Dynamic Evaluation of Desiccant Dehumidification Evaporative Cooling Options for Greenhouse Air-Conditioning Application in Multan (Pakistan)

This study provides insights into the feasibility of a desiccant dehumidification-based Maisotsenko cycle evaporative cooling (M-DAC) system for greenhouse air-conditioning application. Conventional cooling techniques include direct evaporative cooling, refrigeration systems, and passive/active ventilation. which are commonly used in Pakistan; however, they are either not feasible due to their energy cost, or they cannot efficiently provide an optimum microclimate depending on the regions, the growing seasons, and the crop being cultivated. The M-DAC system was therefore proposed and evaluated as an alternative solution for air conditioning to achieve optimum levels of vapor pressure deficit (VPD) for greenhouse crop production. The objective of this study was to investigate the thermodynamic performance of the proposed system from the viewpoints of the temperature gradient, relative humidity level, VPD, and dehumidification gradient. Results showed that the standalone desiccant air-conditioning (DAC) system created maximum dehumidification gradient (i.e., 16.8 g/kg) and maximum temperature gradient (i.e., 8.4 °C) at 24.3 g/kg and 38.6 °C ambient air conditions, respectively. The DAC coupled with a heat exchanger (DAC+HX) created a temperature gradient nearly equal to ambient air conditions, which is not in the optimal range for greenhouse growing conditions. Analysis of the M-DAC system showed that a maximum air temperature gradient, i.e., 21.9 °C at 39.2 °C ambient air condition, can be achieved, and is considered optimal for most greenhouse crops. Results were validated with two microclimate models (OptDeg and Cft) by taking into account the optimality of VPD at different growth stages of tomato plants. This study suggests that the M-DAC system is a feasible method to be considered as an efficient solution for greenhouse air-conditioning under the climate conditions of Multan (Pakistan)

A HYBRID AIR CONDITIONER DRIVEN BY A HYBRID SOLAR COLLECTOR

The objective of this thesis is to search for an efficient way of utilizing solar energy in air conditioning applications. The current solar Air Conditioners (A/C)s suffer from low Coefficient of Performance (COP) and performance degradation in hot and humid climates. By investigating the possible ways of utilizing solar energy in air conditioning applications, the bottlenecks in these approaches were identified. That resulted in proposing a novel system whose subsystem synergy led to a COP higher than unity. The proposed system was found to maintain indoor comfort at a higher COP compared to the most common solar A/Cs, especially under very hot and humid climate conditions. The novelty of the proposed A/C is to use a concentrating photovoltaic/thermal collector, which outputs thermal and electrical energy simultaneously, to drive a hybrid A/C. The performance of the hybrid A/C, which consists of a desiccant wheel, an enthalpy wheel, and a vapor compression cycle (VCC), was investigated experimentally. This work also explored the use of a new type of desiccant material, which can be regenerated with a low temperature heat source. The experimental results showed that the hybrid A/C is more effective than the standalone VCC in maintaining the indoor conditions within the comfort zone. Using the experimental data, the COP of the hybrid A/C driven by a hybrid solar collector was found to be at least double that of the current solar A/Cs. The innovative integration of its subsystems allows each subsystem to do what it can do best. That leads to lower energy consumption which helps reduce the peak electrical loads on electric utilities and reduces the consumer operating cost since less energy is purchased during the on peak periods and less solar collector area is needed. In order for the proposed A/C to become a real alternative to conventional systems, its performance and total cost were optimized using the experimentally validated model. The results showed that for an electricity price of 0.12 $/kW-hr, the hybrid solar A/C's cumulative total cost will be less than that of a standard VCC after 17.5 years of operation

Experimental Study on a Finned-tube Internally Cooled Contactor for Liquid Desiccant air conditioning systems with Ionic Liquid

This paper presents an experimental study on the dehumidification performance of a finned-tube internally cooled contactor as compared to that of an adiabatic contactor in liquid desiccant air conditioning systems with ionic liquid. The contactor is the most significant component in liquid desiccant systems; it is the component responsible for the dehumidification and regeneration processes. When air and absorptive solution are in contact in the contactor, absorption/desorption of the solution occurs due to the difference in vapor pressure. This results to the transfer of heat and mass between the air and solution. Conventionally, adiabatic contactors, which only have air and solution interaction are being used for the dehumidification/regeneration process of liquid desiccant systems. On the contrary, internally cooled contactors are being suggested as these have the possibility of realizing a more efficient dehumidification process. This is possible as internally cooled contactors can maintain the dehumidification ability of the absorptive solution by utilizing cooling water as a third fluid in the contactor for removing the heat of absorption. In other words, internally cooled contactors have the possibility of reducing the circulating solution mass flux and, hence, the power consumption of the solution pumps. In this research, the dehumidification ability of a finned-tube internally cooled contactor is experimentally studied. In order to increase the heat transfer ability of the cooling water, aluminium, which has a high thermal conductivity, is used as the contactor material. Although Lithium Chloride solution is a conventional absorptive solution, it corrodes aluminum; therefore, ionic liquid is used as the absorptive solution in this experiment since it does not corrode aluminum. Research on this new combination of contactor and absorptive solution is not extensively done at present; this research provides new and valuable information for future research. Moreover, the results were compared with that of an adiabatic contactor in order to analyze the difference in dehumidification ability between the two of contactors. As a result, outlet air dew point temperatures lower than the cooling water temperature were achieved, which emphasize the advantage of liquid desiccant air conditioning system to conventional vapor compression air conditioning systems. Furthermore, the outlet air dew point temperatures of the internally cooled contactor were lower than that of adiabatic contactor for low mass fluxes, and converged at higher solution mass flux. This suggests the significant effect of the cooling water to the dehumidification ability of the absorptive solution. Experimental data of the dehumidification ability of this new combination of aluminum finned-tube contactor and ionic liquid solution are promising for further research about the structure of contactors. These results provide significant information for the improvement in the design of liquid desiccant air conditioning systems

Mathematical Model and Performance Analysis of a Liquid Desiccant Dehumidification Tower

A finite difference model simulating a liquid desiccant dehumidification tower with lithium chloride as the desiccant solution has been developed. The model determines the packing height needed for a condensation rate. Comparisons with experimental data illustrates that the model produces valid results. Air and desiccant solution temperatures within the dehumidification tower show that a temperature increase is experienced for both the air and desiccant solution from their respective entrances and exits from the tower. Increasing the air mass velocity or the amount of moisture removed from the air supply causes an increase in packing height. Increasing the desiccant mass velocity decreases the packing height

제습제 코팅 열교환기를 적용한 전기자동차용 히트펌프 시스템 성능 분석

학위논문(박사) -- 서울대학교대학원 : 공과대학 기계항공공학부(멀티스케일 기계설계전공), 2021.8. 김민수.In this study, a heat pump system of an electric vehicle (EV) with a novel dehumidifier is suggested and validated by modeling and experiment. The aim of the study is the determination of the energy consumption of the proposed system. The driving range of a conventional EV sharply drops when operating the MHP system for heating or defogging. Because the traditional MHP consumes a lot of energy since it used the condensing method to remove moisture. It means that the air temperature must be lower than dew points to occurs condensation on the metal fins of a heat exchanger, then the air should be reheated to supply into the cabin. In this study, to solve this irrational process for dehumidification, a solid desiccant coated heat exchanger (DCHE) is introduced which is able to heat and mass transfer simultaneously for removing water vapor in the cabin air and recovering waste heat from power electronics and electric machineries (PEEM). To attach the desiccant material onto the metal fin of a heat exchanger, a binder should be necessary. Thus, the proper pair of the desiccant and binder is selected. After analyzing the physical properties of the adsorbent, the optimum binder contents ratio is obtained. Then, the numerical model of the DCHE was developed base on the thermal resistance method to predict the adsorption performance of the DCHE. To validate the predicted results, the DCHE was fabricated and the test facility was also constructed. The simulation results show good agreement with the experimental data. To obtain the power consumption of the MHP, the numerical model of the MHP was developed. The compressor characteristics were determined by preliminary test since it is a crucial component of the MHP and it strongly affects the performance of the MHP system. Similar to the DCHE model, heat exchangers of the MHP also modeled using the thermal resistance method by discrete as small segments. To validate the developed MHP model, the experimental apparatus was constructed and conducted experiments. As a result, the simulation results reveal small differences as compared with the experimental data. Owing to determine the effect of the DCHE on the energy consumption of the MHP to satisfy the cabin target condition, the simulation was conducted by integrated the developed numerical model in the Simulink program. Simulation results reveal that the system with DCHE achieves a reduction in energy consumption as compared to the traditional system. Because the DCHE led to decreasing the operation time of the MHP by adsorption the water vapor in the cabin air, and by heating to approach the cabin air temperature to the setpoint. In conclusion, the novel configuration which is utilized the DCHE in the automobile heat pump system is suggested in this study. And the DCHE effects on the energy reduction of the automobile heat pump system were investigated. Conclusively, the DCHE helps to reduce energy consumption.차량 탑승객의 열쾌적성과 운전 안전성 확보를 위하여, 냉난방 공조 시스템을 가동하여 차량실내 냉난방 및 김서림 제거한다. 이러한 공조시스템을 운전하기 위한 에너지 소비는 불가피하다. 기존 내연기관 차량의 경우, 충분한 연소열량을 활용하여 난방 및 김서림 방지를 위해 사용할 수 있었다. 하지만 전기자동차의 경우, 내연기관 차량과 달리 충분한 열원이 존재하지 않을뿐더러 탑재된 배터리에 저장된 에너지량에 따라 주행거리가 의존적이므로, 공조시스템을 운전할수록 전기자동차의 주행거리가 급감하는 문제가 존재한다. 이를 해결하기 위해서는 공조시스템의 에너지 사용량을 줄이고 효율을 높여야 한다. 기존 차량에서는 김서림 제거를 위하여, 실내공기를 이슬점보다 낮게 만들어 공기내 수분이 열교환기에 응축시켜 제습한 후 재가열하여 실내로 공급하는 방법을 보편적으로 사용하고 있다. 이는 불합리적인 에너지 소비를 야기한다. 이러한 문제를 해결하기 위해, 고체 제습제를 활용하여 공기내 수분을 직접 흡착시켜 제습하는 방안을 고안하였다. 또한, 모터 및 인버터와 같은 전장품들의 폐열을 회수하여 공조에 활용하기 위해 추가 열교환기를 고려하였다. 본 연구에서, 제습제 코팅 열교환기 (DCHE, Desiccant coated heat exchanger)를 제안하고, 해당 열교환기를 적용한 전기자동차용 히트펌프 시스템의 에너지 사용량에 대한 분석을 실시하였다. 이를 위하여, 차량실내 열적 모델, 제습제 코팅 열교환기 모델, 그리고 차량용 히트펌프 모델을 구축 및 검증하였다. 탑승자의 호흡 및 피부에서 증발하는 수분량을 계산하여 차량실내 열적 모델을 구축하고, 다른 연구진의 모델과 비교 검증하였다. 제습제 코팅 열교환기의 해석 모델을 열 및 물질 저항 모델을 활용하여 차분화하여 구축하였다. 이 해석 모델을 검증하기 위하여, 다양한 조건에서 DCHE의 흡착 성능측정을 실험하여 그 결과를 예측 성능과 비교하였다. 제습제 코팅 열교환기는 흡착제와 접착제의 비율에 따른 흡착성능을 분석한 결과를 바탕으로 제작하였다. 차량용 히트펌프 실험장비를 구축하고 다양한 조건에서 실험하였으며, 그 결과를 차량용 히트펌프 해석 모델의 예측 성능값과 비교하여 검증하였다. 따라서, 개발 및 검증된 모델을 Simulink에 활용하여 다양한 운전조건에 대한 시스템의 소비동력에 미치는 영향을 분석하였다. 그 결과, 기존 전기자동차에 비하여 제습제 코팅 열교환기를 적용할 경우, 차량용 히트펌프의 냉매압축기 소비동력이 줄어든다는 결론을 얻었다. 본 연구에서 제시한 제습제 코팅 열교환기를 전기자동차에 적용한다면, 전기자동차용 공조시스템이 사용하는 에너지를 줄임으로써, 겨울철 차량의 주행거리를 확보할 수 있을 뿐만 아니라 미래 전기자동차의 보급 및 확산에도 기여할 수 있을 것으로 기대한다.Chapter 1. Introduction 1 1.1. The motivation of the study 1 1.2. Literature survey 11 1.2.1. Desiccant coated heat exchanger 11 1.3. Objectives and scopes 16 Chapter 2. Electric vehicle thermal loads analysis 19 2.1. Introduction of the cabin model 19 2.2. Numerical model of the cabin thermal load 20 2.3. Numerical model of the wet air 27 2.4. Validation of the cabin model 32 2.5. Sensitivity analysis of the cabin model 36 2.5.1. Ambient temperature and the number of passengers 38 2.5.2. Vehicle velocity profile 40 2.6. Summary 44 Chapter 3. Design and performance analysis of the desiccant coated heat exchanger 45 3.1. Introduction of the DCHE 45 3.1.1. Principle of the adsorption 46 3.1.2. Selection of the solid desiccant and the binder 49 3.2. Physical properties of the adsorbent 55 3.2.1. The surface area of the adsorbent 55 3.2.2. The image analysis using the scanning electron microscope 64 3.2.3. The vapor sorption capacity of the adsorbent 71 3.3. Numerical analysis of the DCHE 78 3.4. Experimental of the DCHE 87 3.4.1. Experiment set-up of the desiccant coated heat exchanger 87 3.4.3. Experimental validation of the DCHE model 96 3.5. Alternate control methods for DCHE 98 3.5.1. Absolute humidity gap method 98 3.5.2. Absolute humidity slope method 99 3.5.3. Water contents ratio method 101 3.5.4. Integrated area ratio method 103 3.6. Summary 105 Chapter 4. Design and performance analysis of the heat pump 107 4.1. Introduction of the automobile heat pump 107 4.1.1. Selection of the refrigerant 107 4.1.2. Selection of the lubricant 115 4.2. Numerical analysis of the automobile heat pump 117 4.2.1. Calculation method and assumption 117 4.2.2. Compressor 119 4.2.3. Heat exchangers 120 4.2.4. Expansion device 126 4.3. Experiment of the automobile heat pump 126 4.3.1. Experimental apparatus 127 4.3.2. Data reduction and uncertainty analysis 136 4.3.3. The optimum charge amounts 139 4.3.4. Performance of the heat pump system 143 4.3.5. Validation of the heat pump model 148 4.4. Summary 153 Chapter 5. Integrated System Simulation 155 5.1. Introduction 155 5.2. Simulation conditions 163 5.3. Simulation results 164 5.3.1. Effect of the additional heat exchanger 164 5.3.2. Effect of the DCHE frontal area 168 5.3.3. Effect of the fresh-recirculation air ratio 171 5.3.4. Effect of the ambient temperature 175 5.3.5. Effect of the DCHE inlet coolant temperature 180 5.3.6. Effect of the number of the passenger 184 5.3.7. Effect of the refrigerant type 187 5.3.8. Effect of the number of the DCHE 192 5.4. Summary 196 Chapter 6. Conclusions 199 References 203 국 문 초 록 222박

Solar Cooling Technologies

This chapter describes different available technologies to provide the cooling effect by utilizing solar energy for both thermal and photovoltaic ways. Moreover, this chapter highlights the following points: (i) the main attributes for different solar cooling technologies to recognize the main advantages, challenges, disadvantages, and feasibility analysis; (ii) the need for further research to reduce solar cooling chiller manufacture costs and improve its performance; (iii) it provides useful information for decision-makers to select the proper solar cooling technology for specific application. Furthermore, some references, which include investigation results, will be included. A conclusion about the main gained investigation results will summarize the investigation results and the perspectives of such technologies

Experimental Investigation on the Operation Performance of a Liquid Desiccant Air-conditioning System

A large share of energy consumption is taken by an air-conditioning system. It worsens the electricity load of the power network. Therefore, more and more scholars are paying attention to research on new types of air-conditioning systems that are energy- saving and environment-friendly. A liquid desiccant air conditioning system is among them, as it has a tremendous ability for power storage and low requirements for heat resources. Heat with low temperatures, such as excess heat, waste heat, and solar power, is suitable for the liquid desiccant air-conditioning system. The feasibility and economical efficiency of the system are studied in this experimental research. The result shows that when the temperature of the regeneration is about 80?, the thermodynamic coefficient of the system is about 0.6, and the supply air temperature of the air-conditioning system remains stable at 21?, the air-conditioning system can meet human comfort levels

Study on Desiccant and Evaporative Cooling Systems for Livestock Thermal Comfort: Theory and Experiments

The present study considers evaporative cooling and desiccant unit-based air-conditioning (AC) options for livestock AC application. In this regard, proposed systems are investigated by means of experiments and thermodynamic investigations. Air-conditioning requirements for animals are theoretically investigated and temperature-humidity index (THI) is estimated. A lab-scale heat mass exchanger based on the Maisotsenko-cycle evaporative cooling conception (MEC) is set up and its performance is evaluated at different ambient air conditions. In addition, a desiccant-based air-conditioning (DAC) unit is thermodynamically evaluated using a steady-state model available in the literature. The study focuses on the ambient conditions of Multan which is the 5th largest city of Pakistan and is assumed to be a typical hot city of southern Punjab. The study proposed three kinds of AC combination i.e., (i) stand-alone MEC, (ii) stand-alone desiccant AC, and (iii) M-cycle based desiccant AC systems. Wet bulb effectiveness of the stand-alone MEC unit resulted in being from 64% to 78% whereas the coefficient of performance for stand-alone desiccant AC and M-cycle based desiccant AC system was found to be 0.51 and 0.62, respectively. Results showed that the stand-alone MEC and M-cycle based desiccant AC systems can achieve the animals’ thermal comfort for the months of March to June and March to September, respectively, whereas, stand-alone desiccant AC is not found to be feasible in any month. In addition, the ambient situations of winter months (October to February) are already within the range of animal thermal comfort

Assessment of a desiccant cooling system in a traditional and innovative nanofluid HVAC system

The topic of energy saving is a constant in everyday life, and it is widespread all over the world. Space heating using solar panels is the most used renewable source of energy, but the application of solar energy for cooling the fluids used for refrigeration is growing very fast. Among the techniques used for refrigeration, this work focused on Desiccant Cooling. In particular, with the use of dynamic simulation software, it was possible to study the heat supplied and the energy consumption of a Heating Ventilation Air Conditioning (HVAC) system of a university building and to compare consumption with those of a Desiccant Cooling system applied to the same building. Four different cases were simulated: two related to the HVAC system, one of which operates with water and glycol and the other one with nanofluid, and the other ones to the Desiccant Cooling system with both types of fluids mentioned above. Keeping the same energy demand of the building in all the simulations, it was found that in summer the Desiccant Cooling system had higher performance than the traditional HVAC system and that the use of the nanofluid in both types of conditioning systems further increased the performance of 21%. Simulations were carried out using TRNSYS software