Chilled Water Storage System Research Articles

Optimizing single-stage double-effect LiBr-H2O absorption chiller in micro-trigeneration system using an atom search optimization algorithm

Wastes produced from several processes are focused on by many scientific researchers in order to reuse them, achieve energy savings, and reduce cost and environmental pollution. Recently, many organizations have utilized a micro-trigeneration system as a primary energy source, as it produces cooling, heat, and power in a combined effect. Various scholars designed numerous trigeneration systems in recent years. However, it is challenging to attain energy-efficient operation. Therefore, this current research focuses on developing an optimal micro combined cooling, heating, and power generation (MCCHP) to improve energy efficiency and reduce cost. The major components of the trigeneration system are the diesel engine, heat exchanger, boiler, absorption chiller, and chilled water storage system. In order to improve the cooling output of the proposed system, a single-stage, double-effect absorption chiller (LiBr-H2O absorption chiller) is utilized with the atom search optimization (ASO) algorithm. The variables of the condenser in the absorption chiller are given as input for optimization. The results show that the proposed system has a cooling capacity of 16 kW. Compared with the existing algorithms, it is efficient with 98% temperature minimization and cost-effectiveness. This micro-trigeneration device can be used in hospitals and the food production industry and is cost-effective.

Optimization design of the octagonal water diffuser with uniform flow orifice plate

Energy storage technology has been widely used in many fields, mainly due to the continuous development of social economy, resulting in increasing power consumption and peak valley load difference. This technology can play the role of adjusting the electric network load. Among them, water storage technology is the most representative. Naturally stratified technology is the most economical and effective method in chilled water storage technique and its core is the design of water diffuser. Octagonal water diffuser with the uniform flow orifice plate is a more effective water distribution mode in the naturally stratified chilled water storage system. In order to get the higher chilled water storage efficiency, the fluid dynamics software was used to make an optimization research on its parameters. Based on the scheme of octagonal diffuser and uniform flow orifice plate, the simulation analysis of the outlet mode of water distribution pipe and the opening parameters of orifice plate were carried out. According to the numerical simulations on the different volume water storage tanks, the comprehensive analysis showed that the diffusion performance of circular opening was better than slot opening, and the thickness of thermocline was thinner when the opening ratio of the orifice plate was 20% than the case of 30% and 45%. In addition, it was pointed out that the porous media model could almost replace the two-dimensional actual opening model under the low opening rate.

Diffuser design and experimental research of a large-scale chilled water storage system

ABSTRACT Naturally stratified technology is the most economical and effective method in chilled water storage technique and its core is the design of water diffuser. The better the performance of diffuser and the higher the efficiency of chilled water storage is. With the development of science and technology, many large-scale scientific facilities come into being, most of which need to be equipped with large-scale water storage system and run in the extreme operating conditions. If these water storage systems adopt the naturally stratified technology, it is necessary to optimize the design of the diffuser to achieve an ideal storage efficiency, which can not only save energy but also guarantee the operation of the facilities. The water storage system of Steady High Magnetic Field Facilities is one of the representative water storage systems with large flow rate and large temperature difference. By establishing the discrete equation of heat conduction, the results show that the convection doping related to the design of the diffuser is the primary factor affecting the thickness of thermocline. It was also verified by experiments that the large-scale chilled water storage device with well-designed octagonal diffuser and uniform flow orifice can achieve ideal storage efficiency under the operation conditions of large flow rate and large temperature difference.

Analysis of district cooling system with chilled water thermal storage in hot summer and cold winter area of China

A typical district cooling system (DCS) with a chilled water storage system is analyzed in hot summer and cold winter area in China. An analysis method concerning operation modes is proposed based on measured data, which is obtained by long term monitoring and on-site measurements of cooling season. The DCS operates at partial load for a large proportion of the cooling time; in particular, the partial-load rate (PLR) can be less than 25% for more than 50% of the total cooling season. In the night, PLR reaches 5% of the peak load. Thus, it is critical to achieve efficient operation under partial-load conditions of the DCS. Installation of chilled water thermal storage presents a solution to improve the working condition of the DCS and chillers. From the beginning to the end of the cooling season, the DCS operation can be summarized by typical operation modes according to cooling demand and chiller operation. For each mode, the base-load chiller operated at a high-load rate, with an average value of 0.88, and the coefficient of performance (COP) remained in a small range, between 4.2 and 5.2. The average energy efficiency ratio (EER) of the DCS for the cooling season was 3.65 and 3.81 for Years A and B, respectively. With respect to the economics, chillers used 90.2% of off-peak electricity, at only half the price of peak electricity.

Experimental analysis and FLUENT simulation of a stratified chilled water storage system

The purpose of this study is to figure out the hydrodynamic disturbance characteristics and chilled water storage efficiency improvement technique of a storage tank by a series of experimental analysis and FLUENT simulation. A new type of diffusion nozzle was designed, which stemmed from the Coanda effect, and an optimization is done by the numerical simulation method. Comparison analysis by FLUENT simulation on different diffusion angles of the nozzle was made, and the hydrodynamic disturbance was minimal when the diffusion surface was flat and the outlet edge of the nozzle was radial. The diffuser performance testing platform was designed and installed for comparative experimental analysis of various types of diffuser. Three groups of experiments are carried out under the original octagonal diffuser, the octagonal diffuser with nozzles and the octagonal diffuser with nozzles and uniform flow orifice. The chilled water storage efficiency could reach up to 90% when the third scheme was selected.

A New Approach for the Dimensioning of an Air Conditioning System with Cold Thermal Energy Storage

In this work, a new approach for the design of air conditioning systems with cold thermal energy storage is described and tested, considering the case study represented by a vapor-compression chiller, coupled with a chilled water storage system, producing cooling for a small multi-apartment building situated in Italy. In the present approach, at the aim of limiting shut-downs and start-ups of the chiller, which involve inefficiencies during transients, and can lead to a drastic reduction of the equipment lifetime, the nominal power of the chiller, and the amount of cooling to be stored are first estimated in a pre-design phase. Successively, the outputs of the pre-design are used to fix the size of the cold storage tank, and to set up the numerical simulation of the cold thermal energy storage system. Finally, the results of the numerical simulation of the cold storage system are used to evaluate the effective size of the chiller. Both the pre-design and the numerical simulations of the cold storage systems have been done by means of home-made numerical tool realized with Simulink.In the paper, the specifications relative to the operational strategy are explored, and the analytical models used for the numerical simulation of the cold storage system relative to the Italian case study are reported in detail. Finally, the results of the pre-design, and of the cold storage system simulations relative to the case study are presented and discussed. The results relative to the Italian case study demonstrates the effectiveness of the present approach in limiting the number of shut-downs and start-ups of the chiller.The present approach can represent a useful tool for the economic optimization of the design of air conditioning systems.

Retrofitting building fire service water tanks as chilled water storage for power demand limiting

Peak demand cost usually contributes a large proportion of the total electricity bills in buildings. Using existing building facilities for power demand limiting has been verified as effective measures to reduce monthly peak demands and associated costs. Fire service water tanks exist in most commercial buildings. This paper presents a comprehensive study on how to effectively retrofit existing building fire service water tanks as chilled water storage for power demand limiting. Important technical and economic factors that may affect the implementation of the proposed retrofitting are addressed. Two retrofitting schemes, i.e. a small ΔT (storage temperature difference) scheme and a large ΔT scheme are proposed for integrating the chilled water storage system into an existing all-air system and an existing air-water air conditioning system, respectively. Two optimal demand limiting control strategies, i.e. time-based control and demand-based control, are proposed for maximizing the monthly peak demand reduction of buildings with regular and variable peak occurring time, respectively. The cost-effectiveness of different retrofitting schemes in three real buildings in Hong Kong is analysed. Results show that substantial cost savings can be achieved with short payback periods (0.7–2.6 years) for the retrofits in these three buildings. Practical application: This paper presents a techno-economic analysis on retrofitting existing building fire service water tanks as chilled water storage for power demand limiting and operational cost saving. The proposed retrofitting schemes and demand limiting control strategies enable chilled water storage systems to be readily applied to most existing buildings. Building owners can benefit from the peak demand cost saving as the monthly peak demand can be significantly reduced by using chilled water storage. The extra costs involved in tank retrofits and system integrations can be paid back within three years.

Optimal design and application of a compound cold storage system combining seasonal ice storage and chilled water storage

Seasonal cold storage using natural cold sources for cooling is a sustainable cooling technique. However, this technique suffers from limitations such as large storage space and poor reliability. Combining seasonal storage with short-term storage might be a promising solution while it is not explored sufficiently. This paper presents a compound cold storage system that combines a heat pipe-based seasonal ice storage system with a chilled water storage system. The seasonal ice storage system automatically charges winter cold energy in the form of ice. In summer, the stored ice is extracted for cooling, and then the melting ice is used as a chilling medium for chilled water storage. Design optimization of the seasonal ice storage system and the compound storage system is addressed, including the sizes of heat pipes, the configuration and volume of the cold storage tank and the chiller capacity. A case study is conducted to demonstrate the design and the application of the proposed system in a real building in Beijing. Results show that the appropriate combination of the two types of cold storage can greatly improve the applicability of the seasonal cold storage and reduce the life-cycle cost of a building cooling system by 40%.

A novel air-conditioning system for proactive power demand response to smart grid

Power demand response is considered as one of the most promising solutions in relieving the power imbalance of an electrical grid that results a series of critical problems to the gird and end-users. In order to effectively make use of the demand response potentials of buildings, this paper presents a novel air-conditioning system with proactive demand control for daily load shifting and real time power balance in the developing smart grid. This system consists of a chilled water storage system (CWS) and a temperature and humidity independent control (THIC) air-conditioning system, which can significantly reduce the storage volume of the chilled water tank and effectively enable a building with more flexibility in changing its electricity usage patterns. The power demand of the proposed air-conditioning system can be flexibly controlled as desired by implementing two types of demand response strategies: demand side bidding (DSB) strategy and demand as frequency controlled reserve (DFR) strategy, in respond to the day-ahead and hour-ahead power change requirements of the grid, respectively. Considerable benefits (e.g., energy and cost savings) can be achieved for both the electricity utilities and building owners under incentive pricing or tariffs. A case study is conducted in a simulation platform to demonstrate the application of the proposed system in an office building.

A Novel Air-conditioning System for Proactive Power Demand Response to Smart Grid

This paper presents a novel air-conditioning system with proactive demand response to smart grid. The system consists of a chilled water storage system (CWS) and a temperature and humidity independent control (THIC) air-conditioning system. Using this system, building power demand can be flexibly controlled as desired by implementing two demand response strategies: demand side bidding (DSB) strategy and demand as frequency controlled reserve (DFR) strategy, in respond to the day-ahead and hour-ahead power balance requirements of the grid, respectively. Considerable benefits can be achieved for both power companies and end-users under incentive pricing mechanisms. A case study concerning on the demand response performance of the proposed system is also conducted in an office building.

A New Air-Conditioning System with Chilled Water Storage

For the purpose of grid peak load shifting, chilled water storage has been paid more and more attentions to integrated with air-conditioning system. In this paper, a new air conditioning system with directly chilled water storage is given. With peak-valley Price, cost for power consumption can be saved 15%-20% by coordinated operation between chilled water storage system and air conditioning system. By sensitivity analysis of system economic performance on ratio of peak price to valley price, it is revealed that with much higher ratio of peak price to valley price, not only system economic performance can seldom be improved, but also chilled water storage is restricted for engineering utilization. This paper supplies theory reference for engineering application of chilled water storage technology.

Study on Energy Materials with the Impact of Using Chilled Water Storage Systems on the Performance of Air Cooled Chillers

In the air conditioning (AC) industry chilled water storage (CWS) systems are one form of cool thermal storage technology that can be used to time shift the electrical load of the system from the peak day periods to off peak night time periods. In this paper the data for the actual exported and generated electrical energy obtained for the power stations has been used to estimate the electrical energy consumption and the peak electrical load of AC systems. It is estimated AC systems represent about 62% of the peak electrical load. The results demonstrate that CWS can reduce the peak electrical load of a chiller in an air cooled AC system by up to 100% and reduce the nominal chiller size by up to 33% depending up on the operating strategy adopted. This is achieved with only a 4% increase in power consumption of the chiller for all CWS strategies except for full storage where the energy consumption actually decreases by approximately 4%.

The Impact of Using Mathematics Principles on the Performance of Chillers

In AC industry chilled water storage (CWS) systems are one form of cool thermal storage technology that can be used to time shift the electrical load of the system from the peak day periods to off peak night time periods. In this paper the data for the actual exported and generated electrical energy obtained for the power stations has been used to estimate the electrical energy consumption and the peak electrical load of AC systems. Since the chiller in an air cooled AC system represent more than 75% of the total electrical power consumed by an AC system during the peak demand period, the impact of using CWS systems with alternative operating strategies including partial(load leveling ),partial (demand limiting) and full load has been investigated. In our conclusions we estimate that approximately 45% of the total annual exported electrical energy is consumed solely by AC systems as a result of the very high ambient temperatures. Furthermore, it is estimated AC systems represent about 62% of the peak electrical load. The results demonstrate that CWS can reduce the peak electrical load of a chiller in an air cooled AC system by up to 100% and reduce the nominal chiller size by up to 33% depending up on the operating strategy adopted. This is achieved with only a 4% increase in power consumption of the chiller for all CWS strategies except for full storage where the energy consumption actually decreases by approximately 4%.

Methodology for determining the optimal operating strategies for a chilled-water-storage system—Part I: Theoretical model

This article proposes a new methodology for determining the optimal operating strategies for a chilled-water storage system under a time-of-use electricity rate structure. It is based on a new classification of operating strategies and an investigation of multiple search paths. Each operating strategy consists of a control strategy and the maximum number of chillers running during the off-peak and on-peak periods. For each month, the operating strategy with the lowest monthly billing cost and minimal water level higher than the set-point is selected as the optimal operating strategy for the current month. A system model is developed to simulate the tank water level at the end of each time step and the system total power during each time step. This model includes six sub-models: plant, thermal energy storage tank, loop, chiller, control strategy, and nonplant power. This method considers the interaction among plant, tank, and loop, and it is easy for users to apply it to different projects, modify individual models, or implement new sub-models. The final results will be a table showing the monthly control strategy and maximal number of chillers staged-on during the off-peak and on-peak periods, an operation schedule that is easy for the operators to follow.

Tank size and operating strategy optimization of a stratified chilled water storage system

Abstract In the downtown area of Austin, Texas, United States, it is planned to build a new naturally stratified chilled water storage tank and share it among four separated chilled water plants in order to reduce the utility billing cost. Each plant is charged with a typical time-of-use utility rate including energy charge and demand charge. This paper presents the method of determining the optimal tank size as well as corresponding optimal operating strategies for this project. A simplified thermal energy storage plus four plants model is built based on some assumptions. Three conventional control strategies (full storage, chiller priority, and storage priority) with limitations on the maximum number of chillers running during the off-peak and on-peak periods are simulated. The results show that a 3.5 million gallon (13,249 m 3 ) tank has the shortest simple payback time and the projected total capital cost is within the budget. Full storage strategy is selected for the summer months and storage-priority strategy is selected for the winter months. The annual billing cost savings are estimated at $907,231 and the simple payback time is 12.5 years.

A STUDY ON THE ENERGY EVALUATION OF THE BUILDING THERMAL MASS STORAGE SYSTEM WITH THE CHILLED WATER STORAGE SYSTEM

In this paper the energy characteristics of the building thermal mass storage system with the chilled water storage system is evaluated. A typical commercial building model is simulated by a computer and the influence of the regions, the daily weather and the heat load in the room is examined. The results show that the increase rate of the cooling load and the electricity consumption is high in the months of the low cooling load comparing with the non-storage case. And the building thermal mass storage system with the water storage reduces the primal energy consumption by 2.7% and the exhaust carbon dioxide by 10.4% in the optimized case in Tokyo.

The impact of using chilled water storage systems on the performance of air cooled chillers in Kuwait

In the air conditioning (AC) industry chilled water storage (CWS) systems are one form of cool thermal storage technology that can be used to time shift the electrical load of the system from the peak day periods to off peak night time periods. In this paper the data for the actual exported and generated electrical energy obtained for the power stations in Kuwait has been used to estimate the electrical energy consumption and the peak electrical load of AC systems. Since the chiller in an air cooled AC system represent more than 75% of the total electrical power consumed by an AC system during the peak demand period, the impact of using CWS systems with alternative operating strategies including partial (load levelling), partial (demand limiting) and full load has been investigated. In our conclusions we estimate that approximately 45% of the total annual exported electrical energy is consumed solely by AC systems as a result of the very high ambient temperatures occurring between March and October. Furthermore, it is estimated AC systems represent about 62% of the peak electrical load. The results demonstrate that CWS can reduce the peak electrical load of a chiller in an air cooled AC system by up to 100% and reduce the nominal chiller size by up to 33% depending upon the operating strategy adopted. This is achieved with only a 4% increase in power consumption of the chiller for all CWS strategies except for full storage where the energy consumption actually decreases by approximately 4%.

Experiments on stratified chilled-water tanks: Expériences menées avec des reservoirs d'accumulation d'eau glacée à stratification

This paper presents experimental studies on thermal stratification in chilled-water storage systems. A fibreglass storage tank in static and dynamic modes of operation is used. The parameters varied are aspect ratio, flow rates, initial temperature difference and thickness of insulation. Emphasis is given to the effects of mixing at the inlet, leading to the definition of the mixing coefficient. The thermocline decay increases with the value of mixing coefficient, which is expressed as a function of Reynolds number and Richardson number.

Parametric studies on thermally stratified chilled water storage systems

An analysis of the stratification decay in thermally stratified vertical cylindrical cool storage systems is presented using a one dimensional conjugate heat conduction model. The degree of thermal stratification depends upon the length to diameter ratio, wall thickness to length ratio, the thermo-physical properties of the material of the storage tank, the type and thickness of the insulation and the design of the admission system for both cold and warm water. A parametric study of the stratified chilled water storage tanks in charging, discharging and stagnation modes of operation is made. The thermoclines degrade due to the heat transfer from the ambient, thermal diffusion in the storage tank, axial wall conduction and mixing due to admission of the fluid in the storage tank during charging and discharging. The degree of thermal stratification in storage tanks is expressed in terms of either heat capacity (thermal capacitance ratio) or modified Biot Number. A mixing parameter accounts for the effect of mixing on thermal stratification in both charge and discharge cycles.

Experimental investigation of chilled water storage technique for peak power shaving

A cool storage-assisted cooling system using chilled water was designed, installed and tested. A small capacity conventional chiller was used for cooling. The chilled water storage consists of two thermally stratified vertical fibreglass tanks each of 7500 l capacity. Collection of performance data commenced in June 1987 and repetitive performance data were collected for the system simulated in a residential and a non-residential application. The project provided valuable experience and necessary expertise for design, installation and operation of cool storage-assisted cooling systems for commercial and residential sectors. Performance results of the chilled water storage system are in accordance with earlier analytical estimates. However, the electricity consumption by the cool storage-assisted system was found to be more than the earlier estimated values. Nevertheless, the storage system showed excellent economics such as a 50% reduction in the capital cost and over 25% reduction in the cost of cooling.