rrrr----value misconceptionsvalue misconceptions...u. s. d epartmentof energy configuration of the...

1

RRRRRRRR--------Value MisconceptionsValue MisconceptionsValue MisconceptionsValue MisconceptionsValue MisconceptionsValue MisconceptionsValue MisconceptionsValue Misconceptions

How The Same Wall Can Have How The Same Wall Can Have How The Same Wall Can Have How The Same Wall Can Have How The Same Wall Can Have How The Same Wall Can Have How The Same Wall Can Have How The Same Wall Can Have Several Different RSeveral Different RSeveral Different RSeveral Different RSeveral Different RSeveral Different RSeveral Different RSeveral Different R--------VALUES ???VALUES ???VALUES ???VALUES ???VALUES ???VALUES ???VALUES ???VALUES ???

Jan Kośny, Ph.D.Jan Kośny, Ph.D.

Better Building Better Building

by Design Conferenceby Design Conference

Burlington, VTBurlington, VT

February 14th , 2008February 14th , 2008

OAK RIDGE NATIONAL LABORATORY

U. S. DEPARTMENT OF ENERGY

RELEVANCE OF HVAC LOADS GENERATED RELEVANCE OF HVAC LOADS GENERATED RELEVANCE OF HVAC LOADS GENERATED RELEVANCE OF HVAC LOADS GENERATED BY RESIDENTIAL WALLSBY RESIDENTIAL WALLSBY RESIDENTIAL WALLSBY RESIDENTIAL WALLS

Load Distribution in Residential Buildings in Trilion BTU's/year

by J.Huang 1999, 2002, Infiltration Distribution by Dickerhoff 1982

-1000

-500

0

500

1000

1500

2000

solar equip people floor Infiltration Roof Walls Windows

infiltration as separate bar infiltration distributed

Floor

32%

Roof

18%

Walls

35%

Window s

15%

Infiltration

8% more than windows

39% more than roof

30% more than floors

Heating and Cooling Loads Associated with Wall Area

Are Highest Among all Building Envelope Systems

2



Above-Grade Walls

WALL TECHNOLOGIES; WALL TECHNOLOGIES; WALL TECHNOLOGIES; WALL TECHNOLOGIES; Typical Residential ApplicationsTypical Residential ApplicationsTypical Residential ApplicationsTypical Residential Applications



Above-Grade Walls


Foundation Wall Technologies

3



Above-Grade Walls


Foundation Wall Technologies

Attic Vertical Diaphragms



WALL TECHNOLOGIES; WALL TECHNOLOGIES; WALL TECHNOLOGIES; WALL TECHNOLOGIES; Numerous Architectural ComponentsNumerous Architectural ComponentsNumerous Architectural ComponentsNumerous Architectural Components

Clear Wall

4



WALL TECHNOLOGIES; WALL TECHNOLOGIES; WALL TECHNOLOGIES; WALL TECHNOLOGIES; Numerous Architectural ComponentsNumerous Architectural ComponentsNumerous Architectural ComponentsNumerous Architectural Components

Wall/Roof Intersection

Wall/Door Intersections

Wall/Window

Intersections

Corner Intersections

Wall/Foundation Wall Intersection

Wall/Slab Intersection

Clear Wall



POTENTIAL FOR POSITIVE CHANGES; POTENTIAL FOR POSITIVE CHANGES; POTENTIAL FOR POSITIVE CHANGES; POTENTIAL FOR POSITIVE CHANGES; Wide Selection of TechnologiesWide Selection of TechnologiesWide Selection of TechnologiesWide Selection of Technologies

5



Understanding R-value Measurements



Heat-Flow Apparatus Measurements Show Material Thermal Performance

Usually Usually

presentedpresented

as Ras R--per in.per in.

ASTM C518

6



Hot Box R-value Measurements Show System Thermal Performance

Clear Wall RClear Wall R--valuevalue

ASTM C1363



Understanding Construction Reality

7



REALITY FOR US CONSTRUCTIONS;REALITY FOR US CONSTRUCTIONS;REALITY FOR US CONSTRUCTIONS;REALITY FOR US CONSTRUCTIONS;Currently built houses are larger and larger... Their Currently built houses are larger and larger... Their Currently built houses are larger and larger... Their Currently built houses are larger and larger... Their architecture is getting more complex. Amount of structural architecture is getting more complex. Amount of structural architecture is getting more complex. Amount of structural architecture is getting more complex. Amount of structural framing is increasing.framing is increasing.framing is increasing.framing is increasing.

2002 research study

performed by

Enermodal

for California

Energy Commission,

and ASHRAE

demonstrated that

Framing Factor in

currently built

California houses

is for walls - 27% !!!

average for US is

25%



Framing Factor Framing Factor Framing Factor Framing Factor –––– 27% ???27% ???27% ???27% ???

Whole building energy

MBTUs/Year

26 28 30 32 34

R-14.5 walls R-8.8 walls

1500 sqft one-story

rancher located in

Bakersfield, CA

• R-value for 2x4 wall insulated with R-13 fiberglass batts (nominal R-value of R-14.5) is in the range between R- 8.5 to 9.0.

• This is 35 – 40% reduction of Clear Wall R-value

• This is equivalent to R-value of additional 1-1/2-in. of EPS

• This means that houses built in this way would require approximately 10-12% more energy to provide heating and cooling.

• In whole-country scale it means additional and unnecessary 0.8 –1.0 quad of energy consumed by residential buildings

8



Examples of Most-Common Areas for Misinformation about R-value



Many Energy Standards Developed for Wood Framed Walls

Simplified configuration

used in

development of many

energy codes

REALITYREALITY

9



Steel Framed Walls in Many Codes

Wall configuration: Wood stud wall Steel stud wall Steel stud wall

Base 16-in. Base 16-in. ¾-in. XPS

Air temperature of the

metering box [ºF] 100.1 100.0 100.0


climate side [ºF] 50.1 50.0 50.0

Temperature difference 45.5 43.1 45.4

T(mean) [ºF] 74.3 73.6 74.1

Clear wall R-value

[h·ft2·ºF/BTU]

(measured)

9.65 5.78 9.37

Center-of-Cavity

R-value

[h·ft2·ºF/BTU]

13.95 13.95 17.95

%-difference in

R-values 30.8% 58.6% 47.8%

9.7 5.8 9.4Not thermally

equivalent



Thermal Mass R-factors for Many Concrete and Masonry Systems

10



Many So-Called Green Technologies like Earth Blocks or Straw-Bale Walls



R-value of Hand-Crafted Logs

Very often a nominal

log thickness is used

for R-value estimates

Real R-value is

about 50% lower

11



Reflective Insulations Used in Concrete Slabs

Reflective insulation has to face Reflective insulation has to face

air cavity to be effectiveair cavity to be effective



Different Definitions of R-value

12



R-value is the Mostly-Used Measure of Wall Thermal Performance Today

Problems with Definition of R-value

• Typical homeowner

• Realtor

• HVAC Engineers

• Some contractors

• Some architects

• Code officials

• ???

No framing

6% - 9% framing

11% - 14% framing 25% framing



First Finding:First Finding:First Finding:First Finding:First Finding:First Finding:First Finding:First Finding:Center-of-cavity R-values can be Significantly Higher from Measured Clear-Wall R-values

Hot-box Test Results for Wood and Steel-Framed Wall Assemblies with Studs Installed at 16-in. OC

Wall configuration: Wood stud wall Steel stud wall Steel stud wall

Base 16-in. Base 16-in. ¾-in. XPS


metering box [ºF] 100.1 100.0 100.0


climate side [ºF] 50.1 50.0 50.0

Temperature difference 45.5 43.1 45.4

T(mean) [ºF] 74.3 73.6 74.1

Clear wall R-value

[h·ft2·ºF/BTU]

(measured) 9.65 5.78 9.37

Center-of-Cavity

R-value

[h·ft2·ºF/BTU]

13.95 13.95 17.95

%-difference in

R-values 30.8% 58.6% 47.8%

13



More numbers to play around:More numbers to play around:Comparison of approximate R-values and framing factors for nominal 2x4 in. (5.1x10.2 –cm) wood stud walls.

In-Series

R-14*

Only studs included

(base case)

Studs and plates included Wall with 25% framing factor

Stud

spacing:

Framing

factor

R-value

h·ft2·ºF/BTU

Framing

factor

R-value

h·ft2·ºF/BTU

%

difference

Framing

factor

R-value

h·ft2·ºF/BTU

%

difference

16-in. 9.4% 12.7 14.1% 12.0 5.2% 25.0% 10.5 17.2%

24-in. 5.2% 13.3 11.0% 12.5 6.1% 25.0% 10.5 20.9%

* R-value calculated in the center of wall cavity (without considering of framing members) was R-14 (2.46 m2K/W)



Dilemma of Building Energy Modelers

• What is my R-value?

− Test results (availability)

− Calculated (what method)

− Required by Standard

− Nominal (center-of-cavity)

• How to distribute my amount of framing???

• How to incorporate 3-D effects into 1-D wall computer model

• How to represent proper transient characteristics

8'

8'

16"

14



MORE CONFIGURATIONS TO CONSIDER

96.0

96.0

2.0



Thermal Effects of Different Stud Distributions (24% of framing)

9.5

5.15

9.35

4.91

9.32

4.77

0

1

2

3

4

5

6

7

8

9

10

R-v

alu

e [

hft

2F

/Btu

]

All studs in center Studs equally

distributed

Horizontal

members added

wood studs steel studs

~7.5%~7.5%

15



Second Finding:Second Finding:Second Finding:Second Finding:Second Finding:Second Finding:Second Finding:Second Finding:Clear wall RClear wall RClear wall RClear wall R----value can be very misleading value can be very misleading value can be very misleading value can be very misleading for many currently built houses.for many currently built houses.for many currently built houses.for many currently built houses.



Is it what we test in the hotIs it what we test in the hotIs it what we test in the hotIs it what we test in the hot----box similar to box similar to box similar to box similar to REALREALREALREAL wall assemblies?wall assemblies?wall assemblies?wall assemblies?

?

16



NOT MUCH!!!NOT MUCH!!!NOT MUCH!!!NOT MUCH!!!

Window perimeter details

Corner detail

Wall/foundation detail

Wall/roof detail



Scale of Differences in Thermal Scale of Differences in Thermal Scale of Differences in Thermal Scale of Differences in Thermal PerformancePerformancePerformancePerformance

0

2

4

6

8

10

12

14

16

R-v

alu

e

clear wall

corner

wall/roof

wall/floor

window header

window sill

window side

door header

door side

2x6 wall assembly2x6 wall assembly

17



Evaluation of Scale of Thermal Effects Generated by Different Types of Insulation and Installation Quality

Is it possible to Is it possible to

properly insulate properly insulate

this busy this busy

thermally thermally

bridged area bridged area

with batt with batt

insulation???insulation???



Effects Generated by Differences in Types of Insulation and Installation Quality – TWO OPTIONSTWO OPTIONSTWO OPTIONSTWO OPTIONSTWO OPTIONSTWO OPTIONSTWO OPTIONSTWO OPTIONS

18



Effects Generated by Differences in Types of Insulation and Installation Quality

Possible Insulations Configurations for Possible Insulations Configurations for Possible Insulations Configurations for Possible Insulations Configurations for Possible Insulations Configurations for Possible Insulations Configurations for Possible Insulations Configurations for Possible Insulations Configurations for RRRRRRRR--------value Calculations (value Calculations (value Calculations (value Calculations (value Calculations (value Calculations (value Calculations (value Calculations (stud clusters 2-in. spacing))))))))

Wood framing

Steel framing



Third Finding:Third Finding:Third Finding:Third Finding:Third Finding:Third Finding:Third Finding:Third Finding:Wood stud walls can be almost as bad as steel framing (in areas of intense framing)

5.65

3.85

9.24

4.17

0

4.3

0

1

2

3

4

5

6

7

8

9

10

R-v

alu

e [h

ft2F/B

tu]

Empty air gaps Insulation in spacing All cavities insulated

wood studs steel studs

1. Wood-framed walls are

more sensitive than

steel structures to

imperfections in

installation of

insulation.

2. Batt insulated wood-

frame walls can locally

perform as bad as

steel-framing in areas

of busy framing

19



Understanding Architectural Details



Whole Wall Rating Procedure simplifies and Whole Wall Rating Procedure simplifies and Whole Wall Rating Procedure simplifies and Whole Wall Rating Procedure simplifies and speeds up wall thermal analysis and creates a speeds up wall thermal analysis and creates a speeds up wall thermal analysis and creates a speeds up wall thermal analysis and creates a level playing field for energy saving comparisons.level playing field for energy saving comparisons.level playing field for energy saving comparisons.level playing field for energy saving comparisons.

20



Configuration of the building can be Configuration of the building can be Configuration of the building can be Configuration of the building can be very important for Whole Wall Rvery important for Whole Wall Rvery important for Whole Wall Rvery important for Whole Wall R----valuevaluevaluevalue

Two floor plans – same floor area

Floor area z 1550 sqft.



Whole Wall RWhole Wall RWhole Wall RWhole Wall R----value can be different for value can be different for value can be different for value can be different for different buildings using the same wall different buildings using the same wall different buildings using the same wall different buildings using the same wall technologytechnologytechnologytechnology

2x4 wood-framed wall with R-11 fiberglass insulation

21



Example How Hot Box Testing Can Be Helpful in Wall System Thermal

Improvement (Log Walls)



Hot Box Test of 10-in. Coped Round-Log Wall

Test didn’t go too well because of intense air leakage and thermal bridge effects on both wall sides (only~ R-5.8)

Round log shape is not very efficient from thermal perspective

22



Hot Box Test of 10-in. Coped Round-Log Wall

When foam insulation was installed on both wall sides hot-box test showed ~R-1.0 improvement in thermal bridge effects (~ R-6.8)



Lessens Learned from Hot Box Tests of10-in. Coped Round-Log Wall

Proposed action:

Improve windows and door details, because they are very important building shell components effecting energy efficiency and durability in log houses

17%

difference

in R-value

23



Chinking can Help:Hot Box Test of 10-in. Round-Log Coped Wall

Test showed little bit of improvement in thermal bridge effectsfoam insulation was installed on both wall sides (~ R-6.8)

Hot-box test showed additional extra improvement in thermal performance - after foam gasket and chinking were installed, wall R-value was lifted to R-7.5 - Extra 14% improvement



Hot Box Test of 10-in. Coped Round-Log Wall Larger foam gaskets and more chinking were installed between logs

Lesson learned:

Additional foam gaskets between logs improved R-value to R-8.4

Extra 27% comparing to the first test

24



Conclusions:

•• Misunderstanding of thermal bridging can be expensive.Misunderstanding of thermal bridging can be expensive.

• We need a single definition of wall R-value used by codes, energy modelers, designers, builders, and realtors.

• New wall testing configurations may be needed to fully represent higher framing ratios.

• It is good to remember that center-of-cavity R-values are significantly higher than measured clear-wall R-values.

• Wood-framed structures are less sensitive to differences in framing configuration then steel structures.

•• WoodWood--frame walls are more sensitive than steel structures frame walls are more sensitive than steel structures to imperfections in the wallto imperfections in the wall--cavity insulation.cavity insulation.

•• Small air gaps between wood studs degrade woodSmall air gaps between wood studs degrade wood--frame frame walls performance to the level of steelwalls performance to the level of steel--frame wallsframe walls.



Jan Kosny Ph.D.Jan Kosny Ph.D.

Ph: 865Ph: 865--574574--93539353

EE--mail: KYO @ ORNL . GOVmail: KYO @ ORNL . GOV

Thank you …….Thank you …….Thank you …….Thank you …….Thank you …….Thank you …….Thank you …….Thank you …….

rrrr----value misconceptionsvalue misconceptions...u. s. d epartmentof energy configuration of the...

Documents