Next-generation HVAC: Prospects for and limitations of desiccant and membrane-based dehumidification and cooling

Recently, next-generation HVAC technologies have gained attention as potential alternatives to the conventional vapor-compression system (VCS) for dehumidification and cooling. Previous studies have primarily focused on analyzing a specific technology or its application to a particular climate. A comparison of these technologies is necessary to elucidate the reasons and conditions under which one technology might outperform the rest. In this study, we apply a uniform framework based on fundamental thermodynamic principles to assess and compare different HVAC technologies from an energy conversion standpoint. The thermodynamic least work of dehumidification and cooling is formally defined as a thermodynamic benchmark, while VCS performance is chosen as the industry benchmark against which other technologies, namely desiccant-based cooling system (DCS) and membrane-based cooling system (MCS), are compared. The effect of outdoor temperature and humidity on device performance is investigated, and key insights underlying the dehumidification and cooling process are elucidated. In spite of the great potential of DCS and MCS technologies, our results underscore the need for improved system-level design and integration if DCS or MCS are to compete with VCS. Our findings have significant implications for the design and operation of next-generation HVAC technologies and shed light on potential avenues to achieve higher efficiencies in dehumidification and cooling applications

Investigation of Water Vapor Transport in Membrane Mass Exchangers for HVAC Applications

Vapor compression systems have dominated the HVAC area for close to 100 years. These systems require significant amounts of energy to complete the compression cycle and the refrigerants used are known contributors to global warming. As a result, new innovations are being sought and a membrane-based system, the subject of this thesis, is one such technology. Water selective membrane materials offer a promising alternative to vapor compression for dehumidification of building air. For HVAC systems, process air pressure drop constrains flow path design in a membrane-based approach. The transport resistance for water vapor from air flow channels is experimentally investigated for a plate-type membrane mass exchanger design. Convective and diffusive resistances are measured for polymer membranes with varying flow channel dimensions. A series of experiments and analyses is developed to separate diffusive and convective transport resistance to water vapor removal from supply air. Results are compared with empirical Sherwood number correlations to enable improved mass exchanger design. The validated mass transfer correlations were used to develop a mass transfer model and later implemented for the simulation of a 3 rTon (1 rTon = 3.516kW) membrane heat pump dedicated outdoor air systems. From the various analyses, maintaining process air pressure drop at less than 50 Pa while at a typical HVAC face velocity results in a convective resistance that is 6 times greater than the diffusive resistance to water vapor through an ionic membrane. Furthermore, the tradeoff between required membrane area, system size, pressure-drop and effective latent cooling is explored. Simulation results show that when conforming mass exchanger designs to meet ASHRAE standards, a system electrical COP of 7.5 or greater can be achieved

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

A Comprehensive Review of Dehumidifiers and Regenerators for Liquid Desiccant Air Conditioning System

This is an Accepted Manuscript of an article published by Elsevier in Energy Conversion and Management on July 15, 2021, available at: https://doi.org/10.1016/j.enconman.2021.114234Peer ReviewedLiquid desiccant air conditioning systems (LDAS) are an energy-efficient and eco-friendly alternative to conventional air conditioning systems. The performance of a LDAS significantly depends on its simultaneous heat and mass transfer components, namely dehumidifier and regenerator. These components are referred to as liquid desiccant energy exchangers (LDEEs) since the working fluids (air and desiccant) exchange both heat and moisture. There has been a lot of research on LDEEs over the last two decades to improve their performance, thereby enhancing the efficiency of the LDAS. The main objective of this comprehensive review paper is to summarize the developments of LDEEs. The desiccant material, and design, operating, and performance parameters of LDEEs are explained in detail. Even though a lot of research has been done on LDEEs, they are not much utilized in the practical heating, ventilation, and air conditioning (HVAC) systems. To address this issue, future research should prioritize its focus on (i) practical problems of LDEEs such as cross contamination, and leakage and blockage of the membrane, (ii) long term performance study in the practical systems, (iii) noncorrosive and inexpensive solution, (iv) compatible material for efficient heat and mass transfer, and (v) generalized design and performance control methodology. The discussions presented in this communication will be useful to ascertain the crucial research gaps that need to be addressed by future research studies

ISHPC 2021 proceedings – online pre-conference 2020

For decades there has been intense research and development on sorption heat pumping and cooling processes; still, looking at the sales numbers, it is mainly a niche technology. The current transition to an energy system based on renewables changes the boundary conditions. Sorption heat pumps will have an indispensable place in this context, especially for its potential to make use of waste heat. We want to look at the future of sorption heat pumping devices including the newest research developments, as well as reports about pilots and mature technology

Removal of Water from Natural Gas Using Zeolite 4A and Zeolite 5A

This report is discussed regarding the research on Removal of Water from Natural Gas using Zeolite 4A and Zeolite 5A. The natural gas that comes from the well usually is saturated with water. Tri-ethylene glycol (TEG) is being used for many decades in the industry as one of the absorbent in removing water from natural gas but there are some problems and difficulties when dealing with this type of absorbent. Therefore, this project is conducted to find the alternatives in removing water from natural gas and to evaluate whether zeolites can be practiced and applied for offshore practices. Zeolites have been proved that they able to remove carbon dioxide from natural gas. A lot of research done proves that zeolites have a big potential to remove water vapour from natural gas effectively. To know the properties of chosen zeolites, characterization by using Surface Area Analyzer, X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Field-Emission Scanning Electron Microscope (FESEM) and Thermogravimetric Analyzer (TGA) has been executed. Surface Area Analyzer is used to determine pore size and pore volume. Zeolite 4A has higher surface area, pore diameter and micropore volume compared to Zeolite 5A. Both of zeolites exhibit monolayer and chemisorption type of adsorption. XRD shows that Zeolite 4A is more crystal than Zeolite 5A.Both of zeolites are cubic crystal system with identical lattice parameters. XRF is performed to know the elemental composition in zeolites and from the result, it is confirm that Zeolite 4A in a sodium form and Zeolite 5A in a calcium form. FESEM is executed to observe the morphology of the zeolite. From the image obtained, pore size and interconnecting pores of Zeolite 5A seems bigger than Zeolite 4A. TGA result shows both zeolites have higher degradation temperature than 900 °C. It was concluded that by using certain techniques, Zeolite 4A and Zeolite 5A can be identified for their pore area and pore volume, structure properties, elemental composition, morphology and thermal stability. Dynamic Performance Study has been conducted by varying pressure20 to 60 bar, with constant flowate of 5LPM and constant temperature of 50°C in order to study the performance of the zeolites in removing water from natural gas. The best zeolite was selected based on adsorbent capacity and percentage of removing water from natural gas.It was concluded that lower pressure give better result since it give higher adsorption capacity and total water of removal from natural gas. Zeolite 5A is found give better performance in removing water from natural gas than Zeolite 4A due to its affinities towards water

Solar cooling integrated facades

Solar cooling systems have gained increased attention these last years, for their potential to lower indoor temperatures using renewable energy. However, architectural integration of these systems in buildings has not been fully explored. Current developments such as small scale solar driven heat pumps and solar cooling kits commercially available for application raise questions about how to successfully integrate these systems into buildings, while present interesting opportunities for the development of new performance based façade components or even self-sustaining cooling façade modules for high-performing commercial buildings. So, what are the conceptual issues and state-of-the-art components and systems to consider for solar cooling façade integration? This chapter discusses current possibilities for façade integration of solar cooling systems, generating a framework for the understanding and further development of solar cooling façade systems. The proposed framework was made by means of a review of solar cooling technologies and solar cooling façade concepts reported by several researchers. The outcomes of the chapter are a matrix outlining the possibilities for the integration of several components and subsystems from the entire cooling process (cooling generation, distribution and delivery), and an early assessment of the development level of state-of-the-art experiences within the field considering examples from current research projects and working prototypes, for the development of solar cooling integrated façade concepts

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

MODELLING CRYSTALLIZATION FOULING IN LIQUID-TO-AIR MEMBRANE ENERGY EXCHANGERS

Micro-porous membranes are used in membrane-based separation processes to separate water from an aqueous solution. Liquid-to-air membrane energy exchangers (LAMEEs) use membranes to control humidity and temperature in heating, ventilation and air-conditioning (HVAC) systems. A semi-permeable hydrophobic membrane is used in LAMEEs to separate an air stream from an aqueous solution stream while allowing simultaneous heat and moisture transfer between the streams. However, the membrane of LAMEEs may be subjected to crystallization fouling under some operating conditions which impacts performance. The primary goal of this thesis is to establish a model for LAMEEs that can predict the crystallization fouling rate, decline in moisture transfer flux due to fouling, and the operating/design conditions where fouling is likely to occur. In this thesis, a semi-empirical model is developed to predict crystallization fouling of the membrane in LAMEEs. The solution concentration at solution-membrane interface is determined analytically using mass and energy balance equations, while the fouling (i.e., blockage of the membrane pores) is predicted using an empirical equation from the literature. As the fouling progresses and more of the membrane pores are blocked, moisture transfer flux through the membrane reduces. The model is validated with experimental data available in the literature and is used to determine the effect of design and operating parameters on the fouling rate. The model is also used to estimate the time when the moisture transfer flux declines to a specific value (e.g. 50% reduction) which is helpful in determining the membrane cleaning frequency. Then, the model is used to predict the conditions where crystallization fouling is likely to occur under different operating conditions for three different desiccant solutions, namely magnesium chloride (MgCl2), calcium chloride (CaCl2) and lithium chloride (LiCl). The model is expanded to determine the fouling limits (which is attainment of saturation condition at the solution-membrane interface at the LAMEE outlet) in a counter-flow LAMEE. In addition, the moisture transfer flux decline due to crystallization fouling is analyzed for MgCl2 at various locations along the LAMEE

Paraffin

Paraffin waxes make up the majority of commercial waxes. Waxes are characterized by the carbon number, hardness, crystal shape, composition, and molecular weight. These characteristics determine the condition of separating the wax. Paraffin wax is widely used in different industries such as ink, paper, cosmetics, ceramics using powder injection molding and energy storage as phase change materials. Consumption of wax products has increased in the world; especially for food, pharmaceutical products, cosmetics, as well as specialty products. The increase of profitability of wax production will lie in the improvement of blending and modification techniques for macro and micro-crystalline waxes used as the base materials