Non-Vapor Compression Cooling

Overview

Traditional cooling systems rely heavily on vapor-compression cycles using synthetic refrigerants, many of which are potent greenhouse gases. While vapor compression heat pumps offer strong performance and are well-established in the market, the growing need for energy-efficient, climate-safe alternatives has prompted interest in non-vapor compression (NVC) technologies—especially those leveraging solid-state cooling mechanisms. This section outlines the background, principles, and current state of emerging NVC technologies including elastocaloric, magnetocaloric, electrocaloric, and barocaloric systems. It is designed as a reference for practitioners to better understand the potential of these alternative technologies.

Background: Why Explore Non-Vapor Compression Cooling?

Environmental Drivers: Vapor compression systems often rely on HFCs, which have high Global Warming Potentials (GWPs). Even low-GWP options like HFOs have trade-offs in cost, flammability, or lifecycle impacts.

Regulatory Pressures: Policies such as California's refrigerant phasedown and international HFC bans under the Kigali Amendment are accelerating demand for alternatives.

Technology Gaps: Many alternatives either underperform in certain applications or present safety/performance tradeoffs. Non-vapor compression offers a new path by eliminating refrigerant fluids altogether.

What Are Caloric Cooling Technologies?

Caloric systems are based on reversible thermal effects in solid-state materials that undergo phase changes when exposed to external fields. These phase changes cause changes in entropy and temperature, enabling heating and cooling without refrigerants.

Types of Caloric Effects

Elastocaloric – Induced by mechanical stress. Ex: Ni-Ti-based shape memory alloys.

Magnetocaloric – Triggered by magnetic fields. Ex: Gadolinium-based materials.

Electrocaloric – Activated by an electric field. Ex: Dielectric polymers like P(VDF-TrFE).

Barocaloric – Driven by changes in hydrostatic pressure. Still in early research stages.

Advantages

No refrigerants (zero direct emissions)

Potential for higher efficiency

Reduced system complexity (fewer moving parts)

Compact and scalable design possibilities

Challenges

Prototype maturity: Most technologies are still in lab or early-stage demo phase

Material fatigue and cost

System integration and durability under repeated cycling

Current Status

While many caloric-based systems remain pre-commercial, interest is growing. Select elastocaloric and magnetocaloric systems now show COPs comparable to vapor-compression under narrow conditions. Continued R&D, supported by demand signals and policy clarity, could accelerate commercialization.

Additional Resources

REEF Solid-State Cooling Webinar

Caloric Cooling: State-of-the-Art and Perspectives (Nature Communications, 2017)

DOE BTO Non-vapor Compression Workshop (2021)