Air Conditioning Units Research Articles

Association of Mold Levels in Urban Children’s Homes With Difficult-to-control Asthma

To assess the association of overall and specific mold levels in homes of urban children and difficult-to-control asthma.The study included 265 children from the Asthma Phenotypes in the Inner-City (APIC) study, aged 6 to 17 years old with asthma, and living in 8 urban cities across the United States. The study used 265 frozen-dust samples previously collected from the homes of APIC study-enrolled participants for analysis of mold concentrations. Although a total of 465 samples were collected during the APIC study, only the 265 samples that remained were used for post hoc analysis.The study was a cross-sectional analysis of 2 asthma cohorts: children with either difficult-to-control (DTC) and easy-to-control (ETC) asthma. DTC asthma participants required daily therapy of greater than or equal to 500 mcg fluticasone (with or without a long-acting β-agonist), and ETC asthma participants required less than or equal to 100 mcg fluticasone. Quantitative polymerase chain reaction assays were performed on frozen-dust samples that were obtained by wiping above-floor surfaces in participants’ homes using a Swiffer cloth (Procter and Gamble, Cincinnati, Ohio). The Environmental Relative Moldiness Index (ERMI) metric was used to classify mold species into 2 groups: group 1 (26 molds indicative of water damage in the home) and group 2 (10 molds commonly found indoors, even in homes without water damage). Average ERMI values and average concentrations of each of the 36 molds were compared in homes of children with DTC versus ETC asthma.No significant differences were found in average ERMI or average mold concentrations between homes of children with DTC asthma and ETC asthma. Mucor was the only mold with significantly greater average concentration in homes of children with DTC versus ETC asthma (average of 295 vs 67 cell equivalents per mg dust, P < .001). In homes with window air-conditioning (AC) units, the study found that Mucor concentration increased the probability of having DTC asthma (22% increase; 1.6 odds ratio) compared with ETC asthma.This study found that Mucor concentration is a predictor of DTC asthma, and homes with window AC units were more likely to have higher Mucor levels.Previous studies have shown an association between mold exposures and asthma. This study found that Mucor exposure in urban homes is associated with DTC asthma in a pediatric cohort with high geographic representation. Additionally, the study showed the association between elevated Mucor concentration, window AC units in urban homes, and the probability of DTC asthma. Further studies are needed to assess the role of decreasing home Mucor levels in reducing DTC asthma.URL: www.pediatrics.org/cgi/doi/10.1542/peds.10.1016/j.jaci.2021.07.047

Determinação do consumo de energia elétrica para os sistemas de ar-condicionado – um estudo de caso

The survey of the thermal load of refrigerated environments allows us to determine in a safe and concrete way the amount of thermal load required for the studied environment, also the conditioned air systems’ electric energy consumption of. Any educational institution should maintain its students in a comfortable environment to achieve a better educational performance. The objective of this work is to present a case study at the Federal Institute of Education, Science and Technology of Para - Campus Parauapebas, determining the electric power consumption of the classrooms’ air conditioning at this institute. Initially, a flow chart was proposed to study activities to be carried out in order to guarantee this reach. At first, it was necessary to catalog the values for the currents and voltages for each of the air conditioning units in the classrooms of the institution under study, thus, one can identify the average monthly consumption for each appliance. With this information, it is possible to demonstrate the monetary expenditure of the energy consumption. Then it is possible to estimate of the financial economy after the survey of the total consumption of the electric energy. It should be pointed out that this cataloging was carried out in more intense seasonal periods and in certain months to complete the information for the values to be obtained (voltage and current). In order to carry out the project, we have used important sources of exploratory research, aiming to expand the study of the case. The results showed a voltage variation around 209 to 214 Volts (V) and a current of 11 to 14 Amperes (A) for power devices of 18,000 BTU from that point, it is tried to establish efficient methods to reverse the economic picture of the institution through analyzes and perspectives carried out according to the data collected.

Development of a platform for the assessment of demand-side flexibility in a microgrid laboratory

Demand-side flexibility has gained attention as a powerful tool to increase the flexibility of the electricity system and counteract the uncertainties caused by the increase of Renewable Energy Sources. Up to date, few markets allow the participation of Demand Aggregators, which are key to make use of the flexibility of small consumers. Therefore, research surrounding demand aggregation is in many cases limited to simulations or resource consuming pilot programs. This project integrates a microgrid laboratory with a commercial aggregation platform in order to set up and configure the necessary tools to operate the laboratory as a platform to test flexibility. The flexibility platform defined in this work offers a customizable and controllable environment for Demand Response and aggregation testing, while providing a realistic assessment due to the consideration of a commercial aggregator and the use of real and emulated devices. As a first application of the platform, two customer types have been defined and tested: a residential one with a Heating Ventilation and Air Conditioning Unit and a prosumer owning a second-life Electric Vehicle battery in a solar Photovoltaic self- consumption system. The scenarios have shown how, for defined users, the interaction with the aggregator can be beneficial for all sides, as long as proper activations and incentives are defined for the customers. Through future applications of the platform, new use cases can be covered and used to gather valuable information for the aggregator or any interested stakeholder.

Numerical comparison of ventilation modes on the transmission of coughing droplets in a train compartment

The ventilation system in the indoor environments plays a significant role in controlling the cross-infection of viruses and the risk of infection. This work investigated the effects of prevailing high-speed train ventilation modes on the spatial distribution features of droplets through computational fluid dynamics (CFD) simulation. The results revealed that under the current ventilation modes, the airflow barrier was formed in the middle of the aisle, and more than 77.36% of the released droplets were limited to accumulate in the releasing side. Moreover, we found that the strong recirculation flows appeared in the circumstance of top air supply mode suppressed the longitudinal transport of droplets. Also, compared to the standard ventilation case of mixed air supply mode, the suspending droplet fraction in the breathing zone decreased by 37.9% for 10 μm after 60 s under top air supply mode, while those decreased by 33.7% for 50 μm. Therefore, the potential infection risk in the high-speed train was less when the air-condition unit implemented top air supply mode. The research outcomes can be useful to optimize air-conditioning flow and reduce the contagion risk in high-speed trains and other public transport environments with similar air supply strategies.

Bacterial Communities in Various Parts of Air-Conditioning Units in 17 Japanese Houses.

HVAC systems have a significant impact on the indoor environment, and microbial contamination in HVAC systems has a significant effect on the indoor air quality. In this study, to gain a better understanding of the microbial contamination inside ACs, we used NGS to analyze the 16S rRNA gene of bacteria adhering to AC filters, cooling coils, fans, and air outlet surfaces. The five phyla in terms of the highest relative abundance were Proteobacteria, Firmicutes, Actinobacteria, Cyanobacteria, and Bacteroidetes. The surface of an AC filter provides a history of indoor airborne bacterial contamination, and of the 10 bacterial genera we detected with the highest abundance (in the following order: Pseudomonas > Staphylococcus > Paracoccus > Corynebacterium > Acinetobacter > Streptococcus > Methylobacterium > Enhydrobacter > Sphingomonas > Actinotignum) on the filter surface, the top 6 genera were Gram-negative bacteria. Furthermore, the seventh-most abundant genus adhering to the filter surface (Methylobacterium) was the second-most abundant genus on the cooling coil and fan, and the ninth-most abundant genus on the air filter (Sphingomonas) was the third-most abundant genus on the cooling coil. Various factors impact the bacterial flora inside AC units, including the location of the house, AC unit usage, and occupant activity.

Study of the efficiency of heating, ventilation and air conditioning units for electric trucks and buses in Russian climatic conditions

In this paper, a study was made of the thermodynamic efficiency of the cycles of heating, ventilation and air conditioning (HVAC) installations, depending on the seasonal modes of operation of electric vehicles, both in the heating mode in winter and in the air conditioning mode in summer, using freons R134A, R-290, R404a, R407C, R410a, R502, R507a, R-744, R1234YF. Keywords: air conditioning, heating, vapor compression refrigeration, HVAC, efficiency, freon, electric heavy duty vehicle, electric bus

Improving Energy Management through Demand Response Programs for Low-Rise University Buildings

Recently, energy costs have increased significantly, and energy savings have become more important, leading to the use of different patterns to align with the characteristics of demand-side load. This paper focused on the energy management of low-rise university buildings, examining the demand response related to air conditioning and lighting by measuring the main parameters and characteristics and collecting and managing the data from these parameters and characteristics. This system seeks to control and communicate with the aim of reducing the amount of peak energy using a digital power meter installed inside the main distribution unit, with an RS-485 communication port connected to a data converter and then displayed on a computer screen. The demand response and time response were managed by power management software and an optimization model control algorithm based on using a split type of air conditioning unit. This unit had the highest energy consumption in the building as it works to provide a comfortable environment based on the temperatures inside and outside the building. There was a renewable energy source that compensated for energy usage to decrease the peak load curve when the demand was highest, mostly during business hours. An external power source providing 20 kWh of solar power was connected to an inverter and feeds power into each phase of the main distribution. This was controlled by an energy power management program using a demand response algorithm. After applying real-time intelligent control demand-side management, the efficient system presented in this research could generate energy savings of 25% based on AC control of the lighting system. A comparison of the key system parameters shows the decrease in power energy due to the use of renewable energy and the room temperature control using a combination of split-type air conditioning.

Boosting the air conditioning unit performance using phase change material: Impact of system configuration

Boosting the energy efficiency of air conditioning (AC) systems will considerably impact on lowering domestic power consumption. Innovative methods are being developed to enhance AC performance. One promising method involves integrating phase change materials (PCM) with the AC systems. The significant PCM charging period is a primary limitation of coupling AC systems with PCM in the previous research. The current study aims to investigate the impact of coupling an AC unit with various PCM container configurations (e.g., parallel plates, staggered and aligned tubes, and elliptical tubes) on PCM charging and discharging, and AC performance. During the nighttime, the low ambient temperature is charged inside the PCMs. Then, during the daytime, the hot ambient air is cooled by passing through the cold PCM heat exchanger before passing over the unit condenser. A complete dynamic mathematical model for the proposed system is constructed and solved numerically using ANSYS software. Results indicate that applying the cylindrical arrangement lowers the solidification time of the PCM at night by approximately one-third compared to the plate arrangement. Also, raising the inflow air temperature of the air-PCM heat exchanger increases the air temperature difference through the heat exchanger and saving percentage of the AC's power and decreases the PCM's charging and discharging time. For inflow air temperatures of 318.15 K, 313.15 K, and 308.15 K, the maximum average percentage of saved power is around 25 %, 18.7 %, and 12.5 %, respectively for 2 h working and around 8.4 %, 7.2 %, and 6.3 %, respectively for 8 h working of the AC unit. Cylindrical configuration is preferable for daily use of AC systems as the charging process can be achieved through the nighttime.

COMPARISON OF INITIAL CLIMATIC INFORMATION FOR CALCULATIONS OF SEASONAL ENERGY CONSUMPTION BY AIR CONDITIONING UNITS

In order to calculate seasonal energy consumption for processing in air conditioning units, the initial climatic information shall contain data on the distribution of outdoor air temperature and humidity over time. The article compares the completeness of the coverage of outdoor air parameters for the Moscow construction area in two climatic models: probabilistic - statistical and climatic curve. The article provides a comparison in the repeatability of the temperature and relative humidity of the outside air for the two mentioned models, as well as for the probabilistic - statistical model built on data from different years. In addition, a comparison of the consumption of heat, water and electricity obtained using the models under consideration for the three summer months is given.

Modeling investigation for energy storage system including mixture of paraffin and ZnO nano-powders considering porous media

In this work, air conditioning unit with involve of porous media has been presented. The duct has several five-lobed cylinders containing the paraffin (RT27) and for augmenting the conductivity of such material, it was mixed with nano-sized particles of ZnO. To include the related terms of porous media, wiremesh approach was applied and turbulent regime for air zone was considered. Owing to solar irradiation, air becomes warmer up to T = 311.15K outside the duct and with entering within the duct makes paraffin to convert to liquid. So, not only the solar energy can be stored, but also the needed cool air inside the building can be provided. Mixing nanoparticles with paraffin leads to higher level of conduction which decline the required time for full melting about 5.22% when Re = 7000, γ = 0.95. With utilizing porous media, the needed time will be decreased about 37.15% when Re = 7000, φ = 0.035. As power of blower augments, the period of melting decreases around 41.77% when γ = 0.95, φ = 0.035. Among the scrutinized cases, the minimum required time for achieving full melting is 7985s which can be attained if γ = 0.95, φ = 0.035, Re = 7000.

Design on intermittent ventilation strategy for radon removal in underground space

Ventilation to reduce radon was one of the most widely used, important, and effective means to reduce radon concentration in underground engineering. The largest energy consumption of underground buildings was the building ventilation system. Taking the radon migration process in a room as an example, this paper built a numerical model that accounted for the mechanism of radon production, exhalation, and diffusion process, by proposing a novel intermittent ventilation strategy to mitigate radon concentration in underground space. Three ventilation strategies (no ventilation, continuous ventilation, and intermittent ventilation) were compared under various wind speeds and fresh air ratios. Under the same safe duration of radon concentration, when intermittent ventilation was operated with the same wind speed, the startup time was reduced by 79.4%, 86.0%, 90.8%, 92.8%, 91.25%, with compared with continuous ventilation. The higher the fresh air ratio, the lower the radon concentration limit, and the faster the dynamic equilibrium state of radon concentration will be reached. During intermittent ventilation, reducing the fresh air ratio can greatly increase the recovery and utilization of the return air heat, thereby reducing the power of the air conditioning unit. Considering the comprehensive energy-saving benefits of the ventilation system, the appropriate intermittent ventilation plan should be made to meet radon reduction requirements in the range of low wind speed. If low wind speed was selected, there existed advantages of low ventilation noise and more comfortable, as well.

Hybrid liquid desiccant air-conditioning system with a direct expansion evaporative cooler

There is a need to control air temperature and humidity in humid regions, especially when fresh air is demanded. This study investigates the performance of a hybrid liquid desiccant (LD) air-conditioning system with a direct expansion (DX) evaporative cooler. Temperature, relative humidity, and power consumption were measured and reported using a wireless data-logging system at the air conditioning unit's key locations. The results showed that the hybrid unit reached a 34 % saving in the cooling load. In addition, the air hybrid liquid desiccant air-conditioning system with the direct expansion evaporative cooler saved about 32% in power consumption, compared to an uncooled desiccant air conditioning system that saved 23%.

Vulnerable, Resilient, or Both? A Qualitative Study of Adaptation Resources and Behaviors to Heat Waves and Health Outcomes of Low-Income Residents of Urban Heat Islands.

Little is known of how low-income residents of urban heat islands engage their knowledge, attitudes, behaviors, and resources to mitigate the health impacts of heat waves. In this qualitative study, we conducted semi-structured interviews with 40 adults in two such neighborhoods in Los Angeles California to explore their adaptation resources and behaviors, the impacts of heat waves on physical and mental health, and threat assessments of future heat waves. Eighty percent of participants received advanced warning of heat waves from television news and social media. The most common resource was air conditioning (AC) units or fans. However, one-third of participants lacked AC, and many of those with AC engaged in limited use due primarily to the high cost of electricity. Adaptation behaviors include staying hydrated, remaining indoors or going to cooler locations, reducing energy usage, and consuming certain foods and drinks. Most of the participants reported some physical or mental health problem or symptom during heat waves, suggesting vulnerability to heat waves. Almost all participants asserted that heat waves were likely to increase in frequency and intensity with adverse health effects for vulnerable populations. Despite limited resources, low-income residents of urban heat islands utilize a wide range of behaviors to minimize the severity of health impacts, suggesting they are both vulnerable and resilient to heat waves.

Performance Analysis of Evaporation and Heat Wheel-Based Building Air Conditioning Systems

Abstract Air conditioning in composite weather is relatively more challenging and also carries importance as it resembles conditions of hot-dry, cold, and warm-humid climates. Bifurcation of cooling and ventilation tasks happens to be one of the attractive techniques to design energy-efficient air-conditioning systems. It deals with the concept of providing a dedicated outdoor air system (DOAS) in conjunction with the air-conditioning unit. This study establishes the electrical energy consumption behavior of a building air-conditioning unit when modifications are done along the air pathway of the desiccant-integrated DOAS. For a 511 m2 building situated in composite weather, simulations in energyplus are carried out after necessary validations with the available standards. Here, two modes are discussed: in the first one, an indirect evaporation cooler (IEC)-based system is analyzed, while in the second mode, a heat wheel has been studied. For regeneration, a solar collector and supplementary electrical heater are provided. For the dynamic pattern of site environmental conditions, variations of room air temperature, humidity, thermal load, electricity, thermal energy, and solar fraction have been studied. Current analysis demonstrates that approximately 2994 kWh of the total thermal energy delivered by solar collector and supplementary electrical heater system can be saved through heat wheel instead of IEC. The usage of a heat wheel in the airflow pathway of the desiccant-integrated DOAS can offer energy savings up to 5.04% of the electrical energy with respect to IEC-integrated DOAS. Furthermore, the suggested design delivers a higher solar fraction.

Phase change material based thermal energy storage applications for air conditioning: Review

• Application of PCM TES for indoor environment control is presented. • From assessments made, 5% energy savings can be achieved by using PCM TES. • PCMs integration in AC unit enhance its coefficient of performance by ∼ 1.8% least. • Optimized PCM TES units can reduce CO 2 emissions by 30%. Phase change material thermal energy storage is a potent solution for energy savings in air conditioning applications. Wherefore thermal comfort is an essential aspect of the human life, air conditioning energy usages have soared significantly due to extreme climates, population growth and rising of living standards. Resultantly research efforts have shown increasing innovation towards the integration of phase change material based thermal energy storage technology with space heating/cooling systems to achieve significant savings. The review therefore focuses on the previous published experimental and theoretical works to organize these important milestones, analyze energy saving avenues as well as giving highlights on best practices and widely accepted techniques and recommendations for all reviewed studies to achieve cost cutting but accurate results. It also discusses the useful enhancements that can be implemented for optimum performance of the PCMs. The reviewed potential benefits of PCMs integration in air conditioning units include enhancements in the coefficient of performance by ∼1.8% at minimum, at least 5% energy savings and estimated reduction of CO 2 emissions by about 30%.

Using Fire Dynamics Simulator to reconstruct a fire scene in a hospital-based long-term care facility

This study conducted a fire scene reconstruction on the seventh floor of a long-term care facility in a hospital in New Taipei City, Taiwan, using the Fire Dynamics Simulator software tool and applying computational fluid dynamics. The location of the point of origin and the cause of fire was determined based on the fire scene investigation and an official fire investigation report. Through a computer simulation, this study revealed that if a partition wall inside a room was not fully attached to the upper floor, or no fire protection stuffing was employed in the through-penetrations and construction openings inside a partition wall, thick smoke would diffuse and spread through these channels. Its flow would be accelerated by the self-contained air-conditioning unit in each room. In the rooms that were on fire, thick smoke entered from above the decorative ceiling through a return air vent, and it was then absorbed by a self-contained air-conditioning unit before exiting through an air outlet and channeled to other rooms, which complicated the evacuation of the persons in the affected rooms. On the basis of an analysis of the blaze and the flow of smoke layers, the recommended emergency egress time for rooms on fire (A = 35.13 m2, H = 2.8 m) was 179 s after fire occurrence. Even if the doors of a room on fire were closed, thick smoke still traveled to other rooms through air inlets, return air vents, and the compartment above the decorative ceiling that was not connected to the actual ceiling. The mortality rate of the residents who failed to evacuate in time increased due to the inhalation of excessive thick smoke. Therefore, responders should shut the doors of each room after completing an evacuation. In addition, the various aspects of the overall building structure, partition walls that connect to the ceiling, fire safety equipment, thorough implementation of educational training, and fire risk management should be considered.

Emulator-type load-based tests for dynamic performance characterization of air conditioners

Current air-conditioning performance evaluation procedures are based on experimental tests conducted at a fixed compressor speed while deactivating the native control system to simplify data acquisition and ensure reproducibility of the results. Conversely, the actual operation of air conditioners responds to thermal loads with variable or cyclic modulations of the compressor speed and expansion valve opening according to the native control system.This study aimed to establish a new reproducible and representative methodology for evaluating the dynamic performance of air conditioners. The developed emulator-type dynamic performance testing facility features hybrid characteristics consisting of an emulator, which is used to simulate the dynamic response of indoor and outdoor environments, and the hardware of a testing facility for performance measurement. This study demonstrates the integrity of the constructed testing facility and the ability of the emulator-type testing methodology to determine the dynamic performance of an air conditioning unit using its native control system, in response to variations in the room-side environment.

Experimental Study of a Heat Pump Clothes Dryer Using Air-Conditioner’s Waste Heat

The urbanised living in Malaysia is progressing toward having clothes dryers as essential household equipment. The major problems with the commercially available clothes dryer are the high-power consumption and the possible damage to the environment. This study aims to mitigate these issues with an eco-friendly heat pump clothes dryer. The heat pump principle is derived based on the waste heat from the condenser side of the indoor air conditioner units. The study analyses the feasibility and potential of a heat pump clothes dryer replacing the available clothes drying methods. A small-scale clothes dryer was fabricated using low-cost materials, and the air properties were measured to assess the shift in the drying process. The fabricated prototype can dry faster by approximately 3 hours than outdoor drying at the balcony. This moderate drying is gentle on clothes compared to commercial high-temperature dryers. The study also indicates the impact of temperature settings of the air conditioner on the drying time of clothes. The heat pump dryer can dry up to 1.5 kg of clothes in 3 hours using a portable air conditioner with a power rating of 1.5 HP. It is found from a simple cost analysis that implementing the heat pump clothes dryer can significantly reduce the equipment and electricity cost of the household

Air quality and thermal comfort management for energy-efficient large public buildings

Maximizing indoor comfort while minimizing energy costs has been a challenging problem for building management systems. This problem is significantly exacerbated for large public buildings with varying occupancy levels. A practical approach to measure occupants’ comfort has been to evaluate the indoor thermal comfort using Fanger’s Predictive Mean Vote (PMV) model, parameterized by the ambient temperature and Relative Humidity (RH). Such an approach is, however, one dimensional and does not consider other possible sources of discomfort like indoor air quality. Interestingly, the ambient temperature and RH, in addition to thermal comfort, also influence the amount of emissions from indoor furnishings, which is a prime source of indoor air quality degradation. Taking this into account, in this paper, we adapt the definition of comfort to include indoor air quality as well. Since occupancy levels, occupants’ activities and outdoor temperature vary with time, one way to achieve desired comfort goals is to continuously adapt the settings of Heating, Ventilation, and Air Conditioning (HVAC) units in buildings. Such a continuous adaptation results in significant energy costs, especially in geographical locations where outdoor temperatures can be significantly higher/lower than desired indoor temperatures. In this context, we propose a location-aware multi-objective optimization model for indoor comfort and energy cost management. We combine conflicting objectives—improving air quality and thermal comforts, and minimizing energy cost—to determine cost-driven, comfort-driven and Pareto optimal solutions using Multi-Objective Genetic Algorithm (MOGA). The proposed model is envisioned to enable building operators to determine suitable temperature and RH as per occupants’ requirement. The solution can be personalized based on the building structure and macro- and micro-location parameters. To ease configuration and customization of our model based on building- and geography-specific settings, we also present a MATLAB-based GUI that operators can leverage to understand the comfort-cost trade-off for buildings.

Production of high-quality drinking water from chillers and air conditioning units’ condensates using UV/GAC/MF/NF hybrid system

In hot and humid regions, like the Middle East nations, where access to drinking water is minimal, water recycling and purification are essential. In this work, high-quality drinking water was produced by treating the condensates obtained from the air conditioning units. A membrane-based hybrid system consisting of ultraviolet irradiation, granular activated carbon, microfiltration, and nanofiltration membranes (UV/GAC/MF/NF) was applied in series to minimize the NF membrane fouling and enhance the product water quality. The microbial, organic, and ionic species of the feed and the product water were analyzed, and the target was defined to maximize the permeate flux (JV) and minimize the concentration of the organic matter in the product water (CODP). The effects of trans-membrane pressure (TMP, 2–5 bar) and feed flow rate (QF, 340–510 L h−1) on the target parameters were investigated through the Taguchi design of experiments and the ANOVA method. The obtained results showed that at the optimum conditions, almost a complete reduction of TDS (>98.37%), of COD (>97.87%), of BOD5 (>96.04%), of the total and digestive coliforms (100%), and turbidity (91.06%) were achieved. Additionally, it was found that the TMP and the QF were the most influential parameters on JV and CODP, respectively. The product water analysis at different stage cuts showed that the hybrid system is capable of recovering more than 97% of the feed water while the TDS, BOD5, and turbidity of the product water are only 2.58 ppm, 2.62 mg. L−1, and 0.22 NTU, respectively.