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In the present research, a yearly performance of a gas turbine unit and the unit with the added inlet air cooling technologies (IACTs) was investigated in terms of performance and output power using TRNSYS software. The existing system was retrofitted with five different IACTs, namely Config. A: existing system integrated with an evaporative media, Config. B: existing system integrated with a fogging unit, Config. C: existing system integrated with a mechanical chiller, Config. D: existing system integrated with an absorption chiller, and Config. E: existing system integrated with a thermal energy storage. The configurations were examined to determine the most proper configuration. The study revealed that Config. C was superior and was the optimal configuration for the gas turbine unit and it was recommended for the existing system. The study showed that Config. C was capable of enhancing the yearly output power with about 10.62%. After determining the proper configuration, a method benefiting a passive energy technology of heat pipe structure was also proposed. In the proposed method, a water-to-air heat pipe heat exchanger (HPHX) consisting of single heat pipe tubes was planned to be added to Config. C as a pre-cooling equipment. To this end, the mathematical performance of the water-to-air HPHX was derived to be defined in TRNSYS studio. It was shown that a considerable amount of energy could be obtained after adding the water-to-air HPHX to Config. C. The exergy analysis also proved that application of IACT improves the exergy efficiency of the whole system. Keywords Gas turbine units • Inlet air cooling technologies (IACT) • Output power • Performance • TRNSYS List of symbols A Heat transfer area (m 2) a Tube distance in a row in Eq. (39) (mm) b Distance between the tubes in two successive rows in Eq. (39) (mm) bbl Barrel of oil C Heat capacity (J/s K) C pa Specific heat of air at constant pressure (kJ/ kg K) C pg Specific heat of turbine outlet gases at constant pressure (kJ/kg K) C 1 Constant in Eq. (21) (0.535) * M. Ahmadzadehtalatapeh

The energy demand in residential sector constitutes an important fraction of the entire energy consumption (40% in EU). Solar district heating (SDH) is a key strategy to reduce use of fossil fuels in buildings. Inside the European project REPLICATE, financed by Horizon 2020 SCC1 Smart Cities and Communities, a SDH with a seasonal storage (STES) has been designed to be realized in the city of Florence. It is the first example of solar district heating with a STES in Italy. The design phase has aimed to size properly the extension of solar field and the volume of seasonal storage based on several parameters such as number of dwellings to feed, heat demand, solar resource, geology of the location and economic reasons. The paper deals with the model that has been realized through TRNSYS to describe the energy fluxes of heating plant andtheir optimization process. The computational model depicts the possible operating conditions and leads to define the control strategies of solar field and seasonal storage, integrated with commercial components that complete theplant such as gas boiler, heat pump and overall circuit. Hot water tank TES has been selected as the appropriate typology of storage for this application based on geological considerations. The thickness of insulation material and various layers have been determined. The numerical analysis fixes the volume of TES to be 3800 m3 and a solar field of about 1000 m2. The solar fraction expected by the district heating is 44%.