Top PDF Performance of desiccant enhanced evaporative cooling system based on high-low control

Performance of desiccant enhanced evaporative cooling system based on high-low control

Performance of desiccant enhanced evaporative cooling system based on high-low control

Published: 8 November 2018 Abstract: Desiccant enhanced evaporative cooling system is a sustainable air-conditioning (A/C) system which deals the latent load and sensible load separately by a dehumidifier and an evaporative cooler. A LDD-RIEC system consists of a liquid desiccant dehumidifier (LDD) and a regenerative indirect evaporative cooler (RIEC) were investigated. The LDD-RIEC system is characterized by low energy consumption compared with conventional mechanical cooling system, but the main shortcoming is the high dependency on ambient air conditions. To maintain stable indoor temperature, a control scheme is essential. However, very limited research work regarding control strategy can be found in open literatures. In this paper, a novel controller named high-low (H-L) control is proposed. Multi-speed technology is utilized for primary air fan and secondary air fan operating either at high speed or at low speed. The annual performance of a LDD-RIEC system is simulated in Hong Kong, a typical hot and humid region. The results indicate that H-L control is effective in maintaining stable indoor thermal comfort with temperature fluctuation from 24 °C to 27 °C for 99% of time.
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Experimental Verification of Indirect Evaporative Cooling-Assisted Internally Cooled Liquid Desiccant Dehumidifier

Experimental Verification of Indirect Evaporative Cooling-Assisted Internally Cooled Liquid Desiccant Dehumidifier

Figure 8 shows the overall coefficient of performance of the ICLD used in this study, which was indicated to be from 6.97 to 13.94, which varied based on the difference in working airflow. It can be seen that the AFR of 0.5 resulted in the highest COP value, i.e., 13.94, owing to the relatively high cooling capacity and low electric energy consumption. In these experiments, 40 W capacity pumps were used to maintain a constant mass flow rate of both the desiccant solution and water, and thus the pressure drops in the process and working air channels did not show a significant difference. Thus, the overall COP value depended on the cooling capacity of the ICLD, and showed similar patterns in the results of the cooling capacity.
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Desiccant Enhanced Evaporative Air-Conditioning (DEVap): Evaluation of a New Concept in Ultra Efficient Air Conditioning

Desiccant Enhanced Evaporative Air-Conditioning (DEVap): Evaluation of a New Concept in Ultra Efficient Air Conditioning

DEVap’s thermodynamic potential overcomes many shortcomings of standard refrigeration- based direct expansion cooling. DEVap decouples cooling and dehumidification performance, which results in independent temperature and humidity control. The energy input is largely switched away from electricity to low-grade thermal energy that can be sourced from fuels such as natural gas, waste heat, solar, or biofuels. Thermal energy consumption correlates directly to the humidity level in the operating environment. Modeling at NREL has shown that the yearly combined source energy for the thermal and electrical energy required to operate DEVap is expected to be 30%–90% less than state-of-the-art direct expansion cooling (depending on whether it is applied in a humid or a dry climate). Furthermore, desiccant technology is a new science with unpracticed technology improvements that can reduce energy consumption an additional 50%. And unlike most heating, ventilation, and air-conditioning systems, DEVap uses no environmentally harmful fluids, hydrofluorocarbons, or chlorofluorocarbons; instead, it uses water and concentrated salt water.
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Solar assisted desiccant evaporative cooling system for office buildings in Iran: a yearly simulation model

Solar assisted desiccant evaporative cooling system for office buildings in Iran: a yearly simulation model

Abstract. In this research, the feasibility of solar assisted desiccant evaporative cooling system for oce buildings was studied. An oce building located in Chabahar, Iran, as a high cooling load demanding region, was considered as the case study. Dierent congurations as desiccant-based cooling systems were examined to determine the most appropriate conguration in terms of established indoor air conditions and required cooling energy. The congurations were simulated hourly, and the monthly mean values were determined. TRNSYS software was used for this purpose. The results indicated that the desiccant-based cooling system operating in the recirculation cycle with pre- cooling Cong. E has the potential to keep the indoor air conditions within the standard recommendations. In addition, it was shown that Cong. E is the superior conguration in terms of the energy performance and can meet the cooling energy requirements of the space. The potential for providing the desiccant regeneration heat by the solar energy was also investigated. Three standard solar thermal panels were explored to propose the most proper array plant. The study showed that an array of solar panels, consisting of two rows of four unglazed solar thermal collectors, could meet the heat energy requirement by the regenerating process.
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Experimental Study on the Performance of Cross Flow Regenerator in Liquid Desiccant Cooling System

Experimental Study on the Performance of Cross Flow Regenerator in Liquid Desiccant Cooling System

3.) Hybrid Desiccant System: a hybrid system, the desiccant dehumidifier handles the latent cooling load and VCS/VAS handles the sensible cooling load. In contrast, a hybrid solid desiccant system has to first dehumidify the air in a desiccant wheel and then cool it in a cooling coil. In both the cases the required chemical dehumidification would be less than the stand alone DCS, as no further moisture needs to be added (in an evaporative cooler) to achieve cooling. Further, as the cooling coil is maintained at higher apparatus dew point (ADP) than a standalone VCS, the overall COP is also high. Waste heat from condenser may also be used for regeneration (part or full) of desiccant. So considerable energy savings can be achieved by using these systems instead of conventional systems using refrigerated coils alone, especially for high latent load and low humidity applications.
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Solar pond powered liquid desiccant evaporative cooling

Solar pond powered liquid desiccant evaporative cooling

2.3.1.3 Wetted wall (falling film) column Wetted wall/falling film column arrangements consist of a set of tubes (Fig. 5a) or plates (Fig. 5b) over which desiccant solution flows down by gravity while air is blown through it. The liquid flows as thin film over the vertical surfaces represented by the tubes or plates, and the air is brought into contact with the surface of flowing liquid film. Besides having low pressure drop and low initial cost, these columns also provide large contact surface area per unit volume [56]. However, in practice there is the difficulty of ensuring a thin film over the entire surface, especially for large towers [57, 58]. The measure of the degree of wetness achieved is termed wetness factor or wettability, and can influence the performance of the system. Studies have shown that the wettability can be enhanced using micro/nano scale surface treatment [59]. The experimental study by Kim et.al [59] emphasised that as a result of the improved wettability achieved on roughened tubes, higher heat and mass transfer performances was observed for the roughened tubes (relative to smooth tubes).
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Feasibility of a solar panel-powered liquid desiccant cooling system for greenhouses

Feasibility of a solar panel-powered liquid desiccant cooling system for greenhouses

performance was set against which the proposed system was judged. In Chapter 3 we determined the properties of bitterns and investigated further the concept of using them as liquid desiccants; we showed that bitterns are suitable for greenhouse cooling and that they do have similar physical properties with pure MgCl2 solutions (Lychnos et al, 2010). In Chapters 4 and 5 the essential components of the proposed cooling system i.e. the regenerator and desiccator were designed and constructed and their performance was critically assessed by conducting a series of experiments. The mathematical models developed in the relevant chapters for the regenerator and the desiccator were used in Chapter 6, along with a greenhouse model, to build the whole system model. This enabled us to investigate the performance of the solar powered liquid desiccant cooling system at different locations around the world and thus assess its cooling capacity (Chapter 7). Where the evaporative cooling system failed to produce enough cooling the solar powered liquid desiccant cooling system achieved further cooling which was enough to sustain the greenhouse air temperature below 30 o C thus suggesting that the cultivation period in greenhouses can be extended all year round. However, the best results were achieved when the thickness of the desiccator was increased from 0.1 to 0.2 m, which would increase the cost. It is worth of remark that under hot and dry conditions such as in Muscat the cooling effect drops. This suggests that under extreme high temperatures the system would not be able to generate enough cooling. Although the predicted cooling effect was not quite as good as previously suggested (Davies, 2005) it showed that the proposed system can be an alternative cooling system that improves cooling especially in hot and humid places such as Havana, Chittagong, etc. This research has successfully investigated a solar liquid cooling system for greenhouses which utilises bitterns as desiccants and based on the findings it is suggested that the problem of high temperatures induced in greenhouses during summer in hot and humid places can be addressed.
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PERFORMANCE OF A SOLID DESICCANT BASED EVAPORATIVE COOLING SYSTEM IN WARM AND HUMID CLIMATIC ZONE OF INDIA

PERFORMANCE OF A SOLID DESICCANT BASED EVAPORATIVE COOLING SYSTEM IN WARM AND HUMID CLIMATIC ZONE OF INDIA

Desiccant material is a powerful weapon against moisture and humidity. Moisture presents in air is a serious threat to product integrity in a variety of industries. The property of desiccant material is to absorb moisture from air by creating an area of low vapour pressure at the surface of the desiccant. for absorbing the moisture from air a wheel is used i.e. Desiccant wheel. A Desiccant wheel has honeycomb structure holes for passing humid air. Honeycomb structure is preferred due to low pressure drop of air in the wheel. Fig.1 show a typical desiccant wheel with honeycomb structure. Some common adsorbent materials used are LiCl,SiO 2 (Silica
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Desiccant Cooling System for Thermal Comfort: A Review

Desiccant Cooling System for Thermal Comfort: A Review

The most important concluding remarks in this study are: Some desiccant cooling cycles have been analyzed and suggested a most efficient desiccant cooling cycle for selected climatic conditions. Direct and indirect evaporative cooling methods can be used for different cycles of desiccant cooling system. Many studies emphasized on the optimization of operating parameters and used exergetic manufacturing cost (EMC) method for deciding the minimum regeneration temperature and R/P ratio. The effect of different operating parameters on the performance of desiccant cooling system analysed and presented minimum running cost. Optimum wheel speed of about 17.5 rpm for high moisture removal and maximum COP. The R/P ratio, regeneration temperature, desiccant material, rotation of desiccant wheel, outdoor conditions etc. are the important parameters which affect the performance of desiccant wheel. The operating cost of the desiccant system in summer Italian conditions, interesting saving up to 35% are obtained and reduced thermal cooling power up to 52% and pay back period obtained about 5-7 years. Among the Ventilation, Recirculation and Dunkle cycle, the Dunkle cycle is better for wide range of outdoor conditions. Many studies evaluated the performance of different desiccant material and found the material which has the higher moisture adsorption capacity. Hybrid desiccant cooling system economies 37.5 % electricity power when the process air temperature and relative humidity are maintained at 30 ºC, and 55% respectively. Solar energy may be suitable option for regeneration of desiccant cooling system and it saves the regeneration power. Some studies stressed the energy saving potential by solar assisted desiccant cooling system. Mathematical modeling and simulation study of solar based desiccant cooling system performed by some researchers. A composite wheel can be absorbs more moisture than conventional desiccant wheel with same operating conditions. Compounding of desiccant wheel obtained the greater moisture adsorption rate. Some researchers applied the system in different fields and proved the feasibility of the DCS.
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Overview Of Liquid Desiccant Based Indirect Evaporative Cooling System

Overview Of Liquid Desiccant Based Indirect Evaporative Cooling System

was found that maximum effectiveness between 0.55 and 0.706 with concurrently cooling and without cooling it was 0.38 to 0.55, i.e effectiveness of internally cooled packed bed dehumidifier is larger than adiabatic ones. Yonggao Yin et al. [5] by using LiCl as desiccant studied internally cooled plate fin heat exchanger for dehumidification. The results suggested that plate fin heat exchanger had good cooling performance for the desiccant also low desiccant temperature cause more mass transfer. Improved dehumidification performance can be obtained using simultaneous internal cooling dehumidifier. Yonggao Yin et al. [6], by using LiCl as liquid desiccant investigated internally cooled dehumidifier and heated regenerator. The study shows that internally heated regenerator will avoid dehumidification risk which might happen in adiabatic one, and additionally it might provide higher regeneration potency that the adiabatic one. The internally cooled dehumidifier may also give higher dehumidification performance examination with adiabatic one, but its profit would be not nearly as good as internally heated regenerator. The commonly used liquid desiccants are inorganic salts like lithium chloride (LiCl), lithium bromide (LiBr) and calcium chloride (CaCl2). LiCl and LiBr are strong desiccants than CaCl2. A therotical model was proposed by I.P. Koronaki et al. [7] under the same operating condition for a small counter flow adiabatic dehumidifier. LiCl has the best efficiency, can reduce humidity ratio by 10% compared to LiBr 8% and CaCl2 6%. . For cross flow liquid desiccant dehumidifier C. G. Moon et al. [8], developed new empirical correlation by experimenting dehumidifier with CaCl2 as liquid desiccant. It was found that air flow rate, air humidity ratio, air temperature, solution
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Investigating performance of solid desiccant dehumidification in an evaporative cooling system

Investigating performance of solid desiccant dehumidification in an evaporative cooling system

thermostat for the control of wet and dry bulb temperatures respectively. This system is a suitable alternative to mechanical vapour compression systems and can be efficiently used for air-conditioning applications with fewer power requirements (5). Sultan et al. (2) review of the solid desiccant cooling system showed that at this stage, the actual large size of the system is an obstacle in the way of its acceptance as a technological advantage over alternative vapour compression (VC) system. For example, the Energy Efficiency Ratio (EER) for split and multi-split air conditioners is 2.5 (6) even though this value is still high compared to the coefficient of performance (COP) of DEC system. Dezfouli et al.(7) have reported a COP of 1.06 for two-stage solar desiccant cooling system and Jani et al. (8) have achieved a COP of up to 2.0 for solid desiccant-vapour compression hybrid air-conditioning system, some of the researchers also reported that DEC can be more acceptable for central cooling. At the same time, there is a lack of knowledge and familiarity with desiccant technology amongst designers, developers, architects and end users. As a result, it will be difficult for DEC to expand into the market unless highly efficient desiccant systems are designed and there is a wide acceptance by the end user due to government incentives. For this to happen, there is need for more research into the design of compact and efficient DEC and its performance assessed and quantified. The design should then be validated by the appropriate regulatory body.
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Design of Evaporative Air Cooling System for Seminar Hall

Design of Evaporative Air Cooling System for Seminar Hall

2 INTERNATIONAL JOURNAL OF EMERGING TECHNOLOGY AND ADVANCED ENGINEERING “Design Optimization and Installation of the Evaporative Cooler.”, Md. Almostasim Mahmud, Dr. Md. Alamgir Hossain, M.A.Muktadir : This Evaporative cooling is an environmentally friendly air cooling system that operates using induced processes of heat and mass transfer, where water and air are the working fluids. It consists, specifically, in water evaporation, induced by the passage of an air flow, thus decreasing the air temperature. In Bangladesh, Evaporative cooler is already being used in different industries that is imported from varies countries. But most of the cases these are not efficient due to installation error & lack of adjustment with climate change over the year. Initially this paper presents the construction of an evaporative cooler using a test bench of cooling tower for the air flow and water supply facility where local materials were used as evaporative pad. Afterwards; it presents installation in different situation & adjustment of the cooling units with the climate. It concludes that under proper installation, evaporative cooling system is very cost effective & has a very large potential to propitiate thermal comfort and can still be used as an alternative to conventional systems in regions where the design wet bulb temperature is low.
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Neural Network Based Modeling and Control for a Batch Heating/Cooling Evaporative Crystallization Process

Neural Network Based Modeling and Control for a Batch Heating/Cooling Evaporative Crystallization Process

Normally, a production’s goal is to achieve product properties such as crystal size, purity and crystal size distributions that influence downstream processing operations such as filtering, drying and storage. However, since the batch crystallization process is a high complexity and nonlinear system, the control of this process based on the application of neural network is a significant challenge. For instance, Damour et al [20] presented the implementation of Neural Network Model Predictive Control (NNMPC) for an industrial crystallization process using model-based observers. A neural network model based on the estimates of crystal mass was used as internal model to predict the process output. Besides, their work compared the performances between NNMPC and industrial data from a PID-controlled process. Kittisupakorn et al. [21, 34-36] used neural network as a model in the model predictive control (MPC) algorithm for a steel pickling process. Furthermore, the neural network is incorporated into a model based predictive control technique in many researches [22-24].
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Evaporative Cooling and Humidification

Evaporative Cooling and Humidification

b. What parameters would be affected? The parameters that will be affected will be mass flow rates, temperature and enthalpy. 5. Conclusion The group learned how to use the heat exchanger and the cooling tower. For the entering air, the relative humidity reached its highest value on Trial 4 and remained constant until Trial 6. For the exiting air, the range of the relative humidity is close to each other but did not become constant averaging to 68%. Its highest relative humidity happened in Trial 4 with 70.2%.

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Energy Reduction by Enhanced Evaporative Cooling of Buildings in Martime Climates

Energy Reduction by Enhanced Evaporative Cooling of Buildings in Martime Climates

ABSTRACT Direct cooling of buildings by water evaporation has traditionally been seen as appropriate, only, in dry and arid climates, which experience high levels of wet bulb temperature depression. The technique has generally not been applied in maritime climates where low levels of wet bulb temperature depression are frequently found. However, recent developments in enhancing heat and mass transfer in cooling towers, together with the success of high temperature sensible cooling systems, such as chilled ceiling panels and beams, have prompted a review of the evaporative cooling technique as an effective and low energy means of cooling modern deep plan buildings, in maritime climates. At present, however, there is little in depth research and analysis of the performance, energy efficiency, and availability of this form of cooling in maritime conditions. To address these issues an experimental research programme has been established with a view to demonstrating the potential and optimising the design of this form of cooling under low approach conditions.
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Developing A Multi Water Droplets Evaporative Cooling System

Developing A Multi Water Droplets Evaporative Cooling System

Direct evaporative cooling is known to be the earliest and easiest form of evaporative cooling. This system works in a manner that ambient air flows coming into contact with water which allows the conversion of heat, mainly sensible to heat. Various ways of implementation can be observed across a lengthy timeline for air conditioning purposes such as placing pad with water holding traits as a screen through the flow of air. Direct evaporative coolers maybe classified into two different groups, namely active or passive direct evaporative coolers. They differ mostly in terms of power consumption where active direct evaporative cooler requires electricity for operation while passive direct evaporative coolers does not require power consumption [17].
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Second-law-based performance evaluation of cooling towers and evaporative heat exchangers

Second-law-based performance evaluation of cooling towers and evaporative heat exchangers

Various references [5–9] contain examples that illustrate ap- plication of the second law of thermodynamics to a variety of Heating Ventilating and Air-Conditioning (HVAC) processes. In these references, a ratio of exergy of the products to the ex- ergy supplied was used to measure the second-law efficiency of the processes. This was found to be confusing; for exam- ple, certain quantities were not used in the calculations even though they were contributing to the overall efficiency of the process. Specifically, in the steam-spray humidification process discussed by Wepfer et al. [6], efficiency was seen to be- come negative under certain operating conditions, which will be demonstrated later. Krakow [10] and Kestin [11] used the actual and ideal cycle values to estimate how well the ac- tual cycle approaches a thermodynamic perfection. Akau and Schoenhals [12] described various methods for calculating the second-law efficiency for a heat pump system using water as a heat source and a heat sink. The second-law efficiency was de-
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Solar Assisted Desiccant Cooling System – A Critical Review

Solar Assisted Desiccant Cooling System – A Critical Review

and compared. The outcomes demonstrate that for Kish, this framework indicates high potential for comfort cooling in structures contrasted with different areas in the same climatic zone. It might be concluded that, the execution of desiccant cooling system is very affected by surrounding air moistness proportion. Higher is the ambient air humidity ratio bring down is the COP. [8] Gholamreza Goodarzia et al. (2017) had conducted a performance of a solid desiccant wheel regenerated by waste heat or renewable energy. To remove moisture, solid desiccant wheel innovation shows a energy efficient alternative to traditional systems particularly when solar energy and waste heat come into play. Solid desiccant wheels can be combined with different systems to give provide air quality. Programming gave by Novel Aire Company is utilized to compute outlet ventilates. Utilizing the product, the execution of a rotary dehumidifier is studied based on effective parameters including moisture removal capacity (MRC), sensible coefficient of execution (COPSen), inactive coefficient of execution (COPLat) and total coefficient of execution (COP Total). In addition, affecting factors change as described inlet air temperature between 15 °C to 40 °C, regeneration temperature between 65 °C to 110 °C, humidity ratio between 10 to 20 g/kg, air flow rates between 0.72 Kg/s to 1.28 m/s, and rotational speed of wheel between 10 to 40 RPH. DW programming gave by Novel Aire Company is utilized to investigate desiccant wheel execution in view of various parameters consisting of COPlat, COPsen, COPtotal, and MRC. All influencing factors expect inlet process air temperature have positive relationship with COPs and MRC.
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Low energy, wind catcher assisted indirect-evaporative cooling system for building applications

Low energy, wind catcher assisted indirect-evaporative cooling system for building applications

75$57 . The results obtained from the tests of the three pre 4 prototypes have shown low performance compared to the rating capacity given by their manufacturer of 1kW, 2kW and 3kW for the three units. For instant the rated 2 kW pre 4 prototype unit have produced only one quarter of its rated cooling capacity. This has increased to 830 W (i.e. under half of the rated capacity). Investigations of the design have highlighted a number of possible performance improvements. Among these is the geometry of the PEC core housing, which blocks the air flow. Most of the air recirculates inside the PEC housing with very little leaving at the supply air outlet. The supply fan was installed, a large gap between the fan blades and the PEC casing, causing some air to escape as a result before entering the PEC core. Another factor is the optimum ratio of the water flow to the air flow rates. The water spraying was not sufficient with only part of evaporative media wetted.
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A Review on Potential of Indirect Evaporative Cooling System

A Review on Potential of Indirect Evaporative Cooling System

Sergey Anisimov, et al, [6] presented Numerical study of the Maisotsenko cycle heat and mass exchanger. For numerical model they used Ɛ-NTU method. It is reviewed that wet bulb effectiveness of the mentioned unit is between 94% to 120%. Maximum dew point effectiveness that can be achieved was 88%. Maximum temperature difference that can be obtained was 20 °C and for secondary air stream, maximum humidity ratio difference was 10 g/kg. They also reviewed that the changes of plate and fin material heat conductivity have a very little impact on effectiveness of heat exchanger. Simulations were carried out for heat conductivity between 0.1 to 100 W/m.K and found that heat flux has been changed by only 0.5%. The another study was carried out on inlet temperature keeping other parameters constant and found that as the inlet temperature increases (25 °C to 45 °C) the heat transfer effectiveness increases. Simulations results were also shown that as the channel height increases (2.5mm- 20mm) the effectiveness gradually decreases. The analysis was also carried out for type of surfaces and results were shown that for cooling performances flat channel is more effective than square and triangle channel. For small channel height construction of flat surface heat exchanger is easier and economical compare to triangle and square surfaces.
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