European Standards on Thermal Heat Bridges

The European standards "Thermal Bridges in building construction Heat flows and surface temperatures - Part 1: General calculation methods" (EN ISO 10211-1) pertaining to aspects of thermal performance of building constructions are already available since 1996. The EN ISO 10211:2007 "Thermal bridges in building construction — Heat flows and surface temperatures — Detailed calculations" shows further development of the standardisation. The standard EN ISO 6946 "Building Components or Building Elements - Calculation of Thermal Transmittance" is also available. The EN ISO 10077-2:2003 "Thermal performance of windows, doors and shutters - Calculation of thermal transmittance - Part 2: Numerical method for frames" shall be also considered.

The ramifications of the adoption of these European Standards became apparent: they describe the substance of essential tasks for designers, manufacturers, and builders, as well as their significance for quality control in the field of energy conservation.

The purpose of the standard EN ISO 10211 "Thermal Bridges - Calculation of Surface Temperatures and Heat flows" is explicitly stated as:

• the calculation of minimum (lowest) surface temperatures in order to assess the risk of surface condensation
  and
• the calculation of heat flows in order to predict overall heat loss from a building (for the constant, steady state flow case; i.e. time independent temperature distribution)
  and
• determination of linear and point thermal transmittance and surface temperature coefficients (of thermal bridges).

Furthermore, "high precision methods" of calculation are demanded, whereby precision criteria which must be satisfied by the method chosen are defined in the standard.

According to EN ISO 6946 "Building Components or Building Elements - Calculation of Thermal Transmittance", calculation of heat transfer coefficients of parallel plane surface building components shall be performed based, of course, on one-dimensional models. For such components, composed of surface parallel layers of thermally homogeneous or non-homogeneous materials, a well-known method of estimation (ISO-method) can be implemented in order to obtain a design thermal resistance - assuming the maximum relative error remains "negligible".

For all other heat flow patterns, i.e. for all cases of more than one dimension, in particular in the presence of thermal bridges, the standard EN ISO 10211 "Thermal Heat Bridges" requires the implementation of numerical methods of evaluation.

Further standards to be considered (exemplary):

• ISO 7345 "Thermal insulation - Physical quantities and definitions"
• ISO 10456 "Building materials and products - Hygrothermal properties - Tabulated design values and procedures for determining declared and design thermal values"
• ISO 13370 "Thermal performance of buildings - Heat transfer via the ground - Calculation methods"
• ISO 13786 "Thermal performance of building components - Dynamic thermal characteristics - Calculation methods"
• ISO 13788 "Hygrothermal performance of building components and building elements - Internal surface temperature to avoid critical surface humidity interstitial condensation - Calculation methods"
• ISO 13789 "Thermal performance of buildings - Transmission and ventilation heat transfer coefficient - Calculation method"
• ISO 14683 "Thermal bridges in building construction - Linear thermal transmittance - Simplified methods and default values"
• etc.

A calculation program as instrument

In order to perform tasks imposed by European regulations in practice, the qualified planner, designer, or expert needs a calculation program which:

• meets the demands of the European Standards with respect to input data and more importantly output data requirements (evaluation results),
• is capable of executing calculation with high precision,
• and is sufficiently convenient to the user in application (providing ease and clarity of operation, as well as speed).

AnTherm® possesses these instrumental characteristics

• AnTherm facilitates the generation of geometrical models by supporting a graphic input display of building structures, as well as by providing an entirely independent, fully automatic method of fine subdivision (which can also be influenced by the user through manual manipulation of parameters).
• It delivers complete input model documentation (geometry of material elements, thermal design values of materials, spaces, heat sources...) upon request.
• It allows the precision of numerical solutions to be influenced and controlled by the user (definition of calculation parameters).
• AnTherm provides results conformant to European standards:
  • generally applicable results in the form of g-values and conductance matrices. These conform to the temperature weighting factors and "thermal coupling coefficients" defined in the European Standards, including the required information on calculation precision,
  • specific results, applicable to particular air temperature conditions in spaces thermally coupled by the building components analyzed, in the form of surface temperature minima and maxima as well as respective dewpoints,
• It creates graphic plots and prints of isotherms, surface temperatures or temperatures along an edge (2- or 3-dim. models), as well as heat flow diagrams (not limited to 2-dim. models only, but also in 3D).
• AnTherm meets all demands of the European Standards with respect to input data and - more importantly - output data requirements (evaluation results) - validated according to EN ISO 10211: AnTherm has been qualified as a "Class A" tool – as for two- and three-dimensional, stationary precision method.

See also: Validation according to EN ISO 10211:2007, Validation according to EN ISO 10077-2:2003, Structure of the application