Thermo-economic optimization of vertical farms exploring multiple design options for the built environment and HVAC system

New challenges in the agricultural sector, arising from demographic growth, resource depletion, energy and environmental concerns, and food security, are driving the development of sustainable crop cultivation techniques such as vertical farming. This approach enables year-round, localized production while significantly reducing water and land use. However, its higher energy demand, particularly due to artificial lighting and climate control, necessitates a thorough analysis of energy consumption and economic factors, which may also be influenced by the external climate conditions where the system is implemented. This study aims to perform a multi-objective design optimization of vertical farms using a genetic algorithm, identifying the optimal combination of design parameters to achieve the best trade-off between specific primary energy consumption (SPEC), investment costs (SCI), and energy costs (SCE), and assuming the use of gas boiler, electric chiller and proper walls insulation materials. Key design variables include building dimensions, building envelope thickness and materials (such as phase change materials and different insulation types), as well as the design characteristics of chillers and boilers. The analysis considers three climate conditions, Athens (warm), Strasbourg (mild), and Helsinki (cold). Results indicate that SPEC, SCI, and SCE decrease when increasing building volume, air recirculation ratio, air temperature at the air conditioning outlet, and when minimizing solar radiation absorption, except in cold climates. The non-dominated solutions on the Pareto front range from 0.8 to 1.4 €∙kg−1 for SCI, with slightly lower SPEC observed in colder climates due to predominant cooling and dehumidification needs (until 42 kWh∙kg−1 for Athens, 40 kWh∙kg−1 for Strasbourg and 38 kWh∙kg−1 for Helsinki). The lowest values are achieved when ammonia is used as the chiller working fluid, due to its higher volumetric capacity compared to other refrigerants. Furthermore, using phase change materials as only layer may be beneficial in some optimal solutions in terms of energy savings, despite the increased costs.