[en] Highlights: • The flow instability of ultra-supercritical water in parallel channels was investigated. • Three regions of flow instabilities were found. • The effects of parameters on flow instabilities were analyzed. • The flow stability map of flow instabilities was derived. -- Abstract: An experimental study on the flow instabilities of ultra-supercritical water in the water wall tubes of an ultra-supercritical circulating fluidized bed (CFB) boiler was conducted. The material of the tubes is 1Cr18Ni9Ti. The scope of experimental parameters is as follow: pressure from 23 to 30 MPa, mass flow rate from 0.05 to 0.2 kg·s⁻¹; inlet water temperature from 200 to 390 °C, inlet pressure drop coefficient from 0 to 5.5, and heat flux from 0 to 500 kW·m⁻². Variations of mass flow rate and pressure in the parallel channels were recorded with the occurrence of flow instability, and oscillation curves of the wall temperature were obtained. The starting points and factors that affect various types of oscillations were analyzed to derive a stability map. Results show that pressure and mass flow rate display a reverse phase pulsation during oscillation. With the increase in heat flux, three regions of oscillations, namely, region1, region2 and region3, appeared. The oscillations in region1 and region2 are observed for the first time under ultra-supercritical pressure. Among them, oscillations in region1 and region2 are system oscillations, and they have long periods and large amplitudes. Oscillation in region3 belongs to density wave oscillation (DWO), which is the intertube oscillation and has a short period and small amplitude. Increases in system pressure, inlet mass flow rate, inlet pressure drop coefficient or decreasing the inlet water temperature are conducive to system stability.

[en] Highlights: • A Trombe wall with purification blinds based on photo-thermal driven purification. • The integration of heating, cooling and formaldehyde degradation. • The effect of purification blind angle. • The optimal operation strategy on blind angle. -- Abstract: This article proposes a year-round purified Trombe wall with ventilation blinds based on solar photo-thermal driven purification that realizes formaldehyde degradation in whole year, space heating in winter and space cooling in summer. The purification blinds are installed in the air channel in traditional Trombe wall, with a photocatalytic layer and thermal catalytic layer on both surfaces, respectively. Firstly, the purification blinds were designed and manufactured. Secondly, based on the verified models, a numerical model of Trombe wall with ventilation blinds considering heat and mass transfer processes was established. Thirdly, the effect of blinds angle on the energy performance was investigated. Finally, the annual optimal operation strategy on blinds angle was investigated. Main results are: (1) The purification performance in summer mode is better than that of in winter mode because of the combination effect of photocatalytic and thermal catalytic purification. (2) The optimal operation angles on purification blinds from January to December are 45°, 45°, 45°, 15°, 30°, 15°, 15°, 15°, 15°, 15°, 0° and 15°, respectively. (3) Applying the annual optimal operation strategy on blinds angle, the total volume of annual generated clean air is 7.12 * 10⁴ m³/m². The total reduced heating loads for Trombe wall with ventilation blinds in winter seasons are 986 MJ/m², which is 1.75 times larger than that of in Trombe wall. While based on Trombe wall, Trombe wall with ventilation blinds could save the total reduced cooling loads of 141 and 59.2 MJ/m² in summer and transition seasons, respectively.

[en] Highlights: • Summer and winter dynamic performance of a Trombe wall was assessed in three localities. • Summer ventilation strategies of a Trombe wall have been investigated. • Considerable reductions of yearly energy requirements were found. -- Abstract: Efficient low consumption buildings require the building envelope to be scrupulously designed from an early stage. Passive solar technologies, such as the Trombe wall, can contribute to the reduction of the heating energy demand and, if properly operated, they can also impact the building summer behaviour. The use of such a solution has been limited, especially in warm climates, as severe problems of indoor overheating can occur even beyond the cooling period. Through the dynamic simulation software DesignBuilder, the authors investigated the energy performance of two different residential buildings equipped with a Trombe wall in different climatic contexts. The authors proposed the adoption of proper ventilation strategies to further reduce cooling needs. The validity and effectiveness of the proposed solutions was verified in warm climates where the Trombe reduced heating requirements by up to 71.7% and decreased the cooling energy demand by 36.1%. In a cold climate, heating savings were 18.2% with a cooling energy reduction of 42.4%. The study highlighted the fundamental importance of the definition of proper ventilation strategies based on climatic parameters to prevent drawbacks in intermediate seasons, with an evident limitation of the system performance.

[en] In a typical solar water heating system, cold water is replenished into the storage tank as soon as the load is served. However, it is possible to determine the water replenishment profile (i.e., the quantity of the cold makeup water to be supplied to the storage tank over a day) that optimizes the overall system. In this paper, the effect of water replenishment on the system sizing is studied and a novel strategy for water replenishment is proposed to improve the design and performance of solar water heating systems. Based on an analytical technique, an approximate water replenishment profile is proposed to size a solar water heating system near-optimally. The problem is analyzed using a methodology called design space approach. Design space of a solar water heating system identifies all possible and feasible designs on a collector area vs. storage volume diagram. For illustration of the proposed methodology, an example problem is solved. It is observed that the annualized system cost can be reduced by 13.7%. For the cost-optimal system configuration, a reduction of 12.7% in the collector area and 10.2% reduction in the storage volume are observed. The proposed methodology is particularly important and advantageous for large commercial and industrial solar water heating systems

[en] Highlights: • Definition of solar wall and Trombe wall systems. • Dynamic energy simulations were used to compare scenarios. • Solar and Trombe walls can be efficient in the Mediterranean climate. • Shading devices combined with vents enhance the performance of these passive devices. • Trombe wall system may contribute to a reduction of more than 20% in heating needs. Solar and Trombe walls are envelope solutions that can contribute to reduce the energy consumption of the building sector. However, few studies have looked at their behaviour in warm/hot climates, particularly at avoiding and counteracting the overheating risk. This study therefore set out to assess how subtypes of the Mediterranean climate would affect the energy performance of these systems. Shading devices such as overhangs or blinds, combined with interior and exterior vents were studied. Parameters such as thermal mass, channel width and vent dimensions were also evaluated. Dynamic energy simulations were performed using EnergyPlus v8.1 and Designbuilder v5.0.1 user interface. The results demonstrate that solar and Trombe walls can both lead to significant reductions in net energy demands if properly tailored shading devices and vents with specific seasonal and daily operation schedules are implemented. The night ventilation strategy is crucial to reducing cooling needs. The Trombe wall system helped to cut demand for heating by more than 20% without compromising the cooling season. In the southernmost locations, the inclusion of night ventilation leads to a decrease in cooling demands (average reduction of more than 35%).

[en] Highlights: • Computational Fluid Dynamics capture trend of boiler heat uptake at reduced loads. • Imperative to capture flame position and radiation shielding in superheater volumes. • Requires explicit modelling of superheater elements with variable surface temperatures. • Reveals high temperature spots on the final superheater tubes at reduced loads. -- Abstract: This paper describes a CFD modelling methodology used to evaluate the thermal performance of the water wall evaporator, platen and final stage superheaters of a subcritical pulverized coal-fired boiler at full and reduced boiler loads. The heat exchanger elements are modelled as explicit walls with an effective thermal resistance boundary condition rather than fixed wall temperatures. This enables the direct radiation component to be properly accounted for together with variations in the wall temperatures. The modelling approach was applied to the boiler of a 620 MWe power plant. The results for 99%, 81% and 60% boiler loads compare well with experimental data. The proposed methodology forms the bases for a co-simulation framework which combines the CFD with a systems-level process modelling tool that can capture the internal steam maldistribution at low loads and the resultant effect on the metal temperatures.

[en] The title survey was carried out to acquire a detailed overview of the activities of Dutch energy utilities on the application of solar energy, in particular the use of solar water heaters. This report contains a summarized overview of the survey results. The results for each energy utility are published in a separate appendix, which is not available to the public. 1 fig., 10 tabs., 3 appendices

[en] Solar plants are increasingly used not only for hot tap water heating but also for the assistance of space heating. These plants produce much more energy in summer than needed, which often results in stagnation. Because of stagnation-temperatures of todays selective collectors up to 200 deg. C, the collector fluid evaporates. In several plants a high noise level and a vibration of the plant during this evaporation phase is reported. This is due to the occurrence of water hammers in the system, when liquid collector fluid passes areas where the fluid was already evaporated and superheated. The remaining vapor bubbles deflate rapidly and the liquid phases collide with high velocity, which results in a rapid pressure increase. This paper describes the theory of condensate-induced water hammers and conditions of solar plants, under which this can happen. A simulation model for the evaporation phase of the collector is presented to give a deeper understanding about the influences of solar radiation, the size of the tubing, and the size of the expansion device on the process of the evaporation. Three hydraulic layouts of the collector area are discussed for there possibilities producing water hammers. (au)

[en] This article reports on the UN Environment Programme's (UNEP's) work in supporting the banking and financing sector by creating clean energy finance markets in developing countries. Details are given of the shifting of cash markets to credit, financing solar home systems in India, solar thermal lending in Tunisia, the financing of hotel based solar water heating in Morocco, and the Green Village Credit initiatives in the Yunnan province of China. The importance of providing banks with information needed to gain awareness and experience of renewable energy systems is stressed. The fundamentals of a bank engagement programme, financial catalysts, structuring market oriented approaches, and linking bank lending to policy making are discussed along with the need to shift to credit enhancements to help banks set up their first loan portfolios

[en] The results of numerical research on the determination of the temperature value of the internal surface of the heat-removing channel (HRC) walls of the light-absorbing heat-exchange panels (LAHPs) with the tubeon- sheet and thin-parallelepiped form of flat-plate solar water-heating collectors (FPSWHCs) are presented. The research method is based on compilation of the system of the balance equations for the light-absorbing plate (LAP) and HRCs of the LAHPs of the studied types and their designs with respect to the desired parameter. A practical example of calculation of the determination of the temperature value of the internal surface of the HRC wall of the tube-on-sheet LAHP, where the results of experimental research on the determination of the specific thermal efficiency of the mean-quality FPSWHC in full-scale terms, as well as laboratory and numerical research on determination of the optical and thermotechnical indicators of the copper tube-on-sheet LAHP.