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HVAC > Theory > Flashcards

Theory Flashcards

1
Q

What are physical properties that space conditioning is trying to control?

A

Temperature
Humidity
Freshness

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2
Q

What types of spaces are classified in HVAC design?

A

Residential buildings
Commercial buildings (e.g., office, retail)
Places of assembly (e.g., school, arena, hospital)
Specialty area (e.g., car, cargo truck, aircraft)

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3
Q

Enthalpy is most relevant to…

A

A) Temperature
B) Flowrate (velocity, m/s)
C) Pressure
D) Elevation

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4
Q

What is convection?

A

Energy transferred between a surface and fluid in contact with the surface.
A combination of heat conducted at the fluid-surface interface, conduction and mixing within the moving fluid, and thermal energy carried by the flow.

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5
Q

What are the two duties of the mechanical engineer?

A

Determine the capacity of the equipment that is to be installed
Determine the annual energy consumption of the equipment and the cost of operating the HVAC system

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6
Q

What is the influence from the weather?

A

Design conditions: specified extreme weather conditions 8==> equipment sizing
Track the instantaneous system performance hourly 8==> summing up for the annual performance

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7
Q

Does feeling equal satisfaction?

A

No

If they feel it, doesn’t mean they’re satisfied. Story of my life..

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8
Q

What is Sol-air temperature (Tsa)?

A

A “hypothetical” outside temperature that considers the radiation effect
It’s not air temperature (TA)

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9
Q

What does one MET equal?

A

Average person at rest

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10
Q

Which decision factor has a stronger influence to conduction gain and solar gain, respectively?

A

Conduction = Construction aka window panes

Solar Gain = surface treatment

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11
Q

What are the three types of VAV boxes?

A

Throttling Box
Induction Box
Fan-Powered Box

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12
Q

What are the design variables in duct distribution?

A 
Amount of outside air
Inlet temperature
Duct sizes
Pressure drop of different sections
Fan types and sizes
Volume flow rate
Air velocity
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13
Q

How do you determine the friction rate?

A

Low friction rate: if the cost of energy is high and duckwork is inexpensive (bigger duct)
High friction rate: if the cost of energy is low and duckwork costs are high

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14
Q

Define static regain method..

A

“With this procedure approximately the same static pressure exists at the entrance to each branch, which simplifies terminal unit selection and aids system balancing.”*

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15
Q

What are the two characteristics of static regain method?

A

Need lower velocity to regain the static pressure

Resulting in relative large duct size

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16
Q

What is the trend of duct size if we look for a longer term of LCC?

A

BIGGER DUCTS

WBVD

17
Q

Air Diffusion Performance Index (ADPI)

A

ADPI is a measure of the effectiveness of the air distribution system in distributing conditioned air throughout the zone
An ADPI close to 100 % is desirable

18
Q

Jet throw

A

The distance that the air jet from the outlet travels before the velocity drops below a minimum value (50 fpm or 0.25m/s)

19
Q

What are the possible applictions of psychrometrics?

A 
Plenum chamber for mixing of air streams
Heating or cooling coil
Cooling tower
Evaporative cooler
Desiccant dehumidifier
Humidifier
Air washer
20
Q

Evaporative coolers are best used in what climate?

A

Hot and dry climates

21
Q

Air stream in evaporative cooler is cooled by

A

A matrix that is continuously wetted by water

22
Q

Why are evaporative coolers constant wet bulb?

A

This is because there is no change in the amount of energy in the air. The energy is merely converted from sensible energy to latent energy. The moisture content of the air increases as the water is evaporated which results in an increase in relative humidity along a line of constant wet bulb temperature.

23
Q

How is efficiency affected by NTU?

A

Higher NTU means Higher efficiency

24
Q

How is efficiency affected by C*?

A

Lower C* means Higher efficiency

HVAC (1 decks)

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