Overview
EN ISO 11855-2:2021 - Building environment design: Embedded radiant heating and cooling systems - Part 2 - specifies methods to determine the design heating and cooling capacity of water‑based surface (embedded) radiant systems. The standard defines procedures and calculation conditions so designers and manufacturers can determine heat flux as a function of the medium differential temperature, using either general numerical methods or simplified approaches. Results include surface temperature, temperature uniformity, nominal heat flux, nominal medium differential temperature, and characteristic curves relating heat flux to governing variables.
Key technical topics and requirements
- Scope limited to water‑based embedded surface heating and cooling systems; covers calculation methods (not physical testing).
- Provides a general method based on numerical modelling - finite element method (FEM) or finite difference method (FDM) - for detailed steady‑state analysis.
- Offers simplified calculation methods for common pipe positions and building structure types to support practical design workflows.
- Requires calculation outputs that include:
- Surface temperature and its uniformity across the heated/cooled surface
- Nominal heat flux between water and occupied space
- Associated nominal medium differential temperature
- Characteristic curves showing heat flux vs. determining variables
- Normative and informative annexes support practical implementation:
- Annex A: Calculation of heat flux (normative)
- Annex B: General resistance method (informative)
- Annex C: Pipes in wooden construction (informative)
- Annex D: Verification method for FEM/FDM programs (normative)
- Annex E: Typical thermal conductivity values (normative)
- Annex F: Maximal surface temperatures for floor heating (informative)
- References ISO 11855‑1 for definitions, symbols and comfort criteria.
Practical applications and users
Who uses ISO 11855‑2:2021?
- HVAC and building services engineers performing steady‑state sizing and verification of embedded radiant systems (e.g., radiant floors, walls, ceilings)
- Building designers and consultants specifying system performance and compliance
- Manufacturers developing radiant panels, tubing layouts and technical data
- Energy modelers and simulation specialists integrating detailed heat‑flux data into building performance models
- Regulatory bodies and certification organizations assessing conformity by calculation
Typical applications:
- Determining design heating or cooling capacity for tender documents and technical specifications
- Producing heat flux vs. medium temperature characteristic curves for system selection
- Verifying performance of pipe layouts and structural assemblies (concrete, timber, composite)
- Supplying documented calculation output for compliance and commissioning
Related standards
- ISO 11855‑1: Definitions, symbols and comfort criteria
- ISO 11855‑3 to ISO 11855‑7: Design & dimensioning, TABS dynamic calculation, installation, control, and input parameters for energy calculation
Keywords: embedded radiant heating and cooling systems, water-based surface heating and cooling, ISO 11855-2:2021, design heating and cooling capacity, heat flux, surface temperature, FEM, FDM, HVAC design.