- ItemOpen AccessNumerical analysis of the combination of radiative collectors and emitters to improve the performance of water-water compression heat pumps under different climates(Elsevier, 2023) Vilà Miró, Roger; Medrano Martorell, Marc; Castell, AlbertRadiative cooling allows to cool down surfaces in a renewable way. It can be combined with solar collection functionality to produce heat and cold in a single device known as Radiative Collector and Emitter (RCE). In this paper we propose to combine a RCE with compression heat pumps to improve its performance, producing both heat and cold. Two combined systems are studied: a peak load shifting configuration where radiative cooling and cold production for demand occur simultaneously, and a decoupled configuration with an intermediate tank. The research numerically simulates both systems in different cities and climates, and compares them to a reference system based on a conventional heat pump. The results reveal and improvement of the performance in both configurations: a greater performance of the heat pump is found in the intermediate tank configuration; but after considering the electrical consumptions of all components of the system, peak load shifting configurations exhibit the best performance in most of the cities. Denver, Lleida and Rome – cities with dry climate and moderate cooling requirements – are the top cities with the greatest improvement of the performance. In the solar heating mode, the facilities show an underutilization of the collection field.
- ItemOpen AccessMapping Nighttime and All-Day Radiative Cooling Potential in Europe and the Influence of Solar Reflectivity(MDPI, 2021) Vilà Miró, Roger; Medrano Martorell, Marc; Castell, AlbertRadiative cooling is a natural process to cool down surfaces through the rejection of thermal radiation using the outer space as a cold sink, taking advantage of the transparency of the atmospheric windows (8–14 µm), which partially matches the infrared radiation band. With the development of new materials that have a high reflectivity of solar radiation, daytime radiative cooling can be achieved. This phenomenon depends on the optical properties of the surface and the local weather conditions. In this research, climatological data from 1791 weather stations were used to present detailed nighttime and all-day radiative cooling maps for the potential implementation of radiative cooling-based technologies. The paper offers a parametric study of the variation of the potential as a result of decreasing the solar reflectivity. The results show that southern Europe is the region with the highest potential while northern Europe holds more hours of available radiative cooling. After varying the solar reflectivity from 1 to 0.5 the average power reduces from 60.18 to 45.32 W/m2 , and energy from 527.10 to 264.87 kWh/m2 ·year. For solar reflectivity lower than 0.5, all-day radiative coolers behave as nighttime radiative coolers, but power and energy values improve significantly for high values of solar reflectivity. Small variations of solar reflectivity have greater impacts on the potential at higher reflectivity values than at lower ones.
- ItemOpen AccessAdaptive covers for combined radiative cooling and solar heating. A review of existing technology and materials(Elsevier, 2021-09-15) Vilà Miró, Roger; Martorell, Ingrid; Medrano Martorell, Marc; Castell, AlbertRadiative cooling is a promising technology for space cooling. This technology can be combined with solar heating applications, enabling the production of both energy demands -heat during daytime and cold during nighttime- in a single device; thus, reducing the non-renewable primary energy consumption for space conditioning and domestic hot water. Radiative cooling and solar heating appear in different wavelength ranges, 8-14 μm and 0.25-2.5 μm respectively, thus the device must be able to switch between ranges in each mode. An adaptive cover placed on top of the radiator/absorber can provide this switch by combining materials with suitable optical properties for each mode. Another effect derived from the usage of covers is the reduction of convective heat losses, enhancing the performance of the device. This paper aims to review the existing materials used in solar collectors, and radiative coolers as well as available smart materials used in other fields for its potential use as adaptive covers for combined radiative cooling and solar heating applications.
- ItemOpen AccessThermal Monitoring and Simulation of Earthen Buildings. A Review(MDPI, 2021) Carrobé, Ariadna; Rincón, Lídia; Martorell, IngridSince ancient times, raw earth has been used worldwide as a construction material. Today, it is well known for its good environmental properties of recyclability and low embodied energy along the production process. Earthen walls regulate the interior temperature of the buildings, providing comfortable temperatures with a very low carbon footprint. As a result of those advantages, earthen building techniques have been revived and used for contemporary architecture. The aim of this paper is to review the state of the art about the thermal behaviour of earthen building, including all the monitoring and simulation analysis of real earthen constructions up to now. The paper presents the different earthen techniques known nowadays, analysing the most important thermal parameters and the thermal comfort achieved with each technique. Regardless the wide differences among the analyzed cases, the authors conclude that earth building is a suitable solution in hot and arid climates, since it preserves the indoor temperature within the thermal comfort limits most part of the time without any active system.
- ItemOpen AccessAnalysis of the Thermal Behavior of an Earthbag Building in Mediterranean Continental Climate: Monitoring and Simulation(MDPI, 2020) Rincón, Lídia; Carrobé, Ariadna; Medrano Martorell, Marc; Solé Cutrona, Cristian; Castell, Albert; Martorell, IngridNearly 30% of humanity lives in earthen dwellings. Earthbag is a sustainable, cheap, feasible and comfortable option for emergency housing. A comparative monitoring-simulation analysis of the hygrothermal behavior of an Earthbag dwelling in Mediterranean continental climate, designed under bioclimatic criteria, is presented. The dome shape Earthbag dwelling has a net floor area of 7.07 m2 , a glass door facing south and two confronted windows in the east and west facades. A numerical model (EnergyPlus v8.8) was designed for comparison. Twenty-four hour cross ventilation, night cross ventilation, and no ventilation in free floating mode and a controlled indoor temperature were the tested scenarios. Comparisons between experimental data and simulation show a good match in temperature behavior for the scenarios studied. Reductions of 90% in summer and 88% in winter, in the interior thermal amplitude with respect to exterior temperatures are found. Position of the glazed openings was fundamental in the direct solar gains, contributing to the increase of temperature in 1.31 ◦C in winter and 1.37 ◦C in the equinox. Night ventilation in the summer period had a good performance as a passive system. Passive solar gains made a reduction of heating energy consumption of 2.3% in winter and 8.9% in equinox.