Transcript WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY Building Science Basics WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 1 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM –

WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY
Building Science Basics
WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
1 | WEATHERIZATION
ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Learning Objectives
BUILDING SCIENCE BASICS
• Explain the difference between thermal and air
boundaries.
• Locate thermal and air boundaries.
• Name the driving forces of air leakage.
• Describe the connection between air leakage, energy
waste, and moisture problems.
• Describe how air ducts affect pressure balances within
the home.
• Explain the principle behind the blower door as a tool for
measuring air leakage.
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Comfort, Safety, and Efficiency
BUILDING SCIENCE BASICS
A comfortable, safe, and energy-efficient home
requires:
• A fully insulated thermal envelope.
• A well-sealed air barrier.
• The thermal and air boundaries to be continuous and
in contact with one another.
• Efficient, properly sized equipment to condition the
living space and heat water.
• A well-designed and balanced distribution system.
• Healthy indoor air quality.
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Thermal Boundary
BUILDING SCIENCE BASICS
The thermal boundary:
• Limits heat flow between inside and outside.
• Is easy to identify by presence of insulation.
The location of insulation in relation to other
building components is critical to its effectiveness.
Even small areas of
missing insulation are
very important.
Voids of 7% can
reduce effective R-value
by almost 50%.
Graphic developed for the US DOE WAP Standardized Curricula
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Photo courtesy of NRCERT
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Air Barrier
BUILDING SCIENCE BASICS
The air barrier:
• Limits airflow between inside and outside.
• Is more difficult to identify.
• Is not always where you think it is.
• Is located by using a blower door.
Graphic developed for the US DOE WAP Standardized Curricula
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Air Leakage
BUILDING SCIENCE BASICS
Air leakage requires:
• A hole.
• Pressure difference across that
hole.
The bigger the hole or higher the
pressure difference, the more airflow.
To reduce airflow, we can reduce the
size of the hole or lower the pressure
difference.
Graphic developed for the US DOE WAP Standardized Curricula
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Air Leakage
BUILDING SCIENCE BASICS
• Airflow is measured in cubic feet per minute, also
written as ft3/min, or CFM
• 1 CFM OUT = 1 CFM IN
• Airflow takes the path of least resistance
• Air moves from high- to low-pressure areas
• Air usually moves from high- to low-temperature areas
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Air Leakage
BUILDING SCIENCE BASICS
Direct leakage
occurs at direct openings
to outdoors. Leakage
enters or exits the
building envelope directly
at this location.
Indirect leakage
enters at one location,
moves through building
cavities, and exits at a
different location.
Graphic developed for the US DOE WAP Standardized Curricula
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Air Leakage
BUILDING SCIENCE BASICS
Ventilation = Controlled air leakage
Infiltration =
Exfiltration =
Air leaking in
Air leaking out
Graphic developed for the US DOE WAP Standardized Curricula
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Driving Forces of Air Leakage
BUILDING SCIENCE BASICS
Driving Forces of Air Leakage
Temperature and pressure differences–
usually between inside and outside the house.
The bigger the temperature or pressure difference,
the greater the air and heat flow.
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Air Leakage: Temperature
BUILDING SCIENCE BASICS
T = Temperature Difference
Winter
Summer
70
10
90
T=60
70
T=20
cold
hot to _____
Flow is from _____
more heat and air want
The higher the T, the ______
to escape or enter the building.
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Graphic developed for the US DOE WAP
Standardized Curricula
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Air Leakage: Pressure
BUILDING SCIENCE BASICS
P = Pressure Difference
Positive
Negative
positive (high) to ______________
negative (low) pressure.
Flow is from ______________
exits
enters one CFM _______.
For every CFM that _______,
least resistance.
Flow takes the path of _______
Graphic developed for the US DOE WAP Standardized Curricula
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Air Leakage: Driving Forces
BUILDING SCIENCE BASICS
Types of Driving Forces
Wind
Heat – Stack effect, combustion
Fans – Exhaust fans, duct leaks, interior doors
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Driving Forces: Wind Effect
BUILDING SCIENCE BASICS
Wind Direction
Positive
pressure
Negative
pressure
…which creates a
negative pressure
on the other sides
of the house.
Wind creates a positive
pressure on the
windward side of the
building...
Graphic developed for the US DOE WAP Standardized Curricula
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Driving Forces: Stack Effect
BUILDING SCIENCE BASICS
Stack Effect
Warmer air rises
and escapes out of
the top of the
house…
…which creates a
suction that pulls in
outside air at the
bottom of the
house.
Positive pressure
Neutral
pressure
plane
Negative pressure
Graphic developed for the US DOE WAP Standardized Curricula
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Stack Effect
BUILDING SCIENCE BASICS
Positive pressure
(with reference to outside)
Neutral pressure plane
Negative pressure
(with reference to outside)
Photo courtesy of David Keefe, Vermont Energy Investment Corp.
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Driving Forces: Combustion & Fans
BUILDING SCIENCE BASICS
Combustion Equipment and Exhaust Fans
Negative
pressure
Exhaust
Fan
Negative
pressure
Graphic developed for the US DOE WAP Standardized Curricula
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Driving Forces: Duct Leakage
BUILDING SCIENCE BASICS
Duct Leakage
Duct leakage can create
positive and negative
pressures in different areas
of the house.
The pressures associated with
duct leaks can be larger and
more important because the
driving force is stronger.
Return
Supply
All holes are not created equal!
Graphic developed for the US DOE WAP Standardized Curricula
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Driving Forces: Duct Leakage
BUILDING SCIENCE BASICS
Duct Leakage
Closed doors prevent supply
air from getting back to a
return.
This causes positive
pressures in those rooms
with supply vents, and
negative pressure in the zone
where the return is located.
Return
Supply
Graphic developed for the US DOE WAP Standardized Curricula
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Driving Forces: Imbalances
BUILDING SCIENCE BASICS
Room Pressure Imbalances
Master
Bedroom
Utility Room
Kitchen
Whole-house
return in hallway
Living Room
Bedroom
Bath
Graphic developed for the US DOE WAP Standardized Curricula
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Controlled Driving Force
BUILDING SCIENCE BASICS
Use a Blower Door as a
Controlled Driving Force
Using the blower door
depressurizes the
house, drawing air
through all the holes
between inside and
outside the house.
Negative
pressure
Blower
Door
Graphic developed for the US DOE WAP Standardized Curricula
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Summary
BUILDING SCIENCE BASICS
• Pressure and thermal boundaries should be continuous
and in contact with each other.
• Air carries heat and moisture.
• Air leakage requires a hole and pressure difference.
• Wind, heat, and fans drive pressure differences.
• Duct location and condition can cause room
pressure imbalances.
• The blower door is a controlled driving force for
quantifying air leakage.
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