Desiccant Cooling Research Articles

Dynamic Simulation of Desiccant Cooling System with Simultaneously Using Solar and Ground Renewable Energies in Hot-Humid Regions

This paper presents the dynamic operation of a desiccant cooling system combined with solar and ground source energies. Solar energy is used for providing the required energy for regenerating the desiccant wheel, and the ground source heat exchanger is exploited as an air pre-cooling component. The potential of the system in providing thermal comfort is assessed in hot-humid regions. Results reveal that this system is capable of providing thermal comfort in these regions with low-grade regeneration temperatures (lower than 75 ℃). As a new perspective, the maximum value of the desiccant wheel regeneration temperature is controlled. The effect of the desiccant wheel performance and its maximum regeneration temperature is evaluated on the behavior of the system. With results, high performance desiccant wheel increases the provided thermal comfort up to 40% and the contribution of solar energy up to 14% compared with its low performance. Reducing the maximum regeneration temperature to 50 ℃, decreases the achieved thermal comfort to lower than 30%. Ground source heat exchanger enhances the thermal comfort and a specified level of that can be provided with lower regeneration temperatures. The economical assessment shows that in entirely provided thermal comfort conditions by the system, the payback period is calculated to be 8.2 years.

Experimental and Statistical Analysis of Relative Humidity and Temperature of Moist Air in a Flat Plate Multi-Layer Desiccant Cooling System

ABSTRACT Sensible load and latent load are the two main factors for effective space air conditioning. In recent times, for comfort space air conditioning, several efforts have been made to drop the Relative Humidity (RH) and Temperature of the ambient moist air to meet the comfort conditions. In the present work, dehumidification of ambient processed air has been performed using a novel flat plate multi-layer liquid desiccant cooling system to achieve a comfortable environment for human beings. The experimental investigation has been performed to analyze the effects of operating parameters including processed air velocity, desiccant solution flow rates, and its concentration, relative humidity (RH) and temperature (T) of the ambient processed air. Response surface methodology has been implemented to execute the statistical modeling of the RH and T of the processed air during the dehumidification process. Analysis of variance (ANOVA) has been implemented at a confidence interval of 95% of process parameters (processed air velocity, desiccant solution flow rates, and solution concentration) on the responses (RH and T) of the processed air. Finally, few experiments were also performed to validate the developed model. It has been perceived that the value of output parameters decrease with decrease in processed air velocity and increase in solution concentration while these parameters increase with increase in solution flow rates. The results revealed that the relative humidity and temperature of the processed air reduced up to 12.8% (8.73 g/kg as humidity ratio) and 4.1◦C, respectively, in comparison to the inlet air conditions.

Performance Analysis of Hybrid Desiccant Cooling System with Enhanced Dehumidification Capability Using TRNSYS

In a field test of a hybrid desiccant cooling system (HDCS) linked to a gas engine cogeneration system (the latter system is hereafter referred to as the combined heat and power (CHP) system), in the cooling operation mode, the exhaust heat remained and the latent heat removal was insufficient. In this study, the performance of an HDCS was simulated at a humidity ratio of 10 g/kg in conditioned spaces and for an increasing dehumidification capacity of the desiccant rotor. Simulation models of the HDCS linked to the CHP system were based on a transient system simulation tool (TRNSYS). Furthermore, TRNBuild (the TRNSYS Building Model) was used to simulate the three-dimensional structure of cooling spaces and solar lighting conditions. According to the simulation results, when the desiccant capacity increased, the thermal comfort conditions in all three conditioned spaces were sufficiently good. The higher the ambient temperature, the higher the evaporative cooling performance was. The variation in the regeneration heat with the outdoor conditions was the most dominant factor that determined the coefficient of performance (COP). Therefore, the COP was higher under high temperature and dry conditions, resulting in less regeneration heat being required. According to the prediction results, when the dehumidification capacity is sufficiently increased for using more exhaust heat, the overall efficiency of the CHP can be increased while ensuring suitable thermal comfort conditions in the cooling space.

Preparation and Application of UiO-66 in Desiccant-Coated Heat Exchanger-Based Desiccant Cooling Systems

Dehumidification performance of a high-efficient compact desiccant cooling component named desiccant-coated heat exchanger (DCHE) highly depends on coated desiccant materials. Currently, mesoporous...

Experimental Testing of an Indigenous Solar Driven Desiccant Cooling System for Local Conditions of Pakistan

Experimental Testing of an Indigenous Solar Driven Desiccant Cooling System for Local Conditions of Pakistan

Comparative Analysis of Indoor Environmental Control and Thermal Performance of Heat Pump Assisted Desiccant Cooling Systems Under Dynamic Conditions

Comparative Analysis of Indoor Environmental Control and Thermal Performance of Heat Pump Assisted Desiccant Cooling Systems Under Dynamic Conditions

Effect of Evaporator Position on Heat Pump Assisted Solid Desiccant Cooling Systems

The packaged terminal air conditioning with reheat (PTACR) system, as a commonly used dehumidification system, faces the problem of extra energy consumption in the deep-cooling and reheating processes. Therefore, different heat pump assisted hybrid solid desiccant cooling (HPDC) systems were proposed and their characteristics were investigated via EnergyPlus simulations. The system energy efficiency presents an upward trend with the increase in outdoor temperature and humidity. A high-humidity climate leads to the improvement of system performance. The dehumidification performance of the desiccant wheel in the HPDC system declines when outdoor humidity increases. Compared with the PTACR system, the energy consumption of the HPDC system in which the evaporator was placed upstream of the desiccant wheel is reduced by 36%, 66%, and 64%, respectively, under different high-humidity climates. The system maintained the indoor environment within the comfort zone, and eliminated the need for a heat source for desiccant regeneration. In conclusion, the HPDC system is an available alternative that considers both energy consumption and system performance. Placing the evaporator upstream of the desiccant wheel is more advantageous in high-temperature and high-humidity climates.

Effects of Supply Angle on Thermal Environment of Residential Space with Hybrid Desiccant Cooling System for Multi-Room Control

In this study, local measurement and computational fluid dynamics (CFD) were employed to evaluate the thermal comfort in a residential environment where desiccant cooling is performed in an outdoor air condition, which is the typical summer weather in Korea. The desiccant cooling system in the present study has been developed for multi-room control with a hybrid air distribution, whereby mixing and displacement ventilation occur simultaneously. Due to this distribution of air flow, the thermal comfort was changed, and the thermal comfort indicators conflicted. The evaluation indicators included the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) comfort zone, predicted mean vote (PMV), and effective draft temperature (EDT). The dry-bulb temperature displayed a distribution of 26.2–26.8 °C in the cooling spaces, i.e., living room, kitchen, and dining room. When determined based on the standard ASHRAE comfort zone, the space where desiccant cooling takes place entered the comfort zone for summer. Due to the influence of solar radiation, the globe temperature was more than 2 °C higher than the dry-bulb temperature at the window. A difference of up to 6% in humidity was observed locally in the cooling space. In the dining room located along the outlet of the desiccant cooling device, the PMV entered the comfort zone, but was slightly above 1 in the rest of the space. Conversely, as for the EDT, its value was lower than −1.7 in the dining room, but was included in the comfort zone in the rest of the space. By adjusting the discharge angle upward, the PMV and EDT were expected to be more uniform in the cooling space. In particular, the optimum discharge angle obtained was 40° upward from the discharge surface.

A Mathematical Model of Desiccant Wheel in Desiccant Cooling

The desiccant wheel performance of desiccant cooling system components is very important whose function is to regulate air humidity levels as well as to the capability, size and cost of the entire system. Mathematical models for predicting the performance of desiccant wheels in the development of mathematical models is one of the effective methods for analyzing the performance of wheel this moisture-reducing. This mathematical model can also be used in guiding system operation, delivering experimental results and automation in designing this cooling system. The purpose of this paper is to provide an overview of efforts to mathematically model the process of heat transfer and mass transfer that occurs in the moisture-reducing wheel. The desiccant wheel model built here is a gas and solid system including basic principles, heat and mass transfer mechanism and model building. The model is based on ideal assumptions, equations, additional conditions and the method of solution and also the main results. The gas-solid model is a more precise and more complex model than the other models. From these results the evolutionary process of the mathematical model is obtained and the aspects of calculation of pressure loss, air leakage, and optimal rotation speed of the drying wheel / dehumification.

Development and Implementation of Solar Assisted Desiccant Cooling Technology in Developing Countries: A Case of Saudi Arabia

This paper presents a comprehensive overview of the potential and feasibility of using solar thermal cooling systems in the Kingdom of Saudi Arabia (KSA). The performance of a desiccant cooling system has been determined based on climatic data of 32 cities spread all over the territory of the country. The investigation has been carried out keeping in view the high energy consumption for cooling applications in the country. The analysis has been done using the overall performance of the system, sensible energy ratio, and cooling and regeneration loads. The main objective of this study is to encourage the implementation of solar thermal cooling systems in the country for the development of sustainable buildings. The economic analysis shows that thermal cooling technology can reduce the cost of cooling units, remarkably. Furthermore, the utilization of the proposed system will decrease the dependence on primary energy resources. The saving factor of the proposed system with 1 ton capacity in comparison to the conventional vapor compression unit is found to be 34.6%. The present study also recommends that the government subsidies and incentives can further improve the development and utilization of solar air conditioning technology in developing countries.

Application of Liquid Desiccant Cooling Technology in Built Environment: A Review

Application of Liquid Desiccant Cooling Technology in Built Environment: A Review

Performance Enhancement of Hybrid Solid Desiccant Cooling Systems by Integrating Solar Water Collectors in Taiwan

A hybrid solid desiccant cooling system (SDCS), which combines a solid desiccant system and a vapor compression system, is considered to be an excellent alternative for commercial and residential air conditioning systems. In this study, a solar-assisted hybrid SDCS system was developed in which solar-heated water is used as an additional heat source for the regeneration process, in addition to recovering heat from the condenser of an integrated heat pump. A solar thermal collector sub-system is used to generate solar regeneration water. Experiments were conducted in the typically hot and humid weather of Taichung, Taiwan, from the spring to fall seasons. The experimental results show that the overall performance of the system in terms of power consumption can be enhanced by approximately 10% by integrating a solar-heated water heat exchanger in comparison to the hybrid SDCS system. The results show that the system performs better when the outdoor humidity ratio is large. In addition, regarding the effect of ambient temperature on the coefficient of performance (COP) of the systems, a critical value of outdoor temperature exists. The COP of the systems gradually rises with the increase in ambient temperature. However, when the ambient temperature is greater than the critical value, the COP gradually decreases with the increase in ambient temperature. The critical outdoor temperature of the hybrid SDCS is from 26 °C to 27 °C, and the critical temperature of the solar-assisted hybrid SDCS is from 27 °C to 30 °C.

Exergy Analysis of Fluidized Desiccant Cooling System.

One of the main challenges in the design and implementation of fluidized desiccant cooling (FDC) systems is increasing their low COP (coefficient of performance). Exergy analysis is one of the tools especially suitable for improvement and optimization of FDC systems. The improvement of performance is impossible as long as the main sources of exergy destruction are not identified and evaluated. In this paper, the exergy analysis was applied in order to identify these components and processes of the FDC system that are mainly responsible for exergy destruction. Moreover, the exergy efficiency of a simple fluidized desiccant cooler was determined. The results showed that fluidized beds and regenerative heat exchanger were the main exergy destruction sources with a 32% and 18% share of total exergy destruction, respectively. On the other hand, the direct evaporative cooler and air cooler placed after the desorbing fluidized bed were characterized by the lowest exergy efficiencies. This work contributes to better understanding of FDC operation principles and improvement of the performance of FDC technology.

Integration of Solid Oxide Fuel Cell with Liquid Desiccant Cooling for Generation of Combined Cooling and Power for a Server

In this study the integration of a solid oxide fuel cell with liquid desiccant system is considered for powering and cooling a data center at the rack level. The novel idea is that each single fuel cell (~12 kW) is used to power one server rack and the waste heat from the fuel cell is used to regenerate a desiccant to provide dehumidification or cooling. The heat concentrates the liquid desiccant solution that is then stored. When moisture must be removed, the high concentration solution is used to dehumidify the outside air. The objective of this study is to theoretically investigate the capability of the integrated system to provide enough cold and dehumidified air to keep the server rack in the safe range of temperature and humidity. Results show that the SOFC waste heat can produce cold and dehumidified air that is in the safe range for server racks. However, with continuous outside air conditions of 25oC and 70% relative humidity the heat from the current SOFC system is enough to provide only 25% of the air flow demand for each server rack.

Feasibility of Liquid Desiccant Cooling (LDC) system under Mediterranean climate

Contrary to the conventional air conditioning systems, the liquid desiccant cooling (LDC) systems are considered efficient systems to control the indoor air conditions. In addition, the LDC technologies are more adequate for the hot and humid climates. In this paper, we present an analytical investigation at assessing the feasibility of a LDC technology under Mediterranean climate. The mathematical equations including the sensible and latent heat transfer equations in both air stream and desiccant solution are presented. The impacts of climatic and operating parameters on the supplied air qualities, moisture removal rate (MRR) and sensible heat ratio (SHR) are evaluated. As a consequence, this study provides a solution to investigate the feasibility of this type of air conditioning technologies under hot and humid climate.

Performance analysis of a CPV/T-DC integrated system adopted for the energy requirements of a supermarket

In this paper, a model that analyses the coupling of a concentrating photovoltaic and thermal (CPV/T) system with a desiccant cooling (DC) system used to satisfy the energy loads required by a supermarket, is presented. A detailed analysis of the supermarket electrical and thermal loads is conducted in different periods of the year: summer, winter and half seasons. A CPV/T system linear focus configuration is considered, and its sizing as a function of the solar Direct Normal Irradiance (DNI) is realized for each period of the year. Hence, an Artificial Neural Network (ANN) is used to model carefully the DNI adopting experimental data in the simulation process. The coupling between the CPV/T and DC systems allows to obtain energy and economic savings during the year compared with a conventional solution, considering accurately in the modelling: supermarket energy loads, solar radiation, environmental conditions, etc. In particular, the analysis of three case studies is performed, where the main aim has been to size the CPV/T-DC integrated system and to study how it can match the different supermarket energy needs. The three solutions are analyzed from an energetic and economic point of view in order to demonstrate the effectiveness of the solution proposed.

Performance Analysis of Solar-Assisted Desiccant Cooling System Cycles in World Climate Zones

The demand for affordable, environment-friendly, and reliable water conditioning systems has led to the introduction of several standalone and/or hybrid alternatives. The technology of desiccant evaporative cooling (DEC) has proven to be dependable and has gained success at places where initially it was deemed unfeasible. Today, a number of related technologies and configurations are available. Among them, solar-assisted desiccant cooling system (SADCS) offers a cheap eco-friendly alternative, especially in hybrid configurations. Most studies have investigated the performance of numerous SADCS configurations in specific climatic conditions; however, at the global- and system-level scale, no such study is available. The current study investigates five different SADCS configurations using equation-based object-oriented modeling and simulation approach in five different climatic conditions. The selected climatic conditions cover a wide range of global weather data including arid/semiarid (Karachi), dry summer tropical (Adelaide), and mesothermal (Sao Paulo, Shanghai) to continental conditions (Vienna). The performance of all selected SADCS configurations (ventilation cycle, recirculation and ventilated-recirculation cycles, dunkle and ventilated-dunkle cycle) is analyzed for specified cooling design day of the selected cities. A uniform system control strategy based on the idea of displacement distribution (ventilation) system is used for each configuration and climatic zone. By monitoring their performances based on the values of cooling capacity (CC) and coefficient of performance (COP), the best SADCS configuration is proposed for each considered climatic condition in the world. The results revealed that the climates of Vienna, Sao Paulo, and Adelaide favor the use of ventilated-dunkle cycle configuration with average COP of 0.36, 0.84, and 0.93, respectively, while ventilation cycle based on DEC configuration suits the climate of Karachi and Shanghai with an average COP of 2.32 and 2.90, respectively.

Experimental investigations on heat and mass transfer performances of a liquid desiccant cooling and dehumidification system

The last decades have witnessed the growth interest in Liquid Desiccant Dehumidification Systems (LDDS). In the conventional LDDS, the high dilution rate of desiccant solution in dehumidifier leads to a high desiccant regeneration frequency, which consequently results in more thermal energy consumed by desiccant regeneration system. Therefore, a more energy efficient Liquid Desiccant Cooling and Dehumidification (LDCD) system is developed in this study, which mainly composes of a cooling coil and dehumidifier. A simple static model is proposed to predict the performances of heat and mass transfer process in this system. The thermal efficiency, moisture effectiveness and desiccant dilution rate are utilized as the performance indicators. The influences of several relevant parameters on the cooling and dehumidification performances of LDCD system are investigated. The model predictions are compared with the experimental data, and the results show that the model predictions are well in line with the experimental data with the maximum errors less than 10%. Moreover, the feasibility of LDCD system in reducing the dilution rate of desiccant solution and the system energy consumption is validated. The results indicate that the dilution rate of desiccant solution and energy consumption of the LDCD system are reduced by 39.64% and 22.3% over the conventional LDDS, respectively.

A Theoretical Model on Internally Cooled Liquid Desiccant Dehumidification and Cooling Processes

A simple theoretical model has been developed on the coupled heat and mass transfer processes involved in the internally cooled liquid desiccant dehumidification and cooling processes for air-conditioning applications. Governing seven coupled differential equations are solved simultaneously with appropriate boundary conditions using the 4th order Runge-Kutta scheme. The calculation speed is improved remarkably (computational time is less than 6 minutes). The simulation results showed good agreement with the published data with the maximum discrepancy of about 6%. The validated model is used to investigate the performance of dehumidification and cooling of air under different operating conditions. Simulation results show that the internally cooled liquid desiccant dehumidification and cooling processes can dehumidify the air effectively. However, additional sensible cooling of the air is required to maintain comfort condition for air-conditioning applications.

A-58 吸着ローターを用いた減湿型空調システムについて : (その1)システムシミュレーション

A-58 吸着ローターを用いた減湿型空調システムについて : (その1)システムシミュレーション