Overview
ISO 13789:2017 - "Thermal performance of buildings - Transmission and ventilation heat transfer coefficients - Calculation method" specifies a clear, steady‑state calculation method and conventions for determining the transmission and ventilation heat transfer coefficients of whole buildings and parts of buildings. Applicable to both heat loss and heat gain situations, the standard assumes a uniform internal (conditioned) temperature and provides templates and default choices to ensure consistent use across energy performance of buildings (EPB) assessments.
Key technical topics and requirements
- Scope and assumptions: Steady‑state approach; heated/cooled space considered at uniform temperature; applicable to heat loss and heat gain.
- Transmission heat transfer coefficient: Method to compute heat transfer through the building fabric, including the mean thermal transmittance of elements and direct transmission between internal and external environments.
- Ventilation heat transfer coefficient: Procedures to quantify heat transfer via air change and infiltration.
- Ground and adjacent-space effects: Conventions for transmission through the ground and heat transfer to/from unconditioned spaces and adjacent buildings; Annex C provides a steady‑state method to estimate temperatures in unconditioned spaces.
- Input, measurement and boundaries: Requirements for input data, measurement of geometry and defining conditioned‑space boundaries.
- Calculation intervals and conventions: Guidance on time intervals, conventional surface heat transfer coefficients, variable U‑values and air‑change rates for unconditioned spaces.
- Reporting and templates: Annex A (normative) and Annex B (informative) provide input/data‑sheet templates and default choices to support transparent, reproducible calculations.
- Compatibility with EPB modular structure: Positioned within EPB standards (see ISO 52000‑1) to feed into broader energy performance workflows.
Practical applications and intended users
- Applications
- Input data generation for annual energy use and heating/cooling load calculations.
- Expressing or verifying building transmission and ventilation characteristics for compliance and specification.
- Comparative assessments across building stocks and retrofit scenario analysis.
- Who uses ISO 13789:2017
- Architects, building services and energy engineers
- Energy assessors and building simulation specialists
- Regulators and certification bodies implementing national/regional EPB requirements
- Consultants and researchers analyzing thermal performance and retrofit measures
Related standards and context
- Part of the EPB family; aligns with ISO 52000‑1 modular structure and other ISO/TC 163 documents.
- Works alongside standards for dynamic energy calculations and component U‑value methods; Annex templates support national or regional adaptations (national annex/data sheets).
Using ISO 13789:2017 ensures consistent, transparent steady‑state derivation of transmission and ventilation heat transfer coefficients - a fundamental input for building energy performance assessment, compliance and design optimization.
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