Plant factories: Reducing energy demand at high internal heat loads through facade design

The increase in global food demand has led to the introduction of new food production systems. One key example is the plant factory. Plant factories face the same challenge as many high-tech building functions: high energy demands resulting from high internal heat loads. In this study we investigate how this energy demand can be reduced through facade design. Energy efficient design closely follows function, facade construction and local climate. Therefore, we analysed the effects of facade properties on the energy use in plant factories for three disparate climate zones: Sweden (Dfc), the Netherlands (Cfb) and the United Arab Emirates (BWh). We coupled the building energy simulation program EnergyPlus with a crop transpiration model to calculate the lighting, sensible cooling, latent cooling, and heating demand from the energy balance. In terms of energy demand (kWh m(-2)), opaque facades with high U-values and optimised albedo can reduce the facilities' cooling demand by 18.8%, 30.0% and 30.4%, and their energy demand by 6.1%, 12.5% and 9.5%, for the United Arab Emirates, the Netherlands and Sweden, respectively. In terms of electricity use (kWhe m(-2)), transparent facades are more efficient, as they allow the use of freely available solar energy instead of artificial light. These facades can reduce electricity use by 9.4%, 7.6% and 7.4%, for the United Arab Emirates, the Netherlands and Sweden, respectively. The presented facade design strategies can significantly reduce energy demand in plant factories. The investigation provides a foundation for the energy efficient design of high-tech buildings, tailored to local climate.