Hybrid Air Conditioning System Research Articles

Exergy analysis of hybrid air-conditioning systems with different evaporative-cooling condensers under hot-humid climates

Evaporative cooling (EC) technology can effectively improve the energy efficiency of the mechanical vapor compression (MVC) system by enhancing the heat exchange capacity of its condenser. However, the current evaporative-cooling condenser system is usually only equipped with a single-stage evaporative cooler as the precooling unit, and these designs are mainly suitable for hot-dry conditions. In this study, three hybrid air-conditioning systems with different two-stage evaporative-cooling condenser configurations were proposed, one is single-condenser type and the other two are dual-condenser type, which are used to improve the exergy performance and adaptability of the evaporative condenser system under hot-humid climates. Then, the all systems were modeled via the distributed parametric method and analyzed comparatively based on the exergy method. A suitable exergy reference temperature at air saturation was discussed. Finally, the effect of four key parameters (ambient temperature and relative humidity, outdoor airflow rate and room heat load) was studied. The results showed that under the high temperature, relative humidity or room heat load conditions, the hybrid systems have a low exergy efficiency ratio (EXR) and high exergy efficiency (ηx,OEC). Among them, the newly countercurrent dual-condenser configuration (MVC-TSEC(C)) exhibits the best exergy performance under most hot-humid conditions. Compared to the conventional MVC system, the EXR and ηx,OEC of MVC-TSEC(C) increased by at most 35.0 % and 78.2 %, respectively. Moreover, its components like compressor, condenser and expansion valve have the maximum reduction rates of exergy destruction of 43.5 %, 17.2 % and 55.3 %, respectively.

Energy saving of vacuum-based membrane dehumidification with indirect evaporative cooling in a low sensible-heat-ratio building

In hot and humid climates, dehumidification generally consumes more energy than cooling, and conventional mechanical vapor compression system is not efficient for dehumidification. Vacuum-based membrane dehumidification system have been developed as a more environmentally friendly alternative for dehumidification due to non-refrigerant system and isothermal dehumidification process. In this study, a novel hybrid air conditioning system that combines vacuum-based membrane dehumidification with an indirect evaporative cooler for pre-cooling is proposed to achieve efficient air conditioning in building with low sensible heat ratio. The energy performance of the proposed system is investigated by detailed thermodynamic simulations and compared with conventional variable air volume (VAV) system and indirect evaporative pre-coolers combined VAV system. The simulation results show that when the average sensible heat ratio of the space is 0.73 and the COP of the vacuum-based membrane dehumidifier is 1.0, the proposed system can reduce energy consumption by 16.1 % compared to conventional VAV system and by 6.4 % compared to indirect evaporative pre-cooler combined VAV system during the cooling season. The energy performance of the proposed system is significantly affected by the sensible heat ratio of the building and the energy efficiency of the vacuum-based membrane dehumidifier. When the COP of the vacuum-based membrane dehumidifier reaches 2.0, the proposed system can achieve an energy savings of 48.2 % compared to conventional VAV system.

Hybrid air conditioning and seawater desalination system assisted by solar energy: thermoeconomic investigation and optimization

The demand for freshwater has become progressively critical due to population growth and water scarcity. The current work investigates the energetic performance of a hybrid absorption refrigeration and desalination system. A parametric study for the system operating conditions has been performed to get the optimal conditions. Also, economic analysis and a multi-objective optimization method are used with the aim of maximizing the energy utilization factor of the system and minimizing total costs. The specific cost of desalinated water from the multi-objective optimization is calculated as (1.728 Cent/L) with the greatest energy utilization factor of (2.214). It turns out that, the system performs optimum at condensation and generation temperatures of 30 and 65 °C respectively, with resultant COP and GOR of 0.84 and 1.37. Using the optimum conditions, TRNSYS has been used to investigate the transient performance of the system for Marsa–Matrouh City in Egypt. The cooling and freshwater demands are 10 kW and 24 L/h. It was concluded that the input energy required to run the hybrid system decreased by about 65% less than that required for separate systems. With the assistance of solar energy, it became clear that the energy required was 60% less than the hybrid system as well.

Implementation of a solar-thermal hybrid air conditioning system in Muscat for energy conservation

Implementation of a solar-thermal hybrid air conditioning system in Muscat for energy conservation

Experimental study on wavy fin desiccant coated heat exchanger for hybrid air conditioning systems

The desiccant-coated heat exchanger (DCHE) is an energy-efficient alternative dehumidification equipment for humidity control in air conditioning. It exhibits a higher dehumidification performance than other solid desiccant systems and can simultaneously handle both latent and sensible loads. Taking the clue of research outcomes from the alternative heat exchangers to enhance the performance, a wavy fin DCHE is designed, fabricated and tested. Objectives of the study are to (i) analyse the dynamic performance of DCHE, (ii) compare the heat and mass transfer characteristics of plain and wavy fin-type DCHEs, and (iii) examine the influence of different operating parameters on the performance. The experimental investigation shows that the dehumidification capacity and thermal coefficient of performance of the proposed wavy fin DCHE are 0.34 g/s and 1.041, respectively, which are 75% and 60% higher than the conventional plain fin type. In addition, the developed DCHE has an average cooling capacity of 0.85 kW, which is 42% higher. Besides, the total quantity of moisture adsorbed also increased by 35%. Furthermore, the sensitivity analysis of the parametric study identified air velocity, cold water temperature, and inlet humidity ratio as the most influential operating parameters on the performance of wavy fin DCHE.

Experimental & CFD analysis of Hybrid Air-Conditioning system using nanofluid via Heat & Mass Transfer Characteristics

Experimental & CFD analysis of Hybrid Air-Conditioning system using nanofluid via Heat & Mass Transfer Characteristics

Comparative study of three hybrid air-conditioning systems based on multiple evaporative coolers and run-around reheating coils

Existing evaporative-cooling hybrid air conditioning systems cannot fully utilize the synergistic energy-saving potential of multiple evaporative-cooling technologies. Moreover, they cannot meet simultaneously the energy-saving requirements of standard mechanical vapor compression (MVC) systems in the terms of fresh air pre-treatment, condenser pre-cooling and supply air reheating. Therefore, in this paper, integrating MVC system with the indirect evaporative cooler, outdoor-air evaporative-cooling unit, and run-around reheating coils, three alternative hybrid systems were proposed to meet the aforementioned three requirements. The three hybrid systems have different outdoor-air unit configurations (single condenser with direct evaporative cooler, dual condenser with direct evaporative cooler, and dual condenser with two-stage evaporative-cooling configuration) and reheat sources (exhaust, outdoor, and mixed air of fresh and return air). Then, the parameter effects and application potentials of the three hybrid systems were analyzed comparatively based on detailed numerical models. The results showed that the third proposed hybrid system (HAC-R3) exhibits the best energy-saving advantages in almost the range of ambient temperature, relative humidity and fresh airflow rate studied. The first proposed hybrid system (HAC-R1) has the simplest outdoor-air side configuration, which is also a good choice in medium–low humidity conditions. In hot-humid summer in southern China, HAC-R3 has the highest average energy-saving rate and seasonal COP of 16.0 % and 7.0 respectively. In addition, HAC-R1 has the lowest static equipment payback period of 3.3 years, slightly lower than that of HAC-R3 (3.4 years).

Effect of system configuration on the performance of a hybrid air conditioning system based on R-1234yf

The study presents theoretical results on a hybrid air conditioning system in which the sensible and latent loads are separately managed. The problem studied is significant in view of the growing demand for air conditioning systems globally, and also due to the adverse impact of these systems on global warming. In order to reduce the environmental impact of the air conditioning systems, this study proposes a hybrid system comprised of a vapour compression heat pump and a desiccant wheel. Due to restrictions on high global warming potential (GWP) refrigerants, R-1234yf, a low GWP refrigerant is considered as the working fluid for the heat pump. An enthalpy wheel is included to reduce the ventilation load on the system. The proposed hybrid system’s performance is evaluated using the first and second laws of thermodynamics and psychrometric principles. Results are compared with that of a conventional air conditioning system. Based on the calculated values of component and process wise irreversibility, further modifications to the hybrid system are proposed. These modifications consist of addition of a liquid-to-suction heat exchanger and use of a split condenser. Results show that depending upon the latent load on the conditioned space, the compressor power input can be reduced by as much as 47% using the proposed hybrid system. Compared to the conventional system, the modified hybrid system shows excellent performance under both high as well as low latent loads, whereas the simple hybrid system performs very well in applications involving high latent loads. The work presented is novel as it considers both first and second laws of thermodynamics to arrive at an optimum hybrid system configuration using an environment friendly refrigerant. It is expected that the study will be useful in the development of energy efficient and environment friendly air conditioning systems that operate equally well under low and high latent loads.

Energy and Exergy Analysis of an Automobile Hybrid Ejector Refrigeration System Utilizing Its Exhaust Waste Heat

Abstract A major current focus of refrigeration and air-conditioning research is energy usage and environmental impact (e.g., the influence of refrigerants and air-conditioning systems on ozone layer depletion and global warming). The ejector-based refrigeration system is a technology that, it is hoped, can save power while using environment-friendly refrigerants to reduce any adverse effects on nature. The reduction of compressor dependency is the first and essential aim of this study; the second is to demonstrate the replacement of R134a with the new refrigerant R1234yf in motor vehicle air-conditioning systems, establishing the benefits of employing R1234yf in conjunction with a hybrid air-conditioning system. In such a system, the engine's exhaust gases are used to operate the ejector. A numerical model has been developed which estimates the ejector entrainment ratio at a specified spindle and primary nozzle exit position. A theoretical model using energy and exergy analysis illustrates the impact of hybrid systems on performance under different operating conditions (i.e., engine exhaust, ambient air, and evaporator temperatures). At a specified exhaust temperature, a detailed comparison has been conducted between a current air-conditioning system with R134a and the hybrid system with R1234yf. It was found that the R1234yf hybrid system reduced compressor energy consumption by 44.43% and operating exhaust heat levels by 12.79%. The coefficient of performance increased by 41.42%, while the exergetic efficiency reduced from 37.14% to 13.85%. Cooling capacity dropped by 12.73%. The hybrid air-conditioning system based on R1234yf demonstrated tremendous potential for improving vehicle air-conditioning system efficiency.

A Comparison of a Transparent Thermal Insulation System Filled with Refrigerants and a Pig-Fat Based PCM

In this research sustainable refrigerants are tested as filler gases in Transparent Thermal Insulation (TTI) for the first time. These are compared with pig fat, a readily available material with good thermal inertia that is proposed as an organic phase change material (PCM). The aim of this paper is to compare the thermal behaviour of a Hybrid Air Conditioning System (HACS) with TTI filled with R134a, R1233zd and a pig-fat-based PCM. Numerical simulations using the OPAQUE 3 program and two online platforms are used to evaluate the possible application of TTI and PCM as passive systems. Additionally, three TTI models are used to simulate the heat transfer processes of TTI, PCM and R134a. The velocity of the flow in the air gap is also analysed numerically in both laminar and turbulent states. For the assessment, infrared thermographic imagery is used to measure the temperatures in the HACS, giving values of 46.17 °C by day and 38.05 °C at night. The results show that the heat loss and heat gain in the combination TTI filled with refrigerants and pig-fat-based PCM are between 2.22 and 1.51 W/m2. In addition, the HACS was able to keep a small box warm during the night. The flow in the air gap of the HACS can be controlled by installing Ni-Ti wire actuators with a cooling temperature of 23 °C and a heating temperature of 70 °C. The Ni-Ti wire actuators can open and close the dampers at 23 °C and 51 °C, respectively. By installing a 5-watt solar-power fan, the velocity of the flow in the air gap in the HACS can be increased, thus improving the efficiency of the system. In all the experiments, the pig fat proved to be suitable for use in building applications as a non-flammable organic material.

НЕСТАНДАРТНЫЕ ПОДХОДЫ К ОРГАНИЗАЦИИ КЛИМАТИЧЕСКИХ СИСТЕМ В ЦЕНТРАХ ОБРАБОТКИ ДАННЫХ

The article is devoted to comparison of air conditioning systems in a data processing center, taking into account peculiarities of its location, in Perm Krai, RF. It is established that the use of more expensive, but modern, hybrid air conditioning system is economically feasible in this region. Purpose of work. The aim of the work is to assess the feasibility and effectiveness of different air cooling systems from an economic point of view, under the conditions of the location of the facility in the Perm region. Materials and methods. Two cooling systems are compared. The first cooling system is based on a direct supply of cold air. This system has restrictions on the temperature of application, it can only be used at ambient temperatures lower than the temperature of the cooled room, about 20 °С. Current costs in the form of consumed electricity to cool the room in this case will be less. The second, classic air conditioning system. In which cooling occurs due to boiling of freon in evaporator and the following compression by compressor and transitions to liquid phase in condenser. There are different variations of this system for almost any climate zone. Running costs (electricity) caused by operation of this system are higher. But the initial costs are less, since this system costs less. The task is to determine whether there will be a positive economic effect from the introduction of a system with direct cold air supply. The research is done with the help of theoretical methods. For this purpose, data on the air temperature in the city of Perm for 2021 by day and hour were taken. The results of the study. Determined how many days and hours, can work one or the other system. Classical air conditioning or a hybrid system, with the possibility of direct supply of cooled air. Calculated the cost of electricity when working in the first and second modes. Determined the number of necessary climate control equipment, taking into account its redundancy under the scheme N+1. Approximate costs for the implementation of the systems have been determined. Discussion and conclusion. It was found that the cost of introducing a more expensive hybrid system with the support of direct chilled air, compared with the classical air conditioning system will pay off in a few years. Significant advantages of such systems are also identified. Longer service life due to less use of the compressor in the refrigeration system.

A Novel H2O/LiBr Absorption Heat Pump with Condensation Heat Recovery for Combined Heating and Cooling Production: Energy Analysis for Different Applications

The aim of this study is to analyze the feasibility of the single-effect H2O/LiBr absorption heat pump cycle to produce combined heating and cooling. To achieve this, first, the main changes that the absorption cycle requires are described in comparison with the conventional single-effect absorption chiller. Then, the cycle’s operational limits in terms of temperature lift and LiBr crystallization are evaluated. In this sense, driving heat temperatures required for these applications range from 85 °C to 120 °C. The energy and exergy performance (in terms of cooling and heating capacities, cooling and heating coefficient of performance, and exergy coefficient of performance) of the cycle is theoretically studied for five different types of applications that require simultaneous heating and cooling: building air conditioning, a 4th generation district heating and cooling network, a sports center with an indoor swimming pool, a hybrid air conditioning system with an absorption heat pump and a desiccant evaporative cooling system, and simultaneous cooling and water purification application for coastal areas. The system performance in terms of the cooling coefficient of performance varies in the range of 0.812–0.842, in terms of heating coefficient of performance from 0.58 to 1.842, and in terms of exergy coefficient of performance from 0.451 to 0.667. The application with the highest exergy coefficient of performance is the 4th generation district heating and cooling network.

Energy and Comfort Evaluation of Fresh Air-Based Hybrid Cooling System in Hot and Humid Climates

Maintaining mechanical ventilation has been identified as a potential strategy for reducing the risk of virus infections. However, in hot and humid climatic conditions, delivering fresh air to a building comes at an energy cost and could impact occupant comfort due to the persistent need for simultaneous cooling and dehumidification. In this paper, the performance of a novel hybrid air conditioning system that handles fresh air is studied. In this system, dehumidification is accomplished by a solid desiccant dehumidifier coupled with a cooling coil integrated with the cooling tower of an existing chiller system. Using the data available from an operational desiccant cooling system, a system-level model has been developed and validated to study the potential application of the system in hot and humid climates. The study found that such a system is effective in delivering sensible cooling in all types of climates; thanks to the two-stage cooling in cooling coil and chilled water coils, respectively. However, the system is effective in delivering thermal comfort in regions where the climate has a relatively moderate ambient humidity. For the tropical cities of Darwin, Kuala Lumpur and Bangkok, the system can provide comfortable temperatures, but faces challenges in keeping the humidity within the comfort zone. The system electrical coefficient of performance (COP) is higher than that of refrigerative systems. This system also has the benefit over the refrigerative system of the supply air, which is entirely fresh ambient air and is expected to improve the indoor environmental quality largely.

Performance Analysis of an Ejector Based Hybrid Air-Conditioning System Integrated with Solar Thermal Collector

Performance Analysis of an Ejector Based Hybrid Air-Conditioning System Integrated with Solar Thermal Collector

Energy Performance of a Novel Hybrid Air Conditioning System Built on Gravity-Assisted Heat Pipe-Based Indirect Evaporative Cooler

A hybrid air conditioning system, which is composed of a novel gravity-assisted heat pipe (GAHP)-based indirect evaporative cooler (IEC) and direct expansion (DX) cooling coil, is proposed and investigated here. After developing a mathematical model to describe the performance of the GAHP-based IEC, the hybrid system is evaluated during the cooling design day for providing thermal comfort for an office building in Poland. The results are obtained and compared with the combination of a rotary heat exchanger (RHE) and DX cooling coil as the conventional hybrid system. The comparison is performed by analyzing cooling capacity, electricity consumption, and coefficient of performance profiles, which describe the technical, energy, and efficiency aspects, respectively. The results show that the GAHP-based IEC hybrid system is able to enhance the energy performance significantly compared to the conventional one. The proposed hybrid HVAC system improves COP by 39.2% and reduces electricity consumption by 45.0%, according to the design-day of 24 August and the outdoor temperature of 30 °C. As a result, the total operating cost for the assumed cooling season is reduced by 51.7%.

Design and development of a novel multichannel data acquisition system using labview for an automobile air conditioning application

To sustain in the ever-changing environment and to combat the atmospheric effect, development of a highly efficient and an environment friendly air conditioning system which can run in parallel or as an alternative to an existing vapor compression system is the need of the hour and such novel hybrid air conditioning system are under development today. For the parameters attribution mapping of such novel hybrid air conditioning system, todays commercially available data acquisition systems (DAS) need to be customized to the requirements of addition of sensor nodes and their integration with triggering mechanism for actuation of devices for its programmed operation. Therefore, this paper describes the design and development of novel multichannel data acquisition system (NMDAS) for automobile air conditioning application. The details of the hardware design, software design, error analysis and testing of the NMDAS are presented. The proposed NMDAS uses PLC module DVP16SP configured with analog reader DVP 04TC for temperature measurement at 32 nodes and DVP04AD for pressure or humidity measurements at 8 nodes. The triggering circuit for activation of the relay is enabled using NI LabVIEW user interface and PLC data. The output of the NMDAS is integrated with processor by RS 232 port for data storage and processing. The error analysis of temperature, pressure and humidity measurements are done by comparing with reference calibration standards. The average thermal stability of the temperature sensors over the operating range of -5˚C to 150˚C is 0.0015°C. The average accuracy of pressure transmitters for operating range of pressure 0 to 40bar is estimated 98.219%. The minimum error in the output current is 0.375% and maximum error is 7.125% over relative humidity span of 0%RH to 100% RH respectively. The proposed NMDAS is used for testing of the novel hybrid air conditioning system of automobile during development stage and is found expedient.

Direct evaporative cooling from wetted surfaces: Challenges for a clean air conditioning solution

AbstractEvaporative cooling has a major role to play in fighting climate change and in achieving a low‐carbon economy. As it helps to reduce energy demand for air conditioning, it is gaining attention in terms of improving energy efficiency in buildings. Evaporative cooling from wetted media can enhance water–air contact, thereby improving heat and mass transfer further and avoiding aerosols. Wetted media are commonly called evaporative cooling pads and are widely used in greenhouses, intensive livestock farming, and industrial facilities. However, a deep understanding of evaporative cooling pad performance can enhance their application to indoor occupied spaces such as residential or commercial cooling, or in hybrid air conditioning systems. Most studies analyze pad performance mainly in terms of pressure drop and saturation effectiveness. However, some studies propose alternative cooling efficiency parameters and others provide insights into key aspects such as power requirements and the coefficient of performance, water consumption, risk of water entrainment, material decay, and air quality, as well as the effect of water temperature and salinity, solar radiation, or wind speed. Existing results on these less studied performance issues are reviewed, and we identify the gaps in the literature in addition to highlighting the main challenges encountered, in an effort to guide future researchers in the field and enhance the application of direct evaporative cooling.This article is categorized under: Energy Efficiency > Systems and Infrastructure Energy Systems Analysis > Systems and Infrastructure

A Mathematical Model for Predicting the Performance of the Solar Energy assisted Hybrid Air Conditioning System (SEAHACS) with One-Rotor Six-Stage Rotary Desiccant Cooling System. (Dept. M)

A mathematical model for predicting the performance of solar energy assisted hybrid air conditioning system (SEAHACS) is presented. The honeycombed silica gel desiccant wheel was used in this study, one-rotor six-stage rotary desiccant cooling system, in which two-stage dehumidification process, two –stage pre-cooling process and two-stage regeneration process are realized by only one wheel. Three air streams are involved in the present system. The mathematical model has been validated with the experimental data. As the key operating and design parameters, the range of regeneration air inlet temperature from 65-140 oC, area ratio of process air to generation air change from 1-3.57, regeneration air inlet velocity from 1.5-5.5 m/s have been examined for a range of rotation speed from 6-20 rev/h. the optimization of this parameters is conducted based on the moisture removal capacity D, relative moisture removal capacity, dehumidification coefficient of performance and thermal coefficient of performance. At last, the influences of these main parameters on optimal rotation speed are discussed

Climatic Effect on the Exergetic Performance of Conventional to Hybrid Evaporative Coolers With Varying Dead-State Temperatures in India

Abstract A comprehensive exergy, exergo-economic, and sustainability assessment of seven conventional to hybrid air-conditioning systems comprising direct and indirect evaporative coolers with direct expansion system and their several combinations integrated into an eight-story domestic building for five different cities corresponding to arid, semi-arid, humid subtropical, tropical wet and dry, and tropical wet climatic zones across India are investigated based on simulation output from energyplus. The exergetic performances are reported for varying dead state temperatures ranging from 5 °C to 40 °C, while the saturated humidity ratio and pressure at system outlet are two other dead state properties. The results reveal that the specific exergy of moist air and exergetic efficiency decreases with increasing dead state temperature and becomes least at a dead state temperature near American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) comfort temperature of 23 °C. In arid, semi-arid, and humid subtropical climates, the three-stage evaporative cooling system exhibits the lowest exergy destruction of 100 J/kg1 and the highest exergy efficiency of 90% at a dead state temperature of 40 °C. The two-stage direct evaporative-direct expansion cooling system exhibits superior exergy efficiency in tropical wet and dry and tropical wet zones. Furthermore, the Grassmann diagram based on the climate of Hyderabad indicates that the three-stage cooling system is energetically and exergetically optimum with exergy destruction of 28.86%.

Thermal Analysis of a Hybrid Air Conditioning System with Geothermal Energy

Hybrid air conditioning systems can allow significant energy saving and emissions reductions with respect to conventional air-conditioning systems. Thermal analysis of a desiccant wheel, a heat exchanger, a ground source circulation system, and a solar collector for a hybrid air conditioning system is performed in this study. The effects of these parameters have been studied: Inlet air temperature, Inlet air humidity ratio, wheel speed, regeneration temperature, regeneration mass flowrate, heat exchanger effectiveness, ground source circulation effectiveness, and solar radiation on the behavior of the outlet air temperature and the outlet air humidity ratio from the desiccant wheel, the area of solar air collector, the solar collector efficiency, the cooling coil load, and the coefficient of performance. The hybrid system is more efficient than the vapor compression system. The hybrid system significantly decreases the cooling coil load, the cooling coil load of the hybrid system is approximately 48 % lower than the vapor compression system.