ASHRAE Psychrometrics and Moist Air Properties 2

Question 1

Which psychrometric process occurs when air passes over a cooling coil whose surface temperature is below the air's dew point?

Accepted Answer

Cooling and dehumidification as moisture condenses on the coil

Answer

Sensible cooling only, with no change in moisture content

Answer

Sensible heating with increased relative humidity

Answer

Humidification with simultaneous sensible cooling

Question 2

What is the sensible heat ratio (SHR) of an air conditioning process?

Accepted Answer

The ratio of sensible heat change to total heat change (sensible plus latent) in the process

Answer

The ratio of latent heat change to total heat change in the process

Answer

The ratio of dry-bulb temperature change to wet-bulb temperature change

Answer

The ratio of outdoor air enthalpy to return air enthalpy

Question 3

On a psychrometric chart, an adiabatic saturation (evaporative cooling) process follows which type of line?

Accepted Answer

A line of constant wet-bulb temperature

Answer

A line of constant dry-bulb temperature

Answer

A line of constant dew point temperature

Answer

A line of constant relative humidity

Question 4

What happens to the humidity ratio during a pure sensible heating process?

Accepted Answer

Humidity ratio remains constant while dry-bulb temperature increases

Answer

Humidity ratio increases proportionally with dry-bulb temperature

Answer

Humidity ratio decreases as dry-bulb temperature increases

Answer

Humidity ratio and dry-bulb temperature both remain constant

Question 5

What does bypass factor (BF) represent for a cooling and dehumidifying coil?

Accepted Answer

Fraction of air that passes through the coil without reaching the apparatus dew point condition

Answer

Percentage of supply air that bypasses duct filters

Answer

Ratio of outdoor air to return air in the mixed airstream

Answer

Thermal efficiency rating of the cooling coil heat exchanger

Question 6

How is the resulting condition of a mixed airstream determined when two airstreams at different psychrometric states are combined?

Accepted Answer

By the lever rule: the mixed point lies on the straight line between the two state points, divided by mass flow rate proportions

Answer

By simple arithmetic average of the dry-bulb temperatures of both streams

Answer

By taking the geometric mean of both inlet air conditions

Answer

By selecting the dominant stream with the higher volumetric flow rate

Question 7

What is the apparatus dew point (ADP) of a cooling coil?

Accepted Answer

The hypothetical coil surface temperature on the saturation curve where all air would leave if contact were perfect

Answer

The dew point temperature of supply air leaving the coil

Answer

The minimum coil surface temperature required to prevent frost formation

Answer

The temperature of condensate collected in the drain pan below the coil