• Energy Research

Abstract The performance of different thermal energy storing systems to provide over-night air-conditioning for a limited space in an institutional building in south Spain are compared with conventional air-conditioning (both for refrigeration and heating). In summer, the storage tanks are charged with a solar-assisted absorption chiller during day-time, and used to cover the over-night demand, whereas in winter a heat exchanger is used during the day to charge the tanks. Thermal energy has been stored in two chilled water tanks (with total capacity of 5000 L) or in two tanks (total volume 4000 L) containing two phase change materials (PCM): a PCM with melting point of 10 ° C for refrigeration, and a PCM with melting temperature of 46 ° C for heating. Our results show that the storing in PCM is more convenient, providing air-conditioning service for approximately 4 h 30 min in refrigeration, with a significant reduction of the electricity consumption with respect to the conventional system. The chilled water tanks can cover the demand for 4 h (scaled down to 3 h 12 min if the capacity is 4000 L), with even lower electric consumption. In winter, on the other hand, the tanks can cover fully the demand of overnight heating. Our results prove the viability of thermal storing, in particular using PCM, to extend the application solar cooling and heating to night-time, which is economically feasible, in a fully operational building.

Granite is one of those materials that due to its thermal parameters is used as a filling for storage beds, including high-temperature ones. The article analyzes local material that was extracted in Strzegom, Poland. The purpose of the paper is the assessment of storage material with regard to its cooperation with a heat source that is available for a short time, e.g., a solar installation. Three different shapes of granite material were tested: rock, cube and sphere. Each shape has its advantages and disadvantages, which are associated with economic and strength aspects. The article presents experimental tests of the material, which were conducted in order to determine the efficiency of the charging process. The results show that rock-shaped granite filling elements are characterized with the best parameters during the charging process, and that they obtained the highest first- and second-law efficiency in the entire tested range of inlet air temperature and flow rate. The efficiency of the cube-shaped granite was lower than the sphere-shaped granite. This means that the efficiency does not directly depend on the coefficient of sphericity of the elements that fill the storage bed. The determination of the second law efficiency showed that the highest use of energy supplied with hot air occurs after 1 h of charging the accumulator in the case of all the analyzed geometries. At the end of the paper, the influence of the obtained results on the process of modelling the charging of a storage bed filled with elements of non-spherical geometry is also discussed.

When designing a year-round home heating system that uses only solar radiation energy, the cooperation of an architect and an HVAC (heating, ventilation, and air conditioning) designer is necessary. These systems occupy a large area in relation to a building’s floor surface, especially when they are located in a climate like Central Europe or colder. The aim of the article was to create a balanced integration process by implementing the subsequent steps that are necessary to integrate a solar heating system within a building. In the first stage, a solar collector and a heat accumulator were selected. The innovation of the system involves the use of a solar concentrating collector as an air heater. Assessment criteria were then proposed in order to show the influence of the location of the solar heating system on the building’s architecture, functionality, and energy balance, while at the same time assuming its passive standard. System integrations concerning both an existing and new building were analyzed. The system’s basic components were selected for the three chosen solutions, taking into account the possibility of using heat losses resulting from the location of the installation.

An important element of a solar installation is the storage tank. When properly selected and operated, it can bring numerous benefits. The presented research relates to a project that is implemented at the Solar Energy Research Center of the University of Almeria in Spain. In order to improve the operation of the solar cooling and heating system of the Center, it was upgraded with two newly designed storage tanks filled with phase change materials (PCM). As a result of design works, commercial material S10 was selected for the accumulation of cold, and S46 for the accumulation of heat, in an amount of 85% and 15%, respectively. The article presents in detail the process of selecting the PCM material, designing the installation, experimental research, and exergy analysis. Individual tasks were carried out by research groups cooperating under the PCMSOL EUROPEAN PROJECT. Results of tests conducted on the constructed installation indicate that daily energy saving when using a solar chiller with PCM tanks amounts to 40% during the cooling season.

Abstract This paper presents the results of experimental validation of energy conversion in a concentrated solar air-heater with internal multiple-fin array. A novel high temperature solar air heater was proposed to convert solar energy to heat for space heating in climatic conditions of Poland. The aim of the study was to verify the previously created mathematical model of heat transfer processes. The collector’s performance was analysed experimentally against the reduced temperature difference. During the experiments, an electrical air heater was used to change the air temperature at the inlet of the receiver according to the test demands. Additionally, two daily performance evaluation tests were done. During the tests the all-day measured data was collected automatically and recorded at 1-min intervals. Hourly and daily thermal efficiency was calculated. Validation of the model showed its correctness and proved that the model can be accepted.

Abstract This study presents a thermo-hydraulic analysis of a solar air heater with an internal multiple-fin array. A preliminary simple test was carried out to confirm the efficiency enhancement of the proposed arrangement. A mathematical model of heat transfer processes was proposed. A thermo-hydraulic efficiency test was used to find the best fin arrangement of the receiver. For an applied set of ducts, calculations were carried out to find the thermo-hydraulic efficiency of the collector against the volumetric air flux. As a comparison, a smooth pipe arrangement was used. Calculation results of the mathematical model showed an existing optimum of thermo-hydraulic efficiency against the volume flux, fin thickness and duct width. If there is no limitation of the air speed, proposed half-pipe finned technology enables a 14% efficiency improvement in relation to the smooth pipe arrangement of the solar collector with black paint and double glass envelope, and 3.3% for the solar collector with selective layer and single glass envelope. If 5 m/s speed limit of air in piping system is assumed, proposed half-pipe finned technology enables a 13% efficiency improvement in relation to the smooth pipe arrangement of the solar collector with black paint and double glass envelope, and 11% for the solar collector with selective layer and single glass envelope. Proposed multiple fin-array technology enables to decrease the demanded air flux of 7–10 times in comparison to the smooth pipe arrangement of the absorber. Even with the flux decreased, the efficiency of internal multiple-fin array arrangement is higher than the one available for smooth pipe arrangement. The solution could be applied in solar space heating with rock bed storage systems or in solar dryers.

Thermal performance was tested during cycling work for latent heat storage systems based on KNO3 and NaNO3 (weight ratio 54:46). For heat transfer improvement, cast aluminum honeycomb-shaped structures were produced via 3D printing of polymer model and investment casting. Different wall thicknesses were tested at 1.2 mm and 1.6 mm. The obtained results were compared to working cycles of pure PCM bed. The use of enhancers is reported to improve the rate of charging and discharging of the deposit. In the next step, the structures were examined with numerical simulation performed with ANSYS Fluent software. The wall thicknesses taken into consideration were the following: 0.8, 1.2, 1.6, and 2.0 mm. An insert with a greater wall thickness allows for smaller dT/dt and better heat distribution in the vessel. The investment casting process enables the manufacturing of complex structures of custom shapes without porosity and contamination.

This article presents an analysis of selecting a seasonal heating system for an existing greenhouse. The analyzed object is located in Poland near Wroclaw, where summer flowers are grown. Appropriate thermal conditions must be ensured continuously for four heating months. The primary source of heat in the examined flower greenhouse was a coal-fired furnace. The analysis presented in the article shows a method of thermal balancing the object, determining heat demands in the analyzed period using the experiment plan, and also selecting a new heating system in the form of a heat pump. The analysis of the operation of the heating system was performed for air and ground source heat pumps to determine the profitability of their application in Polish climatic conditions. An economic analysis was also included and the investment impact on pollution emissions was calculated.