Enhancing resource use efficiency in plant factory

The operational costs and resource-use efficiency of multi-tier-based plant factory systems can be improved by appropriate production-system design modifications for key technologies and control strategies while considering the crop-specific minimum environmental requirements. Lack of detailed engineering analysis in the system design can lead to inefficient use of resources (i.e. energy, CO2, water), non-uniform environment, higher system costs, and limit production quality, yield, and profitability. For indoor farming, the outdoor climates, characteristics of building envelope, and HVAC systems have a significant effect on the heating and cooling thermal loads of an indoor plant factory and therefore influence energy consumptions. In this study, potential factors that affect energy consumption of an indoor farm for growing lettuces were studied. These factors include outdoor climate (with four typical climate zones: very cold, hot and dry, cold moderate, and hot and humid), different day period and dark period temperatures, operating schedule for day and dark periods, and light efficiency. Energy saving was evaluated with energy consumption in kWh and energy use efficiency in kWh per kg of the fresh weight of lettuce. The results show that operating an indoor farm in a cold climate and choosing lights in high efficiency can help to reduce energy consumption. Setting day period temperature and dark period temperature with maximum lettuce production was suggested for maximizing energy use efficiency. Scheduling day periods during the night can also help to save energy and avoid high cooling demand during the peak heat of a day. It also helps to reduce the electricity bill by shifting the photoperiod to off-peak hours.