Future outlook on vapor injection and thermal energy storage integration for air source heat pump defrosting: a review.

The electrification of heating systems is crucial for reducing greenhouse gas emissions. Electric air source heat pumps (ASHPs) are a viable alternative to fossil fuel systems, offering high coefficients of performance (COP), significantly lower emissions, and dual functionality for heating and cooling. However, ASHP efficiency suffers in cold climates due to high-temperature lift requirements, and frost formation on outdoor coils causes further performance degradation, hindering widespread adoption. Vapor injection technology prevents excessive compressor discharge temperatures, improves heating capacity, and shortens defrosting time by increasing the refrigerant mass flow rate. Meanwhile, thermal energy storage (TES) provides an alternative heat source, enabling efficient defrosting under frosting conditions. Both technologies show strong potential for addressing defrosting challenges in ASHP systems. This review explores their respective strengths, evaluates studies on vapor injection and TES, and highlights the need for further research and development to integrate these technologies for improved ASHP defrosting performance.