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8/7/2019 BS Fundamentals by John Ring
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Fundamentals of
Building Science
Presented by John H. RingEnergy Wise Solutions, Inc.
Knowledge for Building Rightin the 21st Century
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Learn what Building Science is and why we
need to understand it
Understand the basic physical principals of Building Science
Be prepared to apply those principals to real
life building
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Course Objectives
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It is the study of the interaction between Occupants
Building Components & Systems
Environment
Focusing on the flows through the buildingenclosure of Heat
Air Moisture
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What is Building Science?
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We no longer accept indoor environmental
conditions that we used to tolerate
We demand more control of our indoor environment
We have a limited supply of energy for
which demand & costs continue toincrease, so we must consider energy
conservation
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Building requirements
have changed
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Tighter building assemblies
More thermal insulation
More power vented furnaces & heaters
Air conditioning with flexible air ductdistribution systems
A multitude of new products to deal with Often combined in new ways
Copyright Energy Wise Solutions, Inc. 5
How do we build differently today
than we did even 30 years ago?
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Unsafe conditions
Unhealthy conditions
People are uncomfortable
Energy is wasted
Materials are wasted
Increased operating costs Failure of components or systems
We damage the environment
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What happens when buildings
don¶t work?
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A building creates an interior
environment that is different from the
exterior environment ± it is anEnvironmental Separator
Its function is to separate the inside
from the outside as required by the local environment
according to the wishes of its occupants
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Think of a House as
Your Environmental Separator
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A building provides shelter From the elements
From other dangers
The interior environment should be
controllable by the occupants in a
manner their meets their needs
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The Building System ±
Functional Relationships
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Studies the interaction of all of
these functional relationships
It tells us how buildings actuallywork
It tells us how to design, build,
operate, diagnose, and fix them
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Building Science
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Provide strength and rigidity
Control rain, wind & ground water
Control fire Control heat flow, air flow, and
moisture flow
Control contaminants, environmentalhazards and odors, insects, rodentsand critters
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We ask a Building to do
ManyT
hings
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Control light and solar radiation
Limit noise and vibration
Provide comfort
Be durable
Be economical to purchase and
operate
Be aesthetically pleasing
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SAFE
HEALTHY
COMFORTABLE
DURABLE
ENERGY EFFIC
IENT
ENVIRONMENTALLY FRIENDLY
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The Goal of Building Science
is to Provide a Home that is
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Building Science is the study of
Heat Flow
Air Flow
Moisture Flow
through the building enclosure
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Let¶s Review
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Not all these forces are equal
All are important, but some more than
others In buildings, aside from safety, control of
HEAT
AIR
MOISTURE
stand above all other considerations
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We have the bread on the outside ±we call that the Building Envelope ±
and the HAM on the inside
HEAT
AIR MOISTURE
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An easy way to remember what Building Science is:
Think of a the House as a
HAM SANDWICH
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THE LAWS OF PHYSICS
ALWAYS
WIN OVER OPINIONS
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Building Science
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Everything in a house interacts,
from the footing to the roof ± andall components and systems in
between CHANGING ONE PART OF THE
SYSTEM WILL AFFECT OTHER
PARTS OF THE SYSTEM
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The House is a System
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In the 1970s, in response to theenergy crisis ± yes, we did have one
in the past ± the levels of insulationwere substantially raised in homes. Also, following concepts transplantedfrom cold climates, houses in cooling
climates were sealed tighter andplastic was wrapped over thatinsulation.
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The House as a System
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Yup, it did save energy and increased comfort, butthat plastic trapped a lot of moisture and many of those houses have had problems with mold andstructural rot.
These problems came about because of a lack of system thinking ± no one considered the effect on thehouse of the combination of all that added insulation,plastic and the other changes.
While a few recognized the reasons for the problems,
it is only in the past 8 years that even the buildingcode has begun to change to reflect the need for System Thinking.
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The House as a System
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If you build an airtight house (as youshould), and wrap it in a layer of insulation, the rest of the house willreact as our bodies do if we were towear a winter coat year round. Theairtight, insulated house will keep theconditioned air in, but it will also keep
moisture and pollutants in as well. Anyone who designs, builds or remodels must always be aware of this.
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The House is an Interacting
System with People in the Middle
PeopleMechanicalSystems
Heat Lossand Gain
AirMovement
Moisture
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Building Science strives to providehouses that are ±
SAFE ± HEALTHY ± COMFORT ABLE ±
DURABLE ± ENERGY EFFICIENT ±
ENVIRONMENT ALLY FRIENDLY
Of these, for most people, what issuedo you think is of primary importance?
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Let¶s Review
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COMFORT
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³ that condition of mind in
which satisfaction isexpressed with the
thermal environment´1993 ASHRAE
Handbook of Fundamentals
Chapter 8
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What isC
omfort?
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Many homeowners complaints grow out of
comfort problems
COMFORT is the canary in the coal mine
What is causing the comfort problem may
also be causing problems with:
Safety & Health
Building durability Energy efficiency
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Comfort Problems =
System Problems
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Activity
Clothing
Temperature
Air Velocity
Moisture in the air (Rh) Radiant Surface Temperatures
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Comfort Variables
Comfort complaints areexpressed in terms of airtemperature, but radiant
surface temperatures are usually the primary cause.
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Now, let us discuss those things
that Building Science is all about
± the first is
HEAT FLOW
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HEAT FLOWHeat flow is the movement of
heat from one surface to
another, or from one space to
another, through one or more
heat transfer mechanisms
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Conduction
Convention
RadiationCopyright Energy Wise Solutions, Inc. 30
Methods of Heat Movement
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The action of HOT moving to COOL
is always trying to take place by oneor more of these mechanisms.
The greater the temperature
differential, the stronger themovement.
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Equi l ibri um is everything!
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H OT COLD
=
WARM WARM
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E verything in nat ure tries to
reac h a balanc e.
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The transmission of heat
through matter withoutmotion of the conducting
body as a whole.
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Conduction
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Requires two solids to be in
contact with each other.
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Conduction
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Takes place within an object
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Conduction
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How do we control conductive
heat loss?
By slowing down the heat transfer with
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Conduction
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The transfer of heat
when the motion of agas or fluid takes place
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Convection
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Is caused by: temperature differential
(natural)
mechanical action (forced).
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Convection
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Natural
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Convection
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Forced
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Convection
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ForcedYou run a ceiling fan or floor fan
to cool you
on a hot day.
H ow does
this w ork?
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Convection
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Natural convection works only by gravity;
that is, it works only up.
The warmer air, being lighter, rises.
Forced convection can work in any
direction:
It can work down as when the driving force ± a
ceiling fan, for example ± moves air down. It can work sideways, as with the fan in the
cartoon on the previous slide
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Convection
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Controlling Convection can only
be done with a
Barrier
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Convection
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The transfer of heat
through
empty space
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Radiation
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Radiation
Can
takeplace
in a
vacuum
Needsline of
sight
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You go up into your attic to storesome items on a sunny day in
summer. The heat in the attic is
almost overwhelming. You get athermometer and find that thetemperature at the roof peak is
140º.W hat is happening?
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Radiation
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Radiation from the sun is heating the shingles.
The shingles, primarily through Conduction, heat
the roof sheathing below.
The hot sheathing, primarily through Radiation,heats solid surfaces below that are
within the line of sight of the roof sheathing.
Convection also plays a role in keeping the roof
peak hotter than the space below.
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Radiation
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Radiation
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The previous example is illustrative of how a single
source of heat can result in all three heat flow
methods working at the same time to either cause
problems or do good.
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Heat flow mechanisms
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On a cold winter day you sit in your favorite
chair six feet from a single pane window and
don¶t feel comfortable
even with the ther-
mostat set at 78º.
H ow can this be so?
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Heat flow mechanisms
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Your body, and the clothing you have on,
are all at a higher temperature than the
window, and likely even the wall around it.
Your body heat moves by radiation to the
cold surfaces. You lose heat, making you
feel cool.
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Radiation & Comfort
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Because Radiation requires line of
sight to take place,
Blocking the Line of Sight
stops Radiation
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Radiation
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In Summary
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The next part of our building
³HAM´ sandwich is
AIR FLOW
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Air flow is the movement
of air - within a space
from one space to another
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Air Flow
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For air to flow into or out of a
building, or within two adjacent
inside spaces there must be
A hole and
A driving force
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Air Flow in Buildings
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Building Science is concerned withtwo types of holes that allow air movement into, out off, or within a
building: Designed - holes you pay for up front
Controlled by the occupants
Undesigned - these are free but cancost you a lot later
NOT occupant controlled
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Air Flow in Buildings
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Designed holes are ± Ones we deliberately open & close
Doors and windows
Ones that are usually tightly dampered andopen only when needed
Kitchen exhaust fan vents
Dryer vents
Laundry room fans
Bathroom fans
Ventilation air-in systems
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Air Flow in Buildings
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Air Flow in Buildings Undesigned holes -
Any wall penetration
Light fixtures
Switches & receptacles
Plumbing lines
Bottom and top plates
Rough openings
Boots in ceilings/floors
Fireplace inserts
In back of fireplace
inserts Exterior walls behind
tubs and showers
Attic entries
Under-eaves entries
Band joist areas
between floors
In-between floor chases Under door thresholds
Dropped soffits
Joist cavities under attic
kneewalls
Seams between rigidexterior sheathing
Ceiling height transitions
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The best houses are those with
the fewest undesigned holes
It is not possible to eliminate allundesigned holes, but good
building practices will take care
of most of them
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Air Flow in Buildings
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It used to be that little attention was paid
to building well sealed ± ³tight´ ±
houses. It was thought, and still is bymany, that a house needs to ³breath´,
and the numerous undesigned holes
allowed it to do that.
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Air Flow in Buildings
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Today we know this is not true. We know
that all those undesigned holes decrease
comfort and increase energy costs.Today we understand that if the only
holes in the building envelope are the
ones we design, and the ³breathing´ is
deliberately controlled, the house willfunction much better.
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Air Flow in Buildings
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Is this your house? Leaking all the air
you paid to condition!!
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Air Flow in Buildings
You have two choices:
1. Keep pouring in the conditioned air.
2. Plug the holes.
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We now know, based upon SCIENCE, that we must:
BUILD TIGHT
&
VENTILATE RIGHT
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Large undesigned holes must besealed first.
However, remember that smallholes add up. For example: an average 1/8´ gap
around an attic stairs hatch cover is
the same as a 4´ x 5´ hole in theceiling!
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Air Flow in Buildings
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When air enters or leaves
a space it can be: Hot or Cold
Wet or Dry
Clean or Polluted
A combination of the above
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Air Flow Fact
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Air flow, in building science
terms, is measured in Cubic Feet per Minute (CFM) or
Cubic Feet per Hour (CFH)
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Air Flow Fact
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When we think of air pressure we used to
thinking in terms of Pounds per Square
Inch (PSI). However, within a building weare usually looking at very small pressure
differences. Those units are called:
PASCALS (Pa)
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Air Flow Fact
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A Pascal is about the amount of
pressure exerted by a pat of butter on
bread, or the weight of couple of stickynotes.
1 PSI = 6,894 Pascals
There are 220,600 Pascals of
pressure in an auto tire at 32 psi!
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Air Flow Fact
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Driving forces are: Heat (the chimney/stack effect)
Wind
Fans ± mechanical systems
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Air Flow in Buildings
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One unit in = one unit out
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Air Flow Rule 1
1 ft³ in
1 ft³ out
Air in the
house
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Stack pressure is a function of
two things: T
he height of the building A 2-story house has twice the stack
pressure of a 1-story house
Temperature difference (
(T)indoors to outdoors
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Stack effect (Heat)
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Stack effect
NPP = Neutral Pressure Plane
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Wind
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Wind patterns
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There are a lot of fans in the modernhouse. Some can cause seriousdepressurization of a house if make-upair is not provided. Bathrooms
Kitchen range hoods vented to the exterior
Downdraft exhaust cooktops
Clothes dryers
Central vacuums Whole house fans
Powered attic fans
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Fans
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The effect of fans is
cumulative and if several of
the major ones are on at thesame time the house can
really suck!
It adds up quickly!
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Fans
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Fans
150 CFM + 700 CFM + 50 CFM
= 900 CFM
Where is the make-up air coming from in a tightlybuilt house? In a 2250 ft² house this situation
would change all the air in the house in 30
minutes. Remember, 1 unit out ± 1 unit in!
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Houses ± spaces ± with a positive
pressure in them BLOW
Houses ± spaces ± with a negativepressure in them SUCK
The major consistent cause of houses
that BLOW or SUCK is leaking ducts
outside the conditioned space
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Fans - Mechanical Systems
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If the dominant leakage is in the return
system, the house BLOWS
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Fans - Mechanical Systems
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What happens when a house, or a
portion of a house blows? Conditioned air is forced out of the house
replaced by unconditioned air resultingin:
Increased energy consumption
Decreased comfort Possible durability problems
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Air flow
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If the dominant leakage is in the output
system, the house SUCKS.
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Mechanical Systems
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What happens when a house, or a portion of
a house sucks? Unconditioned air is drawn in and conditioned
air is forced out resulting in: Potentially serious safety issues
Potential health problems if air is polluted
Possible durability problems
Increased energy consumption Decreased comfort
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Air flow
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Air, like water,
will tend to
move through
the nearest,largest
opening with
the least
amount of resistance.
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Air Flow Rule 2
What if the window isnt the nearest,largest opening with the least resistance?
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Air likes to be balanced. If there is a
pressure difference between two
spaces the air will move from the
area of high pressure
to the area of low
pressure to remove
the difference.
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Air Flow Rule 3
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Remember that air pressure isrelative. You cannot simply say
that a room has high pressure in it.
It must be³with reference to´
(WRT) another space. For
example: ³the master bedroom is
at a higher pressure than (WRT)
the adjacent hall.´
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Heated air rises Cooled air falls
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Air Flow Rule 4
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In order for a house to perform properly
and efficiently there must be
a continuous Air Barrier surrounding the house. It provides one
part of what is known as the
Thermal Barrier
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Air Barrier
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The Building Envelope is
defined as those systems
and components thatseparate the interior
environment from the
exterior environment.
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The Building Envelope
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The Thermal Barrier
includes an unbroken Air
Barrier with a contiguous
layer of Insulation in
contact with it.
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The Building Envelope
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The Thermal Barrier
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For air to flow into, out of, or
within a building it needs:
An opening A driving force:
Stack pressure
Wind Fans
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Air Flow SUMMARY
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Warm air rises, cool air falls
One unit of air in = one unit of air out
Air flows from high pressure to low
pressure
When trying to reach equilibrium, air seeks
the path of least resistance:
The nearest, largest opening with the leastamount of resistance
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Air Flow SUMMARY
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Now we move to the last part of our
³HAM´ sandwich:
MOISTURE
FLOWCopyright Energy Wise Solutions, Inc. 96
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Moisture Flow has great
significance with regard to how a
house performs and functions asa system.
Most building performance
problems are caused bymoisture.
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Moisture Flow
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Moisture Flow
Affects: Health:
Mold Dust mites
Cockroaches
Bacteria
Durability &
Safety:
Wood decay
Corrosion
Termites
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Moisture moves from
WET to DRYWhen materials get wet or they dry, it
is by moisture moving from the wetter
place to the dryer place in order to
achieve a balanced state.
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Moisture Flow
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There are four moisture
transport mechanisms:
Bulk Capillarity
Air Transported (Infiltration)
Vapor Diffusion
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Moisture Flow
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Moisture Flow
Bulk:
liquid water
(poor drainage,
water, roof,siding &
plumbing
leaks)
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Moisture Flow
Capillarity:
wicking through
porous materials(concrete, wood,
brick, cellulose
insulation,
gypsum board)
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Moisture Flow
Air Transportedor Infiltration:
whenever air moves,whatever is init moves with it,
including water vapor.
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Moisture Flow
Vapor Diffusion: The movement of
moisture in mole-cular form from an
area of higher
vapor pressure to
lower vapor
pressure.
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Moisture migratesto conditioned spaceby vapor diffusion.
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Because we know that in a mixed humidclimate (most of NC) building materials and
walls often get wet, it is essential that they be
able to dry in both directions, usually by vapor
diffusion. Thus, except in very cold climates,the only place in a house where there should
be a vapor barrier is
under the slab
or on the crawl space floor.
Copyright Energy Wise Solutions, Inc. 105
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Moisture Damage is caused by: Wet conditions (100% Rh) for a short time
Very high humidity (80%+) over a long time
Time Duration for damage depends on: The material affected
Temperature
The higher the temperature the more
accelerated the process
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Moisture Damage
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Three basic rules for deterring
moisture damage in absorbent
building materials: Keep the material dry!
Don¶t let the material get wet!!
Keep water away from the
material!!!
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Moisture Damage
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Moisture is transported four ways ± listed in
the order of wetting: Bulk Water Flow (liquid)
Capillarity (liquid) Air Transported (liquid or vapor)
Vapor Diffusion (vapor)
In terms of the HEALTH & DURABILITY of a
house, moisture control is of the greatestimportance.
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Moisture Flow - SUMMARY
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Everything we do in Green Building and
Remodeling should be based upon sound
Building Science principles. Without under-
standing these principles and how the house
works as a system we will not achieve the goal
of providing homes, schools and workplaces that
are Safe, Healthy, Comfortable, Durable, Energy
Efficient and Environmentally Friendly.
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