Air Conditioning Research Articles

Material and Parametric Design Optimization of Improved Heat Transfer Rate of AC Condenser

Air conditioner system is made up of a condenser that removes unwanted heat in an enclosure through the refrigerant and transfers the heat outside. Improving the heat transfer of air conditioning condenser is still a difficult task because of the broader set of materials and various parametric designs involved. Due to this high cost, the experimental set-up cost cannot be modified, instead, simulation analysis was introduced in the optimization process in order to achieve a near-optimal solution. The aim of this research is to improve the heat transfer rate for air conditioning condenser by material and parametric design optimization. The system was designed based on one basic parameter optimization: varying the condenser tube diameter. This variable was changed in order to improve the heat transfer of the condenser. Simulations using Computational Fluid Dynamic (CFD) analysis and thermal analysis were carried out to have a better understanding and distinct visualization of the fluid flow and materials used, and to compare the results. The materials that were used for CFD analysis are R32 and R290, and for thermal analysis are copper (C12200) and aluminum. The analysis was done using Analysis System (ANSYS) software. Different parameters were calculated from the results that were obtained and graphs were plotted between various parameters such as heat flux, static pressure, velocity, mass flow rate and total heat transfer. From the CFD analysis, the result shows that R32 has more static pressure, velocity, mass flow rate and total heat transfer than R290 at a condenser tube diameter of 7mm. In thermal analysis, the heat flux is more for copper (C12200) material at a condenser tube diameter of 7mm than aluminum.

An artificial neural network approach for out‐of‐control stream identification in multiple stream processes

AbstractA multiple stream process (MSP) is a process at a point in time that generates several streams of output with quality variables and specifications that are identical in all streams. Statistical process control (SPC) schemes for MSPs are designed to issue an out‐of‐control (OC) signal when a possible change occurs from the in‐control (IC) state of the process. However, the SPM literature for MSPs lacks contributions regarding post‐hoc identification of the stream or group of streams responsible for an OC signal. In this article, we propose an artificial neural network (NN) specifically trained for this purpose and, through a Monte Carlo simulation, show its superiority in correctly identifying OC streams, since an OC signal has been correctly issued. The research is motivated by the need for a post hoc diagnosis of the heating, ventilation, and air conditioning (HVAC) systems installed on modern train coaches, generating multiple streams of quality variables of interest. A case study in this area based on the HVAC data (openly available online at https://github.com/unina‐sfere/NN4OCMSP) illustrates the practical applicability of the proposed approach, which is implemented in the Python package NN4OCMSP and published on the PyPI software repository.

Impact of Air Conditioning Type on Outdoor Ozone Intrusion into Homes in a Semi-Arid Climate

Outdoor ozone (O3) is elevated on hot, sunny days when residential air conditioning is used most. We evaluated the impact of direct evaporative coolers (ECs) and vapor-compression air conditioners (ACs) on indoor O3 concentrations in homes (N = 31) in Utah County, Utah, United States of America. Indoor and outdoor O3 concentrations were measured for 24 h at each home using nitrite-impregnated glass-fiber filters. AC homes (n = 16) provided a protective envelope from outdoor O3 pollution. Only one AC home had O3 levels above the limit of detection (LOD). Conversely, EC homes (n = 15) provided minimal protection from outdoor O3. Only one EC home had O3 levels below the LOD. The average indoor O3 concentration in EC homes was 23 ppb (95% CI 20, 25). The indoor-to-outdoor (I/O) ratio for O3 in EC homes was 0.65 (95% CI 0.58, 0.72), while the upper bound for the I/O ratio for AC homes was 0.13 (p < 0.001). Indoor exposure to O3 for residents in EC homes is approximately five times greater than for residents of AC homes. Although ECs offer energy and cost-saving advantages, public health awareness campaigns in O3-prone areas are needed, as well as research into O3 pollution controls for direct ECs such as activated carbon filtration.

The Potential Impact of Heat on Athletes' Sleep at the Paris 2024 Olympics and Paralympics Games

AbstractIn 2024, Paris will host the Olympic (during July and August) and Paralympic (during September) Summer Games. Despite temperatures often exceeding 40°C in Paris in July, the International Olympic Committee (IOC) has indicated that there will be no installation of air conditioning in the athletes' rooms. High ambient temperatures can impair the quantity and quality of sleep and, consequently, impair athletic performance. In this overview, we present the rationale behind and explain the process of how a warm environment is unfavorable to the sleep of Olympic and Paralympic athletes, as well as offer practical recommendations on how to mitigate the effects of environment heat for a restful and effective night's sleep during the Paris 2024 Olympics and Paralympics Games.

Analisa Penghawaan dan Pencahayaan terhadap Kenyamanan Termal pada Rindang Cafe and Eatery Palembang

Rindang Cafe and Eatery Palembang is one of the cafes that applies the open concept. The use of this concept is expected to reduce artificial energy consumption, including lighting and ventilation, so as to ensure the comfort of a building. This research uses a quantitative approach that evaluates theory by explicitly measuring variables in the field. Opening area, temperature, and humidity were measured using a thermometer, hydrometer, and meter. This research uses a quantitative approach that evaluates theory by measuring variables explicitly in the field. The purpose of this study is to determine the level of thermal comfort in cafes that operate with different air conditioning and lighting conditions from afternoon to evening. This study shows that thermal comfort at Rindang Cafe and Eatery Palembang is strongly influenced by the layout of the air conditioning and lighting. The findings have important implications for the design of cafes and other open space facilities in areas with hot climates.

Sleep quality and thermal comfort assessment in the hot and humid climate of Malaysia

ABSTRACT This study examines the relationship between thermal comfort and sleep quality among 417 Malaysian adults via an online survey conducted from November 2019 to April 2020. Participants provided demographic information, thermal comfort, and sleep quality data. The research explores how factors such as air conditioning and pre-sleep behaviours influence individuals’ perceptions of thermal comfort and sleep quality. Findings reveal that thermal sensations change during sleep, with respondents reporting a 50% decrease in warmer sensations upon waking compared to before sleep, and a nearly threefold increase in preference for warmer conditions. Sleep quality responses indicate high levels of calmness and satisfaction, with minimal awakenings at an average of 0.9. Air conditioning, available to 60% of respondents, showed limited improvement in perceived sleep quality, with more air-conditioned individuals reporting night awakenings (68%) compared to those without (53%). Pre-sleep behaviours, such as consuming drinks, were associated with lower thermal sensation upon waking, suggesting a potential cooling effect, while taking a shower before sleep correlated with increased overall comfort, potentially enhancing the sleep experience.

7484 Pseudohypoglycemia In A Patient With Raynaud’s Phenomenon

Abstract Disclosure: J. Fedorko: None. P. Subarajan: None. A.P. Amblee: None. C.A. Poku: None. Background: The term ‘pseudohypoglycemia’ is used to describe the disparity between actual and measured capillary glucose and clinical presentation. It has been used to describe situations when a patient has the characteristic symptoms of low blood glucose (BG) Whipple’s triad), but the patient’s BG levels are within normal limits. Alternatively, this term can also be used to describe falsely low BG levels on finger-stick (capillary) readings in a patient with normal serum glucose levels and without the characteristic Whipple’s triad. Case: A 55-year-old female with Raynaud’s phenomenon was seen in Endocrine clinic with persistent hypoglycemia noted on finger-stick glucose readings. Her finger-stick glucose reading was 43, and was subsequently given 24 grams of glucose gel. Ten minutes later, a repeat finger stick BG was 44. She had no weakness, tremors, shakiness, vision changes, confusion, seizures, lightheadedness, dizziness, tachycardia, palpitations, nervousness, hunger, paresthesias irritability, confusion, seizures, loss of consciousness, or any other symptoms or signs of hypoglycemia. She had no such previous episodes and her fasting BG ranged from mid-70s to 80, with post-meal BG ranging from 100 to mid-100’s. Her most recent hemoglobin A1c was 5.5. She regularly experiences cyanosis of fingers consistent with Raynaud’s phenomenon, triggered by cold air in winter and air conditioners in summer. She does not take any medications for these episodes. Given the absence of classic Whipple triad and normal BG from peripheral blood draw, the patient’s low finger stick BG readings were attributable to Raynaud’s phenomenon. It is postulated to be secondary to decreased perfusion in the digital microcirculation and increased blood transit time in the fingers, resulting in a local increase in glucose consumption and thus low capillary finger stick BG levels. Simultaneously done serum glucose levels are usually normal. Conclusion: Pseudohypoglycemia can occur in patients with impaired peripheral circulation such as Raynaud’s phenomenon, acrocyanosis, peripheral vascular disease, shock, or with increased glycolysis by blood cells like in leukemia, polycythemia and rare infections like African trypanosomiasis, hyperviscosity syndromes like Waldenstrom’s and monoclonal gammopathy of undetermined significance. In patients with low finger-stick (capillary) glucose levels who do not display Whipple’s triad, and have comorbid conditions that might interfere with the BG reading, it is important for clinicians to recognize the difference between true and pseudohypoglycemia. This can be confirmed with a simultaneously done normal serum glucose level and will prevent unnecessary investigations or excessive treatment. Presentation: 6/3/2024

Performance and PV benefits analysis of multi-source renewable energy systems for different types of buildings on university campus

Due to the large campus area and high personnel density, universities experience significant building energy consumption. The comprehensive utilization of renewable energy can greatly alleviate energy consumption in higher education institutions. To explore the application prospects of renewable energy systems in universities, this study takes a university in Wuhan as a case example, investigating the performance and potential of various types of Photovoltaic-assisted Heating, Ventilation, and Air Conditioning (PV-HVAC) systems. First, the building load was calculated using DeST software. Subsequently, the potential for solar energy application on campus was assessed using a combination of QGIS, Labelme, and Python. Moreover, three types of PV-HVAC systems were designed for five categories of buildings based on their distinct characteristics, and TRNSYS software was utilized for performance simulation and analysis. The results indicate that the annual performance coefficients of the three systems are 3.8, 3.2, and 4.5, with corresponding annual energy self-sufficiency rates of 114 %, 72 %, and 32 %, respectively. Finally, the overall energy self-sufficiency rate of the PV-HVAC system across the campus is 65 %. This research provides valuable insights for achieving nearly zero-energy HVAC systems in university campuses.

Practical application of machine learning in energy and thermal management: Long-term data analysis of solar-assisted AC systems in portable cabins in Kuwait and Australia

Machine learning techniques are advancing rapidly in theoretical grounds, but their practical application and real evaluation in engineering disciplines are limited. This study investigates one-year of experimental data for indoor air conditions and energy monitoring of two identical portable cabins in Kuwait. Additionally, a 9-month period of solar photovoltaic energy production is experimentally obtained for assessing energy saving aspects of a solar assisted air conditioning system in one of the cabins. A transient system simulation tool model is developed and validated for the portable cabins. Both one-year experimental data and the validated simulation data are used for developing machine learning models for six case studies in Kuwait and Australia. In simulations, there are issues related to lack of access to real-time weather data from a locally installed weather station. In experimental works, there were issues related to disruption of data collection due to power or internet shutdowns. To resolve these issues, nineteen regression models are investigated. It was found that all models performed very well although the Matern 5/2 and Exponential gaussian process regression model performed slightly better, with all models achieving high accuracy, as indicated by R-squared values close to 1.0 in all six case studies. Overall, it was found that the photovoltaic solar-assisted air conditioning system could save annually 26.2 % and 75.7 % energy in Kuwait and Rockhampton, Australia, respectively.

Energy efficient design of buildings in hot climates through cooling of the envelope

The building envelope can afford many enhancements for lowering the cooling load in hot regions. In this paper, an active upgraded model utilizing an evaporative system to cool the envelope will be tested in the relatively humid climate of the coastal area of the Arabian Gulf. A couple of buildings were erected for this purpose. One was fully enclosed by a secondary structure around it, and the gap between the two was cooled using an evaporative cooler. This was compared to the second, which was insulated according to Dubai Municipality standards. A third comparison was also performed, which concerned the standalone secondary envelope with no evaporative cooling. The interior of all three cases was cooled using DX window-type air conditioners, and the power consumption measured. Thermal simulations were performed on similarly designed models using Ecotect 5.5 to see how each system would perform in full-scale functioning buildings. The measured tests on the building models showed a reduction of electrical consumption in both upgrades compared to the regulation insulated reference. The secondary envelope provided savings of 40 % and 47.3 % in the hot months of June and July, while the evaporative solution saved 52.1 % and 53.7 %, respectively. The simulation of a full-size building over the entire year showed the secondary envelope saving 48.9 % and the evaporative assisted 57.15 %.

Research on faradic capacitive deionization regeneration method for absorption air conditioning system

The development of renewable energy driven air conditioning system is of importance for curbing the CO2 emission. Absorption air conditioning systems could be a good choice but for its low regeneration efficiency. Capacitive deionization (CDI) regeneration method has been proposed to improve the efficiency of absorption system by eliminating the energy waste in the traditional thermal regeneration method. The core part of CDI is the electrode normally made from porous carbon materials, which often suffers from low charge storage capacity and co-ion repulsion. On the purpose of performance optimization, this paper proposes a hybrid deionization (HCDI) regeneration method by fabricating the electrode from Faraday materials. Experimental research has been made on the regeneration capacity of the prepared electrodes. Investigation has been conducted on the performance of the HCDI method based absorption system. The influence of different parameters has been revealed. Compared with the porous carbon electrode, the Faraday electrode has raised the charge efficiency by 20%, and raised both the regeneration capacity and overall performance by 40%. Under optimized working conditions, the COP of the HCDI based absorption system has reached 3.51 in the experiments, which shows great potential for future application.

Multiphysical design for optimised ventilation and noise attenuation in ducts: an approach using metamaterials

Noise generation and propagation through mechanical ventilation and air conditioning (MVAC) ducts have been increasingly investigated since commercial solutions allow sensible noise attenuation while reducing the duct section. So, a commercial silencer forces the MVAC power to rise to overcome the flow resistance, increasing the noise source. For this reason, this study focuses on soundproofing ventilation ducts through acoustic metamaterials with no inner duct section decreasing. A crucial part of this study falls into the multiphysical interaction between acoustics and fluid dynamics, which is a phenomenon that may result in a challenging analytical model. In conditions of flowing motion, the wave vector has been modelled according to the Lighthill model: the component of the velocity rotor potential becomes significant, influencing the soundproofing performance due to the metamaterial placed at the edge of the inner surface of the duct. FEM analysis helped design a series of samples which then have been tested experimentally in static conditions. Once the numerical method is calibrated, further multiphysical numerical analysis are used to implement the sound insulation properties of the metamaterial-based filter through dynamic flow conditions. Guidelines for multiphysical setup for wave-based simulation are drawn, and preliminary experimental results are presented.

Energy and Exergy Performance Analysis of Solar-Assisted Thermo-Mechanical Vapor Compression Cooling System

Air conditioning is vital for indoor comfort but traditionally relies on vapor compression systems, which raise electricity demand and carbon emissions. This study presents a novel thermo-mechanical vapor compression system that integrates an ejector with a conventional vapor compression cycle, incorporating a thermally driven second-stage compressor powered by solar energy. The goal is to reduce electricity consumption and enhance sustainability by leveraging renewable energy. A MATLAB® model was developed to analyze the energy and exergy performance using R1234yf refrigerant under steady-state conditions. This study compares four solar collectors—evacuated flat plate (EFPC), evacuated tube (ETC), basic flat plate (FPC), and compound parabolic (CPC) collectors—to identify the optimal configuration based on the collector area and costs. The results show a 31% reduction in mechanical compressor energy use and up to a 44% improvement in the coefficient of performance (COP) compared to conventional systems, with a condenser temperature of 65 °C, a thermal compression ratio of 0.8, and a heat source temperature of 150 °C. The evacuated flat plate collectors performed best, requiring 2 m2/kW of cooling capacity with a maximum exergy efficiency of 15% at 170 °C, while compound parabolic collectors offered the lowest initial costs. Overall, the proposed system shows significant potential for reducing energy costs and carbon emissions, particularly in hot climates.

Prediction of train interior noise due to the HVAC system

In recent years, the significance of acoustic comfort in rail vehicles has grown considerably, owing to its direct impact on passenger well-being. As a consequence, interior noise levels are progressively becoming more restrictive. Meeting these requirements is a key challenge for rolling stock manufacturers. The predominant source in stationary condition is the HVAC (Heating, Ventilation, and Air Conditioning) system. To effectively assess and potentially reduce the noise generated by the HVAC system, the availability of tools and methodologies for predicting the propagation of noise through the air ducts and interior noise levels in the passenger compartment during the design phase is crucial. This paper presents a simulation methodology for predicting interior noise levels by evaluating various alternatives within a commercial software. Input data for the simulations encompass the geometry and materials of the supply and return ducts, along with the acoustic power of each outlet measured at the source. This data is associated with the nominal operating mode of the HVAC system. Finally, the paper establishes a correlation between the simulation results and in-situ measurements conducted on the completed train, with the HVAC equipment operating under nominal conditions.

Comparison of community response to road traffic noise by housing category

In 2023, a socio-acoustic survey on community response to road traffic noise was conducted in residential areas along several arterial roads in Kanagawa Prefecture as part of the Kanagawa University Cross-disciplinary Research Promotion Project. The survey targeted residents living in detached houses and apartment buildings. A questionnaire used for the survey was designed based on new findings from a survey conducted in 2021 using the Image Grid Method. Factors we focused were economic burden due to increased use of air conditioner, harmful impact of noise on family members, and importance of measures reducing noise. Regarding the noise exposure, we estimated Lden using noise maps, which were created for the survey. This paper presented the frequency distribution of the importance of measures reducing noise. In addition, applying multiple logistic regression analysis to individual data, we developed the exposure-response function for economic burden and harmful impact as well as listening disturbance and annoyance. Based on the results obtained, we discussed the importance of measures reducing noise and difference in exposure-response function between housing categories.

Using geothermal energy in enhancing all-air HVAC system performance - Case study, thermal analysis and economic insights

The background is the same for addressing the twin challenges of attaining thermal comfort and concurrently reducing energy use and CO2 emissions. As a safeguard against worsening contamination, combining geothermal energy with an All-Air Heating, Ventilating, and Air Conditioning system (HVAC) with 100 % fresh air intake is also crucial in the context of the lessons learned from the COVID-19 pandemic. As a result, this study suggests using geothermal energy as a backup source to run a typical All-Air centralized HVAC system. The resulting system is referred to as a combined system from now on, and its primary goals are to lower the amount of operating energy needed while being environmentally and financially sound. In this context, the creative way of combining the suggested geothermal duct with the All-Air HVAC system possesses various insights, as demonstrated by the thorough thermal analysis and related design. Strong conclusions were derived from a thorough case study focused on Lebanon: adding 100 % fresh air intake leads to an astounding yearly energy savings of 67 %, whereas configurations with 10 % and 30 % fresh air produced energy savings of 52 % and 36 %, respectively. In the study, a geothermal multi-duct system was also suggested and looked at. The research revealed that the 311-m length of the single geothermal duct connected to a pressure of 7000 Pa was reduced to 210 m and the pressure drop was lowered to 140 Pa when a geothermal multi-duct system was employed. Furthermore, as the computed payback period makes clear, the integrated system presents an appealing chance to drastically cut resource usage during energy consumption, lower CO2 emissions, and provide 100 % fresh air circulation.

Modelling Newtonian noise of vibroacoustic origin in the Virgo gravitational wave detector

With ~100 detections by the LIGO-Virgo-KAGRA network, gravitational astronomy has definitely begun. The Virgo detector is a modified Michelson interferometer with two arms of 3km each, made of optical resonator housing ~100 kW laser beams. It can measure a gravitational strain (ΔL/L) of ~10^(-21). The detector is susceptible to various sources of noise within specific frequency bands. Among these, the "Newtonian" or "gravity-gradient" noise (seismic and atmospheric/acoustic) could limit the low-frequency sensitivity (below a few tens of Hz) of LIGO and Virgo as they reach their full sensitivity, as well as that of next-generation detectors such as the European Einstein Telescope and the US Cosmic Explorer. This paper focuses on modeling Newtonian noise of acoustic origin, which refers to the small fluctuations in the gravity field resulting from the acoustic field present in the experimental halls. The fluctuating gravitational field directly causes random forces on sensitive optical elements, such as the interferometer test masses. The induced noise is quantified using a numerical acoustic model of the experimental room when it is excited by the air conditioning system.

Thermal performance assessment of traditional Japanese wooden houses with short-term measurements: Machine learning approaches

Traditional Japanese wooden houses are sustainable and vernacular in nature; however, energy consumption owing to poor insulation is inevitable in the winter. These wooden houses in Japan are an integral part of historical landscapes and are protected from the potential risks of retrofitting. To continue using these houses without bearing additional energy burdens, it is necessary to better understand their actual thermal performance. Therefore, this study proposes a combined approach to assess the thermal performance of traditional Japanese-style rooms using in-situ thermal measurements and machine learning predictive methods. The in-situ thermal measurements evaluated the actual thermal environment of traditional Japanese-style rooms with and without air conditioners (AC) during winter. Similarly, two machine learning models, support vector regression (SVR) and random forest regression (RFR) were developed to predict the indoor temperature based on the external factors and their adjacent rooms temperature. The result revealed strong thermal interaction between adjacent rooms, likely driven by heat transfer dynamic. To further investigate these interactions, thermal images of each room were analyzed after the AC was in use. The result revealed the presence of hot and cold spot within the gap of sliding fusuma (thick paper made door) and ranma (transom or indoor ventilation), indicating significant heat transfer between the AC and non-AC rooms. Consequently, the prediction model for the AC room temperature was notably influenced by the thermal conditions of adjacent non-AC room. Thus, this study proposes a simple yet reliable approach that enables resident to prioritize thermal improvements for efficient and cost-effective renovations.

A Study on the Energy Efficiency of an Energy Management System for Convenience Stores

This research presents a solution for improving energy efficiency in convenience stores by implementing a building energy management system (BEMS) that uses new logic control in air conditioning and refrigeration systems. These systems currently consume the most energy in convenience stores. Implementing this system not only reduces the energy consumption of the compressors in both systems but also minimizes energy loss due to low desired temperatures in the sale area while maintaining the cabinet temperature at the same level. An experiment was conducted at a 314-square-meter convenience store that was open from 6:00 a.m. to 11:00 p.m., and we demonstrated a 4.4-year payback period by controlling AC units close to the desired sale-area temperature of 25 degrees Celsius and increasing the suction pressure at a medium-temperature CDU by 0.3 bar or 31 kPa. This resulted in energy savings of 7.1 kilowatt-hours per day, or 2591.5 kilowatt-hours per year, for the air conditioning system and 2.8 kilowatt-hours per day, or 1022.0 kilowatt-hours per year, for the refrigeration system, resulting in a total energy savings of 9.9 kilowatt-hours per day, or 3613.5 kilowatt-hours per year. The convenience store can use the results of this research to improve the energy efficiency of its cooling system, which includes air conditioning and refrigeration systems, thereby promoting sustainable energy conservation.

Improving solar HVAC performance by incorporating sutterby SiO2–Cu/C3H8O2 hybrid nanofluid flow via a collocation based Gegenbauer wavelets technique: Effects of electromagnetic control and Smoluchowksi's temperature slippage

AbstractThe utilization of solar energy in heating, ventilation, and air conditioning (HVAC) systems has gained significant attention as a sustainable and environmentally friendly solution to meet the increasing energy demands. Therefore, this research work introduces a novel engineering study that explores solar‐HVAC systems. However, the study utilized hybrid nanofluids (HNFs) consisting of silicon dioxide and copper nanoparticles, with propylene glycol serving as the base fluid. Furthermore, this exploration features a magnetohydrodynamics (MHD) driven rotating flow with activation energy to enhance the heat transfer performance of solar‐HVAC systems. To increase the model novelty, 3D mathematical models were developed to characterize boundary conditions, which include the speed slippery and Smoluchowski temperature slippage. The partial differential equations in the model are transformed into ordinary differential equations (ODEs) through the use of similarity transformations. The Wavelets and Gegenbauer wavelets method in Mathematica was utilized to solve ODEs and investigate physical attributes such as plate friction, Nusselt number, Sherwood number, and mass flux. The findings show that the solar thermal radiation and magnetic field improve the thermal transfer efficiency of solar‐HVAC. Therefore, the findings of the research have practical applications in solar energy for HVAC systems and can contribute to technological improvements in the manufacturing industry.