ISO 21773:2021

Overview

ISO 21773:2021 - Methods of test and characterization of performance for energy recovery components - defines standardized laboratory methods to test and characterize air-to-air heat/energy exchangers used in ventilation systems. The standard applies to fixed-plate (recuperators), rotary exchangers (heat wheels / total energy wheels / regenerators) and heat pipe exchangers (excluding mechanically pumped heat-transfer media). ISO 21773:2021 supports reliable performance metrics for product rating and for calculating the energy performance of buildings. It does not cover measurement of exchanger response to frost formation.

Key topics and technical requirements

• Performance metrics: definitions and calculation methods for effectiveness (sensible, latent, total), recovery efficiency ratio (RER), outside air correction factor (OACF), exhaust air transfer ratio (EATR), and energy/ humidity transfer rates.
• Pressure drop: procedures for measured and standardized pressure-drop testing across exchangers.
• Leakage testing: methods to quantify air cross-transfer and leakage that affect indoor air quality and net recovery.
• Test rig and installation: requirements for test apparatus, station locations, static pressure management, and instrument calibration.
• Test procedures: stability limits, data sampling rates, data collection periods, inlet temperature and humidity conditions, and test temperature limits for effectiveness tests.
• Uncertainty and inequality limits: specified limits for uncertainty in effectiveness, pressure drop, RER and leakage tests to ensure repeatable results.
• Reporting: required test result formats and content. Informative annexes include example data collection/calculation, best practices, and expressions for system-level performance calculations.

Practical applications and users

ISO 21773:2021 is intended for:

• HVAC product manufacturers - to test, develop and benchmark energy recovery components.
• Testing and calibration laboratories - to perform accredited, repeatable performance tests (aligned with ISO/IEC 17025).
• Energy modelers and building performance engineers - to obtain reliable exchanger metrics for building energy simulations and compliance calculations.
• Consultants, specifiers and commissioning agents - to select equipment and verify in-situ performance accounting for EATR and OACF.
• Regulators and certification bodies - to define product rating and labeling criteria.

Using ISO 21773:2021 improves comparability of test data, supports accurate building energy calculations, and helps optimize HVAC system efficiency and indoor air quality.

Related standards

• ISO 3966 (flow measurement), ISO 5167-1 (differential pressure flow), ISO 5801 (fan testing), ISO 13253 (ducted air-conditioner testing) and ISO/IEC 17025 (laboratory competence) are normative references cited by ISO 21773:2021.