stud
bud
Sign up
Log in
Home
Library
Explore
SAT
More
OES-3033 Test 2 study Flashcards | StudBud
Explore
/
OES-3033 Test 2 study
OES-3033 Test 2 study
50 terms
·
StudBud Administration
·
3 plays
Imported from external platform
Flashcards
50 cards
F
Practice quiz
P
Host live
L
Questions
50
Answers
1
Multi-zone central HVAC systems differ from single-zone systems by:
Using a completely separate air handling unit for each zone
Eliminating the need for any ductwork in the building
Using one AHU that can deliver mixes of warm and cool air to separate zones
2
In a
multi-zone air handling unit
(with hot and cold decks), how are different zone temperature requirements met?
By mixing controlled proportions of warm air and cool air for each zone
By varying the fan speed to each zone independently
3
Which of the following air cleaning devices uses
electrostatic
principles to remove particles?
An electronic air cleaner (electrostatic precipitator)
A HEPA filter unit
4
Which of the following is a disadvantage of using many
window air conditioners
in a building compared to a single c
They are noisier and less eff, and each requires an opening in the exterior
They allow each room individual control (which is undesirable)
5
A replaceable "dry" air filter in an HVAC system is typically made of:
Activated charcoal material
Fiberglass or pleated paper media
6
Which type of filter would be most suitable for an environment that requires extremely high air purity?
A standard pleated residential HVAC filter
A HEPA filter (high-efficiency particulate air filter)
7
Ultraviolet germicidal lamps (UVGI) in ductwork are primarily used to:
Filter out fine dust particles from the air
Sterilize the air by killing bacteria, viruses, and mold spores
8
In a
unitary air conditioning system
, each room or zone is typically served by:
Ductwork from a large central air handling unit
Its own self-contained AC unit located in or near that space
9
Natural ventilation in a building can be achieved by
Opening windows or vents to let outdoor air flow in
Operating a furnace blower without heat
Running the air conditioner on a high setting
Using powered fans to draw in outside air
10
Ventilation rates in buildings are commonly measured in
Cubic meters of water flow per minute
Degrees of temperature change per hour
Percentage of relative humidity
Air changes per hour (ACH)
11
For maximum heat transfer efficiency, how should water flow through a heating or cooling coil relative to the airflow?
In counter-flow arrangement (water flowing opposite the air direction)
In parallel-flow (water and air moving the same direction through the coil)
12
Which of the following is an example of a
unitary HVAC unit
?
A window-mounted air conditioner serving one room
A boiler that serves multiple buildings
A central cooling tower for a campus
A large built-up air handler with duct distribution
13
How should a hot water coil be piped to ensure it can be properly vented of air?
With the water entering at the bottom of the coil and exiting at the top
With both the supply and return connections at the bottom of the coil
14
It has been observed that steam coils often freeze
more frequently at around 0°C
outside air than at colder temperatures
At milder freezing temps, the steam control valve may be nearly closed
There is no explanation
Steam coils only freeze when outside air is at exactly 0°C
15
What is a known drawback of using an electrostatic precipitator
without
a pre-filter?
It produces excessive airflow resistance in the duct
It may allow larger dust particles to pass through and accumulate
16
Which ventilation strategy might inadvertently create
negative pressure
inside a building if not balanced?
Mechanical exhaust with natural (passive) air intake
Energy recovery ventilation with balanced flow
Mechanical supply and mechanical exhaust (balanced)
17
Which of the following is a typical airborne contaminant that HVAC filters aim to remove?
Dust and pollen particles
Odors from paint (without any filtration media)
Carbon dioxide gas
Sound and vibration
18
Why are HVAC system filters important for the operation of finned-tube coils?
They prevent dust from clogging the coil fins,maintaining heat transfer eff
They add heat to the air before it reaches the coil
19
Ina typical central
splitsystem
air conditioner what flows between indoor evaporatorcoil unit andoutdoor condenser unit?
Refrigerant circulates through piping between the indoor and outdoor units
Chilled water flows from the indoor unit to the outdoor unit
20
Why is maintaining a slightly
positive pressure
in a commercial building often desirable?
To reduce the load on exhaust fans by leakage
To draw more natural ventilation through cracks
To make exterior doors harder to open for security
To prevent unfiltered outside air from infiltrating into the building
21
Adding more fins per inch on a coil will generally:
Increase both the heat transfer and significantly reduce required fan power
Increase the coils heat transfr capacity but also inc the air pressure drop
22
What is a characteristic feature of a
rooftop HVAC unit
?
It is used exclusively for residential homes
It always uses chilled water from a remote chiller plant
It is a self-contained heating and cooling unit installed on the roof
It requires a large indoor mechanical room for installation
23
What is the purpose of a
steam trap
on a steam heating coil?
To regulate the steam pressure entering the coil
To remove condensate (condensed steam) from the coil
24
Which statement best describes a typical
unit ventilator
(such as those found in hotel or classroom settings)?
It is a large central ventilating unit serving the whole building
It only provides ventilation without any heating or cooling function
It pulls in a controlled amount of out air, mixes it with indoor air
25
Approx how much heat transfer capacity can be lost if a water coil is piped in parallel flow instead of counter-flow?
On the order of 10–15% capacity loss
Virtually 0% (no measurable difference)
Over 50% loss in capacity
At least 30% loss in capacity
26
In a
central air conditioning system
, the cooling of air typically occurs:
In a central AHU or furnace, then the air is distributed via ducts
Individually within each room by a separate refrigerant cycle
Only at the exterior condenser, which directly cools the rooms
By opening windows on each floor for natural cooling
27
In HVAC terminology,
CAV
stands for "Constant Air Volume." What is the key characteristic of a CAV system?
It maintains a constant air velocity in the ducts regardless of load
It supplies air at constant flow rate to space, controlling temp by heating
28
Which of the following is a primary purpose of ventilation in HVAC systems?
To pressurize a building so no air can escape
To control the flow of refrigerant in the system
To supply fresh air to occupants and remove stale indoor air
To increase the speed of air through ductwork for cooling
29
How should steam heating coils ideally be oriented when installed, to avoid condensate accumulation and cold spots?
Tubes should be perfectly horizontal with no slope
Tubes should be vertical (or at least sloped toward the condensate outlet)
30
A forced-air
split-system
with a furnace and an indoor cooling coil, plus an outdoor condenser unit, is an example of:
A central air conditioning system for a single-family home
A ductless mini-split system
A unitary packaged system
31
Compared to a central AHU system, what is an issue with relying on
unit ventilators
in each room for an entire building?
can be difficult to ensure consistent vent rates, and near sources of fumes
Occupants have no local control over their room conditions
32
Which of the following is a
freeze protection guideline
for hot water coils in an air handling unit?
Cycle the water flow on and off to avoid freezing (intermittent flow)
Maintain a min water temperature. so the coil fluid never reaches freezing
Use parallel-flow arrangement so the water exits at the coldest air point
33
What is a primary energy drawback of a
terminal reheat
HVAC system (central cooling with reheat coils in zones)?
It wastes energy by cooling air to a low temperature and then reheating it
It cannot maintain different temperatures in different zones
34
Why might an HVAC system use two heating coils in series (one after the other in the air stream) in a very cold climate?
To double the total heating capacity
To stage heating
To allow using steam in one coil and hot water in the second coil
35
In a direct-expansion (DX) cooling coil, what flows inside the coil tubing to achieve cooling?
Refrigerant that evaporates inside the tubes, absorbing heat from the air
Chilled water supplied from a central chiller plant
36
During operation of a window air conditioner, where is the condenser located and how is it cooled?
The unit does not have a true condenser coil since it’s self-contained
The condenser coil is at the back/outside part of the unit
The condenser is inside the room, cooled by the indoor air stream
37
What does the term
HEPA
stand for in the context of air filters?
High Efficiency Particulate Air (filter)
High Energy Particle Absorption
Heat Exchange Performance Apparatus
Humidity Evaporation Purification Assembly
38
What problem can occur if a steam heating coil and its control valve are
oversized
for the load?
The steam trap will fail due to high pressure
During cold conditions the steam flow may be so low that condensate pools
39
Which type of coil is generally
more prone to freezing
when outdoor air is cold and flow is low
Hot water coils freeze more easily than steam coils
Steam coils, especially at low steam flow, are more prone to freezing
40
What is the main reason HVAC coils (heating or cooling coils) have many metal
fins
attached to their tubes?
To reduce the overall weight of the coil assembly
o increase the surface area for heat exchange
41
Why is it recommended to have the outside air intake damper
close
when steam supply pressure is low
To reduce fan noise during startup
To prevent a rush of freezing outside air from hitting an unheated
42
In HVAC air treatment, what is the main purpose of an
air washer
device?
To scrub the air with droplets, removing dust and also humidifying the air
To absorb odors using chemical media
To electrically charge particles for filtration
43
What is one limitation or disadvantage of a
dual-duct
HVAC distribution system?
It cannot accommodate more than two or three zones
It requires 2 parallel set of ducts (hot and cold air) through the building
44
What min water velocity is generally recommended through hot water heating coil to help stop freezing in cold conditions
Velocity does not matter for freeze protection in coils
At least 10 m/s, a very high speed to scour the pipes
On the order of 0.9 m/s (approximately 3 ft/s) or higher
Around 0.1 m/s, a very slow flow to avoid turbulence
45
Why is a good bond between the fins and the tubes important in a finned-tube coil?
It ensures efficient heat conduction from the tube into the fin
It prevents the fins from vibrating and making noise
46
What method is commonly used to create a tight bond between fins and tubes in a
continuous plate fin
coil?
Expanding the tubes (using a mandrel or hydraulic expansion)
Soldering or brazing each fin to the tube at multiple points
47
What is one advantage of a
central HVAC system
over having many separate unitary units in a large building?
Much lower initial cost for very large buildings
Easier maintenenc and higher eff by consolidating equipment in one location
No need for ductwork or piping of any kind in the building
48
A
packaged air conditioner
(indoor packaged unit) typically contains:
All the refrigeration components(compressor, evaporator,etc) in one cabinet
A gas furnace and no cooling components
Only an evaporator coil, with the compressor and condenser located elsewher
49
If an HVAC system operated on
100% recirculation
with no fresh air intake, which indoor air quality issue would occur?
Over-pressurization of the building interior
Buildup of carbon dioxide and indoor pollutants over time
50
Which type of filter is often used to remove odors and gaseous pollutants from the air?
Activated carbon filters
HEPA filters
