The growing global energy demand has been faced with increasing concerns about climate change over recent decades. In order to cover the additional demand and to mitigate CO2 emissions, one option is to utilize renewable energies such as solar and wind power. These energy sources are, however, intermittent by nature. Therefore, it is inevitable that a quick balancing and back-up power should be available to maintain grid stability at a certain level. Gas turbine (GT) technology could certainly be one alternative for back-up/balancing power and could be utilized to complement renewable energy in the energy market. However, the GT industry needs to consider innovative cycle configurations to attain higher system performance and lower emissions and to cope with renewable powers. In this regard, the humid air turbine (HAT) cycle and the exhaust gas recirculation (EGR) cycle are amongst the promising GT cycles. In the current study a micro gas turbine (MGT), a Turbec T100, has been selected as the base case for further investigation. A thermodynamic model for the base case has been developed in IPSEpro software and validated using experimental data obtained from an existing test facility in Stavanger, Norway. Based on this validated model, system performance calculations for other alternative cycles, i.e. EGR and HAT cycles, have been carried out. Results confirm that the performance improvement potential is significant for the HAT cycle with only minor modifications to the baseline MGT cycle. The EGR cycle, with a maximum attainable recirculation ratio of 50%, shows a slightly lower level of performance compared to the base case. However, its potential for future CO2 capture is greater compared to the base case and the HAT cycle. The overall cycle efficiencies for the base case, the HAT, and the EGR cycles at full load operation, i.e. 100kW power, are 31.1%, 32.8%, and 30.4%, respectively.
This work deals with the optimization of a solar-assisted ground-source CO2 heat pump system using the Taguchi method and the utility concept. Nine control factors were investigated, including the Borehole Heat Exchanger (BHE) length, BHE spacing, BHE number, solar collector (SC) area, tank thermal energy storage volume, BHE-SC mass flow rate, space heating return temperature, heat pump high-side pressure, and heat pump's output temperature. The seasonal performance factor (SPF), levelized cost of heating (LCOH), and the estimated maximum annual ground temperature change (GTC) were chosen as the response factors to evaluate system performance. The system model was developed using Modelica and 27 simulation runs were implemented according to the L27 (9 3 ) Taguchi orthogonal array. Single objective optimizations were first performed using the Taguchi method to determine the parameter combinations that would optimize the SPF, LCOH, and GTC, separately. After that, multi-objective optimization was performed using the combined Taguchi method-utility concept to determine the control factor combination that would give the optimal overall performance when all response factors are considered simultaneously and given equal importance. Single objective optimizations show that the SPF, LCOH, and GTC are individually most sensitive to the target output temperature of the heat pump, the BHE length, and the SC area, respectively. Optimizing the response factors individually resulted in an SPF of 4.2, an LCOH of 0.122 USD/kWh, and a GTC of 100.24%. Multi-objective optimization resulted in a control factor combination that gave an SPF of 3.58, LCOH of 0.165 USD/kWh, and GTC of 100.03%. When optimized, this system exhibited a performance that is almost comparable to that of conventional systems.
Previously published studies have addressed modifications to the engines when operating with biogas, i.e. a low heating value (LHV) fuel. This study focuses on mapping out the possible biogas share in a fuel mixture of biogas and natural gas in micro combined heat and power (CHP) installations without any engine modifications. This contributes to a reduction in CO2 emissions from existing CHP installations and makes it possible to avoid a costly upgrade of biogas to the natural gas quality as well as engine modifications. Moreover, this approach allows the use of natural gas as a “fallback” solution in the case of eventual variations of the biogas composition and or shortage of biogas, providing improved availability. In this study, the performance of a commercial 100kW micro gas turbine (MGT) is experimentally evaluated when fed by varying mixtures of natural gas and biogas. The MGT is equipped with additional instrumentation, and a gas mixing station is used to supply the demanded fuel mixtures from zero biogas to maximum possible level by diluting natural gas with CO2. A typical biogas composition with 0.6 CH4 and 0.4 CO2 (in mole fraction) was used as reference, and corresponding biogas content in the supplied mixtures was computed. The performance changes due to increased biogas share were studied and compared with the purely natural gas fired engine. This paper presents the test rig setup used for the experimental activities and reports results, demonstrating the impact of burning a mixture of biogas and natural gas on the performance of the MGT. Comparing with when only natural gas was fired in the engine, the electrical efficiency was almost unchanged and no significant changes in operating parameters were observed. It was also shown that burning a mixture of natural gas and biogas contributes to a significant reduction in CO2 emissions from the plant.
Energy consumption for cooling is the fastest-growing use of energy in buildings, and the space cooling systems have become one of the major end-users in building service systems. In recent years, phase change materials (PCM) have been increasingly adopted to reduce cooling energy consumption. This paper presents the simulations of an integrated latent heat thermal energy storage (ILHTES) system for residential buildings, which includes the PCM-to-air heat exchanger (PAHX) and air conditioner (AC). In this study, the Modelica language is adopted to develop the numerical model of the ILHTES system. A numerical heat transfer model has been used to simulate the performance of PCM-to-air heat exchanger, and it has been validated against data from the literature. Using the Modelica library AixLib, a simulation of the dynamic behavior and energy consumption of the building is performed. With the help of the ILHTES model, the optimal design of the system can be obtained using the results of the simulations throughout the cooling season. This study evaluates the energy savings potential of the ILHTES system over the conventional air conditioning system under realistic climate conditions in Budapest. The results show that an energy saving ratio of 32.4% can be achieved. The effect of PCM type on energy consumption of the ILHTES system is investigated, the results show that for three commercially available PCMs, RT25, RT20, and RT18, the ILHTES system using RT25 can utilize less energy and obtain a higher energy saving ratio.
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