ISO 11855-1:2021

Overview

ISO 11855-1:2021 - Building environment design - Embedded radiant heating and cooling systems - Part 1: Definitions, symbols, and comfort criteria - provides the foundational terminology, symbols and occupant comfort requirements for the design and assessment of embedded radiant heating and cooling systems. This part of the ISO 11855 series establishes common language and comfort metrics for water‑based (and other fluid or electric) embedded surface systems integrated into floors, walls or ceilings. It does not cover plant equipment or testing methods.

Key topics and technical requirements

• Terms and definitions (Clause 3): Standardized definitions for components and performance parameters such as design heating/cooling capacity, design heat flux, circuit and distributor, circuit thermal resistances, and conductive regions of slabs.
• Symbols and abbreviations (Clause 4): Recommended symbols and abbreviated terms to ensure consistent documentation and calculation across projects.
• Comfort criteria (Clause 5): Requirements and metrics to assess thermal comfort in spaces served by embedded systems, including:
  • General thermal comfort: operative temperature and the use of PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) indices.
  • Local thermal discomfort: surface temperature limits, radiant temperature asymmetry and vertical air temperature differences that affect perceived comfort.
  • Acoustical comfort: guidance on water velocity, noise limits and acoustical considerations for water‑based systems and Thermally Active Building Systems (TABS).
• Informative annexes: additional guidance on floor surface temperatures and draught (air movement) considerations.
• Scope limitations: applies primarily to embedded systems integrated with building structure (not suspended panel systems, heated/chilled ceiling panels or beams) and is not a test standard.

Practical applications

• Use ISO 11855-1 when specifying or documenting embedded radiant heating and cooling systems to ensure consistent terminology and comfort targets across design, calculation and installation stages.
• Apply the comfort criteria during early design, HVAC load calculations, energy modeling and occupant comfort assessments for office buildings, residential projects, educational and healthcare facilities.
• Combine with other parts of the ISO 11855 series to progress from definitions to capacity determination (Part 2), design and dimensioning (Part 3), installation (Part 5), control strategies (Part 6) and energy input parameters (Part 7).

Who should use this standard

• HVAC engineers, building services designers and energy modelers
• Architects and façade/structural engineers coordinating embedded systems in building elements
• Product manufacturers, installers and commissioning teams for TABS and floor/wall/ceiling radiant systems
• Standards writers and compliance officers specifying thermal comfort requirements

Related standards

• ISO 11855 series (Parts 2–7) - for design methods, dynamic analysis, installation and control
• ISO 11855-5:2021 is specifically cited as a normative reference for installation practices

Keywords: ISO 11855-1, embedded radiant heating and cooling systems, radiant heating, radiant cooling, comfort criteria, operative temperature, PMV, PPD, TABS, water‑based systems.