•A constraint equivalent model for heat networks is proposed. In this model, the operational constraints of heat networks are mapped to the feasible region of CHP units, which protects the privacy of ...heat networks.•A boundary point search method is further developed to efficiently solve the constraint equivalent model and construct a high-accuracy approximation of actual feasible region.•A cooperation method with the rolling horizon strategy is proposed considering the uncertainties of heat and power loads. In the proposed cooperation method, the feasible region of CHP units is provided to the power system only once, which alleviates the communication burden.•Compared with other cooperation methods, simulation results show the advantages of the proposed cooperation method in balancing privacy protection and the quality of the solution.•The impact of heat storage tanks and uncertainties of heat loads on the boundaries of the feasible region is further analyzed.
The cooperation of combined heat and power (CHP) systems can improve efficiency in energy utilization by fully utilizing the complementarity between heat and power. However, heat and power systems are operated by different companies where data sharing is restricted for privacy reasons, thus posing significant obstacles to collaboration. This paper proposes a coordinated operation method for CHP systems based on the constraint equivalent model. To preserve the operational constraints of heat networks and protect data privacy, a boundary point search method is firstly developed, where the operational constraints of heat networks are mapped to the feasible region of CHP units. Then, a multi-period cooperation model considering uncertainties of both networks is established based on the proposed constraint equivalent model and the rolling horizon strategy. Moreover, the impact of heat storage tanks and uncertainties of heat loads on the boundaries of the feasible region for heat networks is further analyzed. Simulation results demonstrate the effectiveness of the proposed constraint equivalent model and the cooperation method.
The impact of the enhanced heat transfer performance of longitudinal fins on the entire process of melting and solidification in a phase change heat storage unit is investigated through experiments ...and numerical simulations in this paper. The position and structure of the longitudinal fins are optimized by using the response surface method while ensuring that the total volume of the heat storage medium remains unchanged. Studies have identified that some challenging zones in melting and solidification significantly impact the heat transfer of the entire heat storage cycle. Specifically, the challenging zone in melting primarily exists in the lower part of the unit during the charing process, while the challenging zone in solidification is mainly distributed around the unit during the discharging process. Through optimization, the optimized structure (fin spacing is 22.5 mm, fin width is 6.05 mm) can reduce the charging and discharging time by 16.94 % and 45.90 %, respectively. Additionally, the round trip time is significantly reduced by 39.19 %, and the mean heat absorption rate during the melting process is enhanced by 20.28 %. Moreover, the mean heat release rate during solidification is enhanced by 80.23 %.
The presented research project uses an innovative measurement technology to investigate large atmospheric heat storage tanks with water as heat storage medium. For this type of heat storage tanks ...only a few scientific descriptions are available in literature. Measurement data combined with simulation results offer further insight into the temperature field. The findings enable assessment of thermal losses, improvements on load management and thereby reduction in of primary energy use.
The thermal advantages by utilizing discharge from different levels in solar storage tanks are investigated, both for a small SDHW system and for a solar combisystem.
The investigations showed that ...it is possible to increase the thermal performance of both types of systems by using two draw-off levels from the solar tanks instead of one draw-off level at a fixed position.
The best position of the second draw-off level is in the middle or just above the middle of the tank. For the investigated small SDHW system with a realistic draw off hot water temperature of 40
°C and 45
°C and an auxiliary volume temperature of 50.5
°C the increase of the thermal performance by the second draw-off level is about 6%.
For the investigated solar combisystem the increase in thermal performance by using one extra draw-off level, either for the domestic hot water heat exchanger or for the heating system, is about 3%, while an improvement of about 5% is possible by using a second draw-off level both for the domestic hot water heat exchanger and for the heating system.
In response of the current situation of the low efficiency of power to gas utilization and the limitations of only configuring heat storage tanks to improve the ability of absorbing wind power, this ...paper constructs a combined heat and power system with the coordination operation of power to gas heat recovery and heat storage tanks. The principle of the system for wind power consumption is firstly deeply described, and the carbon trading mechanism is introduced into the model considering the carbon emission. Furthermore, a low-carbon economic optimization model is set up with the objective to minimize the total cost of system operation. Finally, the simulation analysis in different operation scenes for a regional combined heat and power system is discussed in detail to verify the validity and availability of the proposed method in the paper.
The heat storage tank is an important element in any heating system where the heat source is not able to provide heat accordingly to consumer demand (for example solar collector systems, solid fuel ...boilers etc). Better heat storage efficiency can be achieved by providing good thermal stratification in the heat storage tanks. One of the best methods of increasing the degree of thermal stratification is the stratification pipes. In the Environmental monitoring laboratory of the Institute of Energy Systems and Environment (Riga Technical University, an experimental heat storage system has been developed and used for testing and studying stratification devices under different thermodynamic and hydraulic conditions. The experimental study carried out on the efficiency of the stratification pipe produced by German company SOLVIS Solar Systeme GmbH under different flow parameters, has been analyzed. The main aim of the experimental study was to define optimal heating system operation parameters to achieve good performance of the stratification pipe and a high degree of thermal stratification in the heat storage tank.
The distribution of temperature according to the height in the heat storage stratified water tanks designed for the heating of premises is uneven. In order to determine possible thermal energy amount ...stored in the tank it is necessary to know the residual water temperature in the tank. In the experiments with vertical thermal energy storage tanks of 0.31, 0.9 and 1.5
m diameter, we determined that at a duration of charging of 8
h, and discharging of 16
h, the value of temperature transitional zone height at 90% probability is 0.47±0.03
m. Using analytical methods we worked out carry-overs for the determination of residual temperature of heat accumulating tanks with external and internal heat sources. It was determined that in the heat storage tanks with internal heat source fitted at the bottom of the tank the residual water temperature is higher, and the amount of accumulated thermal energy is lower than in the tanks with external heat source.
Recently, district heating and cooling (DHC) plants with heat storage tanks have become common. But the optimization of the operational planning for these systems requires much computation time. In ...this paper, an optimal planning method for operation of these systems using a genetic algorithm (GA) was proposed. The proposed method has three new characteristics. Firstly, the optimization of DHC plant operation schedule to minimize both running costs and the dynamic load variation can be obtained. Secondly, it makes the search for optimal value more effective to use operator's know-how. Lastly, the probabilities of “crossover” and “mutation” can be changed dynamically to avoid converging to a local minimum value. Simulations demonstrated that the proposed method gives ten times faster computation time of dynamic programing needed to obtain the minimum operation cost and small load variation.
•Cost-emission performance of PV/battery/fuel cell hybrid energy system is studied.•Multi-objective optimization model for cost-emission performance is proposed.•ε-constraint method is proposed to ...produce Pareto solutions of multi-objective model.•Fuzzy satisfying approach selected the best optimal solution from Pareto solutions.•Demand response program is proposed to reduce both cost and emission.
Optimal operation of hybrid energy systems is a big challenge in power systems. Nowadays, in addition to the optimum performance of energy systems, their pollution issue has been a hot topic between researchers. In this paper, a multi-objective model is proposed for economic and environmental operation of a battery/fuel cell/photovoltaic (PV) hybrid energy system in the presence of demand response program (DRP). In the proposed paper, the first objective function is minimization of total cost of hybrid energy system. The second objective function is minimization of total CO2 emission which is in conflict with the first objective function. So, a multi-objective optimization model is presented to model the hybrid system’s optimal and environmental performance problem with considering DRP. The proposed multi-objective model is solved by ε-constraint method and then fuzzy satisfying technique is employed to select the best possible solution. Also, positive effects of DRP on the economic and environmental performance of hybrid system are analyzed. A mixed-integer linear program is used to simulate the proposed model and the obtained results are compared with weighted sum approach to show the effectiveness of proposed method.
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