Search

The latent heat storage of phase change materials (PCMs) can be used in refrigeration and air conditioning systems. Storing cool energy during the nighttime (off-peak hours) and releasing the cool energy during the daytime (on-peak hours) to reduce the number of starts of the chiller and pumps is a practical approach for achieving energy saving and carbon reduction. Therefore, selecting PCMs is vital for improving energy efficiency and preventing future energy shortages. However, selecting PCMs is complicated by their unique characteristics and types. The purpose of this study was to establish a PCM selection model by combining the Delphi, analytic hierarchy process (AHP), and VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) methods to select the optimal PCM type applied in cold storage. A numerical example was used to verify the model's usability, confirming that A9 is the optimal PCM for the cold storage of an air conditioning system. This three-stage PCM selection model combining the Delphi, AHP, and VIKOR approaches provides a more suitable selection model and considers the selection method of material criteria. Moreover, it can solve the problem of difficult PCM selection. Simultaneously, it considers mechanisms to incorporate a company's primary considerations into material selection for real-world applications. These results can facilitate material evaluation and selection during system design and material qualification, helping companies achieve the goals of energy saving, carbon reduction, and sustainable management in the future. [ABSTRACT FROM AUTHOR]

Aiming at the issues of unreasonable cooperation schemes and inappropriate setting of parameters of the refrigeration system with multi-chiller plants, this paper presents a cooperative optimization method to improve the energy performance of the system composed of water-cooled chillers and air-cooled heat pumps. The cooperative optimization process includes scheme optimization and parameter optimization. To content the dynamic cooling load, the working sequence of air-cooled heat pumps and water-cooled chillers with variable frequency chilled water pumps is first optimized. Based on the optimal scheme, a back-propagation neural network (BPNN) coupled with particle swarm optimization (PSO) is implemented to explore the preferred operating parameters of multiple chiller plants corresponding to the best coefficient of performance (COP). Compared with the performance of the initial operation module, the energy consumption of the water pump and fan decreases by over 50%, and the COP of the refrigeration system is improved by 16% (COP = 3.85) through the scheme operation. After parameter optimization, the total energy consumption is reduced by 21.7%, and COP is increased by 26.5% (COP = 4.20). Therefore, the proposed cooperative optimization method can provide useful operation guidance for the refrigeration system with multi-chiller plants. [ABSTRACT FROM AUTHOR]

Many installed solar thermally driven cooling systems suffer from high auxiliary electric energy consumption which makes them not more efficient than conventional compression cooling systems. A main reason for this is the use of non-efficient controls with constant set points that do not allow a chiller power modulation at partial-load and therefore lead to unnecessary high power consumption of the parasitics. The aims of this paper are to present a method to control efficiently solar thermally driven chillers, to demonstrate experimentally its applicability and to quantify the benefits. It has been shown that the cooling capacity of a diffusion absorption chiller can be modulated very effectively by adjusting both the temperature and the flow rate of the cooling water. With the developed approach and the use of optimization algorithms, both the temperature and the flow rate can be controlled simultaneously in a way that the cooling load is matched and the electricity consumption is minimized. Depending on the weather and operating conditions, electricity savings between 20% and 60% can be achieved compared to other tested control approaches. The highest savings are obtained when the chiller is operated at partial load. The presented method is not restricted to solar cooling systems and can also be applied to other conventional heating ventilation and air conditioning (HVAC) systems. [ABSTRACT FROM AUTHOR]

Trigeneration plants can use different types of chillers in the same plant, typically single effect and double effect absorption chillers, vapour compression chillers and also cooling storage systems. The highly variable cooling demand of the buildings connected to a district heating and cooling (DHC) network has to be distributed among these chillers to achieve lower operating costs and higher energy efficiencies. This problem is difficult to solve due to the different partial load behaviour of each chiller and the different chiller combinations that can cover a certain cooling demand using an appropriate sizing of the cooling storage. The objective of this paper is to optimize the daily plant operation of an existing trigeneration plant based on cogeneration engines and to study the optimal cooling load sharing between different types of absorption chillers using a mixed integer linear programming (MILP) model. Real data from a trigeneration plant connected to a DHC close to Barcelona (Spain) is used for the development of this model. The cooling load distribution among the different units is heavily influenced by the price of the electricity sold to the grid which rules the duration of the operation time of the engines. The main parameter to compare load distribution configurations is the primary energy saving indicator. Cooling load distribution among the different chillers changes also with the load of the whole plant because the chiller performance changes with load. [ABSTRACT FROM AUTHOR]

The scheduling of both absorption cycle and vapour compression cycle chillers in trigeneration plants is investigated in this work. Many trigeneration plants use absorption cycle chillers only but there are potential performance advantages to be gained by using a combination of absorption and compression chillers especially in situations where the building electrical demand to be met by the combined heat and power (CHP) plant is variable. Simulation models of both types of chillers are developed together with a simple model of a variable-capacity CHP engine developed by curve-fitting to supplier's data. The models are linked to form an optimisation problem in which the contribution of both chiller types is determined at a maximum value of operating cost (or carbon emission) saving. Results show that an optimum operating condition arises at moderately high air conditioning demands and moderately low power demand when the air conditioning demand is shared between both chillers, all recovered heat is utilised, and the contribution arising from the compression chiller results in an increase in CHP power generation and, hence, engine efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid algorithm to solve the optimal energy dispatch of an ice storage air-conditioning system. Based on a real air-conditioning system, the data, including the return temperature of chilled water, the supply temperature of chilled water, the return temperature of ice storage water, and the supply temperature of ice storage water, are measured. The least-squares regression (LSR) is used to obtain the input-output (I/O) curve for the cooling load and power consumption of chillers and ice storage tank. The objective is to minimize overall cost in a daily schedule while satisfying all constraints, including cooling loading under the time-of-use (TOU) rate. Based on the Radial Basis Function Network (RBFN) and Ant Colony Optimization, an Ant-Based Radial Basis Function Network (ARBFN) is constructed in the searching process. Simulation results indicate that reasonable solutions provide a practical and flexible framework allowing the economic dispatch of ice storage air-conditioning systems, and offering greater energy efficiency in dispatching chillers. [ABSTRACT FROM AUTHOR]

Considerable efforts have been made to reduce the energy consumption of buildings due to the energy crisis, and, the Korean government has supported the use of renewable energy through various grants. Among the possible renewable energy sources, geothermal energy can be used regardless of the outside weather. Therefore, energy consumption can be reduced considerably in summer and winter. Despite the increasing use of renewable energy, the use of renewables has not been operating appropriately. Therefore, this study examined some of the problems of the operation of renewable energy and some possible improvements. The aim of the study is to evaluate a building containing an actual installed multi-geothermal heat pump (Multi-GHP) system, in terms of the energy efficiency. In addition, this study evaluated the present control system and the method of complex operation regarding existing heat sources systems and GHP systems through a simulation. The results can be regarded as the result of a hybrid operation method for the improvement of an existing operation. Therefore, the Multi-GHP system energy use of a hybrid operation condition of the Multi-GHP systems and the absorption (ABS) chiller-heater system was reduced compared to the operation condition of the Multi-GHP system, and the total energy consumption of the heat source equipment was reduced. The proposed operation plan was evaluated after applying the system to a building. These results showed that the efficient operation of a Multi-GHP hybrid operation method is possible. As a result, the GHP energy use of Multi-GHP systems and the ABS chiller-heater system was reduced by 30% compared to existing operation and the total energy consumption of heat source equipment was reduced by 78%. [ABSTRACT FROM AUTHOR]

In the present study, dynamic analysis and performance evaluation of a solar-powered continuous operation adsorption chiller are introduced. The adsorption chiller uses silica gel and water as the working pair. The developed mathematical model represents the heat and mass transfer within the reactor coupled with the energy balance of the collector plate and the glass cover. Moreover, a non-equilibrium adsorption kinetic model is taken into account by using the linear driving force equation. The variation of solar radiation, wind speed, and atmospheric temperature along a complete cycle are considered for a more realistic simulation. Based on the case studied and the baseline parameters, the chiller is found to acquire a coefficient of performance of 0.402. The average thermal efficiency of the solar collector is estimated to be 62.96% and the average total efficiency approaches a value of 50.91%. Other performance parameters obtained are 363.8 W and 1.82 W/kg for the cooling capacity and the specific cooling power of the chiller, respectively. Furthermore, every 1 kg of silica gel inside the adsorption reactor produces a daily chilled water mass of 3 kg at a temperature of 10 °C. In addition, the cooling system harnesses 25.35% of the total available solar radiation and converts it to a cooling effect. [ABSTRACT FROM AUTHOR]

An absorption chiller model for tri-generation (combined cooling, heating, and power) is developed and incorporated with the high temperature- (HT-) proton exchange membrane fuel cell (PEMFC) system model that was developed in our previous study. We employ a commercially available flow simulator, Aspen HYSYS, for solving the energy and mass balances of various system components, including an HT-PEMFC stack that is based on a phosphoric acid-doped PBI membrane, natural gas-fueled reformer, LiBr-H2O absorption chiller, balance of plant (BOP) components, and heat exchangers. Since the system's operating strategy for tri-generation must be changed, depending on cooling or heating loads, a major focus of this study is to analyze system performance and efficiency under different requirements of electricity generation, cooling, and heating conditions. The system simulation results revealed that high-current fuel-cell operation is essential in raising the cooling capacity, but the overall system efficiency is slightly reduced as a result. Using a lower fuel-air ratio for the burner in the reforming module is one alternative that can minimize the reduction in the overall system efficiency under high-current fuel-cell operation and large cooling-capacity modes. [ABSTRACT FROM AUTHOR]

Large buildings cause more than 20% of the global energy consumption in advanced countries. In buildings such as hospitals, cooling loads represent an important percentage of the overall energy demand (up to 44%) due to the intensive use of heating, ventilation and air conditioning (HVAC) systems among other key factors, so their study should be considered. In this paper, we propose a data-driven analysis for improving the efficiency in multiple-chiller plants. Coefficient of performance (COP) is used as energy efficiency indicator. Data analysis, based on aggregation operations, filtering and data projection, allows us to obtain knowledge from chillers and the whole plant, in order to define and tune management rules. The plant manager software (PMS) that implements those rules establishes when a chiller should be staged up/down and which chiller should be started/stopped according different efficiency criteria. This approach has been applied on the chiller plant at the Hospital of León. [ABSTRACT FROM AUTHOR]

In Taiwan, over 45% of the energy in common buildings is used for the air-conditioning system. In particular, the chiller plant consumes about 70% of the energy in air-conditioning system. The electric energy consumption of air-condition system in a clean room of semiconductor factory is about 5–10 times of that in a common building. Consequently, the optimal chiller loading in energy saving of building is a vital issue. This paper develops a new algorithm to solve optimal chiller loading (OCL) problems. The proposed two-stage differential evolution algorithm integrated the advantages of exploration (global search) in the modified binary differential evolution (MBDE) algorithm and exploitation (local search) in the real-valued differential evolution (DE) algorithm for finding the optimal solution of OCL problems. In order to show the performance of the proposed algorithm, comparison with other optimization methods has been done and analyzed. The result shows that the proposed algorithm can obtain similar or better solution in comparison to previous studies. It is a promising approach for the OCL problem. [ABSTRACT FROM AUTHOR]

In this paper, an optimal energy management scheme for building microgrids with rooftop greenhouse is proposed. A building energy management system (BEMS) is utilized for the optimal fulfilment of energy demands in the building and the greenhouse. The exhaust heat generated due to the operation of air conditioners in the building is used for fulfilling the cooling demands of the greenhouse via chillers. In addition to thermal and cooling demands, the four major control parameters (temperature, humidity, light intensity, and CO2 concentration) are also considered for optimal growth of crops in the greenhouse. A multi-agent system (MAS) is adopted to realize the interaction among several households of the building, the greenhouse, and the BEMS. The MAS comprises of several inner-level, intermediate level, and upper-level agents, which are responsible for their respective tasks. The performance of the proposed optimization strategy is evaluated for two seasons of a year, i.e., summer and winter. Numerical simulations have demonstrated the effectiveness of the proposed operation scheme for optimal operation of building microgrids with rooftop greenhouses. [ABSTRACT FROM AUTHOR]

Exergy analysis has widely been used to assess resource consumption, and to identify opportunities for improvement within manufacturing. The main advantages of this method are its ability to account for energy quality and consumption. However, its application in industrial practice is limited, which may be due to the lack of its consistent application in practice. Current energy management standard, that facilitate consistent application of procedures do not consider the quality aspects of energy flows. An exergy based energy management standards is proposed in this paper that would take into account energy quality aspects, while facilitating the consistent application of exergy analysis in industrial practice. Building on ISO50001, this paper presents guidelines for implementing energy and resource management in factories, incorporating the concepts of exergy and holistic factory simulation, as illustrated through a manufacturing case study. From the factory level analysis, a chilling process was identified to have significant improvement potential. A dry fan cooler, using ambient air was proposed for the improved efficiency of the chillers. Energy based metrics portrayed a system that operated at high efficiency, however exergy analysis indicated much room for further improvement, therefore impacting decision making for technology selection. The contribution of this paper is in presenting a set of prescriptive guidelines that could possibly be further developed into a new energy management standard that would utilize the advantages of exergy analysis towards improved energy and resource management in manufacturing. [ABSTRACT FROM AUTHOR]