Overview
EN ISO 11855-4:2021 (ISO 11855-4:2021) defines methods for dimensioning and calculating the dynamic heating and cooling capacity of Thermo Active Building Systems (TABS). Published in 2021 and adopted as a European standard (EN ISO 11855-4:2021), this part of the ISO 11855 series focuses on non‑steady state (dynamic) calculation of peak cooling capacity for TABS (Type V per ISO 11855-1) and the associated cooling power demand on the water side used to size chillers, pumps and fluid flow rates.
Key topics and technical requirements
- Scope: Calculation of peak cooling capacity based on heat gains (solar, internal, ventilation) and conversion to water-side cooling power for system sizing.
- Dynamic methods: Detailed procedures for non‑steady state analysis rather than steady‑state approximations.
- Calculation approaches included in the standard:
- Rough sizing methods and simplified sizing by diagrams
- Simplified finite-difference (FDM) based model for slab, hydraulic circuit and room interaction
- Use of dynamic building simulation programs and input requirements for such simulations
- Ancillary considerations: Effects of suspended acoustic ceiling units on TABS cooling performance, and guidance for preparing inputs for computer energy simulations.
- Normative and informative material: The standard contains a normative calculation method plus informative annexes (simplified diagrams, tutorial guide, example computer program) to support implementation.
Practical applications
This standard is a practical tool for professionals designing and specifying embedded radiant heating and cooling systems, particularly TABS. Typical applications:
- Sizing chillers, pumps and piping (chiller capacity, fluid flow rate) for buildings using TABS
- Determining peak cooling loads from dynamic gains (solar, occupants, equipment, ventilation)
- Verifying TABS performance under transient conditions for energy-efficient or low-temperature systems
- Preparing accurate input data for whole‑building energy models that include thermally active building elements
Who should use this standard
- HVAC and building services engineers
- Energy modelers and simulation specialists
- Architects and façade/structural designers integrating TABS
- System manufacturers and installers of embedded radiant systems
- Consultants specifying chillers, hydraulic circuits and control strategies for low‑exergy systems
Related standards
- ISO 11855-1: Definitions, symbols and comfort criteria
- ISO 11855-2: Determination of design heating and cooling capacity (steady‑state)
- ISO 11855-3: Design and dimensioning
- Other parts of ISO 11855 covering installation, control and energy calculation inputs
Keywords: Thermo Active Building Systems, TABS, embedded radiant heating and cooling, ISO 11855-4, dynamic heating and cooling capacity, peak cooling capacity, chiller sizing, non-steady state calculation, building energy simulation.
