Evaluate Cladding Jonathan Baron, AIA BEC Boston February 25, 2013
BEC Thermal Bridging Series January available products Knight Wall Systems Cladding Corp. Exo tec February evaluating products March reducing structural thermal bridges (balconies, steel, etc.)
"Essentially, all models are wrong, but some are useful" George Box
Agenda: Continuous Cladding vs. Cladding Brackets Options for Non continuous Cladding Support Modeling THERM vs. WUFI Modeling Absolute vs. Relative Values Sample Problem (Residential Wall) Case Study evaluating the performance of a bracket system compared to continuous zees The Problem Approach Process Analysis Results
Reducing energy consumption requires tighter building envelopes and increased insulation.
Reducing energy consumption requires tighter building envelopes and increased insulation. Efficacy of increased insulation is often compromised due to thermal bridging of studs and cladding support.
Reducing energy consumption requires tighter building envelopes and increased insulation. Efficacy of increased insulation is often compromised due to thermal bridging of studs and cladding support. Standard practice of continuous cladding support does not meet building codes.
Reducing energy consumption requires tighter building envelopes and increased insulation. Efficacy of increased insulation is often compromised due to thermal bridging of studs and cladding support. Standard practice of continuous cladding support does not meet building codes. Performance loss due to thermal bridging is substantial, but HOW MUCH.
Reducing energy consumption requires tighter building envelopes and increased insulation. Efficacy of increased insulation is often compromised due to thermal bridging of studs and cladding support. Standard practice of continuous cladding support does not meet building codes. Performance loss due to thermal bridging is substantial, but HOW MUCH. How to effectively design better performing walls.
Options available for reduced thermal bridging: Residential Vertical Furring Strips on Exterior Insulation
Options available for reduced thermal bridging: Residential Vertical Furring Strips on Exterior Insulation Commercial Non continuous Brackets (BEC January)
Options available for reduced thermal bridging: Residential Vertical Furring Strips on Exterior Insulation Commercial Non continuous Brackets (BEC January) How to evaluate and justify use of nonstandard construction
Thermal Modeling: THERM vs. WUFI
Thermal Modeling: THERM vs. WUFI THERM is a state of the art, Microsoft Windows based computer program developed at Lawrence Berkeley National Laboratory (LBNL) for use by building component manufacturers, engineers, educators, students, architects, and others interested in heat transfer. Using THERM, you can model two dimensional heat transfer effects in building components such as windows, walls, foundations, roofs, and doors; appliances; and other products where thermal bridges are of concern. THERM's heat transfer analysis allows you to evaluate a product s energy efficiency and local temperature patterns, which may relate directly to problems with condensation, moisture damage, and structural integrity. WUFI Oak Ridge National Laboratory (ORNL)/Fraunhofer IBP is a menu driven PC program which allows realistic calculation of the transient coupled one dimensional heat and moisture transport in multi layer building components exposed to natural weather. It is based on the newest findings regarding vapor diffusion and liquid transport in building materials and has been validated by detailed comparison with measurements obtained in the laboratory and on outdoor testing fields.
Thermal Modeling: THERM vs. WUFI Heat transfer through building components Heat and moisture tranport in multi layer building components
Thermal Modeling: THERM vs. WUFI Heat Flow Thermal Two dimensional (slice) Through a geometric assembly of materials of different properties Static Output Model through a detail Heat and Moisture Flow Hygrothermal One dimensional (slice) Through a layered assembly of materials of different properties Dynamic Output Model through an opaque wall
Thermal Modeling: THERM vs. WUFI Good for studying thermal bridges Not good for studying moisture and mold potential Not good for studying thermal bridges Good for studying moisture and mold potential
Thermal Modeling: Relative value as opposed to absolute value Relative this detail should allow less heat flow than that one. Minimal effort (few hours) Moderate value of data (larger factor of error) Moderate understanding of building science required Absolute based on given external and internal temperatures and humidities, we can expect condensation to happen at this point in the assembly. Extreme effort (days or weeks) Precise data (smaller factor of error) Expert understanding of building science required
Thermal Modeling: Relative value as opposed to absolute value Value Effort
Thermal Modeling: Sample Case Residential Wall Siding Building Felt Sheathing Batt Insulation GWB
Thermal Modeling: Sample Case Residential Wall Siding Building Felt Sheathing Batt Insulation GWB
Thermal Modeling: Sample Case Residential Wall Siding Building Felt Sheathing Batt Insulation GWB U Factor 0.0686 U=1/R R Value 14.5
Thermal Modeling: Sample Case Residential Wall
Thermal Modeling: Sample Case Residential Wall U Factor 0.0747 U=1/R R Value 14.5 13.4
Thermal Modeling: Sample Case Residential Wall Framing Factor 25%
Thermal Modeling: Sample Case Residential Wall Framing Factor 25% U Factor 0.0851 U=1/R R Value 14.5 13.4 11.8 19% reduction
Thermal Modeling: Sample Case Residential Wall
Thermal Modeling: Sample Case Residential Wall
Thermal Modeling: Metal Studs
Thermal Modeling: Metal Studs Nominal Value 14.5 R Value 6.8 53% reduction
The base case (from exterior to interior: The test case Cladding Cladding Vertical hat channels Vertical hat channels 2 or 4 insulation coplanar with 2 or 4 insulation coplanar with Continuous Zees Brackets @ 32 o.c. v. / 30 o.c. h. and continuous angle Air barrier Air Barrier 1/2 Sheathing 1/2 Sheathing 6 metal studs coplanar with or without 6 metal studs coplanar with or without 6 batt insulation 6 batt insulation 5/8 Gypsum Board 5/8 Gypsum Board Brackets based on Cladding Corp. F2.10
The base case (from exterior to interior: The test case
Brackets based on Cladding Corp. F2.10
How to craft the problem for study using thermal modeling Therm allows a 2D slice Wall is a 3D assembly Solution: Create two models, one exterior (vertical) and one interior (horizontal)
How to craft the problem for study using thermal modeling Using Thermal Modeling to
Model Process: Draw Geometry Determine representative samples (model length) CAD linework (.dxf v.12) Import as an underlay Trace geometries Assign materials (use ASHRAE Handbook of Fundamentals for non default materials) Set boundary conditions (Exterior, Interior, Adiabatic) To gain U value data, set boundary condition as a U factor surface Run model
Model Process: Draw Geometry Determine representative samples (model length) CAD linework (.dxf v.12) Import as an underlay Trace geometries Assign materials (use ASHRAE Handbook of Fundamentals for non default materials) Set boundary conditions (Exterior, Interior, Adiabatic) To gain U value data, set boundary condition as a U factor surface Run model
Model Process: Draw Geometry Determine representative samples (model length) CAD linework (.dxf v.12) Import as an underlay Trace geometries Assign materials (use ASHRAE Handbook of Fundamentals for non default materials) Set boundary conditions (Exterior, Interior, Adiabatic) To gain U value data, set boundary condition as a U factor surface Run model
Model Process: Draw Geometry Determine representative samples (model length) CAD linework (.dxf v.12) Import as an underlay Trace geometries Assign materials (use ASHRAE Handbook of Fundamentals for non default materials) Set boundary conditions (Exterior, Interior, Adiabatic) To gain U value data, set boundary condition as a U factor surface Run model
Model Process: Draw Geometry Determine representative samples (model length) CAD linework (.dxf v.12) Import as an underlay Trace geometries Assign materials (use ASHRAE Handbook of Fundamentals for non default materials) Set boundary conditions (Exterior, Interior, Adiabatic) To gain U value data, set boundary condition as a U factor surface Run model
Model Process: Adiabatic Draw Geometry Determine representative samples (model length) Exterior CAD linework (.dxf v.12) Import as an underlay Trace geometries Assign materials (use ASHRAE Handbook of Fundamentals for non default materials) Set boundary conditions (Exterior, Interior, Adiabatic) To gain U value data, set boundary condition as a U factor surface Adiabatic Interior Run model Adiabatic: occurring without gain or loss of heat.
Model Process: Draw Geometry Determine representative samples (model length) CAD linework (.dxf v.12) Import as an underlay Trace geometries Assign materials (use ASHRAE Handbook of Fundamentals for non default materials) Set boundary conditions (Exterior, Interior, Adiabatic) To gain U value data, set boundary condition as a U factor surface Interior Run model
Model Process: Draw Geometry Determine representative samples (model length) CAD linework (.dxf v.12) Import as an underlay Trace geometries Assign materials (use ASHRAE Handbook of Fundamentals for non default materials) Set boundary conditions (Exterior, Interior, Adiabatic) To gain U value data, set boundary condition as a U factor surface Run model
Model Process: Model each condition Base case (zees) Test case (bracket at bracket) Test case (bracket at field) Perform for 2 XPS, 2 MW, 4 XPS, 4 MW
Model Process: Model each condition Base case (zees) Test case (bracket at bracket) Test case (bracket at field) Perform for 2 XPS, 2 MW, 4 XPS, 4 MW
Model Process: Model each condition Base case (zees) Test case (bracket at bracket) Test case (bracket at field) Perform for 2 XPS, 2 MW, 4 XPS, 4 MW
Model Process: Model each condition Base case (zees) Test case (bracket at bracket) Test case (bracket at field) Perform for 2 XPS, 2 MW, 4 XPS, 4 MW
Model Process: Model each condition Base case (zees) Test case (bracket at bracket) Test case (bracket at field) Perform for 2 XPS, 2 MW, 4 XPS, 4 MW
Model Process: Model each condition Base case (zees) Test case (bracket at bracket) Test case (bracket at field) Perform for 2 XPS, 2 MW, 4 XPS, 4 MW
Data Analysis: Average the data as necessary 32 28 4
Data Analysis: Average the data as necessary Add exterior model results to interior model
Results: The base case (from exterior to interior: The test case No batt Nom. R = 14.7 Modeled = 14.1 4% reduction No batt Nom. R = 14.7 Modeled = 10.0 30% reduction
Results: The base case (from exterior to interior: The test case With batt Nom. R = 33.7 Modeled = 19.8 With batt Nom. R = 33.7 Modeled = 15.7
Results: Using Thermal Modeling to No Batt in Batt in Stud Cavity Cavity R Values R Values 2" XPS Nominal Value 14.67 33.67 Modeled Value with Cont. Z @ 24" o.c. 10.02 15.72 Mod. Value w/ Brackets 30" o.c. x 32" o.c. 14.11 19.80 4" XPS Nominal Value 23.29 42.29 Modeled Value with Cont. Z @ 24" o.c. 10.33 16.77 Mod. Value w/ Brackets 30" o.c. x 32" o.c. 22.62 29.06 2" Mineral Wool Nominal Value 13.03 32.03 Modeled Value with Cont. Z @ 24" o.c. 9.07 15.51 Mod. Value with Brackets 30" o.c. x 32" o.c. 12.14 18.58 4" Mineral Wool Nominal Value 19.99 38.99 Modeled Value with Cont. Z @ 24" o.c. 10.05 16.49 Mod. Value with Brackets 30" o.c. x 32" o.c. 18.34 24.78
Why is this important? Using Thermal Modeling to
Conclusions: Reducing bridges results in reduced heat flow. Architects can and should model bridges to accurately predict assembly performance. The bigger the bridge, the greater the heatloss. Understand relative value of models rather than absolute. Better predictions should be factored into HVAC design. Smaller HVAC systems = energy savings. "Essentially, all models are wrong, but some are useful" George Box
Resources: THERM Google THERM and LBNL. http://windows.lbl.gov/software/therm/therm.html for the free download http://windows.lbl.gov/software/therm/6/therm63_docs.htm for manual http://windows.lbl.gov/software/therm/tutorials.html for tutorials WUFI Google WUFI and ORNL http://www.ornl.gov/sci/ees/etsd/btric/wufi/software.shtml for download BETEC LinkedIn Group: http://tinyurl.com/betecgroup Discussion BEC Boston LinkedIn Group: http://tinyurl.com/bec boston