Expanding cities across the world rely increasingly on the global food network, but should they? Population growth, urbanisation and climate change place pressure on this network, bringing its resilience into question. For decades urban agriculture has been discussed in popular media and academia as a potential solution to improve food security, quality and sustainability. The new idol in this discussion is the plant factory: A fully closed system for crop production. Arrays of LEDs provide light and hydroponics provide water and nutrients to vertically stacked layers of crops, hence the term vertical farming. The plant factory features more extensive climate control than high-tech greenhouses. The question remains whether this level of climate control is necessary, effective and/or efficient. The scope of this research is therefore to investigate the potential and limitations of plant factories for urban food production. The STACKED method was developed to address the performance of plant factories across multiple scales, from leaf to facility to city. The role of plant processes in the total energy balance was outlined first. Performance was assessed by analysing the resource requirements, including energy, electricity, water, CO2 and land area use, for the production of fresh vegetables. The impact of façade and cooling system design was analysed in detail. Lastly, the effects of local food production on the urban energy balance were assessed for various scenarios. The results of this dissertation can serve as a foundation for future studies on the application of plant factories in both theoretical and real world applications.Expanding cities across the world rely increasingly on the global food network, but should they? Population growth, urbanisation and climate change place pressure on this network, bringing its resilience into question. For decades urban agriculture has been discussed in popular media and academia as a potential solution to improve food security, quality and sustainability. The new idol in this discussion is the plant factory: A fully closed system for crop production. Arrays of LEDs provide light and hydroponics provide water and nutrients to vertically stacked layers of crops, hence the term vertical farming. The plant factory features more extensive climate control than high-tech greenhouses. The question remains whether this level of climate control is necessary, effective and/or efficient. The scope of this research is therefore to investigate the potential and limitations of plant factories for urban food production. The STACKED method was developed to address the performance of plant factories across multiple scales, from leaf to facility to city. The role of plant processes in the total energy balance was outlined first. Performance was assessed by analysing the resource requirements, including energy, electricity, water, CO2 and land area use, for the production of fresh vegetables. The impact of façade and cooling system design was analysed in detail. Lastly, the effects of local food production on the urban energy balance were assessed for various scenarios. The results of this dissertation can serve as a foundation for future studies on the application of plant factories in both theoretical and real world applications. ... Read more

The municipality of Amsterdam has set stringent carbon emission reduction targets: 55% by 2030 and 95% by 2050 for the entire metropolitan area. One of the key strategies to achieve these goals entails a disconnection of all households from the natural gas supply by 2040 and connecting them to the existing city-wide heat grid. This paper aims to demonstrate the value of considering local energy potentials at the city block level by exploring the potential of a rooftop greenhouse solar collector as a renewable alternative to centralized district heating. An existing supermarket and an ATES component complete this local energy synergy. The thermal energy balance of the three urban functions were determined and integrated into hourly energy profiles to locate and quantify the simultaneous and mismatched discrepancies between energy excess and demand. The excess thermal energy extracted from one 850 m2 greenhouse can sustain up to 47 dwellings, provided it is kept under specific interior climate set points. Carbon accounting was applied to evaluate the system performance of the business-as-usual situation, the district heating option and the local system. The avoided emissions due to the substitution of natural gas by solar thermal energy do not outweigh the additional emissions consequential to the fossil-based electricity consumption of the greenhouse’s crop growing lights, but when the daily photoperiod is reduced from 16 h to 12 h, the system performs equally to the business-as-usual situation. Deactivating growth lighting completely does make this local energy solution carbon competitive with district heating. This study points out that rooftop greenhouses applied as solar collectors can be a suitable alternative energy solution to conventional district heating, but the absence of growing lights will lead to diminished agricultural yields. ... Read more

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 façade design. Energy efficient design closely follows function, façade construction and local climate. Therefore, we analysed the effects of façade 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 façades 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 façades are more efficient, as they allow the use of freely available solar energy instead of artificial light. These façades can reduce electricity use by 9.4%, 7.6% and 7.4%, for the United Arab Emirates, the Netherlands and Sweden, respectively. The presented façade 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. ... Read more

Population growth and rapid urbanisation may result in a shortage of food supplies for cities in the foreseeable future. Research on closed plant production systems, such as plant factories, has attempted to offer perspectives for robust (urban) agricultural systems. Insight into the explicit role of plant processes in the total energy balance of these production systems is required to determine their potential. We describe a crop transpiration model that is able to determine the relation between sensible and latent heat exchange, as well as the corresponding vapour flux for the production of lettuce in closed systems. Subsequently, this model is validated for the effect of photosynthetic photon flux, cultivation area cover and air humidity on lettuce transpiration, using literature research and experiments. Results demonstrate that the transpiration rate was accurately simulated for the aforementioned effects. Thereafter we quantify and discuss the energy productivity of a standardised plant factory and illustrate the importance of transpiration as a design parameter for climatisation. Our model can provide a greater insight into the energetic expenditure and performance of closed systems. Consequently, it can provide a starting point for determining the viability and optimisation of plant factories. ... Read more

Research on closed plant production systems, such as artificially illuminated and highly insulated plant factories, has offered perspectives for urban food production but more insight is needed into their resource use efficiency.
This paper assesses the potential of this ‘novel’ system for production in harsh climates with either low or high temperatures and solar radiation levels.
The performance of plant factories is compared with cultivation in traditional greenhouses by analysing the use of resources in the production of lettuce. We applied advanced climate models for greenhouses and buildings, coupled with a lettuce model that relates growth to microclimate. This analysis was performed for three different climate zones and latitudes (24–68°N). In terms of energy efficiency, plant factories (1411 MJ kg−1 dry weight) outperform even the most efficient greenhouse (Sweden with artificial illumination; 1699 MJ kg−1 dry weight). Additionally, plant factories achieve higher productivity for all other resources (water, CO2 and land area). With respect to purchased energy, however, greenhouses excel as they use freely available solar energy for photosynthesis. The production of 1 kg dry weight of lettuce requires an input of 247 kWhe in a plant factory, compared to 70, 111, 182 and 211 kWhe in greenhouses in respectively the Netherlands, United Arab Emirates and Sweden (with and without additional artificial illumination).
The local scarcity of resources determines the suitability of production systems. Our quantitative analysis provides insight into the effect of external climate on resource productivity in plant factories and greenhouses. By elucidating the impact of the absence of solar energy, this provides a starting point for determining the economic viability of plant factories. ... Read more

This paper presents an alternative approach and preliminary results to developing a sustainable campus by connecting research, education and real estate management. It is coined ‘ShowHow’: the deployment and display of the knowhow of all stakeholders in a university. The approach is built upon five pillars: (1) Projects: the initiation of a variety of projects; (2) Intensive real estate involvement: the introduction of sustainability and innovation to all levels of real estate strategy and decision-making processes; (3) Programmatic themes: the development of multi-faculty, overarching programmatic themes; (4) Stakeholder integration: The involvement of and intense liaison and co-creation with real estate, facility management, professors, and students, and (5) Outreach: the provision of impetus for regional/national sustainability systems with campus projects. The results are encouraging: In a short period of time, one year, more than 20 projects have been developed, the board of the Real Estate department adopted sustainable development as a key value, three programmatic lines are under construction, personal connections between students, operational and scientific staff were established, and 2020 goals for greening the energy supply will be met in 2017. Additionally, the University also performs a catalyst role for regional sustainable heating transformations. New PhD positions could be established. This approach seems very promising, generating enthusiasm throughout the university. It has elements, typical for technical universities, but the formula may be replicated at other universities in general, by deploying non-technical knowhow, and by including existing local sustainability themes and opportunities ... Read more