Search

In 2017, CEN (European Committee for Standardization) introduced a 2nd edition of standards for the assessment of buildings technical system energy performance (EN 15316 series of standards) supporting the Energy Performance of Buildings Directive. The main novelty is the introduction of an hourly time step calculation methods and of the new standard which takes into account dynamic temperature variations within the storage tank (EN 15316-5:2017). This standard contained many errors in the provided energy balance equations and ambiguities related to calculation procedure. Therefore, the revision of this standard has been made (prEN 15316-5:2023) and is now under approval of the relevant technical committee CEN/TC 228/WG4. prEN 15316- 5:2023 comprises two methods applicable to the different types of water-based storage systems and related control system. Particularly interesting is the Method A, which considers the temperature stratification within the storage tank. In the Method A several assumptions, concerning the modelling of water flow through the tank, homogeneity of water temperature within the layer, conduction and convection between the layers, had to be implemented in the calculation procedure. Currently, there are no analyses in the open literature that validate the introduced assumptions. To address this, the present paper provides a comprehensive analysis of the method accuracy in the case of solar storage by comparison with the results obtained by CFD simulations. Furthermore, the influence of the temperature distributions within the storage tank obtained by 1-layer (Method B of prEN 15316- 5:2023), 4-layer, 5-layer model and CFD simulation on the obtained solar collector thermal efficiency is given. The results show are no significant differences in calculated thermal efficiencies, except for the 1-layer model where the differences are up to 8% relative to the CFD simulation.

U sklopu diplomskog rada numerički je modelirana izmjena topline i strujanje vode unutar akumulacijskog spremnika solarnog toplovodnog sustava za pripremu potrošne tople vode i grijanje prostora. Dinamičke simulacije samog rada spremnika provedene su za odabrani period dana i režim korištenja u računalnom programu ANSYS Fluent. Zapremnina spremnika iznosila je 283,7 l, a odabrani učini izmjenjivača topline solarnog kruga te pomoćnog izvora prilagođeni su odabranom solarnom sustavu, dnevnoj potrošnji tople vode te potrebnoj energiji za grijanje prostora. Naglasak je dan analizi provođenja topline te slobodnoj konvekciji na temperaturnu raspodjelu u spremniku. Uspoređeni su rezultati simulacija s rezultatima proračuna temperaturne raspodjele u spremniku prema normi prEN 15316-5:2021, prilikom čega je spremnik podijeljen na više volumnih dijelova (segmenata). Zaključno, procijenjen je utjecaj rezultata simulacija i proračuna prema standardiziranoj proceduri na toplinsku učinkovitost solarnog kolektora u promatranom vremenskom periodu. In this work numerical modelling and analysis of heat transfer and water flow in solar storage tank was performed. Dynamic simulations of the tank in operating and heating mode for selected time of day, were carried out in computer software ANSYS Fluent. Capacity of stoarge tank is 283,7 l. Thermal output of heat exchanger for solar water heating and output of auxilliary heat exchanger were adapted for selected solar heating system, daily consumption of domestic hot water and required heating energy for space heating. Special attention was given to analysis of influence of conduction and natural convection on thermal stratification of storage tank. Simulation results were compared to ones acquired by using norm prEN 15316-5:2021. In doing so, storage tank was divided into multiple volume parts. Finally, impact of results of simulations and ones obtained by the norm on thermal efficiency of solar collector in selected time frame was assesed.

U sklopu ovog rada provedena je analiza toplinskih karakteristika dva različita člankasta radijatora. Analiza je provedena u Laboratoriju za toplinu i toplinske uređaje prema normi HRN-EN 442-2 za tri različite temperature ogrjevnog medija. Također bilo je potrebno provesti mjerenja brzina i temperatura zraka oko i između rebara radijatora te temperature prednjih ogrjevnih ploha radijatora. Uvodno je dan opis, glavne karakteristike te osnovna podjela radijatora. Nadalje opisan je postupak ispitivanja iz norme HRN EN 442-2. Dan je opis mjerne linije te samog mjerenja mjernom opremom koja se sastojala od anemometra sa žarnom niti, termoparova i termografske kamere. Rezultati mjerenja su podvrgnuti analizi te su korišteni za proračun koeficijenta prijelaza topline. Na kraju je dana usporedba rezultata dobivenih eksperimentalno za dva različita radijatora. In this work an analysis of the thermal characteristics of two different column radiators was conducted. Analysis was conducted in the Laborathory for heat and thermal devices according to norm HRN EN 442-2 for three different temperatures of working fluid. This work also contains measurements of velocities and temperatures of air around and in between radiator ribs and temperatures of front surfaces of radiators. This project work begins with an introduction where the elements of the test room and the standard of HRN EN 442-2, measuring line and measuring devices which consisted of hot-wire anemometer, thermocouples and thermographic camera are described. Results of the measurements were analysed and used in the calculation of the heat transfer coefficient. In the end experimental results for the two radiators are compared.