Air Conditioning Plant Research Articles

Performance evaluation of solar-activated integrated double-stage water desalination and air conditioning plant

The condenser's rejected heat in a vapour compression refrigeration system when thrown into the surrounding air results in its thermal pollution and gets wasted, while it has the potential to be recovered. Another major targeted concern is freshwater scarcity which is faced by the population in many areas. Addressing these difficulties, a double-stage integrated humidification-dehumidification and air conditioning system that recovers the condenser's waste heat and is assembled in a novel duct architecture is proposed. The obtained results of the developed model are established using the experimental data. The analysis explores the outcomes of the integrated system and investigates the influences of saline water temperature, humidifier efficiency, ambient temperature, and relative humidity on the output and performance metrics. The system provides air conditioning of 31.410 kJ and desalination of 65.020 mL from a unit volume of air using 0.661 kW of power and mitigates the environmental impact of existing technology. The coefficient of energy performance, cooling performance, gained output ratio, and exergy efficiency at the specified working situations are 0.958, 1.320, 6.809, and 2.701 %, respectively. A litre of freshwater costs $ 0.0068486.

Numerical and experimental investigation of laminar and turbulent convective heat transfer in a coiled flow reverser with twisted tape insert

This paper presents a comprehensive investigation of heat transfer enhancement and pressure drop in a Coiled Flow Reverser (CFR) with a twisted tape insert. Both laminar (10 < Re < 2000) and turbulent (12,000 < Re < 18,000) regimes have been studied using both experimental and numerical methods. The effects of twist ratio of twisted tape, inlet Reynolds number, and perforating the twisted tapes have been investigated. The study found that the best performance in the laminar regime is achieved with a twisted tape with a twist ratio of 15.73 and no holes on it at a Reynolds number of 2000. In the turbulent regime, the same twisted tape performs the best at a Reynolds number of 17,000. The highest Thermal Performance Ratio (TPR) in laminar regime is 1.55 and in turbulent regime is 0.99. In comparison to the straight pipe, all types of CFRs show better performance in heat transfer enhancement. Also, as the Reynolds number increases, the friction coefficient decreases in all configurations. The study reveals that the twisted tape insert enhances heat transfer performance while increasing pressure drop. This study provides valuable insights into the design and optimization of heat exchangers with CFR. The findings can be used to improve the efficiency and performance of various industrial processes, such as refrigeration systems, air conditioning, and power plants.

Review on Current Application of Microchannel Heat Exchanger

This paper considers various applications of heat exchangers in refrigerators, air conditioning, and nuclear power plants in recent years, current issues and trends, including the required capacity of refrigerator heat exchanger and the corresponding advantages of microchannel heat exchanger, refrigerator application of frost problems, ash problems and improve the performance of the relevant research; Examples of application of microchannel heat exchanger in air conditioning, comparison with traditional heat exchanger, and improvements to problems such as frost, the distribution of fluids, corrosion found in experiments; Study on advantages of compact microchannel heat exchanger in nuclear power plant. The purpose of this paper is to fill the gap in the application of microchannel heat exchanger and provide reference for future research.

Determining Regression Models for Photosynthesis and Stomatal Resistance as Affected by Temperature and Light Intensity in Tomato (Lycopersicon Esculentum Mill.) and Eggplant (Solanum Melongena L.) Grown in Glasshouses

This study was carried out to examine the relationships between net leaf photosynthesis and temperature and light intensity, between stomatal resistance and temperature and light intensity in tomato and aubergine grown with a range temperature from 10 to 30 °C and different light intensities from 3 to 7 MJm-2 d-1. The study was carried out in a six-compartment greenhouse (size 4 m * 8 m), the temperature of which can be controlled by air conditioning, on tomato and eggplant plants. Each of the six greenhouse compartments was set to have maximum temperatures of 10, 12, 16, 18, 20 and 24 °C. Commercial varieties named "Counter" for tomato and "Bonica" for eggplant were used. "Fisons M2" commercial compost was used in all growing media and nutrient was applied equally. In the study, different sowing and planting dates were applied to benefit from natural light conditions (between 3 and 7 MJm-2d-1). Average temperature in each compartment was recorded using a 'Combine' data logger at 15 minute intervals. A porometer (Delta-T device, MT -3) was used to measure the stomatal resistance of tomato and eggplant leaves. The stomatal resistance measurements of the plants were made at the same time of the day (between 11.00-13.00) at 15-day intervals at the top, middle and lower levels of the crown of four different plants in different environmental conditions. In tomato, leaf photosynthesis increased curvilinearly with temperatures up to about 20.5 °C at low light intensity and declined at higher temperatures. The highest photosynthesis was obtained from the plants grown at a temperature of 22.5 °C and 7 MJm-2d-1 light intensity. The lowest photosynthesis was at 10 °C and 3 MJm-2d-1. In aubergine, at low light intensities, net photosynthesis increased curvilinearly up to 23 °C while it increased up to 20 °C at high light intensities and declined at higher temperatures. Maximum net leaf photosynthesis was found to be greater in tomato than aubergine.

Air to Water Generator Integrated System Real Application: A Study Case in a Worker Village in United Arab Emirates

The water crisis is currently affecting billions of people. To mitigate the issue, unconventional water sources should be taken into account. Among them, atmosphere is a promising possibility, but it is still considered a novel source, and more studies, based on real results concerning the behaviour of the Atmospheric/Air-to Water Generator (AWG) systems, also known as Atmospheric Water Harvesting (AWH) systems, are needed to prove the water extraction sustainability. The current research work describes the real application of an integrated AWG system, based on a thermodynamic reverse cycle, designed to extract water from air and take advantage of the other useful effects of the cycle at the same time. The integrated machine was placed in Dubai, in a worker village, and tested. The machine is able to provide, at the same time, with the same energy consumption, water, heating and cooling energy. On the basis of onsite measurements, calculations about the efficiencies, using the Water Energy Transformation (WET), plastic savings, due to bottled water avoidance, and economic sustainability were carried out. The work answers to research questions concerning the potentiality of integrated systems in Heating Ventilation Air Conditioning (HVAC) plants revamping, the economic sustainability of water extraction from air and the lack of tests on real AWG machines of thousand-litre production capability (large size).

The Design of Wheat Warehouse: Ventilation System Design and Unit Price Analysis-II

Havalandırma, depolanan tahılın korunması için yaygın olarak kullanılan bir yöntemdir. Bu teknoloji, ürün depolama yapısının mikro iklimini değiştirmek; tahılda zararlı organizmaların gelişmesi için elverişsiz tahıl kalitesinin sürekli korunması için uygun koşullar yaratmak için kullanılır. Mevcut durumda yapılmış olan depoların eksiklikleri göz önünde bulundurularak buğday ürünü için 1500 ton depolama kapasitesine sahip yatay bir betonarme deponun teknik verilere uygun şekilde havalandırma sisteminin tasarlanması ve yaklaşık maliyetinin belirlenmesi amaçlanmıştır. Çalışma sonucunda emniyetli ve güvenli bir depolama için depo ortam sıcaklığının optimum durumda sağlanabilmesi için 73164.99 W’ lık toplam ısı ihtiyacı belirlenmiştir. Toplam soğutma ihtiyacı ise 105157.42 W olarak hesaplanmıştır. Projelemesi yapılan buğday deposunun 2022 yılına ait birim fiyatlarına göre KDV dahil yaklaşık Mekanik sistem (havalandırma, klima santrali ve otomasyon) maliyeti 586052.90 ₺, Elektrik tesisatı yaklaşık maliyeti 195145.39 ₺, İnşaat yapı elemanları yaklaşık maliyeti 2334272.79 ₺ olmak üzere toplam yaklaşık maliyeti 3115471.08 ₺ olarak belirlenmiştir.

Virtual temperature sensor using Support Vector Machines for autonomous uninterrupted automotive HVAC systems control

This paper presents the design and application of a virtual sensor used in case of failure of the main physical sensor for temperature readings in automotive air conditioning. Using auxiliary temperature and pressure physical sensors combined with Support Vector Machine (SVM) Regression, the model of the virtual sensor is derived and prepared to be used as a redundant sensor until the broken physical sensor maintenance. Thus, enabling the system to operate continuously and maintaining its original power and thermal comfort features until the physical sensor replacement. In total, 32 h of training and test data involving different environmental conditions were used to generate the model that was further integrated. The designed virtual sensor presented a Mean Square Error (MSE) of 1,3oC, a Mean Absolute Percentage Error (MAPE) of 3,6%, and a Pearson Correlation Coefficient of 0,90. The results enabled the continuous and autonomous operation of the air conditioning plant respecting the designed thermal comfort guidelines even when under the physical sensor failure condition.

A Preliminary Assessment of Size-Fractionated Microplastics in Indoor Aerosol-Kuwait's Baseline.

The omnipresence of microplastic (MP) in various environmental samples, including aerosols, has raised public health concerns; however, there is presently very limited information on MPs in indoor aerosol. This paper presents a unique dataset where smaller MPs have been sampled using a six-stage cascade impactor from indoor environments in Kuwait. The MP concentration in the indoor air varied between 3.2 and 27.1 particles m−3, and the relative MP concentration decreased linearly from the lowest to the highest size fraction. A significant effect of location was observed for the total number of MPs (F2,14 = 5.80, p = 0.02) and the inhalable fraction (F2,14 = 8.38, p = 0.005), while location had no effect on the respirable fraction (F2,14 = 0.54, p = 0.60). A significant effect of the type of air conditioning used was also observed for the total number of MPs (F2,19 = 5.58, p = 0.01) and the inhalable fraction (F2,19 = 6.45, p = 0.008), while location had no effect on the respirable fraction (F2,19 = 1.30, p = 0.30). For the total number of MPs and the inhalable fraction, the concentration was significantly higher for the split unit air-conditioning as compared to the central air-conditioning plants. The presence/absence of carpets had no significant effect on the MP concentrations (total: F1,19 = 4.08, p = 0.06; inhalable: F1,19 = 3.03, p = 0.10; respirable: F1,19 = 4.27, p = 0.05). The shape was dominantly fibers, with few fragments in lower size fractions. These datasets represent the first baseline information for Kuwait, and the smaller MPs in all the samples further underscore the need to develop standardized protocols of MP collection in the ≤2.5 µm fraction that can have more conspicuous health implications.

Fifteen years of research in innovative heating, ventilation and air conditioning plants at the Department of Management and Engineering (University of Padova)

At the Department of Management and Engineering (DTG) of the University of Padova (Italy), the research team led by Prof. Renato Lazzarin, formed by the authors, worked during the first fifteen years of the millennium on different topics focused on innovative heating, ventilation and air conditioning technologies. Both experimental and theoretical/modelling studies were carried out: an air conditioning system with liquid desiccant operating for annual climatization was designed, realized, and tested; a self-regenerating liquid desiccant cooling system based on an electric heat pump was installed and monitored in a new building of the Vicenza Hospital for dehumidification, heating and cooling; a gas engine heat pump plant for the air conditioning of a building of the DTG was designed, realized, and monitored for a long period; a multisource heat pump plant was modelled and dynamically simulated, and then realized and monitored for the climatization of a school building; hybrid water/phase change materials tanks were modelled, designed and tested for thermal energy storage; finally, thermal and electric solar cooling plants were modelled and dynamically simulated for evaluating energy performance. The paper highlights the main theoretical and experimental approaches and the results of the research during the fifteen-year period.

Thermodynamic and hydraulic design characteristics of the fin tube heat exchanger

Heat exchangers are crucial devices that are used to exchange heat between two different fluids: one that is hot and one that is cold. Amongst them, finned tube heat exchangers play a vital role in today’s thermal industry. Due to the increased surface area of the tubes' outer surface (or fins) when utilizing finned tube heat exchangers, the heat transfer rate may be improved as a consequence of the increased surface area of the fins. It is often referred to as a compact heat exchanger in order to highlight the comparatively large heat transfer surface area to volume ratio of the exchanger. They have many vital applications in the field of refrigeration, air conditioning, IC engines, and power plants. The fin and tube heat exchanger has been analyzed for three different cases in the present study: preheater, condenser, and evaporator. The Engineering Equation Solver (EES) software has been used to analyze the heat exchanger for the various thermal, hydrodynamic, and design parameters. Results have been plotted by comparing the various thermal parameters such as overall and inside heat transfer coefficient, Nusselt number, and rate of heat transfer with respect to Reynolds number. Similarly, the hydrodynamic parameters such as Colburn factor, friction factor, and the design parameters such as the number of fins and fin spacing.

Bayesian optimization with reference models: A case study in MPC for HVAC central plants

We present a framework for exploiting reference models in Bayesian optimization (BO). Our approach is motivated by a model predictive control (MPC) tuning application for central heating, ventilation, and air conditioning (HVAC) plants. Evaluating the closed-loop performance of MPC by trial-and-error is time-consuming (e.g., a closed-loop simulation can involve solving thousands of optimization problems). The BO algorithm can accelerate this process by treating the functional relationship between the closed-loop performance of MPC and its tuning parameters (e.g., constraint back off terms and objective weights) as a black-box model and by systematically navigating the parameter space to maximize MPC performance. Traditional BO algorithms have been recently developed to tune controllers but such frameworks tend not to use pre-existing (prior) system information. In this work, we propose to incorporate such information in the form of reference models and we show that such models can be constructed in creative ways. Specifically, we propose to construct a reference model by evaluating the closed-loop performance of a low-complexity MPC controller. We show that the use of a reference model changes the goal of BO from learning the objective function to learning the residual function (error between the reference and the objective function), which is a much easier task. Specifically, we show that the use of a reference model can help BO to more judiciously sample the parameter estimate and more rapidly discover regions where the solution exists. This feature significantly reduces the number of function evaluations and can help avoid getting stuck in local minima. The effectiveness of our BO framework is demonstrated using a central HVAC plant study with realistic data. The reference model is built by training a kriging model based on data collected for 21 low-fidelity, closed-loop MPC simulations. Using this reference model, we show that our BO method can find the optimal constraint back-off terms within 3 high-fidelity, closed-loop simulations (total computation time of 20 h). In contrast, a traditional BO approach without a reference model requires 14 high-fidelity, closed simulations (total time of 28 h). Our approach thus reduces the computational time by 28%.

IoT Open-Source Architecture for the Maintenance of Building Facilities

The introduction of the Internet of Things (IoT) in the construction industry is evolving facility maintenance (FM) towards predictive maintenance development. Predictive maintenance of building facilities requires continuously updated data on construction components to be acquired through integrated sensors. The main challenges in developing predictive maintenance tools for building facilities is IoT integration, IoT data visualization on the building 3D model and implementation of maintenance management system on the IoT and building information modeling (BIM). The current 3D building models do not fully interact with IoT building facilities data. Data integration in BIM is challenging. The research aims to integrate IoT alert systems with BIM models to monitor building facilities during the operational phase and to visualize building facilities’ conditions virtually. To provide efficient maintenance services for building facilities this research proposes an integration of a digital framework based on IoT and BIM platforms. Sensors applied in the building systems and IoT technology on a cloud platform with opensource tools and standards enable monitoring of real-time operation and detecting of different kinds of faults in case of malfunction or failure, therefore sending alerts to facility managers and operators. Proposed preventive maintenance methodology applied on a proof-of-concept heating, ventilation and air conditioning (HVAC) plant adopts open source IoT sensor networks. The results show that the integrated IoT and BIM dashboard framework and implemented building structures preventive maintenance methodology are applicable and promising. The automated system architecture of building facilities is intended to provide a reliable and practical tool for real-time data acquisition. Analysis and 3D visualization to support intelligent monitoring of the indoor condition in buildings will enable the facility managers to make faster and better decisions and to improve building facilities’ real time monitoring with fallouts on the maintenance timeliness.

Dual dynamic programming for multi-scale mixed-integer MPC

We propose a dual dynamic integer programming (DDIP) framework for solving multi-scale mixed-integer model predictive control (MPC) problems. Such problems arise in applications that involve long horizons and/or fine temporal discretizations as well as mixed-integer states and controls (e.g., scheduling logic and discrete actuators). The approach uses a nested cutting-plane scheme that performs forward and backward sweeps along the time horizon to adaptively approximate cost-to-go functions. The DDIP scheme proposed can handle general MPC formulations with mixed-integer controls and states and can perform forward-backward sweeps over block time partitions. We demonstrate the performance of the proposed scheme by solving mixed-integer MPC problems that arise in the scheduling of central heating, ventilation, and air-conditioning (HVAC) plants. We show that the proposed scheme is scalable and dramatically outperforms state-of-the-art mixed-integer solvers.

Influence of fluence, beam overlap and aging on the wettability of pulsed Nd3+:YAG nanosecond laser-textured Cu and Al sheets

Superhydrophobic and hydrophobic surfaces on Al and Cu have a wide range of applications in electronics, industrial devices, air conditioning, and refrigeration plants, and home appliances due to their excellent electrical and thermal characteristics. In many of these applications, the wettability of their surface is essential. This work presents the fabrication of superhydrophobic and hydrophobic surfaces on Al and hydrophobic surfaces on the Cu metal sheets via laser processing and aging without any additional chemical treatment. Texturing with laser spot overlap is used to generate naturally formed nanoscale textures by scanning the whole sample surface. The influence of laser parameters on the dimension and shape of the fabricated surface textures and their impact on wettability is analyzed along with the evolution of wetting behavior over time. The laser textured surfaces, which are initially hydrophilic, are found to transform hydrophobic over time upon exposure to atmospheric conditions. Experimental evidence using X-ray photoelectron spectroscopy (XPS) and ATR-FTIR spectroscopy corroborates this transition is owing to the adsorption of organic molecules present in ambient. The depth profiling using XPS reveals carbon contamination around 60–70 nm from the sample surface. Furthermore, textures exhibiting static contact angles of up to ~154° have been achieved with Al sheets, whereas contact angles up to ~122° have been attained in the Cu sample. These experimental findings enable control of wettability of Al and Cu sheets through precise tuning of laser parameters for desired properties.

A Scientific Approach of using the DMAIC Methodology to Investigate the Effect of Cutting Tool Life on Product Quality and Process Economics: A Case Study of a Saudi Manufacturing Plant

One of the major priorities for manufacturing companies in the globalized economy is the ability to offer high-quality products to customers at the lowest production cost. Globally, process improvement methods and techniques are used to reduce waste and improve product and service quality. This paper aims to propose a systematic model based on process improvement methodologies and tools to help the manufacturing companies decide on cutting tool life and other manufacturing issues. This research seeks to prove that some common industry practices, such as changing cutting tools in machining processes, can significantly affect the economics of production and the overall performance of the plant. The research is mainly based on analyzing real field data using the DMAIC methodology to identify improvements in order to achieve a balance between economy and quality in a Saudi manufacturing plant. Although the study was concerned only with changing cutting tools in the machining process in an air conditioning plant, its findings and conclusions can be generalized to all manufacturing processes.

Solar Photovoltaic/Thermal Supply for Combined Water and Air Conditioning Plant

Solar Photovoltaic/Thermal Supply for Combined Water and Air Conditioning Plant

Role of Thermal Storage in Distributed Air-Conditioning Plants: Energy and Environmental Analysis

Energy efficiency is becoming a crucial target in the construction of a decarbonized society to guarantee sustainable development and tackle climate change issues. The building sector is one of the major players being responsible for a huge amount of primary energy, mostly related to heating and cooling services. Aside from intervening on the building envelope, intending to reduce energy demand, it is of fundamental importance to consider appropriate air-conditioning systems that can easily integrate renewable sources and rationalize energy use. Heat pumps are an appealing solution because of the renewable energy available in the external sources and because of the possibility to drive them with PV systems. Solar assisted heat pumps have therefore become a promising solution for energy efficiency in buildings, allowing lower primary energy demands and generating lower CO2 emissions. The ulterior integration of thermal storage in the systems allows for a further improvement of energy efficiency. This paper investigates the achievable energy savings after interventions of energy efficiency on a building aggregate composed of four buildings. In particular, two different scenarios of improvement of the HVAC system substituting the existing plant with PV-assisted heat pumps are considered. The performances obtained with the use of single-heat pumps and a centralized one with thermal storage are investigated employing dynamic simulations conducted in the TRNSYS environment.

Performance evaluation of novel solar-powered domestic air cooler with Peltier modules

Shifting of air conditioning and ventilation plants from conventional to renewable energy systems is one of the effective ways to save energy and attain sustainability. In this experimental study, an effort has been made to design, fabricate, and evaluate the cooling performance of a solar-powered domestic air cooler with Peltier plates to meet the comfort criteria as per ASHRAE standards. It also investigates the effect of Peltier modules on the performance of conventional room air cooler. The experiments were conducted in a 12×12 room with one, two, three, and four Peltier modules operating at various ambient temperatures. The experiments were repeated three times at specified conditions. Peltier effect was used to decrease water temperature, and subsequently cooled water was used to decrease the temperature of the air after coming in contact with this water. The cooled air was then used to create a comfort zone. The results indicated a decrease in temperature of the experimental zone by 5 %, 13 %, 19 %, and 23 % using one, two, three, and four Peltier modules respectively. The increase in relative humidity was recorded as 5 % at 27 °C temperature of the experimental zone. The results of energy analysis showed a substantial amount of energy savings in this study and suggest that more than 200 MW energy can be saved by replacing conventional electric air coolers all over the country with proposed Peltier based domestic solar powered air cooler.

The employment of an earth-to-air heat exchanger as pre-treating unit of an air conditioning system for energy saving: A comparison among different worldwide climatic zones

A great fraction (20–40%) of primary energy is required for building air conditioning, so the use of renewable energy sources is increasing. The geothermal energy for Heating, Ventilating and Air Conditioning (HVAC) systems can be used considering an Earth-to-Air Heat eXchanger (EAHX). This work analyses the performance of an EAHX through a mathematical model (2D), as a function of diameter and length of the air ducts. The problem is solved with finite element method. A case study office building is analyzed. The air conditioning plant is characterized by fan-coil units and primary air; the EAHX is positioned upstream the Air Handling Unit (AHU) to pre-cool/pre-heat the air. The building is virtually placed initially in six Italian cities (different climatic zones according to Italian regulation DPR 412/93) and subsequently in eight worldwide cities according to Köppen climate classification. The following parameters are calculated: air temperature variation and thermal efficiency of the EAHX; the decreasing of cooling and heating capacity of the coils into the AHU. The best results refer to a duct length of 100 m for Ottawa (warm-summerhumid continental climate, 65% capacity reduction), the worst ones for Rio de Janeiro (tropical wet and dry climate, maximum 24% reduction).

Performance Indexes of an Air-Water Heat Pump Versus the Capacity Ratio: Analysis by Means of Experimental Data

The spread of near-Zero Energy Buildings (nZEB) involves the employment of high performant air-conditioning plants where renewable sources can be integrated easily. In this context, heat pumps appear as a promising solution given their ability to exploit aerothermal, hydrothermal and geothermal sources and to supply both heating and cooling loads with the same device. In order to evaluate the energy performances in transient conditions, the actual winter (COP) and summer (EER) performance indexes, in the function of the sources’ temperatures and the capacity ratio (CR), have to be available. Nevertheless, heat pump manufactures often provide the trend of the performance indexes in the function of the temperatures of the sources specifically for nominal conditions, whereas the dependence of the performance indexes in the function of CR, that takes into account the part-load operation, is almost always not provided. Alternatively, specific technical standards suggest the use of a correction factor to modify nominal COP and EER for the attainment of the real performance indexes. In this paper, by using data from an experimental set-up equipped with air-water heat pumps, these correlations were tested and tuned. Winter results showed that correction factors suggested by standards have to be modified in the presence of a storage system. In summer, instead, a new correlation was developed to find a function between nominal and actual EERs in the function of CR by exploiting a similar approach employed for the COP calculation.