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Two pre-industrial prototypes of a new ammonia/lithium nitrate absorption chiller, a water-cooled one and an air-cooled one, have been built and experimentally characterized. The single-effect configuration of the absorption refrigeration cycle was selected for both prototypes in which brazed plate heat exchangers were used in all thermal components. These prototypes, designed for air conditioning applications, were tested under various operating conditions to assess their performance. The water-cooled prototype yields 12.9 kW of cooling capacity and an electrical COP elec of 19.3, when operating at a 15 °C chilled water temperature, 90 °C hot water temperature and a 35 °C cooling water temperature. In the case of the air-cooled prototype, at a 15 °C chilled water temperature, 90 °C hot water temperature and a 35 °C ambient air temperature, the cooling capacity is 9.3 kW and the electrical COP elec is 6.5. [ABSTRACT FROM AUTHOR]

Highlights: [•] Propose a method that enhances the COP compared to conventional methods. [•] A theoretical approach in fine tuning double and combined effect absorption chillers. [•] Possibility to utilize two different heat sources simultaneously in cooling. [•] Improved utilization of waste heat compared to conventional methods. [ABSTRACT FROM AUTHOR]

Highlights: [•] Studied heat transfer in floor plenum in buildings with UFAD system. [•] The heat lost could be significant if the air is supplied without duct. [•] The computer models were validated by experimental data. [•] Chiller used less and boiler and fans more energy in UFAD than those in mixing systems. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] The addition of a new back-smoothing technique enables real-time FDD. [•] Algorithm can detect the occurrence of multiple and simultaneous faults. [•] Noisy and erroneous sensor data do not lead to erroneous FDD solutions. [•] Proposed solution updates fault probabilities in less than 5s. [•] Three common chiller plant faults detected despite significant noise in sensor data. [Copyright &y& Elsevier]

Thermochemical technologies of cooling capacity production are ecologically effective processes of utilizing a heat stream combined with electricity production. Apart from poly-generation systems, their applications are found in air conditioning systems cooperating with solar installations and other industrial installations generating heat as a by-product. Unlike the widely commercialized absorption chillers, continuous research on improving the heat utilization efficiency in adsorption systems gives innovative nature to this technology. This paper presents a work analysis of the adsorption cooling device. The construction, working principle, and variability of defined performance parameters in time for a representative cooling cycle were also presented. [ABSTRACT FROM AUTHOR]

SUMMARY The world is becoming increasingly interested in renewable energy including geothermal energy. The utilization of geothermal systems is currently low because geothermal systems and existing source systems are used independently, but the supply rate of a geothermal system is increasing. Therefore, suggesting efficient operation plans and evaluations of the energy consumption and efficiency of a geothermal system is needed. This paper reports the results of a field study and survey of the present applications and operation conditions of a geothermal system. In addition, this paper proposes an efficient operation strategy for a geothermal system and compares this operation strategy with an existing operation strategy through simulation. The problems of existing operation condition were found out through a field study, and alternatives were proposed. The improvements were evaluated using the transient systems simulation program. And it would be possible for the reduction of the energy consumption through the comparative analysis of equipment efficiency and energy consumption. The result of analyzing the proposed combination header method through simulations compared with existing operation conditions can increase the use of geothermal systems, but the combined cooling and hot water of a geothermal heat pump and existing thermal source system reduced the efficiency of the heat pump. As a result of simulation on individual load-sharing method, efficiency of geothermal system is increasing compared with the combination header method. This method was especially made to separate geothermal system's water loop and existing thermal source system's water loop. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights: [•] Theoretically proposed models of water flow rates for multiple parallel chillers. [•] Both the total and partial flow rates of chillers can be determined by the models. [•] Providing a method to determine the distribution of water flow rates in chillers. [•] Providing actual water flow rate of each chiller for other researches such as FDD. [Copyright &y& Elsevier]

Abstract: This paper presents the development of benchmarking models for the ongoing commissioning of heat recovery process in a cooling and heating plant that provides chilled water and heating water to HVAC (heating, ventilation and air conditioning) systems on a university campus. The heat recovered from the chillers in the summer was used for the heating water loop. The proposed ongoing commissioning approach and GUI (graphical user interface) are presented. The benchmarks were developed using measurements from the BAS (Building Automation System). The results indicated that the performance indices should be analyzed at both levels: the heat exchanger and the whole heat recovery system. Although the heat exchanger (HX3) effectiveness was reduced from an average value of 0.85 in 2008 to 0.60 in 2010, the effectiveness was greater than the benchmarks limits of 0.13–0.15. That reduction did not translate into a significantly lower performance of the whole heat recovery system. The BAS was able to control the system adaptation to this degradation of performance of HX3, by increasing the heating water flow rate, with an increase of electric power of pumps of only 6%. As a result, additional heat input to the system was never required. The whole heat recovery system works within the benchmarking limits. [Copyright &y& Elsevier]

Highlights: [•] Assessing and comparing the performance of three types of absorption refrigeration systems. [•] Investigating the effect of considering the chemical exergy of LiBr–H2O solution in computations. [•] Determining energy and exergy performance using energy and exergy analysis methods. [•] Comparing the cost and CO2 emission of the systems. [Copyright &y& Elsevier]

Highlights: [•] Field demonstration of chiller FDD is a big challenge. [•] A decoupling-based FDD method was fully implemented and evaluated on a field chiller. [•] The proposed FDD method can address multiple simultaneous faults in chillers. [•] A step by step process of implementing the proposed method is presented. [•] The proposed method has potential to be incorporated within commercial FDD products. [ABSTRACT FROM AUTHOR]

Highlights: [•] The environmental impacts of a solar absorption chiller system (AC) are calculated. [•] The impacts are compared with an equivalently sized vapor compression system (VC). [•] The cooling production of the AC is simulated using system-specific parameters. [•] The VC system use-phase is the largest phase contributor to life cycle impacts. [•] The AC system yields lower impact potentials for all four impact categories. [ABSTRACT FROM AUTHOR]

Abstract: To experimentally evaluate the performance of an ejector working as a liquid re-circulator in a horizontal-tube falling-film evaporator with R134a, experimental tests are performed using a horizontal-tube falling-film water chiller prototype. Experimental observations on intertube liquid flow pattern of tube bundle validate the feasibility of the liquid re-circulation system using a liquid–liquid ejector. The analysis results show that the influence of the motive flow rate on the entrainment ratio of the ejector is small, and the average entrainment ratio of the ejector is about 2.03. With the increase of the valve opening of the regulating valve, the evaporating capacity of the falling-film water chiller rises 4.8%, from 940.2 kW with the re-circulation ratio of one, to 985.5 kW with the re-circulation ratio of 1.135. The COP of the falling-film water chiller reaches a maximum and then drops down with the increase of the re-circulation ratio, and the optimal re-circulation ratio is 1.135. [Copyright &y& Elsevier]

A multivariable fuzzy controller was developed and implemented for the regulation of the secondary fluid temperature in a chiller using both the rotation frequencies of the pump and the compressor as manipulated variables. Its performance was measured using the integral of time-weighted absolute error ( ITAE) index and the energy consumption. The proposed control strategy proved able to adequately control the chiller in all experiments. For comparison purposes, similar experiments were carried out with fuzzy control strategies in which only one variable was manipulated at a time. Comparing the performance of the proposed controllers with the fuzzy single input-single output controllers for regulatory control, a mean percentage reduction of at least 88.5% was observed in the ITAE. Good results were also observed in control effort and energy consumption. Besides, the implementation of the control strategy was quite simple. Practical Applications Refrigeration systems are of fundamental importance for food conservation. Besides, to maintain the temperature into a narrow range needs an efficient control system and implies energy consumption and equipment wear. The use of a fuzzy controller with two manipulated variables to regulate the secondary fluid temperature has proved to be an efficient control configuration. Desirable characteristics like small or no overshoot, reduced control effort were achieved by the proposed multivariable fuzzy controller. Therefore, this proposed strategy is a valuable alternative to control processes that require strict variability or long periods of operation without stopping. [ABSTRACT FROM AUTHOR]

Highlights: [•] Methanol adsorption dynamics on loose grains of activated carbon was studied. [•] Recommendations on enhancing specific cooling power of adsorption chillers are made. [•] Grain size insensitive mode of the dynamics is revealed for 0.8–4.0mm grains. [•] Dynamics is invariant in respect to ratio S/m of heat transfer area to adsorbent mass. [•] The increase in S/m-ratio of the system “heat exchanger – adsorbent” is recommended. [ABSTRACT FROM AUTHOR]

The use of ammonia-based working fluids for absorption prevails in a wide range of applications due to the low freezing temperature of the refrigerant and the absence of crystallization as well as the lack of problems under vacuum conditions. This paper presents a comprehensive overview on the use of ammonia-based absorption chillers and heat pumps. The thermodynamic and physical properties of pure ammonia and binary and ternary ammonia mixtures are presented in correlation formulas. Developments and applications in subfreezing refrigeration, heating/domestic hot water, renewable energy utilization, waste heat recovery, thermal energy storage and miniaturization of absorption systems are presented and summarized. In subfreezing refrigeration, the evaporation temperatures for single-stage absorption lie mainly between −30°C and −5°C, and they can reach as low as −70°C in advanced absorption systems. Air-source and ground-source absorption heat pumps are suggested for heating/domestic hot water applications in cold regions. For renewable energy uses, ammonia-based solar absorption applications with various working fluids are quite popular, whereas geothermal and biomass energy systems are less studied. In thermal energy storage, ammonia-based working fluids are not advantageous for storage capacity or cycle efficiency, but they prevail for subfreezing energy storage. Additionally, ammonia-based fluids are also attractive options for the miniaturization of absorption systems due to the absence of crystallization. [ABSTRACT FROM AUTHOR]

Highlights: [•] The air-conditioning system of a datacenter in Beijing is tested. [•] COPsys is approaching to 9 for free cooling while about 3 for mechanical cooling. [•] Suggestions are proposed to improve the temperature distribution of cabinet. [•] An innovative LTD (large temperature difference) distribution system is proposed. [•] It is of significant improvement in energy efficiency for this new process. [ABSTRACT FROM AUTHOR]

Abstract: Within the scope of the project AgroKühl, a pilot plant of a solar thermally driven cold store has been developed and installed near Freiburg in Germany. The system consists of a linear concentrating Fresnel collector system with mirror area of 88 m2, an ammonia-water absorption chiller of 12 kW cooling capacity with an integrated cooling tower, two ice storages of 52 kWh latent storage capacity and a cold store of 100 m3. With the aim to guarantee observation of quasi-realistic system behaviour and to avoid restrictions in the operation, the cold store was equipped with computer-controlled fan heaters and humidifiers. This allows the emulation of sensible and latent loads in the room. The system was installed in summer 2012 and since August 2012 it is in continuous operation during summer period. This publication describes the system in detail, summarizes the first operational results and highlights optimization potential of the plant. [Copyright &y& Elsevier]

Concentrating solar collectors provide high efficiency at high driving temperatures favourable for thermally driven chillers. Therefore, they offer applications for hot climates and industrial process integration, especially in combination with NH3–H2O chillers that provide refrigeration temperatures below 0 °C. The presented solar cooling installation comprises a linear concentrating Fresnel collector that provides the driving heat for two NH3–H2O absorption chillers at temperatures up to 200 °C. Chilled water temperatures are produced in the range between ?12 °C and 0 °C. Collector capacities reached up to 70 kW at peak times and the total cooling capacity of both chillers showed peak values up to 25 kW. For good operating conditions, the thermal system EER was 0.8 and an electrical system EER of 12 was easily achieved. The system showed a sound operating behaviour. The performance of different operation and control strategies was analysed, evaluated and enhanced within the two year operation phase. [ABSTRACT FROM AUTHOR]

Abstract: Typically the cooling capacity of absorption chillers is controlled by adjusting the driving hot water temperature according to the load. Meanwhile the cooling water temperature is controlled to a constant set value. In order to increase the solar cooling fraction and/or to decrease the operating costs of solar assisted cooling systems (SAC-systems) a new control strategy has been developed which controls hot and cooling water temperature simultaneously. Hereby the specific cost of cold – generated from solar or conventional heat – can be reduced. The basic concept of the strategy is explained and results are shown for the SAC-system at the Federal Environment Agency in Dessau, Germany. Here a recently developed absorption chiller is now used instead of a former adsorption chiller. With the new absorption chiller and the control strategy the seasonal energy efficiency ratio SEER is above 0.75, electric efficiency is 35% higher and water consumption is reduced by 70%. [Copyright &y& Elsevier]

An all-variable-speed chiller plant has been advocated so that the chillers and their associated pumps can work at reduced speed during part-load conditions for energy saving purposes. In this new building project, the savings merit is certainly attractive. However, an existing chiller plant or retrofit project, which is constrained by the performance of installed equipment and the configuration of a hydronic circuit, may not benefit from the an ideal extent of savings. As such, an existing chiller plant serving a typical commercial building was used to evaluate this. Through year-round dynamic simulation, it is found that there were about 5%, 6%, and 8% energy savings of the whole chiller plant when applying variable flow control on secondary chilled water pumps only, both primary and secondary chilled water pumps, and all chilled and condenser water pumps, respectively. If constant-speed centrifugal chillers were substituted by the variable-speed ones, an additional 4% savings could be achieved, which was, however, less than that incurred from the associated pumps. The payback periods of different variable flow control strategies were well below 1 year, indicating the techno-economical feasibility for wider application in existing chiller plants in subtropical climates. [ABSTRACT FROM AUTHOR]

This paper presents experimental explorations on cooling performance of thermoelectric chillers being driven by solar cells, as well as comparison results to the performance being driven by fixed direct current. Solar energy is clear and limitless and can be collected by solar cells. We use solar cells to drive thermoelectric chillers, where the cold side is connected to the water tank. It is found that 250 mL of water can be cooled from 18.5°C to 13°C, where the corresponding coefficient of performance (COP) is changed between 0.55 and 1.05, when solar insolation is changed between 450 W/m² and 1000 W/m². The experimental results demonstrate that the thermoelectric chiller driven by solar cell is feasible and effective for energy saving issues. [ABSTRACT FROM AUTHOR]

Solar energy refrigeration is very attractive for low-temperature grain storage because the cooling load of low-temperature grain storage is roughly in phase with solar energy availability. In this study, a solar-powered adsorption chiller was developed with aim of developing an alternative refrigeration device for low-temperature grain storage. The solar-powered adsorption chiller was put into experimental operation during summer and autumn. Test results show that the solar-powered adsorption chiller can produce a cooling capacity about 66–90 W per m2collector area. Its daily solar-cooling COP (coefficient of performance) is about 0.1–0.13 under the climatic conditions of daily solar radiation being about 16–21 MJ/m2·day. With appropriate ventilation appliance, this kind of solar-powered adsorption chiller could be considered as an alternative for low-temperature grain storage in most areas of China. [ABSTRACT FROM PUBLISHER]

Environmental concerns and the rising energy cost necessitate looking for renewable energy driven environmentally benign adsorption cooling systems. Solar powered adsorption chillers with non-concentrating flat plate or evacuated tube collectors face the problem of not getting adequate driving source temperature during some months of the year. Multi-staging of the adsorption cycle is then needed to exploit the low driving source temperature. A simulation study of a solar thermal driven dual-mode, four-bed silica gel–water adsorption chiller is undertaken in this work. The solar thermal collector data of Durgapur (23.48 °N, 87.32 °E), India has been used as the heat source for the dual-mode chiller. For a driving source temperature above 60 °C, the chiller works as a single stage four-bed adsorption chiller; while the chiller functions as a two stage adsorption chiller when the driving source temperature falls below 60 °C. With a cooling water temperature of 30 °C, this two stage chiller has been found to produce cooling effect with a driving source temperature as low as 40 °C. Results indicate that the dual-mode chiller is capable of providing cooling throughout the year under the climatic condition of Durgapur, India. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present an innovative occupancy and chilled water storage-based operation mode. [•] This mode was implemented to the solar-assisted air-conditioning system. [•] It permits to save 42% of total electrical energy during one cooling period. [•] It allows storing the excess cooling capacity of the absorption chiller. [•] It prevents the sudden start/stop (on/off cycles) of the absorption chiller. [ABSTRACT FROM AUTHOR]

Abstract: In building management systems, the fault-free data are usually available while the fault data are generally insufficient. The fault detection task can be considered as a typical one-class classification problem, which aims to differentiate the fault-free data class from all other possible fault data classes. In this study, a pattern recognition-based chiller fault detection method is proposed using a novel one-class classification algorithm, i.e. Support Vector Data Description (SVDD). Its basic idea is to find a minimum-volume hypersphere in a high dimensional feature space to enclose most of the fault-free data. When a fault occurs, the fault data will be outliers of the hypersphere. Compared with Principle Component Analysis (PCA), it has no Gaussian assumption and is effective for nonlinear process modeling. It can also compress process variables of wide-range operating conditions into a single model with higher fault detection accuracy. This method is validated using the experimental data from ASHRAE Research Project 1043 (RP-1043). Results show that the SVDD-based method has better chiller fault detection performance compared with PCA-based methods. [Copyright &y& Elsevier]

In this study, characteristics of a chiller system are investigated. The experimental setup consist of an air cooled condenser, a liquid type shell-tube evaporator, and a scroll compressor. Compressor speed is changed between 30-60 Hz via PWM type frequency inverter. Mass flow rate of the refrigerant R134a is controlled by an electronic expansion valve (EEV) and a thermostatic expansion valve (TXV) in the system. The cooling capacity of the chiller system is about 3 kW. For determining the performance characteristics of the system eight parameters are considered. These are the EEV opening, superheating, subcooling, evaporation/condensing temperatures, and refrigerant flow rate. It is found that the COP decreased to its half and cooling capacity increased 37% by increasing the frequency from 30 Hz to 60 Hz. According to analysis, superheating changing affects various parameters in the system and also it is important to monitor this parameters. [ABSTRACT FROM AUTHOR]

Abstract: Recently, in refrigeration industry the use of efficient dual-evaporator refrigeration systems has been paid a lot of attention. These systems sound even more interesting when they are a combination of different kinds of conventional refrigeration systems. In this paper three thermally driven chillers consisting of absorption refrigeration and ejector-expansion transcritical cascade CO2 cycles are proposed and investigated thermodynamically. The systems are called “hybrid dual-evaporator” cycles. The absorption cycle in the systems is either the single-effect or double-effect series-flow or double-effect parallel-flow cycle for each of which a solar collector is considered to supply the required heat in their generator. The performances of hybrid dual-evaporator systems are analyzed and optimized, using the Engineering Equation Solver and applying the principles of conservation of mass and energy as well as the exergy balance to each component of each system. Results indicate that combing the double-effect parallel absorption refrigeration system with ejector-expansion system gives the highest coefficient of performance among the other configurations. However, a combination of single-effect absorption refrigeration system with ejector-expansion cycle may be preferred due to its less complexity and reasonable exergy efficiency. Results also reveal that at optimum generator temperature of 72.92 °C the coefficient of performance and exergy efficiency of hybrid dual-evaporator with single-effect absorption are 1.182 and 0.2564, respectively. In addition, it is observed that increasing the cooling capacity ratio from 1 to 6 results in increases of the coefficient of performance and exergy efficiency of configurations by up to 36.32% and 11.5% respectively. [Copyright &y& Elsevier]

Abstract: An increased interest in absorption chillers has been observed [1] because these systems can utilize solar, geothermal and biomass energy sources, but also because they are quiet, vibration-free, require little maintenance and are ecological [2]. Instead of a compressor system, which uses electricity, an absorption cooling system, using renewable energy and kinds of waste heat energy, may be used for cooling. This paper presents the simulation of a single stage solar absorption chiller operating with an ammonia–water mixture under steady state conditions. This simulation is based on heat and mass balances for each component. The heat and mass transfers in the absorber, the condensation of binary vapor of ammonia–water in the condenser and a thermosyphon desorber placed under the purification column were modeled. The numerical model was compared and validated with experimental data obtained with a solar absorption chiller. The calculated results agree well with experimental data. Simulations based on experimental data were used to predict the temperature and concentration profiles in each heat exchanger. A parametric study was conducted to investigate the effect of evaporator and desorber temperature on the absorption chiller's performance. The COP decreases by 25% with a decrease of 10 °C in evaporator temperature and the COP increases by 4% with an increase of 10 °C in desorber temperature. [Copyright &y& Elsevier]

Abstract: A state-space model has been developed to investigate the dynamic behaviors of refrigeration system. By using vector-matrix notation and linearization, the ordinary differential equations describing the chiller's dynamic thermal behaviors are transformed into a representation form of the state space. The model has been validated by a series of dynamic response experiments of a chiller with the refrigerant R-134a. The average errors of the model results compared with the experimental data are all less than 10% in the experimental cases. Afterward, the model is used to investigate the transient behaviors of the exit cold carrier temperature of evaporator under different A disturbances. The state-space model developed in this study helps us have a good idea of the dynamic performance of a refrigeration system under transient conditions and design optimized control strategies for a high-energy-efficiency HVAC system. [Copyright &y& Elsevier]

Irreversibility analysis of a double effect direct fired LiBr-water vapor absorption chiller with reverse parallel flow arrangement is presented in this research. The irreversibility method is a powerful tool for optimization of the performance of absorption refrigeration systems. Analysis is performed for 4 different operating conditions of the chiller. Mass flow rates, specific enthalpies, specific entropies, energy balance and irreversibility changes were calculated for all components of the system. The results reveal that irreversibility changes in condenser, evaporator and heat exchangers are less as compared to the irreversibility changes in generators and absorber. The results show that COP of the absorption chiller increases by increasing the temperature of high temperature generator. However, irreversibility changes also increase with this increase in temperature thus reducing the availability of energy. Thermo economic optimization of LiBr-water vapor absorption chiller can be done by using these results. These results play an important role for improvement of absorption system. It is observed that analysis of absorption system using the irreversibility method can improve potential thermodynamic performance, which is impossible through numerical techniques. [ABSTRACT FROM AUTHOR]

Optimization of the performance of absorption systems during such transient operations as start-up and shut-down to minimize lifetime costs is particularly important for small-capacity chillers and heat pumps. Dynamic models in the literature have been used to study responses to step changes in single parameters, but more complex transient processes, such as system start-up, have not been studied in detail. A robust system-level model for simulating the transient behavior of an absorption chiller was developed here. Individual heat and mass exchangers were modeled using detailed segmental models. System parameters used in the model were representative of a 1-RT (3.5-kW cooling) absorption chiller currently under development. Representative simulations were performed for the full “cold start-up” process and for system responses to step changes in the desorber coupling-fluid temperature and valve settings. Results from this analysis can be used to optimize start-up and steady-state performances. [ABSTRACT FROM AUTHOR]

The performance of XP10, a new refrigerant with a reduced global warming potential, in a centrifugal chiller designed for HFC-134a with a cooling capacity of 1969.44 kW (560 tons) was measured under full- and part-load conditions and compared to performance with HFC-134a. Measured chiller energy efficiencies with XP10 were comparable to those with HFC-134a. They resulted in 0.6% higher energy consumption for XP10 when integrated over a representative profile of partial loads as described by AHRI Standard 550/590 (AHRI 2003). Based on the measured chiller performance, XP10 could be considered a near drop-in replacement for HFC-134a in centrifugal chillers. It could replace HFC-134a in existing chillers or enable optimized new chiller designs without extensive equipment and no flammability code modifications. The total equivalent warming impact of a chiller with XP10 was estimated under representative scenarios and compared to total equivalent warming impact with HFC-134a. Use of XP10 could significantly reduce chiller global warming impact relative to HFC-134a, when chiller refrigerant losses are unavoidably high or when electricity is generated with low GHG emissions. XP10 has the potential to be a more environmentally sustainable future option for medium-pressure centrifugal chillers. [ABSTRACT FROM AUTHOR]

Abstract: Adsorption chillers are capable of utilizing inexpensive or free low grade thermal energy such as waste heat and concentrated solar thermal energy. Recently developed low regeneration temperature working pairs allow adsorption chillers to be driven by even lower temperature sources such as engine coolant and flat plate solar collectors. In this work, synthetic zeolite/water was implemented into a 3 kW adsorption chiller test facility driven by hot water at 70 °C. The zeolite was coated onto two fin-and-tube heat exchangers, with heat recovery employed between the two. Cyclic steady state parametric studies were experimentally conducted to evaluate the chiller's performance, resulting in a cooling coefficient of performance (COP) ranging from 0.1 to 0.6 at different operating conditions. Its performance was compared with published values for other low regeneration temperature working pairs. The physical limitations of the synthetic zeolite revealed by parametric study results were then discussed. A novel operating control strategy was proposed based on the unique characteristics of synthetic zeolite. In addition, a physics-based COP prediction model was derived to predict the performance of the chiller under equilibrium loading, and was validated by the experiment results. This analytical expression can be used to estimate the cyclic steady state performance for future studies. [Copyright &y& Elsevier]

The central chilled water plant is one of the major power-consuming units of a building. Even small reductions in power consumption could achieve significant energy conservation. Hence, optimization of a chiller plant is necessary for energy savings without compromising the comfort level of the end user. The present work deals with identifying the system parameters and developing a novel formulation for a chiller plant and its optimization using a hybrid optimization technique. The optimization model formulation is based on finding an optimal mix of equipment and operating parameters in the chiller plant for minimum electrical power consumption. It takes into account the performance characteristics of the chillers, cooling towers and pumps, and optimizes the energy consumed based on the required loads and the ambient atmospheric conditions. Sequential quadratic programming combined with the modified branch and bound method was used to develop the hybrid optimization algorithm. A case study is presented for a typical chiller plant. The results indicate that the present optimization method could be a potential method of making energy savings. [ABSTRACT FROM AUTHOR]

This article presents the optimal cycle time and performance of two different types of silica gel–water-based three-bed adsorption chillers employing mass recovery with heating/cooling scheme. A new simulation program has been developed to analyze the effect of cycle time precisely on the performance of the systems. The particle swarm optimization (PSO) method has been used to optimize the cycle time and then the optimum performances of two chillers are compared. Sensitive analysis of cycle time has been conducted using the contour plot of specific cooling power (SCP) with driving heat source temperature at 80°C. It is found that the center point of the contour indicates the maximum SCP value and optimal cycle time, which are comparable with the quantitative values obtained for the PSO method. Both three-bed mass recovery adsorption cycles can produce effective cooling at heat source temperature as low as 50°C along with a coolant at 30°C. The optimal SCP is similar for both cycles and is greater than that of the conventional two-bed adsorption system employing the same adsorbent–refrigerant pair. Consequently, the proposed comparison method is effective and useful to identify the best performance of adsorption cycles. [ABSTRACT FROM AUTHOR]

Abstract: Three power and fresh water cogeneration systems that combine a GT (gas turbine) power plant and a RO (reverse osmosis) desalination system were compared based on the exergy viewpoint. In the first system, the GT and RO systems were coupled mechanically to form a base system. In the second and third systems, a VCR (vapor-compression refrigeration) cycle and a single-effect ACWater–LiBr (water/lithium bromide absorption chiller) were used, respectively, to cool the compressor inlet air and preheat the RO intake seawater via waste heat recovery in the VCR condenser and ACWater–LiBr absorber. A parametric analysis-based exergy was conducted to evaluate the effects of the key thermodynamic parameters including the compressor inlet air temperature and the fuel-mass flow rate on the system exergy efficiency. Parameter optimization was achieved using a GA (genetic algorithm) to reach the maximum exergy efficiency, where the thermodynamic improvement potentials of the systems were identified. The optimum values of performance for the three cogeneration systems were compared under the same conditions. The results showed that the cogeneration system with the AC is the best system among the three systems, since it can increase exergy and energy efficiencies as well as net power generation by 3.79%, 4.21%, and 38%, respectively, compared to the base system. [Copyright &y& Elsevier]

SUMMARY The standard working pairs for absorption chillers, ammonia/water and water/lithium bromide show problematic behaviours like crystallisation and corrosiveness. Because of their convenient solving properties and their low vapour pressure, ionic liquids are a new promising class of sorbents for absorption cooling purposes. In this study, the working pairs water/1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) and water/1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM][DMP]) are implemented in AspenPlus. The performance of a single effect cycle with these pairs is simulated and compared to results of a cycle with water/LiBr. For [EMIM][DMP] a coefficient of performance (COP) comparable to that of LiBr or even higher (up to 0.85) is found. [MMIM][DMP] shows a smaller maximum COP but a largely wider operating temperature range than LiBr. Results are compared with those of other groups, discrepancies discussed and improvements suggested. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]