Overview
EN ISO 11855-4:2021/A1:2023 is Amendment 1 to ISO 11855‑4 (published as a CEN/ISO European Standard). It focuses on the dimensioning and calculation of the dynamic heating and cooling capacity of Thermo Active Building Systems (TABS) - Type V. The amendment updates the introduction, key clauses and figures, and clarifies methods for calculating peak cooling capacity and the water‑side cooling power required to size cooling plant and fluid circuits.
Key keywords: EN ISO 11855-4:2021/A1:2023, Thermo Active Building Systems, TABS, embedded radiant heating and cooling systems, dynamic heating and cooling capacity, dimensioning, peak cooling capacity.
Key topics and technical requirements
- Scope for Type V TABS: Methods to calculate peak cooling capacity based on heat gains (solar, internal, ventilation) and to determine cooling power demand on the water side for equipment sizing (e.g., chiller capacity, flow rate).
- Dynamic calculation approach: Emphasis on time‑dependent (dynamic) performance rather than only steady‑state results, enabling peak‑shaving and system interaction assessment.
- Equivalent resistances for simulation: Clause 8 was revised to provide methods for deriving equivalent thermal resistances between the pipe level (heat conduction layer) and upward/downward surfaces to support dynamic building simulations.
- Calculation clarification: For certain system types, equivalent inward and outward resistances are calculated directly; for others they are derived from inward/outward specific heat flux and total surface heat transfer coefficient (convection + radiation).
- Included formula: The amendment retains the equivalent resistance relationship in the form:
R = Δθ / q_t − 1 / h
where Δθ is the medium temperature difference, q_t the specific heat flux, and h the total heat transfer coefficient (convection + radiation).
- Updated figures and diagrams: Figures showing pipe positions, simple TABS schematics, peak‑shaving examples and temperature/PMV profiles were revised for clarity.
Practical applications and target users
- Who uses this standard
- HVAC and MEP engineers designing slab‑integrated radiant systems (TABS)
- Building energy modelers and simulation specialists
- System integrators sizing chillers, pumps and control loops
- Architects and consultants specifying low‑energy building services
- Manufacturers of radiant piping and hydronic equipment
- Where it applies
- Sizing of TABS for commercial, institutional and residential buildings
- Dynamic simulation workflows for energy‑efficient designs and peak load reduction
- Determining water‑side cooling requirements and chiller selection
- Integrating renewable low‑temperature heat/cold sources with building mass
Related standards
- ISO 11855‑1 (comfort criteria, system types)
- ISO 11855‑2, ‑3, ‑5, ‑6, ‑7 (steady‑state methods, design/dimensioning, installation, control, input parameters for ISO 52031)
This amendment ensures clearer, harmonized calculation and simulation inputs for designers implementing energy‑efficient TABS solutions.
