Flood Restoration Psychrometrics and Humidity Control 1 — Questions and Answers
Question 1: In psychrometrics, which measurement expresses the actual amount of moisture in the air regardless of temperature?
- Relative humidity
- Wet bulb temperature
- Grains per pound (GPP) (Correct answer)
- Dry bulb temperature
Correct answer: Grains per pound (GPP)
Grains per pound (GPP) is an absolute measure of water vapor in air, unlike relative humidity which changes value as temperature changes.
Question 2: Relative humidity (RH) is best defined as:
- The weight of water vapor per pound of dry air
- The ratio of actual moisture in air to the maximum it can hold at that temperature (Correct answer)
- The temperature at which air becomes fully saturated
- The rate of evaporation from wet building surfaces
Correct answer: The ratio of actual moisture in air to the maximum it can hold at that temperature
RH expresses moisture content as a percentage of the air's maximum water-holding capacity at a specific temperature.
Question 3: As indoor temperature increases during structural drying, what happens to the air's capacity to hold moisture?
- It decreases, causing condensation on surfaces
- It remains constant regardless of temperature
- It increases, allowing more moisture to evaporate from materials (Correct answer)
- It fluctuates in proportion to relative humidity
Correct answer: It increases, allowing more moisture to evaporate from materials
Warmer air can hold significantly more water vapor, which is why raising room temperature accelerates the evaporation and drying process.
Question 4: The dew point temperature is defined as:
- The temperature at which air must be cooled to reach 100% saturation and condensation begins (Correct answer)
- The maximum temperature recorded during a drying cycle
- The point at which dehumidifiers stop removing moisture effectively
- The difference between indoor and outdoor ambient temperatures
Correct answer: The temperature at which air must be cooled to reach 100% saturation and condensation begins
The dew point is the temperature at which air becomes fully saturated (100% RH) and water vapor begins to condense into liquid.
Question 5: A refrigerant dehumidifier removes moisture from air by:
- Heating the air to force moisture to evaporate out
- Cooling the air below its dew point to condense moisture onto cold coils, then reheating it (Correct answer)
- Filtering moisture particles through HEPA media
- Chemically bonding with water molecules using silica gel
Correct answer: Cooling the air below its dew point to condense moisture onto cold coils, then reheating it
Refrigerant dehumidifiers cool incoming air below the dew point so moisture condenses on evaporator coils, then the now-drier air is reheated before being exhausted back into the space.
Question 6: According to IICRC S500 guidelines, what relative humidity level should be maintained in the structure to inhibit secondary mold growth during drying?
- Above 70% RH
- Between 60–70% RH
- Below 60% RH (Correct answer)
- Between 40–50% RH
Correct answer: Below 60% RH
Maintaining indoor RH below 60% deprives mold spores of the moisture they need to germinate and colonize building materials.
Question 7: Psychrometric charts are primarily used in flood restoration to:
- Calculate repair costs based on moisture meter readings
- Determine the relationship between temperature, relative humidity, dew point, and grains per pound (Correct answer)
- Map the spatial extent of water damage throughout a structure
- Schedule maintenance intervals for drying equipment
Correct answer: Determine the relationship between temperature, relative humidity, dew point, and grains per pound
Psychrometric charts graphically display the interdependencies of dry bulb temperature, wet bulb temperature, relative humidity, dew point, and absolute moisture content.
Flood Restoration Psychrometrics and Humidity Control 1
In psychrometrics, which measurement expresses the actual amount of moisture in the air regardless of temperature?