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This paper introduces novel modification for conventional air conditioning systems through utilizing a thermal ice storage system integrated with solar panels. Alexandria and Aswan, cities in Egypt, are chosen to represent two climates for hot-humid and hot-dry climates respectively. Exergy analysis is performed for the proposed solar-ice thermal storage system based on transient analysis. Results showed that, the proposed system is more effective approach in hot-humid than hot-dry climate and more efficient with all-water system than with all-air system. The maximum energy saving is 205.16 GJ having a percent of 27.5% in August for all water system in case of Alexandria city and 224.67 GJ with a percent of 25.38% in August for all-water system in case of Aswan city. All air system simulation showed maximum energy saving of 175.05 GJ with a percent of 18.13 % in case of August for Alexandria and 175.45 GJ having a percentage of 17.43% in case of Aswan in August. Moreover, the all-water system achieved a reduction in CO2 emissions by 467 tons/year in Aswan city and 390 tons/year in case of Alexandria city. These reductions decrease to be 435 and 353 tons/year when the all-air system used for the same two cities.

Ice thermal storage (ITS) performance for cooling systems is greatly influenced by the poor thermal conductivity of phase change material (PCM). The effect of natural convection on the melting process is significant for heat transfer enhancement. Thus, the melting performance of PCM in a shell-and-tube latent heat storage (STLHS) unit is numerically studied by considering natural convection in terms of various heat source positions and configurations, i.e., central position, eccentric position, and flat-tube type. Temperature distribution, melting time, and the overall heat transfer coefficient during the process are investigated. The results show that the circulation vortex formed by natural convection is a dominant factor that affects melting front evolution and the overall heat transfer coefficient. When input heat flux is relatively weak, PCM below the heat source is liquefied first. In contrast, PCM in the upper part melts earlier when the heat flux is excellent. The overall heat transfer coefficient decreases sharply with the increase in melting time in the early stage. Then, the heat transfer coefficient tends to be constant. PCM in an STLHS unit with a heat source in a lower position and a configuration of vertical flat-tube type has a desirable performance when compared with other cases, which could provide good support for ITS application. [ABSTRACT FROM AUTHOR]

Abstract Mature and inexpensive ice thermal storage was employed to replace battery bank in energy storage, and photovoltaic directly driven technology was also combined in this paper. A 3HP household air conditioning assisted with ice thermal storage was investigated in four operating conditions. First, directly driven by photovoltaic arrays, the (COP)rs were almost 6.31% than that of refrigerator driven by power grid for the instantaneous solar irradiance, and the stored cooling capacity decreased 18.63% under the intermittent influence of solar irradiance. Moreover, the (COP)r of refrigerator operating in out‐of‐box mode was about 1.38 times that of operating in ice storage mode. Next, the inevitable compress motor fluctuation, caused by instantaneous solar irradiance, was investigated by experiment and simulation. In three typical weathers, compressor fluctuating time was approximately 65.22 s, 197.05 s, and 270.48 s in full irradiance range. When the lower solar irradiance limit was optimized from 150 to 80 Wm−2, refrigerator operated stably and continuously in any weather conditions. The ice production and the (COP)r were improved by 40.91% and 12.36%, respectively.

• Validated simulation model for a new compination air conditioning systems were presented. • Two different integration cases were presented according to the air condtioning system used. • Energy and Exergy analysis of new compination systems were studied under two different climates. • A reduction in CO 2 emissions was observed when using the proposed ssystems. This paper introduces novel modification for conventional air conditioning systems through utilizing a thermal ice storage system integrated with solar panels. Alexandria and Aswan, cities in Egypt, are chosen to represent two climates for hot-humid and hot-dry climates respectively. Exergy analysis is performed for the proposed solar-ice thermal storage system based on transient analysis. Results showed that, the proposed system is more effective approach in hot-humid than hot-dry climate and more efficient with all-water system than with all-air system. The maximum energy saving is 205.16 GJ having a percent of 27.5% in August for all water system in case of Alexandria city and 224.67 GJ with a percent of 25.38% in August for all-water system in case of Aswan city. All air system simulation showed maximum energy saving of 175.05 GJ with a percent of 18.13 % in case of August for Alexandria and 175.45 GJ having a percentage of 17.43% in case of Aswan in August. Moreover, the all-water system achieved a reduction in CO 2 emissions by 467 tons/year in Aswan city and 390 tons/year in case of Alexandria city. These reductions decrease to be 435 and 353 tons/year when the all-air system used for the same two cities. [ABSTRACT FROM AUTHOR]

A large number of bubbles generated by the air agitation device in an external melting ice storage system can cause the disturbance of the ice–water mixture, which can enhance the heat transfer and contribute to the reduction in energy consumption. The structural design and optimization of the air agitation device in an external melting ice storage system is the key issue for energy savings. In this study, the influence of different orifice spacings and diameters on the distribution of the gas–liquid flow field, gas holdup, heat-transfer coefficient, and power consumption in the ice storage tank was investigated by numerical simulation. The simulated results showed that the heat-transfer coefficient of the ice–water mixture with air bubbles should be 3–5 times higher than the natural convection when the air superficial velocity is 0.03 m/s. The gas holdup was mainly affected by the orifice spacing, and the maximum varied from 5.0% to 8.2%. When the orifice spacing was less than 150 mm, the gas holdup changed a little in the horizontal direction, and the uniformity became worse when the orifice spacing was larger than 180 mm. An orifice diameter larger than 3 mm can improve the heat transfer and cause less air-compressing energy consumption, which decreased by approximately 1.62%. [ABSTRACT FROM AUTHOR]

A novel plate-shaped ice thermal storage device is constructed with multichannel flat tube. The different temperatures and flow rates of heat transfer fluid (HTF) on the variations in the internal temperature and the store/release power are experimentally investigated. Results indicate that the reduction in temperature of cold HTF from −3 °C to −4 °C is notably to shorten the super-cooling process, reduced the freezing time by 35.04% and increased the average storage power by 24.9%, its effect gradually weaken with decrease in temperature. Furthermore, numerical simulation and response surface method are adopted to gain predictive models of four response indices for estimating the behavior of the device in terms of five different design parameters, and the interaction effects of design parameters on responses are investigated. Finally, the multi-objective joint optimization is developed based on an efficient storage device with goals of excellent thermal performance and thermodynamic perfection, while its manufacturing cost is low. The optimization results recommend the fin height, number and thickness are 30.1 mm, 10, and 0.5 mm, respectively, temperature and flow rate of cold HTF are −4.01 °C and 0.2 m3/h, respectively, to maximize ice formation rate, exergy efficiency, and fin efficiency and minimize the metal consumption. [ABSTRACT FROM AUTHOR]

Mature and inexpensive ice thermal storage was employed to replace battery bank in energy storage, and photovoltaic directly driven technology was also combined in this paper. A 3HP household air conditioning assisted with ice thermal storage was investigated in four operating conditions. First, directly driven by photovoltaic arrays, the (COP)rs were almost 6.31% than that of refrigerator driven by power grid for the instantaneous solar irradiance, and the stored cooling capacity decreased 18.63% under the intermittent influence of solar irradiance. Moreover, the (COP)r of refrigerator operating in out‐of‐box mode was about 1.38 times that of operating in ice storage mode. Next, the inevitable compress motor fluctuation, caused by instantaneous solar irradiance, was investigated by experiment and simulation. In three typical weathers, compressor fluctuating time was approximately 65.22 s, 197.05 s, and 270.48 s in full irradiance range. When the lower solar irradiance limit was optimized from 150 to 80 Wm−2, refrigerator operated stably and continuously in any weather conditions. The ice production and the (COP)r were improved by 40.91% and 12.36%, respectively. [ABSTRACT FROM AUTHOR]

A large number of bubbles generated by the air agitation device in an external melting ice storage system can cause the disturbance of the ice–water mixture, which can enhance the heat transfer and contribute to the reduction in energy consumption. The structural design and optimization of the air agitation device in an external melting ice storage system is the key issue for energy savings. In this study, the influence of different orifice spacings and diameters on the distribution of the gas–liquid flow field, gas holdup, heat-transfer coefficient, and power consumption in the ice storage tank was investigated by numerical simulation. The simulated results showed that the heat-transfer coefficient of the ice–water mixture with air bubbles should be 3–5 times higher than the natural convection when the air superficial velocity is 0.03 m/s. The gas holdup was mainly affected by the orifice spacing, and the maximum varied from 5.0% to 8.2%. When the orifice spacing was less than 150 mm, the gas holdup changed a little in the horizontal direction, and the uniformity became worse when the orifice spacing was larger than 180 mm. An orifice diameter larger than 3 mm can improve the heat transfer and cause less air-compressing energy consumption, which decreased by approximately 1.62%.

An evaluation of using a thermal storage system utilized with air conditioning cycle in Egypt is the main aim of this paper. This study includes the addition of an energy storage system to two types of air conditioning systems: an all-air (AHU) and an all-water (FCU) air conditioning system. The exergy analysis is based on the transient analysis for a conventional cycle and a proposed ice storage cycle for the administration (FCU) and control (AHU) buildings in the New Abu-Qir Thermal Power Plant in Alexandria, Egypt, and it is presented as a case study. Results revealed that a significant increase in the system COP can be observed. The proposed ice storage cycles accomplish a 2.784 average coefficient of performance for the administration building and a 2.811 for control building, whereas the conventional system's COP is 2.593 and 2.617 for both buildings, respectively. The ice storage tank can supply cooling for 8 h for the administration and control buildings. As a result, the ice storage systems save 53,517 kW h year−1 (6.88% power saving) for the administration building and 55,716 kW h year−1 (6.89% power saving) for the control building in 360 working days within the year (8640 h). [ABSTRACT FROM AUTHOR]

In this paper, bubble-driven flow mechanism is applied to an ice thermal storage device based on micro heat pipe arrays. A visual experimental system is established to investigate the effect of bubble-driven flow on the performance of proposed device. The temperature distribution of water/ice, charging/discharging time, charging/discharging power, real-time phase change behaviors and phase change rate without bubble injection and at different bubble flow rates are compared. Based on without bubble injection, the temperature uniformity are significantly promoted by 57.14% and 56.07% in the sensible heat charging/discharging stage, while the improvement of the latent heat charging/discharging stage is not obvious. In addition, the negative effect of bubble-driven flow in the latent heat charging stage is greater than the positive effect in the sensible heat charging stage, thereby the charging time increases by 19.46%, and the charging power decreases by 17.91%. However, bubble-driven flow is positive for the entire discharging process, especially for the latent heat discharging stage, bubbles boost the decomposition of ice layer, the discharging time decreases by 20%, and the discharging power raises by 31.07%. Therefore, the operation strategy of turning on bubble driven-flow during the discharging process and turning it off during the charging process is recommended. [ABSTRACT FROM AUTHOR]

The benefits of thermal energy storage using phase change materials are well documented in the literature. Despite all the potential benefits of thermal energy storage, its commercial and widespread application remains limited. This is due to the high initial cost of phase change materials, extensive rework required in buildings, major modifications in HVAC systems, and the potential for leakage, fire and toxicity hazards. There is a strong need for a simple thermal energy storage solution which can be adopted by large number of consumers. Ductless split air-conditioners are portable, low cost, efficient and account for 70% of all air-conditioning systems sold worldwide each year. The present research provides a novel and low cost solution that incorporates thermal energy storage in these air conditioners, allowing them to run without electricity for 3 h. The paper deals with the detailed design aspects and engineering challenges that arise when incorporating thermal energy storage in these small units. A prototype air-conditioner with in-built thermal energy storage was developed, and all performance parameters presented have been validated through data obtained from the prototype. Our results indicate that thermal energy storage can be incorporated in split units in low cost and with minimal drop in overall energy efficiency of the system. Practical application: Incorporating thermal energy storage in split air-conditioners which enables them to run without grid for many hours has immense practical applications. Since around 50% power in any building is consumed by HVAC systems, being able to provide cooling during peak hours without using grid can significantly reduce load on the grid without compromising user comfort. For developing countries where load shedding is frequent, the users can run these air-conditioners without the use of generators or batteries thus saving costs and the environment. [ABSTRACT FROM AUTHOR]

Abstract In this paper, an integrated control strategy for a solar cooling system directly driven by distributed photovoltaics (PVs) without a battery is proposed; this strategy matches the optimal operating impedance of the PV array by periodically perturbing the running frequency of the compressor. The theoretical working principle of the control strategy is explained, and two experimental processes are analysed under different solar irradiance levels. Furthermore, comparative tests of the control system with and without a controller were conducted to evaluate the performance of the solar cooling system. The results of the experiment under the impedance matching control strategy reveal that the average photoelectric conversion efficiency reached approximately 0.129 and improved by 83.7% relative to the control system without a controller. The coefficient of performance (COP solar) reached 0.263 using an ice thermal storage model, which was an improvement of 60.4%. The compressor ran continually when the instantaneous irradiance exceeded 143 W/m2. The average efficiency of the control system reached 0.96, and the average three-phase power factor was approximately 0.71. The COP of the refrigeration unit was 2.10, and the total cooling capacity was 103.5 MJ, which was sufficient for cooling a 25.5-m2 air-conditioned room for 8.5 h. Highlights • An impedance matching control strategy for solar cooling system was proposed. • The impedance matching relationship was verified with theory and experiments. • Comparative tests with and without controller were conducted for proposed system. • The compressor ran stably when the instantaneous irradiance exceeded 143 W/m2. • The COP solar reached 0.263 in ice-making thermal storage model. [ABSTRACT FROM AUTHOR]

This paper explores the impact of different control strategies and electric tariff structures on the optimal ice storage capacity in relation to system economy for four typical buildings of hotel, restaurant, mall and office. The ice storage rate and electric price ratio are introduced to denote the various ice storage capacities and the different electric tariff structures, respectively. Then the chiller capacity and economic evaluation index value corresponding to each typical building with various ice storage rates and electric price ratios under three control strategies (chiller priority, storage priority, and optimizing) are calculated. The results indicated that there is respective optimal ice storage rate corresponding to both the minimal chiller capacity and the minimal economic evaluation index value. The optimal ice storage rate in relation to minimal chiller capacity is constant value under each control strategy. Such optimal values under both chiller priority and optimized control strategies are equivalent and less than that under storage priority control strategy. However, the optimal ice storage rate in relation to minimal economic evaluation index value under each control strategy is significantly affected by the electric tariff structures. The corresponding optimal ice storage rates under both chiller priority and optimized control strategies are equivalent and increase to a definite value with the increase in the electric price ratio. While the optimal ice storage rate under storage priority control strategy will appear when electric price ratio is greater than 3. The results also showed that, when electric price ratio increases to a certain value, the optimal ice storage rates corresponding to both minimal economic expense and minimal chiller capacity under each control strategy for the four typical buildings are equivalent. [ABSTRACT FROM AUTHOR]

Abstract: Ice slurry is used widely as phase change materials (PCMs) to reduce the peak demand for power system. Drop formation plays a key role during ice slurry production in liquid–liquid circulating fluidized bed. In the present work, drop formation in a co‐current liquid–liquid flow was investigated via a 3D model. Volume of fluid method was adopted to study drop characteristics by tracking the interface. Major influences of the water velocity, the oil velocity, the jet size, and the jet number on drop formation were analyzed for drop characteristics. The results indicate that properties of drop formation vary significantly according to the different conditions. The drop size was distributed mainly as the normal distribution, and the average drop diameter varies with different conditions. The drop size varies from 0.7 to 1.9 mm at the water velocity of 0.5 m/s, whereas the size of drop size varies from 1.8 to about 2.65 mm at the water velocity of 1.5 m/s. Furthermore, the residence time of drop decreases obviously with the increase of the oil velocity. When the oil velocity is 0.1 m/s, a drop leaves the top outlet at about 0.44 s. When the oil velocity is 0.3 m/s, a drop reaches the outlet at about 0.15 s. Additionally, the simulated results were compared with the relevant experimental results and the previous simulated results. Reasonable agreements have been gained, which can validate the established model to some extent. [ABSTRACT FROM AUTHOR]

• Proposed novel direct-expansion ice thermal storage system based on micro heat pipe arrays. • Developed the energy and exergy analysis of the system. • Investigated the effects of operating parameters on the system performance. • The EER and exergy efficiency of the system can reach 2.31 and 11.12 %. Direct-expansion ice thermal storage (DX-ITS) system can overcome the mismatch between cold energy supply and demand, and also exhibit the characteristics of high energy efficiency, simple pipeline and minimal installation space. However, existing DX-ITS failed to achieve simultaneous high-efficiency heat transfer in the processes of charging and discharging, thereby limiting its widespread use. This study developed a novel DX-ITS system based on three-fluid heat exchanger modules employing micro heat pipe arrays to address the proceeding issue. Temperature distribution, pressure, charging and discharging power, energy efficiency ratio, exergy efficiency and ice packing factor during the charging and discharging processes at different compressor speeds, cooling-air temperature and flow rates were experimentally studied. Results demonstrated that maximum charging power, energy efficiency ratio, exergy efficiency, ice packing factor and discharging power of proposed system using a 4 HP compressor under experimental conditions reached 5.71 kW, 2.31, 11.12 %, 82.1 % and 4.99 kW, respectively. Moreover, cooling-air temperature had a more significant effect on system performance compared with cooling-air flow rate and compressor speed. The 11.7 %, 25.9 %, 24.3 %, and 20.6 % reductions in charging power, energy efficiency ratio, exergy efficiency, and ice packing factor were observed with an increase of cooling-air temperature from 18 °C to 35.5 °C. [ABSTRACT FROM AUTHOR]

Ice thermal storage device using micro heat pipe arrays and closed rectangular fins has been proven to exhibit excellent thermal performance. However, neither the details of ice formation inside the device nor the dominant factors affecting the performance of the device and the optimal fin geometric parameters, have been reported. In this study, numerical simulations were performed to investigate the ice packing factor, dynamic ice front evolution, and effects of fin geometric parameters including fin height, thickness, and spacing on the thermal performance of the proposed device. Results demonstrated that the fins effectively improved ice formation homogeneity and accelerated ice formation. The decreased fin height and spacing, increased fin thickness were positive to enhance thermal characteristics. Taguchi method was used to obtain the contribution ratio of independent fin parameter and optimal geometric fin configuration to the thermal performance. Fin thickness played a dominant role with a contribution rate of up to 44.52%, followed by 28.65% for fin height and 26.83% for fin spacing. From the perspective of trade-off between ice formation rate and manufacturing cost, the optimal height, spacing, and thickness of the fin structure for practical engineering application were determined to be 15, 10.1, and 0.25 mm, respectively. • The heat transfer characteristics of MHPA-ITSD during ice formation process was analyzed. • Effect of height, spacing and thickness of closed rectangular fins are numerical investigated. • Fin thickness plays a leading role in the ice thermal storage efficiency. • The optimal parametric combination of closed rectangular fins is given using Taguchi method. [ABSTRACT FROM AUTHOR]

Highlights: [•] We compare few district cooling schemes to minimize the overall electricity charges. [•] We show that local tariff structures play an important role on the total energy (electrical) cost in a district building. [•] Only marginally saving can be achieved due to the local tariff conditions and low ΔT. [•] Energy saving in the range of 0.08–3.13% if a new tariff is adopted. [•] A total of further saving of 1.26–2.43% if ITS is operated. [ABSTRACT FROM AUTHOR]

Abstract: Based on the cumulative exergy analysis method, the effect of incorporating the Ice Thermal Storage (ITS) air conditioning system in power supply is analyzed. Not only the cumulative exergy of air conditioning system is considered, but also that of the processes consuming the power generated by the same peak regulating unit. The results show that the total cumulative exergy consumption of all processes consuming the power supplied by the peak generating unit, increases as the ITS system is applied. However, the average cumulative exergy variation, which is the ratio between the increment of the cumulative exergy consumption (ΔCEx) and the cooling load of the ITS system (QITS ), decreases slightly as QITS increases. It exhibits a linear relationship with the operating load of the power generating unit and QITS . And, it decreases as either of the two parameters increases. These results are verified by two case studies. [Copyright &y& Elsevier]

Abstract: This study attempts to predict the potential cost savings of employing ice thermal storage (ITS) systems in the office buildings cooling application in Malaysia over the next 20 years. During the past decades, huge amount of daytime peak power has been shifted to the off-peak hours by using cool thermal energy storage (CTES) systems around the world. However, the contribution of CTES systems in Malaysia is still small in comparison with its potential. This study is conducted for three different scenarios of retrofitting 10%, 25% and 50% of the existing conventional AC systems with new ITS systems. The overall results show that the full storage strategy can reduce the annual costs of the air conditioning system up to 35 percent while this reduction is limited to around 8 percent for load leveling strategy. [Copyright &y& Elsevier]

Abstract: The study applies the software Transient Systems Simulation Program (TRNSYS) to estimate the air conditions as well as the energy consumption of a typical library located in a tropical climate country. The simulation uses Typical Meteorological Year (TMY) weather data for Kuala Lumpur as the research site, which is the Dentistry library in University of Malaya is located in Kuala Lumpur. The current HVAC and R systems of the library are found to be inherently energy-inefficient and potentially improvable with an ice slurry-cooling coil. The impact on energy consumption and space thermal comfort of a custom-built AHU with an ice slurry-cooling coil incorporated in the HVAC and R systems is simulated in comparison to the baseline system. Based on this investigation, it is recommended that an ice slurry-cooling coil could be incorporated in tropical climate HVAC and R systems for improvement in energy management and dehumidification enhancement. [Copyright &y& Elsevier]

In this study, a compact ice thermal storage device that combines multichannel flat tube and closed rectangular fins is designed to improve solidification performance. To analyze the heat transfer characteristics and visualize the ice formation process, a numerical model was formulated and solved using enthalpy-porosity method. The temperature distribution, liquid fraction, and ice front evolution were studied during solidification process. The effect of heat transfer fluid on the performance of storage device at different inlet temperatures and flow rates was numerically investigated. Results show that when the inlet temperature was reduced from -3 °C to -6 °C, the ice packing factor increased by 32.2% and the storage power forms a linear relationship with the inlet temperature. When the flow rate was increased from 0.1 m3/h to 0.2 m3/h, the ice packing factor increased by 8.7% but the effect of flow rate was less obvious than the inlet temperature. Furthermore, the heat transfer characteristics of closed rectangular fins were compared with traditional longitudinal fins. We found that the former can achieve more uniform temperature distribution and a higher ice formation rate. The average solidification enhancement ratios of the both are 2.28 and 2.08, respectively, the former being 9.6% higher than the latter. [Display omitted] • A novel ITSD with multichannel flat tube and closed rectangular fins is proposed. • The HTF inlet temperature and flow rate have a significant impact. • CRF achieve a more uniform temperature distribution and enhance the ice formation rate. • Solidification enhancement ratio of CRF is 9.6% higher than of longitudinal fins. [ABSTRACT FROM AUTHOR]

In China, the annual energy consumption for cooling represents a relatively large and rising trend. District cooling systems (DCSs) have attracted increasing attention owing to their energy-saving operation and high-efficiency. However, a reasonable operation strategy for DCSs with multi-cold sources is still a problem. The main objective of this paper is to present a computer model to investigate the performance of large-scale DCSs in China based on survey data. To evaluate the performance of the system, we established a baseline model and a DCS model with ice thermal storage (ITS). We also developed a control logic that can respond to real-time load changes in a timely manner for both models. A comparison of the two models under a set control strategy revealed that the carbon dioxide emissions (CDEs) and energy consumption of the DCS and ITS (DCS&ITS) were 9% higher than the baseline model without ITS, but the cumulative cooling capacity also increased by 20% to satisfy users 14% of the cooling load demand. ITS has eased the pressure on the power grid while reducing operating costs. The annual operating cost of DCS&ITS was reduced by 6.78% compared with the baseline model, and the overall system efficiency increased by 9.46%. [Display omitted] • The multi-cold source DCS in subtropical climate was studied. • The baseline model and DCS&ITS model were developed based on TRNSYS. • The ice storage module in TRNSYS and its related mathematical models were elaborated. • The optimal control program of all devices in the DCS was designed. • The performance of two models was evaluated from multiple perspectives. [ABSTRACT FROM AUTHOR]