Exterior envelopes for Passive Houses in very cold climates have not been developed, tested, and used as extensively as those in more mild climates such as central Europe. The purpose of this investigation was to push that development further by testing and comparing the performance of a variety of North American and Scandinavian envelope types that have been used in limited numbers for Passive Houses in those regions. A group of eight envelopes were selected and tested with a number of software analyses: Athena life cycle analysis, WUFI hygrothermal modeling, and THERM and EN ISO 6946 2-D U-value calculations for thermal bridging. Finally, the Passive House Planning Package (PHPP) was used to confirm that the envelopes met Passive House energy performance requirements in a very cold climate using a basic passive solar house design. Although significant variation was found in the performance of these eight envelope types, almost all of them were found capable of meeting the energy efficiency and thermal bridging requirements of the Passive House certification in a very cold climate, while maintaining moisture safety, durability, and significant life-cycle energy and carbon savings. These findings demonstrate that even in cold climates, a variety of envelope types can be used successfully for certified Passive Houses.
Envelope types: 1) Advanced 2x6 framing24” on center with interior cross strapping and exterior insulation, insulated with mineral wool, 2) Advanced 2x6 framing24” on center, insulated with high-density spray polyurethane foam and exterior rigid foam, 3) Double 2x4 stud wall with studs 16” on center, insulated with blown cellulose, 4) I-joist (TJI) balloon framing 24” on center, insulated with blown fiberglass, 5) Insulated concrete form wall (ICF), using integral rigid EPS foam insulation, 6) Concrete block wall, insulated with exterior mineral wool, 7) Massivtre/Structural engineered panel (SEP), insulated with exterior rigid foam, and 8) Structural insulated panel (SIP), using integral EPS rigid foam insulation. For comparison, a base option was also studied: Standard 2x6 framing 16” on center with fiberglass batt insulation. See Appendix for diagrams of each envelope.
Table of Contents
Introduction
Envelope Descriptions/Diagrams
Envelope Selection and Thermal Resistance (2D R-value modeling)
Thermal Bridges (THERM modeling)
Passive House Verification and House Model (PHPP modeling)
Hygrothermal Performance and Risk (WUFI modeling)
Life Cycle Environmental Impact Analysis (Athena LCA modeling)
Summary and Conclusion
Appendix A - Detailed Methodology
2D R-value modeling
THERM modeling
PHPP modeling
WUFI modeling
Athena LCA modeling
Appendix B - Common Material Properties: Thermal Resistance
Appendix C - Common Material Properties: Vapor Permeance
Appendix D - Energy Modeling Assumptions
Appendix E - WUFI Modeling Assumptions
Appendix F - Moisture Storage @80RH and 68°F (20°C)
Appendix G - Athena Modeling: Envelope materials and layer thicknesses
Appendix H – THERM Modeling: Thermal Bridge Details
Research Objectives and Topics
This research evaluates eight different envelope types used in Passive House and low-energy projects within very cold climates (DOE climate zones 6 and 7). The study aims to determine which envelope designs ensure moisture safety while simultaneously meeting the rigorous energy efficiency requirements of Passive House certification and providing significant life cycle savings in energy and carbon emissions.
- Insulation value and thermal performance
- Thermal bridge analysis of various construction details
- Overall building energy performance simulation
- Hygrothermal (moisture) performance and mold growth risk
- Embodied energy and life cycle environmental impacts
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Thermal Bridges (THERM modeling)
Thermal bridges generally come in two types, structural and geometric. A structural thermal bridge occurs when one of the layers in a building assembly is not continuous. For example, a structural thermal bridge occurs where the insulation in an exterior wall is interrupted by a penetration such as a window frame, rim joist, stud, or merely a change from one assembly to another - as at the junction of a concrete block wall and stud wall. The second type of thermal bridge, a geometric thermal bridge, occurs at corners - as at the corner of a roof and exterior wall. Even if a corner assembly is perfectly continuous with no interruption or change in materials or thickness, a geometric thermal bridge still occurs in that location. However, corners are frequently characterized by a combination of geometric and structural thermal bridges because corners typically have additional structural elements (such as studs) that reduce or interrupt the thickness of insulation.
Heat loss through a thermal bridge is measured by a psi (Ψ) value, which is somewhat similar to a U-value. Just as a U-value is multiplied by the area of the wall or roof surface to calculate the total heat loss, a Ψ value is multiplied by the length of the thermal bridge to calculate the total heat loss.
Summary of Chapters
Introduction: This chapter outlines the research focus on eight Passive House envelope types, covering insulation, thermal bridging, energy performance, moisture management, and environmental impacts in cold climates.
Envelope Descriptions/Diagrams: Provides technical specifications and visual representations of the eight tested envelope assemblies plus a baseline standard frame case.
Envelope Selection and Thermal Resistance (2D R-value modeling): Discusses the selection criteria for envelopes based on climate data from Minnesota and Scandinavia and details the R-value calculation methodologies.
Thermal Bridges (THERM modeling): Explains the modeling of linear thermal bridges using THERM software and the application of "thermal bridge free" guidelines.
Passive House Verification and House Model (PHPP modeling): Describes the modeling of a baseline home in Minneapolis using PHPP to verify energy efficiency compliance for all envelope types.
Hygrothermal Performance and Risk (WUFI modeling): Evaluates the moisture balance, drying potential, and mold growth risks for each envelope assembly under simulated cold climate conditions.
Life Cycle Environmental Impact Analysis (Athena LCA modeling): Quantifies the environmental impacts of the envelope assemblies, including embodied energy and global warming potential, using Athena software.
Summary and Conclusion: Synthesizes the findings, offering comparative analysis and recommendations for envelope selection in cold climates.
Keywords
Passive House, Cold Climate, Building Envelope, Thermal Bridging, Hygrothermal Modeling, WUFI, PHPP, Embodied Energy, Life Cycle Analysis, Moisture Safety, Insulation, Energy Efficiency, Sustainability, Construction Details, Building Science
Frequently Asked Questions
What is the primary focus of this research?
The research investigates the performance of eight specific building envelope types designed for Passive House certified homes in cold climates, such as the upper Midwest and Scandinavia.
What are the key performance metrics evaluated?
The study evaluates insulation value, thermal bridging, overall energy performance, moisture management, and life cycle environmental impacts.
What is the main objective regarding Passive House certification?
The goal is to determine if these specific envelope types can meet the stringent Passive House space heating and primary energy requirements while maintaining moisture safety and durability.
Which methodologies were employed for the analysis?
The study used EN ISO 6946 for R-value calculations, THERM 6.3 for thermal bridge analysis, PHPP 2007 for energy simulation, WUFI Pro 5.1 for hygrothermal modeling, and Athena Impact Estimator 4.1 for life cycle analysis.
What does the main body of the work cover?
It covers detailed descriptions and diagrams of the envelopes, climate comparisons, methodology for thermal and moisture modeling, energy certification verification, and environmental impact assessments.
What are the defining keywords for this research?
Key terms include Passive House, cold climate design, thermal bridging, hygrothermal performance, embodied energy, and building envelope durability.
How does moisture risk change with increased insulation?
Increased insulation reduces heat flow through walls, which can lead to higher relative humidity levels in exterior sheathing and slower drying times, potentially increasing the risk of mold growth if moisture management strategies are not properly addressed.
Why are concrete-based envelopes generally less environmentally friendly in this study?
Concrete is energy-intensive to produce and releases carbon dioxide during the curing process; therefore, these envelopes show higher embodied energy and global warming potential compared to wood-framed or panelized alternatives.
- Arbeit zitieren
- Rolf Jacobson (Autor:in), 2011, Performance of 8 Cold-Climate Envelopes for Passive Houses, München, GRIN Verlag, https://www.grin.com/document/200508
