IICRC Applied Structural Drying (ASD)

On the psychrometric chart, what does the vertical axis (right-side) represent?

• ADry-bulb temperature
• BSpecific humidity, typically expressed in grains per pound (GPP)
• CWet-bulb temperature
• DAtmospheric pressure

How many grains of water are in one pound of water vapor?

• A1,000 grains
• B7,000 grains
• C10,000 grains
• D454 grains

Air inside a drying chamber reads 75 F and 50 GPP. Outdoor air reads 75 F and 80 GPP. What is the grain depression?

• A30 GPP
• B50 GPP
• C80 GPP
• D130 GPP

Why is specific humidity (GPP) a better measure of drying progress than relative humidity (RH)?

• ARH is a percent and percents cannot be subtracted
• BGPP is absolute and does not change with temperature alone, while RH varies with temperat…
• CGPP is easier to measure in the field
• DRH is only meaningful below 50 F

Dew point is best defined as:

• AThe temperature at which water boils at the current atmospheric pressure
• BThe temperature at which air becomes saturated and condensation begins to form
• CThe wet-bulb temperature minus 5 degrees
• DThe average of dry-bulb and wet-bulb temperatures

Sensible heat refers to:

• AHeat that causes a phase change without temperature change
• BHeat that changes the temperature of a substance without changing its phase
• CThe heat content of a substance at absolute zero
• DHeat lost through radiation only

Latent heat is consumed when:

• AAir is heated from 60 F to 80 F with no moisture change
• BLiquid water evaporates from a wet surface into the air
• CHot air is moved by a centrifugal air mover
• DA psychrometer is calibrated at sea level

Air at 70 F and 50% RH has a specific humidity near 55 GPP. If this same air is heated to 90 F with no moisture added or removed, what happens to its RH and GPP?

• ABoth RH and GPP increase
• BRH stays the same, GPP increases
• CRH decreases, GPP stays the same
• DBoth RH and GPP decrease

Why does evaporation cool the air?

• ABecause evaporation creates a vacuum that lowers temperature
• BBecause liquid water absorbs latent heat from the surrounding air to change state to vapor
• CBecause evaporation increases atmospheric pressure
• DBecause vapor molecules are physically colder than liquid water

Vapor pressure differential between wet materials and the surrounding air drives evaporation. Which condition maximizes the differential to accelerate drying?

• ACold, saturated air immediately next to wet materials
• BWarm air with low specific humidity (low GPP) moving across wet surfaces
• CStill, humid air with no air mover present
• DAir at the same dew point as the wet substrate

Outdoor air is 60 GPP. Indoor drying chamber air is 90 GPP. Which best describes the situation?

• AThe chamber is drier than outdoors — good progress
• BThe chamber is wetter than outdoors — evaporation is loading the air with moisture and de…
• CGPP comparison between indoors and outdoors is meaningless
• DThe chamber must be heated to compensate

Wet-bulb depression is:

• ADry-bulb temperature minus wet-bulb temperature
• BWet-bulb temperature minus dew point
• CWet-bulb temperature minus 32 F
• DIndoor wet-bulb minus outdoor wet-bulb

Saturated air at any temperature has:

• A0% relative humidity
• B100% relative humidity, with dry-bulb temperature equal to wet-bulb temperature and dew p…
• CZero specific humidity
• DA dew point of 32 F

On the psychrometric chart, a horizontal line (constant GPP) represents which process?

• ASensible heating or cooling without moisture change
• BAdiabatic humidification
• CRefrigerant dehumidification
• DEvaporative cooling

A drying chamber holds 60 F and 85 GPP. The same chamber is brought to 80 F with no moisture change. Approximately what happens to RH?

• ARH increases substantially
• BRH decreases substantially
• CRH stays exactly the same
• DRH first rises then falls

Equilibrium moisture content (EMC) for a porous building material is defined as:

• AThe moisture content at which evaporation is zero because vapor pressure inside the mater…
• BThe maximum moisture content the material can absorb before structural failure
• CThe moisture content at which mold growth becomes inevitable
• DThe same moisture content for every type of material

If a drying chamber sees indoor GPP drop from 100 to 70 over 24 hours with no air leakage, what does this indicate?

• ADehumidification is removing more moisture than evaporation is adding
• BAir movers are too strong and need to be turned off
• COutdoor air is being introduced
• DThe materials have absorbed all the air's moisture

A drying environment at 80 F and 30% RH has approximately how many GPP?

• AAround 30 GPP
• BAround 50 GPP
• CAround 100 GPP
• DAround 155 GPP

Which describes a closed drying system?

• AOutdoor air is continuously brought into the structure to flush moisture out
• BThe drying chamber is isolated from outdoor air; HVAC and openings are sealed, and dehumi…
• CAir movers exhaust directly to outdoors
• DOnly desiccant dehumidifiers are used

An open drying system is most appropriate when:

• AOutdoor air is significantly drier (lower GPP) than indoor air and weather is stable
• BIndoor and outdoor conditions are nearly identical
• CThe structure is fully air-conditioned and sealed
• DOutdoor GPP is much higher than indoor GPP

A balanced drying system means:

• AEqual numbers of air movers and dehumidifiers
• BDehumidification capacity matches the evaporative load created by air movers and material…
• CEqual cubic feet between adjacent rooms
• DEqual pints capacity on both sides of the structure

An unbalanced drying system showing rising indoor GPP day over day most likely needs:

• AMore air movers and fewer dehumidifiers
• BAdditional dehumidification capacity or smaller chamber (reduced cubic footage)
• CLower temperature in the chamber
• DRemoval of the vapor barrier

Per ANSI/IICRC S500, Class 4 water loss involves:

• ACategory 3 (grossly contaminated) sewage water
• BWet materials with very low porosity that hold significant moisture and require specialty…
• CLosses affecting fewer than 5% of carpet area
• DWater from clean potable supply lines only

Which is the most appropriate dehumidifier strategy for Class 4 specialty drying?

• AConventional refrigerant only, because Class 4 materials are easy to dry
• BDesiccant dehumidification driving very low GPP (often below 40), combined with heat
• COpen drying with windows wide open
• DAir movers only, no dehumidification needed

Per S500, Class 2 is typically described as:

• ASlow evaporation; affected porous materials limited (e.g., partial carpet only)
• BFast evaporation; significant amount of water absorbed in porous materials throughout an…
• CSpecialty drying for low-evaporation materials such as plaster and hardwood
• DCategory 3 black water that has contacted sewage

Which is the best example of a low-evaporation (Class 4) material?

• ASynthetic carpet pad
• BOpen-cell polyurethane insulation
• CPlaster on wood lath
• DLoose-laid loop carpet

Which drying-system characteristic most reduces the dehumidification load you need to install?

• AAdding more air movers
• BContaining and reducing the cubic footage of the drying chamber
• CHeating the air to 95 F
• DSwitching to axial air movers

A 'heat drying system' adds substantial sensible heat to the chamber. What is the primary mechanism by which this accelerates drying?

• AIt increases the air's saturation vapor pressure, enlarging the vapor pressure differenti…
• BIt causes water to boil off building materials
• CIt improves dehumidifier performance directly without changing air conditions
• DIt increases RH which improves drying

For an open drying system to be effective, indoor GPP must:

• ABe higher than outdoor GPP
• BBe lower than outdoor GPP
• CEqual outdoor GPP
• DAlways be below 50 GPP regardless of outdoor

Why is closed drying generally preferred in modern, tightly built homes?

• AClosed drying is required by every building code
• BOutdoor conditions are uncontrollable, while a closed system lets the technician control…
• CClosed drying does not require any dehumidifiers
• DClosed drying always uses desiccant equipment

The 'Drying Plan' under ASD principles should specify all of the following EXCEPT:

• AInitial estimated number and types of dehumidifiers and air movers
• BContainment strategy and approximate chamber cubic footage
• CTarget drying conditions (temperature, target GPP, target RH)
• DFinal replacement carpet brand and color

When the rate-limiting step is moisture migration out of dense materials (Class 4), increasing the number of air movers beyond a saturation point will:

• ALinearly accelerate drying with each added air mover
• BProvide diminishing or no additional benefit because evaporation at the surface is no lon…
• CCause material structural collapse
• DConvert the loss to Class 2

Three categories of structural dehumidifiers commonly used in ASD are:

• AConventional refrigerant, LGR (Low Grain Refrigerant), and desiccant
• BConventional refrigerant, supercritical CO2, and condensing
• CStandalone, portable, and ducted only
• DAir-cooled, water-cooled, and ground-cooled

An LGR (Low Grain Refrigerant) dehumidifier differs from a conventional refrigerant dehumidifier primarily because:

• ALGRs use a desiccant wheel instead of a compressor
• BLGRs include a pre-cooling heat exchanger that lowers the air's temperature before the co…
• CLGRs run on natural gas
• DLGRs are smaller versions of conventional units

A desiccant dehumidifier removes moisture from air by:

• ACompressing air and condensing water on a cold coil
• BPassing air through a wheel or bed of moisture-absorbing material (silica gel, lithium ch…
• CBubbling air through liquid water
• DAdding a chemical that reacts with water

Conventional refrigerant dehumidifier performance falls off most steeply when:

• AAir temperature exceeds 100 F
• BGPP drops below approximately 55, leaving too little vapor to condense on the coil
• CRelative humidity exceeds 70%
• DWet-bulb depression is greater than 10 F

An AHAM dehumidifier rating represents pints per day at:

• A80 F and 60% RH (approximately 78 GPP)
• B65 F and 60% RH
• CSaturated air at any temperature
• DWhatever conditions the dehumidifier ships at

HGR (High-Grain Refrigerant) ratings differ from AHAM ratings because HGR:

• AIs tested at hotter, wetter conditions and reports higher pints/day numbers that overstat…
• BIs tested at cooler, drier conditions and reports lower pints/day numbers
• CIs a regulatory-mandated rating
• DIs identical to AHAM

Below approximately what GPP does a typical desiccant outperform an LGR by a meaningful margin?

• AAbove 80 GPP
• BAround 60-70 GPP
• CBelow ~40 GPP
• DOnly below 10 GPP

How does a desiccant dehumidifier expel the moisture it captures?

• AIt condenses water on a refrigeration coil and drains it
• BHot 'regeneration air' (often electrically or gas heated) drives the moisture off the des…
• CIt compresses water into a solid and bags it
• DIt releases the water back into the same chamber after a delay

Compared to conventional refrigerants, desiccants typically:

• AUse much less electricity per pint of water removed at warm wet conditions
• BExcel at very low GPP where refrigeration cannot economically condense water
• CRequire no exhaust ducting at all
• DAre only effective in Class 1 losses

A dehumidifier rated 130 AHAM pints/day is operating at 50 GPP and 75 F. Compared to its AHAM rating, you should expect:

• AHigher output because it is running at lower GPP
• BSubstantially lower output because actual conditions are drier than the 80 F / 60% RH (~7…
• CApproximately the same output regardless of conditions
• DOutput limited only by ambient temperature, not GPP

Why is dehumidifier intake/discharge GPP monitoring useful?

• AIt is the only legal way to verify dehumidifier compliance
• BComparing inlet to outlet GPP shows the dehumidifier's actual real-time water removal eff…
• CInlet/outlet GPP affects the warranty
• DIt directly measures total project hours

Which dehumidifier CFM/pint relationship is most accurate?

• AHigher CFM always equals more pints per day
• BCFM and pints/day are independent — a dehumidifier processes a specific volume of air thr…
• CPints/day equals CFM divided by 10
• DCFM has no relevance to dehumidifier sizing

If a dehumidifier's drain hose is kinked and the condensate reservoir fills, what is the typical safety behavior?

• AThe unit continues running and overflows onto the floor
• BAn internal float switch shuts the unit off until the reservoir is emptied or the drain r…
• CThe unit begins exhausting moisture as steam through the discharge
• DThe unit triples its output to push past the blockage

Where should a desiccant dehumidifier's regeneration exhaust be routed?

• AInto the drying chamber to recycle heat
• BOutside the drying chamber and ideally outside the structure
• CInto the HVAC return
• DAnywhere convenient inside the building

Why might a conventional refrigerant dehumidifier produce ice on its coil?

• AIt is performing at peak efficiency
• BAir temperature has dropped too low (typically below ~65 F at the coil) and the coil is o…
• CThe float switch has failed
• DThe refrigerant has been replaced with water