Operation simulation and comparison of solar district heating systems thermal performances

Plan Europske unije je u bliskoj budućnosti u potpunosti zamijeniti fosilna goriva obnovljivim izvorima energije. Jedan od mogućih načina uvođenja obnovljivih izvora energije u sustave daljinskog grijanja je korištenjem solarnih sustava. Time je moguće je riješiti problem grijanja zgrada, pripremu potrošne tople vode te proizvodnju električne energije te tako postati neovisni o fosilnim gorivima, plinu te uvozu energenata. U ovom radu provedena je analiza sustava solarnog daljinskog grijanja na području grada Zagreba. Predviđeno je kako sustav treba pokriti potrebe za toplinskom energijom za 25 stambenih zgrada, odnosno 4000 ljudi. Izrađen je model prema izvedenim sustavima u Danskoj i Austriji (Graz). Sustav se sastoji od kolektorskog polja, sezonskog spremnika topline i dizalice topline. Sa strane učinkovitosti kolektora takvi sustavi se pokazuju boljim rješenjem u odnosu na solarne sustave s toplovodnim kotlom. Model se sastoji od proračuna potrebne energije za grijanje i pripremu potrošne tople vode, sunčevog zračenja na nagnutu plohu te modela kolektora i toplinskog spremnika prema normama HRN EN 15316-4-3:2017 i prEN 15316-5-2021. Kut nagiba kolektora korišten u simulacijama iznosi 45°. Simulacije modela provedene su za pločaste i vakuumske kolektore te za različite površine kolektorskih polja i kapaciteta spremnika kako bi se odabralo optimalno rješenje. Nakon detaljnih analiza, odabran je sustav kolektorskog polja sa vakuumskim kolektorima površine 800 m2 i volumena spremnika 1000 m3 sa dizalicom topline (COP=4,6). Ukupna specifična prikupljena energija u kolektorima iznosi 922 kWh/m2 čime se pokriva 40,73% toplinskih potreba potrošača. Prosječna učinkovitost solarnih kolektora iznosi 0,6, a jednostavni period povrata investicije je prihvatljiv u odnosu na karakteristike sustava. Fotonaponski paneli odabrani su monokristalne strukture sa učinkovitošću od 0,15 prema EN 14316-4-6:2008. Dizalica topline sa fotonaponskim sustavom ima vrijednost SCOP-a 3. Konačna površina fotonaponskih panela iznosi 1954 m2.The plan of the European Union is to completely replace fossil fuels with renewable energy sources in the near future. One of the possible ways of implementing renewable energy sources into district heating systems is the use of solar systems. In this way it is possible to solve the problem of heating, domestic hot water preparation and electricity production, thus becoming independent of fossil fuels, gas and fuel import. In this work, an analysis of the solar district heating system in the area of the city of Zagreb has been carried out. Analyzed system should cover the heat energy consumption of 25 residential buildings, for 4000 people. A model was created based on the systems implemented in Denmark and Austria (Graz). The system consists of a solar collector field, a seasonal thermal energy storage and a heat pump. In terms of collector efficiency, such systems prove to be a better solution compared to solar systems with a hot water boiler. System with heat pump shows better results on the side of solar collector efficiency. The model consists of the calculation of the required energy for heating and domestic hot water preparation. Also, solar radiation on an inclined surface and the model of the collector and seasonal thermal energy storage have been calculated according to the standards HRN EN 15316-4-3:2017 and prEN 15316-5-2021. The collectors are mounted upright at an angle of 45° to the horizontal. Model simulations have been carried out for flat plate and evacuated tubular collectors and for different surfaces of collector fields and tank capacities in order to choose the optimal solution. After detailed analyses, a collector field system with evacuated tubular collectors of 800 m2 surface area and 1000 m3 storage volume with a heat pump (COP=4.6) was selected. The total specific energy collected in the collectors is 922 kWh/m2, which covers 40.73% of the heat energy consumption. The average efficiency of solar collectors is 0.6 and the simple investment return period is acceptable in relation to the characteristics of the system. Photovoltaic panels with monocrystalline structure are selected with an efficiency of 0.15 according to standard EN 14316-4-6:2008. The heat pump with the photovoltaic system has a SCOP value of 3. The final surface of the photovoltaic panels is 1954 m2