Cool Storage System Research Articles

Performance evaluation of district cooling plant with ice storage

District cooling system (DCS) is a massive cooling energy production scheme that serves a group of buildings. The system performance can often be improved by the incorporation of a cool-storage system, in that part of the cooling demand is shifted from peak hours to non-peak hours. This brings mutual benefits to the power supplier and the consumers. In order to evaluate the energy performance and cost effectiveness of such an integrated technology, a feasible district cooling plus ice-storage system was developed for a hypothetical site in Hong Kong. A parametric study making use of the DOE-2 and TRNSYS simulation software was conducted to evaluate the system performance at different partial storage capacities, control strategies, and tariff structures. Other than the basic design factors, the results from 27 cases showed the importance of the tariff structure, the capital and electricity costs in this issue.

A continuous/discrete simulation of controlled atmosphere (CA) cool storage systems: evaluation of plant performance/design and product quality evolution

As an application of the CA cool storage simulation model developed and validated earlier, the implications of different product loading strategies (batch-wise and step-wise) on the product quality, mechanical plants performance and design aspects were investigated by considering a hypothetical CA cool storage facility. The batch-wise product loading was found to be advantageous with regards to firmness loss of the produce but was marginally energy intensive over the step-wise product loading strategy. Moreover, the step-wise loading scheme required low capacity individual evaporators and higher plant capacity of the gas-handling unit (N 2 generator and CO 2 scrubber), as compared to the batch-wise product loading. It was demonstrated that using the model, appraisal of the implication of practical industrial operational procedures such as product loading strategy, on product quality and plant performance/design was possible, owing to the discrete continuous modeling approach.

A continuous/discrete simulation of controlled atmosphere (CA) cool storage systems: validation using industrial CA cool storage

In this paper, a controlled atmosphere storage model, developed earlier, is validated using an industrial CA cool storage facility with stepwise product loading strategy. The proposed combined continuous and discrete CA cool storage simulation model was able to represent the step response transients and continuous events, with accuracy less than the observed variability or at best with accuracy level as set by the measurement instrument. Moreover, the handling of discrete/continuous events enabled the implementation of practical operational procedures and to investigate their implication on plant performance/design and directly on the product quality. The model is a valid working model for design and optimization of CA cool storage facilities both with respect to plant performance and final quality of the stored product.

Gas hydrate growth morphology outside of horizontal heat transfer tube

Visual observation of HCFC141b gas hydrate growth process outside of a horizontal heat transfer tube was done on a visual apparatus of gas hydrate reaction system. Growth processes of two situations (with, or without sodium dodecyl sulfate (SDS)) were observed, their growth morphology were compared and explained with the theory of surface free energy. During the experiment process, phenomenon of gas hydrate fast nucleation from melting ice was found and explained with Zhou & Sloan's hypothesis qualitatively. From the experiment results, it was found that gas hydrate formed in the liquid HCFC141b phase along the heat transfer tube in a system with SDS (SDS water solution–liquid HCFC141b system), while along the glass in a system without SDS (distilled water–liquid HCFC141b system), so the formation heat of gas hydrate can be absorbed more quickly in a system with SDS than in a system without SDS, which lead to a more quick growth rate. According to the above research, some suggestions were presented on the designation of heat exchanger and reaction materials for the gas hydrate indirect-contact cool storage system.

04/03038 Influence of volumetric-flow rate in thecrystallizer on the gas-hydrate cool-storage process in a new gas-hydrate cool-storage system: Bi, Y. et al. Applied Energy, 2004, 78, (1), 111–121

04/03038 Influence of volumetric-flow rate in thecrystallizer on the gas-hydrate cool-storage process in a new gas-hydrate cool-storage system: Bi, Y. et al. Applied Energy, 2004, 78, (1), 111–121

Continuous/discrete simulation of controlled atmosphere (CA) cool storage systems: model development and validation using pilot plant CA cool storage

Simulation of dynamic processes in controlled atmosphere (CA) cool room storage systems has been developed. The model consists of three interacting sub-models for the prediction of the transient behavior of the processes in the three units, namely, the cool room, the refrigeration system and the gas-handling unit. Several modules representing each of the components in these units were developed based on energy and mass balances. The modules were then arranged to form the sub-models, which were interconnected, in turn, into the global CA cool storage system model. The modules were implemented in an object-oriented computational environment, (EcosimPro) which can handle both continuous and discrete events. The model was validated using experimental data from a pilot plant CA cool storage facility. Model predictions of the most important discrete and continuous processes were found to agree to the experimental data with a maximum difference less than the observed spatial variability or at best with the accuracy level as set by the measurement instruments. As product respiration and quality models are incorporated, it is possible to use the model for optimization of plant performance with respect to the final quality of the stored product. Moreover, the handling of discrete/continuous events enables the implementation of practical operational procedures and to investigate their implication directly on the product quality and plant performance/design.

03/02548 Impact of real-time pricing rate uncertainty on the annual performance of cool storage systems: Henze, G. P. Energy and Buildings, 2003, 35, (3), 313–325

03/02548 Impact of real-time pricing rate uncertainty on the annual performance of cool storage systems: Henze, G. P. Energy and Buildings, 2003, 35, (3), 313–325

Influence of volumetric-flow rate in the crystallizer on the gas-hydrate cool-storage process in a new gas-hydrate cool-storage system

Experimental results of the gas-hydrate R141b cool-storage process are used to study the performance of a new type gas-hydrate cool-storage system. The relations among the cooling rate of the cool-storage medium, the degree of subcooling of crystallization, the formation rate of gas-hydrate, the cold energy stored and the volumetric flow rate in the crystallizer are provided. The experimental results indicate that the cool storage effect of the system is better when the volumetric flow rate in the crystallizer is between 150 and 450 l/h, the corresponding cooling rate of the cool-storage medium is between 0.055 and 0.105 °C/min, the degree of subcooling of crystallization is between 1.97 and 3.50 °C, the formation rate of the gas-hydrate is between 0.30 and 0.4 g/s, and the cold energy stored is between 2.9 and 4.0 MJ. The results presented provide guidance for the actual efficient operation of a new type of gas-hydrate cool-storage system.

Impact of real-time pricing rate uncertainty on the annual performance of cool storage systems

This study investigates whether thermal storage systems can be controlled effectively in situations where cooling loads, non-cooling electrical loads, weather information, as well as the cost of electricity are uncertain and have to be predicted. The analysis shows that the reduction in achievable utility cost-savings is small when relying on real-time pricing (RTP) electricity rates that are made available by the utility only 1 h ahead instead of an entire day-ahead. Real-time pricing rate data from two utilities, one in the South and one on the West Coast of the United States, were used in both a day-ahead (24 h rate certainty) and an hour-ahead (1 h rate certainty) fashion. Using measured data for a hotel and an office building in the United States, predictive optimal control strategies delivered greatly superior utility cost-saving performance compared to conventional partial-storage thermal energy storage strategies, even with inaccurate forecasts. The more accurate the prediction becomes, the greater will be the cost-saving performance of cool storage systems under predictive optimal control, and the smaller will be the impact associated with uncertain RTP rates in the hour-ahead RTP tariff case. Consequently, uncertain electrical utility rates do not imperil the superior cost-saving benefits of cool storage when governed by predictive optimal control.

Technical grade paraffin waxes as phase change materials for cool thermal storage and cool storage systems capital cost estimation

The present paper is confined to the discussion of technical grade paraffin waxes as phase change material (PCM) for cool storage and the cool storage systems capital cost investment. The objective of this study is to determine the potential for using cool storage systems. The thermal properties of technical grade paraffin waxes as PCM are investigated, and static and dynamic cool storage processes are discussed. The capital cost of the cooling storage system is estimated, which indicates the cooling storage system not only saves energy and other operation and maintenance costs, but also saves a significant fraction of the initial capital costs. Installing cool storage, at less cost than conventional nonstorage equipment, can often increase the cooling capacity of the existing system.

Thermal Energy Storage for Space Cooling: An Underutilized Opportunity in Federal Buildings

ABSTRACT Cool storage technology can be used to significantly reduce energy costs by allowing energy-intensive, electrically driven cooling equipment to be predominantly operated during off-peak hours when electricity rates are lower. In addition, some system configurations may result in lower first costs and/or lower operating costs. Cool storage systems of one type or another could potentially be cost-effectively applied in most buildings with a space cooling system. A survey of approximately 25 manufacturers providing cool storage systems or components identified several thousand current installations, but less than 1 percent of these were at federal facilities. With the federal sector representing nearly 4 percent of commercial building floor space and 5 percent of commercial building energy use, federal utilization would appear to be lagging. Although current applications are relatively few, the estimated potential annual savings from using cool storage in the federal sector is $50 million. The first...

Thermal Energy Storage for Space Cooling: An Underutilized Opportunity in Federal Buildings

ABSTRACT Cool storage technology can be used to significantly reduce energy costs by allowing energy-intensive, electrically driven cooling equipment to be predominantly operated during off-peak hours when electricity rates are lower. In addition, some system configurations may result in lower first costs and/or lower operating costs. Cool storage systems of one type or another could potentially be cost-effectively applied in most buildings with a space cooling system. A survey of approximately 25 manufacturers providing cool storage systems or components identified several thousand current installations, but less than 1 percent of these were at federal facilities. With the federal sector representing nearly 4 percent of commercial building floor space and 5 percent of commercial building energy use, federal utilization would appear to be lagging. Although current applications are relatively few, the estimated potential annual savings from using cool storage in the federal sector is $50 million. The first...

Tetradecane and hexadecane binary mixtures as phase change materials (PCMs) for cool storage in district cooling systems

As the demand for refrigeration and air-conditioning has increased during the last decade, district cooling systems have been introduced in some major European cities. In a district cooling system, the combination of central cooling facilities and cool storage systems provides economic advantages over older conventional cooling plants. A cool storage system can meet the same total cooling load as a non-storage system over a given period of time with a smaller chiller. Cool storage systems using Phase Change Materials (PCMs) have a low temperature range and high energy density in the melting solidification of PCMs compared to sensible heat storage. Thus they are advantageous in reducing the storage volume, heat loss, and size of the chilling equipment. In this paper we describe some paraffin waxes and their binary mixtures. We discuss the thermal properties of laboratory-grade tetradecane, hexadecane and their binary mixtures, and we demonstrate their potential for use as PCMs for cool storage. The thermal properties include freezing point, the heat of fusion, thermal stability and volume expansion during the phase change process. In the study, a Differential Scanning Calorimeter (DSC) was used to determine the heat of fusion of these materials and to generate thermal data for study and analysis. The results show that these materials are attractive candidates as potential PCMs for cool storage in district cooling systems. However, because of the high cost of laboratory-grade materials, technical-grade materials must be used for cool storage.

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.

Sub-optimal on–off switching control strategies for chilled water cooling systems with storage

A dynamic model of vapour compression refrigeration system is developed. The overall model consists of the following basic components: a compressor, a condenser, an expansion valve, an evaporator, an evaporative cooler and a cool storage. The integrated system is referred to as chilled water cooling system with storage (CWCS). The mathematical modelling of the CWC system undertaken in this study predicts the change in state of refrigerant in the system with respect to time. A computer program is developed to solve the dynamic equations along with empirical correlations describing refrigerant properties. Open-loop tests are carried out to study the performance characteristics of the system under varied cooling load and compressor speed. The model is intended to serve as an analytical design tool and to provide a basis for control analysis. Based on a heuristic method, ‘sub-optimal on–off control’ strategies for the chilled water cool storage system are developed using a reduced order model. The methodology of generating such control profiles is illustrated and the tests for optimality show that the control profiles are near optimal. The on–off control scheme is simulated on the full order CWC system. The operating performance of the system is described under several simulated cases. The results show that the control scheme is capable of maintaining the chilled water temperature in the chosen range.

Study on a cool storage system using HCFC (Hydro‐Chloro‐Fluoro‐Carbon)‐141B (CCI2 FCH3) (1, 1‐dichloro‐1‐fluoro‐ethane) clathrate

AbstractAn experimental study was performed to obtain design data for a cool storage system using HCFC‐141b (1, 1‐dichloro‐1‐fluoro‐ethane) clathrate, which is a more effective cool storage system than ice. The addition of a 0.05 mass% surfactant enabled HCFC‐141b clathrate formation/decomposition up to 40 mass% of clathrate concentration. The addition of ethylene glycol caused the clathrate formation/decomposition temperature to decrease, resulting in the acquisition of more cooled water.

95/03712 The potential study on the use of cool storage system to decrease electrical peak demand in Thailand

95/03712 The potential study on the use of cool storage system to decrease electrical peak demand in Thailand

A model for evaluating the economics of cool storage systems

Cool storage systems store a cooling medium produced during off-peak hours to be used for cooling purposes in the on-peak hours. Their operation allows the customers' electricity use for cooling to be shifted to off-peak periods, benefitting both the customer and the utility. Reductions in electricity costs the customer must pay are possible and depend upon the schedule of rates for electricity the customer faces. The savings also depend on the climactic conditions of the area and the characteristics of the cool storage system itself. A computer model that can be used to calculate the daily, monthly, annual, and present worth savings of alternate cool storage system designs is presented. The model has been programmed to calculate automatically the sensitivity of the savings for a range of alternative compressor ratings. It has been implemented as part of the ICICLE computer code, a design tool being developed to assist thermal cool storage system designers, electric utilities, and customers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of cool storage for air conditioning

The paper investigates the thermal performance of ice-water cool storage systems theoretically and experimentally. Cool storage systems are used to shift electric demand from periods of high demand to those of low demand. A general lump model to determine the thermal storage characteristics is developed. The solution of the system equations is found through a Laplace transformation method. Experimental data of temperature profiles obtained for both single container and packet containers under the conditions of various flow rates and different inlet coolant temperatures confirm the validity of the theory. A closed form solution of the required time for latent-heat storage has also been established on the basis of the quasi-steady-state assumption of the coolant.

Current cost and performance requirements for residential cool-storage systems

Cool-storage systems have the potential to reduce the overall cost of cooling for residential customers by shifting all or part of the electric load occurring during peak-demand periods to off-peak periods, thus lowering the total electrical bill where time-of-day (TOD) rates exist. The potential energy cost savings are substantial. In some U.S. locales (e.g., within the districts served by Oklahoma Gas and Electric, Arkansas Power and Light, and Wisconsin Electric Power), the difference between the peak and off-peak energy charges are >$0.100/kWh. This savings potential is the primary driving force for developing cool-storage systems for residential applications. This study establishes the current cost and performance requirements that make residential cool-storage technologies economically competitive with conventional residential air-conditioning systems. The results are based on the characteristics of conventional air-conditioning equipment and residential TOD rate structures existing during 1986–1987. Initial capital cost and annual coefficient of performance requirements for cool-storage systems were calculated for three U.S. cities with different climates and utility-rate structures. Both new construction and retrofits were considered.