Chilled Water Tank Research Articles

Energy Management for an Air Conditioning System Using a Storage Device to Reduce the On-Peak Power Consumption

To reduce the on-peak electrical power consumption, storage devices are widely performed with the help of an energy management system. According to IEA, residential air conditioning consumes 70% of the electricity, increasing by 4% every year. To minimize peak power consumption, thermal energy storage (TES) can be used to store cooled water for the air conditioning system. An efficient chilled water tank was designed and computationally investigated. Three-dimensional cylindrical tanks were simulated with seven different heights to diameter (H:D) ratios. At first, the temperature changes in a chilled water tank during discharging and charging periods were studied. An 11-h charging period was carried out during the off-peak time at night, while the discharging period was 13 h during the daytime. Under time constraints regarding peak and off-peak periods, a tank with an H:D = 2.0 can only be used for 13-h discharging. Then the chilled water was simulated with a set temperature of 4 °C during the charging. This resulted in the system being usable for six days, after which it had to be stopped for longer charging. A storage tank with an H:D ratio of 2.0 was found to be suitable for an air conditioning system. If six days of operations (one day off) were used, it could save 15.38% of electrical energy consumption and 51.65% of electricity cost. This saving leads to a 5.55-year payback period.

Thermal analysis of a solar-powered absorption air-conditioning system: Case study for a tent in Mina zone, Saudi Arabia

The present study used a TRNSYS simulation for solar cooling with cold energy storage. It was applied to a tent hypothetically located in Mina zone, KSA, where millions of pilgrims stay in tents for a few days once a year. The required cooling demand was calculated for a tent that can be occupied by 150 pilgrims for 7 days representing Makkah climatic region. The system consisted of a solar thermal system, absorption cooling chiller matched with a cooling tower, storage tank, and fan coil units. The results show that the required cooling capacity for the tent is about 70 kW (20 tons refrigeration) to keep the zone air temperature at 24 °C during summer days where the cooling demand for the tent for 7 days in June is around 8,850 kWh. In addition, the effect of a cold-water storage on the system performance was studied. Using a chilled water tank of 500 m 3 will reduce the absorption chiller capacity from 20 tons to 4.7 ton. Moreover, a PV system was designed to cover the electrical load of the considered absorption system with performance ratio of 70%.

Application of thermal storage in over-night refrigeration of an institutional building

The performance of different thermal energy storing systems to provide over-night air-conditioning for a limited space in an institutional building in south Spain are compared with conventional air-conditioning (both for refrigeration and heating). In summer, the storage tanks are charged with a solar-assisted absorption chiller during day-time, and used to cover the over-night demand, whereas in winter a heat exchanger is used during the day to charge the tanks. Thermal energy has been stored in two chilled water tanks (with total capacity of 5000 L) or in two tanks (total volume 4000 L) containing two phase change materials (PCM): a PCM with melting point of 10°C for refrigeration, and a PCM with melting temperature of 46°C for heating. Our results show that the storing in PCM is more convenient, providing air-conditioning service for approximately 4 h 30 min in refrigeration, with a significant reduction of the electricity consumption with respect to the conventional system. The chilled water tanks can cover the demand for 4 h (scaled down to 3 h 12 min if the capacity is 4000 L), with even lower electric consumption. In winter, on the other hand, the tanks can cover fully the demand of overnight heating. Our results prove the viability of thermal storing, in particular using PCM, to extend the application solar cooling and heating to night-time, which is economically feasible, in a fully operational building.

Modeling Efficient Hybrid Air Conditioning System

The main objective of the present study is to investigate the thermal performance of the air chiller using the heat exchanger using the chilled water tank by Freon R-134a. The air chiller model was designed and fabricated with all measuring devices in the AL-Muthanna city environment. The practical tests were carried out with a change in the factors governing air coolant performance to investigate their effects on the properties of the system. The study covered the values of the cooling water flow rate at (2l/min) and the evaporator water temperature (2.5 to 5.69 °C) and the return water temperature in the reservoir ranged from 11.6 to 19.2 °C). The greatest coefficient of thermal performance in the system was (5) while the lowest coefficient of thermal performance was (3.6) and that agreement to the experimental studies of this type of system. The results showed that the average guidance in the consumption of air-chilled energy by using the water tank and Freon R-134a was about 13% to 32% compared to the conventional air conditioner. All through the results indicated that the addition of a cooling stage to the conventional cooler inside the testing room results in lowering the temperature (dry temperature) by (27%) and reduced the relative humidity by (36%).

Simulation and experimental study of thermal storage systems for district cooling system under commercial operating conditions

The use of ice as a phase change material (PCM) for such latent thermal energy storage (LTES) systems has been well established in industrial thermal storage. Organic phase-change materials (PCMs) such as paraffin waxes present advantages over ice for LTES systems in commercial air conditioning application due to higher phase-change temperatures and negligible volume expansion. In this study, an encapsulated ice thermal storage (EITS) system was analysed, modelled via COMSOL and validated with operating data. The numerical model is employed to analyse a similar theoretical encapsulated PCM (EPCM) system under similar and altered operating conditions using experimentally-derived thermal properties. Key results from this work revealed that the EPCM system is able to attain higher cold energy storage capacity of up to 3 times that of a reference chilled water tank and 9.37% more than that of the EITS under high flow conditions due to greater degrees of solidification. The effect of heat transfer fluid flowrate on solidification ratio and energy charged is also observed to be more pronounced in EPCM systems as compared to EITS systems.

Thermodynamic efficiency comparison between thermal and electric storage for photovoltaic-driven chilling system

Abstract Faced with the ever-increasing pressures from climate change and environmental pollution, stand-alone photovoltaic (PV) power generation is promising in providing electricity to the air conditioners. However, the solar energy is usually susceptible to the weather changes, making the power supply unreliable. To mitigate the effects caused by the solar intermittency, additional energy storage buffer is necessary. In this paper, stand-alone PV chilling systems with water tank thermal energy storage (TES) and battery electric energy storage (EES) strategies are quantitatively compared by evaluating the thermodynamic efficiency, respectively. A chiller model is firstly built, based on which the initial steady states are derived. Secondly, the EES and TES system models are built based on the compressor speed control strategy and refrigeration cycle model. The resulting chilled water temperature fluctuation curves in TES and EES PV chillers are subsequently obtained. Quantitative comparative results in this paper are threefold. i) The average chilled water temperature of the TES strategy is 11.08% lower than that in the EES strategy; ii) The average cooling energy amount stored in the TES strategy is 43.6% larger than that in the EES strategy, indicating that the chilled water tank has a better energy storage potential in the given PV chiller system; iii) The water volume of TES is optimized to derive the maximum cooling energy storage rate which is 76.92% larger than that in the EES system.

A Solar System for Heating and Cooling a House in Misurata

The aim of this work is to design a cooling and heating system that works with solar energy for a 175 m2house located in Misurata. At the beginning of this study, the weather data was collected in order to choose the proper two days for designing the system. Then the cooling and heating loads for the house were calculated. The amount of solar incident radiation on the flat plate solar collector at the two design days was determined mathematically. Also in this study, the area of the flat plate collector that required to cover the heating and cooling loads was found in cases of using single and double-glazed flat plat collectors. The proper size of hot and chilled water tanks for this system was also determined. If the solar system cannot provide adequate space heating and cooling, an auxiliary or back-up system provides the additional heat. Finally, the collector efficiency curve for a single and double-glazed was found. After writing the proper code for the calculations. Microsoft excel was used to analyze the data and to produce the curves.

Improved performance in tube-encapsulated phase change thermal energy stores for HVAC applications

Thermal energy stores can be used to shift building peak electric loads for cooling to off-peak hours. Compact, high-density thermal storage solutions are required for buildings that may not have the space necessary for typical thermal storage systems, such as chilled water tanks. Previous studies show that latent thermal stores using polymer tube-encapsulated paraffin-based phase change materials (PCM) yield acceptable thermal performance at low to moderate encapsulation tube packing densities, but that thermal performance falls as tube packing densities climb due to increasingly restricted heat transfer fluid (HTF) flow paths. This paper reports the experimental results found when using a highly conductive encapsulation material to redistribute the thermal energy around the PCM, mitigating the effect of the restricted HTF flow paths and enabling maximum encapsulation tube packing densities. These experiments show a more than two-fold increase in the percentage of recoverable thermal energy over a similar polymer tube based system, providing thermal performance comparable to that of a low density polymer tube encapsulation system while increasing PCM capacity by 111%. Test results are provided in a format suitable for estimating design criteria for larger thermal stores, and a design parameter – the resistance ratio – is proposed to assist in optimizing encapsulation tube parameters.

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.

Compact PCM-based thermal stores for shifting peak cooling loads

Thermal energy stores, when used as part of a demand management system, can shift peak cooling loads to off-peak hours or to periods when intermittent renewable energy sources are available. This enables more efficient use of baseline and renewable electric capacity, and reduces dependence on less efficient and more costly peak energy power plants. High density thermal stores can be an effective retrofit option for existing buildings and environmental control systems. This paper investigates the development of a simple, compact, high density thermal storage unit suitable for use in small to medium residential or commercial applications that utilize, or can be retrofitted to use, chilled water cooling coils. This thermal store design is based on the use of a widely available phase change material (PCM), macro-encapsulated into cylindrical tubes that are packed into a containment tank. An experimental scale model of this thermal store is constructed for test purposes, and tests are conducted to determine the feasibility of this design and to characterize its operation. A numeric model is developed to demonstrate the feasibility of modeling such a store using simplified assumptions, both for design purposes and real-time predictive control strategies. The results show that such a design increases thermal capacity over that of a simple chilled water tank, and that a simplified numeric model for use by control systems can predict the short-term performance of the store in near real-time.

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.

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.

Study on a compact silica gel–water adsorption chiller without vacuum valves: Design and experimental study

A compact silica gel–water adsorption chiller without vacuum valves was manufactured and experimentally studied. This chiller contains two adsorption/desorption chambers and one chilled water tank. Each adsorption/desorption chamber consists of one adsorber, one condenser and one evaporator. The chilled water tank is adopted to mitigate the variation of the chilled water outlet temperature. A mass recovery-like process, which is a heat recovery process between the two evaporators, was carried out in this chiller. A novel heat recovery process was also fulfilled after the mass recovery-like process to improve the coefficient of performance (COP). The cooling power and COP were 9.60 kW and 0.49 respectively when the average hot water inlet temperature, cooling water inlet temperature, and chilled water outlet temperature were 82.0, 31.6 and 12.3 °C, respectively.

An in‐use comparison of in‐line and in‐tank ultraviolet devices for reduction of the microbial load in water coolers

AbstractTwo ultraviolet (UV) systems were evaluated for use in water‐cooling devices: in‐tank (8 W, held in the centre of a 2‐L chilled water tank) and in‐line (6 W, treating chilled water at the point of dispense). The efficacy of these devices, under conditions of continual dispense (2 L/min), against a range of bacteria commonly associated with drinking water, was investigated. A rate of 1 L/min and the impact of a periodic dispense pattern (machine was not dispensing for 1 min between sampling) was examined with Escherichia coli. At 2 L/min, both devices achieved a 3 log reduction. At 1 L/min, both devices achieved greater than 4 log reduction. During periodic dispense, the in‐line device achieved a 3 log reduction, while the in‐tank device achieved greater than a 4 log reduction. UV was effective at reducing levels of bacteria commonly associated with water to acceptable levels. Under conditions of periodic use, the in‐tank device showed greater potential.

Conditionnements thermiques par fluide intermédiaire et accumulation d'énergie latente

As a result of direct automation of the industrial refrigerating plants the efficiency is generally reduced by: (1) not limiting the peaks of refrigeration demand; (2) not profiting by the permissible temperature variations of the stored goods; (3) allowing unstable cycles of production and distribution. From this ascertainment the authors investigate the advantages of the different forms of storing thermal energy. The conventional thermal energy storage methods are compared such as: (1) the most popular sensible heat storage by means of water or chilled water tank: (2) the storage below freezing by means of liquid solutions (salt, alcohol, glycerol, glycol…); (3) the ice accumulation systems; (4) the eutectic-plate systems. Moreover, temperature fluctuations of the stored goods in a cold store are contemplated as a posible method of storing sensible heat, if moderate (4K for frozen and 2K for fresh goods). The above-mentioned methods, using either sensible or latent heat, are compared in terms of: utilization temperature, accumulation temperature range, and storage capacity per unit mass and unit volume. Loading and unloading rates of the storage device are also significant characteristics. The development of new storage methods are then investigated mainly in respect of energy savings in the field of agro-industries requiring both refrigeration and heating. (1) The accumulation of warm water, using either electric supply during low-fare periods, or heat pumps associated to heat rejection recovery of refrigerating plants, or any combination of both sources; (2) the latent heat accumulation which allows an important space saving compared to sensible heat accumulation. The most important recent improvements are mentioned: (1) physico-chemical (supercooling, non-reversibility of the change-of-phase process, crystallizing rate and heterogeneous crystallization); (2) heat exchange problems; (3) technological constraints; (4) financial amortization. As an illustration of the advantages of heat storage, the authors present a possible application for slaughter houses aiming at energy savings by means of: (1) heat recovery from refrigerant condensation for preheating of process water, with or without thermodynamical amplification (heat pump); (2) optimization of the running cycles of the compressors and adjustment of condensing and evaporating temperature levels. The example of a 10,000 t/year slaughterhouse is presented where an eutectic accumulation device is included in the glycol-water distribution system, allowing for the transfer of a 1250 kWh refrigeration capacity from peak to low level demand periods, with a reduced volume of 25 m 3. As a conclusion, the authors review the main types of application of heat storage.