313D Psychrometrics and Humidity Control

Question 1

What does the term 'psychrometrics' refer to in HVAC?

Accepted Answer

The study of thermodynamic properties of moist air

Answer

Psychrometrics is the engineering science that studies the thermodynamic properties of moist air — mixtures of dry air and water vapor.

Question 2

What is the dew point temperature?

Accepted Answer

The temperature to which air must be cooled for water vapor to begin condensing

Answer

Dew point is the temperature at which air becomes saturated and water vapor condenses into liquid, assuming constant pressure and moisture content.

Question 3

On a psychrometric chart, wet-bulb temperature lines run in which direction?

Accepted Answer

Diagonally downward from the saturation curve toward the lower right

Answer

Wet-bulb temperature lines slope diagonally downward from upper left to lower right on a psychrometric chart and nearly coincide with lines of constant enthalpy.

Question 4

What is relative humidity (RH)?

Accepted Answer

The ratio of actual moisture content to the maximum moisture air can hold at that temperature

Answer

Relative humidity is the ratio of actual water vapor pressure to saturation water vapor pressure at the same temperature, expressed as a percentage.

Question 5

What is the key difference between sensible heat and latent heat in air conditioning?

Accepted Answer

Sensible heat causes a measurable temperature change; latent heat involves phase change without temperature change

Answer

Sensible heat changes the temperature of air (measurable with a thermometer), while latent heat is absorbed or released during phase changes like evaporation or condensation.

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test

313D Psychrometrics and Humidity Control