Literature Summaries

Thermal bridges at the joints between walls and window frames

Erich Cziesielski, Proceedings of Windows in Building Design and Maintenance (1984)

- Looked at changing position of window and the addition of external insulation.
- The major concern is the occurance of a temperature drop at the mounting point between the window frame and outer wall.
- Mentions three methods to detect the occurence of thermal bridges in wall assemblies (hot-box testing, thermography, and analytical computation. In this instance the analytical method is utilized.
- The addition of insulation between the window and the wall reduces the occurrence of condensation.
- Found that windows should be mounted toward the inside or center of the opening.
- Showed that walls without external insulation can have damaging condensation issues.
- Provides evidence that internal insulation is not as effective as external insulation.
- Provides evidence that electric heating of walls using thin wires reduces the thermal bridge effect

Envelope the Steel!

James A. D’Aloisio1, 2, ASCE Structures Congress (2010)
1 Klepper, Hahn & Hyatt
2 SEI Sustainability Committee

- Introduces the basics of building envelopes, heat transfer, and thermal bridges for structural engineers
- Presents limitations and possible materials for thermally effecient design alternatives - Stresses that thermal bridges should be a consideration of structural engineers as it applies to building performance and structural durability
- Provides conceptual solutions to structural related thermal bridges, which include Cold-formed steel studs, roof overhangs, steel lintels, relieving angles, parimeter columns and spandrel beams, roof edges, exposed steel columns, balconies/canopies, and brick ties
- Ends with a mention that the Intergovenmental panel on Climate Change has stated that improved building performance is one of the best ways to reduce manmade negative environmental impacts.

Steel Framing and Building Envelopes

James A. D’Aloisio1, 2, Modern Steel Construction (January 2010)
1 Klepper, Hahn & Hyatt
2 SEI Sustainability Committee

- Begins by mentioning that the consideration of thermal bridges is new to structural engineers, as many assumed that the heat transfer along connections has little effect due to small area of contact.
- Provides a brief example for why small areas bridging the thermal plane have large effects on the heat transfer.
- Lays out a few methods to address energy efficiency in buildings (Thermal Infrared imaging, thermal modeling software, data from building).
- Emphasizes that the detailing of energy efficient connections falls on the structural engineer, and for safety and liability reasons does not the fall to the enclosure consultant or architect.
- States that new energy efficient connection details need to be developed and provides examples that have been implimented in completed projects by Klepper, Hahn & Hyatt.

Structuring Sustainable Thermal Breaks: Opportunities and Liabilities

Russ Miller-Johnson1, ASCE Structures Congress (2010)
1 Engineering Ventures, PC

- Describes the importance of using alternatives to carbon steel at connection details in order to provide a thermal break.
- Provides examples of structural design issues when incorporating thermal breaks at connection details.
- Discusses the liability of using unconventional conection assemblies and materials, which are not typically covered in standards of practice and loss prevention criteria.
- Provides a list of other issues.
- Points out that the incorporation of these details may lead to a lengthy approval process, which may involve testing in addition to several other requirements.
-The paper ends on a brighter note by explaining that the incorporation of successful energy efficient connection details can offer beneficial energy conscience solutions.

Thermal Inefficiencies in Building Enclosures – Causes of Moisture Related Performance Problems

Paul E. Totten1 and M. Pazera1, ASCE Forensics Engineering Congress (2009)
1 Simpson Gumpertz & Heger Inc.

- Discusses the importance of limiting moisture related problems due to the thermal bridges, as well as unwanted air flows and leaks.
- Describes the reasoning for why these undesirable deficiencies should be prevented or remediated.
- Gives a general description of heat transfer mechanisms (conduction, convection, and radiation) and dew point temperature.
- Summarizes the methods to investigate, analyze, and diagnose moisture related issues (visual inspection, tracer smoke test, infrared thermography, and computational thermal analysis).
- Provides two case studies: The first highlights a condensation problem due to unintentional air infiltration and the second illistrates the occurrence of condensation due to thermal bridging.

The Effects of Thermal Bridging at Interface Conditions

Paul E. Totten1, Sean M. O'Brien1, Marcin Pazera1, Building Enclosure Science and Technology (BEST 1) conference (2008)
1 Simpson Gumpertz & Heger Inc.

- Discusses typical interfaces (roof-to-wall, stud framing, window-to-wall, wall-to-balcony, wall-to-wall, and sunshade-to-wall) where thermal bridges can occur, and offers suggestions on preventing or reducing their effects.
- Begins by describing thermal bridging, thermal breaks, and heat transfer.
- At the roof-to-wall interface ensure continuity of the thermal plane, especially for parpets.
- In stud framing construction provide proper amount of exterior insulation. In some instances a combination of cavity insulation and exterior insolation may be needed.
- Provides an example to illustrate that the addition of windows is detrimental to the clear-wall R-value. At window-to-wall interfaces the window thermal breaks should be in-line with the insulation plane.
- Cantilevered balconies act as heat fins. Solutions include the isolation of the balcony from the main structure or the use of proprietary thermal breaks.
- At wall-to-wall interfaces changes in material properties can lead to noticable thermal effects. In some instances lapping of insulation layers may be required.
- For sunshade-to-wall interfaces insulation should be lapped at the anchor and sunshades should not be connected directly to the structure.
- At the end figures are provided showing the temperature distributions for a few of the strateges discussed.

Thermal Bridging Solutions: Minimizing Structural Steel’s Impact on Building Envelope Energy Transfer

SEI/AISC Thermal Steel Bridging Task Committee, Supplement to Modern Steel Construction (March 2012)

- Begins with stating that, "Efforts to reduce energy use has been through improvement of mechanical, electrical, and glazing systems, and not structural thermal bridges.
- highlights that there is a misconception within the structural engineering community that energy efficiency is not the role of structural engineers.
- Includes a brief description of heat transfer through building envelopes (mechanisms, R-values and U-factors, Series vs. parallel flow paths)
- Describes two common methods used to quantify heat loss (Thermal infrared imaging, and building energy modeling).
- Discusses that thermal bridging is not exclusively delt with in codes, such as IECC, IGCC, ASHRAE 90.1, and ASHRAE 189.1, but are being evaluated.
- Mentions alternative materials to carbon steel, which are stainless steel (Conductivity is three times less), and Fiber reinforced plastics (FRP).
- States that codes and loss prevention criteria do not address the use of FRP. Also, AISC Specification for Structural Steel Buildings (ANSI/AISC 360-10) does not address non-steel assemblies.
- Provides descriptions for several conceptual solutions for various details and their feasibility (rooftop grillage posts, roof edge angle, shelf angle, steel lintel, roof canopy.
- Modeled a generic building for various climate zones using TRACE 700.
- Analysis of assemblies used THERM software.
- Follows with explaing the assumptions, limitations, alternatives, chalanges, and ended with the lessons learned.

New Materials and Concepts to Reduce Energy Losses Through Structural Thermal Bridges

R.P. Tye1, J.P. Silvers1, D.L. Brownell1, SE. Smith1, ASHRAE/DOC/BTEC Thermal Performance of the Exterior Envelopes of Buildings III, ASHRAE SP 49 (1986)
Dynatech R/D Company, Research comissioned by US DOE and Oak Ridge National Labratory'

- Discribes several reasons for the occurence of thermal bridges (high thermal conductivity of structural elements, connections, and enclosure penetrations, as well as geometric effects, and faulty installation).
- Performed an intensive literature review of over 400 sources including topics in thermography, energy audits, in-situ measurements, and condensation.
- Based on the literature review the paper states that thermal bridges can have up to a 20% reduction in wall resistivity.
- Discusses solutions for reducing the thermal bridge effect by reducing contact area or material properties, or adding thermal breaks.
- Gives an example where channging from carbon steel ties to stainless steel can reduce the thermal conductivity by 1/3.
- Provides comments from interviews with architects, engineers, contractors, construction officials, manufacturers, and researchers on their familiarity with thermal bridges.
- Looks at new solutions for reducing thermal bridges using specific materials (insulation, insulated panels, masonry, mortar, wood, FRP fasteners, fiber reinforced composites, and honeycomb composites).
- Concludes by stating that the awareness of thermal bridging must be spread and that the current (1986) solutions are available but not well implimented.

Dynamic Evaluation of Thermal Bridges in a Typical Office Building

D.M. Burch1, J.E. Seem2, G.N. Walton1, B.A. Licitra1, ASHRAE Transactions: research (1992)
US National Institute of Standards and Technology
Johnson Controls Inc., Milwaukee, WI

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