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

When air contacts a surface below its dew point, both sensible cooling and dehumidification occur simultaneously as water vapor condenses out of the airstream onto the coil.

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

SHR is the fraction of total heat change that is sensible; it equals sensible heat divided by (sensible + latent heat) and determines the slope of the process line on the psychrometric chart.

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

Because no heat is added or removed in an adiabatic process, evaporative cooling follows a constant wet-bulb temperature line, moving from lower humidity ratio toward the saturation curve.

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

Sensible heating adds only thermal energy (no moisture) to the air, so humidity ratio remains unchanged while dry-bulb temperature rises and relative humidity decreases.

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

Bypass factor is the fraction of airflow that passes through the coil without making effective thermal contact with the coil surface, remaining essentially at entering air conditions.

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers Certification Practice Test

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers Certification Practice Test

ASHRAE Psychrometrics and Moist Air Properties 2