Chilled Water Storage Tank Research Articles

Predictive control of power demand peak regulation based on deep reinforcement learning

As urbanization continues to accelerate, effectively managing peak electricity demand becomes increasingly critical to avoid power outages and system overloads that can negatively impact both buildings and power systems. To tackle this challenge, we propose a novel model-free predictive control method called “Dynamic Dual Predictive Control-Deep Deterministic Policy Gradient (D2PC-DDPG)" based on a deep reinforcement learning framework. Our method employs the Deep Forest-Deep Q-Network (DF-DQN) model to predict electricity demand across multiple buildings, and based on the output of the DF-DQN model, applies the Deep Deterministic Policy Gradient (DDPG) algorithm to optimize coordinated control of energy storage systems, including hot and chilled water storage tanks in multiple buildings. Experimental results show that our proposed DF-DQN model outperforms other traditional machine learning, deep learning, and reinforcement learning methods in terms of prediction accuracy, such as mean absolute error (MAE), mean absolute percentage error (MAPE), and root mean square error (RMSE). Moreover, our D2PC-DDPG method achieves superior control performance and peak load reduction compared to other reinforcement learning methods and an RBC-based control method. Specifically, our method successfully reduced peak load by 27.1% and 21.4% over a two-week period in the same regions. To demonstrate the generalizability of our D2PC-DDPG method, we tested it in five different regions and compared its performance with an RBC-based control method. The results showed that our method achieved an average reduction of 16.6%, 7%, 9.2%, and 11% for ramping, 1-load_factor, average_daily_peak, and peak_demand, respectively. These findings demonstrate the effectiveness and practicality of our proposed method in addressing critical energy management issues in various urban environments.

Transient study of thermal stratification of full-scale chilled water storage tank during optimum discharge condition

Thermal stratification of full-scale Chilled Water Storage Tanks (5855 m3) with 18 m tank diameter, and 23 m water depth during discharge mode and optimum condition was studied. The experimental and numerical analyse of stratified thermal storage tank in full-scale dimension and discharge mode has been studied. A 3D and 2D numerical model was performed. The case simplified to divide into two parts, the first part was to simulate flow in pipes and radial diffuser, and the second part included simulation in the tank according to the part one results. The optimum operation condition which found from many tests of tank operation conditions according to high thermal stratification and low thermal mixing inside the tank. Validation test with experimental data obtained from the present work and literature. The results included to analyse the thermal stratification and the flow characteristics during the discharging mode. Also, thermal performance parameters such as discharge efficiency, Richardson number, stratification efficiency, thermocline thickness, the average temperature in the tank, and discharge temperature were presented. The important result of the above analysis was the optimum stratification phenomena in the tank with low thermal mixing. The contribution of this study was the numerical modelling and simulation setting to capture the experimental results of these phenomena in the full-scale thermal storage tank, moreover to specify the optimum condition of thermal stratification of this tank dimension, diffuser type, and flow rate.

A Review on Performance of Solar Powered Air Conditioning System

Abstract: Solar energy converts the renewable energy to increase growth. The development of energy in to generated worldwide. It in the most easy to construct the process of solar air Conditioning systems. The different energy areinvolved into the solar air conditioning to the decreasing current Sources Then using high oil and concern environmental effects have been Controlling. The most comfortable Process of the solar energy system. It we implemented nowadays, increase in progress. we are air Conditioning systems are using in. every building, malls,Colleges industries, flats, etc. solar power air conditioning system is the hot issue to study building energy Consumer. I Then we indoor and outdoor comfort of air Conditioning while be cold storage system. To increasing the efficiency of air Conditioning intensity of the cooling system. The transient thermal efficiency we can using the storage system to maintain the temperature to indoor,The solar system must be using the different. Parabolic collector from the high accommodation,The basic analysis, to investment of Solar air conditioning system are using 3-phase accumulator. The solar energy using of high rate of low grade energy to high grade of energy are Converting them. It will high efficient process could be panels, collectors, will cool the High temperature can be assumed to use the chilled water storage tank. can be provided due to reduce the system of on and off options. There are improving solar system.It will high efficient process could be panels , collectors, will cool the High temperature can be assumed to use the chilled water storage tank. can be provided due to reduce the system of on and off options. There are improving solar system.it is common for the storage chilling water can be utilized, that can to be operated solar energy.

Globally optimal control of hybrid chilled water plants integrated with small-scale thermal energy storage for energy-efficient operation

The integration of thermal energy storage in chilled water systems is an effective way to improve energy efficiency and is essential for achieving carbon emission reduction. However, the commonly used large-scale thermal energy storage needs significantly larger space, which hinders the wide application of thermal storage in large number of existing buildings. Unlike previous studies, this study integrated a small-scale stratified chilled water storage tank into chilled water plants and proposed a global optimal control strategy to enhance the overall system energy performance. The proposed strategy determines the optimal settings of stratified chilled water storage tank charging/discharging flow rate, chilled water supply temperature, and the number of chillers in order to minimize the daily energy consumption of the chilled water plants under varying load conditions. The stratified chilled water storage tank was modelled as a “virtual chiller” to quantify the energy consumption related to the charging/discharging. Multiple charging/discharging cycles were controlled for optimal chiller loading. The proposed control strategy was evaluated in a simulated complex central chilled water plant. The results show that the proposed optimal control strategy can save the daily energy consumption of the central chilled water plant by 4.35–7.67%, 2.10–3.90%, and 2.30–5.15% in three typical weather conditions.

Numerical Simulation of Ammonia-Water Solution Based Heat Absorber

This article provides an insight into the numerical simulation of an ammonia-water solution-based plate heat absorber, which is a crucial part of an absorption chiller. These chillers could be used as part of a stratified chilled-water storage tank configuration for coupling to a small modular reactor. The common approach utilized in the process of designing the chiller is to call the absorber a "black box" without considering the processes inside. It follows that the resulting design must be highly oversized to ensure reliable operation of the system. This article focuses on the obstacles that needs to be overcome in order to simulate the processes inside the absorber, such as stream breakup into separate droplets or absorption of ammonia. Unfortunately, we do not have any experimental data we could use to validate our simulations and thus this article should be looked at as a "proof of concept" and a possible guideline for simulations of similar phenomenon.

Experimental study on the thermal performance of a novel physically separated chilled water storage tank

Naturally stratified chilled-water storage is widely used to offset the peak electrical demand caused by air-conditioning, but the mixing between cold and warm water greatly influences its thermal performance, especially for a low aspect ratio tank. In this study, a novel physically separated chilled water storage tank is proposed to take place traditional membrane tanks. The thermal performance of this novel tank is evaluated by static and dynamic experiments. The temperature distribution, outlet temperature, figure of merit (FOM1/2/FOM), and percent cold recoverable (PCR) are analyzed when the cold water temperature is approximately 2 °C and 4 °C, and the temperature difference ranges from 7.91 to 13.86 °C. The results demonstrate the excellent thermal performance of the novel tank under a large temperature difference. Compared with conventional temperature conditions, the stability of the outlet temperature under low-temperature conditions is better during the discharging process with the dimensionless temperature increasing by 10% at the end of the process. The full-cycle FOM increases significantly and the PCR decreases slightly with increasing temperature difference. When the FOM reaches its maximum of 93.2%, the PCR exceeds 91%. Therefore, this research work exhibits great application potential of this novel tank due to its ability to improve the thermal performance for a low aspect ratio tank, which provides a new direction for chilled water storage tank design.

A Flow Rate Dependent 1D Model for Thermally Stratified Hot-Water Energy Storage

Stratified tank models are used to simulate thermal storage in applications such as residential or commercial hot-water storage tanks, chilled-water storage tanks, and solar thermal systems. The energy efficiency of these applications relates to the system components and the level of stratification maintained during various flow events in the tank. One-dimensional (1D) models are used in building energy simulations because of the short computation time but often do not include flow-rate dependent mixing. The accuracy of 1D models for plug flow, plug flow with axial conduction, and two convection eddy-diffusivity models were compared with experimental data sets for discharging a 50-gal residential tank and recharging the tank with hot water from an external hot-water source. A minimum and maximum relationship for the eddy diffusivity factor were found at Re <2100 and >10,000 for recirculation of hot water to the top of the tank and vertical tubes inletting cold water at the bottom. The root mean square error decreased from >4 °C to near 2 °C when considering flow-based mixing models during heating, while the exponential decay of the eddy diffusion results in a root mean square error reduction of 1 °C for cone-shaped diffusers that begin to relaminarize flow at the inlet.

Effect of Diffuser Height on Thermocline in Stratified Chilled Water Storage Tank

Chilled water energy storage using thermal stratification technique currently used in the vast area because it contributes to reducing energy consumption and refrigeration capacity as well as its maintenance, operating and capital costs are low. In this paper, experimental tests were carried out on a small-scale vertical cylindrical storage tank equipped with an elbow-type conventional diffuser at inlet heights of 20, 170, 320 and 470mm for flow charging rates from 1.5-7.5l/min. in order to obtain a good thermal separation. The degree of stratification was estimated by means of temperature distributions and performance metrics, which involve thermocline thickness, the half-cycle figure of merit and equivalent lost tank height. The results show that the decrease in diffuser height above the tank floor tends to the steep thermocline or satisfactory thermal separation, the stratification and thermal performance were obtained at diffuser height of 20 mm within the limiting volume flow rates 1.5-4.5 l/min. better than those at volume flow rates ranging from 5.5-7.5l/min. and much better than at diffuser heights of 170, 320 and 470mm for various flow rates.

Optimization analysis of waste heat recovery district cooling system on a remote island: Case study Green Island

The power supply of a remote island is mainly from the diesel generator due to nature and environmental constraints for developing renewable electrical power generation. Recovering waste heat from diesel generators can reduce cost and satisfy the concurrent need for electricity, district heating or cooling on a remote island. This study investigates the optimization design of a district cooling system (DCS) on a remote island by the dynamic programming method. In a case study on Green Island, the waste heat from the diesel power plant can be recovered to drive an absorption chiller that satisfies the peak cooling load of 756 kW. The objective function of the optimization design includes the capital cost and the running cost during the period of the life cycle. The dynamic programming method is adopted to minimize the objective function, and the constraint involves the conservation of energy between the chiller and the chilled water storage tank. The results showed that a 510 kW absorption chiller and a storage tank capacity of 1978 kW-h achieved the optimization of the DCS. The averaged energy conservation rate was about 75.7%. Moreover, the electricity consumption and CO2 emission were reduced by 955.8 MWh and 675 tons per year, respectively. Based on the difference in the electricity prices of electric utility companies, the investment in the DCS is expected to have a four-year payback period. These optimization results are based on an evaluation of energetic, economic and environmental effects, which are also suitable for any kind of regions without direct access to interconnected electrical networks.

Effect of height to diameter ratio of chilled water storage tank on temperature gradient during discharging

When air condition system is operated with chilled water storage tank, it is expected that peak demand of the system can be reduced. Basically, chilled water is produced and charged into a tank during off-peak period and it is used or discharged to the cooling system during peak time. In this research, temperature gradient of water inside the storage tank is simulated for various H:D ratios of the tank. Effect of physical dimension of the tank on the temperature gradient during discharging is investigated. ANSYS Fluent version 15.0, a computational fluid dynamics program is used for numerical investigation. The H:D ratios of the tank are varied as 0.7, 0.8, 1.1, 1.2, 1.4, 1.6 and 2.0 with a constant of volume of 1,755 m3. 25 L/s of chilled water flow out at 5°C and flow in at 15°C during discharging. The simulated results revealed that the 5°C water is enough to be used for 13 hours of discharging and the H:D = 2.0 gave highest remaining cold water.

Exergy analysis of a solar-assisted air-conditioning system: Case study in southern Spain

This work describes the exergy analysis applied to a single effect LiBr-H2O refrigeration system working together with a flat-plate-collector array. The main objective was to properly match the refrigeration cycle and the heat source. I used the experimental data collected from a solar-assisted air-conditioning system operating in the Solar Energy Research Center (Ciesol). The system employs a flat-plate-collector array, a hot-water single-effect LiBr-H2O absorption chiller, a cooling tower, two hot storage tanks, an auxiliary heater, as well as two chilled water storage tanks. The findings demonstrate that, from the exergetic point of view, I can achieve best results by supplying the absorption chiller with water within a temperature range of 70–80°C supporting it with the action of the chilled water storage tanks. As a result of this analysis, I recognized that there is great optimization potential for the control system of the studied system. At the same time I have ensured a proper balance between the refrigeration cycle and the heat source, making the solar-assisted air-conditioning system less energy intensive and safeguarding environmental protection.

Experimental and Numerical Study of Heat Transfer Process of Chilled Water Storage Tank

Cool thermal energy storage using thermal stratification becomes one of the widespread applications because of the ability to shift the electrical cooling loads from on-peak to off-peak periods and significantly contributes to reducing the capacity of the refrigeration system and operating costs. Seven flow rate tests varying from 1.5 to 7.5 l/min for charging cycle were performed on small-scale vertical cylindrical storage tank equipped with three primary inlet diffusers, an elbow, two-ring linear and radial circular diffusers. The storage tank with inlet diffusers was assessed using temperature distributions and performance measures including thermocline thickness(ht), the half-cycle figure of merit ( ) and equivalent lost tank height (ELH). Commercial finite volume code was used to predict temperature distributions in a stratified water tank model, temperature data acquired from experimental tests and simulation models were compared for validation purpose. The results suggested that the storage tank with two-ring linear circular diffuser produced better performance and higher stratification than two-ring radial circular diffuser for various flow rates by 1.4% , 20.6% ELH and 10.6% ht, and much better than an elbow diffuser by 1.7% , 24% ELH and 31.1% ht, furthermore, the degree of mixing was affected essentially the flow velocity which in turn causes an increase or decrease in thermocline thickness. Temperature distributions obtained from finite volume model are found to be in very close agreement with those obtained experimentally.

Rankine cycle power augmentation: a comparative case study on the introduction of ORC or absorption chiller

The search for more efficient processes to save resources and avoid further environmental damages is mandatory in the current society. Increase in power and efficiency of already existing power plants play important role in the transition to more efficient cycles. This work compares two different thermal arrangements that can be fitted in already existing Rankine cycle power plants to improve their power and efficiency. These arrangements are possible when fuel sulfur concentration is reduced to meet stricter SO x emission legislation. The first thermal arrangement is composed of an absorption chiller and a chilled water storage tank designed to make use of the energy remaining in boiler exhaust gases. Thermal accumulation enables the use of an absorption chiller to produce chilled water during the period of 24 h. This chilled water is used in the condenser during peak hours to increase power output and the efficiency of the plant. The second option is fitting an optimized organic Rankine cycle (ORC) also powered by the exhaust gases from the boiler. Results show that fitting an ORC using n-butane as a working fluid represents a gain of 409.3 kW on net power and 0.42% on efficiency against 55.92 kW and 0.07% obtained using the absorption chiller. Therefore, from a thermodynamic point of view, it is more interesting to use optimized ORCs than absorption chillers for existing power plants operating under the operational conditions evaluated.

Modeling Hybrid Nuclear Systems With Chilled-Water Storage

Air-conditioning loads during the warmer months of the year are large contributors to an increase in the daily peak electrical demand. Traditionally, utility companies boost output to meet daily cooling load spikes, often using expensive and polluting fossil fuel plants to match the demand. Likewise, heating, ventilation, and air conditioning (HVAC) system components must be sized to meet these peak cooling loads. However, the use of a properly sized stratified chilled-water storage system in conjunction with conventional HVAC system components can shift daily energy peaks from cooling loads to off-peak hours. This process is examined in light of the recent development of small modular nuclear reactors (SMRs). In this study, primary components of an air-conditioning system with a stratified chilled-water storage tank were modeled in FORTRAN 95. A basic chiller operation criterion was employed. Simulation results confirmed earlier work that the air-conditioning system with thermal energy storage (TES) capabilities not only reduced daily peaks in energy demand due to facility cooling loads but also shifted the energy demand from on-peak to off-peak hours, thereby creating a more flattened total electricity demand profile. Thus, coupling chilled-water storage-supplemented HVAC systems to SMRs is appealing because of the decrease in necessary reactor power cycling, and subsequently reduced associated thermal stresses in reactor system materials, to meet daily fluctuations in cooling demand. Also, such a system can be used as a thermal sink during reactor transients or a buffer due to renewable intermittency in a nuclear hybrid energy system (NHES).

Solar assisted conditioning of residences with floor heating and ceiling cooling: review and simulation results

Solar or solar assisted heating and cooling systems are becoming widespread to reduce CO2 emissions. Efficient radiant space heating and cooling systems can be used to decrease the energy bills and improve occupant thermal comfort in buildings. This study uses the TRNSYS program, for the modeling and simulation of solar assisted radiant heating and cooling of a building with the domestic hot water supply, to examine the effects of various parameters on energy consumption. Calculations are performed for a typical meteorological year (TMY) and ten attached houses in Istanbul, Turkey with hot water and chilled water storages on a six minute time step basis. Graphs showing variations of the room temperature and room relative humidity indicate satisfactory thermal comfort. Daily average COP of the absorption cooling system is improved by suitable choice of the type and size of the collectors. Sizes of the hot water and chilled water tanks are also important parameters; their roles are shown by their effect on the discarded portion of the heat from the collectors and the energy amount supplied by the auxiliary heater. It is concluded that the presented model for a solar assisted radiant heating and cooling of ten attached houses, with the domestic hot water supply, natural gas fueled auxiliary heater, hot water and chilled water storage tanks have considerable advantages; these should be maximized by optimizing the sizes of the solar collectors and storage tanks using a simulation program.

MPC-based optimal scheduling of grid-connected low energy buildings with thermal energy storages

The mismatch between the energy demand and energy supply is one of the major problems in low or zero energy buildings with distributed power generations. The policy of time-sensitive electricity pricing provides a possibility to improve the energy efficiency of the building energy systems. A model predictive control (MPC)-based strategy using nonlinear programming (NLP) algorithm is proposed to optimize the scheduling of the energy systems under day-ahead electricity pricing. Evaluations are conducted using a reference building based on the Hong Kong Zero Carbon Building. A stratified chilled water storage tank is introduced as the thermal energy storage, which makes possible to optimize the scheduling of the building energy systems. The distributed power generation in the building consists of a combined cooling and power system and a photovoltaic (PV) system. Two types of grid-connections (i.e., selling electricity to grid is allowed/forbidden) are considered. Results show that the proposed optimal scheduling strategy can achieve significant reductions in carbon dioxide emission, primary energy consumptions and operation cost. Sensitivity analysis shows uncertainties in the inputs do not affect the performance of the proposed method significantly.

Modeling and optimization of a chiller plant

A data-driven approach is utilized to model a chiller plant that has four chillers, four cooling towers, and two chilled water storage tanks. The chillers have varying energy efficiency. Since the chiller plant model derived from data-driven approach is nonlinear and non-convex, it is not practical to solve it by using the traditional gradient-based optimization algorithm. A two-level intelligent algorithm is developed to solve the model aiming at minimizing the total cost of the chilled water plant. The proposed algorithm can effectively search the optimum under the non-convex and nonlinear situation. A simulation case is conducted and the corresponding results are discussed.

Reducing a solar-assisted air-conditioning system’s energy consumption by applying real-time occupancy sensors and chilled water storage tanks throughout the summer: A case study

This study describes an innovative occupancy and chilled-water storage-based operation sequence implemented in a solar-assisted air-conditioning system. The core purpose of this solar-assisted air-conditioning system is to handle the cooling and heating load of the Solar Energy Research Centre (CIESOL), thus minimising its environmental impact. In this study, the cooling mode was investigated with special attention focused on the chilled-water storage circuit. The critical concern is that the solar-assisted air-conditioning system should always operate considering the actual load conditions, not using an abstract maximum load that is predetermined during the system’s design process, which can lead to energy waste during periods of low occupancy. Thus, the fundamental problem is to identify the optimum operation sequence for the solar-assisted air-conditioning system that provides the best energy performance. The significance of this work lies in the demonstration of a new operation strategy that utilises real-time occupancy monitoring and chilled-water storage tanks to improve the efficiency of solar-assisted air-conditioning systems, thereby reducing their electricity consumption. Adopting this strategy resulted in a large energy-saving potential. The results demonstrate that during one cooling period, it is possible to conserve approximately 42% of the total electrical energy consumed by the system prior to the adoption of this operation strategy.

Performance evaluation of solar-assisted air-conditioning system with chilled water storage (CIESOL building)

This study presents the performance of solar-assisted air-conditioning system with two chilled water storage tanks installed in the Solar Energy Research Center building. The system consists mainly of solar collectors’ array, a hot-water driven absorption chiller, a cooling tower, two hot storage tanks, an auxiliary heater as well as two chilled storage tanks. The chilled water storage tank circuit was further investigated in order to find the optimum solar system’s operation sequence while providing the best energy performance. Firstly, we carried out a study about the dynamics of building’s cooling load and the necessity of the integration of chilled water storage tanks to solar system. Subsequently, the new system’s operation mode was proposed to reduce the energy consumption. The results demonstrate that we can save about 20% of the total energy consumption and about 30% of water consumption applying the new operation sequence, which takes into account the chilled water tanks action. Moreover, it was demonstrated that the integration of chilled water storage tanks allows to reduce the sudden absorption chiller on/off cycles, thereby improving the efficiency of the solar-assisted system.

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.