SIST EN ISO 24664:2025 PDF

Overview

EN ISO 24664:2024 (ISO 24664:2024) is a CEN-endorsed international standard that provides methods for the calculation and sizing of pressure relief devices and their associated piping in refrigerating systems and heat pumps. The standard covers calculation of mass flow rates, discharge capacities for pressure relief valves and other devices (including bursting discs), and pressure losses in inlet and outlet lines. Its scope includes relieving to atmosphere or to a lower-pressure part of the refrigerating system and addresses causes of excessive pressure such as internal and external heat loads, compressor effects and thermal expansion of trapped liquid.

Key topics and requirements

• Sizing of pressure relief devices: Methods to determine the required mass flow and minimum discharge capacity for protecting parts of refrigerating systems.
• Discharge capacities: Criteria and necessary data for sizing pressure relief valves and bursting discs when discharging to atmosphere or to another part of the system.
• Piping pressure losses: Calculation of pressure loss in inlet and outlet lines, total pressure loss and guidance for connection of multiple valve outlets to a common line.
• Sources of overpressure: Identification and treatment of overpressure causes, including external fire/heat, internal heat sources (heaters, compressors), compressor-induced pressure rises and trapped-liquid expansion.
• Annexes supporting calculations:
  • Annex A: values of factors and refrigerant properties
  • Annex B: flow-area calculations for flashing and non‑flashing liquids
  • Annex C: worked example for sizing relief devices and piping
  • Annex D: guidance for outlet lines where velocity may exceed speed of sound

Practical applications

EN ISO 24664:2024 is intended for practical use in the design, safety assessment and compliance activities for refrigeration and heat pump systems. Typical applications include:

• Sizing and selection of pressure relief valves, bursting discs, and associated inlet/outlet piping.
• Engineering design checks to prevent excessive pressure under normal and abnormal heat input scenarios.
• Preparing documentation and calculations required for conformity with pressure equipment and safety regulations.
• Integrating relief device sizing into system design workflows for industrial refrigeration, commercial HVAC and heat-pump installations.

Who should use this standard

• Mechanical and refrigeration engineers designing or verifying refrigeration and heat-pump installations
• Safety and compliance professionals responsible for pressure equipment conformity
• Manufacturers and suppliers of pressure relief devices, valves and bursting discs
• Consultants and certifying bodies assessing system safety and regulatory compliance

Related standards

• ISO 4126-1:2013 / Amd 1:2016 - Safety devices for protection against excessive pressure (safety valves)
• ISO 4126-2:2018 - Bursting disc safety devices
• ISO 21922:2021 - Valves for refrigerating systems and heat pumps
• EN 378-2:2016 and ISO 5149-2:2014 - Refrigeration system safety requirements
• Directive 2014/68/EU - Pressure Equipment Directive (informative relationship in Annex ZA)

Keywords: refrigerating systems, heat pumps, pressure relief devices, pressure relief valves, bursting discs, discharge capacity, pressure loss, sizing, EN ISO 24664:2024, ISO 24664:2024.