Current state of research in air-conditioning condensate utilization and challenges: A review approach

•Air-conditioning condensate holds potential as a water and energy substitute.•Treatment is required to ensure condensate quality before use as a water source.•Thermal quality of condensate determines its suitability for energy recovery.•Condensate-assisted thermal energy storage systems offer energy-saving.•Bridging research gaps in condensate utilization supports sustainability. Recovery and reuse of condensate generated from the air conditioner are studied extensively for building a sustainable environment. Recent research on the quantity and quality analysis of condensate generation and its usage in existing applications such as cooling towers, irrigation, and domestic consumption and its challenges, are reviewed thoroughly to understand its significance. The applicability of utilizing condensate for the above-mentioned applications is endorsed by comparing it with the national standards. Further, the usage of condensate as an energy source for a new application area - radiant cooling is proposed. Significant cooling energy loss to the surrounding is the major drawback of condensate usage in applications. Hence, the usage of thermal energy storage system as an intermittent unit to overcome the energy loss is reviewed in detail. This article also provides a detailed analysis of using phase change materials in thermal energy storage systems and discusses the associated challenges. The limitations of the researchers on the use of condensate as a water or energy source are addressed and the research gap is highlighted. The potential options, scope and roadmap to recover and reuse condensate are suggested to the research community to build a green and sustainable environment together.