timed, two-position action. --> this prevents the temperature of the room air from overshooting the temperature of the thermostat
59
Are heat anticipators found in electronic thermostats?
No. The anticipation is replaced by accurate electronics that can see the rate of temperature increase to the hundredths of a degree, and turn off the heat supply at the appropriate time
60
T/F: Open-contact switches are only used in light-duty thermostats controlling low-voltage current circuits.
True
61
What do heavy-duty thermostats that control high-voltage or heavy currents require?
They require switches that open and close instantly to prevent burning of the contact points.
62
What are remote bulb thermostats used for?
To control the temperature of air in ducts, or of liquids in tanks or boilers. --> can also be used as limits or alarms in systems
63
What type of voltage are remote bulb thermostats designed for?
Designed for use with line voltage or low voltage
64
What is a volatile liquid?
A substance that readily expands, and can vaporize on the application of heat
65
How do remote bulb thermostats function?
1) They have a sensing bulb/capillary tube/ bellows combination contains a volatile liquid 2) part of the liquid in the sensing bulb is turned into vapour when the temperature of the controlled medium rises 3) the resulting increase in pressure causes the bellow to expand 4) expanded bellow then operates the control switch through a lever system at a set temperature --> opposite happens when the temperature of the medium falls
66
What are immersion thermostats (aquastats) used for?
Used to sense and control the temperature of water or other liquids in boilers, piping, tanks, etc.
67
How do immersion thermostats work?
- contains a sensing element that is liquid filled - the switch is operated by the expansion and contraction of the liquid when there is a temperature change of the controlled medium
68
What are duct thermostats used for?
Used to control the air temperatures in ducts and plenums
69
How do duct thermostats work?
- contains a bimetal sensing element that is protected by an open metal guard tube
70
Where are bimetal thermostats used typically?
In residential, commercial, and institutional buildings.
71
How do modulating thermostats work?
---> similar to others, in that it uses a bimetal strip/bellows/or remote bulb sensing unit .... different in how it controls the operation of a device - adjusts the position of the controlled device in direct proportion to the heat demand (cannot use on-off switch for this) - equipped with a special regulatory mechanism (ex. the variable potentiometer), that changes the resistance when the temperature changes
72
Describe a multi-position thermostat.
Similar to on-off thermostat, but is equipped with two or more switches that are operated in sequence --> each switch controls part of the heat supply
73
What does L, C, and H mean in a two-stage control circuit?
L: low or 1st stage C: common or power H: high or 2nd stage
74
How does a multi-position thermostat / two-stage heating system work?
- as temperature falls, the top bulb rotates and the mercury falls toward the left of the tube --> supplies power to the 1st stage gas valve - if temp. continues to fall, the bottom bulb will rotate and the mercury will encompass its probes --> supplies power to the 2nd stage gas valve
75
Where should the location of room thermostats be?
*should be located in a way that is can sense the average temperature of the area being heated* - mounted on an inside wall - 1.5 m above the floor - in the path of natural air circulation (when system is off) - also in the path of the circulating air (when heating system is in operation)
76
What locations should be avoided when installing a thermostat?
- behind doors, furniture, or drapes - in cold drafts from doors / windows - next to concealed ducts or piping - in direct rays of sun or a fireplace - near warm air outlets, lamps, radios, TV sets, or other sources of heat
77
What is the function of a humidity controller (aka humidistat)?
Measures the relative humidity of air in a room or an air duct, by responding to changes in humidity and controlling the operation of a humidifier
78
How does a humidity controller work?
--> sensing device consists of hygroscopic element ; uses multiple strands of moisture-sensing nylon - nylon will increase in length when humidity of air increases // nylon will decrease in length when humidity of air decreases - change in length of nylon activates a controller mechanism (ex. on-off control switch), which controls the humidifier
79
How are humidistats used with heating systems?
The humidistat will open the contacts of the switch, and stop the operation of the humidifier when the required humidity level has been reached
80
What are the two classes of pressure controllers?
1) high-pressure controllers: --> measure and control high pressures or vacuums (ex. steam or water pressures in an air conditioning system) --> measured in kPa or mm of mercury 2) low-pressure controllers: --> measure and control low pressures and vacuums (ex. pressure in an air duct) --> measured in mm of water
81
T/F: high and low-pressure controllers have the same size diaphrams
False. However, both diaphragms are exposed to the pressure to be controlled and the other side is in contact with a reference pressure.
82
What is the sequence of operations for a pressure controller?
- when static pressure drops, the reference pressure will cause the diaphragm to rise and lift the main lever - lever will rise off the nozzle and cause the branch pressure to drop - change in branch pressure will cause the control divide to respond and increase the static pressure - increased static pressure will be detected by the static pressure side of the sensor and cause the main lever to drop - dropped lever decreases the amount of air lose through the nozzle - controller will stabilize
83
What does an electric thermostat control?
- a fuel valve (in the supply line to the burner of a furnace / boiler) - an electric relay (which switches the circulator in a hydronic system on or off) - an electric radiator valve (in the supply line to one or more steam/hot water convectors) - a three-way mixing valve (controlling the temp of the water supply to a heating system) - a three-way diverter valve (controlling the water flow to a heating system) - a damper motor
84
Describe an electric radiator valve.
An electrically operated, single-seated valve thats used for two-position (on-off) control of steam or hot water to radiators, etc. --> has an electric motor that opens the valve when controller is energized, and closes the valve when the control circuit is de-energized
85
Describe a motor-operated valve
Used in heating systems to modulate or use two-position control of steam or hot water supply lines where tight shutoff is required. --> motor operator uses a reversible driving motor and reduction gears (in sealed casing) that is submerged in oil. It places the valve in an open/partially open position through use of a linkage system
86
Describe a three-way valve.
Used in hydronic heating systems for either mixing service or diverting service, in order to regulate the heat supply to all / parts of the heating system. --> 3-way valve is double seated and has 3 ports... - valves will allow flow between all ports in an intermediate position - if valve plug is against upper seat, will permit flow between ports A & B, but not A & C. - if valve plug is against lower seat, will permit flow between A & C, but not A & B.
87
How are 3-way valves used in diverting services?
The flow of water can be diverted to bypass the heat exchanger and thus, reduce the heat supply to match a reduced heat demand.
88
What are the 2 main purposes for electoral control motors?
1) motors for valve operation 2) motors for damper operation
89
Describe the construction of a capacitor-type control motor.
It is built with the rotor and gear train sealed in a housing (partially filled with oil) --> eliminates need for further lubrication
90
What is the operating sequence of a basic electric control circuit system?
1) the thermostat (controller) senses a drop in air temperature below the set point temp. 2) the thermostat switch (controller mechanism) closes and sends an electric signal 3) the electric current is transmitted through an electric wire (connecting link) to the burner (controlled device) 4) the burner starts up and raises the temp. of the heat transfer medium (ex. air), which transfers heat throughout the building 5) the thermostat sense the increase in air temp. 6) switch opens and burner shuts down when the air temp reaches the temperature setting of the thermostat
91
MC: A controller is a device that reacts to which of the following to provide two-position, floating, or proportioning control of an actuator or relay? a) pressure b) temperature c) humidity d) all of the above
(d)
92
MC: A room thermostat should be mounted on an inside wall about ___ above the floor and in the path of natural air circulation when the heating system is off. a) 4.5 m (15 ft) b) 1.5 m (5 ft) c) 2.5 m (8 ft) d) 3.5 (11.5 ft)
(b)
93
MC: A capacitor type control motor has the rotor and gear train sealed in a housing partially filled with... a) water b) glycol c) oil d) grease
(c)
94
MC: The electric current is transmitted through an electric wire, called the ____, to the burner a) connecting link b) positive loop c) negative loop d) neutral
(a)
95
MC: Which of the following types of switching devices are used in conjunction with bimetal strips to control high voltage circuits? a) open-contact switch b) thermostatic switch c) bimetal switch d) mercury bulb switch
(d)

5th Class PWR ENG (11 decks)

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