Robert FehrEmeritus Professor

Biosystems and Agricultural Engineering Department

ENERGY 101Heat Flow and Control

1

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.

2

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

3

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

4

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

5

Occupied Vs Unoccupied House

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

7

Pressure vs Flow

Path connecting two regions may be a:• Conductor – allows rapid movement• Resistor – slows movement• Barrier – stops movement

8

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

9

Calculating Energy Loss

FLOW RATE related toPATH, RESISTANCE and PRESSURE

AMOUNT related to FLOW RATE and TIME

10

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

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.

12

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.

First Floor

Second Floor

BasementCrawl Space

Attic Attic

Attic

Defining the Thermal Boundary

First Floor

Second Floor

BasementCrawl Space

Attic Attic

Attic

Defining the Thermal Boundary

Walk-Up Attics

16

Where Is the Thermal Boundary? Where Should It Be?

Walk-Up AtticsIf the client does not use the attic often:

17

• 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

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

Walk-Up AtticsIf the client uses the attic and there is an HVAC system in the attic:

19

• Insulate roof deck

• Make attic conditioned space

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

20

Basements – Unconditioned?

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

21

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?

22

Simple Heat Flow, q, Calculation

What about the wood framing?

2x4 R-value = 4.38 (1.25 per inch)

23

Simple Heat Flow, q, CalculationMinimum Wood Framing

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Approximately 10 2x4s, 10 ft long = 12.5 ft212.5% Framing

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%)

25

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

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

27

Framing + Window28

Window:Size 3 ft x 5 ft = 15 ft2

U-factor = 0.40

What if there is a window in the wall?

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

29

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

30

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

Conduction + Convection + Radiation

Day

Reducing Conduction, Convection & Radiation in Windows

Day

Vacuum

Argon – Gas Heavier than Air

Day Vacuum

Argon – Gas Heavier than Air

Reflective SurfaceSolar

HeatGain

Coefficient

Reducing Conduction, Convection & Radiation in Windows

Day Vacuum

Argon – Gas Heavier than Air

Thermal Break

Thermal Break

Reflective SurfaceSolar

HeatGain

Coefficient

Reducing Conduction, Convection & Radiation in Windows

Cool Vacuum

Argon – Gas Heavier than AirLow-e Coating

Thermal Break

Thermal Break

Reflective SurfaceSolar

HeatGain

Coefficient

Warm

Reducing Conduction, Convection & Radiation in Windows

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

48

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

50

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

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

59

Thermal Lag60

https://www.omniblock.com/omni-advantage-thermal-performance-concepts/

Thermal Lag61

http://tri-stateicf.com/home-owner/why-use-icf/

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

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

Insulation

Heat TransmissionInsulated Wall

conduction dominate

Uninsulated Wall

radiation and convection dominate

65

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

66

Fiberglass

Insulating Walls

Warm Cool

Insulating Walls - Voids

Warm Cool

Insulating Walls - Gaps

Warm Cool

Insulating Walls – Thermal Bypass

Warm Cool

Thermal Bypass

Thermal Bypass

Thermal Bypass

Insulating Kneewalls - Problem

Warm Cool

75

Knee Walls

Thermal image of a knee wallwithout an air barrier.

Insulating Kneewalls - Solution

Warm Cool

Insulating Attics – Loose Fill

Warm

Cool

Convection in Fiberglass Insulation

Insulating Floors - Problem

Air Flow

Garage

Bonus Room

Insulating Floors - Solution

Garage

Bonus Room

Diminishing Returns

Design heat loss for a 1000 ft2 attic with ∆T = 60

Fiberglass

• Made from glass– 30% recycled content

• Not an air barrier– Must be protected from air movement

Blowing fiberglass behind an air permeable wall covering avoids problems with gaps created when batts are improperly installed.

83

Fiberglass

Fiberglass

Blowing fiberglass with a binding agent to avoid problems with gaps created when batts are improperly installed.

84

• 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.

Blown Insulation Values on Bag86

Fiberglass Under Floors

What is the thickness?

87

Insulation Grades – Grade III88

89

Insulation Grades – Grade II90

91

Insulation Grades – Grade II

Insulation Grades – Grade I92

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.

93

Flame Spread Index and Smoke Developed Index

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.

Dense Pack Insulation

• Fiberglass and Cellulose– Blown into confined space (insulating existing walls)– Provides some reduction in air infiltration– Increased R values

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

96

Cellulose

• Made from paper– Up to 85% recycled materials content– Can absorb moisture– Treated with fire retardants

Cellulose98

In Wall Cavities• Water binder• Allow to dry

Cellulose – R-value99

• R 3.2/inch loose• R 3.8/inch high density

• 3.5 lbs/ft2

Cellulose – Dense Pack100

High density blown R-3.7/inch , density – 3.5 pounds / ft2 or higher

Expanded polystyrene101

Extruded Polystyrene102

Polyisocyanurate 103

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”

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)9.2@3.5”6.1@5.5″

Open-cell Foam - Roof106

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)

107

•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

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

109

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.

110

Conditioned Sealed Crawl Space111

Attics

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

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

Example for Climate Zone 4

Unvented Attic Assemblies withAir-permeable Insulation

R-above = 15

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

116

Attic Access

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.

Key to Quality Energy Efficient Houses

Planning

118

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

Questions120