Feasibility of a heat pump-assisted liquid desiccant system for continuous dehumidification and regeneration in temperate oceanic climatic greenhouses

Effective thermo-hygrometric control is essential for buildings and greenhouses, particularly in green and low-carbon production. There is growing interest in integrating heat pumps with liquid desiccant systems to enhance energy efficiency and reduce system size in air moisture control. The current study investigates a novel liquid desiccant system combined with a heat pump for continuous, energy-efficient dehumidification and regeneration in horticultural crop cultivation in greenhouses. The uniqueness of the developed system lies in its integration, contrasting with previous liquid desiccant systems designed with separate dehumidifier and regenerator. A semi-theoretical model is developed and validated using in-house experimental datasets to simulate novel liquid desiccant system performance. Results demonstrate that the system effectively maintains air humidity levels, with a maximum enthalpy demand for dehumidification of 99.1 kJ/kg at a solution temperature difference of 40 °C during summer. The minimum achieved moisture content with lithium chloride, calcium chloride, and potassium formate is 7.64 g/kg_da, 8.1 g/kg_da, and 7.78 g/kg_da, respectively, while regeneration produces maximum moisture contents of 23.5 g/kg_da, 23.9 g/kg_da, and 23.7 g/kg_da. The system's maximum effectiveness reaches 76 %, 75 %, and 74 % for lithium chloride, calcium chloride, and potassium formate, respectively. When dehumidification demand exceeds 1,500 h annually, the payback period is five years or less, making the system suitable for new installations and retrofits. A case study considering outdoor conditions in the northeastern United Kingdom presents simulation results for two distinct scenarios, demonstrating the system's potential in real-world applications.