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{{Short description|Object reducing thermal resistance}}
[[File:Thermal bridge by Zureks.png|thumb|Temperature distribution in a thermal bridge]]
[[File:Thermal bridge by Zureks.png|300px|thumb|Temperature distribution in a thermal bridge]]
[[File:Aqua Tower thermal imaging.jpg|thumb|This thermal image shows a thermal bridging of a high-rise building ([[Aqua (skyscraper)|Aqua]] in [[Chicago]])]]A '''thermal bridge''', also called a '''cold bridge''', '''heat bridge''', or '''thermal bypass''', is an area or component of an object which has higher [[thermal conductivity]] than the surrounding materials,<ref name="Binggeli">{{cite book|title=Building Systems for Interior Designers|last=Binggeli|first=C.|date=2010|publisher=John Wiley & Sons|location=Hoboken, NJ}}</ref> creating a path of least resistance for [[heat transfer]].<ref name="oxford">Gorse, Christopher A., and David Johnston (2012). "Thermal bridge", in ''Oxford Dictionary of Construction, Surveying, and Civil Engineering''. 3rd ed. Oxford: Oxford UP, 2012 pp. 440-441. Print.</ref> Thermal bridges result in an overall reduction in [[thermal resistance]] of the object. The term is frequently discussed in the context of a building's [[thermal envelope]] where thermal bridges result in heat transfer into or out of conditioned space.


Thermal bridges in buildings may impact the amount of energy required to heat and cool a space, cause condensation (moisture) within the building envelope,<ref name=":1">{{Cite web|url=https://www.nrel.gov/docs/fy16osti/65147.pdf|title=Construction Guidelines for High R-Value Walls without Exterior Rigid Insulation|last=Arena|first=Lois|date=July 2016|website=NREL.gov|publisher=National Renewable Energy Laboratory (NREL)|location=Golden, CO}}</ref> and result in thermal discomfort. In colder climates (such as the United Kingdom), thermal heat bridges can result in additional heat losses and require additional energy to mitigate.
A '''thermal bridge''', also called a '''cold bridge''',<ref name=Viking>[http://www.viking-house.co.uk/cold-bridge-thermal-bridge.html viking-house.co.uk]'' Cold Bridge-Thermal Bridge''</ref> is a fundamental of [[heat transfer]] where a penetration of the insulation layer by a highly conductive or noninsulating material takes place in the separation between the interior (or conditioned space) and exterior environments of a building assembly (also known as the building enclosure, [[building envelope]], or thermal envelope).<ref name=Allen>[Allen, E, & Iano, J. (2009). Fundamentals of Building Construction: materials and methods. Hoboken, NJ: John Wiley & Sons Inc.]'' Fundamentals of Building Construction''</ref>


There are strategies to reduce or prevent thermal bridging, such as limiting the number of building members that span from unconditioned to conditioned space and applying continuous insulation materials to create [[thermal break]]s.
Thermal bridging is created when materials that are poor [[thermal insulation|thermal insulators]] come into contact, allowing heat to flow through the path of least [[thermal resistance]] ([[R-value (insulation)|R-value]]; or a material's effectiveness in resisting the [[conduction (heat)|conduction]] of heat) created, although nearby layers of material separated by airspace allow little heat transfer.<ref name=Binggeli>[Binggeli, C. (2010). Building Systems for Interior Designers. 2nd. Hoboken, NJ: John Wiley & Sons, Inc.] '' Building Systems for Interior Designers''</ref>

Insulation around a bridge is of little help in preventing heat loss or gain due to thermal bridging; the bridging has to be eliminated, rebuilt with a reduced cross-section or with materials that have better insulating properties, or with a section of material with low [[thermal conductivity]] installed between metal components to retard the passage of heat through a wall or window assembly, called a [[thermal break]].

The thermograph photograph on the right shows that if thermal bridges at balconies are not taken care of, the balconies act as “cooling fins”; conducting the heat off the building and cooling the rooms adjacent to the balconies.<ref>http://www.schock-us.com/en_us/solutions/thermal-break-technology-186</ref>
[[File:Aqua Tower thermal imaging.jpg|thumb|Thermal Image of Aqua Tower, Chicago, IL USA]]


==Concept==
==Concept==
[[File:Jonction plancher haut-mur extérieur 2.jpg|thumb|200px|right|Thermal bridge at junction. Heat moves from the floor structure through the wall because there is no thermal break.]]
Several properties of materials affect heat transfer. Examples include thermal conductivities, specific heats, material densities, fluid velocities, fluid viscosities, and surface reflectance and emittance characteristics. Thermal bridges are characterized by multi-dimensional heat transfer, and therefore they cannot be adequately approximated by the one-dimensional models of calculation typically used in norms and standards for the thermal performance of buildings ([[U-value]]s). Surface moisture due to [[condensation]], typically occurring in such regions as floor-wall connections and window installations, as well as [[mold]] growth in [[humid]] environments can also be effectively prevented by means of multi-dimensional evaluation during planning and detail design.
Heat transfer occurs through three mechanisms: [[convection]], [[Thermal radiation|radiation]], and [[Thermal conduction|conduction]].<ref>{{Cite book|title=Essentials of Heat Transfer: Principles, Materials, and Applications|last=Kaviany|first=Massoud|publisher=Cambridge University Press|year=2011|isbn=978-1107012400|location=New York, NY}}</ref> A thermal bridge is an example of heat transfer through conduction. The rate of heat transfer depends on the thermal conductivity of the material and the temperature difference experienced on either side of the thermal bridge. When a temperature difference is present, heat flow will follow the path of least resistance through the material with the highest thermal conductivity and lowest thermal resistance; this path is a thermal bridge.<ref name=":0">{{Cite web|url=https://passipedia.org/basics/building_physics_-_basics/thermal_bridges/thermal_bridge_definition|title=Definition and effects of thermal bridges [ ]|website=passipedia.org|language=en|access-date=2017-11-05}}</ref> Thermal bridging describes a situation in a building where there is a direct connection between the outside and inside through one or more elements that possess a higher thermal conductivity than the rest of the envelope of the building.


==Identifying Thermal Bridges==
==Examples==
Surveying buildings for thermal bridges is performed using passive [[infrared thermography]] (IRT) according to the [[International Organization for Standardization]] (ISO). Infrared Thermography of buildings can allow thermal signatures that indicate heat leaks. IRT detects thermal abnormalities that are linked to the movement of fluids through building elements, highlighting the variations in the thermal properties of the materials that correspondingly cause a major change in temperature. The drop shadow effect, a situation in which the surrounding environment casts a shadow on the facade of the building, can lead to potential accuracy issues of measurements through inconsistent facade sun exposure. An alternative analysis method, Iterative Filtering (IF), can be used to solve this problem.


In all thermographic building inspections, the thermal image interpretation if performed by a human operator, involving a high level of subjectivity and expertise of the operator. Automated analysis approaches, such as [[Laser scanning]] technologies can provide thermal imaging on 3 dimensional [[CAD]] model surfaces and metric information to thermographic analyses.<ref>{{cite book |last1=Previtali |first1=Mattia |last2=Barazzetti |first2=Luigi |last3=Roncoroni |first3=Fabio |title=Computational Science and Its Applications – ICCSA 2013 |chapter=Spatial Data Management for Energy Efficient Envelope Retrofitting |volume=7971 |pages=608–621 |date=24–27 June 2013 |doi=10.1007/978-3-642-39637-3_48|series=Lecture Notes in Computer Science |isbn=978-3-642-39636-6 }}</ref> Surface temperature data in 3D models can identify and measure thermal irregularities of thermal bridges and insulation leaks. Thermal imaging can also be acquired through the use of [[unmanned aerial vehicles]] (UAV), fusing thermal data from multiple cameras and platforms. The UAV uses an infrared camera to generate a thermal field image of recorded temperature values, where every pixel represents radiative energy emitted by the surface of the building.<ref>{{cite journal |last1=Garrido |first1=I. |last2=Lagüela |first2=S. |last3=Arias |first3=P. |last4=Balado |first4=J. |title=Thermal-based analysis for the automatic detection and characterization of thermal bridges in buildings |journal=Energy and Buildings |date=1 January 2018 |volume=158 |pages=1358–1367 |doi=10.1016/j.enbuild.2017.11.031 |hdl=11093/1459 |hdl-access=free }}</ref>
*[[Concrete]] balconies that extend the [[floor slab]] through the building envelope<ref name=Treehugger>[http://www.treehugger.com/files/2008/04/why-there-are-few-green-buildings.php Why there are so few green buildings]'' Heavy advertising site!''</ref> are a common example of thermal bridging.
*In commercial construction, steel or concrete members incorporated in exterior wall or roof construction often form thermal bridges.<ref name= Allen />
*Metal ties in cavity walls are another type of thermal bridge commonly found in masonry construction.<ref name= Allen />


==Thermal Bridging in Construction==
==Thermal Bridging in Construction==
Frequently, thermal bridging is used in reference to a building’s thermal envelope, which is a layer of the building enclosure system that resists heat flow between the interior conditioned environment and the exterior unconditioned environment. Heat will transfer through a building’s thermal envelope at different rates depending on the materials present throughout the envelope. Heat transfer will be greater at thermal bridge locations than where insulation exists because there is less thermal resistance.<ref>{{Cite news|url=https://buildingscience.com/documents/reports/rr-0901-thermal-metrics-high-performance-walls-limitations-r-value/view|title=RR-0901: Thermal Metrics for High-Performance Walls—The Limitations of R-Value|work=Building Science Corporation|access-date=2017-11-19|language=en}}</ref> In the winter, when exterior temperature is typically lower than interior temperature, heat flows outward and will flow at greater rates through thermal bridges. At a thermal bridge location, the surface temperature on the inside of the building envelope will be lower than the surrounding area. In the summer, when the exterior temperature is typically higher than the interior temperature, heat flows inward, and at greater rates through thermal bridges.<ref>{{Cite book|title=Mechanical and Electrical Equipment for Buildings|last1=Grondzik|first1=Walter|last2=Kwok|first2=Alison|publisher=John Wiley & Sons|year=2014|isbn=978-0470195659}}</ref> This causes winter heat losses and summer heat gains for conditioned spaces in buildings.<ref name=":2">{{Cite journal|last=Larbi|first=A. Ben|title=Statistical modelling of heat transfer for thermal bridges of buildings|journal=Energy and Buildings|volume=37|issue=9|pages=945–951|doi=10.1016/j.enbuild.2004.12.013|year=2005}}</ref>
[[File:Waermebruecke konstruktiv.jpg|thumb|right|200px|Thermal bridge caused by floor]]
Classification:
*Repeating thermal bridges - where bridges occur following a regular pattern, such that made by wall ties penetrating a [[cavity wall]]
*Non-repeating thermal bridges - such as the bridging of a [[cavity wall]] by a single [[lintel]]
*Geometrical thermal bridges - placed at the junction of two planes, such as at the corner of a wall


Despite insulation requirements specified by various national regulations, thermal bridging in a building's envelope remain a weak spot in the construction industry. Moreover, in many countries building design practices implement partial insulation measurements foreseen by regulations.<ref>THEODOSIOU, T. G, and A. M PAPADOPOULOS. 2008. “The Impact of Thermal Bridges on the Energy Demand of Buildings with Double Brick Wall Constructions.” Energy and Buildings, no. 11: 2083.</ref> As a result, thermal losses are greater in practice that is anticipated during the design stage.
===Thermal bridge concept and interior insulation===


An assembly such as an exterior wall or insulated ceiling is generally classified by a [[R-value (insulation)|U-factor]], in W/m<sup>2</sup>·K, that reflects the overall rate of heat transfer per unit area for all the materials within an assembly, not just the insulation layer. Heat transfer via thermal bridges reduces the overall thermal resistance of an assembly, resulting in an increased U-factor.<ref>{{Cite journal|last1=Kossecka|first1=E.|author-link= Elżbieta Kossecka|last2=Kosny|first2=J.|date=2016-09-16|title=Equivalent Wall as a Dynamic Model of a Complex Thermal Structure|journal=Journal of Thermal Insulation and Building Envelopes|language=en|volume=20|issue=3|pages=249–268|doi=10.1177/109719639702000306|s2cid=108777777}}</ref>
Interior insulation is used for preventing heat as well as cold from escaping or entering the building envelope, individual rooms, as well as pipes and various appliances. Heat loss of a building is prevented primarily by exterior insulation in the walls because they cover the most surface area of any building. There are many different types of materials which can be used for insulation with different characteristics. The different spaces for insulation in a building define different uses for it.<ref name= Allen />


Thermal bridges can occur at several locations within a building envelope; most commonly, they occur at junctions between two or more building elements. Common locations include:
===Insulation requirements relating to thermal bridging===
*Floor-to-wall or balcony-to-wall junctions, including slab-on-grade and [[concrete]] balconies or outdoor patios that extend the [[floor slab]] through the building envelope
*Roof/Ceiling-to-wall junctions, especially where full ceiling insulation depths may not be achieved
*Window-to-wall junctions<ref name=":6">{{Cite journal|last1=Christian|first1=Jeffery|last2=Kosny|first2=Jan|date=December 1995|title=Toward a National Opaque Wall Rating Label|journal=Proceedings Thermal Performance of the Exterior Envelopes VI, ASHRAE}}</ref>
*Door-to-wall junctions<ref name=":6" />
*Wall-to-wall junctions<ref name=":6" />
*Wood, steel or concrete members, such as studs and joists, incorporated in exterior wall, ceiling, or roof construction<ref name="Allen">Allen, E. and J. Lano, ''Fundamentals of Building Construction: materials and methods''. Hoboken, NJ: John Wiley & Sons. 2009.</ref>
*Recessed luminaries that penetrate insulated ceilings
*Windows and doors, especially frames components
*Areas with gaps in or poorly installed insulation
*Metal ties in masonry cavity walls<ref name="Allen" />


Structural elements remain a weak point in construction, commonly leading to thermal bridges that result in high heat loss and low surface temperatures in a room.
There are many different materials that are used for insulation, and new ones are often being created as the need for energy efficiency, sustainable design, and cheaper costs are currently what are driving new innovation. Currently, the types of insulation that are being used are:
* Fiberglass or [[rock wool]] insulation,
* [[Insulating glass]] or [[polystyrene]] rigid board insulation, formed in place polyurethane insulation,
* Cellulose/perlite/vermiculite loose fill, and insulated pre-cast concrete insulation.


===Masonry Buildings===
Each type of insulating material is used most effectively in various parts of buildings including interior walls, exterior envelopes, flooring, roofing, and basements. All insulating materials have a specific [[R-value (insulation)|R-value]], which determines their [[thermal resistance]]. A good insulating material resists the conduction of heat. The higher the thermal resistance of a part of the building envelope is, the slower the heat loss. The larger the difference between the temperature inside and outside the building, the faster the building gains or losses heat. Designing a building’s walls, roofs, and floors for the maximum amount of thermal resistance results in optimal body comfort and energy conservation.<ref name= Binggeli />
While thermal bridges exist in various types of building enclosures, [[Masonry|masonry walls]] experience significantly increased U-factors caused by thermal bridges. Comparing [[list of thermal conductivities|thermal conductivities]] between different building materials allows for assessment of performance relative to other design options. Brick materials, which are usually used for facade enclosures, typically have higher thermal conductivities than timber, depending on the brick density and wood type.<ref name=":5">{{Cite book|title=2017 ASHRAE Handbook: Fundamentals|last=American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc. (ASHRAE)|publisher=ASHRAE|year=2017|isbn=978-1939200570|location=Atlanta, GA}}</ref> Concrete, which may be used for floors and edge beams in masonry buildings are common thermal bridges, especially at the corners. Depending on the physical makeup of the concrete, the thermal conductivity can be greater than that of brick materials.<ref name=":5" /> In addition to heat transfer, if the indoor environment is not adequately vented, thermal bridging may cause the brick material to absorb rainwater and humidity into the wall, which can result in mold growth and deterioration of building envelope material.


===Curtain Wall===
==One-dimensional analysis==
Similar to masonry walls, [[Curtain wall (architecture)|curtain walls]] can experience significantly increased U-factors due to thermal bridging. Curtain wall frames are often constructed with highly conductive aluminum, which has a typical thermal conductivity above 200 W/m·K. In comparison, wood framing members are typically between 0.68 and 1.25 W/m·K.<ref name=":5" /> The aluminum frame for most curtain wall constructions extends from the exterior of the building through to the interior, creating thermal bridges.<ref name="Totten">{{cite journal|last1=Totten|first1=Paul E.|last2=O’Brien|first2=Sean M.|date=2008|title=The Effects of Thermal Bridging at Interface Conditions|journal=Building Enclosure Science & Technology}}</ref>
One-dimensional analysis is based on simple, [[steady state]], flow of heat, which means that heat is driven by a temperature differences that does not fluctuate so that heat flow is always in one direction. The product (kA) of thermal conductivity (k) and cross sectional area (A) of the heat flow path can be used in evaluating heat flow.

=== Impacts of Thermal Bridging ===
Thermal bridging can result in increased energy required to heat or cool a conditioned space due to winter heat loss and summer heat gain. At interior locations near thermal bridges, occupants may experience thermal discomfort due to the difference in temperature.<ref name=":3">{{Cite journal|last1=Ge|first1=Hua|last2=McClung|first2=Victoria Ruth|last3=Zhang|first3=Shenshu|title=Impact of balcony thermal bridges on the overall thermal performance of multi-unit residential buildings: A case study|journal=Energy and Buildings|volume=60|pages=163–173|doi=10.1016/j.enbuild.2013.01.004|year=2013}}</ref> Additionally, when the temperature difference between indoor and outdoor space is large and there is warm and humid air indoors, such as the conditions experienced in the winter, there is a risk of condensation in the building envelope due to the cooler temperature on the interior surface at thermal bridge locations.<ref name=":3" /> Condensation can ultimately result in mold growth with consequent poor [[indoor air quality]] and insulation degradation, reducing the insulation performance and causing insulation to perform inconsistently throughout the thermal envelope<ref name="Miimu">{{cite journal|last1=Matilainen|first1=Miimu|last2=Jarek|first2=Kurnitski|date=2002|title=Moisture conditions in highly insulated outdoor ventilated crawl spaces in cold climates|journal=Energy and Buildings|volume=35|issue=2|pages=175–187|doi=10.1016/S0378-7788(02)00029-4}}</ref>

==Design Methods to Reduce Thermal Bridges==
There are several methods that have been proven to reduce or eliminate thermal bridging depending on the cause, location, and the construction type. The objective of these methods is to either create a [[thermal break]] where a building component would span from exterior to interior otherwise, or to reduce the number of building components spanning from exterior to interior. These strategies include:

*A continuous thermal [[building insulation|insulation]] layer in the thermal envelope, such as with rigid foam board insulation<ref name=":0" />
*Lapping of insulation where direct continuity is not possible
*Double and staggered wall assemblies<ref name=":4">{{Cite book|title=Residential Compliance Manual for the 2016 Building Energy Efficiency Standards|last=California Energy Commission (CEC)|publisher=California Energy Commission|year=2015}}</ref>
*[[Structural insulated panel|Structural Insulated Panels]] (SIPs) and [[Insulating concrete form|Insulating Concrete Forms]] (ICFs)<ref name=":4" />
*Reducing framing factor by eliminating unnecessary framing members, such as implemented with advanced framing<ref name=":4" />
*Raised heel trusses at wall-to-roof junctions to increase insulation depth
*Quality insulation installation without voids or compressed insulation
*Installing double or triple pane windows with gas filler and low-emissivity coating<ref name=":7">{{Cite journal|last1=Gustavsen|first1=Arild|last2=Grynning|first2=Steinar|last3=Arasteh|first3=Dariush|last4=Jelle|first4=Bjørn Petter|last5=Goudey|first5=Howdy|title=Key elements of and material performance targets for highly insulating window frames|journal=Energy and Buildings|volume=43|issue=10|pages=2583–2594|doi=10.1016/j.enbuild.2011.05.010|year=2011|osti=1051278|s2cid=72987269 }}</ref>
*Installing windows with thermally broken frames made of low conductivity material<ref name=":7" />

==Analysis Methods and Challenges==
Due to their significant impacts on heat transfer, correctly modeling the impacts of thermal bridges is important to estimate overall energy use. Thermal bridges are characterized by multi-dimensional heat transfer, and therefore they cannot be adequately approximated by steady-state one-dimensional (1D) models of calculation typically used to estimate the thermal performance of buildings in most building energy simulation tools.<ref>{{Cite journal|last1=Martin|first1=K.|last2=Erkoreka|first2=A.|last3=Flores|first3=I.|last4=Odriozola|first4=M.|last5=Sala|first5=J.M.|title=Problems in the calculation of thermal bridges in dynamic conditions|journal=Energy and Buildings|volume=43|issue=2–3|pages=529–535|doi=10.1016/j.enbuild.2010.10.018|year=2011}}</ref> Steady state heat transfer models are based on simple heat flow where heat is driven by a temperature difference that does not fluctuate over time so that heat flow is always in one direction. This type of 1D model can substantially underestimate heat transfer through the envelope when thermal bridges are present, resulting in lower predicted building energy use.<ref>{{Cite journal|last1=Mao|first1=Guofeng|last2=Johanneson|first2=Gudni|date=1997|title=Dynamic Calculation of Thermal Bridges|journal=Energy and Buildings|volume=26|issue=3|pages=233–240|doi=10.1016/s0378-7788(97)00005-4}}</ref>

The currently available solutions are to enable two-dimensional (2D) and three-dimensional (3D) heat transfer capabilities in modeling software or, more commonly, to use a method that translates multi-dimensional heat transfer into an equivalent 1D component to use in building simulation software. This latter method can be accomplished through the equivalent wall method in which a complex dynamic assembly, such as a wall with a thermal bridge, is represented by a 1D multi-layered assembly that has equivalent thermal characteristics.<ref>{{Cite journal|last1=Kossecka|first1=E.|last2=Kosny|first2=J.|date=January 1997|title=Equivalent Wall as a Dynamic Model of a Complex Thermal Structure|journal=J. Therm. Insul. Build. Envelopes|volume=20|issue=3|pages=249–268|doi=10.1177/109719639702000306|s2cid=108777777}}</ref>


==See also==
==See also==
*[[Damp proofing]]
*[[Damp proofing]]
*[[List of thermal conductivities]]
*[[Thermal conduction]]
*[[Building Science]]
*[[Thermography]]
*[[Heat Transfer]]

==References==
{{Reflist}}


==External links==
==External links==
{{commons category|Thermal bridges}}
{{Commons category|Thermal bridges}}
*[http://www.schock-us.com/en_us/solutions/thermal-break-technology-186 Manufactured Structural Thermal Breaks.]
*[https://www.schock-na.com/view/5752/ Design Guide: Solutions to Prevent Thermal Bridging.]
*[https://www.schock-na.com/en-us/applications Manufactured Structural Thermal Breaks.]
*[http://www.buildup.eu/communities/thermalbridges EU Information Portal BUILD UP - energy solutions for better buildings: Community 'Thermal bridge forum']
*[http://www.asiepi.eu/wp-4-thermal-bridges.html EU IEE SAVE Project ASIEPI: topic 'Thermal bridges' - An effective handling of thermal bridges in the EPBD context]
*[http://www.asiepi.eu/wp-4-thermal-bridges.html EU IEE SAVE Project ASIEPI: topic 'Thermal bridges' - An effective handling of thermal bridges in the EPBD context]
*[[Passivhaus|Passivhaus Institute]]: [http://www.passivhaustagung.de/Passive_House_E/passive_house_avoiding_thermal_brigdes.html Thermal Bridges in construction - how to avoid them]
*[[Passivhaus|Passivhaus Institute]]: [http://www.passivhaustagung.de/Passive_House_E/passive_house_avoiding_thermal_brigdes.html Thermal Bridges in construction - how to avoid them] {{Webarchive|url=https://web.archive.org/web/20120321044858/http://www.passivhaustagung.de/Passive_House_E/passive_house_avoiding_thermal_brigdes.html |date=2012-03-21 }}
*[http://bookstore.ashrae.biz/journal/download.php?file=building_sciences_1.pdf A bridge too far - ASHRAE Journal article on thermal bridging] {{Webarchive|url=https://web.archive.org/web/20090902215631/http://bookstore.ashrae.biz/journal/download.php?file=building_sciences_1.pdf |date=2009-09-02 }}
* [http://www.kornicki.com/antherm/EN/ Analysis of Thermal behavior of Building Constructions with Thermal Heat Bridges ]
*[http://www2.iccsafe.org/states/phoenix/Phoenix_IBC/PDFs/Chapter%2012.pdf International Building Code, 2009: Interior Environment] {{Webarchive|url=https://web.archive.org/web/20120724124025/http://www2.iccsafe.org/states/phoenix/Phoenix_IBC/PDFs/Chapter%2012.pdf |date=2012-07-24 }}
*[http://bookstore.ashrae.biz/journal/download.php?file=building_sciences_1.pdf A bridge too far - ASHRAE Journal article on thermal bridging]
*[http://energy.concord.org/energy2d/thermal-bridge.html Online Energy2D simulation of thermal bridge (Java required)]
* [http://www.kornicki.com/antherm/Help/Content_EN/PrimaryConcepts/BasicsAndSomeTheory.htm Basics and Some Theory of AnTherm]
*[http://passipedia.passiv.de/ppediaen/basics/building_physics_-_basics/heat_transfer/thermal_bridges What Defines Thermal Bridge Free Design] {{Webarchive|url=https://web.archive.org/web/20160315224806/http://passipedia.passiv.de/ppediaen/basics/building_physics_-_basics/heat_transfer/thermal_bridges |date=2016-03-15 }}
* [http://www.kornicki.com/antherm/Help/Content_EN/Theory/TheoretischeGrundlagen.htm Theoretical background]
*[https://www.bchousing.org/research-centre/library/residential-design-construction/building-envelope-thermal-bridging-guide&sortType=sortByDate Building Envelope Thermal Bridging Guide]
* [http://www.cbe.berkeley.edu/research/briefs-thermmodel.htm University of California, 2008: Center for the Built Environment. Advanced Human Thermal Comfort Model]
*[https://www.iso.org/home.html]
* [http://www2.iccsafe.org/states/phoenix/Phoenix_IBC/PDFs/Chapter%2012.pdf International Building Code, 2009: Interior Environment]
*[https://cdn.ymaws.com/www.nibs.org/resource/resmgr/BEST/BEST1_034.pdf] {{Webarchive|url=https://web.archive.org/web/20201021130833/https://cdn.ymaws.com/www.nibs.org/resource/resmgr/BEST/BEST1_034.pdf |date=2020-10-21 }}
* [http://resourcecenter.pnl.gov/cocoon/morf/ResourceCenter/article/114 Building Energy Codes Resource Center, 2009: What is the Building Envelope?]
* [http://blog.titanwall.com/2010/12/thermal-performance-of-building-envelopes.html TitanWall Blog, 2010: Thermal Performance of Building Envelopes]
* [http://passivehousebklyn.net/passive-house-bklyn-i/envelope/ Passive House BKLYN, 2010: Energy Revolution in a Brooklyn Townhome – Building Envelope]
* [http://energy.concord.org/energy2d/thermal-bridge.html Online Energy2D simulation of thermal bridge (Java required)]


{{Authority control}}
==References==
;Notes
{{reflist}}


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[[el:Θερμογέφυρα]]
[[es:Puente térmico]]
[[fr:Pont thermique]]
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[[it:Ponte termico]]
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Latest revision as of 23:39, 14 November 2024

Temperature distribution in a thermal bridge
This thermal image shows a thermal bridging of a high-rise building (Aqua in Chicago)

A thermal bridge, also called a cold bridge, heat bridge, or thermal bypass, is an area or component of an object which has higher thermal conductivity than the surrounding materials,[1] creating a path of least resistance for heat transfer.[2] Thermal bridges result in an overall reduction in thermal resistance of the object. The term is frequently discussed in the context of a building's thermal envelope where thermal bridges result in heat transfer into or out of conditioned space.

Thermal bridges in buildings may impact the amount of energy required to heat and cool a space, cause condensation (moisture) within the building envelope,[3] and result in thermal discomfort. In colder climates (such as the United Kingdom), thermal heat bridges can result in additional heat losses and require additional energy to mitigate.

There are strategies to reduce or prevent thermal bridging, such as limiting the number of building members that span from unconditioned to conditioned space and applying continuous insulation materials to create thermal breaks.

Concept

[edit]
Thermal bridge at junction. Heat moves from the floor structure through the wall because there is no thermal break.

Heat transfer occurs through three mechanisms: convection, radiation, and conduction.[4] A thermal bridge is an example of heat transfer through conduction. The rate of heat transfer depends on the thermal conductivity of the material and the temperature difference experienced on either side of the thermal bridge. When a temperature difference is present, heat flow will follow the path of least resistance through the material with the highest thermal conductivity and lowest thermal resistance; this path is a thermal bridge.[5] Thermal bridging describes a situation in a building where there is a direct connection between the outside and inside through one or more elements that possess a higher thermal conductivity than the rest of the envelope of the building.

Identifying Thermal Bridges

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Surveying buildings for thermal bridges is performed using passive infrared thermography (IRT) according to the International Organization for Standardization (ISO). Infrared Thermography of buildings can allow thermal signatures that indicate heat leaks. IRT detects thermal abnormalities that are linked to the movement of fluids through building elements, highlighting the variations in the thermal properties of the materials that correspondingly cause a major change in temperature. The drop shadow effect, a situation in which the surrounding environment casts a shadow on the facade of the building, can lead to potential accuracy issues of measurements through inconsistent facade sun exposure. An alternative analysis method, Iterative Filtering (IF), can be used to solve this problem.

In all thermographic building inspections, the thermal image interpretation if performed by a human operator, involving a high level of subjectivity and expertise of the operator. Automated analysis approaches, such as Laser scanning technologies can provide thermal imaging on 3 dimensional CAD model surfaces and metric information to thermographic analyses.[6] Surface temperature data in 3D models can identify and measure thermal irregularities of thermal bridges and insulation leaks. Thermal imaging can also be acquired through the use of unmanned aerial vehicles (UAV), fusing thermal data from multiple cameras and platforms. The UAV uses an infrared camera to generate a thermal field image of recorded temperature values, where every pixel represents radiative energy emitted by the surface of the building.[7]

Thermal Bridging in Construction

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Frequently, thermal bridging is used in reference to a building’s thermal envelope, which is a layer of the building enclosure system that resists heat flow between the interior conditioned environment and the exterior unconditioned environment. Heat will transfer through a building’s thermal envelope at different rates depending on the materials present throughout the envelope. Heat transfer will be greater at thermal bridge locations than where insulation exists because there is less thermal resistance.[8] In the winter, when exterior temperature is typically lower than interior temperature, heat flows outward and will flow at greater rates through thermal bridges. At a thermal bridge location, the surface temperature on the inside of the building envelope will be lower than the surrounding area. In the summer, when the exterior temperature is typically higher than the interior temperature, heat flows inward, and at greater rates through thermal bridges.[9] This causes winter heat losses and summer heat gains for conditioned spaces in buildings.[10]

Despite insulation requirements specified by various national regulations, thermal bridging in a building's envelope remain a weak spot in the construction industry. Moreover, in many countries building design practices implement partial insulation measurements foreseen by regulations.[11] As a result, thermal losses are greater in practice that is anticipated during the design stage.

An assembly such as an exterior wall or insulated ceiling is generally classified by a U-factor, in W/m2·K, that reflects the overall rate of heat transfer per unit area for all the materials within an assembly, not just the insulation layer. Heat transfer via thermal bridges reduces the overall thermal resistance of an assembly, resulting in an increased U-factor.[12]

Thermal bridges can occur at several locations within a building envelope; most commonly, they occur at junctions between two or more building elements. Common locations include:

  • Floor-to-wall or balcony-to-wall junctions, including slab-on-grade and concrete balconies or outdoor patios that extend the floor slab through the building envelope
  • Roof/Ceiling-to-wall junctions, especially where full ceiling insulation depths may not be achieved
  • Window-to-wall junctions[13]
  • Door-to-wall junctions[13]
  • Wall-to-wall junctions[13]
  • Wood, steel or concrete members, such as studs and joists, incorporated in exterior wall, ceiling, or roof construction[14]
  • Recessed luminaries that penetrate insulated ceilings
  • Windows and doors, especially frames components
  • Areas with gaps in or poorly installed insulation
  • Metal ties in masonry cavity walls[14]

Structural elements remain a weak point in construction, commonly leading to thermal bridges that result in high heat loss and low surface temperatures in a room.

Masonry Buildings

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While thermal bridges exist in various types of building enclosures, masonry walls experience significantly increased U-factors caused by thermal bridges. Comparing thermal conductivities between different building materials allows for assessment of performance relative to other design options. Brick materials, which are usually used for facade enclosures, typically have higher thermal conductivities than timber, depending on the brick density and wood type.[15] Concrete, which may be used for floors and edge beams in masonry buildings are common thermal bridges, especially at the corners. Depending on the physical makeup of the concrete, the thermal conductivity can be greater than that of brick materials.[15] In addition to heat transfer, if the indoor environment is not adequately vented, thermal bridging may cause the brick material to absorb rainwater and humidity into the wall, which can result in mold growth and deterioration of building envelope material.

Curtain Wall

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Similar to masonry walls, curtain walls can experience significantly increased U-factors due to thermal bridging. Curtain wall frames are often constructed with highly conductive aluminum, which has a typical thermal conductivity above 200 W/m·K. In comparison, wood framing members are typically between 0.68 and 1.25 W/m·K.[15] The aluminum frame for most curtain wall constructions extends from the exterior of the building through to the interior, creating thermal bridges.[16]

Impacts of Thermal Bridging

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Thermal bridging can result in increased energy required to heat or cool a conditioned space due to winter heat loss and summer heat gain. At interior locations near thermal bridges, occupants may experience thermal discomfort due to the difference in temperature.[17] Additionally, when the temperature difference between indoor and outdoor space is large and there is warm and humid air indoors, such as the conditions experienced in the winter, there is a risk of condensation in the building envelope due to the cooler temperature on the interior surface at thermal bridge locations.[17] Condensation can ultimately result in mold growth with consequent poor indoor air quality and insulation degradation, reducing the insulation performance and causing insulation to perform inconsistently throughout the thermal envelope[18]

Design Methods to Reduce Thermal Bridges

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There are several methods that have been proven to reduce or eliminate thermal bridging depending on the cause, location, and the construction type. The objective of these methods is to either create a thermal break where a building component would span from exterior to interior otherwise, or to reduce the number of building components spanning from exterior to interior. These strategies include:

  • A continuous thermal insulation layer in the thermal envelope, such as with rigid foam board insulation[5]
  • Lapping of insulation where direct continuity is not possible
  • Double and staggered wall assemblies[19]
  • Structural Insulated Panels (SIPs) and Insulating Concrete Forms (ICFs)[19]
  • Reducing framing factor by eliminating unnecessary framing members, such as implemented with advanced framing[19]
  • Raised heel trusses at wall-to-roof junctions to increase insulation depth
  • Quality insulation installation without voids or compressed insulation
  • Installing double or triple pane windows with gas filler and low-emissivity coating[20]
  • Installing windows with thermally broken frames made of low conductivity material[20]

Analysis Methods and Challenges

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Due to their significant impacts on heat transfer, correctly modeling the impacts of thermal bridges is important to estimate overall energy use. Thermal bridges are characterized by multi-dimensional heat transfer, and therefore they cannot be adequately approximated by steady-state one-dimensional (1D) models of calculation typically used to estimate the thermal performance of buildings in most building energy simulation tools.[21] Steady state heat transfer models are based on simple heat flow where heat is driven by a temperature difference that does not fluctuate over time so that heat flow is always in one direction. This type of 1D model can substantially underestimate heat transfer through the envelope when thermal bridges are present, resulting in lower predicted building energy use.[22]

The currently available solutions are to enable two-dimensional (2D) and three-dimensional (3D) heat transfer capabilities in modeling software or, more commonly, to use a method that translates multi-dimensional heat transfer into an equivalent 1D component to use in building simulation software. This latter method can be accomplished through the equivalent wall method in which a complex dynamic assembly, such as a wall with a thermal bridge, is represented by a 1D multi-layered assembly that has equivalent thermal characteristics.[23]

See also

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References

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  1. ^ Binggeli, C. (2010). Building Systems for Interior Designers. Hoboken, NJ: John Wiley & Sons.
  2. ^ Gorse, Christopher A., and David Johnston (2012). "Thermal bridge", in Oxford Dictionary of Construction, Surveying, and Civil Engineering. 3rd ed. Oxford: Oxford UP, 2012 pp. 440-441. Print.
  3. ^ Arena, Lois (July 2016). "Construction Guidelines for High R-Value Walls without Exterior Rigid Insulation" (PDF). NREL.gov. Golden, CO: National Renewable Energy Laboratory (NREL).
  4. ^ Kaviany, Massoud (2011). Essentials of Heat Transfer: Principles, Materials, and Applications. New York, NY: Cambridge University Press. ISBN 978-1107012400.
  5. ^ a b "Definition and effects of thermal bridges [ ]". passipedia.org. Retrieved 2017-11-05.
  6. ^ Previtali, Mattia; Barazzetti, Luigi; Roncoroni, Fabio (24–27 June 2013). "Spatial Data Management for Energy Efficient Envelope Retrofitting". Computational Science and Its Applications – ICCSA 2013. Lecture Notes in Computer Science. Vol. 7971. pp. 608–621. doi:10.1007/978-3-642-39637-3_48. ISBN 978-3-642-39636-6.
  7. ^ Garrido, I.; Lagüela, S.; Arias, P.; Balado, J. (1 January 2018). "Thermal-based analysis for the automatic detection and characterization of thermal bridges in buildings". Energy and Buildings. 158: 1358–1367. doi:10.1016/j.enbuild.2017.11.031. hdl:11093/1459.
  8. ^ "RR-0901: Thermal Metrics for High-Performance Walls—The Limitations of R-Value". Building Science Corporation. Retrieved 2017-11-19.
  9. ^ Grondzik, Walter; Kwok, Alison (2014). Mechanical and Electrical Equipment for Buildings. John Wiley & Sons. ISBN 978-0470195659.
  10. ^ Larbi, A. Ben (2005). "Statistical modelling of heat transfer for thermal bridges of buildings". Energy and Buildings. 37 (9): 945–951. doi:10.1016/j.enbuild.2004.12.013.
  11. ^ THEODOSIOU, T. G, and A. M PAPADOPOULOS. 2008. “The Impact of Thermal Bridges on the Energy Demand of Buildings with Double Brick Wall Constructions.” Energy and Buildings, no. 11: 2083.
  12. ^ Kossecka, E.; Kosny, J. (2016-09-16). "Equivalent Wall as a Dynamic Model of a Complex Thermal Structure". Journal of Thermal Insulation and Building Envelopes. 20 (3): 249–268. doi:10.1177/109719639702000306. S2CID 108777777.
  13. ^ a b c Christian, Jeffery; Kosny, Jan (December 1995). "Toward a National Opaque Wall Rating Label". Proceedings Thermal Performance of the Exterior Envelopes VI, ASHRAE.
  14. ^ a b Allen, E. and J. Lano, Fundamentals of Building Construction: materials and methods. Hoboken, NJ: John Wiley & Sons. 2009.
  15. ^ a b c American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc. (ASHRAE) (2017). 2017 ASHRAE Handbook: Fundamentals. Atlanta, GA: ASHRAE. ISBN 978-1939200570.{{cite book}}: CS1 maint: multiple names: authors list (link)
  16. ^ Totten, Paul E.; O’Brien, Sean M. (2008). "The Effects of Thermal Bridging at Interface Conditions". Building Enclosure Science & Technology.
  17. ^ a b Ge, Hua; McClung, Victoria Ruth; Zhang, Shenshu (2013). "Impact of balcony thermal bridges on the overall thermal performance of multi-unit residential buildings: A case study". Energy and Buildings. 60: 163–173. doi:10.1016/j.enbuild.2013.01.004.
  18. ^ Matilainen, Miimu; Jarek, Kurnitski (2002). "Moisture conditions in highly insulated outdoor ventilated crawl spaces in cold climates". Energy and Buildings. 35 (2): 175–187. doi:10.1016/S0378-7788(02)00029-4.
  19. ^ a b c California Energy Commission (CEC) (2015). Residential Compliance Manual for the 2016 Building Energy Efficiency Standards. California Energy Commission.
  20. ^ a b Gustavsen, Arild; Grynning, Steinar; Arasteh, Dariush; Jelle, Bjørn Petter; Goudey, Howdy (2011). "Key elements of and material performance targets for highly insulating window frames". Energy and Buildings. 43 (10): 2583–2594. doi:10.1016/j.enbuild.2011.05.010. OSTI 1051278. S2CID 72987269.
  21. ^ Martin, K.; Erkoreka, A.; Flores, I.; Odriozola, M.; Sala, J.M. (2011). "Problems in the calculation of thermal bridges in dynamic conditions". Energy and Buildings. 43 (2–3): 529–535. doi:10.1016/j.enbuild.2010.10.018.
  22. ^ Mao, Guofeng; Johanneson, Gudni (1997). "Dynamic Calculation of Thermal Bridges". Energy and Buildings. 26 (3): 233–240. doi:10.1016/s0378-7788(97)00005-4.
  23. ^ Kossecka, E.; Kosny, J. (January 1997). "Equivalent Wall as a Dynamic Model of a Complex Thermal Structure". J. Therm. Insul. Build. Envelopes. 20 (3): 249–268. doi:10.1177/109719639702000306. S2CID 108777777.
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