The paper presents an application of the Finite Elements Method for stress and strain analysis of the hot water boiler structure. The aim of the research was to investigate the influence of the boiler scale on the thermal stresses and strains of the structure of hot water boilers. Results show that maximum thermal stresses appear in the zone of the pipe carrying wall of the first reversing chamber. This indicates that the most critical part of the boiler are weld spots of the smoke pipes and pipe carrying plate, which in the case of significant scale deposits can lead to cracks in the welds and water leakage from the boiler. The nonlinear effects were taken into account by defining the bilinear isotropic hardening model for all boiler elements. Temperature dependency was defined for all relevant material properties, i. e. isotropic coefficient of thermal expansion, Young’s modulus, and isotropic thermal conductivity. The verification of the FEA model was performed by comparing the measured deformations of the hot water boiler with the simulation results. As a reference object, a Viessmann - Vitomax 200 HW boiler was used, with the installed power of 18.2 MW. CAD modeling was done within the Autodesk Inventor, and stress and strain analysis was performed in the ANSYS Software

Article Highlights• Applied method -Energy and exergy analysis • Paper goal -Application of energy and exergy analysis of hot water boiler • The obtained results: largest energy loss -flame pipe, largest exergy -leaving flue gasses • Investigation of possibilities of design modification to increase reliability and availability • Proposing and analyzing more reliable solution AbstractIn engineering practice, exergy can be used for technical and economic optimization of energy conversion processes. The problem of increasing energy consumption suggests that heating plants, i.e., hot water boilers, as energy suppliers for household heating should be subjected to exergy and energy analysis. Heating plants are typically designed to meet energy demands, without the distinguished difference between quality and quantity of the produced heat. In this paper, the energy and exergy analysis of a gas fired hot water boiler is conducted. Energy analysis gives only quantitative results, while exergy analysis provides an insight into the actually available useful energy with respect to the system environment. The hot water boiler was decomposed into control volumes with respect to its functional components. Energy and exergy of the created physical model of the hot water boiler is performed and destruction of exergy and energy loss in each of the components is calculated. The paper describes the current state of energy and exergy efficiency of the hot water boiler. The obtained results are analyzed and used to investigate possibilities for improvement of availability and reliability of the boiler. A comparison between the actual and the proposed more reliable solution is made.Improving energy efficiency as well as energy saving represents one of the major problems of modern developed countries worldwide. Hot water boilers, common in district heating systems, should be subjected to reliability, safety and efficiency research [1]. The efficiency of a hot water boiler has a large impact on thermal performance in district heating systems. In order to improve efficiency, heat transfer from flue gases to water is increased to reduce energy losses Correspondence: M.N. Todorović, Faculty of Mechanical Engineering,

Multi-dimensional numerical simulation of the atmospheric saturated pool boiling is performed. The applied modelling and numerical methods enable a full representation of the liquid and vapour two-phase mixture behaviour on the heated surface, with included prediction of the swell level and heated wall temperature field. In this way the integral behaviour of nucleate pool boiling is simulated. The micro conditions of bubble generation at the heated wall surface are modelled by the bubble nucleation site density, the liquid wetting contact angle and the bubble grow time. The bubble nucleation sites are randomly located within zones of equal size, where the number of zones equals the nucleation site density. The conjugate heat transfer from the heated wall to the liquid is taken into account in wetted heated wall areas around bubble nucleation sites. The boiling curve relation between the heat flux and the heated wall surface temperature in excess of the saturation temperature is predicted for the pool boiling conditions reported in the literature and a good agreement is achieved with experimentally measured data. The influence of the nucleation site density on the boiling curve characteristic is confirmed. In addition, the influence of the heat flux intensity on the spatial effects of vapour generation and two-phase flow are shown, such as the increase of the swell level position and the reduced wetting of the heated wall surface by the heat flux increase.

A polygeneration system is an energy system capable of providing multiple energy outputs to meet local demands, by application of high process integration. In this paper, optimal configuration and capacity of a polygeneration system for an indoor swimming pool building is determined by application of a method based on TRNSYS simulation and GenOpt optimization software. Based on the applicability, a superstructure of the polygeneration system is integrated, consisting of the following polygeneration modules: an internal combustion engine cogeneration module, a vapor compression chiller, and adsorption chiller, a ground source heat pump, flat plate solar thermal collectors, photovoltaic collectors, and heat storage. Annual behavior of energy loads of the public swimming pool building during a typical meteorological year and the polygeneration system are modeled and simulated using TRNSYS software, whereas techno-economic optimization is performed by GenOpt optimization. The results indicated the optimal configuration of the polygeneration system for the modelled energy demands, as well as the optimal capacity of the polygeneration modules, thus defining the optimal capacity of the polygeneration system for the energy demands of the public swimming pool building.

Buildings with indoor swimming pools have a large energy footprint. The source of major energy loss is the swimming pool hall where air humidity is increased by evaporation from the pool water surface. This increases energy consumption for heating and ventilation of the pool hall, fresh water supply loss and heat demand for pool water heating. In this paper, a mathematical model of the swimming pool was made to assess energy demands of an indoor swimming pool building. The mathematical model of the swimming pool is used with the created multi-zone building model in TRNSYS software to determine pool hall energy demand and pool losses. Energy loss for pool water and pool hall heating and ventilation are analyzed for different target pool water and air temperatures. The simulation showed that pool water heating accounts for around 22%, whereas heating and ventilation of the pool hall for around 60% of the total pool hall heat demand. With a change of preset controller air and water temperatures in simulations, evaporation loss was in the range 46-54% of the total pool losses. A solar thermal sanitary hot water system was modelled and simulated to analyze it's potential for energy savings of the presented demand side model. The simulation showed that up to 87% of water heating demands could be met by the solar thermal system, while avoiding stagnation.paper. Pool water heating and pool hall air heating using heating, ventilation and air conditioning (HVAC) equipment increases water evaporation and relative air humidity, which raises energy demands of the building. A careful design and control of the HVAC system is needed to maintain water and air temperatures and air humidity at optimal levels for efficient operation. In this paper, target values of PW and SPH air temperatures were varied in the simulations to determine their impact on energy losses and address the problem of optimal values of these parameters. Energy balance models are usually a starting point of any performance, design or energy efficiency analysis of swimming pools [2, 4-6], but the impact of desired air and water temperatures on the SPH energy balance was not considered. The highest thermal loads in indoor swimming pools, often originate from water evaporation from the pool water surface, but the effect of evaporation is difficult to model with precision [7].Due to a similar profile of heat demand and available solar radiation, solar energy has been used to heat swimming pools for decades. The utilization of solar energy, due to relatively low temperatures at the demand side, is especially significant for open swimming pools. In 1963, Czarnecki [8] proposed a method for solar heating of outdoor swimming pools using a transparent plastic pool cover, which raised solar radiation gains while reducing evaporative loss. Szeicz and McMonagle [9] made an energy balance of urban swimming pool in 1982, and found the use of solar collectors and pool blankets to be most effective. The performance of an open absorption system and mechanical heat pump for use...