Overview
ISO 24664:2024 - Refrigerating systems and heat pumps - Pressure relief devices and their associated piping - Methods for calculation provides standardized calculation methods for sizing and specifying pressure relief devices and their piping in refrigerating systems (the term includes heat pumps). The standard defines how to determine mass flow, discharge capacity and piping pressure losses so that pressure relief valves, bursting discs and associated piping protect equipment against excessive pressure from internal or external heat sources, compressors and thermal expansion of trapped liquid.
Key topics and technical requirements
- Sizing of pressure relief devices
- Calculation of mass flow rates required to size relief devices for parts of a refrigerating system.
- Determination of minimum required discharge capacity for protection against overpressure events.
- Discharge capacity and device types
- Methods to calculate discharge capacities for pressure relief valves and bursting discs, including data for relieving to atmosphere or into a lower-pressure part of the system.
- Piping pressure loss
- Procedures to compute pressure loss in inlet and outlet lines, and guidance for connecting multiple relief outlets to a common discharge line.
- Causes of excessive pressure
- Requirements for selection of devices considering external and internal heat sources, compressor-induced pressure increases, heaters and thermal expansion of trapped liquid.
- Supporting material
- Annex A: values of factors and refrigerant properties.
- Annex B: flow-area calculations for non-flashing and flashing liquids.
- Annex C: worked example for sizing devices and piping.
- Annex D: guidance when outlet velocity approaches or exceeds the speed of sound.
Practical applications and users
ISO 24664:2024 is intended for:
- HVAC/R and refrigeration system designers and engineers sizing safety devices.
- Manufacturers of pressure relief valves, bursting discs and associated piping components.
- Safety engineers, commissioning teams and compliance officers who must ensure systems meet overpressure protection requirements.
- Asset owners and maintenance personnel responsible for safe operation and regulatory compliance.
Typical uses:
- Sizing relief devices during system design or modification.
- Verifying discharge capacities and outlet piping layouts.
- Demonstrating conformity with safety requirements and harmonizing design across projects.
Related standards
- ISO 4126-1:2013/Amd 1:2016 (safety valves)
- ISO 4126-2:2018 (bursting discs)
- ISO 21922:2021 (refrigerating valves - requirements, testing, marking)
- EN 13136:2013+A1:2018 (basis referenced in development)
- Supports compliance with EN 378-2 and ISO 5149-2 (pressure relief device requirements)
Keywords: ISO 24664:2024, refrigerating systems, heat pumps, pressure relief devices, pressure relief valves, bursting discs, discharge capacity, piping pressure loss, sizing methods, HVAC/R safety.