Flat plate solar collectors face the problem of overheating and the ensuing high thermal stresses and general collector damage lead to high maintenance costs. To address this challenge, absorber coatings with a passive optical switch at critically high operating temperatures are proposed. The remarkable near- and mid-infrared spectral modulation of thermochromic VO 2 makes it a promising material for smart selective absorbers with temperature dependent optical selectivity. Single VO 2 films readily achieve thermal emittance modulations of 40% points (p.p.) at a phase transition temperature of 66 °C. With 5 at.% Ge added to the VO 2 thin film, the transition temperature is increased to 82 °C. When VO 2 and VO 2 :Ge films are combined with a selective CuCoMnO x layer and an SiO 2 top layer, a thermal emittance modulation of 31 p.p. and 33 p.p. is retained, respectively. However, a simultaneous increase of the solar absorptance α sol by 7 p.p. and 5 p.p. limits the drop in collector efficiency at elevated temperatures. Simulations show that adding an absorber layer between the Al substrate and thermochromic VO 2 , decreasing solar absorptance over the phase transition is achieved. In line with these findings, a TiAlSiN//VO 2 :Ge//SiO 2 multilayer is prepared. Below the phase transition temperature, the efficiency of the thermochromic collector is similar to that of standard collectors. At the transition temperature, α sol decreases from 0.93 to 0.91 and ϵ th increases from 0.08 to 0.24. Such a decrease in α sol accompanied by an increase in ε th for increasing temperature has been achieved for the first time. The subsequent drop in selectivity, limits the maximum stagnation temperature of the thermochromic collector to 160 °C, 17 °C lower than for a standard collector in identical conditions. The absorber durability is confirmed through accelerated aging tests in dry and humid conditions alike. • Thermochromic VO 2 and VO 2 :Ge based selective absorber coatings are deposited. • ε th increases at 66 °C for VO 2 and 82 °C for VO 2 :Ge with 5 at.% Ge. • First absorber designs with both increasing ε th and decreasing α sol are reported. • High collector efficiencies and reduced stagnation temperatures are achieved. • Accelerated aging test in dry and humid conditions are successfully completed.

<p>A structural health monitoring system installed in a bridge produces a vast amount of sensor data that is analyzed and periodically reported to a bridge owner at an aggregate level. The data itself typically remains in the monitoring service of a service provider; it may be accessible to clients and third parties through a dedicated user interface and API. This paper presents an ontology to defining the monitoring model based on the Semantic Sensor Network Ontology by W3C. The goal is to enable an asset owner to utilize preferred tools to view and access monitoring data from different service providers, and in longer term, increase the utilization of monitoring data in facility management. The ultimate aim is to use BrIM as a digital twin of a bridge and to link external datasets to improve information management and maintenance over its lifecycle.</p>

Renewable energies are foreseen as a major energy resource for next generations. Among several energy sources and technologies available, Concentrated Solar Power (CSP) technology has a great potential, but it needs to be optimised, in particular to reduce the costs, with an increase of the operating temperature and long term stability. This goal can be achieved by tailoring the composition and multilayer structure of films. In this work we present and discuss the results obtained from solar absorber coatings based on nitride/oxynitride structures. A four-layer film structure, W/CrAlSiNx(HA)/CrAlSiNxOy(LA)/SiAlOx, was deposited on stainless steel substrates using magnetron sputtering deposition method. Simulations were performed to establish the best spectral properties of the multilayer stacks with optical constants of single layers and film thickness. The elemental analysis was performed using Rutherford Backscattering Spectrometry (RBS) and Time of flight Elastic Recoil Detection Analysis (TOF-ERDA). To assess the thermal stability of the coatings the samples were thermal annealed at 400 °C, in air, and at 600 °C, in vacuum. The results obtained by RBS and TOF-ERDA reveal good oxidation resistance and thermal stability. Also, the optical measurements confirm the potential of these materials for the use in CSP technology.

This study presents a design of multilayer solar selective absorber for high temperature applications. The optical stack is composed of four layers deposited by magnetron sputtering on stainless steel substrates. The first is a back-reflector tungsten layer, which is followed by two absorption layers based on CrAlSiNx/CrAlSiOyNx structure for phase interference. The final layer is an antireflection layer of SiAlOx. The design was theoretically modelled with SCOUT software using transmittance and reflectance curves of individual thin layers, which were deposited on glass substrates. The final design shows simultaneously high solar absorbance α = 95.2% and low emissivity ε = 9.8% (calculated for 400 °C) together with high thermal stability at 400 °C, in air, and 600 °C in vacuum for 650 h.

It is reported in this work the development and study of the optical and structural properties of a solar selective absorber cermet based on AlSiOx:W. A four-layer composite film structure, W/AlSiOx:W(HA)/AlSiOx:W(LA)/AlSiOx, was deposited on stainless steel substrates using the magnetron sputtering deposition method. Numerical calculations were performed to simulate the spectral properties of multilayer stacks with varying metal volume fraction cermets and film thickness. The chemical analysis was performed using X-ray photoelectron spectroscopy and the results show that in the high metal volume fraction cermet layer, AlSiOx:W(HA), about one third of W atoms are in the W0 oxidation state, another third in the Wx+ oxidation state and the last third in the W4+, W5+ and W6+ oxidation states. The X-ray diffractograms of AlSiOx:W layers show a broad peak indicating that both, W and AlSiOx, are amorphous. These results indicate that this film structure has a good spectral selective property that is suitable for solar thermal applications, with the coatings exhibiting a solar absorptance of 94–95.5% and emissivities of 8–9% (at 100°C) and 10–14% (at 400°C). The samples were subjected to a thermal annealing at 450°C, in air, and 580°C, in vacuum and showed very good oxidation resistance and thermal stability. Morphological characterizations were carried out using scanning electron microscopy and atomic force microscopy. Rutherford Backscattering experiments were also performed to analyze the tungsten depth profile.

Thermal cooling systems are particularly attractive in locations supplied by district heating based on cogeneration heating plants (CHP). Moreover, solar thermal energy is a major renewable source for the provision of thermal energy, fulfilling demands for space heating, domestic hot water, process heat, and cooling. This energy source can be suitably used also in Nordic Countries.The presented paper focuses on two configurations of a cooling solar-driven thermal system for an office building located in Finland. Dynamic simulation approach has been used through TRNSYS software. In particular, the configurations differ from the connection between the hot storage tank, the solar collectors and the chiller. Particularly, in the first configuration only the tank can supply the chiller (Case 1), while in the second, the chiller can be supplied either by the tank or the solar collectors directly (Case 2). System performance indexes, in case of district heating as main building heating supply system in winter and as auxiliary heating system for the chiller in summer, have been evaluated as a function of the tank and solar thermal field sizes.Results show that Case 2 has better performance than Case 1, because of the versatility shown in summer. Particularly, when the solar irradiance is low, Case 2 solutions perform far better than Case 1 solutions, benefitting from the direct connection between the solar collectors and the chiller. This study has highlighted also the potential of this technology in cold climate areas supplied by means of DH based on CHP plants. Indeed, the adoption of such cooling technology, in addition to reduce both heating and cooling consumed energy and to shave summer electricity peaks, can potentially allow some CHP plants to operate also in summer, fulfilling the future energy networks aims: being able to provide electricity, heat and cooling energy.

<p>Crusell Bridge is a cable stayed bridge recently built in the city center of Helsinki. In the very beginning of the project the Client City of Helsinki decided to utilize the newest technology in all phases. The project was a pilot project in using Building Information Modeling (BIM) technology in design and construction and finally in monitoring as part of maintenance. In order to develop modern maintenance scheme, an intelligent monitoring system was designed and installed in the bridge. The monitoring system has been tested by a loading test and comprehensive test results have been compared with theoretical calculation analysis. The results verified the design and gave designers guidelines to specify alarming limits to monitoring system. The owner of the bridge will get a summary report from the maintenance system once per year.</p>

Coatings with a double absorbing layer based on AlSiN/AlSiON were deposited on stainless steel substrates by magnetron sputtering technique, with different Al:Si ratios. A tungsten layer was used as a back reflector and AlSiOy or SiOx thin films were used as antireflection top layers. Prior the structure design, several single layers were deposited on glass substrates by varying the reactive gases flows, which allowed the stacking of a series of layers with different optical properties. Experimental transmittance and reflectance were modelled for the assessment of the spectral optical constants, which were then used to design a coating stack with optimized solar absorptance and thermal emittance. Optical properties, microstructure, morphology, composition and chemical bonding were investigated by employing optical spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The samples were annealed in air at 400°C and vacuum at 580°C with the purpose to evaluate their oxidation resistance and thermal stability, which was subsequently correlated with the Al:Si ratio. Optimum results were achieved for an Al:Si ratio of 2.3:1, whereas for significantly higher Si content resulted in detrimental performance. The solar absorbance and thermal emittance for the optimized multilayer selective coatings is 93–94% and 7–10% (at 400°C), respectively.

Solar selective coatings based on double Al2O3:W cermet layers and AlSiN/AlSiON bilayer structures were prepared by magnetron sputtering. Both were deposited on stainless steel substrates using a metallic tungsten (W) layer as back reflector. The coating stacks were completed by an antireflection (AR) layer composed of Al2O3, SiO2, or AlSiOx. Spectrophotometer measurements, X-Ray diffraction, Scanning electron microscopy, Energy Dispersive X-Ray Spectroscopy and Rutherford Backscattering Spectrometry were used to characterize the optical properties, crystalline structure, morphology and composition of these coatings. The spectral optical constants of the single layers were calculated from the reflectance and transmittance measurements and used to design the optical stack. The coatings exhibit a solar absorptance of 93–95% and an emissivity of 7–10% (at 400°C). The coatings also exhibit excellent thermal stability, with small changes in the optical properties of the coating during heat-treatments at 400°C in air for 2500h and at 580°C in vacuum for 850h. The coating based on the AlSiN/AlSiON bilayer structure was obtained with an Al:Si ratio of 2.5:1. These coatings revealed similar performance as the one obtained with coatings based on Al2O3:W cermet layers.

The paper presents results of using continuous beam analytical differential equation method to dynamics behavior design of complex heat transfer orthotropic platens which are used in the recovery boilers. The goal is to obtain a predictive model for increasing the reliable useful operation time. The platens are supported vertically with fixed ends. They are loaded by hot flue gas and by accumulating mass loads due to operation conditions. The loads cause alternating stresses fracturing tube branch connections. The beam deflection and bending stress histories at the junction of tube and chamber are obtained using an analytical beam model. The model gives the lowest eigenfrequency close to the measured value which is somewhat larger than that obtained by FEM model. The beam model can be used for further optimal redesign of the tube branch connections and the mean time to failure of the process equipment.