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1st Year Sheet Metal > Residential Hvac Theory > Flashcards

Residential Hvac Theory Flashcards

1
Q

If the heat is supplied by a fuel it is a what?

A

Furnace

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2
Q

If the heat is supplied by a liquid medium it is a what?

A

Fan coil

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3
Q

What are the four set of combustion components in a furnace

A

Fuel supply component
Air supply component
Heat exchanger
Safety controls

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4
Q

What measure is used to define heat in the imperial system?

A

Btu, which is defined as British thermal unit. One btu is defined as the amount of heat required to raise one pound of water 1 degree F. One btu will heat approximately 55 cubic feet of air 1 degree F.

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5
Q

What is the purpose of a gas valve?

A

The gas valve will not let fuel flow into the manifold until other controlls say it is safe to do so.

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6
Q

What is a manifold?

A

The manifold is designed to distribute gas evenly to a number of orfices thay are sized to regulate the flow of fuel to the furnace.

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7
Q

What is the heating value of natural gas and propane?

A

Natural gas is 1000 btus/cu ft and propane is 2500btus/cu ft.

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8
Q

What is the ratio of air to gas needed for combustion?

A

10:1

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9
Q

What is the burner of choice for high rates of combustion in an oil furnace?

A

Atomizing burner called an oil burner gun.

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10
Q

What is dilution air?

A

Typically found in low efficient furnaces it is the air mixed with products of combustion to cool them before they exit the flue. accomplished by use of a draft hood.

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11
Q

What is a heat exchanger?

A

It separates the air that circulates through the house from the products of combustion.

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12
Q

What are the two types of safety controls in a furnace?

A

One type monitors the flame and shuts off the flow of fuel in the case of flame or ignition failure. The other type monitors the temperature and shuts off the flow of fuel if the heat rises too high.

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13
Q

What safety controls are used to monitor the flame on natural gas and propane furnaces?

A

Older furnaces use a thermocouple and new furnaces use an electronic flame sensor.

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14
Q

What is used to monitor high temperature in the furnace?

A

A high limit control will shut the gas valve off in the case of high temperature. Flame rollout switches can be incorporated.

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15
Q

What does an oil furnace use for flame sensing?

A

Cadmium sulfide cell (Cad) which senses light

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16
Q

What are the types of blowers in furnaces?

A

Belt driven

Direct drive

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17
Q

What are the efficiencies of low mid and high?

A

Low is less than 78%
Mid is 78 percent and up
High is 88%

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18
Q

Oil and solid fuel furnace use a more presuse draft regulator called what?

A

Barometric damper

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19
Q

How is better efficiency achieved from low to mid efficiency?

A

The elimination of the draft good, increased heat exchanger area and the use of electronic controls.

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20
Q

How is better efficiency achieved from mid to high efficent.

A

By condensing the water vapour from the flue gases.

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21
Q

What does the inducer motor do in a high efficent furnace?

A

It must force the products of combustion outside in addition to drawing air through the heat exchanger.

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22
Q

What is another name for a fan coil?

A

Air handlers

23
Q

What is air conditioning and what does this include?

A

Air conditioning refers to the conditioning of the air, not just cooling. It includes tempering (temperature), filtering, hummidifying, cooling, dehumidifying, and freshening.

24
Q

What is optimal humidity levels?

A

Between 30 and 55%

25
Q

What is cubic feet per minute?

A

This refers to the amount (volume of air), in cubic feet, that a fan will supply or exhaust in one minute. A 100 cm fan draws in and pushes out 100 cubic feet of air in one minute.

26
Q

What is feet per minute?

A

Fpm refers to the speed (velocity) of the air or how far the air from a fan will travel in one minute.

27
Q

Explain gravity furnace?

A

Heat causes the warm air to rise up pipes usually in the middle of the house. Return airs were used on the perimeter to draw air back.

28
Q

What is radial type heating.

A

It has one central r/a and a plenum. Heat runs all come off plenum like an octopus. It is used when space is not a priority and is easily installed.

29
Q

What is perimeter radial?

A

It has a perimeter loop of pipe that goes around the perimeter. Outlets are installed. Furnace is in the middle and has several lines connecting to the loop.

30
Q

Extended plenum and reduced extended plenum?

A

This is the system we use today. Reduced has an increaser and the other is straight duct.

31
Q

Masonry chimneys are best for solid and liquid fuelled furnaces due to their high heat resistance as well as A-vent.

A

True

32
Q

What are two factory built chimneys that can be used for oil burning appliances?

A

A-vent and L-vent.

33
Q

When venting a gas furnace through a masonry chimney you must use an aluminum chimney liner.

A

True. The lining of the chimney is done to reduce the size of the flue to the correct size.

34
Q

What does pvc stand for in venting?

A

Polyvinyl chloride

35
Q

Name the components of a fresh air system?

A

Exhaust that is designed to remove stale air from the building.
Exhibit air that removes obvious contaminants from the air.
Fresh air or make up air that replaces exhausted air by various fans.

36
Q

What is the uncontrolled leakage of air from a building called?

A

Exfiltration

37
Q

What is infiltration?

A

Air that comes into the house uncontrollably or unwanted like drafts.

38
Q

The heart of an hvac system is the air recirculation fan.

A

True

39
Q

Duct reducers must be used on any run that exceeds 30 feet.

A

False. It must be used after 24 feet.

40
Q

What does the plenum do?

A

It allows the air leaving the furnace to lose some of its turbulence and equalize pressures and speeds before being delivered to the rooms.

41
Q

What does the pto do?

A

It is designed to assist airflow from the plenum to the duct and it is accepted trade practice to maintain the inlet of the pto at 1.5 times the cross-sectional area of the duct it is being attached to.

42
Q

What is the accepted ratio between duct width and depth.

A

It should never exceed 4:1.

43
Q

What is a shortway elbow?

A

Another name is a stack elbow. The short dimension is on the cheek. An 8 by 12 elbow would change direction on the 8” side. Ordered as cheek size x heel/throat size.

44
Q

What is a longway elbow?

A

Also called a sweep elbow has the long dimension of the fitting on the cheek. A 12 by 8 elbow changes direction on the 12” side.

45
Q

Describe a change elbow.

A

It is a change in size from one end to the other. The change takes place only on the cheek. 18 x8 to 12 x 8, 90 c/w 6” throat.

46
Q

Offsets and risers

A

An offset changes direction horizontally from side to side. A riser moves up and down the vertical plane. When ordering the first number is always the cheek size.

47
Q

What is underslab heating?

A

It is forced air heating run under the concrete slab. It is designed to use round duct (usually spiral) that is encased in concrete. Concrete strengthens this.

48
Q

In 2006 what type of venting was made mandatory?

A

ULC S636 was made mandatory for BH venting (special venting).

49
Q

What is a vent connector?

A

The portion of the combustion venting system that conveys the flu gases from the appliance to the common vent or chimney. Ex. b-vent.

50
Q

When a vent connector passes through a combustible wall a ventilated thimble must be used.

A

True. Garage heaters use this.

51
Q

What is the main purpose of exhaust fans?

A

To remove moisture from the building

52
Q

What two characteristics affect air flow?

A

One is the speed of the air. change in velocity produces an uneven airflow and create turbulance. The 2nd is pressure of the air. These losses of air are called dynamic losses.

53
Q

Common reasons for dynamic loss?

A

Shape of duct
Changes in direction
Changes in cross-sectional area
Material of duct (smooth or rough)

54
Q

Round duct is best for air flow, followed by square duct, then rectangular duct.

A

True

1st Year Sheet Metal (5 decks)

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