This research develops a bottom-up procedure to assess the potential of food-energy-water (FEW) systems on the rooftops of buildings in an urban district in Spain considering the urban morphology of the built environment and obtains accurate assessments of production and developmental patterns. A multicriteria decision-making technique implemented in a geographical information system (GIS) environment was used to extract suitable rooftop areas. To implement this method, the slope (tilt), aspect (azimuth), shading, and solar radiation of the rooftops were calculated using LiDAR (Light Detection and Ranging) data and building footprints. The potential of FEW system implementation was analysed at the building and morphology levels. The results showed several differences between residential and non-residential urban morphologies. Industrial areas contained the highest productivity for FEW systems. The production was 2.51 kg of tomatoes/m², 48 kWh of photovoltaic energy/m², and 0.16 l of rainwater/m². Regarding the residential urban morphologies, the more compact tents resulted in better performance. Among the FEW systems, although water could best benefit from the features of the entire roof surface, the best production results were achieved by energy. The food system is less efficient in the built environment since it requires flat roofs. The methodology presented can be applied in any city, and it is considered optimal in the European context for the development of self-production strategies for urban environments.

The COVID-19 crisis has changed daily habits and the time that people spend at home. It is expected that this change may have environmental implications because of buildings’ heating energy demand. This paper studies the energy and environmental implications, from a Life Cycle Assessment (LCA) approach, due to these new daily habits in residential buildings at their current level of thermal insulation, and in different scenarios of thermal retrofit of their envelope. This study has a building-to-building approach by using Geographical Information Systems (GIS) for the residential housing stock in the case of Barcelona, Spain. The results show that a change in daily habits derived from the pandemic can increase the heating energy consumption and carbon dioxide emission in residential buildings by 182%. Retrofitting all buildings of Barcelona, according to conventional energy renovation instead of nearly Zero Energy Buildings (nZEB), will produce between 2.25 × 10⁷ and 2.57 × 10⁷ tons of carbon dioxide. Retrofitting the building stock using energy recovery is the option with better energy and emission savings, but also is the option with higher payback time for buildings built until 2007. The methodology presented can be applied in any city with sufficient cadastral data, and is considered optimal in the European context, as it goes for calculating the heating energy consumption.

District heating and cooling systems are designed and optimized to respond to the latest challenges of reducing energy demands while fulfilling comfort standards. Thermal energy storage (TES) with phase change materials can be employed to reduce the energy demands of buildings. This study considers a residential district located in Spain, where a general framework has been established to identify optimal combinations of energy conversion, delivery technologies, and operating rules. The Life Cycle Assessment (LCA) methodology was implemented within a mathematical model, and the objective function considered the minimization of environmental loads. Two environmental impact assessment methods were applied within the LCA methodology: IPCC 2013 GWP 100y and ReCiPe. Four optimal configurations were considered: a reference system (gas boiler and split-type air conditioners) and then three TES-based systems: one sensible (STES, water) and two latent (LTES1—paraffin emulsion and LTES2—sodium acetate trihydrate). Hourly environmental loads associated with electricity imports from the national grid were available. The conventional energy system always presented the worst performance from an environmental viewpoint, being penalized by the high consumption of natural gas. Regarding carbon emissions, LTES1 showed the lowest emissions, followed by STES and LTES2. Reductions in energy demands compensated the impact of paraffin, and results of STES are strongly dependent on tank design. However, considering the ReCiPe method, STES presented the lowest loads, followed by LTES1 and LTES2. Overall impacts of LTES1 with paraffin are higher than STES with water, mainly due to the paraffin and the high volume required. Graphic abstract

The concentration of the population in cities has turned them into sources of environmental pollution, however, cities have a great potential for generating clean energy through renewable sources such as a responsible use of solar energy that reaches its rooftops. This work proposes a methodology to estimate the level of energy self-sufficiency in urban areas, particularly in a district of the city of Zaragoza (Spain). First, the Energy Self-Sufficiency Urban Module concept (ESSUM) is defined, then the self-sufficiency capacity of the city or district is determined using Geographical Information Systems (GIS), Light Detection and Ranging (LiDAR) point clouds and cadastral data. Secondly, the environmental implications of the implementation of these modules in the rooftops of the city using the LCA methodology are calculated. The results obtained show that total self-sufficiency of Domestic Hot Water (DHW) can be achieved using 21 % of available rooftop area, meanwhile the rest of rooftop area, dedicated to photovoltaic (PV), can reach 20 % of electricity self-sufficiency, supposing a final balance of a reduction in CO₂ emissions of 12,695.4 t CO_2eq/y and energy savings of 372,468.5 GJ/y. This corresponds to a scenario where full self-sufficiency of DHW was prioritized, with the remaining roof area dedicated to PV installation. In addition, other scenarios have been analyzed, such as the implementation of the energy systems separately.