ISO 11855-8:2023

Overview

ISO 11855-8:2023 - part of the ISO 11855 series on building environment design - provides standardized calculation procedures for the thermal performance of embedded electrical surface heating systems. The standard specifies how to determine heat flux relative to the medium differential temperature using design documents and a model, producing results such as mean surface temperature, temperature uniformity, and nominal heat flux density. It applies to systems integrated into walls, floors or ceilings (no open air gaps) in residential, commercial and industrial buildings. Note: ISO 11855-8 covers calculation methods (not physical testing).

Key topics and technical requirements

• Scope and applicability
  • Embedded electrical heating systems integrated into building structure (no open gaps).
  • Applicable alongside water-based and other fluid systems where appropriate; not for ceiling panels/beams with open gaps.
• Calculation procedure
  • Stepwise method to compute thermal resistances of covering and internal layers.
  • Determination of part-heat coefficients (κ), mean surface and lamella temperatures, and heat fluxes into adjacent spaces.
  • Use of a lamella (heat-conducting strip) sub-model and handling of air gaps, filling layers and heat-conduction strips.
  • Iterative calculations for surface excess temperatures and heat transfer coefficients.
  • Guidance for non‑circular heating element cross-sections (equivalent diameter conversion).
• Outputs and conformity
  • Surface temperature, temperature uniformity, and heat flux density between the electrical heated layer and space.
  • Uniform assessment method to compare product/system designs to the standard’s calculation model.

Practical applications

• Design and dimensioning of embedded electrical radiant heating systems for new builds and renovations.
• Thermal performance assessment during design reviews to ensure compliance with comfort and energy criteria.
• Specification and product development for manufacturers of embedded electrical heating elements and lamella solutions.
• Energy modelling and building performance assessments where precise surface heat flux inputs are required.

Who should use this standard

• HVAC and building services engineers
• Building designers and architects specifying embedded heating
• Product manufacturers and R&D teams for electrical surface heating
• Energy assessors, consultants and code reviewers
• Specifiers preparing technical design and compliance documentation

Related standards

• ISO 11855 series (Parts 1–7) - definitions, comfort criteria, dimensioning, installation and control methods for embedded radiant systems
• ISO 52000-1 - energy performance of buildings (overarching EPB framework)
• ISO 52031 - system energy requirement calculations (space emission systems)

Keywords: ISO 11855-8:2023, electrical heating systems, embedded radiant heating, heat flux calculation, surface temperature, thermal performance, building environment design, dimensioning, installation, control.