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HVAC Troubleshooting > Commercial HVAC Equipment > Flashcards

Commercial HVAC Equipment Flashcards

1
Q

What does DDCV stand for?

A

Dual Duct Constant Velocity

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2
Q

What does DDVAV stand for?

A

Dual Duct Variable-Air-Volume

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3
Q

Which system supplies heating and cooling at the same time through separate ducts to the zone?

A

Dual Duct Constant Velocity (DDCV) system

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4
Q

The duct (DDCV system) that holds and uses the heating coil is known as?

A

The Hot Deck

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5
Q

The duct (DDCV system) that holds and uses the cooling coil is known as?

A

The Cold Deck

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6
Q

Which part of the DDCV system varies the hot and cold air streams to a given space?

A

The dual duct box

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7
Q

What is the biggest difference between a “constant volume dual duct system” to a “variable air volume dual duct system”?

A

The air is not drawn into the building by a constant volume fan and DDVAV is split into two airstreams that flow through two variable volume fans, where as DDCV has one airstream.

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8
Q

What can the mixing boxes do for the DDVAV system?

A

They can vary both the proportions of hot and cold air as well as the total flow rate of air to the zone.

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9
Q

What does MUA stand for?

A

Makeup Air Unit

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10
Q

What happens to the building if the exhaust fan is in operation and there is no air being replaced?

A

The building experiences a negative pressure

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11
Q

What would be an indicator of negative pressure in a building?

A

Back drafting of combustion appliances such as gas hot water heater or furnace. … A musty smell or stagnant, stale air. A rush of air or draft when opening an exterior door. Exhaust fans not working properly.

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12
Q

Are there filters used in a make-up air unit?

A

Yes

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13
Q

What are the two types of MUA systems?

A

Direct gas fired and indirect gas-fired

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14
Q

Is there a heat exchanger installed in a Direct Fired make up air unit?

A

No

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15
Q

Where are the products of combustion discharged into from a DFMUA?

A

Discharged into the makeup airstream and supplied to the building or process.

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16
Q

When referring to a recirculating direct fired MUA, where is the return air damper located compared to the burner?

A

Right behind the burner

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17
Q

What is the isolation damper used for in a DFMUA?

A

Prevent cold air from dropping through a unit into a warm building.

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18
Q

What helps prevent the burners from operating if the dampers are not fully open?

A

The damper actuator motor end switch

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19
Q

The air that is flowing past the burner comes from where in a DFMUA?

A

Outside

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20
Q

What is the average range of air that needs to pass the burner for proper burner combustion?

A

2500 to 3200 fpm

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21
Q

What is the average discharge supply air temperature for a direct fired MUA?

A

Between 50 degrees F (10 degrees C) and 100 degrees F (38 degrees C)

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22
Q

List the common safety components that could be included in a MUA.

A

Flame proving sensors, high velocity air switches, low velocity air switches, and high temperature limit

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23
Q

When would a high velocity Air Switch open for a DFMUA?

A

When the air flowing through the unit becomes too high

24
Q

When would a low velocity Air Switch open for a DFMUA?

A

When the air is lower than the set value

25
Q

Main gas shut off, pilot gas manual valve, pilot solenoid valve, main gas pressure regulator, are a part of what in the DFMUA?

A

The housing

26
Q

What does an indirect fired make up air have that a direct fired make up air does not?

A

A heat exchanger

27
Q

What is the substance that a heat pump uses to transfer heat from one place to another?

A

Refrigerant

28
Q

Will the evaporator coil in a heat pump absorb heat or release heat from its surroundings?

A

Absorbs heat

29
Q

What is the main difference between a standard cooling system and heat pump?

A

The heat pump cycle is fully reversible and can provide heat in the winter and cooling and dehumidifying in the summer.

30
Q

List the components of a heat pump.

A

Refrigerant, reversing valve, coil, evaporator, compressor, expansion device, plenum, and suction line accumulator

31
Q

Which component of a heat pump reverses the refrigerant flow to change from heating to cooling mode?

A

The reversing valve

32
Q

Which device lowers the pressure of the refrigerant in a heat pump system?

A

The expansion device

33
Q

What happens to the efficiency of the heat pump when there is frost build up?

A

Decreases reducing its ability to transfer heat to the refrigerant.

34
Q

The indoor coil should be installed where when using a forced air gas furnace?

A

The warm downstream side of the furnace

35
Q

What does EES stand for?

A

Earth Energy Systems

36
Q

List the possible residential heat pump loop systems

A

Open loop systems, closed loop systems, domestic hot water heating systems, supplementary heating systems, heat distribution systems

37
Q

Where is the heat absorbed from in an open loop system?

A

Ground water from a conventional well

38
Q

What are the two types of energy recovery systems?

A

Open system and closed system

39
Q

What does an HRV do for a building?

A

It captures the heat from a buildings exhaust air and transfers it to the fresh air entering the building.

40
Q

When looking at an HRV, do the two air streams, the exhaust air and fresh air, come into contact with each other?

A

No

41
Q

Can an HRV be used in the summer months?

A

Yes but its more important to use in colder climates

42
Q

What happens if there is frost buildup inside the HRV’s heat exchanger?

A

Its defrost mechanism comes on

43
Q

An HRV is designed to remove excess what?

A

Heat

44
Q

At what temperatures do the efficiencies of an HRV become negligible?

A

20 degrees F (-7 degrees C)

45
Q

Are there filters used in the HRV units?

A

Yes

46
Q

What are the two different types of duct systems an HRV can be installed?

A

A stand alone system and a forced air duct system

47
Q

What are the three different methods that an HRV duct system can be installed?

A

Fully ducted systems, simplified systems, and exhaust-ducted systems—fully ducted systems are best

48
Q

What type of HRV duct system would be used for radiant heating?

A

Stand alone system

49
Q

What kinds of problems could there be if there is a negative pressure in the house?

A

Can cause spillage of carbon monoxide and other combustion by products.

50
Q

What kinds of problems could there be if there is a positive pressure in the house?

A

Causes moist air to be pushed into the walls and roof.

51
Q

Could the low speed operation of an HRV system meet the ventilation requirements?

A

Yes

52
Q

Can an HRV be used for an air cleaner?

A

Yes

53
Q

What is the approximate temperature that the HRV will activate the Defrost cycle?

A

23 degrees F (-5 Degrees C)

54
Q

What is another way of preventing frost build up in the HRV?

A

By using dampers

55
Q

What does ERV stand for?

A

Energy recovery ventilation

56
Q

What is the biggest difference between an HRV to an ERV?

A

The rotating enthalpy wheel on the ERV

57
Q

What is the material used for the ERV’s heat wheel to transfer water molecules to the other air stream?

A

Type A silica gel

HVAC Troubleshooting (6 decks)

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