Sustainability Assessment of Alternatives for Heat Generation and Transfer in Saunas

In the search for renewable energy sources, solar energy appears, among others, as a powerful alternative;mainly for those countries located at Earth’s equatorial region. This is the case of a Fresnel device that uses solar radiation to warm-up the air;for instance, within saunas. Authors coined the term sustainable technological innovation to refer to a technological innovation in accordance to the principles of sustainability. The object of this research was comparing the sustainability of a Fresnel Lens Solar Concentration (FLSC) against the sustainability of other twelve alternatives to generate heat. This article assesses the sustainability of fourteen technological options for heat generation and transfer to saunas in the northwest region of Mexico where temperatures often reach above 45 C and where there is a greater potential for exploiting solar energy. Emergy accounting, economic analysis, and global warming potential are the three indicators considered in quantifying sustainability. Results show that infrared ceramic photovoltaic, infrared carbon photovoltaic and infrared metal photovoltaic are the most sustainable systems. The Fresnel device reached the fourth and tenth position, using electricity from photovoltaic and from grid respectively, among all fourteen assessed devices, respectively. Although Fresnel equipment does not release any global warming gases into the atmosphere, or even it demands low amount of non-renewable resources, 1.40 and 4.47 E17 seJF/yr. it requires high economic investment, 20,800 and 79,600 USD/yr, for the implementation and operation phases, which decrease its sustainability performance compared to twelve other evaluated devices.

Urban constructed wetlands: Assessing ecosystem services and disservices for safe, resilient, and sustainable cities

Climate change and rapid urbanization are pressing environmental and social concerns, with approximately 56% of the global population living in urban areas. This number is expected to rise to 68% by 2050, leading to the expansion of cities and encroachment upon natural areas, including wetlands, causing their degradation and fragmentation. To mitigate these challenges, green and blue infrastructures (GBIs), such as constructed wetlands, have been proposed to emulate and replace the functions of natural wetlands. This study evaluates the potential of eight constructed wetlands near Beijing, China, focusing on their ecosystem services (ESs), cost savings related to human health, growing/maintenance expenses, and disservices using an emergy-based assessment procedure. The results indicate that all constructed wetlands effectively purify wastewater, reducing nutrient concentrations (e.g., total nitrogen, total phosphorus, and total suspended solids). Among the studied wetlands, the integrated vertical subsurface flow constructed wetland (CW-4) demonstrates the highest wastewater purification capability (1.63E+14 sej/m^(2)/yr) compared to other types (6.78E+13 and 2.08E+13 sej/m^(2)/yr). Additionally, constructed wetlands contribute to flood mitigation, groundwater recharge, wildlife habitat protection, and carbon sequestration, resembling the functions of natural wetlands. However, the implementation of constructed wetlands in cities is not without challenges, including greenhouse gas emissions, green waste management, mosquito issues, and disturbances in the surrounding urban areas, negatively impacting residents. The ternary phase diagram reveals that all constructed wetlands provide more benefits than costs and impacts. CW-4 shows the highest benefit-cost ratio, reaching 50%, while free water surface constructed wetland (CW-3) exhibits the lowest benefits (approximately 38%), higher impacts (approximately 25%), and lower costs (approximately 37%) compared to other wetlands. The study advocates the use of an emergy approach as a reliable method to assess the quality of constructed wetlands, providing valuable insights for policymakers in selecting suitable constructed wetlands for effective urban ecological management.