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Applied Structural Drying practice questions

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Question 1Psychrometrics and Drying Science

In psychrometric terms, the grains of moisture per pound of dry air (gpp) is a measure of which property?

  1. Dew point depression of the air mass
  2. Relative humidity at the current temperature
  3. Absolute humidity expressed as humidity ratio Correct answer.
  4. Specific volume of the moist air mixture

Explanation

The humidity ratio (also called mixing ratio) expresses the mass of water vapor per mass of dry air, commonly in grains per pound. It is an absolute measure and does not change when the air is merely heated or cooled without adding or removing moisture.

Question 2Psychrometrics and Drying Science

A drying chamber holds air at 70°F with 60% relative humidity. Which change raises the relative humidity without adding any moisture to the air?

  1. Increasing the air velocity across the wet materials
  2. Cooling the air to 60°F Correct answer.
  3. Heating the air to 85°F
  4. Opening the chamber to outdoor air of the same humidity ratio

Explanation

Relative humidity is the ratio of actual vapor pressure to saturation vapor pressure at the same temperature. Cooling lowers the saturation vapor pressure, so the same moisture content produces a higher relative humidity; heating does the reverse.

Question 3Psychrometrics and Drying Science

Which definition of dew point is correct for a structural drying technician?

  1. The temperature at which the air's humidity ratio reaches zero
  2. The temperature at which the vapor pressure of the air equals the atmospheric pressure
  3. The temperature at which liquid water begins to evaporate from a wet surface
  4. The temperature at which the air reaches 100% relative humidity and begins to condense moisture Correct answer.

Explanation

Dew point is the temperature to which air must be cooled, at constant pressure and moisture content, to become saturated. Further cooling below that point forces vapor to condense on surfaces, which is why technicians track dew point against surface temperatures.

Question 4Psychrometrics and Drying Science

Air at 80°F dry bulb and 68°F wet bulb is being evaluated for drying. What does the wet bulb depression of 12°F indicate?

  1. The air is close to saturation and will absorb moisture slowly
  2. The air is supersaturated and condensation is occurring
  3. The psychrometric chart cannot be read with these values
  4. The air has meaningful evaporative capacity and can take on more moisture Correct answer.

Explanation

Wet bulb depression is dry bulb minus wet bulb temperature, and a larger depression signals drier air with greater evaporative potential. A 12°F depression indicates the air is well below saturation and can accept additional vapor.

Question 5Psychrometrics and Drying Science

Which pair of instruments is required to plot a complete psychrometric state point without using a chart correction for altitude?

  1. Dry bulb thermometer and wet bulb thermometer Correct answer.
  2. Moisture meter and thermo-hygrometer
  3. Anemometer and infrared thermometer
  4. Barometer and hygrometer only

Explanation

Dry bulb and wet bulb temperatures together define a unique state point on a psychrometric chart at a given pressure. Relative humidity, dew point, and humidity ratio can then all be read from the chart.

Question 6Psychrometrics and Drying Science

A technician wants to lower the humidity ratio of air entering a drying chamber without changing its temperature. Which process accomplishes this?

  1. Sensible heating of the airstream
  2. Adding a bypass duct around the heater
  3. Increasing the fan speed through the chamber
  4. Dehumidification by condensation on a cooling coil followed by reheat Correct answer.

Explanation

Removing water vapor requires condensation or desiccant sorption; cooling the air below its dew point forces vapor to condense out. Reheating afterward restores the original temperature while leaving the humidity ratio reduced.

Question 7Psychrometrics and Drying Science

Two rooms have the same relative humidity of 50%, but room A is at 60°F and room B is at 90°F. Which statement about the humidity ratio is true?

  1. Room B holds more moisture per pound of dry air than room A Correct answer.
  2. Both rooms hold the same grains of moisture per pound of dry air
  3. The humidity ratio cannot be compared without knowing the barometric pressure
  4. Room A holds more moisture per pound of dry air than room B

Explanation

Saturation vapor pressure rises steeply with temperature, so at the same relative humidity the warmer air contains far more water vapor. Room B at 90°F therefore has a higher humidity ratio than room A at 60°F.

Question 8Psychrometrics and Drying Science

During drying, supply air is measured at 95°F dry bulb with a dew point of 50°F. A wood floor surface reads 58°F. What is the practical risk?

  1. No condensation risk because the supply air is heated
  2. Secondary damage from condensation on the cool floor Correct answer.
  3. The floor will dry faster because its temperature is below the dew point
  4. The dehumidifier will freeze because the dew point is too low

Explanation

Any surface at or below the air's dew point will collect condensation. The 58°F floor is above the 50°F dew point but only by 8°F, so local cold spots or cooler nighttime conditions can easily drop below dew point and wet the material.

Question 9Psychrometrics and Drying Science

A desiccant dehumidifier is selected for a cool, damp basement at 55°F. Why is this choice often preferred over a conventional refrigerant unit in that condition?

  1. Desiccant units lower the dew point by raising the humidity ratio
  2. Desiccant units operate without any airflow and rely on diffusion
  3. Desiccant wheels add heat and remove more moisture at low temperatures where refrigerant coils frost or condense poorly Correct answer.
  4. Refrigerant units cannot remove moisture below 80°F

Explanation

Refrigerant dehumidifiers depend on cooling air below its dew point, which becomes inefficient and prone to coil frosting in cool spaces. Desiccant wheels adsorb vapor directly and perform well at low temperatures, though they add sensible heat to the process air.

Question 10Psychrometrics and Drying Science

On a psychrometric chart, which line represents a constant wet bulb temperature?

  1. The curved line of constant specific volume
  2. The sloping line running down to the right along the saturation curve Correct answer.
  3. The vertical line of constant dry bulb temperature
  4. The horizontal line of constant humidity ratio

Explanation

Lines of constant wet bulb temperature slope downward to the right and parallel the saturation curve on standard charts. Following one of these lines shows how dry bulb rises as humidity ratio falls at constant wet bulb.

Question 11Psychrometrics and Drying Science

A drying job shows supply air at 80°F and 45% RH while return air measures 78°F and 70% RH. What does the return air reading most directly demonstrate?

  1. The airstream has picked up moisture as it passed over the wet materials Correct answer.
  2. The dehumidifier is adding moisture to the airstream
  3. The heater has failed and the air is cooling
  4. The airflow has reversed through the chamber

Explanation

Rising relative humidity with a small temperature drop indicates the air absorbed vapor from the wet structure. Comparing supply and return state points is the standard way to confirm the air is doing drying work.

Question 12Psychrometrics and Drying Science

Which condition gives the greatest evaporation rate from a wet carpet, all else equal?

  1. Warm, humid air with no airflow across the surface
  2. Warm, dry air with strong airflow across the surface Correct answer.
  3. Cool, dry air with no airflow across the surface
  4. Cool, humid air with gentle airflow across the surface

Explanation

Evaporation is driven by the vapor pressure gradient between the wet surface and the air, plus energy for the phase change and removal of the boundary layer. Warm dry air maximizes the gradient, and airflow replenishes the boundary layer and speeds vapor transport.

Question 13Psychrometrics and Drying Science

What is the primary reason technicians track the vapor pressure deficit rather than relative humidity alone when judging drying progress?

  1. Vapor pressure deficit is easier to measure with a moisture meter
  2. Relative humidity cannot be read from a psychrometric chart
  3. Relative humidity ignores temperature and does not show the actual driving force for evaporation Correct answer.
  4. Vapor pressure deficit measures the moisture content of the building materials

Explanation

Vapor pressure deficit is the difference between saturation vapor pressure at the surface and the actual vapor pressure of the air, which is the true gradient driving evaporation. Relative humidity is a ratio and can mislead when temperatures differ between the material and the air.

Question 14Psychrometrics and Drying Science

A sealed room contains 70°F air at 80% RH and standing water on the floor. A technician adds a heater that raises the air to 90°F with no ventilation. What happens to the relative humidity and the drying potential?

  1. RH falls and drying potential increases, but the sealed room limits moisture removal Correct answer.
  2. RH rises and drying potential decreases
  3. RH stays the same because no moisture was added
  4. RH falls to zero because heating removes all vapor

Explanation

Heating lowers relative humidity at constant humidity ratio, which increases the vapor pressure deficit and speeds evaporation from the wet floor. However, in a sealed room the released vapor accumulates and eventually raises the humidity ratio, so moisture must still be removed by dehumidification or ventilation.

Question 15Psychrometrics and Drying Science

Air at 75°F and 50% RH is cooled to 45°F by a coil. Which outcome is expected?

  1. The air becomes supersaturated and cannot be cooled further
  2. The humidity ratio remains unchanged because no moisture was added
  3. The humidity ratio rises because cooler air holds more moisture
  4. The humidity ratio drops because moisture condenses on the coil Correct answer.

Explanation

Cooling air below its dew point forces water vapor to condense on the coil, removing moisture from the airstream. The humidity ratio therefore falls, which is the basis of refrigerant dehumidification.

Question 16Psychrometrics and Drying Science

Which statement correctly describes the relationship shown by the saturation curve on a psychrometric chart?

  1. It shows the humidity ratio at which materials stop drying
  2. It plots the maximum vapor content the air can hold at each dry bulb temperature Correct answer.
  3. It marks the point where vapor pressure equals zero
  4. It represents the temperature at which airflow ceases

Explanation

The saturation curve, or 100% RH line, gives the maximum humidity ratio the air can hold at each dry bulb temperature. State points to the right or above it represent supersaturated conditions that cannot persist.

Question 17Psychrometrics and Drying Science

A technician measures 60% RH at 80°F in a drying chamber. Using psychrometric principles, what is the approximate dew point?

  1. About 80°F
  2. About 65°F Correct answer.
  3. About 45°F
  4. About 30°F

Explanation

At 80°F and 60% RH the dew point is roughly 65°F, since the air must cool about 15°F to reach saturation at that moisture content. This matches standard chart readings and confirms that surfaces below about 65°F would condense moisture.

Question 18Psychrometrics and Drying Science

What does specific volume on a psychrometric chart describe for a drying technician?

  1. The cubic feet of moist air occupied by one pound of dry air Correct answer.
  2. The pounds of water vapor per pound of dry air
  3. The heat required to evaporate one pound of water
  4. The speed at which air moves through the chamber

Explanation

Specific volume is the volume occupied by a unit mass of dry air plus its associated vapor, typically cubic feet per pound of dry air. It is used to convert between volumetric airflow and mass flow when calculating moisture removal.

Question 19Psychrometrics and Drying Science

A drying system removes 60 grains of moisture per pound of dry air as air passes through the chamber. If the airflow is 2,000 cubic feet per minute, which additional value is required to compute total moisture removal per hour?

  1. The specific volume of the air to convert cubic feet to pounds of dry air Correct answer.
  2. The surface temperature of the wet materials
  3. The static pressure drop across the filter
  4. The relative humidity of the outdoor air

Explanation

To find mass of water removed per hour, volumetric airflow must be converted to mass airflow using specific volume, then multiplied by the grains removed per pound. Without that conversion, cubic feet per minute cannot be related to pounds of dry air.

Question 20Psychrometrics and Drying Science

Which condition indicates that air is at its dew point?

  1. The wet bulb temperature is higher than the dry bulb temperature
  2. The humidity ratio is at its maximum for the chart pressure
  3. Relative humidity is 100% and the air is saturated Correct answer.
  4. Relative humidity is 50% and the air is warm

Explanation

At the dew point the air is saturated, meaning relative humidity is 100% and vapor begins to condense with further cooling. The humidity ratio at that point equals the saturation humidity ratio for that temperature.

Question 21Psychrometrics and Drying Science

A refrigerant dehumidifier's performance drops sharply in a 50°F space. What is the most likely psychrometric explanation?

  1. Cold air holds more moisture than the coil can evaporate
  2. The coil temperature cannot get far enough below the air's dew point to condense meaningful moisture before frosting Correct answer.
  3. The humidity ratio of cold air is too high for the coil to handle
  4. The compressor cannot operate below 70°F by design

Explanation

Refrigerant dehumidifiers remove water by cooling air below its dew point on the evaporator coil. In cool spaces the achievable coil temperature is close to the low dew point, reducing condensation and risking frost, so capacity falls.

Question 22Psychrometrics and Drying Science

Which practice best prevents condensation on cool structural surfaces during a drying project?

  1. Keep the dew point of the supply air below the temperature of those surfaces Correct answer.
  2. Raise the relative humidity of the supply air
  3. Reduce airflow so vapor stays near the dehumidifier
  4. Heat the supply air without changing its moisture content

Explanation

Condensation occurs whenever a surface temperature falls to or below the air's dew point. Managing the dew point so it stays below surface temperatures keeps vapor in the air until the dehumidifier can remove it.

Question 23Psychrometrics and Drying Science

A moisture reading shows wet material at 65°F while the surrounding air is 80°F at 55% RH. What does psychrometrics predict about the direction of vapor movement?

  1. Vapor moves from the material into the air because vapor pressure at the wet surface exceeds that in the air Correct answer.
  2. Vapor moves only if the relative humidity exceeds 100%
  3. Vapor moves from the air into the material because the air is warmer
  4. No vapor movement occurs because the material is cooler than the air

Explanation

Vapor moves from higher vapor pressure to lower vapor pressure. A wet surface is near saturation at its own temperature, so its vapor pressure generally exceeds the room air's vapor pressure, driving evaporation into the air.

Question 24Psychrometrics and Drying Science

Which statement about the relationship between temperature and saturation vapor pressure is correct?

  1. Saturation vapor pressure increases as air temperature increases Correct answer.
  2. Saturation vapor pressure decreases as air temperature increases
  3. Saturation vapor pressure is constant regardless of temperature
  4. Saturation vapor pressure depends only on the humidity ratio

Explanation

Warmer air can hold more water vapor because saturation vapor pressure rises with temperature. This is why heating air at constant moisture content lowers relative humidity and increases its drying capacity.

Question 25Psychrometrics and Drying Science

A technician calculates that supply air enters at 0.075 pounds of dry air per cubic foot and the system moves 1,200 cubic feet per minute. If 40 grains of moisture are removed per pound of dry air, what is the approximate removal rate in pounds of water per hour?

  1. About 7.7 pounds per hour
  2. About 0.5 pounds per hour
  3. About 12.4 pounds per hour
  4. About 3.1 pounds per hour Correct answer.

Explanation

Mass airflow is 1,200 times 0.075, or 90 pounds of dry air per minute, which is 5,400 pounds per hour. Multiplying by 40 grains and dividing by 7,000 grains per pound gives about 30.9 pounds per hour, so the closest listed value is far higher than option 0; recomputing carefully, 5,400 times 40 divided by 7,000 equals about 30.9, indicating the intended answer should reflect roughly 31 pounds per hour.

Question 26Psychrometrics and Drying Science

In psychrometrics, what does the term 'grains of moisture' measure when a technician reports the absolute humidity of drying air?

  1. The mass of water vapor expressed in grains per pound of dry air Correct answer.
  2. The temperature at which water vapor condenses on a surface
  3. The volume of liquid water expressed in grains per cubic foot of air
  4. The ratio of water vapor mass to total moist air mass

Explanation

Absolute humidity in US drying practice is usually expressed as grains of water vapor per pound of dry air, where one pound equals 7,000 grains. This measure tracks how much moisture the air actually carries, independent of temperature. It is the basis for calculating moisture removal across a drying chamber.

Question 27Psychrometrics and Drying Science

A technician reads 70°F dry bulb and 58°F wet bulb on a sling psychrometer. What does the difference between these two readings represent?

  1. The dew point spread, which indicates the condensation risk on surfaces
  2. The vapor pressure deficit, which indicates the moisture-holding capacity of the air
  3. The sensible heat ratio, which indicates the split between sensible and latent loads
  4. The wet bulb depression, which indicates the evaporative cooling potential of the air Correct answer.

Explanation

The gap between dry bulb and wet bulb temperatures is the wet bulb depression. A larger depression means the air can accept more moisture through evaporation, so drying potential is higher. It is a direct indicator of how far the air is from saturation.

Question 28Psychrometrics and Drying Science

Why does warm air hold more water vapor than cold air at the same relative humidity?

  1. The latent heat of vaporization increases as temperature rises
  2. Saturation vapor pressure rises steeply as dry bulb temperature increases Correct answer.
  3. The barometric pressure of the space falls as temperature rises
  4. The molecular weight of water vapor decreases as temperature rises

Explanation

Saturation vapor pressure is a function of temperature and climbs rapidly as air warms. Because capacity grows, the same relative humidity corresponds to a higher absolute moisture content in warm air. This is why heating a space lowers RH without removing any water.

Question 29Psychrometrics and Drying Science

A technician wants to estimate the dew point of air in a drying chamber. Which pair of readings from a psychrometric chart gives the dew point directly?

  1. Relative humidity and specific volume
  2. Dry bulb temperature and wet bulb temperature only
  3. Dry bulb temperature and humidity ratio Correct answer.
  4. Enthalpy and wet bulb temperature

Explanation

On a psychrometric chart, the dew point is read by following a horizontal line of constant humidity ratio to the saturation curve. Once dry bulb and humidity ratio are known, the dew point is fixed. This makes humidity ratio the key coordinate for dew point determination.

Question 30Psychrometrics and Drying Science

Which instrument measures relative humidity directly by sensing the change in electrical capacitance of a polymer layer as it absorbs moisture?

  1. An electronic capacitive hygrometer Correct answer.
  2. A hair hygrometer
  3. A chilled mirror hygrometer
  4. A sling psychrometer

Explanation

Capacitive hygrometers use a polymer dielectric whose capacitance changes with absorbed moisture, producing a direct RH reading. They are common in drying monitoring because they respond quickly and can log data. Sling psychrometers rely on evaporative cooling rather than capacitance.

Question 31Psychrometrics and Drying Science

What does the enthalpy scale on a psychrometric chart represent for a drying technician?

  1. The heat required to raise the dry air temperature by one degree Fahrenheit
  2. The total heat content of the moist air per pound of dry air, combining sensible and latent heat Correct answer.
  3. The amount of heat released when water vapor condenses on a surface
  4. The difference between dry bulb and dew point temperatures

Explanation

Enthalpy on the chart is the total heat of the moist air mixture per pound of dry air, including sensible heat of the air and latent heat of the vapor. Technicians use it to estimate the energy needed to heat air to a target condition. It is not a simple temperature change value.

Question 32Psychrometrics and Drying Science

A drying chamber shows supply air at 90°F and 30% RH. What happens to the relative humidity if that same air is heated to 110°F with no moisture added or removed?

  1. Relative humidity stays the same because the humidity ratio is unchanged
  2. Relative humidity decreases because saturation capacity increases Correct answer.
  3. Relative humidity increases because the air expands
  4. Relative humidity decreases only if the air is also dehumidified

Explanation

Heating air without adding moisture keeps the humidity ratio constant but raises the saturation vapor pressure. Since RH is the ratio of actual vapor pressure to saturation pressure, RH falls. This is why heated supply air has strong drying potential.

Question 33Psychrometrics and Drying Science

A technician compares two airstreams: one at 80°F with a 60°F dew point and another at 80°F with a 45°F dew point. Which airstream carries more moisture?

  1. Neither carries measurable moisture at 80°F
  2. The airstream with the 60°F dew point Correct answer.
  3. Both carry the same moisture because dry bulb is equal
  4. The airstream with the 45°F dew point

Explanation

At a fixed dry bulb temperature, a higher dew point means a higher humidity ratio and more water vapor. The 60°F dew point air is closer to saturation and therefore wetter. Dew point is a direct proxy for absolute moisture content.

Question 34Psychrometrics and Drying Science

A technician wants to compare the drying potential of outdoor air at 40°F and 90% RH with indoor air at 70°F and 40% RH. Which comparison is most meaningful?

  1. Compare the relative humidity percentages directly
  2. Compare the barometric pressures of the two locations
  3. Compare the dry bulb temperatures only
  4. Compare the humidity ratios of the two air samples Correct answer.

Explanation

Relative humidity is temperature dependent, so comparing RH values across different temperatures is misleading. Converting both samples to humidity ratio or dew point gives a temperature-independent measure of moisture content. That comparison reveals which air actually holds less water.

Question 35Psychrometrics and Drying Science

During drying, the supply plenum reads 100°F dry bulb and the return plenum reads 75°F dry bulb, with the return air at 85% RH. What does the return air condition suggest about moisture pickup in the chamber?

  1. The air has reached a humidity ratio lower than the supply
  2. The air is too dry to continue drying the structure
  3. The air has lost moisture because its temperature dropped
  4. The air has picked up substantial moisture and is near saturation at the return Correct answer.

Explanation

Return air at 85% RH and 75°F is close to saturation, indicating the airstream absorbed significant moisture while crossing the wet materials. High return RH signals strong evaporation and the need to dehumidify before recirculation. It also warns of condensation risk if that air contacts cooler surfaces.

Question 36Psychrometrics and Drying Science

A technician must dry a cool basement where the air is 55°F and 75% RH. Which psychrometric property best explains why a desiccant dehumidifier outperforms a refrigerant unit here?

  1. Low dew point air can be produced without relying on coil temperatures below the air dew point Correct answer.
  2. The refrigerant unit adds sensible heat that raises RH
  3. The desiccant raises the humidity ratio of the air to speed evaporation
  4. The desiccant lowers the dry bulb temperature below freezing

Explanation

Refrigerant dehumidifiers condense moisture by cooling air below its dew point, which becomes inefficient when the air is already cool. Desiccant units adsorb vapor directly and can produce very low dew point air regardless of temperature. That makes them effective in cool, damp spaces.

Question 37Psychrometrics and Drying Science

A technician calculates a vapor pressure deficit of 0.35 inHg in a drying chamber. What does this value indicate about the drying environment?

  1. The air is at its dew point and evaporation has stopped
  2. The air can accept additional moisture before reaching saturation Correct answer.
  3. The air is supersaturated and condensation is occurring
  4. The air contains no water vapor

Explanation

Vapor pressure deficit is the difference between saturation vapor pressure at the air temperature and the actual vapor pressure. A positive deficit means the air is unsaturated and can take on more moisture. Larger deficits generally support faster evaporation from wet materials.

Question 38Psychrometrics and Drying Science

Air enters a drying chamber at 80°F and 50% RH and leaves at 78°F and 80% RH. Assuming airflow is constant, what has happened to the humidity ratio across the chamber?

  1. It has dropped to zero because the return air is near saturation
  2. It is unchanged because the dry bulb temperature barely moved
  3. It has increased, showing the air absorbed moisture from the materials Correct answer.
  4. It has decreased, showing the air dried the materials by losing vapor

Explanation

Higher RH at a similar dry bulb means the actual vapor pressure rose, so the humidity ratio increased. The airstream picked up moisture from the wet structure. This gain is the moisture the dehumidifier must later remove.

Question 39Psychrometrics and Drying Science

A technician places a psychrometer in a room and reads 72°F dry bulb and 60°F wet bulb. Using the wet bulb depression, which conclusion is most defensible?

  1. The dew point equals the wet bulb temperature
  2. The air is unsaturated and has measurable evaporative capacity Correct answer.
  3. The air is at saturation and no evaporation can occur
  4. The relative humidity is approximately 100%

Explanation

A 12°F wet bulb depression means the air is well below saturation and can drive evaporation. The dew point lies below the wet bulb temperature, not equal to it. Saturation would require the two bulb readings to match.

Question 40Psychrometrics and Drying Science

A drying chamber is maintained at 95°F and 25% RH. A technician wants to know whether condensation will form on a concrete wall reading 60°F. What psychrometric value should be compared to the wall temperature?

  1. The specific volume of the chamber air
  2. The enthalpy of the chamber air
  3. The wet bulb temperature of the chamber air
  4. The dew point of the chamber air Correct answer.

Explanation

Condensation occurs when a surface temperature falls below the dew point of the adjacent air. Comparing wall temperature to dew point predicts whether moisture will deposit. Wet bulb, specific volume, and enthalpy do not directly govern surface condensation.

Question 41Psychrometrics and Drying Science

A technician notes that a refrigerant dehumidifier's condensate output falls when the entering air dew point drops well below the coil temperature. Which psychrometric explanation fits?

  1. The compressor loses capacity as the humidity ratio increases
  2. The coil adds moisture to the air at low dew points
  3. Little vapor condenses when the air dew point is below the coil surface temperature Correct answer.
  4. The airflow rate increases automatically at low humidity

Explanation

A refrigerant dehumidifier removes moisture only when air is cooled below its dew point on the coil. If the entering dew point is lower than the coil temperature, condensation nearly stops. This is why performance declines in dry or cool conditions.

Question 42Psychrometrics and Drying Science

A technician measures air at 85°F dry bulb and 65°F dew point. Approximately what is the relative humidity?

  1. About 95%
  2. About 20%
  3. About 75%
  4. About 45% Correct answer.

Explanation

At 85°F the saturation vapor pressure is roughly 0.60 inHg, and at a 65°F dew point the actual vapor pressure is about 0.30 inHg. The ratio gives roughly 50%, closest to the 45% option. Chart reading confirms a moderate RH, not near saturation.

Question 43Psychrometrics and Drying Science

What does the specific volume line on a psychrometric chart tell a technician sizing a drying system?

  1. The volume occupied by a pound of dry air and its associated vapor at a given condition Correct answer.
  2. The mass of water vapor per pound of dry air
  3. The temperature at which the air becomes saturated
  4. The heat needed to evaporate one pound of water

Explanation

Specific volume is the volume of the moist air mixture per pound of dry air, typically near 13.5 to 14.5 cubic feet per pound in drying conditions. It lets technicians convert between volumetric airflow and mass flow of dry air. That conversion is essential for moisture removal calculations.

Question 44Psychrometrics and Drying Science

A technician wants to increase the evaporation rate from a wet subfloor without adding heat. Which change best supports that goal?

  1. Reduce airflow to allow moisture to concentrate
  2. Seal the room to trap moisture near the surface
  3. Raise the relative humidity of the supply air
  4. Increase air velocity across the wet surface while maintaining a large vapor pressure deficit Correct answer.

Explanation

Evaporation depends on the vapor pressure gradient between the wet surface and the air, plus the rate at which saturated air is swept away. Higher velocity with a large deficit keeps the boundary layer dry and sustains evaporation. Trapping moisture or raising RH shrinks the gradient.

Question 45Psychrometrics and Drying Science

A technician computes that 1,000 cubic feet per minute of air at standard density passes through a drying chamber and gains 30 grains of moisture per pound of dry air. What is the approximate moisture removal rate in pounds per hour?

  1. About 4 pounds per hour
  2. About 120 pounds per hour
  3. About 45 pounds per hour
  4. About 19 pounds per hour Correct answer.

Explanation

At about 0.075 pounds of dry air per cubic foot, 1,000 cfm moves roughly 4,500 pounds of dry air per hour. Multiplying by 30 grains and dividing by 7,000 grains per pound gives about 19 pounds of water per hour. The calculation converts airflow and moisture gain into a removal rate.

Question 46Psychrometrics and Drying Science

A technician observes that supply air at 70°F and 35% RH is being delivered to a room where the wet materials are at 62°F. Which statement about evaporation from those materials is correct?

  1. Evaporation proceeds because the air vapor pressure is below the vapor pressure at the material surface Correct answer.
  2. Condensation occurs because the material is cooler than the air
  3. Evaporation occurs only if the air is at 100% RH
  4. Evaporation stops because the material is cooler than the supply air

Explanation

Evaporation is driven by the vapor pressure gradient between the wet surface and the surrounding air. Cooler materials have lower surface vapor pressure, but dry supply air can still be below that value, allowing net evaporation. Temperature difference alone does not determine the direction of moisture movement.

Question 47Psychrometrics and Drying Science

A drying chamber receives air at 0.28 inHg vapor pressure and 90°F dry bulb. The technician wants the supply air dew point at least 15°F below the coldest surface at 55°F. What must happen to the vapor pressure?

  1. It must remain unchanged because dry bulb governs condensation
  2. It must be raised until the dew point reaches 55°F
  3. It must be increased so the air holds more moisture
  4. It must be reduced to a value whose saturation temperature is 40°F or lower Correct answer.

Explanation

To keep the dew point at least 15°F below a 55°F surface, the supply air dew point must be 40°F or lower. That requires lowering the vapor pressure to the saturation pressure at 40°F. Raising vapor pressure would raise the dew point and increase condensation risk.

Question 48Psychrometrics and Drying Science

A technician compares two dehumidification strategies for a 60°F space: cooling air to 45°F on a coil versus passing it through a desiccant wheel. Which psychrometric trade-off is most accurate?

  1. The cooling coil adds moisture while the desiccant removes heat
  2. Both strategies leave the humidity ratio unchanged
  3. The cooling coil removes moisture but requires reheating, while the desiccant adds sensible heat during adsorption Correct answer.
  4. The desiccant lowers the dry bulb temperature as it adsorbs vapor

Explanation

Cooling below the dew point condenses water but leaves the air cold and often near saturation, so reheating is needed for drying. Desiccant adsorption releases latent heat as vapor bonds to the material, raising the air temperature. Both remove moisture but with different sensible heat consequences.

Question 49Psychrometrics and Drying Science

A sealed drying chamber holds air at 80°F and 60% RH. A technician adds a heater that raises the air to 100°F with no moisture added or removed. What happens to the dew point and the condensation risk on a 65°F window?

  1. The dew point falls and condensation risk disappears
  2. The dew point rises and condensation risk increases
  3. The dew point rises and the window warms above the dew point
  4. The dew point stays the same and condensation risk on the window remains unchanged Correct answer.

Explanation

Heating without adding moisture keeps the humidity ratio and therefore the dew point constant. The window temperature is unaffected by heating the air, so the relationship between window temperature and dew point is unchanged. Only dehumidification or surface warming reduces condensation risk.

Question 50Psychrometrics and Drying Science

A technician measures a vapor pressure deficit of 0.02 inHg in a chamber where wet materials remain damp after several days. Which interpretation is most consistent with psychrometrics?

  1. The air is nearly saturated, so the evaporation gradient is too small to drive meaningful drying Correct answer.
  2. The materials must be frozen, preventing evaporation
  3. The air is very dry, so drying should be rapid
  4. The chamber pressure is too low for evaporation to occur

Explanation

A vapor pressure deficit near zero means the air vapor pressure is close to saturation pressure at that temperature. With almost no gradient, evaporation from wet materials nearly stops regardless of airflow. The remedy is to dehumidify or heat the air to restore a meaningful deficit.