Phase change materials for thermal energy storage applications in greenhouses: A review

Greenhouses represent one of the largest energy-demanding sectors, requiring energy for indoor environment control for plant growth and crop yield. Thermal energy storage using phase change materials (PCMs) has been identified as a potential solution to achieve considerable energy savings in greenhouse heating/cooling. This review investigates the latest technological advancements in greenhouse heating/cooling systems integrated with PCMs. PCMs store excess heat from active or passive heating systems in greenhouses, including heaters, heat pumps, solar thermal collectors, or greenhouse northwalls. In addition, the PCMs kept inside the greenhouses are capable of providing passive cooling by the absorption of excess solar energy diurnally and passive nocturnal heating by releasing the stored heat. Various systems integrated with PCMs provide a diurnal temperature decrease up to 7 degrees C and nocturnal temperature increase up to 9 degrees C compared to the ambient temperature and can cover up to 30% of the greenhouse heating demand. The higher installation costs of PCMs can be compensated by the lower maintenance costs in addition to the environmental concerns raised by fossil fuels. Appropriate design parameters should be selected based on the climatic conditions and the required environmental control to achieve significant savings in energy and cost.