Overview
ISO 21978:2023 - "Air to water heat pumps - Testing and rating at part load conditions and calculation of seasonal coefficient of performance for space heating" - defines test conditions and calculation methods to determine the seasonal performance of electrically driven air-to-water heat pumps used for space heating. The standard covers packaged units (single-supply assemblies) and addresses part‑load behaviour, auxiliary energy uses (standby, crankcase heater, thermostat-off), and the calculation of seasonal coefficient of performance (S COP).
Key topics and technical requirements
- Part‑load testing and rating: Procedures for setting capacity ratios, external static pressure for ducted units, and tests for fixed, staged and variable‑capacity units.
- Design conditions and temperature applications: Specifies three design climate conditions (average, colder, warmer) and three water/brine outlet regimes - 35 °C, 45 °C and 55 °C temperature applications - that define representative operating points.
- Measurement and installation: Requirements for test apparatus, uncertainties of measurement, test room for the airside, installation of multi‑part heat pump systems and indoor unit environment and electrical supply.
- Heating capacity and power input: Methods for heating capacity testing (steady and transient), capacity corrections (including indoor pump effects), and effective power input calculations.
- Part‑load performance modelling: Determination of degradation coefficients (C values) across part‑load conditions A–G and procedures to derive S COP from bin‑hour or season definitions.
- Energy in non‑active modes: Test methods and uncertainty considerations for standby, thermostat‑off, crankcase heater and off modes.
- Reporting and marking: Required test report data, nameplate information and marking provisions. Annexes provide normative test procedures, pump efficiency determination and worked examples.
Applications and who should use this standard
ISO 21978:2023 is intended for:
- Heat pump manufacturers - to validate and declare seasonal COP and part‑load performance for product datasheets and regulatory compliance.
- Independent testing laboratories - to perform standardized part‑load tests and generate compliant test reports.
- HVAC designers and system integrators - to compare equipment performance across climates and temperature regimes for system design and selection.
- Energy assessors, certifiers and policymakers - to ensure consistent rating methods when evaluating building heating performance, incentives or efficiency regulations.
Related standards (brief)
- ISO/IEC Directives for editorial rules and general standardization practices.
- Other ISO/IEC or regional test standards for heat pumps and HVAC testing may complement ISO 21978:2023 for full product compliance and labeling.
Keywords: ISO 21978:2023, air to water heat pumps, part load testing, seasonal coefficient of performance, S COP, space heating, COP, temperature application, HVAC testing.