This paper presents an integrated methodology for developing polymer flat-plate solar collectors by combining optical characterization, analytical heat-transfer calculations, CFD simulations, and experimental assessment within a single workflow. A conventional metal flat-plate collector was first analyzed as a reference using an analytical calculation to establish baseline performance and efficiency-curve coefficients. In the second phase, analytical calculations were applied to a polymer solar collector while maintaining the same design as the metal collector. This allowed direct comparison, particularly for the tubular configuration, which proved inadequate due to excessive absorber temperatures. To address this, a modified design was proposed. Due to the limitations of analytical calculations, numerical simulations were required to evaluate this design in more detail. As a final step, a new collector design was developed and manufactured using an extrusion process. This prototype underwent experimental testing and detailed 3D numerical simulations, providing insights into the heat transfer phenomena and performance optimization. The developed 3D numerical model showed good agreement with the measurements carried out for the two operating points, with the numerical and experimental thermal-efficiency values agreeing within the corresponding expanded experimental uncertainties; at the higher inlet-water temperature, the outlet-temperature difference was 0.23 °C. The proposed polymer collector with a non-selective coating achieved 15–20% lower thermal efficiency than the state-of-the-art metal flat-plate collector with a selective coating, at the reduced temperature difference Tred = 0.08m2K/W. The parametric analysis showed that applying a selective absorber coating can increase thermal efficiency by up to 8%, while increasing the cover–absorber spacing alone resulted in only minor improvements of up to 2%. Based on these results and previously published work, practical guidelines are formulated to support the development of pre-commercial prototypes. These findings highlight the importance of geometry adaptation and material selection in enhancing thermal performance of polymer solar collectors.

Novel design methodology for low-cost solar simulator for testing standard-sized solar collectors at various incidence angles is introduced. Ray tracing and theoretical approach are used to define development stages. Simulator dimensions are defined in the initial stage. Light source selection and ray tracing analysis are shown for prototype system combining visible spectrum LED reflectors and infrared quartz heaters. Configurations of light sources are assessed using ray tracing to achieve uniform test area irradiation. Prototype assembly and testing are presented and JIS C 8904-9 compliance standard characteristics are determined. Spectral match to solar spectrum results in Class C. Spatial non-uniformity of irradiance is 7.8 % and classified as B. Short-term and long-term temporal instability yields values of 0.39 % and 0.63 %, respectively. Temporal instability achieved Class A. The overall classification of the simulator is CBA. Total simulator power draw is 9.07 kW with a conversion efficiency of 33.6 %. Using the developed prototype, stagnation temperature measurements of polymer collector prototype was conducted using solar simulator and outdoor setup. Prototype collector stagnation temperature without any overheating protection was 95 degrees C in the simulator and 90 degrees C in the outdoor test setup. With overheating protection it reached 73 degrees C in the simulator and 70 degrees C in the outdoor setup.

The presented research deals with an experimental and numerical evaluation of the thermal characteristics of a novel prototype polymer solar collector design. The experimental part comprises an alternative approach for determining the optical characteristics of polymer materials and measurements of thermal efficiency. Functional dependency of thermal efficiency on solar radiation, working fluid and air temperature is computed. In order to validate the numerical model built in the ANSYS FLUENT software package, simulations are performed on a segment of the polymer solar collector, and the findings are correlated with the experimental ones. The efficiency curve is determined for a whole collector consisting of eight analysed segments. The obtained efficiency of the proposed polymer collector design is 20% lower relative to the state-of-the-art flat plate collector during the typical summer operating regime. A parametric numerical analysis of a polymer solar collector is carried out to evaluate the influence of design and operating parameters on thermal performances and to provide design improvement guidelines. In addition, stagnation temperature measurements are conducted in accordance with EN ISO 9806:2017 when a stagnation temperature of 125.1 degrees C is recorded after the application of overheating protection measures.

In this work, the effects of proposed measures for improving environmental footprint of woody and non-woody biomass combustion in residential appliances, comprising partial insulation of combustion chamber and inclusion of combustion intensifier are numerically and experimentally evaluated. In the numerical part, a simplified modeling approach for wood pellets, based on Finite-Rate and Eddy-Dissipation model, is presented and the obtained combustion reaction maps are extensively discussed. The accompanying experiments with wood and agropellets are performed in a multi-fuel boiler equipped with rotary pellet burner. It is found that significant reductions in pollutant emissions are obtained (CO - 31 to 78%, PM - 28 to 56 mg/Nm(3) at standardized oxygen content). The results also show that by combining both measures, CO emissions below 1000 mg/Nm(3) at the standardized oxygen content (limitation for Class 4 according to EN 303-5:2021), without a significant drop in combustion efficiency (approx. 2%), can be expected for agropellets. The optimal combustion conditions can be achieved with lower excess air ratio, whereby a slight reduction in NOx emissions can be accomplished.

This paper presents the methodology for conducting a cost-optimal energy performance calculation of a solar hot water system, used for space heating and domestic hot water needs. The calculation is based on dynamic hourly methods, according to the new Energy Performance of Buildings’ (EPB) set of standards EN 15316:2017, and a revision of the standard EN 15316-5:2017 from the year 2021, dealing with storage-tank water temperature calculations. The paper provides proposals for modifications to these newly introduced standards, in order to overcome the observed ambiguities and shortcomings. The calculation of annual energy performance of a building was performed on an hourly basis over a year for the reference of an nZEB multi-apartment building, for a climate area of the city of Zagreb, taking into account water temperature change in the layers of the storage tank connected to solar collectors and hot water boilers. The cost-optimal solution was then determined by varying individual parameters of the building technical system. The influence of these parameters on the energy efficiency of the building was analyzed in detail. Furthermore, the results were compared against those obtained by the Croatian calculation algorithm based on the previous set of EPB standards, EN 15316:2008, currently used EU-wide for the energy performance certification of buildings. The results indicated that the calculation methods of the present algorithm underestimated the consumption of building primary energy by 12%. The energy delivered by solar collectors was underestimated by 18%.

This paper presents differences in calculations of annual heating and cooling energy need performed by numerical dynamic simulations software IDA ICE and those carried out by the modification of simple hourly method from EN ISO 13790 EN ISO 13790, widely used for determining building energy need. A simple model of a nearly-zero energy building was created and all heat gains and set-points that could lead to a mismatch in initial or boundary conditions were analysed. The impact of those on the annual heating and cooling energy need was examined by adding and/or removing every single one of them. Boundary conditions in numerical dynamic simulations were set up to match those in simple hourly method. Such an approach enables evaluation of differences in results and definition of their origin. The comparison of results has shown that in most cases, annual energy need for heating and cooling calculated using numerical dynamic simulations software differs from that calculated using EN ISO 13790. Among the others, more detailed heat accumulation model of heat gains in building’s envelope in IDA ICE software was marked as the main reason. Fact that solar heat gains seem to be underestimated by EN ISO 13790 and differences in heat transfer towards ground contribute to the differences in results as well.

This paper presents the research on improving combustion of wood and agro pellets in domestic hot water boilers. The novel biomass combustion system concept consisting of rotary burner and two types of combustion intensifiers is proposed, with the aim to allow simple application in the most of existing boilers, as well as to improve the efficiency and emissions to extent the related requirements of the relevant EU standards are met. In this regard, inclusion of the combustion intensifier based on honeycomb structure into conventional combustion system is numerically and experimentally investigated and the most appropriate placement in a furnace found. The results show that, with such implementation of the combustion intensifier, significant reductions in unburned pollutant emissions (CO >40% in case of wood pellets and >30% in case of agro pellets), particulate matter emissions (28–56 mg/mn3 at 10% of O2 in dry flue gases) and improvements in combustion efficiency (>2.6–3.7%) can be obtained. A detailed numerical analysis of the subsequent combustion process within the combustion intensifier lead to the novel combustion intensifier design, aimed at lowering manufacturing cost. Preliminary numerical and experimental results indicate similar or slightly less reduction in unburned pollutants of novel design.

Most of the physical parameters that are used to assess the satisfaction with the ambient thermal condition in a mathematical way are contained within the definition of operative temperature.This temperature, which can be used as a representative of indoor thermal comfort, is a function of the air temperature, the mean radiant temperature and the relative air velocity.In this paper, the room air, mean radian temperature and indoor air velocity were determined experimentally for wall-mounted convector and conventional radiator at controlled room conditions.The room air temperature and indoor air velocity were continuously measured at several positions and heights (0.75 m and 1.5 m) using calibrated T-type thermocouples and hot wire probes, while mean radiant temperature was calculated using the thermograms captured by the IR thermal camera and numerically computed radiation view factors.Each wall was divided into several sections with approximately similar temperatures (differences < 0.5 °C) for which view factors were determined.Thermal heat output of the tested heat emitters was derived according to EN 442-2:2014.Obtained results were analysed and conclusions about the achieved thermal comfort and related energy saving were made accordingly.

This paper presents new approach for determining buildings technical system energy performance. This new methodology describes a mathematical model for accurately predicting indoor temperature and heat losses of the space heating and domestic hot water system components. The entire model is described by system of ordinary differential equations which can be solved using standard numerical techniques. The innovative aspect of the method is the integral approach in mathematical modeling of buildings energy needs and technical systems heat loss, taking into account heat accumulation in all considered parts (building envelope + technical system). Such approach allows a detailed insight of the system behavior for chosen working conditions. This model can serve for energy performance calculations in a wide variety of buildings types and their technical systems. The calculation example is given for family house, equipped with conventional space heating and domestic hot water heating system, with the time step of 1 min and for characteristic day of each month within a year. The results are compared against those obtain from EN ISO 13790 and standard series EN 15316. The comparison shows significant differences in determination of the annual delivered energy to the heating system (33%), as a consequence of difference in estimation of the energy need for heating (15%) and calculation of the technical systems recoverable heat losses utilization factor, which seems to be underestimated. The delivered energy to the space heating and domestic hot water heating system differs 25%, while the energy delivered to the generation system differs 4%. (C) 2016 Elsevier Ltd. All rights reserved.

This handbook aims at providing practical information about application of solar cooling systems in buildings. First part comprises basics on solar energy and its utilization in hot water systems for conversion into useful thermal energy, since solar cooling systems can also be used for domestic hot water and space heating purposes. Second part deals with thermally driven cooling systems including all auxiliary components and design guidelines based on knowledge and experiences gained from design and monitoring of installed systems. The main purpose of this handbook is to provide investors, designers and potential users with practical and reliable information on suitability of solar cooling systems for particular application during the decision-making and the design processes as well to promote usage of such systems which can significantly reduce primary energy consumption in buildings.