Field Of Air Conditioning Research Articles

Energy, exergy, and economic analysis of a novel solar-assisted ejector subcooling CO2 transcritical refrigeration systemt

To further enhance the performance of transcritical CO2 refrigeration cycle (base cycle), a solar-assisted ejector subcooling transcritical CO2 refrigeration cycle (SESRS) is proposed. The base cycle is subcooled utilizing a solar-assisted ejector refrigeration cycle. This research performed energy, exergy, and economic evaluations of SESRS utilizing the eco-friendly refrigerant R152a in the ejector cycle based on the established model. The thermodynamic analysis results demonstrate that SESRS outperform the base cycle. At typical working conditions, the COPm of the SESRS demonstrates a 22.96 % increase compared to that of the base cycle. Although the total cost of the SESRS is 7.98 %–17.9 % higher than that of the base cycle when subcooling degree is 5 °C, the enhancement of COPm is larger and is increased by approximately 18.34 %–26.22 %. The impact of subcooling degree and other parameters on system performance are also investigated. Overall, this study confirms the potential of the SESRS system for utilization in the refrigeration and air-conditioning fields. Considering both the system’s performance and economy, further optimized analysis should be done on key operational parameters, such as subcooling degree and discharge pressure.

Boosting mold aerosol reduction and dehumidification performance in liquid desiccant systems using airborne ultrasound: An experimental study

Indoor mold exposure in hot-humid regions poses considerable risks to public health and food security. Ensuring safe, durable, and energy-efficient air disinfection is crucial for the air-conditioning field. While liquid desiccant air-conditioning (LDAC) systems eliminate condensation-related mold proliferation, their capability to combat airborne mold spores is limited due to the spores' robust resistance. This paper explores a novel airborne ultrasound-assisted liquid desiccant air-conditioning (US-LDAC) system. Experiments were conducted using culture-based methods to compare the system's disinfection capacities against Aspergillus niger spores, a desiccant-resistant species, under ventilation, liquid desiccation dehumidification, and airborne ultrasound-assisted liquid desiccant dehumidification modes. Moreover, the viability and morphological changes of mold spores exposed to airborne ultrasound, with and without liquid desiccants, were analyzed to verify the disinfection effectiveness and extrapolate the improving mechanisms. The results show that irradiating low-intensity airborne ultrasound (∼127 W, harmless mechanical waves) into the dehumidifier significantly increased the disinfection efficiency by 50 % and the dehumidification rate by over 90 % when airflow passed through the dehumidifier (∼0.4 s). The enhanced disinfection is attributed to ultrasonic cavitation, which facilitates the rupture of the desiccant-captured spores through microstreaming-induced shear forces. Notably, the improvements were more pronounced in humid air and with dilute desiccant solutions, suggesting that efficiency can be maintained with lowered desiccant concentrations. The US-LDAC system was particularly adept at removing mold aerosols (2.1–3.3 μm) which are easily inhaled. These findings propose a promising avenue for retrofitting existing LDAC systems to effectively reduce airborne molds and enhance dehumidification, thereby protecting indoor air quality.

Air Conditioning

The working principles and the basic features of air conditioning systems are introduced in this paper. With the improvement of standard of living, air-conditioning has widely been applied. The increasing demand for comfort air-conditioning has brought within the need for greater numbers of practical, technical and sales personal who have should training in basics principles and applications of modern air-conditioning. The technical information presented in this work is intended to satisfy the immediate and fundamental concepts and relevant principles in the field of air-conditioning. The subject of air-conditioning has come to stay with the universities in the country. Keywords: Air-conditioning, Technology, Cooling system

Influence of specific characteristics of subjects and environmental conditions on comfort level during showering

In systems that do not store domestic hot water (DHW), temperature fluctuations occur in the hot water temperature at the outlet when the DHW load changes. If these temperature fluctuations arrive at the tapping point, they influence the users’ perception of comfort. Especially in the shower these temperature fluctuations can lead to a loss of comfort. Unlike in the field of air conditioning, there have been relatively few studies on the perception of comfort in the shower, and these used only males as test subjects. Therefore, we started a study with 120 persons with the aim to involve a representative variety of test subjects. In our test facility a temperature profile with varying rates of change was imprinted and the test subjects provided feedback on whether they noticed temperature changes or found them uncomfortable. In this study, results on the comfort perception of the participants in the shower are examined in relation to individual factors such as gender, age or Body-Mass-Index (BMI), and the outside temperature. We cannot determine a specific impact of these factors on the comfort perception of a group of test subjects. Neither was an influence on the desired temperatures, which ranged between 33 °C and 45 °C, detected.

CARACTERISTICILE DE TRANSFER DE CĂLDURA ALE UNUI VAPORIZATOR CARE ECHIPEAZA O CENTRALA DE TRATARE A AERULUI DESTINATA UNUI DEPOZIT DE SEMINȚE DE CEREALE

In this paper the evaporator from the air handling units (AHU) is being studied, this being connected to an air conditioning installation with mechanical compression of vapors, existing within the Thermodynamics department. In a previous analysis, the heat exchanger (HEX) was checked to see if it complied with the cooling capacity relative to the heat exchange surface by finding the specific criteria equations. A follow-up to the previous article is to calculate based on the thermodynamic cycle, what happens if the refrigerant is replaced with other new refrigerants in the field of air conditioning in order to improve the performance of the air conditioning system (ACS), finding the refrigerant with a low Global warming potential (GWP) and with an appropriate flammability class. The moisture content of seeds is one of the most important storage parameters affecting their quality. In order to obtain the desired effect, the temperature and humidity of the air must be maintained in the warehouse with an air treatment unit. In this study, it is desired to replace the refrigerant and preserve the refrigerating power from the evaporator, by changing the degree of sub-cooling from the condenser. Due to the fact that the temperature in the ambient environment changes substantially during a calendar year and the condenser of the air conditioning installation has the same configuration, thus the decrease in the ambient temperature will result in the appearance of the sub-cooling process and an increase in the performance of the installation.

Study on a direct-coupling thermoacoustic refrigerator using time-domain acoustic-electrical analogy method

Thermoacoustic refrigeration is a clean cooling technology with high reliability. In this study, a time-domain acoustic–electrical analogy (TDAEA) method is proposed and improved, then applied to explore the performance of a high-efficiency 2-stage looped direct-coupling heat-driven thermoacoustic refrigerator. The effectiveness of the method is verified by experiments. Transient evolutions of oscillating pressure and volume flow rate are first presented. System performance under different working gases is explored, and helium is chosen due to its much larger cooling power. The influences of cooling and ambient temperatures and cavity parameters on system performance are then investigated. The results show that a rise in ambient temperature leads to a dramatic decline in cooling power. Moreover, the influences of cavity parameters are complicated. When the diameter and length of the cavity are respectively 95 mm and 440 mm, the cooling power achieves a maximum of 3.65 kW with COP of 0.76; while with diameter and length reaching 90 mm and 360 mm, respectively, a peak COP of 0.82 with cooling power of 1.47 kW is obtained. Furthermore, a comparison between the presented direct-coupling system and a series-connection system is performed. The results show better performance of the direct-coupling system, which achieves a cooling power of 5.08 kW under air-conditioning case, 22.4 % higher than that of the series-connection system, implying its superiority in air-conditioning field for larger cooling capacity and more compact configuration. This study provides a new perspective for understanding ofthermoacoustic refrigerators.

Thermal performance analysis of multi-stage cold storage packed bed with modified phase change material based on Na2SO4·10H2O

Packed bed cold storage integrates a large number of phase change materials (PCMs) in a low-cost way, improves heat transfer performance by providing a larger heat transfer surface, and is considered a promising energy storage method in the field of air conditioning. However, PCM based on eutectic salt is often used for single-stage cold storage packed bed, which has poor cold storage performance and inferior stability. In this paper, the modified PCMs based on Na2SO4·10H2O with solidification temperatures of 5.11 °C, 7.06 °C, and 12.89 °C were proposed for multi-stage packed bed cold storage, and the formula of the material was modified and tested to improve the stability. The test showed that preheating before utilization can further reduce the subcooling degree caused by the freeze–thaw cycle. Through the CFD simulation of the established multi-stage packed bed model containing cylindrical encapsulated capsules, the cold storage capacity of a multi-stage packed bed with different PCMs filling ratios was compared. Results show that the cold storage density of the multi-stage packed bed with the filling ratio of 4:2:4 (PCM1:PCM2:PCM3) is 7.3 % higher than that of the single-stage packed bed, and the cold storage capacity can meet the emergency cooling demand of the air conditioner for at least one hour. This study provides a theoretical basis for the feasibility of the proposed modified eutectic salt PCM applied to multi-stage packed bed cold storage for air conditioning conditions.

Teaching Factory Model Development in Vocational High Schools

This study aims to find a conceptual model of teaching factory in the field of air conditioning and air conditioning engineering in vocational high schools (VHS). The teaching factory development model is expected to have a solid legal foundation and be able to carry out independent financial management so that they are able to carry out sound business practices. This study uses a type of development research, namely research and development (R D), with a 4-D (Four-D) approach. The stages in this research are define, design, development, and disseminate. The conceptual model of the teaching factory was tested for feasibility by the validator of material experts (expert judgment) and the model user, namely by the executor of the teaching factory in the field of refrigeration and air conditioning engineering at VHS 1 Magelang. The results of the study indicate that the teaching factory conceptual model consists of components, namely 1) information technology; 2) PPK-BLUD; 3) HR; 4) block schedule; 5) worksheets; 6) products/services; 7) workshops; 8) industry partnerships; and 9) system management. Based on the results of expert validation and model user responses, the teaching factory conceptual model was declared feasible to be applied in VHS. The teaching factory conceptual model has a solid legal foundation, allows for independent financial management patterns, and can carry out healthy business practices on an ongoing basis (sustainability).

Elements of Competency for Facility Engineers in The Field of Refrigeration and Air Conditioning

The challenge for institutions of higher learning today is to provide the human capital that this industry desperately needs. Past studies have shown that most graduates of local institutions of higher learning do not have the necessary work skills and competencies in the market and there seems to be mismatch in the preparation of graduates for the local job market. This study aims to explore the elements of competency that a facility engineer should have in the field of air conditioning and air conditioning. This study was done to provide a comprehensive overview of the elements of competency that need to be presented to the Facility Engineers in order to help the graduates of the Refrigeration and Air Conditioning Technology course at Universiti Tun Hussein Onn Malaysia (UTHM) to be better prepared for the occupational environment. This study used the Modified Delphi Technique approach for the purpose of obtaining expert approval on constructs in questionnaire instruments as well as using literature survey study through analysis documents. The research instrument used was a set of questionnaires prepared to obtain evaluation from experts. The data were processed by using Statistical Package for the Social Sciences (SPSS) software to obtain the mean score, median and Interquartile Range (IQR) for each item. The findings of the literature review through document analysis produced ten elements and 64 items. Meanwhile, the findings of the modified Delphi study produced the competence of Facility Engineers which has 10 elements and 62 items. Finally, the findings from this study are expected to open further discussion space and can help those involved in improvement to further enhance the quality of graduates in particular creating a skilled workforce according to industry demand.

MODELAREA MATEMATICĂ A UNUI VAPORIZATOR CU AJUTORUL ECUATIILOR CRITERIALE

The paper aims to compare and choose the most suitable criteria equation for the computation of the convective heat transfer coefficient on the refrigerant side of the evaporator. The comparison is carried out by considering a given air handling unit equipped with a specific evaporator operating with refrigerant R134a. A mathematical model is given. The results obtained for criteria equations available in the work of Shah (1982), Gungor and Winterton (1987) and Kandlikar (1999) have been compared. The first criterion equation of Shah (1982) is selected because it leads to a value for the evaporator pipe length close to the one measured on the air handling unit and also it can be applied for a wider range of refrigerants used in the field of air conditioning.

STUDIUL COMPARATIV AL PERFORMANȚEI POMPEI DE CĂLDURĂ APĂ-APĂ ÎNTRE R407C ȘI ALȚI AGENȚI FRIGORIFICI ECOLOGICI

In the paper we presented a comparative analysis of the effect of the refrigerant used on the operation and performance of a heat pump with water-water and heat regeneration. Various sensitivity studies are presented comparatively for some eco-friendly refrigerants (R290, R600a, R454C, R152a) and R407C. Based on the energetic analysis, the energy destruction and loss were estimated for each device, depending on the destination and the operating regime. Graphic and numerical results are presented. In conclusion, a comparative analysis of the defined performance coefficient based on energy and energetic efficiency is presented. The interest of the study is important due to the applicability of geothermal heat pumps in the field of air conditioning of residential and industrial buildings but also in agriculture for animal farms, for drying some agricultural products in a climate with controlled temperature and relative humidity, in addition the water can be used in summer for irrigation.

Experimental study on the disinfection of microbial contamination by the microwave radiation on a typical filter coated with absorbing material

In the air-conditioning system, a high-efficiency air filter can guarantee the capture of dust and biological particles. However, the traditional filter material itself does not have the function of disinfection and self-purification. As a result, the traditional air filter might become a hotbed for the reproduction of the microorganisms. Carried by the airflow, these microorganisms can enter the indoor environment, which might cause secondary pollutions. A properly selected upstream filter can prevent the particulate pollution, while it is hard to prevent the biological pollution inside the air-conditioning system. The microwave radiation is a broad-spectrum and high-efficiency disinfection method because of its disinfection mechanism, penetrability and selective heating property. At present, the microwave disinfection technology is widely used in the disinfection process of food processing, but its application in the air-conditioning field is relatively rare. From this point of view, this paper proposes to apply the microwave disinfection technology to the filters of the air-conditioning system. First, the combination of the filter and absorbing material is proposed to improve its absorption capacity of the microwave. Then, the air-conditioning system experimental platform for microwave disinfection was established and experiments were carried out to explore the disinfection effect of the Staphylococcus aureus on the composite filter under the microwave radiation. Finally, the experimental results and their influencing factors are briefly analyzed.

Experimental performance evaluation and comparison of an absorption refrigeration prototype driven by exhaust heat operating with NH3/LiNO3 and NH3/LiNO3+H2O

Ammonia/salt absorption refrigeration cycle has advantages of low grade heat recovery, excellent thermal performance and simple construction, which may play an important role in refrigeration and air-conditioning fields for energy saving and emission reduction. The present paper introduces a prototype of absorption refrigeration system driven by exhaust heat operating with NH3/LiNO3 and NH3/LiNO3+H2O, which is composed of commonly used devices with the advantages of low cost and simple manufacture. Comprehensive experiments on the prototype were carried out with varying operating conditions (exhaust-gas temperature, chilled-water temperature, cooling-water temperature) to evaluate their influences on performance parameters. The NH3/LiNO3 system was driven by gaseous exhaust heat in the range of 150.1 °C∼325.1 °C, the minimum evaporating temperature reached -25.29 °C, the cooling capacities varied between 0.60 kW and 3.00 W, the electrical coefficient of performance varied between 3.30 and 16.52, and the overall coefficient of performance varied between 0.263 and 0.584. The NH3/LiNO3+H2O system was driven in the range of 125.8 °C∼330.1 °C, the minimum evaporating temperature reached -22.56 °C, the cooling capacities varied between 0.92 kW and 3.91 kW, the electrical coefficient of performance varied between 4.65 and 20.30, and the overall coefficient of performance varied between 0.310 and 0.566. The experimental results were compared with that of NH3/NaSCN system by authors’ previous work, it is found that three ammonia/salt working fluids have respective advantages and optimal working condition ranges. The experimental evaluation and comparison provide significant references for the optimization and practical application of the ammonia/salt absorption refrigeration systems.

Desiccant coated heat exchanger and its applications

Desiccant coated heat exchanger (DCHE) has shown great potential for dehumidification in vapor compression cooling systems and has been widely concerned in the research field of air conditioning, as well as heat and mass transfer in recent years. This paper is aimed at providing fundamental knowledge and research progresses on DCHE for dehumidification and cooling. Initially, DCHE dehumidification is chosen as the research object in this review due to its superiority of the principle by comparing with other two typical dehumidification processes, which are condensation dehumidification and rotary-wheel dehumidification. Then, intermittent dehumidification and continuous dehumidification as two operation modes of DCHE are compared. Finally, the variation characteristics of temperature and humidity during operation are discussed. The current studies of DCHE are reviewed from four aspects, including desiccant coating, cooling source, regeneration heating source and basic heat exchanger. The performance analysis of DCHE is then conducted, according to the different effects of above aspects acting on dehumidification performance, cooling performance and energy efficiency of DCHE. The ongoing researches indicate that the rational construction of DCHE is an effective way to achieve its multi-objective performance optimization. The significant progress of DCHE lays the foundation for applications on other fields. However, further research is required in the field of the selection of desiccant coatings and the structure of heat exchangers to broaden its application market.

Application of Business Model Canvas for Solar Thermal Air Conditioners

Growing populations, burgeoning economies, and technology-driven lifestyles demand an increasing supply of energy. The existing energy supply pattern primarily depends on fossil fuels that have initiated climate change–provoking myriad problems. Integration of renewable energy sources in the existing energy supply system is a complex and challenging task keeping in view the depleting fossil fuels and prevailing environmental challenges. The existing cold storage farms are working on traditional compressors and the HVAC system, causing more use of electricity. Similarly, existing data centers and supermarkets are also using conventional refrigerants. These systems also use hazardous environmental refrigerants, which make these systems more dangerous. In the summer season, comfort cooling and refrigeration requirements rise to peak in hot climate areas forcing utilities to supply more electrical energy to meet the demand. Therefore, a solar thermal cooling system employing a solar absorption chiller operated through a hot water stream generated by a solar evacuated glass tube collector with CO2 as a refrigerant is simulated in the TRNSYS® simulation environment. The results are generated for the hot climate of Multan, Pakistan, and the average obtained temperatures of the three rooms, cold storage, office, and kitchen room, were 18.43, 26.25, and 29.83°C, respectively. However, every startup or new idea needs a proper business model before entering into the market. This article offers a complete insight and a future perspective for the reader to develop a precise business model for the commercialization of his or her project. A business model is designed for solar thermal air conditioners for domestic, cold storage, and data centers applications in the world, after reviewing and interviewing manufacturers and customer segment in air conditioning fields. Data were collected through semi-structured one-to-one interviews from a convenient sample of 10 national and international respondents, and their views were thematically analyzed. The implementation of a business model using a case for the Pakistani market is presented. A business model for a solar cooling system utilizing abundant CO2 as a refrigerant is presented in this article. This business model is equally suitable for designing a business model for any renewable energy product in the world.

Performance Improvement of a Household Refrigerator using Phase Change Material

Thermal energy storage through phase change material has been used for wide applications in the field of air conditioning and refrigeration. The specific use of this thermal storage has been for energy storage during low demand and release of this energy during peak loads with potential to provide energy savings due to this. The principle of latent heat storage using phase change materials (PCMs) can be incorporated into a thermal storage system suitable for using deep freezers. The evaporator is covered with another box which has storage capacity or passage through phase change material. The results revealed that the performance is increased from 3.2 to 3.5 by using PCM.

Mathematical model and energy efficiency analysis of a vacuum-based liquid desiccant regenerator

Liquid desiccant air conditioning (LDAC) has been considered as a promising solution for efficient air temperature and humidity control in air conditioning fields. However, the high regeneration temperature of desiccant solution impedes its spread and application. In this study, a vacuum-based liquid desiccant regenerator (VLDR) for desiccant solution regeneration in LDAC driven by low-grade energy is studied, meanwhile, the mathematical model considering the variation of heat transfer coefficient under different operating conditions is developed to analyze the system performance and energy efficiency. After the model is validated by the experimental data, the regeneration performance and energy efficiency analysis of the VLDR system is simulated and investigated. Simulation results show that hot water temperature, flowrate are the variables that affect the performance of the generator, and the performance of the condenser is influenced by cooling water temperature and flowrate. Opposite influences for vacuum pressure are found on the performances of generator and condenser, therefore the hot water temperature, vacuum pressure, and cooling water temperature should be designed properly to provide the required regeneration capacity with the pressure balance maintained. Moreover, energy efficiency is analyzed by comparing the ratio of water vapor generation rate to the total electricity consumption of the VLDR under different temperatures and vacuum pressures.

Opportunities in Latent Thermal Energy Storage by Phase Change Material for Lower Temperature Applications: A Review

Thermal energy storage through Phase Change Material has been used for wide applications in the field of air conditioning (cooling) and refrigeration, especially at the industrial scale for lower temperature applications like refrigeration and air conditioning, cold storage, cold chain, etc. Generally inorganic and eutectic type phase change materials are used because of long term temperature stability, good latent heat, chemical stability, etc. Latent energy storage technologies, which can improve the thermal inertia of the system, reduce indoor temperature fluctuations, improve thermal comfort, and are becoming an effective way to reduce reliance on traditional systems. In this review, paper attempts have been given to improve the refrigeration system performance by thermal storage with nanoparticles. The use of Phase Change Material may maintain the quality of food for a longer duration of time even though power outage exists. This review paper focuses on different phase change materials used for lower temperature applications. Compared with traditional materials, PCMs can store energy through the utilization of sensible latent heat. The PCMs selected forthe system should possess a suitable melting point, high heat storage density, good thermal conductivity, small volume change; these materials mainly include paraffin waxes, fatty acids, salt hydrates, and eutectics, etc. The main objective of this review paper is to study different latent energy storage materials i.e. organic, inorganic, and eutectic phase change materials for lower temperature applications. How to cite this article: Husainy ASN, Parishwad GV. Opportunities in Latent Thermal Energy Storage by Phase Change Material for Lower Temperature Applications: AReview. J Adv Res Mech Engi Tech 2020; 7(3): 1-8. DOI: https://doi.org/10.24321/2454.8650.202003

4E analysis of thermal recovery potential of industrial wastewater in heat pumps: An invisible energy resource from the iranian casting industry sector

Heat pumps are technologies that use renewable energy and are also environment-friendly and therefore used in different countries. Due to the thermal potential of industrial wastewater they can be used as a suitable source in heat pumps. This study compares the energy, exergy, economic and environmental aspects of an industrial wastewater heat pump (WSHP) with air source heat pump (ASHP) and geothermal heat pump (GSHP) systems in the city of Mashhad. The results showed that the coefficient of performance (COP) and exergy efficiency of the cycle WSHP were 5.104 and 0.3249, respectively, which were higher than the GSHP and ASHP cycles. Using economic analysis, it was found that the higher initial cycle price and lower power consumption of WSHP than ASHP, WSHP made it more economical after 2 years. According to environmental analysis, the use of WSHP reduced CO2 emissions compared to GSHP and ASHP by 15.67 ton/year and 42.2 ton/year, respectively. Also, a comprehensive study was conducted on casting factories in Iran for the use of the WSHP system. The results showed that the amount of heat recovered from casting factories in Iran was about 41 GWh/year. Considering COP of WSHP cycle during the operational condition is 5.104, this cycle can produce thermal energy about 11.8 MW/year, which is used in the field of air conditioning.

Thermo-Economic Analysis of a Hybrid Ejector Refrigerating System Based on a Low Grade Heat Source

The rising of the global energy demand requires the use of alternative energy conversion systems employing renewable sources. In the refrigeration and air conditioning fields, heat driven ejector systems represent a promising way to produce the cooling effect by using available low-grade temperature sources. In this paper, a thermo-economic analysis of a waste heat recovery hybrid ejector cycle (WHRHEC) was carried out. A thermodynamic model was firstly developed to simulate a WHRHEC able to obtain chilled water with a cooling load of 20 kW, by varying the working fluids and the pinch point values in the heat exchangers. Specific single- and two-phase heat transfer correlations were used to estimate the heat transfer surface and therefore the investment costs. The operative ranges that provide a reasonable compromise between the set-up costs and the cycle performances were then defined and compared to the current waste heat-driven technologies, such as absorption chillers and organic Rankine cycles (ORCs) coupled with vapor compression cycles (VCCs). The last part of the paper presents an economic analysis providing the map of the design (plant size) and contingent (specific cost of energy, waste heat availability) variables that lead to the economic convenience of a WHRHEC system when integrated to a conventional VCC plant.