Transcript Moisture Assessment

WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY
Moisture Assessment
WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Learning Objectives
MOISTURE ASSESSMENT
By attending this session, participants will be able to:
• Analyze the symptoms of moisture problems in houses.
• Identify moisture sources.
• Explain moisture terms and concepts.
• Demonstrate how to measure relative humidity.
• Demonstrate how to use a psychrometric chart.
• Apply moisture control strategies.
• Use moisture assessment tools.
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Symptoms #1
MOISTURE ASSESSMENT
Excessive window condensation
Photo courtesy of PA WTC
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Symptoms #2
MOISTURE ASSESSMENT
Frost on underside of roof sheathing
Photo courtesy of PA WTC
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Symptoms #3
MOISTURE ASSESSMENT
Mold on interior surfaces
Photo courtesy of PA WTC
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Photo source: PA WTC Photo
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Symptoms #4
MOISTURE ASSESSMENT
Peeling Exterior Paint
Photo courtesy of PA WTC
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Symptom #5
MOISTURE ASSESSMENT
Standing Water in Basements
Photo courtesy of PA WTC
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Moisture Sources
MOISTURE ASSESSMENT
• Foundations
• Unvented space
heaters
• Unvented dryers
• Disconnected
ventilation fans
• Drying wood indoors
• Excessive
mechanical or
passive
humidification
Photo courtesy of PA WTC
These water stains are a result of fan venting into the attic.
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Sources of Water Vapor
MOISTURE ASSESSMENT
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Important Terms and Concepts
MOISTURE ASSESSMENT
• Condensation: water vapor transformed to liquid water
• Evaporation: liquid water transformed to water vapor
• Absolute humidity (vapor pressure): the ratio of water
vapor to a given volume of air
• Relative humidity (RH): the ratio of the amount of
moisture in the air compared to amount of moisture that
the air can hold
• Dew point: the temperature at which condensation
occurs
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Measuring Relative Humidity
MOISTURE ASSESSMENT
Sling Psychrometers
• Two thermometers side by side
• One is wrapped in wet wick (wet
bulb), the other is dry (dry bulb)
• Spinning it around speeds
temperature stabilization
• Plot wet bulb and dry bulb
temperature on psychrometric
chart to determine dew point and
RH
Photos courtesy of Bacharach
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Psychrometric Chart #1
MOISTURE ASSESSMENT
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Grains of water per pound of dry air
Dry bulb = 80°
Wet bulb = 66°
Dew point = 60°
RH = 50%
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Psychrometric Chart #2
MOISTURE ASSESSMENT
156
Grains of water per pound of dry air
78
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Psychrometric Chart #3
MOISTURE ASSESSMENT
Grains of water per pound of dry air
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Psychrometric Chart #4
MOISTURE ASSESSMENT
Grains of water per pound of dry air
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Psychrometric Chart #5
MOISTURE ASSESSMENT
Grains of water per pound of dry air
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RH: Things to Remember
MOISTURE ASSESSMENT
• Warm, wet air contacting cold surfaces creates
condensation instantly.
• Cold winter air typically contains very little moisture and
therefore has a low RH. When that air is heated, the RH
drops even lower.
• RH below 15% can lead to respiratory problems,
failure of furniture glue and other problems.
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Attic Case Study
MOISTURE ASSESSMENT
Floored Attic and First Condensing Surface
Photo courtesy of PA WTC
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Attic Case – Causes & Solutions
MOISTURE ASSESSMENT
Possible Causes
• Moderate to high interior moisture source
• Attic surface temps are below the dew point of the indoor air
• Air leaks to attic
Control Strategies
• Source control
• Air seal the attic
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Basement Case Study
MOISTURE ASSESSMENT
Symptom
• Condensation evident
on basement walls
Mold on cool
interior corner
Reason
• Light to moderate
interior moisture
source
• Basement walls are
below the dew point
of the indoor air
Photo courtesy of PA WTC
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Basement Case Study Solutions
MOISTURE ASSESSMENT
Control moisture sources.
Remove susceptible materials.
Educate occupants to:
• Mechanically dehumidify.
• Increase air flow in basement (fans).
• Close basement openings during hot humid periods.
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Crawl Space Case Study
MOISTURE ASSESSMENT
Symptoms
• Wet wood
• Condensation on
foundation surfaces
Possible Reasons
• High ground moisture
source
• Warm humid air entering
vents from outside
• Crawl space surfaces
are below the dew point
of the outside air
Photo courtesy of PA WTC
Water droplets of condensation on AC ducts.
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Crawl Space Case Study
Solutions
MOISTURE ASSESSMENT
• Install a ground vapor
retarder.
• Control moisture sources
and remove susceptible
materials.
• Consider converting to a
conditioned crawl space.
Photo courtesy of INCAP
Conditioned crawlspace with air sealed and
insulated walls.
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Tools of the Trade
MOISTURE ASSESSMENT
Clear understanding of moisture management principles.
• Senses - Visual inspection
o Evidence of condensation
o Evidence of mold
• Communication Skills
o Know what questions to ask
o Documentation is vital
• Wood Moisture Meter
o To make quantitative assessments on wood moisture content
• Psychrometer
o To determine real time RH levels
• Digital Camera
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Moisture Meters
MOISTURE ASSESSMENT
Photos courtesy of PA WTC
PhotoSource: PA WTC
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Summary
MOISTURE ASSESSMENT
• The first step in doing a moisture assessment is to look
for visible signs of moisture and moisture sources in the
house.
• Plotting the wet bulb and dry bulb temperatures on a
psychrometric chart gives dew point and relative
humidity.
• Understanding the effects of temperature and vapor
pressure on RH can help identify solutions.
• Source control, air sealing, ventilation, and thermal
improvements are important moisture mitigation
strategies.
• Photos and diagnostic equipment help document
existing conditions.
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