Overview
This webinar discussed the future of solid state cooling technologies, focusing on alternatives to traditional vapor compression refrigeration, with presentations from Pascal and Exogen highlighting barocaloric and elastocaloric systems.
Traditional Cooling Technologies
- Refrigerants are fluids/vapors used in air conditioning and refrigeration systems.
- Traditional systems use the vapor compression cycle: compressing and expanding gases to absorb/release heat.
- Vapor compression refrigerants have environmental issues: leaks, toxicity, flammability, and high global warming potential (GWP).
- Hydrofluorocarbon (HFC) gases are widely used but are being phased down due to climate impacts.
Solid State Cooling: Concepts and Technologies
- Solid state cooling avoids toxic/leaky refrigerants by using solid materials instead of fluids.
- Electrocaloric, magnetocaloric, barocaloric, and elastocaloric methods use different physical effects to generate cooling.
- Barocaloric cooling uses solid-state materials that change structure under pressure, absorbing or releasing heat.
- Elastocaloric cooling uses mechanical stress (compression/stretching) to induce a solid-to-solid phase change in shape memory alloys, resulting in heat transfer.
Technological Advances and Challenges
- Pascal developed barocaloric solids operating at lower pressures (≈10x atmospheric), allowing use of standard HVAC components.
- Key challenges: efficient heat transfer to/from solids, achieving sufficient temperature "lift," and proving long-term material durability.
- Exogen’s elastocaloric systems use compression (not tension) to maximize material fatigue life and performance.
- Nitinol (nickel-titanium alloy) is a primary material, able to cycle millions of times without significant degradation.
- Achieved high thermal efficiency (COP >45) and built multi-kilowatt heat pump demonstrators.
Applications and Market Considerations
- Solid state cooling is suited to applications where zero GWP, non-toxic, and non-flammable refrigerants are desired.
- Target markets: commercial/industrial refrigeration, data centers, and larger heat pump systems.
- Large systems benefit from modular design, improved efficiency, and less complex maintenance.
- Regulatory codes are written for gas refrigerants; standards for solid state refrigerants are still developing.
Performance, Limitations, and Future Directions
- Temperature ranges for caloric materials can reach from -150°C to over 600°C with proper alloy selection.
- Fast, efficient heat transfer remains a challenge due to poor conductivity of solid materials.
- System engineering (not materials science) is now the main barrier to commercial competitiveness.
- Life cycle ownership cost and long-term efficiency are key for market adoption.
Key Terms & Definitions
- Vapor Compression Cycle — Traditional refrigeration method using gas/liquid refrigerants.
- Barocaloric Effect — Heating/cooling from pressure-induced solid-solid phase change.
- Elastocaloric Effect — Heating/cooling from mechanical stress-induced solid-solid phase change in alloys.
- Coefficient of Performance (COP) — Efficiency measure; ratio of heat moved to work input.
- GWP (Global Warming Potential) — Measure of a substance’s impact on climate change.
- Nitinol — Nickel-titanium shape memory alloy used in elastocaloric cooling.
Action Items / Next Steps
- Review Rocky Mountain Institute’s solid state cooling 101 series.
- Optionally, read Dr. Hicham Bourlès' solid state cooling overview for a technical deep dive.
- Monitor the Reef website for webinar recordings, updates, and resources.