ISO 13256-2:2021

Overview

ISO 13256-2:2021 - "Water‑source heat pumps - Testing and rating for performance - Part 2: Water‑to‑water and brine‑to‑water heat pumps" establishes standardized testing and rating procedures for factory‑made, electrically driven mechanical‑compression water‑to‑water and brine‑to‑water heat pumps. Applicable to residential, commercial and industrial equipment, this ISO standard is based on testing matched assemblies and defines how to determine cooling and heating capacities, performance ratings, and related measurement requirements.

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Key topics and technical requirements

• Scope and applicability: Covers factory-made water‑to‑water and brine‑to‑water units (including water‑loop, ground‑water and ground‑loop systems) and excludes units covered by ISO 5151, ISO 13253 and ISO 13256‑1.
• Rating and test conditions: Defines rating points, liquid flow rates, source/load temperature ranges (High/Medium/Low), test liquids and pump adjustments for accurate net capacity determination.
• Performance requirements: Specifies procedures and pass/fail criteria for maximum and minimum operating condition tests, and enclosure sweat/condensate behavior.
• Test methods and data handling: Detailed test setup, reconditioning and data collection periods, net cooling/heating capacity calculation, measurement uncertainties and permitted deviations.
• Marking and publication: Nameplate information, designation of standard ratings and refrigerant identification, plus provisions for publishing official ratings.
• Annexes: Includes refrigerant and liquid enthalpy test methods (Annex A and B) and guidance for legacy rating conversions (informative Annex C).
• Notable updates (2021 edition): Transition to High/Medium/Low source temperature ranges for broader modeling, allowance for multiple heating ratings (Very High to Low), harmonized tolerances, and removal of prescriptive antifreeze composition requirements.

Practical applications and users

ISO 13256-2:2021 is used by:

• Heat pump manufacturers for type testing, product development and labeling.
• Independent test laboratories to run repeatable, comparable performance tests.
• HVAC designers and consultants for accurate equipment selection and system performance modeling.
• Energy modelers and building certifiers who require standardized performance inputs.
• Procurement teams and regulators specifying minimum performance and compliance.

Practical benefits include consistent capacity data for energy modeling, reliable comparisons between products, and standardized reporting for certification and procurement.

Related standards

• ISO 13256‑1 (air‑to‑water heat pumps)
• ISO 5151, ISO 13253 (other HVAC testing and rating standards)
• ISO 817 (refrigerant designation and safety classification)

For manufacturers and specifiers working with water‑source heat pumps, ISO 13256‑2:2021 provides the authoritative methodology to ensure reliable, comparable performance data.