ISO 13256-1:2021

Overview - ISO 13256-1:2021 (water-source heat pumps)

ISO 13256-1:2021 defines standardized testing and rating methods for water-to-air and brine-to-air heat pumps. It applies to factory-made, electrically driven, mechanical‑compression heat pumps used in residential, commercial, and industrial HVAC systems. The standard is based on testing matched assemblies and establishes uniform conditions and procedures to determine cooling and heating performance, power inputs and published ratings.

Key topics and technical requirements

• Scope and applicability
  • Covers water‑to‑air and brine‑to‑air (refrigerant-to-water/brine) heat pumps; excludes individual assemblies and equipment covered by ISO 5151, ISO 13253 or ISO 13256‑2.
  • Notes that equipment rated for one liquid temperature range may not be suitable across all source temperature ranges.
• Rating and test conditions
  • Defines rating conditions for net capacities, fan and pump power inputs, airflow and liquid flow rates, and test liquids.
  • Introduces High/Medium/Low source temperature ranges to support broader operating maps and interpolation for energy modelling.
• Performance requirements and tests
  • Specifies maximum/minimum operating condition tests, enclosure condensate/sweat tests, and steady‑state cooling/heating capacity tests.
  • Harmonized measurement uncertainties and tolerances aligned with modern ISO testing practice.
• Test methods and data
  • Procedures for equipment installation, reconditioning, data collection, and calculation of net cooling/heating capacity.
  • Annexes provide methods for airflow measurement, indoor/ refrigerant/liquid enthalpy tests, condensate measurements and corrections for fan/pump power.
• Marking and publication
  • Nameplate and published rating requirements so manufacturers can communicate certified performance.

Practical applications and who uses this standard

• Manufacturers - to develop, test and publish certified performance data for water‑source heat pumps and for product development across source temperature ranges.
• Independent test laboratories - to perform repeatable, ISO‑compliant HVAC performance testing.
• HVAC designers and specifiers - to compare product performance, select equipment for systems using groundwater, looped water or antifreeze/brine sources, and for accurate energy modelling.
• Regulatory bodies, procurement and certification schemes - to verify claims, support efficiency labeling, and ensure consistent test reporting.
• Energy modelers - use the High/Medium/Low ratings to interpolate performance for building simulation.

Related standards

• ISO 13256 series (other parts)
• ISO 13256-2 (other heat pump types)
• ISO 5151, ISO 13253 (air conditioners and other heat pumps)
• ISO 817 (refrigerant designation and safety)

Keywords: ISO 13256-1, water-source heat pumps, water-to-air heat pump testing, brine-to-air, heat pump performance rating, HVAC testing standard.