Central Air Conditioning Research Articles

Hydro-thermal performance of fabric air duct (FAD): Experimental and CFD simulation assessments

Nowadays, fabric air duct (FAD) systems are the most cost-effective, and aesthetically appealing way to evenly distribute heated or cooled air to large open interior spaces. There is a need to develop a proper procedure to calculate the friction factor and Nusselt number of the air flow inside these types of fabric air ducts because of their great impact on the design of central air conditioning systems. Therefore, the main objective of this research is to carry out laboratory and numerical experiments to establish a certain technique of calculation of the friction factor and Nusselt number inside fabric air ducts and to develop validated CFD air distribution model capable of predicting the air flow pattern and heat transfer parameters inside different configurations of fabric air ducts. By controlling these parameters, FAD systems can be balanced and designed. For this purpose, three fabric air ducts made of porous and non-porous polyester with different outlet ports distribution and have a diameter of 60 cm and a length of 3 m have been experimentally assessed under variation of inlet Reynold numbers ranging from 9.9x103 to 1.47x105. The results showed that the maximum error between laboratory and numerical values for the mean friction factor and mean Nusselt number was 4.9% and 4.8% respectively, which was within an acceptable range according to previous studies. Based on the results analysis empirical correlations were obtained for their importance in achieving a well-balanced FAD system. One of the most significant equations that were obtained in this research was the relationship between the Nusselt number and Reynold number. For porous duct was Nu=127.69Re0.148, non-porous duct 4,8 o'clock air slots was Nu=4.51Re0.49 and non-porous duct 3,9 o'clock air slots was Nu=40.82Re0.139. The relationship between friction factor with Reynold number for porous duct was f=0.251e−0.0000067Re, non-porous duct 4,8 o'clock air slots was f=0.397e−0.000017Re and non-porous duct 3,9 o'clock air slots was f=0.529e−0.000025Re. All correlations are valid only within the range of conditions considered in current experimental study.

RETRACTED: Robust bidding strategy of interconnected multi-carrier systems in the electricity markets under the uncertainty in electricity load

This paper presents a robust bi-level model for optimal bidding of interconnected multi-carrier systems (MCSs) in the wholesale electricity markets under the uncertainty in electricity load. The proposed model implements a robust optimization method (ROM) to model the risk-based bidding of interconnected MCSs under the uncertainty in load in the upper-level problem while including the energy and reserve markets in the lower-level problem. The studied MSCs include combined heat and power (CHP) units, boilers, central air conditioning (CAC) systems, and battery storage units to provide local energy and make the MCSs’ operator capable of participating in the reserve market to gain profit. ROM models the electricity demand and provides different bidding strategies (i.e., risk-seeking, risk-neutral, and risk-averse) for the participation of MCSs’ operator in the energy and reserve markets. The studied bi-level model is converted to a single-level mixed-integer linear programming problem using the Karush–Kuhn–Tucker conditions and strong duality and then solved using the CPLEX solver of the General Algebraic Modeling System. Numerical experiments reveal that the interconnection of MSCs, along with the integration of storage units, enables the MSCs’ operator to control the uncertainty in the electricity load and increase the energy efficiency in order to optimally bid in the day-ahead energy and reserve markets. Results show that by enabling the MCSs to locally trade energy, the total operation cost of MCSs in the risk-seeking, risk-neutral, and risk-averse modes decreases by 5.65%, 4.28%, and 3.49%. Moreover, with the integration of battery storage systems into the interconnected operation of MCSs, the total operation cost of systems in the risk-seeking, risk-neutral, and risk-averse modes decreases by 7.65%, 6.99%, and 6.40%, respectively.

Modeling of the Operational Parameters on the Performance of an Air Conditioning System

Heat and moisture are removed from occupied spaces by air conditioning systems. Air conditioners regulate moisture and temperature, and improve air quality. Human efficiency is dramatically boosted and worker's efficiency is affected by their work environment. Human being is more comfortable and productive with air conditioning. After a few years of excellent operation, the system began to fail, resulting in numerous resident complaints. The goal of this study is to establish operational characteristic models for an air conditioning system's performance in order to fulfill future client requirements. The inlet and output temperatures as a function of local time were measured for the LSBLG 1200/MCF model central water chiller air conditioning system. The COP and EER curves were examined. MiniTAB 16.0 was used to establish the characteristic curves and models, according to the findings. The regression models are statistically significant at 97.7 percent and 91.1 percent for p-value less than 0.05 and R2 , respectively. The COP and EER values were calculated, and it was determined that the best cooling occurred between 1 and 3 p.m. The chiller and cooling tower achieve maximum coefficients of performance (COP) of 52 and 20, respectively. The chiller and cooling tower have EER ratings of 177 and 68, respectively. Regression analysis is used to develop models that characterize the statistical relationship between operational parameters such as input and outlet temperatures as a function of local time and response variables such as COP and EER. The performance of the system can be monitored using existing models. Keywords: Modeling, operational parameters, performance, and air conditioning system.

Control strategy for dynamic operation of multiple chillers under random load constraints

Under the influence of building load stochasticity and thermal inertia of central air conditioning system, the lag of control strategy makes it difficult for the cooling source system to meet the cooling demand of users in real time, which affects the operational energy efficiency ratio of the cooling source system. In this regard, this paper proposes a chiller dynamic optimization method based on Markov chain model predictive control algorithm, which studies the optimization of parallel operation characteristics of multiple chillers on the basis of correcting the occurrence of small probability events and avoiding frequent chiller starts and stops, reveals the prediction law of hourly load distribution of the future air conditioning system, explores the balance point between the prediction time of building load and the calculation time of chiller control strategy, provides a theoretical basis and reference for determining the time limit of the optimal calculation and the output of the optimal control strategy. The study provides a theoretical basis and reference for determining the time limit of the optimal calculation and the output of the optimal control strategy. It is found that the optimal control strategy not only has good optimization effect, but also the confidence is significantly increased by 56.7%.

Deep learning GAN-based data generation and fault diagnosis in the data center HVAC system

The automated fault diagnosis and smart management of heating, ventilation and air conditioning (HVAC) system is essential to the reliability of data centers. The machine learning is an efficient way to develop the smart management tools for HVAC system using historical data. In real data centers, however, the quantity of fault-free data is much more than that of fault data. As a result, the imbalanced training data limits the diagnosis capacity of machine learning models. The deep learning-based generative adversarial network is proposed to integrate with an incremental learning SVM model to diagnose the commonly occurred faults of data center air conditioning system. The adversarial learning between generator and discriminator generates the data of minority class for training purpose in HVAC system. The 8 sensitive features are selected as the inputs through three-step optimal selection strategy: manual screening, correlation feature selection and redundancy feature removing. The incremental learning strategy is proposed to update the FDD model regularly. The refrigerant leakage faults with intensities of 10%, 20%, 30% and 40% are tested and validated under various operational conditions. The experimental results show that the incremental learning SVM integrated with deep learning GAN reaches the acceptable diagnosis accuracies.

EFFECTS OF AIR CONDITIONING SYSTEM ON HEALTH SYMPTOMS AND QUALITY OF LIFE IN RESIDENTS OF HOUSES

Indoor temperature environment and air quality affect the health of residents of houses, and thus efforts are underway to improve the insulation of houses. In this study, we conducted a questionnaire survey to investigate changes in health symptoms and quality of life after moving into a house with a central air conditioner, floor heating, and room air conditioners. The results revealed that residents of houses with central air conditioning tended to have a higher rate of improvement in health symptoms and quality of life compared with other types of air conditioning.

Using a heat pipe as a waste air heat exchanger in a central air conditioner.

The purpose of this work is to analyze the literature on heat pipes to make a decision on the feasibility of using this type of heat exchanger in air conditioning systems. The article describes the principle of operation and design of the heat pipe, provides various ways to return condensate, and also describes in detail its thermodynamic cycle. Considerable attention is paid to various wick structures and working fluids. The following are the restrictions on heat transfer of heat pipes that affect the performance of the heat exchanger. Design recommendations found in the scientific literature and on the websites of manufacturing companies are also described. The diagrams of the heat pipe designs used in central air conditioners and in AC system are given. An example of an installation using heat pipes as a waste air heat exchanger in a central air conditioner is shown. Further, the efficiency and thermal power of various methods of heat recovery are compared with the same initial parameters of the flow rate and temperatures of outdoor, exhaust air. In conclusion, the conclusion is made about the advantages of using heat pipes in AC system for heat recovery. The reason for the rare use of this heat exchanger is also explained. The result of comparing different methods of heat recovery and the answer to the question about the prospects of using a heat pipe in the AC system is given. Recommendations are given on the direction of further research in this topic.

Entropy Analysis of Energy Losses in Heat-Exchanger and Mixing Sections of a Central Air Conditioner

Entropy Analysis of Energy Losses in Heat-Exchanger and Mixing Sections of a Central Air Conditioner

A Fast and Accurate Loss Model of Converter-Fed Induction Motor in Central Air-Conditioning System

In the traditional optimization model of central air-conditioner, the loss model of converter-fed motor is very rough, resulting in a large amount of energy waste. In this paper, a new energy loss model of central air-conditioning system from power to client is proposed. In the establishment of the loss model, the characteristics of pump load and variable frequency speed regulation are fully considered, and the electromagnetic variables which are difficult to be collected are replaced by the motor speed which can be directly calculated, so that the motor loss model can be introduced into the optimization model of the central air-conditioning system. A 5.5 kW converter-fed induction motor is tested under different speeds and loads, and the two-dimensional (2-D) loss data were obtained. Then, one-dimensional data were extracted from the measured 2-D data combined with the load characteristics of the pump, and compared with the calculated values of the proposed model in this article. The results show that the proposed loss model is of good accuracy and versatility. Because the proposed analytical model only needs the variable of motor speed to accurately estimate the losses, it can be easily applied to the optimization of central air-conditioning system.

The Comparison of P, PI and PID Strategy Performance as Temperature Controller in Active Iris Damper for Centralized Air Conditioning System

The topic of maintaining thermal comfort efficiency in the heating, ventilation and air conditioning (HVAC) sector has always been tricky due to numerous challenges. The study focused on the challenge of under-actuated zones in non – residential and commercial buildings. The active iris damper with the integration of thermal controller is proposed to control the indoor temperature. Besides, integration of PID control strategy will be a tempting control system in enhancing the thermal performance of the building. Again, the PID controller has proven good compatibility as a primary closed-loop mechanism to maintain a comfortable room temperature. The development of the control system is done through the Arduino platform with LabVIEW as the front panel and data logging platform. The Heuristic tuning method was employed to obtain optimal gains for P, PI and PID controllers. The performance of each controller was tested by observing their ability to maintain steadily at the desired temperature set point. These tests conveyed that the best controller for this application is the PID controller. It reached the desired temperature set point and maintained it even with a temperature disruption. This study indicates that an active iris damper can effectively maintain the thermal comfort performance of indoor environment with the implementation of PID strategy, thus remedying some of the problems faced by centralized air-conditioning systems.

An Advanced Fractional Order Method for Temperature Control

Temperature control in buildings has been a highly studied area of research and interest since it affects the comfort of occupants. Commonly, temperature systems like centralized air conditioning or heating systems work with a fixed set point locally set at the thermostat, but users turn on or turn off the system when they feel it is too hot or too cold. This configuration is clearly not optimal in terms of energy consumption or even thermal comfort for users. Model predictive control (MPC) has been widely used for temperature control systems. In MPC design, the objective function involves the selection of constant weighting factors. In this study, a fractional-order objective function is implemented, so the weighting factors are time-varying. Furthermore, we compared the performance and disturbance rejection of MPC and Fractional-order MPC (FOMPC) controllers. To this end, we have chosen a building model from an EnergyPlus repository. The weather data needed for the EnergyPlus calculations has been obtained as a licensed file from the ASHRAE Handbook. Furthermore, we acquired a mathematical model by employing the Matlab system identification toolbox with the data obtained from the building model simulation in EnergyPlus. Next, we designed several FOMPC controllers, including the classical MPC controllers. Subsequently, we ran co-simulations in Matlab for the FOMPC controllers and EnergyPlus for the building model. Finally, through numerical analysis of several performance indexes, the FOMPC controller showed its superiority against the classical MPC in both reference tracking and disturbance rejection scenarios.

Analysis of the Energy Efficiency of the Air Conditioning System Based on Absorption Refrigeration Machine with Connection of Heat Pump and Solar Collectors

This article proposes and analyzes a circuit solution for providing heat supply to the generator of an absorption refrigeration machine (AHM) in centralized air conditioning systems using a heat pump unit (HPU) and solar collectors (SOL). Previously, such schemes have already been considered in the scientific works of Russian and foreign authors. The aim of the work is to propose new circuit solutions aimed at improving such systems, as well as confirming higher energy efficiency. This goal is achieved by solving the following problems: additional supply of the circuit with a common storage tank, operation of the absorption refrigeration machine generator and the condenser of the heat pump unit based on a common heat exchanger. Such a solution for the air conditioning complex based on an absorption refrigeration unit has been proposed for the first time. The most important results are the possibility of obtaining high values of the coefficient of performance, the possibility of achieving a number of technological advantages, increasing reliability and efficiency, as well as reducing the metal consumption of an absorption-type plant operating from solar collectors and a heat pump plant compared to similar systems. The significance of the obtained results lies in the fact that the use of a common storage tank and a combined heat exchanger (AHM generator / HPU heater) provides a significant increase in the coefficient of performance, a decrease in the metal consumption (reduction in costs) of the main equipment.

An Energy-Saving Regulation Framework of Central Air Conditioning Based on Cloud–Edge–Device Architecture

As energy plays a fundamental role in our modern life and most of a building’s energy is used for air conditioning, understanding the sustainable regulation theory of central air conditioning remains a significant scientific issue. In view of three shortcomings of existing energy-saving regulation methods of central air conditioning: (1) few studies on low-latency, high-reliability, and safer energy-saving control operation modes, (2) lack of consideration for human comfort, and (3) insufficient analysis of the comprehensive impact of the human–machine–environment, this paper proposes an energy-saving control framework of central air conditioning based on cloud–edge–device architecture. The framework establishes a prediction model of human comfort based on recurrent neural network. An intelligent energy-saving control strategy is proposed to ensure indoor personnel’s thermal comfort, considering the human–machine–environment factors. This study provides a basis for better understanding the sustainable control theory of building central air conditioning. Finally, the experiment proves that the proposed method can effectively reduce the energy consumption of central air conditioning. Compared with traditional regulation approaches, the proposed real-time control strategy can save up to 91% of energy consumption, depending on the environment, and advance control strategies can save an average of 4%.

Flow distribution optimization of parallel pumps based on improved mayfly algorithm

An improved mayfly algorithm is proposed for the energy saving optimization of parallel chilled water pumps in central air conditioning system, with the minimum energy consumption of parallel pump units as the optimization objective and the speed ratio of each pump as the optimization variable for the solution. For the problem of uneven random initialization of mayflies, the variable definition method of Circle chaotic mapping is used to make the initial position of the population uniformly distributed in the solution space, and the mayfly fitness value and the optimal fitness value are incorporated into the calculation of the weight coefficient, which better balances the global exploration and local exploitation of the algorithm. For the problem that the algorithm is easy to fall into the local optimum at the later stage, a multi-subpopulation cooperative strategy is proposed to improve the global search ability of the algorithm. Finally, the performance of the improved mayfly algorithm is tested with two parallel pumping system cases, and the stability and time complexity of the algorithm are verified. The experiments show that the algorithm can get a better operation strategy in solving the parallel water pump energy saving optimization problem, and can achieve energy saving effect of 0.72% 8.68% compared with other optimization algorithms, and the convergence speed and stability of the algorithm have been significantly improved, which can be better applied to practical needs.

Transport of ice slurry in the pipelines of central air conditioning systems in mining plants

The paper presents the phenomena accompanying the processes of non-adiabatic transport of ice slurry with ice mass fraction values below 20% in the transport sections of the system, assuming the conditions of significant changes in hydrostatic pressure. The subject of the analysis presented herein was to indicate the influence of hydrostatic pressure values on melting and secondary recrystallisation phenomena in the case of medium expansion in a vertical shaft pipeline and a three-chamber PES distributor. The paper proposes a computational model to determine the mass fraction of ice in the downstream section of the supply system: upstream and downstream of the PES distributor. The presented calculation results indicate that a reduction in the mass fraction of ice in the range of 0.004% per 1 m of the pipeline could be observed in vertical shaft pipelines. Maximising the enthalpy flux of the slurry at the inlet to the secondary circuit and minimising the temperature of the return water to the chiller favours mixing rates in the PES three-chamber distributor below 7%, which increase as the mass fraction of ice decreases.

Air conditioning system analysis for two floors electronic industrial building size 40 X 25 X 10 meters at PT. CI. in Jakarta

<div><p>Air fresheners or AC (Air Conditioning) systems are increasingly becoming a necessity for urban communities and the industrial world in Jakarta. AC functions to cool industrial rooms, offices and homes. The PT CI Electronic Industry Building, has not yet installed an air conditioning system so that the production room is not comfortable for its employees. The purpose of installing air conditioning in the industrial building is to increase employee comfort and productivity. In installing an air conditioning (AC) system in the industrial building, design data and cooling load analysis are required. Therefore it is necessary to study the design of industrial air conditioners at PT CI by calculating the cooling load, calculating the required electrical power in order to determine the size and type of air conditioner needed. The research methodology starts from determining industrial building data, such as what tools and machines are in the room, the area of the room and the room wall materials, then analyzing the cooling load, determining the power of the cooling machine and determining the cooling system used. From the results of the cooling load analysis in the Electronics Industry building at PT CI, the total load on floors 1 and 2 was 709 kW, or 201,6 TR, including sensible load: 705.83 kW and Latin load: 3.03 kW. The refrigerant used by the AC R 134a engine. The compressor power is 356 HP. Medium large COP 2.8. The cooling system chosen is the central air conditioning system.</p></div>

Automatic temperature control system of supply air in the central air conditioner

The article is devoted to the development of the system mathematical model for automatic control of the supply air temperature in the summer season in the central air conditioner to ensure a safe and comfortable environment in industrial premises. Keywords automatic temperature control system, central air conditioner, transient response, control object, PID controller, control quality index

Justification for choosing a generalpurpose fan type in a central air conditioner for industrial premises

The article is devoted to the issue of choosing and justifying the type of fan in a central air conditioner for industrial premises in order to meet the specified air consumption requirements. In the course of the work done, recommendations on the selection and justification of the type of fan are proposed. Keywords direct-flow air conditioning system, central air conditioning, axial fans, radial fans, aerodynamic characteristics of fans

Influence of transformation coefficient of refrigerating machine on exergetic efficiency of air conditioning system of operating clean rooms

Exergetic method is a universal way of thermodynamic research of various processes of energy transformation in energy technological systems, to which air conditioning system for clean room belongs. Implementation of exergetic analysis for energy technological system makes it possible to determine the influence of various elements of its system on its work and because of this to increase the effectiveness of work of energy technological system in general. Performance of any air conditioning system depends on energy effectiveness of refrigeration machine, which serves it and consumes electricity to reduce the heat of supply air which enters the room. And it means that the main purpose of selection of certain refrigeration machine for air conditioning system is to reach the maximum cooling capacity with minimum energy consumption. Innovative mathematical research model of the implemented central straight flow air conditioning system for operating clean rooms was used in this article. The aim of the model is to make computer estimation of exergetic efficiency of existing air conditioning system depending on different factors which have influence on its work, in particular the coefficient of transformation (or energy efficiency rate, EER) of its refrigeration machine. The dependence of the exergetic output-input ratio of implemented air conditioning system for operating clean rooms on coefficient of transformation of its refrigeration machine by different parameters of outdoor and indoor air and the temperature difference between the indoor and supply air were presented. It is shown that the implemented air conditioning system should be preferably used with higher coefficient of transformation of its refrigeration machine and higher difference between temperatures of indoor and supply air by various temperatures of outdoor air that will give the opportunity to gain the highest exergetic output-input ratio, which means gaining the most cost effective option for the exploitation of implemented air conditioning system.

Ensuring microclimate parameters in the room using radiant ceiling panel cooling systems

The actual purpose of the study was to develop technical solutions for organizing of a panel-radiant cooling system using ceiling devices in a multifunctional building, as well as the calculated justification of its use in comparison with an alternative cooling system: a classic central air conditioning system and a "chiller - fan coil". The comparison was carried out according to the indicators of the microclimate comfort in the serviced room, taking into account the feasibility study. The evaluation method was used to determine the comfort factor of a person's thermal state, taking into account correction coefficients for the main hazards characteristic of multifunctional public buildings. The use of radiant ceiling panel cooling systems increases the comfort of people in the room due to the fact that there are no convective jets with low temperature and high air velocity. At the same time, the most favorable temperature allocation over the height of the room is maintained.