2 energy 101 1hr heat flow and control · heat transmission • include heat flow through the...
TRANSCRIPT
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Robert FehrEmeritus Professor
Biosystems and Agricultural Engineering Department
ENERGY 101Heat Flow and Control
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What you will learn:• How insulation uses basic principles to impact
heat flow.• Where are the most import areas for
consideration in reducing heat flow.• Methods for considering the economic
impact of reduced heat flow.
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Maintaining Heating ComfortHEAT GAINS = HEAT LOSSES
• Heat Gains– Solar Heat– Internal Heat Load– Heat added by the Heating System
• Heat Losses– Air Leakage & Ventilation– Heat Transmission through the Building Shell
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Maintaining Cooling ComfortHEAT GAINS = HEAT LOSSES
• Heat Gains– Solar Heat– Air Leakage & Ventilation– Internal Heat Load– Heat Transmission through the Building Shell
• Heat Losses– Heat Removed by the Cooling System
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Maintaining Comfort• Solar Heat– Windows (Fenestration) Lower with current windows
• Air Leakage & Ventilation– Infiltration– Minimum ventilation required by code
• Internal Heat Load– Occupants, Lights, Equipment• Going down with more efficient lights, refrigerators, etc.
• Heat Transmission through the Building Shell– Insulation
• Heat Removed or Added by the HVAC System
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Occupied Vs Unoccupied House
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Pressure vs Flow
Flow requires a pressure and a pathPressure defines the difference between to points• Heat – temperature• Air – air pressure• Water vapor – concentration of water vapor
molecules
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Pressure vs Flow
Path connecting two regions may be a:• Conductor – allows rapid movement• Resistor – slows movement• Barrier – stops movement
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Pressure vs Flow
• Flow always goes from high-pressure region to a low-pressure region
• If pressure continues flow continues• If pressure equalizes flow stops• If there is pressure but no path there is no flow
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Calculating Energy Loss
FLOW RATE related toPATH, RESISTANCE and PRESSURE
AMOUNT related to FLOW RATE and TIME
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FLOW RATE = PATH * RESISTANCE * PRESSURE
q = U * A * ∆T or q = A/R * ∆T
• FLOW RATE = q (BTU/hr)
• PATH– A = Area or size of the path (FT2 )
• RESISTANCE– U = Conductance (BTU / HR ● FT2 ● °F)
– R = Resistance (HR ● FT2 ● °F / BTU)
• PRESSURE– ∆T = Temperature Difference (°F)
Calculating Energy Loss11
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Building Shell
Thermal boundary• Insulation• Air barrier– Can be on either side of the insulation
Alignment of the air barrier and insulation critical unless the insulation is an air barrier.
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Thermal Boundary (Envelope)
Layer of a building enclosure that controls energy (heat) flow from conditioned to unconditioned spaced.
Defining its location is critical to controlling heat flow.
In some cases it is not an insulated layer, such as a basement floor.
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First Floor
Second Floor
BasementCrawl Space
Attic Attic
Attic
Defining the Thermal Boundary
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First Floor
Second Floor
BasementCrawl Space
Attic Attic
Attic
Defining the Thermal Boundary
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Walk-Up Attics
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Where Is the Thermal Boundary? Where Should It Be?
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Walk-Up AtticsIf the client does not use the attic often:
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• An insulated, airtight cover can be installed on top of stairwell
• The pressure and thermal boundaries are aligned at the level of the attic floor
• This approach brings the stairwell into the conditioned space
• It is also cheaper and faster than the alternative
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Walk-Up AtticsIf the client uses the attic fairly often:
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• The pressure and thermal boundaries must be established at the stairs, stairwell walls, and door tothe attic stairs
• This approach leaves the stairwell open to the attic and outside the conditioned space
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Walk-Up AtticsIf the client uses the attic and there is an HVAC system in the attic:
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• Insulate roof deck
• Make attic conditioned space
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Staircase Walls – Where is the Envelope
Carefully consider how to define the thermal envelope with an unconditioned basement or attic in the area surrounding the stairs
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Basements – Unconditioned?
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Heat Flow Equation - Conduction
q = A * DT or q = U*A* DTR
– where• q = heat flow, Btu/hr• A = area, ft2
• R = resistance, ft2-hr-°F/Btu• U = conductance, Btu/ ft2-hr-°F• DT = temperature differential, °F
Higher temperature – Lower temperature
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Simple Heat Flow, q, Calculation
Assume 10x10 wall A = 100 ft2
Cavity Insulation R value = 13DT = 1 degree
q = 100 * 1 = 7.69 Btuh13
What is missing?
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Simple Heat Flow, q, Calculation
What about the wood framing?
2x4 R-value = 4.38 (1.25 per inch)
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Simple Heat Flow, q, CalculationMinimum Wood Framing
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Approximately 10 2x4s, 10 ft long = 12.5 ft212.5% Framing
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Simple Heat Flow, q, Calculation w/Framing
Total Area = 100 ft2 10x10 wall
Framing R = 4.38
Framing Area = 12.5 ft2 (12.5%)
Cavity Insulation R-value = 13
Cavity Insulation Area = 100 – 12.5 = 87.5 ft2 (87.5%)
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qinsulation = 87.5 * 1 = 6.73 Btuh13
qframing = 12.5 * 1 = 2.85 Btuh4.38
insulation framingqtotal = 6.73 + 2.85 = 9.58 Btuh
70% 30% Heat loss87.5% 12.5% Area
Total Wall R = 10.44
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Simple Heat Flow, q, Calculation w/Framing
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Simple Heat Flow, q, Calculation
What if there is a window in the wall?
Window:Size 3 ft x 5 ft = 15 ft2
U-factor = 0.40
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Framing + Window28
Window:Size 3 ft x 5 ft = 15 ft2
U-factor = 0.40
What if there is a window in the wall?
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Simple Heat Flow, q, CalculationWith Framing + Window
Windows Require Extra Framing Materials
4 extra studs for kings and jacks2x12 36 inch long for the header
Approximately 7.8 ft2 of extra framing
Total framing = 12.5 + 7.8 = 20.3 ft2
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Simple Heat Flow, q, CalculationWith Framing + Window
Total Area = 100 ft2 10x10 wallFraming R-value = 4.38Framing Area = 20.3 ft2
Window U-factor = 0.40Window Area = 15 ft2
Cavity Insulation R-value = 13Cavity Insulation Area = 100 – 20.3 - 15 = 64.7 ft2
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Simple Heat Flow, q, CalculationWith Framing + Window
qinsulation = 64.7 * 1 = 4.98 Btuh13
qframing = 20.3 * 1 = 4.63 Btuh4.38
qwindow = 0.40 *15 * 1 = 6 Btuhinsulation framing window
qtotal = 4.98 + 4.63 + 6 = 15.61 Btuh32% 30% 38% Heat Loss64.7% 20.3% 15% Area
Total Wall R = 6.41
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R-Value Comparison
Cavity Insulation OnlyR = 13
Cavity Insulation + FramingTotal Wall R = 10.44
Cavity Insulation + Framing + WindowTotal Wall R = 6.41
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Building-Shell Heat Flow
• Transmission and Air Leakage Pathways– Floors or foundations– Walls– Ceilings and roofs– Windows
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Points of Weakness - Seams
• Porches• Roof overhangs• Shafts containing chimneys and pipes• Protruding walls• Protruding or indented windows or doors• Crawl spaces or basements
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Points of Weakness - Cavities
• Wall cavities partially void of insulation• Suspended ceilings• Attic and roof cavities• Concentrations of plumbing– Bathroom– Kitchen
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Points of Weakness - Cavities
• Concentrations of electrical wiring• Building cavities used as ducts• Interconnecting spaces between floor, wall,
and ceiling cavities
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Conductivity of Building Materials• Thermal Bridging– When a small area with a high thermal
conductivity • Wood framing• Window frame
• Thermal Breaks– Small thickness of a low thermal conductivity
separating materials with a high thermal conductivity
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Air Leakage
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.
Neutral Pressure Plane
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Air Leakage
• Difficult to estimate• Directly through shell• Indirectly through a series of opening in the
envelop• Require a continuous air barrier
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Fenestration - Windows• U-factor– New 0.35 ~ R-2.9– Old 0.90 ~ R-1.1– Still 4 times more conductive loss that a wall
• Solar heat gain coefficient– New 0.4 or better, lowered to reduce cooling load
New windows designed to meet U-factor for northern climates and SHGC for southern climates
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Fenestration - Windows
• Comfort Factors– Radiant load– Convection Currents
• Window Curtains – Significantly reduce radiant load on occupants– Little impact on convection current• Sealed on top or bottom – which is better?
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Conduction + Convection + Radiation
Night
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Conduction + Convection + Radiation
Day
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Reducing Conduction, Convection & Radiation in Windows
Day
Vacuum
Argon – Gas Heavier than Air
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Day Vacuum
Argon – Gas Heavier than Air
Reflective SurfaceSolar
HeatGain
Coefficient
Reducing Conduction, Convection & Radiation in Windows
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Day Vacuum
Argon – Gas Heavier than Air
Thermal Break
Thermal Break
Reflective SurfaceSolar
HeatGain
Coefficient
Reducing Conduction, Convection & Radiation in Windows
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Cool Vacuum
Argon – Gas Heavier than AirLow-e Coating
Thermal Break
Thermal Break
Reflective SurfaceSolar
HeatGain
Coefficient
Warm
Reducing Conduction, Convection & Radiation in Windows
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Building Diagnostics ProceduresLocating major flaws in the envelop• Blower-door testing – Pressure-testing the air barrier
• Infrared scanning– Viewing heat flows
• Duct-blower testing– Air leakage when HVAC system is running
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NEW KY-HP 1960
Heating Design Load
40
35
30
25
20
15
10
5
0
KB
tuh
Internal Gains = 0
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Heating Annual Load
NEW KY-HP 1960
MM
Btu
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NEW KY-HP 1960
Cooling Design Load15,000
10,000
5,000
0
Btu
h
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Cooling Annual Load
NEW KY-HP 1960
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Calculating Building Heat Flows• Heating Load– BTU/hr required to maintain the building
temperature at the heating design outdoor temperature based on local climate
• Heat Loss– BTU loss through the building shell monthly or
annually– Measure of energy output from the heating
equipment
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Calculating Building Heat Flows
• Cooling Load– BTU/hr required to maintain the building
temperature at the cooling design outdoor temperature based on local climate
– Less predictable then heating load– Include power required to remove moisture
(latent heat)
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Heat Transmission
• Include heat flow through the building shell by– Conduction– Convection– Radiation
• Air leakage and ventilation air are a separate calculation– For every cubic foot of air that enters, one leaves
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Design Air Temperature
• Temperature Difference Between Inside and Outside Air–Outside air = Design temperature• equal or exceeded 97.5% of the time
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Design Air Temperature57
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Calculating Heating LoadWall U-factor and R-value Calculations
Total Wall R = 12.0
Wall Component R (A1) Framing R (A2) Insulation1. Outside Air 0.17 0.17
2. Lapped Wood Siding 0.81 0.81
3. OSB Sheathing 0.62 0.62
4. Framing or Insulation *4.38 13.0
5. Gypsum Wall Board 0.45 0.45
6. Inside Air Film 0.68 0.68
Total R 7.11 15.7
U-factor 0.141 0.0637
Percentage of total wall area 0.25 0.75
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Calculating Cooling Load
• Cooling load temperature difference• Solar Gain, Glass load factors– Shale line factor
• Air exchange– Sensible load– Latent load
• Internal gains
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Thermal Lag60
https://www.omniblock.com/omni-advantage-thermal-performance-concepts/
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Thermal Lag61
http://tri-stateicf.com/home-owner/why-use-icf/
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Types of Heat Flow• Conduction– occurs as hot, rapidly moving or vibrating atoms and
molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles
• Convection– transfer of heat from one place to another by the movement
of a fluid over a solid surface• Radiation– the transfer of heat energy through empty space by means of
electromagnetic waves
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Types of Heat Transfer
• Conduction– occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring
atoms and molecules, transferring some of their energy (heat) to these neighboring particles
• Convection– transfer of heat from one place to another by the movement of a fluid over a solid surface
• Radiation– the transfer of heat energy through empty space by means of electromagnetic waves
• Mass transfer– the physical transfer of a hot or cold object from one place to
another
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Insulation
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Heat TransmissionInsulated Wall
conduction dominate
Uninsulated Wall
radiation and convection dominate
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2 types:• Batt – R-11, 3.14/inch– R-13, 3.71/inch– R-15, 4.29/inch
• Blown-in– R-2.2 to 2.7/inch– Dense pack
• 2x4 wall R-15
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Fiberglass
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Insulating Walls
Warm Cool
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Insulating Walls - Voids
Warm Cool
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Insulating Walls - Gaps
Warm Cool
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Insulating Walls – Thermal Bypass
Warm Cool
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Thermal Bypass
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Thermal Bypass
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Thermal Bypass
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Insulating Kneewalls - Problem
Warm Cool
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Knee Walls
Thermal image of a knee wallwithout an air barrier.
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Insulating Kneewalls - Solution
Warm Cool
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Insulating Attics – Loose Fill
Warm
Cool
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Convection in Fiberglass Insulation
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Insulating Floors - Problem
Air Flow
Garage
Bonus Room
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Insulating Floors - Solution
Garage
Bonus Room
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Diminishing Returns
Design heat loss for a 1000 ft2 attic with ∆T = 60
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Fiberglass
• Made from glass– 30% recycled content
• Not an air barrier– Must be protected from air movement
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Blowing fiberglass behind an air permeable wall covering avoids problems with gaps created when batts are improperly installed.
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Fiberglass
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Fiberglass
Blowing fiberglass with a binding agent to avoid problems with gaps created when batts are improperly installed.
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• Thickness is not a good measure of installed R-Value
• Manufactures specify surface area one bag can cover to get a desired R-Value.
85
Fiberglass
• Using extra pressure creates a thicker level but adversely impacts R-Value at low attic temperatures.
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Blown Insulation Values on Bag86
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Fiberglass Under Floors
What is the thickness?
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Insulation Grades – Grade III88
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Insulation Grades – Grade II90
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Insulation Grades – Grade II
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Insulation Grades – Grade I92
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Standard foil-faced and kraft-faced batts do not conform to the requirements of any modelcode for exposed applications.Their facings have FlameSpread Indices greater than 25.
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Flame Spread Index and Smoke Developed Index
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Loose Fill Insulation Installation94
2009 IECC requires a ruler for every 300 ft2 of attic area, however, depth is a poor measure of insulation R-value because it can be fluffed.
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Dense Pack Insulation
• Fiberglass and Cellulose– Blown into confined space (insulating existing walls)– Provides some reduction in air infiltration– Increased R values
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Rock (Mineral) Wool
• 70% recycled content• 2x4 Wall R-13, 2x6 Wall R-23• Blown R-3.1-4.0/inch• Moisture resistant• Fire resistant
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Cellulose
• Made from paper– Up to 85% recycled materials content– Can absorb moisture– Treated with fire retardants
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Cellulose98
In Wall Cavities• Water binder• Allow to dry
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Cellulose – R-value99
• R 3.2/inch loose• R 3.8/inch high density
• 3.5 lbs/ft2
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Cellulose – Dense Pack100
High density blown R-3.7/inch , density – 3.5 pounds / ft2 or higher
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Expanded polystyrene101
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Extruded Polystyrene102
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Polyisocyanurate 103
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Closed-cell Foam104
Closed-cell Foam• R - 6.5 per inch, use aged value• Limited Expansion 8 to 1• Some Rigidity
Water Vapor Permeability (perms)1.51@1“0.76@2“0.50@3"0.38@4"0.30@5"0.25@6”
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Open-cell Foam105
Open-cell Foam• R – 3.7 per inch• Vapor Retarder over 2 inches• High Expansion 100 to 1• No Rigidity
Water Vapor Permeability (perms)[email protected]”[email protected]″
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Open-cell Foam - Roof106
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Foam Insulation Questions• Closed vs Open on Roof Surface– Vapor Barrier, Condensation on roof surface– Water Barrier, Finding a leak in a roof
• Fire codes when exposed– Flame spread– Smoke development– Exception: Attics and crawlspaces where entry is
only for service of utilities (not used for storage or living space)
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•Magnesium oxide board• Fire rated•Closed cell foam core
•Rigid closed cell foam board•Covered with drywall
•Sprayed closed cell foam•Covered with drywall
Basement Wall Insulation108
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Insulating Existing Walls
• Blown insulation– Cellulose– Fiberglass
• Poured foam– Expands SLOWLY– Expands in direction of least resistance
• Open-cell 60 to 1• Closed-cell 8 to 1
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Insulating Existing Walls
Caution:
Uninsulated walls may work because they are warm inside and have some air flow. Both reduce moisture levels and dry the wall. Sealing them with insulation may result in moisture problems.
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Conditioned Sealed Crawl Space111
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Attics
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Blown Insulation - Soffit Baffle113
Soffit Baffle/Insulation Dam/Eave Dam/Air Chute/Wind Baffles/Rafter Chutes
• Provides air path for ventilation
• Prevents insulation from blocking soffit vents
• Prevents insulation from blocking air flow
• Can be difficult to install in an existing attic
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Vented Versus Unvented Attics• When to consider– HVAC and duct system in attic• Duct leakage to outside ~ zero
– Attic floored and used for storage– Installing a high efficiency gas furnace• Management of condensation in climates below 32 °F
• Caution if any naturally/atmospherically vented gas appliances are located there
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Example for Climate Zone 4
Unvented Attic Assemblies withAir-permeable Insulation
R-above = 15
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Graphics based on: http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11400
Insulate hatches. Note insulation dams.
Scuttle Hole Cover Pull-Down Attic Stairs
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Attic Access
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Future Direction of Energy Codes Climate Zone 4117
2009 2012 2015 2018Attic - R 38 49 49 49
Above Grade Walls -R 13 20 or 13+5 20 or 13+5 20 or 13+5
Basement Walls - R 10/13 10/13 10/13 10/13
Windows - U 0.35 0.35 0.35 0.32
Air Leakage Rates – ACH 50 7 or less 3 or less 3 or less 3 or less
Mechanical Ventilation Required Required Required
Duct Leakage* – cfm/100ft2 12 or less (total) 4 or less (total) 4 or less (total) 4 or less (total)
Return Ducts Can use building
cavity
All ducted All ducted All ducted
Energy Rating Index Option Allowed (54 or less) Allowed (62 or less)
* Duct leakage requirements are for all ducts regardless of location. Only ducts in unconditioned spaces must be tested.
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Key to Quality Energy Efficient Houses
Planning
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Whole-house Energy Efficiency Plan
View a house as an energy system with interdependent parts, rather than separate systems
House
Thermal Insulation
System
Structural System
Moisture Control System
HVACAir Leakage
Control System
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