Performance Of Chiller Research Articles

The technical, economic, and environmental feasibility of a bioheat-driven adsorption cooling system for food cold storing: A case study of Rwanda

This paper studies the technical, economic, and environmental feasibility of a standalone adsorption cooling system thermally driven by biomass combustion and solar thermal energy. The developed cooling package was benchmarked against a baseline vapour compression refrigeration system, driven by grid electricity and the widely investigated adsorption cooling system driven by solar heat. TRNSYS was utilised to imitate the integrated systems, investigate their year-round performance, and optimise their designs by employing the meteorological data for Rwanda and an existing cold room (13 m2 floor area × 2.9 m height) as a case study. The optimisation study for the system revealed that maximum chiller performance (COP = 0.62), minimum biomass daily consumption (36 kg), and desired cold room setting temperature (10 °C) throughout the year can be achieved if the boiler setting temperature, heat storage size, and heating water flow rate are 95.13 °C, 0.01 m3 and 601.25 kg/h. An optimal PV area/battery size combination of 12 modules/16 kWh was obtained from the economic, environmental, and technical viewpoints.

Multi-objective optimization of series system for heat recovery: Technical and economic tradeoff

The refrigeration system on fishing vessels consumes a lot of fuel and increases carbon emissions. The absorption system for ice-making driven with the waste heat of the internal combustion engine is a feasible method to achieve "Nearly Zero Energy" freeze preservation. In this paper, firstly, the ammonia absorption cycle driven by the waste heat of the fishing boat was thermodynamically modeled, and it is found that the absorption chiller's performance is affected by the engine power, cooling water temperature. Secondly, by establishing a thermo-economic model, taking the capital, operation cost into consideration, the thermal economy of the system is analyzed; finally, through the multi-objective of the genetic algorithm, Pareto optimal frontiers of the system were presented. Different clusters of the optimal results show that the investment payback time can reach 2.50 years and 2.58 years; with exergy efficiency 37.81% and 37.86%, respectively.

Modeling and Simulation of a Two-Stage Air Cooled Adsorption Chiller with Heat Recovery Part I: Physical and Mathematical Performance Model

In the proposed work, the MATLAB program was used to model and simulate the performance of the investigated two-stage adsorption chiller with and without heat recovery using an activated carbon/methanol pair. The simulated model results were then validated by the experimental results conducted by Millennium Industries. The model was based on 10th order differential equations; six of them were used to predict bed, evaporator and condenser temperatures while the other four equations were used to calculate the adsorption isotherm and adsorption kinetics. The detailed validation is stated in the next paragraphs; for example, it clearly notes that the simulation model results for the two-stage air cooled chiller are well compared with the experimental data in terms of cooling capacity (6.7 kW for the model compared with 6.14 kW from the experimental results at the same conditions). The Coefficient of Performance (COP) predicted by this simulation was 0.4, which is very close to that given by the Carnot cycle working at the same operating conditions. The model optimized the switching time, adsorption/desorption time and heat recovery time to maximize both cooling capacity and COP. The model optimized the adsorption/desorption cycle time (300 to 400 s), switching cycle time (50 s) and heat recovery cycle time (30 s). The temporal history of bed, evaporator and condenser temperatures is provided by this model for both heat recovery and without heat recovery chiller operation modes. The importance of this study is that it will be used as a basis for future series production.

Energetic and Exergetic Analysis of a Solar-Driven Single-Effect Absorption Refrigeration System Using LiBr + LiCl/H2O Solution Mixture

Abstract Comprising an eco-friendly blueprint, absorption refrigeration systems have attracted a lot of interest as they can use biomass, solar and geothermal energy sources which can mitigate climate change. The current study presents a methodology based on energy and analysis for solar-driven single-effect absorption refrigeration systems, which offer a 50-kW cooling capacity. This study proposes a new mixture ratio of LiBr + LiCl (mass ratio of 2:1)/H2O solution and compared it to LiBr/H2O thermodynamically. Based on the climate data of Kocaeli province in Turkey, an evacuated tube collector is employed to benefit from solar energy to meet the generator heat load of the system. Although at an evaporator temperature of 5 °C, enhanced thermodynamic performance is evident with the use of the LiBr + LiCl/H2O system, and a diminished solar collector area is required compared to the system utilizing LiBr/H2O; there is a level of attrition relating to the impact of the former with a single degree rise in evaporator temperature. However, this remained at a greater value than for the latter system. The final results pointed out that LiBr + LiCl/H2O has a 48.93% lower circulation ratio, 8.81% higher coefficient of performance (COP) of chiller, 8.88% higher solar COP, 8.96% higher exergy efficiency of chiller, 8.90% higher exergy efficiency of solar-driven system, 8.92% lower solar collector area, and 8.91% lower storage tank volume than LiBr/H2O system in the investigated operating temperature ranges. The final results of the present study can be safely tested in the experimental design of single-effect absorption chillers.

Strategical district cooling system operation in hub airport terminals, a research focusing on COVID-19 pandemic impact

Part load ratio is often observed in real operations of airport terminal cooling system. This phenomenon is more obvious during the COVID-19 pandemic, as sudden flight restrictions impacting cooling demand are widely adopted in hub airport terminals. This research aims to propose optimal strategies of multi-chiller in airport terminals based on cooling load characteristics modeling, to tackle the aforementioned issues. Numerical experiments based on a real-world Chinese airport terminal are conducted to validate the proposed method. The results show that an average cooling load drop of 30% is observed from scenario of normal flight before COVID-19 to scenario of COVID-19 Period flight, and the average cooling load drop reaches to 44% from scenario of busy flight before COVID-19 to scenario of COVID-19 Period flight. The results also reflect that cooling load presents synchronous trend with passenger flow, but presents asynchronous trend with outdoor temperature. The influence of outdoor temperature on cooling demand delays due to building envelops. It indicates that simple superimposition according to passenger flow change for chiller operation number is reliable, efficient and effective, but is not suitable for outdoor temperature change. The findings are helpful to develop optimal strategies for further real-time control of multi-chiller.

A facile and reliable approach to enhance the energy storage performance of 1-Decanol for sustainable and energy-efficient cold storage system

The energy efficiency of an ice-based cold storage system (CSS) is intensively affected by its supercooling nature, low phase change temperature and probable nucleation behavior. As a result of this, the chiller should be operated at a lower evaporator temperature to freeze the water as well as to achieve better heat transfer performance. By virtue of this, the coefficient of performance of the chiller is significantly reduced, which in turn results in ineffective utilisation of energy sources for CSS. To tackle this issue, the water should be replaced with a suitable alternate PCM, which has no supercooling and high phase change temperature. In this study, 1-Decanol has been identified as a prospective replacement for water, and its energy storage performance has been enhanced in a practically feasible and economically viable way using an aluminium honeycomb core (AHCC). The effect of different sizes (small, medium and large) of AHCC on the charging performance of 1-Decanol has been explored in the spherical capsule (S.C). Further, the effect of adding AHCC, the diameter of S.C and wall temperature on the energy storage performance of 1-Decanol have been explored. It is found that the medium size AHCC is an optimal size for charging and discharging. Also, −3 °C is an optimal wall temperature for charging. The lower diameter S.C delivered better charging and discharging performance for a specified storage volume. For the 1-Decanol + AHCC based CSS, the effective utilisation ratio is remarkably high (10.49 to 14.96), and the reduction in energy storage capacity is only minimal (1.24% to 1.81%). Experimental results prove that upon adding medium size AHCC, the average enhancement in charging rate is 150.32%. Further, the average reduction in charging time is 60.09%, which signifies that chiller operating time and carbon emission can be reduced by 60.09%. The above results prove that the employment of AHCC to enhance the charging performance of 1-Decanol would lay the foundation for establishing energy-efficient and sustainable CSS.

Efficient modeling of adsorption chillers: Avoiding discretization by operator splitting

Reliable and computationally efficient models are crucial to improve the performance of adsorption chillers. However, modeling of adsorption chillers is challenging due to the intrinsic process dynamics. Currently, adsorption chillers are most often represented by 1-d, lumped-parameter models that use lumped models for all components but resolve the heat exchangers in one spatial dimension. Still, accurate simulations require fine discretization leading to poor computational efficiency. To increase computational efficiency, here, an alternative modeling approach is proposed that avoids discretization by applying operator splitting.The benefits of the proposed modeling approach are demonstrated in two real-world case studies. First, the resulting adsorption chiller model is calibrated and validated with experimental data of a lab-scale one-bed adsorption chiller: The proposed model retains the accuracy of a state-of-the-art model while increasing computational efficiency by up to 70%. Second, the proposed model is applied to a commercial two-bed adsorption chiller with excellent accuracy. Finally, the validity of model is tested by varying the ratio between the overall heat transfer coefficient and the heat capacity rate of the fluid in the heat exchangers. The proposed model is shown to be well suited for the conditions present in most adsorption chillers.

Optimization of chiller sequencing control for district cooling system at the Hong Kong-Zhuhai-Macao Bridge Hong Kong Port

To mitigate the climate change issue, the Government of the Hong Kong Special Administrative Region (HKSAR) proposed the “Hong Kong Climate Change Plan 2030+” with an ambitious goal of reducing the carbon intensity to 65%–70% below 2005 levels by 2030. To achieve this target, the HKSAR Government has developed two District Cooling Systems (DCS) to promote the use of district energy system, enhancing the overall energy efficiency for cooling purpose. One of the government-owned DCSs is located at the Hong Kong-Zhuhai-Macao Bridge Hong Kong Port (HZMB-HKP), producing a total design cooling capacity of 24.16 MW to passenger clearance building and ancillary buildings there. This paper demonstrates how the DCS at HZMB-HKP could enhance overall energy efficiency for cooling purpose, through proper chiller sequencing control, and reduce CO2 emission significantly. An optimal seasonal chiller operation mode is also suggested to be adopted at the DCS at HZMB-HKP from cost-effectiveness perspective. Practical application: District Cooling Systems are considered as a promising solution to alleviate the climate change issue. An optimized chiller sequencing control strategy of DCS can effectively reduce overall cooling energy consumption, so as to achieve carbon neutrality. This paper outlines a case study on a cost-effective operational control strategy of the DCS at HZMB-HKP. The analysis of both the theoretical and practical sequencing control strategy can be taken as a reference for DCS development in the future.

Fault detection and diagnosis for chiller based on feature-recognition model and Kernel Discriminant Analysis

Reliability of chillers is of great significance to maintaining sustainability buildings and reducing carbon emissions. The cause of chiller performance degradation was found in early fault detection and diagnosis technology, and the measure can be taken to save energy. This paper proposed an automatic diagnosis technique for Chiller based on the feature-recognition model and Spectral Regression Kernel Discriminant Analysis (SRKDA). Feature-recognition model would be used to calculate diagnostic parameters, deviations(D) between normal and fault data. At the same time, SRKDA would be applied for mapping original nonlinearly separable feature space to the separable features that are linear and improving the computational speed. For one thing, compared with principal component analysis (PCA) and Fisher Discriminant Analysis (FDA), the proposed method has the lowest false alarm rate and the highest detection rate for fault detection. For another, compared with the FDA and Support vector machine (SVM) for fault diagnosis, the proposed method has excellent accuracy and training time performance. In addition, experiments show that model-based data processing improved the separability of original data and further improved FDD accuracy.

Evaluation and Design of Large-Scale Solar Adsorption Cooling Systems Based on Energetic, Economic and Environmental Performance

In hot and dry regions such as the Gulf Cooperation Council (GCC) countries, the cooling demand is often responsible for more than 70% of electricity consumption, which places a massive strain on the electricity grid and leads to significant emissions. Solar thermal driven Silica-Gel/Water adsorption chillers, used for space cooling, could provide low carbon emission cooling and reduce the reliance on grid electricity. However, a meticulous design is required to make this both economically and environmentally beneficial. This paper aims to evaluate the solar thermal adsorption chiller performance based on large-scale cooling demand through a TRNSYS simulation for 1 year of operation. The proposed system consists of two main parts: first, the solar loop with evacuated tube solar collectors; and second, the adsorption cooling system with a silica-gel/water adsorption chiller. A neighbourhood of 80 typical 197 m2 villas in Riyadh, the capital city of the Kingdom of Saudi Arabia (KSA), was taken as a case study. The solar adsorption cycle’s performance has been compared to the conventional vapour compression cycle in terms of energy, economic and environmental performance. In addition, a parametric study has been performed for the main design parameters. Results reveal that the system can reach a solar fraction of 96% with solar collector area of 5500 m2 and a storage tank volume between 350 and 400 m3. Furthermore, the annual energy cost can be reduced by 74% for the solar adsorption system compared to the conventional vapour compression cycle. Meanwhile, the CO2 saving percentage for the solar adsorption cycle was approximately 75% compared to the conventional vapour compression cycle. Carefully designed solar thermal cooling systems can reduce greenhouse gas emissions while covering a large scale of cooling demands. This can reduce the strain on the electricity grid as well as greenhouse gas emissions.

Fresnel solar cooling plant for buildings: Optimal operation of an absorption chiller through inverse modelling

Increasing comfort conditions in buildings imply higher energy demands. However, these needs can be mitigated by solar cooling solutions. These systems, such as absorption chillers, are complex and require stable operation, with strict control to maximise the solar fraction and minimise gas consumption. This is incompatible with the variability of renewable resources, so they are often coupled with auxiliary gas systems. Although gas-free operation is possible if these systems are optimally controlled, they would require special supervision. This paper aims to develop an experimental validation of an inverse model to manage an absorption chiller coupled with a solar cooling plant. To know its real behaviour, long-term experiments have been performed using this plant, which consists of a linear Fresnel solar collector and an auxiliary natural gas boiler. The inverse model is used as a predictive control tool to decide the auxiliary boiler commands of the absorption chiller to optimise its operation: maximum cooling production by minimising gas consumption and maximising solar contribution. It has been identified with data from two weeks and validated with data from one summer month. Results show that the model estimates, on a time base of fewer than 30 min, are acceptable with errors of less than 5%. In addition, the maximum error of the estimated seasonal COP and the renewable fraction are less than 6% per day. Therefore, the results prove the usefulness of the proposal as a predictive control for optimal operation. Furthermore, it could be used as a baseline for preventive maintenance. If the proposed model is used for optimal management of the absorption chiller, the thermal efficiency of the plant increases significantly, doubling the solar contribution. As a result, the gas consumption of the solar cooling plant is halved and the total cost of air conditioning the building decreases by 16%.

Analysis of a linear programming‐based decision‐making model for microgrid energy management systems with renewable sources

With the increasing share of renewable energy sources in microgrids, systems enhancing the power flexibility at the demand side have become mandatory in microgrid architecture. Thus, the electrical energy storage system has been mostly integrated into microgrids although its capital and operating costs are very high. Hence, diversifying microgrid energy storage based on the end-energy usage can improve the reliability, operating cost, and power demand flexibility of the microgrid. The hereby study integrates an absorption chiller and electrical heat pump coupled to a heat storage into a renewable energy resources-based microgrid and develops its centralized energy management model for both off-grid and on-grid operation modes. The model considers the current energy level of energy storages in the microgrid, current, and forecasted information state to compute the vector-valued decision minimizing a realistic microgrid operating cost. The operating cost includes the energy purchasing/generation, heating/electrical storage, and penalty cost due to load shedding. Hence, such an objective function leads to maximizing the consumption of the generated renewable power, minimizing the energy storage and load shedding cost. The load shedding has been allowed to increase the flexibility in microgrid energy management. However, a high penalty has been imposed on each electrical, heating, or cooling load shedding decision. The decision vector components are thermal and electrical power flow between each energy source to loads and energy storage systems. The problem has been modeled as a Linear Programming with forecasted multi-parametric inputs at different prediction horizons. The effect of the charging/discharging rate and capacity of energy storages, coefficient of performance of absorption chiller and heat pump, prediction horizon, and energy level of storage devices provided to the myopic energy management model has been evaluated for better integration of renewable sources and thermal storage systems into microgrids. Suggestions have been made to improve the microgrid self-consumption, energy efficiency, and myopic decision-making model using the energy level of storage devices obtained from the full look-ahead optimization model. Highlights The optimization problem combining electricity, heating, and cooling is formulated The electrical and thermal storage charging/discharging rate significantly affect the power supplied by the renewable power source decision of the microgrid energy management model. Accurate energy storage level information into the myopic energy management model improves the model decisions. The absorption chiller coefficient of performance greatly impacts the cooling and electrical loads shedding.

Experimental analysis of ON/OFF and variable speed drive controlled industrial chiller towards energy efficient operation

This study demonstrates thermodynamic and energy effects of a Variable Speed Drive (VSD), powering compressor in a partially loaded chiller system. The proposed work fits the gap in the existing literature, which mostly addresses VSD applications in chiller’s auxiliary pumps and fans. The goals of this work are defined by four Research Problems (RP’s): RP1. comparison of thermodynamic extensive parameters, for ON/OFF and VSD controlled systems, RP2. load ranges in which VSD control systems are energy efficient, RP 3. potential energy savings in VSD controlled compressor, and RP 4. mathematical model formulation, useful in energy audit conditions, estimating potential benefits of VSD implementation, based on measurement data from existing ON-OFF controlled chiller. To address these aspects, a set of measurements have been performed on a fully equipped experimental chiller system (UW Oshkosh Teaching and Energy Research Industrial Lab). All data have been collected for a wide spectrum of loads in both control configurations. Data analysis showed significant differences in a chiller operation. VSD operated chiller eliminates fluctuations in all measured thermodynamic parameters (RP1.). The accomplished work demonstrated that the most energy efficient effects can be achieved for a partially loaded, VSD-controlled chiller, working at ∼55–75% of its nominal capacity (RP 2.). The implementation of a Variable Speed Drive for such load levels allows for achieving up to 25% of energy savings (RP 3.) Finally, proposed mathematical model have been experimentally verified as useful in the range of 50–100% of nominal load (RP 4.).

Technical, environmental, and economic evaluation of a solar/gas driven absorption chiller for shopping malls in the Caribbean region of Colombia

This study discusses the technical, environmental, and economic feasibility of using absorption chillers driven by solar energy and/or natural gas, in selected shopping malls in Barranquilla, Caribbean region of Colombia. The high solar irradiation and the low prices of natural gas in the cities of the Caribbean region of Colombia are attractive conditions for the use of absorption chillers. To prove the feasibility of absorption chillers in the Caribbean region of Colombia, the use of water/LiBr absorption chillers of 352 kW cooling capacity was investigated considering the cooling loads in selected malls. A thermodynamic model was developed to study the performance of the absorption chiller and evaluate different scenarios proposed. The results evidenced that the absorption chiller could reach a maximum COP and SCOP of 0.77 and 0.52, respectively. The different alternatives could reduce gas emissions between 17% and 76% depending on the cooling load covered by the absorption chillers and driving energy input as compared to the current use of mechanical compression chillers. The economic results indicated that the best scenario, considering a lifetime of 20 years, is the gas-driven absorption chiller with IRR varying from 40% to 54.6% depending on the mall cooling load covered.

Manipulating Pore Topology and Functionality to Promote Fluorocarbon-Based Adsorption Cooling

ConspectusWith the worldwide demand for refrigeration and cooling expected to triple, it is increasingly important to search for alternative energy resources to drive refrigeration cycles with reduced electricity consumption. Recently, adsorption cooling has gained increased attention since energy reallocation in such systems is based on gas adsorption/desorption, which can be driven by waste/natural heat sources. Eco-friendly sorption-based cooling relies on the cyclic transfer of refrigerant gas from a high to low energy state by the pseudocompression effect resulting from adsorption and desorption. The driving force for energy transfer relies on heat rather than electricity. The performance of a sorption chiller is primarily influenced by this cyclic sorption behavior, which is characterized as the working capacity of the porous sorbent. Thus, increases in this working capacity directly translate to a more compact and efficient cooling system. However, a lack of highly effective sorbent/refrigerant pairs lowers cooling performance and therefore has limited applicability. To this end, synthetic metal-organic frameworks (MOFs) and covalent organic polymers (COPs) possess higher porosity and greater tunability leading to more substantial potential benefits for adsorption, compared to traditional sorbent materials. Similarly, hydrofluorocarbon refrigerants have more favorable applicability given the ease of operation above atmospheric pressures due to suitable saturated vapor pressures and boiling points. For these reasons, our work focuses on an ongoing strategy to promote sorption cooling via improvements in the sorbent/refrigerant pair. Specifically, we target the interaction of hydrofluorocarbon refrigerants with MOF/COP materials at a molecular level by interpreting the host-guest chemistry and the role of framework pore topology. These molecular-level differences translate to cooling performance, which is described herein. These strategies include engineering framework porosity (i.e., pore size, pore volume) by using elongated organic linkers and stereochemistry control during synthesis; manipulating the sorbate/sorbent interaction by introducing functional moieties or unsaturated metal centers to enhance working capacities in narrow pressure ranges; varying pore topology/morphology to impact adsorption isotherm behavior; and leveraging defective sites within the frameworks to further enhance adsorption capability. This atomic level understanding of sorbate-sorbent interactions is conducted using various in situ experimental techniques such as synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, in situ Fourier transform infrared spectroscopy, and direct sorption energies determinization with calorimetry. Moreover, the experimentally studied interactions and the corresponding adsorption mechanism are corroborated by computational studies using density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations. Using this approach, we have made strides toward engineering designed frameworks with precise molecular control to target refrigerant molecules and thereby enhance the performance of desired working pairs for sorption-based cooling.

Exergetic model of a small-scale, biomass-based CCHP/HP system for historic building structures

• Methodology for exergy analysis of bio-solar CCHP/HP systems. • Transient and dynamic model for optimal sizing of gasifier and other components. • Optimal sizing can significantly reduce irreversibility losses. • Biomass types have marginal effect on system exergy efficiency. Biomass-based, small-scale Combined Cooling, Heating and Power (CCHP) systems can increase the energy autonomy of building complexes while reducing their Greenhouse Gases (GHG) emissions. In combination with air-to-water Heat Pumps (HP), highly efficient energy systems can be designed, which allow for high flexibility in serving thermal and electric demands. This study presents an exergy evaluation of such a small-scale CCHP/HP system using a dynamic modelling approach based on gasification of various types of woody biomass. The transient model takes into account the effects of the biomass chemical composition as well as of ambient temperatures on the exergy performance of all key components for various CCHP system sizes supporting an HP system. The model has been applied in a case study for a historic building complex, where the CCHP sub-system would support an HP-subsystem allowing for downsizing the latter. The results show that smaller CCHP systems operate with higher exergy efficiency, because for larger systems the heat transfer from the engine and the operation of the absorption chiller are less exergy efficient. The electric load-following CCHP subsystem reaches exergy efficiencies of up to 13.3%, indicating huge improvement potential for system and sub-system design. It was also found that the biomass composition heavily influences the exergy efficiency of the gasifier and in turn changes the exergy efficiency of the syngas engine and the entire CCHP sub-system.

Chilled water temperature resetting using model-free reinforcement learning: Engineering application

Optimal operation of chillers could be realized by controlling chiller on–off status and resetting chilled water supply/return temperature. The chilled water supply temperature could influence both chiller power and indoor comfort simultaneously. Hence, it is necessary to optimize its set point. By combining the reinforcement learning (RL) technique and expertise knowledge, a hybrid model-free chilled water temperature resetting method for chillers is proposed, to improve the robustness and learning speed of RL control. The proposed method and the comparative expert manual control are applied to control an actual HVAC system in Shanghai. Engineering practice results suggest: (1) the energy-saving performance of the hybrid model-free method is close to that of expert manual control, with limited comfort sacrifice, acceptable robustness, learning speed and control stability; (2) without model establishing and persistent manual overwatch work, the proposed control method could conserve manual labor before and after the intervention of optimized control. Based on the engineering practice, a supplementary simulation study is conducted, which indicates: (1) the performance of the proposed method only takes one cooling season to converge; (2) the proposed hybrid method outperforms both pure RL-based control and pure rule-based control in the first training cooling season, while inferior to model predictive control; (3) the proposed method is an acceptable alternative for systems without sufficient data or certain equipment condition, due to its online self-learning mechanism and low pre-condition requirement on historical data and models.

Increasing the Performance of an Adsorption Chiller Operating in the Water Desalination Mode

The intensive development of the world economy and the expected population growth mean that demand for cooling and water will continue to rise. The use of conventional technologies to meet this demand is associated with an enormous expenditure of electricity, which still comes mainly from non-renewable sources. With the increasing demand for energy, the increasing scarcity of drinking water, and the negative impact of humankind on the environment due to global warming and ozone depletion, intensive research has been carried out to find modern desalination technologies Most of the technologies use electricity for the process of desalination, and over 6% of the world’s electricity is generated from non-renewable sources, thus increasing the emissions of harmful pollutants into the atmosphere. One possibility to reduce emissions is the use of adsorption chillers with desalination function, which allow the production of cooling simultaneously with the process of water desalination. These systems can be powered by low-temperature waste heat from industrial processes or from renewable sources (solar panels) and require little electricity to operate. This paper presents options to improve their performance and increase the production of condensate in the process of desalination of saline water. Moreover, also presented are the results of tests carried out on a two-bed adsorption chiller with desalination function. The aim of the study was to determine the effect of cycle time on the cooling coefficient of performance (COP) and on the production of condensate from water desalination. The obtained results confirmed that increasing the adsorption and desorption cycle time leads to an increase in the COP value of the adsorption chiller, but the efficiency of the desalination process and condensate production decreases with increasing cycle time.

Global Self-Optimizing Control With Data-Driven Optimal Selection of Controlled Variables With Application to Chiller Plant

AbstractIn this paper, we propose a global self-optimizing control (SOC) approach, where nonlinear dynamic model is obtained from historical data of plant operation via the framework of sparse identification of nonlinear dynamics (SINDy) combined with regularized regression. With the nonlinear static input–output map obtained by forcing steady-state operation, the globally optimal solutions of controlled variables (CVs) can be found by tracking the necessary conditions of optimality (NCO) in an analytical fashion. After validation with a numerical example, the proposed method is evaluated using a modelica-based dynamic model of a chilled-water plant. The economic objective for chiller plant operation is to minimize the total power of compressor, condenser water pump, and cooling tower fan, while the cooling tower fan speed and condenser water mass flow rate are used as manipulated inputs. The operating data are generated based on realistic ambient and load conditions and a best-practice rule-based strategy for chiller operation. The control structure with the SOC method yields a total power consumption close to the global optimum and substantially smaller than that of a best-practice rule-based chiller plant control strategy. The proposed method promises a global SOC solution using dynamic operation data, for cost-effective and adaptive control structure optimization.

Experimental and theoretical analysis of a trigeneration system consisting of adsorption chiller and high temperature PEMFC

Trigeneration system offers an effective way to utilize the waste heat from the primary power generation unit and to produce refrigeration. This can be accomplished using adsorption chillers capable of producing chilled water above its freezing point. Experiments were carried out to measure the performance of the adsorption chiller as a standalone system as well in trigeneration system coupled with HT–PEMFC. Waste heat recovery of 2.76 kW was achieved from a 5 kW HT–PEMFC operating at full load condition using an adsorption chiller of 1.99–2.84USTR refrigeration capacity increasing the full system efficiency from 32.0% to 39.8%. Waste heat recovery can be further improved by employing a common intermediate buffer tank heated via heat exchangers connected with multiple fuel cell systems supplying heat to a single high capacity adsorption chiller increasing the expected total system efficiency to 44.9%.Simulation of the adsorption chilling system was accomplished providing further insights of parameters affecting its performance as well as design criterion for heating and cooling requirements for a target refrigeration capacity of the adsorption chiller. The heating requirements were underestimated by 24% for a standalone system and 32% for trigeneration system primarily due to non-accountability of the gaseous adsorbate withheld within the adsorbent bed.