Solar photovoltaic-assisted DC vapour compression with a low-cost ice gel thermal battery for off-grid building cooling

In off-grid areas where extending the grid is costly, traditional AC powered air conditioning units pose challenges for off-grid photovoltaic PV setups due to expensive inverters and battery storage. This leads to an interest in cost-effective solar-driven DC cooling system. However, its efficiency depends on solar energy availability with limited operation during low solar radiation. This study proposes a solar PV-driven DC vapor compression system with variable refrigerant flow (VRF) and low-cost organic phase change material (PCM) ice gel storage. Preliminary experimental work determined the best operational mode namely, Mode A (PV+Thermal Battery), Mode B (PV-electrical battery-3h+Thermal Battery), Mode C (PV-grid+Thermal Battery), and Mode D (Grid+Thermal Battery). Key performance parameters include the Performance Quality Factor of the PV-powered system and levelized cost of cooling (LCOC). Mode B was found the best, and due to the system's complex dynamic variation with environmental parameters, a novel simulation approach combining ANN and TRNSYS was developed and experimentally validated. Thermal comfort is crucial for healthcare facilities as it promotes patient well-being, enhances staff performance, and is vital for infection control, thus a rural healthcare facility in Malaysia was selected for the simulation case-study. Mode B showed at least 50% higher compared to grid reliance, with superior LCOC performance, ensuring sustainable cooling despite limited electricity supply. The low-cost ice gel thermal battery reduced the system cost to 0.06 USD/kWh compared to 0.56 USD/kWh without it and 1.01 USD/kWh with grid extension. These findings offer insights for implementing similar sustainable cooling systems in rural areas.