In the COVID-19 era, a direct relationship has been consolidated between the concentration of the pollutant carbon dioxide (CO₂) and indoor disease transmission. For reducing its spread, recommendations have been established among which air renewal is a key element to improve indoor air quality (IAQ). In this study, a low-cost CO₂ measurement device was designed, developed, assembled, prototyped, and openly programmed so that the IAQ can be monitored remotely. In addition, this clonic device was calibrated for correct data acquisition. In parallel, computational fluid dynamics (CFD) modeling analysis was used to study the indoor air flows to eliminate non-representative singular measurement points, providing possible locations. The results in four scenarios (cross ventilation, outdoor ventilation, indoor ventilation, and no ventilation) showed that the measurements provided by the clonic device are comparable to those obtained by laboratory instruments, with an average error of less than 3%. These data collected wirelessly for interpretation were evaluated on an Internet of Things (IoT) platform in real time or deferred. As a result, remaining lifespan of buildings can be exploited interconnecting IAQ devices with other systems (as HVAC systems) in an IoT environment. This can transform them into smart buildings, adding value to their refurbishment and modernization.

Carbon dioxide concentration, temperature and relative humidity in an indoor environment are some of the main indicators of indoor air quality (IAQ). In addition, these parameters are directly related to the airborne transmission of diseases. In this context, ventilation regulation is essential to balance safety via air renewal, with comfort and energy efficiency. In this research, an educational space of Faculty of Engineering is considered as a case study to control IAQ. To begin with, the weaknesses of the ventilation and air-conditioning systems are analysed and identified. Next, a low-cost device to monitor IAQ remotely is designed, developed and prototyped with a set of sensors and control elements. Then, the room is modelled and simulated by means of computational fluid dynamics (CFD), to select the location (placement/layout and quantity) of the sensors responsible for measuring the environmental parameters that characterise the IAQ. Finally, the wireless collected data are evaluated for interpretation, thanks to an Internet of Things (IoT) platform, in real time or deferred. Key Words: Indoor air quality (IAQ), CO2 concentration, CFD simulation, sensor calibration, Internet of Things (IoT) La concentración de dióxido de carbono, la temperatura y la humedad relativa en un recinto interior son algunos de los principales indicadores de la calidad interior del aire (IAQ). Además, estos parámetros están directamente relacionados con la transmisión aérea de enfermedades. En este contexto, la regulación de la ventilación es esencial para balancear la seguridad, a través de la renovación de aire, con el confort y la eficiencia energética. En esta investigación, se toma un espacio docente de la Escuela Superior de Ingeniería de la Universidad de Cádiz como caso de estudio para controlar la IAQ. Para empezar, se analizan e identifican las debilidades de los sistemas de ventilación y climatización. Seguidamente, se diseña, desarrolla y prototipa un dispositivo de bajo coste para monitorizar la IAQ de forma remota, con un conjunto de sensores y elementos de control. A continuación, se modeliza el recinto y simula por medio de dinámica de fluidos computacional (CFD), para seleccionar la localización (ubicación/disposición y cantidad) de los sensores encargados de medir los parámetros ambientales que caracterizan la IAQ. Finalmente, se evalúan los datos recopilados para su interpretación, gracias a una plataforma de Internet de las Cosas (IoT), en tiempo real o diferidamente. Palabras Clave: Calidad interior del aire, concentración de CO2, simulación CFD, calibración de sensores, IoT

Solar photovoltaic (PV) expansion is depressing midday electricity prices in Spain, eroding plant revenues as installed capacity moves toward the 76 GW PNIEC 2030 target. We ask whether tower-based gravity energy storage (GES) can preserve PV investment viability under this price cannibalization. The question is systemic rather than private: a developer would rarely add storage while a grid-connected PV plant without energy storage (PV-only) remains more profitable, so we value capital at its long-horizon social opportunity cost and trace the concept's viability frontier. A DIAGRID tower with recycled-concrete blocks is assessed through a chronological hourly framework spanning 172,800 design-market cases across three Spanish locations, four PV configurations, tower heights of 18-216 m and four price scenarios. Under 2025 prices, PV-only turns marginal in Oviedo, while the flat-terrain hybrid stays profitable in Guadalajara (110-124%) and Cordoba (122-138%). A decomposed analysis shows the stored-energy stream covers tower capital cost above 108 m and reaches 182-226% at 216 m, and terrain-leveraged deployment favors intermediate towers. The sensitivity analysis reveals a cannibalization-scissors effect: wider intraday spreads can reduce hybrid profitability, as PV surplus revenue falls faster than storage arbitrage gains rise. A dispatch-matched comparison with lithium-ion storage exposes a head-dependent divergence: the two are closely matched at intermediate head, whereas the tower becomes superior in storage profitability and levelized cost at high head, where its structural economy of scale and absence of capacity fade dominate. PV–GES is best understood not as a profit enhancer but as conditional viability insurance, dependent on storage head, PV sizing and hourly price structure.