Overview
ISO 22975-2:2016 - Solar energy - Collector components and materials - Part 2: Heat‑pipes for solar thermal application - Durability and performance specifies definitions and standardized test methods to assess the durability and performance of gravity heat‑pipes used in solar thermal collectors. It applies to heat‑pipes for evacuated tubes (including glass‑metal sealed and double‑glass tubes) and to flat‑plate collectors. The standard defines how to test high‑temperature and freeze resistance plus key performance metrics such as starting temperature, temperature uniformity, and heat transfer power.
Key topics and technical requirements
- Scope and applicability
- Only for gravity heat‑pipes (no internal capillary wicks).
- Applicable for evacuated‑tube and flat‑plate solar collectors.
- Durability tests
- High temperature resistance: Samples placed in a heating chamber (test temperatures typically 180 °C, 230 °C or 280 °C ±5 °C depending on application/manufacturer declaration), ramp ≤ 20 K/min, held for 30 h. Inspection for leakage, breakage or deformation after cool‑down.
- Freeze resistance: For heat‑pipes claimed as freeze‑resistant. Freeze at −20 °C ±1 °C for 60 min, then rapid transfer to thawing at 20 °C ±1 °C; specific measurement points and tilt requirements apply.
- Performance tests
- Starting temperature: Minimum temperature at which a heat‑pipe begins to operate.
- Temperature uniformity: Difference between evaporator and condenser during operation.
- Heat transfer power: Thermal power transferred to the cooling liquid; the heat transfer test is performed after the high‑temperature resistance test.
- Test conditions and sampling
- Tests use the same complete heat‑pipe units; a batch of at least 10 samples is required.
- Typical tilt angle specified (e.g., 90° ±1° for many durability tests).
- Instrumentation accuracy requirements and reporting details are specified.
- Normative references
Practical applications - who uses this standard
- Manufacturers of solar heat‑pipes and evacuated tube or flat‑plate collectors - to validate product durability and performance before market release.
- Testing laboratories and certification bodies - to produce consistent, ISO‑aligned test reports (testing per ISO/IEC 17025 recommended).
- System designers and integrators - to select heat‑pipes with verified starting temperatures, uniformity and transfer power for reliable system sizing and performance modeling.
- Procurement and quality assurance teams - to set acceptance criteria and assess supplier claims (e.g., freeze resistance).
Related standards
By following ISO 22975‑2:2016 testing procedures, stakeholders ensure repeatable, comparable assessments of heat‑pipe durability and operational capability - critical for reliable solar thermal system performance and lifetime.