Overview
EN ISO 11855-1:2021 / ISO 11855-1:2021 establishes the basic definitions, symbols and comfort criteria for embedded radiant heating and cooling systems used in building environment design. Adopted by CEN as EN ISO 11855-1:2021 (superseding the 2015 edition), this part of the ISO 11855 series frames the terminology and thermal comfort parameters that designers, specifiers and regulators rely on when working with embedded radiant systems, including Thermo Active Building Systems (TABS).
Key Topics
- Terms and definitions for embedded radiant heating and cooling systems (e.g., additional thermal resistance, average surface temperature, circuit).
- Symbols and abbreviated terms used consistently across the ISO 11855 series to support clear technical communication.
- General thermal comfort metrics: operative temperature, PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied).
- Local thermal discomfort considerations: surface temperature limits, radiant temperature asymmetry, vertical air temperature difference.
- Acoustical comfort criteria relevant to water-based embedded systems including noise related to water velocity and TABS operation.
- Informative annexes covering floor surface temperature for thermal comfort and draught guidance.
- Normative relationships to other parts of the ISO 11855 series (design, dimensioning, installation, control, dynamic analysis, and energy input parameters).
Applications
EN ISO 11855-1:2021 is practical for professionals involved in the design, specification and operation of building HVAC and radiant systems:
- HVAC engineers & mechanical designers: use the defined comfort criteria to size embedded radiant floors, walls or ceilings and to align system outputs with occupant comfort targets.
- Architects & building designers: integrate surface temperature and radiant asymmetry limits into architectural detailing and material selection.
- Energy modellers & simulation specialists: apply the standard’s operative temperature and comfort definitions when running steady-state and dynamic thermal analyses (linked to other ISO 11855 parts).
- Installers & manufacturers: refer to standardized symbols and terms for clear installation instructions and product information.
- Facility managers & spec writers: specify comfort thresholds and acoustical limits for procurement and commissioning.
Related Standards
- ISO 11855 series (Parts 2–7): determination of capacity, design & dimensioning, TABS dynamic calculation, installation, control, and input parameters for energy calculation.
- ISO 11855-5:2021 (installation) and ISO 52031 (energy calculation inputs) are specifically referenced within the series.
This standard is essential for consistent, interoperable practice in embedded radiant heating and cooling design, ensuring thermal and acoustical comfort criteria are clearly defined and consistently applied across projects.