313D Psychrometrics and Humidity Control 3

Question 1

What is the Apparatus Dew Point (ADP) of a cooling coil?

Accepted Answer

The effective average surface temperature of the coil at which moisture condenses

Answer

The dew point temperature of the return air stream entering the coil

Answer

The temperature of condensate water draining from the coil pan

Answer

The minimum allowable refrigerant temperature within the evaporator

Question 2

How does dehumidification occur in a typical residential split-system air conditioner?

Accepted Answer

Warm humid air is chilled below its dew point over the evaporator coil, causing moisture to condense on the coil

Answer

A desiccant wheel inside the air handler absorbs water vapor from the airstream

Answer

The blower wheel centrifuges moisture droplets out of the airstream by centrifugal force

Answer

Refrigerant vapor directly absorbs water molecules from supply air passing through the coil

Question 3

Under what condition are dry-bulb and wet-bulb temperatures equal?

Accepted Answer

When air is at 100% relative humidity (fully saturated)

Answer

When airflow velocity through the duct exceeds 1,000 FPM

Answer

When the HVAC system is operating at its rated peak efficiency

Answer

When outdoor and indoor dry-bulb temperatures are identical

Question 4

What is humidity ratio (specific humidity) as used in HVAC psychrometrics?

Accepted Answer

The mass of water vapor per unit mass of dry air, expressed in lbs/lb or grains/lb

Answer

The percentage of moisture in air relative to its maximum holding capacity at that temperature

Answer

The temperature at which the air sample becomes fully saturated

Answer

The ratio of latent heat to sensible heat in the conditioned airstream

Question 5

A large wet-bulb depression (big difference between dry-bulb and wet-bulb temperatures) indicates what about the air?

Accepted Answer

The air is relatively dry with low relative humidity

Answer

The air is nearly saturated and close to 100% relative humidity

Answer

The system refrigerant charge is low and needs recharging

Answer

The supply air temperature leaving the coil is too high

Question 6

What are the primary negative effects of high indoor relative humidity on occupants?

Accepted Answer

It promotes mold growth, makes occupants feel warmer, and can cause respiratory irritation

Answer

It increases comfort by preventing static electricity buildup in dry climates

Answer

It improves air quality by causing airborne dust particles to clump and settle

Answer

It reduces the sensible cooling load by lowering the sensible heat ratio

Question 7

On a standard psychrometric chart, which property is represented on the horizontal (x) axis?

Accepted Answer

Dry-bulb temperature

Answer

Wet-bulb temperature

Answer

Relative humidity percentage

Answer

Dew point temperature