Reflective Products: An Energy-Savings Reflective Products: An Energy-Savings Solution for Post-Frame BuildingsSolution for Post-Frame Buildings

David W. Yarbrough, PhD, PEDavid W. Yarbrough, PhD, PE

R&D Services, Inc.R&D Services, Inc.

Cookeville, TNCookeville, TN

Sponsored by The Reflective InsulationSponsored by The Reflective Insulation

Manufacturers Association InternationalManufacturers Association International

Components of this PresentationComponents of this Presentation

Physical Basis: Design of InsulationsPhysical Basis: Design of Insulations Expected PerformanceExpected Performance

Installation - Reflective AssembliesInstallation - Reflective Assemblies

Savings – Reduce Heating/CoolingSavings – Reduce Heating/Cooling

Hybrid SystemsHybrid Systems

A Time LineA Time Line

1650-1850 The physics is established1650-1850 The physics is established 1850-1920 Air space resistance recognized1850-1920 Air space resistance recognized 1920-1950 Reflective systems appear1920-1950 Reflective systems appear 1950-1985 Reflective data base is developed1950-1985 Reflective data base is developed 1985-20001985-2000 Product development Product development 2000- Advanced systems2000- Advanced systems

ProductProduct Categories Categories

Reflective InsulationsReflective Insulationsenclosed air space (0-10 in.)enclosed air space (0-10 in.)R-valueR-valueASTM C 1224, ASTM C 1363ASTM C 1224, ASTM C 1363

Radiant BarriersRadiant Barriers large (ventilated) air space (2-20 ft)large (ventilated) air space (2-20 ft) reduction in heat flowreduction in heat flow ASTM C 1313, ASTM C 1340ASTM C 1313, ASTM C 1340 Interior Radiation Control CoatingsInterior Radiation Control Coatings Increases air film resistance (at surface)Increases air film resistance (at surface) ASTM C 1321ASTM C 1321

A property in common to all of these products: low thermal A property in common to all of these products: low thermal emittance (low emissivity)emittance (low emissivity)

Reflective Insulations and Radiant Reflective Insulations and Radiant Barriers have Low-Emittance SurfacesBarriers have Low-Emittance Surfaces

Reflective InsulationsReflective Insulations

Enclosed air spaceEnclosed air space

Small air gap ( 0-6 in. )Small air gap ( 0-6 in. )

Thermal Resistance ( up to 14 )Thermal Resistance ( up to 14 )

Radiant Barriers (attic)Radiant Barriers (attic)

Open air space (or ventilated Open air space (or ventilated space)space)

Large air gap ( up to 10-15 ft. )Large air gap ( up to 10-15 ft. )

Thermal ResistanceThermal Resistance

Large Scale Test FacilityLarge Scale Test Facility12 by 12 ft. specimen12 by 12 ft. specimen

8 by 8 ft. metering area8 by 8 ft. metering area

Design of InsulationsDesign of Insulations

Insulations Based on AirInsulations Based on Air

Mechanism Mechanism Mass-TypeMass-Type Reflective-TypeReflective-TypeConduction Increases Increases-slightConduction Increases Increases-slight

Convection None DecreasesConvection None Decreases (some exceptions)(some exceptions)

Radiation Decreases Almost ZeroRadiation Decreases Almost Zero

Increase in conduction because solids like glass, wood, Increase in conduction because solids like glass, wood,

concrete, or paper have much higher thermal conductivityconcrete, or paper have much higher thermal conductivity

than air. Air is an excellent thermal insulation.than air. Air is an excellent thermal insulation.

Thermal Conductivity of AirThermal Conductivity of Air

T (°F)T (°F) k (Btuk (Btu∙∙in./ftin./ft22∙∙hh∙∙°F) °F) R/inchR/inch

00 0.1550.155 6.456.45

7575 0.1780.178 5.625.62

100100 0.2010.201 4.784.78

No Convection and No RadiationNo Convection and No Radiation

Thermal Emittance (Thermal Emittance (εε) – A Property) – A Property

A fraction 0 < A fraction 0 < εε < 1 that is measured. < 1 that is measured. εε = 0 no radiation = 0 no radiation εε = 1 maximum radiation (black body) = 1 maximum radiation (black body)

^̂ ↓ ↓(radiation in, Q(radiation in, Qradrad) |) | ↓ ↓ (radiation reflected, r)(radiation reflected, r)______________________________________//______________________________|_ →→(radiation absorbed, a) |_|_ →→(radiation absorbed, a) |_|__________________________________|_|__________________________________|_ ↓ ↓ ↓ ↓(radiation transmitted, t)(radiation transmitted, t)

Radiation TerminolgyRadiation Terminolgy

QQrad rad = Reflected + Absorbed + Transmitted= Reflected + Absorbed + Transmitted If opaque ,then transmitted is zero (t=0)If opaque ,then transmitted is zero (t=0) Expressed as fractionsExpressed as fractions

1 = r + a but 1 = r + a but a = ea = e so we have so we have

1 = r + e1 = r + e

If e is small, then r is largeIf e is small, then r is large

e= 0.03, r= 0.97 systems perform in both directionse= 0.03, r= 0.97 systems perform in both directions

Total Hemispherical Emittance Total Hemispherical Emittance (all directions)(all directions)

PaintsPaints 0.8 < e < 1.00.8 < e < 1.0

WoodWood 0.8 < e < 0.90.8 < e < 0.9

MasonryMasonry 0.9 < e < 1.00.9 < e < 1.0

MetalsMetals 0.02 < e < 0.100.02 < e < 0.10

IRCCIRCC 0.15 < e < 0.250.15 < e < 0.25

aluminum foil aluminum foil 0.03<e<0.040.03<e<0.04

Al metallized film Al metallized film 0.04<e<0.060.04<e<0.06

What to choose ? What to choose ? ε→ε→00

At 75 °F (room temperature)At 75 °F (room temperature)

AluminumAluminum 0.030.03

Polished brassPolished brass 0.030.03

CadmiumCadmium 0.020.02

Polished copperPolished copper 0.030.03

GoldGold 0.02-0.030.02-0.03

NickelNickel 0.040.04

PlatinumPlatinum 0.030.03

TinTin 0.050.05

ZincZinc 0.050.05

American Institute of Physics (early edition)American Institute of Physics (early edition)

Why Emittance is Key PropertyWhy Emittance is Key Property(Boltzmann Equation)(Boltzmann Equation)

Q/A = E * [ Q/A = E * [ σσ * (T * (T4422

– T– T4411)])]

↑ ↑

1/E=1/e1/E=1/e1 1 + 1/e+ 1/e2 2 – 1– 1

ee1 1 ee2 2 E % reductionE % reduction

no foil/film no foil/film 1 1 1 1 1 1 00Foil one side Foil one side 1 0.03 0.03 1 0.03 0.03 9797Foil one side Foil one side 0.03 1 0.03 0.03 1 0.03 9797Foil both sides Foil both sides 0.03 0.03 0.015 0.03 0.03 0.015 98.598.5

Boltzmann 1844-1906 AustriaBoltzmann 1844-1906 AustriaStefan published in 1879 Boltzmann published in 1884Stefan published in 1879 Boltzmann published in 1884Stefan-Boltzmann Law and Stefan-Boltzmann ConstantStefan-Boltzmann Law and Stefan-Boltzmann Constant

5.6704 x 105.6704 x 10-8 -8 W/m W/m22·K·K44

Transfer Mechanisms

0102030405060708090

100

0 0.2 0.4 0.6 0.8 1

Effective Emittance (E)

% o

f T

OT

AL RADIATION

CONVECTION

CONDUCTION

Insulation Assembly DesignInsulation Assembly Design Identify the space to be insulated.Identify the space to be insulated. ChoicesChoices Attach RI to one side or the otherAttach RI to one side or the other to create a single reflective air to create a single reflective air

space. space.

Attach RI in center to form twoAttach RI in center to form two reflective air spaces.reflective air spaces.

Install RI that forms more than twoInstall RI that forms more than two reflective air spaces.reflective air spaces.

Heat Flow Down

4

6

8

10

12

14

16

0 0.05 0.1 0.15 0.2

Emittance

R

1D

2D

Horizontal Heat Flow

4

4.5

5

5.5

6

6.5

7

0 0.05 0.1 0.15 0.2

Emittance

R

1D

2D

Heat Flow Up

33.2

3.43.63.8

44.24.4

4.64.8

0 0.05 0.1 0.15 0.2

Emittance

R 1D

Quick Estimate of SavingsQuick Estimate of Savings Use HDD/CDD dataUse HDD/CDD data CLIMATOGRAPHY OF THE UNITED STATES No. 81 CLIMATOGRAPHY OF THE UNITED STATES No. 81

SUPPLEMENT NO. 2SUPPLEMENT NO. 2 Title: “Annual Degree Days to Selected Bases”Title: “Annual Degree Days to Selected Bases” Heating: 40 to 65 °F Cooling: 45 to 70 °FHeating: 40 to 65 °F Cooling: 45 to 70 °F Louisville HDDLouisville HDD65 65 4352 CDD 4352 CDD70 70 797797 Heat flow out Heat flow out HDD*24*Area/RHDD*24*Area/R Utility Use Utility Use HDD*24*Area/(R*E)HDD*24*Area/(R*E) Heat flow in Heat flow in CDD*24*Area/RCDD*24*Area/R Utility Use Utility Use CDD*24*Area/(R*COP)CDD*24*Area/(R*COP) Convert from BTU/yr to KWH/yr multiply by 0.000293Convert from BTU/yr to KWH/yr multiply by 0.000293 Kwh at 0.1 as exampleKwh at 0.1 as example

Calculation of SavingsCalculation of SavingsLouisville – 1000 square feetLouisville – 1000 square feet

Savings for 1000 square feet

0

500

1000

1500

2000

0 5 10 15 20

Added R (Base R 2)

Sav

ing

s ($

/yr)

Cooling

Heating

Total

Hybrid SystemsHybrid Systems

Combine TechnologiesCombine Technologies

Examples: fiberglass + foamExamples: fiberglass + foam

fiberglass + reflectivefiberglass + reflective

foam + reflectivefoam + reflective

Utilize air spaces to increase R-valueUtilize air spaces to increase R-value

Wall Cavity R vs. R* of Foam

5

7.5

10

12.5

15

17.5

20

3 4 5 6 7

R-per-inch of Foam

Wal

l Cav

ity R

0.5 in.

1.0 in.

1.5 in.

2.0 in.

SummarySummary

Reflective technology is a mature areaReflective technology is a mature area Products: Insulation, radiant barriers, IRCCsProducts: Insulation, radiant barriers, IRCCs Evaluation: laboratory measurementsEvaluation: laboratory measurements

and/or engineering calculationsand/or engineering calculations Quick estimates of savings are possibleQuick estimates of savings are possible Combine technologies: HybridsCombine technologies: Hybrids