ISO 11855-4:2021

Overview

ISO 11855-4:2021 - "Building environment design - Embedded radiant heating and cooling systems - Part 4" - specifies methods to dimension and calculate the dynamic heating and cooling capacity of Thermo Active Building Systems (TABS). The standard enables calculation of peak cooling capacity for TABS (Type V per ISO 11855-1) under non‑steady state conditions and defines how to compute the cooling power demand on the water side for equipment sizing (e.g., chiller size, fluid flow rate).

Key input factors covered include solar gains, internal heat gains, ventilation and transmission; the document also provides guidance for computer simulation inputs and discusses influences such as acoustic ceiling units.

Key technical topics and requirements

• Scope: Dimensioning of TABS cooling capacity in dynamic (time-varying) conditions.
• Calculation targets: Peak cooling capacity, hourly cooling power extracted by embedded circuits, and water‑side cooling demand for hydraulic/equipment sizing.
• Methods and analysis included:
  • General dynamic calculation framework for TABS
  • Rough sizing method and simplified sizing by diagrams
  • Simplified model based on FDM (finite-difference approach) for slab, hydraulic circuit and room interaction
  • Use of dynamic building simulation programs and required input parameters
• Annexes and normative material:
  • Normative calculation method (Annex B)
  • Informative simplified diagrams, tutorial guide, and example computer program
• Considerations: view factors, convective and radiant heat transfer coefficients, thermal nodes for slab/room, safety factors, and limits of simplified methods.

Practical applications and who uses it

ISO 11855-4 is essential for professionals involved in the design, sizing and performance analysis of embedded radiant systems:

• HVAC engineers and system designers sizing TABS and chilled‑water plants
• Energy modelers and simulation specialists performing dynamic thermal analysis
• Architects and building services consultants integrating low‑exergy radiant solutions
• Mechanical equipment suppliers and chiller manufacturers validating water‑side loads
• Building owners and sustainability consultants assessing energy‑efficient cooling strategies

Practical uses include sizing chillers and pumps, defining pipe layout and flow rates, estimating hourly cooling loads for control strategies, and ensuring comfort criteria in conjunction with ISO 11855-1.

Related standards

• ISO 11855-1 - Definitions, symbols and comfort criteria (referenced for Type V TABS)
• ISO 11855-2 - Steady‑state determination of design heating and cooling capacity

ISO 11855-4:2021 supports accurate, dynamic sizing of embedded radiant cooling (TABS), enabling energy-efficient design and reliable equipment selection for modern low‑exergy building systems.