Performance Of Chiller Research Articles

How does the control logic influence the establishment of a data-driven chiller model?

The modelling of chiller performance is critical for chiller optimal control, and fault detection and diagnosis (FDD). Different kinds of chiller models including sophisticated mechanistic models (white-box models), purely data-driven models (black-box models like artificial neural networks, ANN), and semi-physical models (grey-box models like empirical equations) have been proposed and tested. Due to the development of machine learning techniques, data-driven models have become more popular recently. The performance of the established data-driven model (accuracy, robustness, generalization) could significantly affect the model application. To enhance the model performance, a lot of studies have been carried out on investigating and modifying the model structure. However, the influence of the data quality on model training has not been sufficiently studied. When adopting historical data to train models, the data distribution is highly correlated to the control logic. So how does the control logic influence the establishment of data-driven chiller models by affecting the data distribution? In this study, experiments are conducted on an air-cooled chiller under model-free stochastic control to acquire rich and variable operational dataset; then the dataset is grouped into three corresponding to different chiller control logics. Finally, three models trained by three training datasets are evaluated, and the results suggest that when establishing data-driven chiller models, preliminary stochastic operation is cost-effective to acquire rich data for robust chiller modelling.

Performance improvement in an adsorption chiller with stepwise-linear fin height for each module in series

An adsorption chiller is a highly promising cooling technology, but it has not been widespread because there are many uncertainties to solve the complex thermal and mass transfer phenomena. An adsorption chiller is composed of multi-modules and the tube inlet temperature decreases (or increases) during the adsorption process (or desorption process) from module to module in serially connected modules. It has been reported that the optimal fin height depends on the tube inlet temperature, thus using a different fin height for each module should potentially enhance the overall system performance of the adsorption chiller. Till now, there have been few studies which evaluated adsorption chiller performance from a system viewpoint. Most only considered a single fin space. Thus, no study has considered improving total system performance by using different conditions for different modules in series. We conducted a numerical study of 5 modules in series, using different fin heights. The coefficient of performance (COP) and specific cooling power (SCP) of modules with stepwise-linearly decreasing fin height were compared with those of modules with constant fin height. An 8.5% increase in COP and a 9.56% increase in SCP were observed. This enhancement will be much larger if more than five modules are connected to match the cooling capacity. The decrease (or increase) in tube inlet temperature accumulated in the series of modules. The last module, the 5th showed the most significant enhancement in COP and SCP, of 27.9% and 38.4%, respectively.

Optimization strategies for absorption chillers: A performance study on natural gas and LPG utilization

This research aims to investigate optimization strategies for absorption chillers utilizing natural gas and liquefied petroleum gas (LPG) to enhance performance and efficiency. The study employs a combination of experimental analysis and mathematical modeling to evaluate the performance of absorption chillers operating with these two fuels. Through a series of controlled experiments and simulations, key performance metrics such as coefficient of performance (COP), energy consumption, and emissions are analyzed. The optimization process involves the application of advanced algorithms to identify the most efficient operational parameters for each fuel type. The key findings indicate that absorption chillers using LPG demonstrate a higher COP compared to those using natural gas, albeit with increased emissions. Conversely, natural gas-fueled chillers exhibit lower emissions but slightly reduced efficiency. The study also identifies optimal operating conditions for both fuels, which significantly improve overall performance. These findings have substantial implications for the HVAC industry, particularly in regions where natural gas and LPG are prevalent. The optimized strategies can lead to significant energy savings and reduced environmental impact, making absorption chillers a more viable option for sustainable cooling solutions. The results also provide a foundation for future research on further enhancing the performance and sustainability of absorption chillers.

Evaluating the Performance of Water Chillers Equipped with Constant- or Variable-Frequency Centrifugal Compressors

The cooling coefficient of performance (COPR) and energy efficiency ratio (EER) of refrigerant R-134a compressors (single- and double-compressors) with different refrigerant tonnage (200, 250, 300, 380, 500, and 700 RT) for centrifugal and Maglev centrifugal compressors change with different operating performance load percentages (10–100%), and constant-frequency and variable-frequency operation, resulting in performance differences. In particular, a water chiller can have a fixed cooling water inlet temperature of 32 °C and a variable cooling water inlet temperature between 18.33 °C and 32 °C. According to the actual test results, the commercial performance code program and parameter table of the water chiller were established. Based on the performance matching of different load chillers, the on-site load capacity was analyzed and the effective water chiller performance and model matching were determined as the best choice for the tonR number of the deicing machine and unit matching, providing a reference for a future large water chiller that cannot be used on site for a single unit tonR. To achieve energy-saving benefits, different types of compressors, different refrigeration tonR operation, constant-frequency unit and variable-frequency unit alternate operation, and different operating performance load percentage operation can be allocated. Finally, the results show that, when the cooling water inlet temperature is fixed, the Maglev variable-frequency centrifugal compressor water chiller is better than the constant-frequency centrifugal water chiller, and also better than the variable-frequency centrifugal water chiller. The larger the freezing tonR of the variable-frequency centrifugal water chiller, the smaller the difference between COPR and EER. When the cooling water inlet temperature changes, the Maglev variable-frequency centrifugal water chiller is better than the constant-frequency centrifugal water chiller, and it is also better than the variable-frequency centrifugal water chiller. The larger the freezing tonR of the variable-frequency centrifugal water chiller, the smaller the difference between COPR and EER. Moreover, the operating performance of the constant-frequency centrifugal water chiller is between 60% and 90%, which can maintain relatively high COPR and EER values. The operating performance of the variable-frequency centrifugal water chiller is between 40% and 70%, which can maintain relatively high COPR and EER values. Compared with the constant-frequency and variable-frequency, the Maglev variable-frequency centrifugal water chiller can maintain higher COPR and EER values when the operating performance is between 10% and 100%. When the operating performance is between 10% and 70%, it can maintain very high COPR and EER values. When the water chiller is selected in the field, the energy-saving of COPR and EER will be given priority. Therefore, the load capacity can be used to effectively manage the water chiller performance and model selection, so that the operation performance can reach the best percentage and energy saving can be achieved.

Chiller Load Forecasting Using Hyper-Gaussian Nets

Energy load forecasting for optimization of chiller operation is a topic that has been receiving increasing attention in recent years. From an engineering perspective, the methodology for designing and deploying a forecasting system for chiller operation should take into account several issues regarding prediction horizon, available data, selection of variables, model selection and adaptation. In this paper these issues are parsed to develop a neural forecaster. The method combines previous ideas such as basis expansions and local models. In particular, hyper-gaussians are proposed to provide spatial support (in input space) to models that can use auto-regressive, exogenous and past errors as variables, constituting thus a particular case of NARMAX modelling. Tests using real data from different world locations are given showing the expected performance of the proposal with respect to the objectives and allowing a comparison with other approaches.

Optimization of Central Air Conditioning Plant by Scheduling the Chiller Ignition for Chiller Electrical Energy Management

Currently, the demand for electrical energy in homes, buildings, and industry is increasing, in line with population and economic growth. Of course, because of the massive use of electrical energy, it is necessary to increase efficiency. Large shopping malls in some countries are the biggest consume electricity, especially when it comes to cooling systems. Therefore, it is necessary to save energy in shopping centers. Because there are still few tenants and shopping centers that are relatively quiet, the mall's energy consumption is low, so it requires increasing energy-efficient consumption efficiency by optimizing power management and calculating the chiller performance coefficient (COP). This research aims to increase the chiller performance coefficient (COP) to save energy in shopping centers. The optimization method used is to make changes to the chiller ignition schedule when it's used in malls. Through the analysis from this research, it was found that the COP increased to 0.584, and the value before optimization was 6.181. With increasing COP, the chiller performance will increase. The effect of increasing the chiller's performance could optimize the electrical energy efficiency of the chiller in 138.82 kWh/day

A data driven performance assessment strategy for centralized chiller systems using data mining techniques and domain knowledge

Chillers are among the major energy consumers in building heating, ventilation and air conditioning systems and appropriate performance assessment of chiller systems is essential to ensuring their operational optimality while delivering satisfactory indoor thermal comfort. This paper presents a data driven performance assessment strategy for centralized chiller systems using multiple data mining and advanced visualization techniques. The energy consumption patterns of the chiller system were quantitatively and qualitatively analyzed by using the Conditional Inference Tree (CIT) and Agglomerative Hierarchical Clustering (AHC), and Association Rule Mining (ARM), respectively. A performance indicator of Coefficient of Performance (COP) Destruction (%) was introduced to represent the quality of the achieved COP. The performance of this strategy was evaluated using one-year operating data of a centralized chiller system installed in a commercial building. The results showed that the data mining techniques can be effectively used for performance assessment of chiller systems. The results from the quantitative and qualitative analysis showed that the chiller performance was strongly influenced by the temperature difference across the evaporator. The system studied generally showed good performance when the part load ratio was above 45% and the chiller power ratio was above 50%, and it showed relatively poor performance when the temperature difference across the evaporator was below 3.1 °C.

Evidence-based assessment of energy performance of two large centrifugal chillers over nine cooling seasons

The change over time of energy performance of large chillers used in commercial and institutional buildings is seldom presented in the literature. Most studies are based on measurements of small capacities of residential air-conditioners and heat pumps. Authors found in the literature only three papers on this topic. This paper presents the evidence-based assessment of long-term performance of two identical large capacity chillers that serve the cooling system of a university campus. The paper presents the estimation of uncertainty of direct and derived measurements by using as example measurements recorded at 15 min time intervals by the building automation system during the summer of 2016. First, the paper verifies the hypothesis that weekly values of coefficient of performance (COP) of these large chillers do not change significantly over the summer of 2016. Second, the t-test also verifies the hypothesis of no significant change of seasonal COP values from 2009 to 2017. Third, a linear correlation-based model shows a variation of COP values by 1-2% per year between 2009 and 2017. The results show that the seasonal variation of COP is not statistically significant.

Transfer learning based methodology for migration and application of fault detection and diagnosis between building chillers for improving energy efficiency

Faulty operation of HVAC chillers may result in increased energy usage, reduced thermal comfort, and increased maintenance costs. Establishing reliable fault detection and diagnosis (FDD) methods can effectively avoid these adverse effects. Most existing FDD studies only focus on training specific fault diagnostic models for particular chillers. Very few works have been found to address the issue of how to transfer FDD between different chillers, which is a promising but challenging task. This paper presents a generic framework for transferring the prior knowledge of an information-rich source chiller to build the diagnostic model for a new target chiller. Heterogeneous data standardization is firstly presented to standardize the original datasets of different chillers. Domain adaption transfer learning is then applied to overcome the domain shift introduced by the differences of feature distribution across chillers, and domain adversarial neural network is used to generate the diagnostic model for the target chiller where only easy-to-collect normal operation data of the target chiller and the prior knowledge are used for training. To verify the presented transfer learning, two screw chillers are used as the source and target chillers accordingly, and large quantities of fault simulation experiments are performed on them. Results indicate that the transferred diagnostic model for the target chiller yields decent diagnostic performance, the accuracy for the first and second cycles are 81.27% and 74.93%, respectively. In comparison with five conventional machine learning models with accuracy less than 55%, the proposed transfer learning approach has significant performance advantages and practical application potential.

Optimisation of Operation of Adsorption Chiller with Desalination Function

The demand for electricity is growing rapidly along with economic development and increasing population. At present, its production is mainly based on non-renewable sources, which has negative impacts on the environment and contributes to global warming. A large proportion of the produced electricity is consumed by refrigeration equipment. Climate change and the progress of civilisation are additionally increasing the demand for cooling, with increasing electricity consumption as a consequence. One of the options for obtaining eco-friendly cooling is the use of adsorption chillers. These devices are powered by low-temperature heat and their operation only requires a small amount of electrical energy. The source of low-temperature heat can be, e.g., waste heat generated in many industrial processes. Its use allows one to increase energy efficiency and achieve additional financial benefits. However, adsorption chillers are characterised by low coefficients of performance. This paper presents possibilities to improve their performance. It also presents the results of tests carried out on a three-bed adsorption chiller with desalination function. The aim of the investigation was to determine the effect of the cycle time on the coefficient of performance (COP) and specific cooling power (SCP). The working pair was silica gel and water. The results confirmed the effect of the duration of adsorption and desorption on the COP and SCP of the adsorption chiller. Increasing the duration of the cycle led to an increase in the COP.

Method of linear approximation of COP for heat pumps and chillers based on thermodynamic modelling and off-design operation

Often, simple estimates of the coefficient of performance (COP) for heat pumps (HPs) and chillers are used. Depending on the purpose, this may not be sufficient. There are more accurate methods for determining COP, but they may not be used due to complexity, nonlinearity, or limited application of advanced COP estimation methods. Here, we present a new COP approximation method suitable for HPs and chillers. It is based on linear relationships and was developed from a thermodynamic two-stage HP model for design and off-design operation using ammonia as a refrigerant. This approximation method was then applied to a case study investigating the potential of district heating supplied by HPs in Tallinn, Estonia. Groundwater, sewage water, seawater, river water, lake water, and a district cooling return line were explored as potential heat sources. The results show a deviation in COP of less than 1.5% compared to the thermodynamic model. Annual calculations show the applicability of the COP approximation method for calculating hourly COPs at different heat source and heat sink temperatures, as well as changing heat loads, seasonal COP, heat demand ratio, and hourly Lorenz efficiency.

Innovative approach in adsorption chiller: Combination of condenser-adsorber for improving performance

This study aims experimental and numerical investigation of an adsorption chiller having a new combined condenser-adsorbent bed. The designed and manufactured adsorption chiller having a shell and tube type adsorbent bed consisting of 444 tubes of 10 mm inner diameter is simulated. The experimental cycle of the adsorption chiller was successfully obtained. In the numerical study, the influence of desorption temperature and condenser pressure on the performance indicator of adsorption chiller is investigated. In the experimental study, the coefficient of performance of the adsorption chiller is found as 0.80. The system's specific cooling power and volumetric cooling power values were determined as 30 W/kg and 6.7 kW/m3, respectively. Instantaneous transferred heat from heat exchanger fluid to adsorptive in the evaporator during the isobaric adsorption process reached 0.6 kW between 250 and 350 s. The numerical results showed that the increment of desorption temperature and decreased condensation pressure succeeded in increasing the performance indicators.

Performance prediction of a two-bed solar-powered adsorption chiller with heat and mass recovery cycles and adaptive cycle time – A first step towards the design of fully autonomous commercial-scale adsorption chillers

Abstract The previously published literature based on the performance prediction of solar-powered adsorption chillers generally incorporates fixed heat/mass recovery (HR/MR) cycle times which remain unchanged during the entire course of operation of the adsorption chiller. In reality, the dynamics of the HR/MR processes are continuously subject to change due to temporal variations in the solar radiation intensity, and thus fixed HR/MR cycle times might not prove to be compatible with the actual dynamics of a transient solar-powered chiller operation. The current study proposes a numerical scheme for performance modeling of a commercial-scale adsorption chiller with adaptive HR/MR cycle times following the adsorption/desorption (ads/des) cycle. A novel model of the MR cycle has been proposed which, in accordance with the best knowledge of the authors, cannot be find anywhere else in the previously published literature. The ads/des → HR → MR → des/ads half cycle has been predicted to yield an almost 52% higher cycle-averaged value of coefficient of performance ( COP ), an almost 16% higher value of specific cooling power ( SCP ), and a roughly 146% higher value of solar COP ( COP sc ) than the ads/des → MR → HR → des/ads half cycle over the entire course of operation of the adsorption chiller till sunset.

Facile approach to fend off the supercooling phenomenon of water in a spherical enclosure for energy-efficient and sustainable cold thermal energy storage system

Performance of an ice-based cold thermal energy storage system (CTESS) is immensely affected by its supercooling nature. In this research, it was mitigated entirely using 1-Decanol as a nucleating agent, which has favourable properties such as absence of supercooling, low cost, suitable phase change temperature (5 °C) and reasonable freezing enthalpy (200 J g−1). The optimum concentration of 1-Decanol required to eliminate the supercooling nature of water is found to be 2 wt%. Moreover, charging characteristics of water with 2 wt% 1-Decanol were explored in various diameter spherical capsules (42, 51, 64, 75, 85, and 105 mm) at −3, −6, and −9 °C wall temperatures. The addition of 2 wt% 1-Decanol eliminated the supercooling nature of water in all diameter capsules at all wall temperatures. As a result, complete solidification time is considerably reduced. Based on freezing time and charging rate, the optimum wall temperature is found to be −6 °C. Experimental results concede that 1-Decanol is highly reliable in eliminating supercooling, and its addition only led to 0.79% reduction in energy storage capacity. Mitigation of supercooling significantly reduced the chiller operating time and wall temperature required for charging, which further leads to utilisation of energy efficiently and sustainably.

Experimental evaluation of a solar two-bed lab-scale adsorption cooling system

A lab-scale two-bed adsorption chiller can be driven by solar energy was designed, constructed and evaluated experimentally in Thermal Engineering Lab, Alexandria University, Egypt. Isotherms characteristics of silica gel that was packed in the two beds were determined depending on the experimental DVS (dynamic vapor sorption) analyzer results. To visualize the sorption phenomena in the two beds and in the evaporator during the adsorption and desorption cycle, a special transparent glass was used as the upper cover for these components. The time variations for the temperatures and pressures at each component were measured, simulated and analyzed. The system performance was experimentally investigated under various operating conditions. The results showed that the specific cooling capacity (SCC) was about 75 W/kg while the coefficient of performance (COP) was 0.42, when the hot water inlet temperature was 75–80 ℃, the cooling water inlet temperature was 25 ℃, and the chilled water inlet temperature was 14 ℃. Effects of adsorption/desorption times and chilled water temperatures (Tch) on the chiller performance were investigated.

Solar cooling modelling utilising for cooling agro-products cold store under Rwandan environmental conditions

Solar-driven cooling systems can be considered as a sustainable solution for the weak cold chain. Transient Simulation System (TRNSYS) offers component-based 0D modelling capability of different engineering systems. TRNSYS has been employed to model a year-round performance of a PV solar-driven electric chiller to meet the cooling demand of post-harvested foodstuffs under Rwandan metrological data. Various PV module sizes and batteries storage capacities have been investigated to examine their effect on the solar energy fraction powering the electric chiller to maintain the room at the desired temperature. In addition, two different arrangements of chilled water loop, namely one-loop with 3 KW chiller capacity and two-loops with 6 KW chiller capacity have been compared to investigate their effect on the chiller performance and solar fraction. Results revealed that the later arrangement exhibits a higher solar fraction compared to one loop despite the addition of another pump. For 35 PV modules, the two-loops arrangement requires 42 kWh battery capacity to provide about 90% solar fraction, while one-loop needs 66 kWh to deliver the same solar fraction. Accordingly, the battery storage capacity is reduced by a factor of 0.36 which justifies the increase in the chiller capacity from 3 KW to 6 KW. This study provides a selection map to choose between the number of PV panels and batteries capacity required to power the chiller and meet the cooling load.

Performance of oil-free water-cooled chiller for a shopping center air conditioning system

Many researches have been conducted on cooling equipment to reduce its energy consumption, maintenance and operation cost. Oil-free chiller uses a magnetic bearing compressor to avoid friction loss from the bearing’s contact surface. In comparison to a conventional compressor, the magnetic bearing of the motor, with the help of variable speed drive (VSD), runs more efficiently at partial loads. This paper presents the application of oil-free compressors in a chiller plant. The chiller plant also includes a chilled water system. In designing an energy-efficient air conditioning system it is important to choose proper chilled water and cooling water system. The evaporator is used to absorb the heat from the conditioned room while the condenser rejects the heat from the chiller to the environment through circulating cooling water. This research also aims to analyze the chiller plant for the air conditioning system operates in one of the shopping malls in Indonesia and how it affects the performance of the magnetic bearing chiller. The research also presents an analysis of the efficiency of the chiller plant, the coefficient of performance of each compressor, and their compliance with both national and international standards.

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%).

Energy, exergy, economic, and environmental (4E) analyses and optimization of a CCHP system with steam turbine

AbstractDue to finding solutions to reduce energy consumption and improve the electricity production efficiency in the power cycles, using the waste heat of power cycles in the combined generation systems can be a useful approach. Also, by using the wasted energy of the power generation cycles, the cooling and heating demands can be met. Therefore, this study presents energy, exergy, economic, and environmental evaluations of a new configuration of combined cooling, heating, and power (CCHP) or tri‐generation system with a steam turbine. This CCHP system includes a steam boiler, a steam turbine, a heat exchanger, a single‐effect absorption chiller, and pumps. Some important performance parameters such as electrical efficiency, combined electrical and cooling efficiency, combined electrical and heating efficiency, and tri‐generation efficiency, as well as exergy efficiency, are considered. Also, various output and environmental performance parameters such as percentage of operational cost reduction, percentage of fuel consumption reduction, percentage of pollutant emission reduction, and economic and technical issues based on different inlet temperatures and pressures of the steam turbine are investigated. In addition, the performance of the absorption chiller at different operating conditions has been investigated. This study shows that the usage of the CCHP system leads to reduction of 24.91% in carbon dioxide emission, 15.83% in fuel consumption, and 35.34% in operating costs compared with conventional systems. Also, the results show that there is a good improvement in the overall performance of the system with the tri‐generation efficiency of 82.46%.

A GA-LSSVM approach for predicting and controlling in screw chiller

Performance of varying speed screw chiller is affected by many uncertainties. High precision prediction of its characteristics can guide the chiller to reach a better performance. This study presents an artificial intelligence model named least square support vector machine (LSSVM) with genetic algorithm (GA). Five parameters are predicted with the model, including COP, discharge pressure, suction temperature, suction pressure and cooling capacity. By comparing the simulation results with the test results, this model shows a high precision ability to predict the performance of the on-site chiller. Additionally, a newly control strategy is introduced to help the chiller with optimizing performance. Cooling capacity and superheat degree are separately used as input to train the model to control openness of EXV. The prediction of this control strategy process shows enough ability to predict openness of EXV. The results can be used to guide the chiller to reach better performances by adjusting the corresponding parameters.