Utilisation of Flat Plate Photovoltaic Thermal (PV/T) Technology for a Low Temperature Desiccant Air Dehumidification and Cooling System

Utilising solar energy as the main energy source for air conditioning systems can reduce coal fired electricity consumption and greenhouse gas (GHG) emissions. This thesis explored a novel approach to apply photovoltaic thermal (PV/T) technology for desiccant air dehumidification and cooling systems (refer to as 'desiccant cooling system' from here onwards). A desiccant cooling system and a flat plate PV/T water heating application were tested separately. Theoretical models were developed and validated against experimental results. Through a parametric analysis of a coupled flat plate PV/T collector and desiccant air dehumidification system, results showed that by keeping inlet air temperatures low, the dehumidification performance can be enhanced. And thus, lower desiccant regeneration temperatures can be used. Furthermore, this analysis utilised the dimensionless parameter of number of transfer units (NTU) to determine optimal conditions. That is, optimal conditions that reduce heat source temperatures for the desiccant regeneration process. A novel ground coupled flat plate PV/T desiccant cooling cycle was examined. This cycle implements approaches to keep the heat source temperature low which allows the use of flat plate PV/T collectors to provide thermal energy for the desiccant regeneration process, as well as generating electricity. This contributed to high annual system coefficient of performance (COP). Results showed that the novel design, when optimized, can provide sufficient dehumidification while being more energy efficient than the dew point dehumidification approach. In addition, it was found that the examined solar desiccant cooling system can achieve indoor thermal comfort in most climates in Australia. This research demonstrated the feasibility of utilising flat plate PV/T collectors as the main energy source for desiccant cooling systems

Theoretical and experimental study of a dehumidification system based on liquid desiccants for air conditioning applications

La demanda de climatització ha augmentat en els últims anys a causa de l'escalfament global i als estàndards de confort que han augmentat no només als països desenvolupats, sinó també als països en desenvolupament, on la deshumectación té una gran importància. Els sistemes dessecants híbrids són una tecnologia molt eficient quan la temperatura i la humitat han de ser controlats. En aquest sentit, els sistemes dessecants líquids ofereixen interessants avantatges quan es comparen amb els sistemes dessecants sòlids. No obstant això, la corrosió és un problema que encara no ha pogut ser resolt en els líquids. El principal objectiu d'aquesta tesi és realitzar un estudi teòric i experimental d'un sistema híbrid basat en dessecants líquids que utilitza materials no corrosibles i econòmicament viables, mantenint unes bones prestacions del sistema i aconseguint una alta eficiència energètica. El sistema dessecant líquid, al que se li ha acoblat una bomba de calor de compressió de vapor, conté contactores d'aire-solució no adiabàtics de polipropilè, al que se li ha realitzat un tractament superficial de plasma que millora la mojabilidad dels tubs. Aquest tractament millora la transferència de calor i de massa i, per tant, les prestacions globals del sistema. Després de ser dissenyat, dimensionament i muntat, el sistema està operant en dos vestuaris en Taipei (Taiwan). Les prestacions experimentals dels contactores d'aire-solució i del sistema complet durant la seva operació s'han avaluat. La màxima producció de fred mesurada en el sistema és 34 kW i la màxima deshumectación és gairebé 0.012 kgw/kga. A més, el sistema ha aconseguit un bon control de la temperatura i de la humitat. Així mateix, el sistema ha estat modelat per ser simulat dinàmicament. Aquest model ha estat validat amb els resultats experimentals del sistema real. Finalment, el model dinàmic ha estat utilitzat per conèixer les condicions d'operació i l'estratègia de control que optimitzen les prestacions anuals del sistema.La demanda de climatización ha aumentado en los últimos años debido al calentamiento global y a los estándares de confort que han aumentado no sólo en los países desarrollados, sino también en los países en desarrollo, donde la deshumectación tiene una gran importancia. Los sistemas desecantes híbridos son una tecnología muy eficiente cuando la temperatura y la humedad han de ser controlados. En este sentido, los sistemas desecantes líquidos ofrecen interesantes ventajas cuando se comparan con los sistemas desecantes sólidos. Sin embargo, la corrosión es un problema que todavía no ha podido ser resuelto en los líquidos. El principal objetivo de esta tesis es realizar un estudio teórico y experimental de un sistema híbrido basado en desecantes líquidos que utiliza materiales no corrosibles y económicamente viables, manteniendo unas buenas prestaciones del sistema y consiguiendo una alta eficiencia energética. El sistema desecante líquido, al que se le ha acoplado una bomba de calor de compresión de vapor, contiene contactores de aire-solución no adiabáticos de polipropileno, al que se le ha realizado un tratamiento superficial de plasma que mejora la mojabilidad de los tubos. Este tratamiento mejora la transferencia de calor y de masa y, por tanto, las prestaciones globales del sistema. Después de ser diseñado, dimensionado y montado, el sistema está operando en dos vestuarios en Taipei (Taiwán). Las prestaciones experimentales de los contactores de aire-solución y del sistema completo durante su operación se han evaluado. La máxima producción de frío medida en el sistema es 34 kW y la máxima deshumectación es casi 0.012 kgw/kga. Además, el sistema ha conseguido un buen control de la temperatura y de la humedad. Asimismo, el sistema ha sido modelado para ser simulado dinámicamente. Este modelo ha sido validado con los resultados experimentales del sistema real. Finalmente, el modelo dinámico ha sido utilizado para conocer las condiciones de operación y la estrategia de control que optimizan las prestaciones anuales del sistema.The air conditioning demand is rising in the last years because of the global warming and the increasing of the standard of living that is happening not only in industrial countries, but also in developing countries, where dehumidification has a great impact. Hybrid desiccant systems are a very efficient HVAC technology when humidity and temperature are required to be separately controlled. In this sense, liquid desiccant systems offer attractive benefits in comparison with solid desiccant systems. However, corrosion is a big issue to be solved in them. The main objective of this thesis is to make a theoretical and an experimental study of a hybrid liquid desiccant system using rustproof and cost-effective materials, keeping a good performance of the system and achieving high energy efficiency. The liquid desiccant system, which is coupled with a vapour compression heat pump, contains non-adiabatic air-solution contactors made of polypropylene with a plasma surface treatment that improves the wettability of the tubes. This treatment enhances the heat and mass transfer, and, therefore, the global performance of the system. After being designed, sized and assembled, the system is operating in two locker rooms in Taipei (Taiwan). The experimental performance of the air-solution contactors and the complete system during its operation is evaluated. The maximum cooling production measured of the system is 34 kW and the maximum dehumidification is almost 0.012 kgw/kga. Furthermore, good control of air temperature and humidity is achieved. Moreover, the system has been modelled in order to be dynamically simulated. This model has been validated with the experimental results obtained from the real system. Finally, the dynamic model has been used in order to find out the operational conditions and control strategy that optimize the annual performance of the hybrid liquid desiccant system

Performance analysis and design implementation of a novel polymer hollow fiber liquid desiccant dehumidifier with aqueous potassium formate

A novel cross-flow liquid desiccant polymer hollow fiber dehumidifier (PHFD) is investigated numerically in this paper. The main objective of this research is to simulate, and validate the numerical model for future design implementations. The experimentally verified simulation data will be used to develop a set of design and implementation tables and charts as the guidance for selecting the number of fibres and the solution-to-air mass flow ratio of the PHDF under given conditions. A numerical model is developed to simulate the performance of the proposed innovative dehumidifier. This model is validated against three sets of data, i.e. the experimental obtained testing results, analytical correlations and the modelling results from the literature. The influence of various operating conditions such as inlet air properties (i.e. velocity, relative humidity) and inlet solution properties (i.e. temperature, concentration, mass flow rate) on the dehumidification sensible, latent, and total effectiveness, moisture removal rate are numerically analyzed. Dimensionless parameters including the number of heat transfer unit (NTU) and the number of mass transfer unit (NTUm), the solution to air mass flow rate ratio (m*), and the air to solution specific humidity ratio () have been used to evaluate the system performance. The results show that the increase in NTU and NTUm lead to a substantial change in dehumidification effectiveness. When the NTU increases from 0.47 to 7, the sensible effectiveness rises from 0.35 to 0.95. Increasing is another good option for increasing the amount of the absorbed moisture without influencing the latent effectiveness. For an increase of from 1.4 to 2.2, the air inlet and outlet specific humidity difference varies in the range of 0.008 kg/kg and 0.018 kg/kg

Performance testing of a cross-flow membrane-based liquid desiccant dehumidification system

A membrane-based liquid desiccant dehumidification system is one of high energy efficient dehumidification approaches, which allows heat and moisture transfers between air stream and desiccant solution without carryover problem. The system performance is investigated experimentally with calcium chloride, and the impacts of main operating parameters on dehumidification effectiveness (i.e. sensible, latent and total effectiveness) are evaluated, which include dimensionless parameters (i.e. solution to air mass flow rate ratio m∗ and number of heat transfer units NTU) and solution properties (i.e. concentration Csol and inlet temperature Tsol,in). The sensible, latent and total effectiveness reach the maximum values of 0.49, 0.55, and 0.53 respectively at m∗= 3.5 and NTU = 12, and these effectiveness are not limited by m∗ and NTU when m∗ > 2 and NTU > 10. Both the latent and total effectiveness increase with Csol , while almost no variation is observed in the sensible effectiveness. All effectiveness can be improved by decreasing Tsol,in. The experimental data provide a full map of main design parameters for the membrane-based liquid desiccant air conditioning technology

Contribution of an internal heat exchanger to the performance of a liquid desiccant dehumidifier operating near freezing conditions

a b s t r a c t The aim of the present study is to analyze numerically the effect of an internal heat exchanger (IHX) in a liquid-desiccant based dehumidification system operating near freezing conditions that are typical of a refrigerated warehouse. The study is based on previous work done by the authors that showed reduced ice formation on the surface of a cooling coil by dehumidifying the air using liquid desiccants. The results of the present study show that IHX effectiveness has a direct impact on the inlet temperature of the liquid desiccant leaving the absorber. High IHX effectiveness results in high absorber effectiveness. However, IHX effectiveness less than 60% leads to a desorption process where the liquid desiccant concentration increases, augmenting the humidity ratio of the air going through the mass exchanger

A heat pipe internally-cooled membrane-based liquid desiccant dehumidification system

In recent years, membrane-based liquid desiccant dehumidification has emerged as an efficient approach for air humidity control in building air conditioning process, in which the internally-cooled liquid desiccant dehumidifier is regarded as an energy-efficient device with high dehumidification effectiveness and cooling performance. This research project aims at investigating the dehumidification and cooling performance of a heat pipe internally-cooled liquid membrane-based desiccant dehumidification (HP-ICMLDD) system and its application in multi-family terraced houses under subtropical and humid Mediterranean climate conditions. The project also develops an integrated liquid desiccant air-conditioning (ILDAC) system by combining the HP-ICMLDD system with an air-water heat pump (AWHP), photovoltaics-thermal (PVT), and hot water storage. An innovative HP-ICMLDD system is established by integrating the heat pipe internal cooling method with the dehumidification system, where experimental investigation is conducted. Moreover, the energy simulation of the building with the ILDAC system has been conducted via the IES VE and EnergyPro software using the reference buildings (RBs) in Spain, Italy and Greece. The research output indicates that the dehumidification performance is influenced by the heat pipe's internal cooling effect, which is significantly improved by reducing the cold water temperature and increasing the cold water flow rate. The optimal operating conditions for the complete LDD system have been determined. For the dehumidifier in the HP-ICMLDD system, the optimal inlet cold water temperature, mass flow rate, solution temperature and solution concentration are 18 ℃, 0.017 kg/s, 18℃, 32%, respectively; For the regenerator in the system, the optimal solution temperature is 55 ℃. The correlations of thermal, electrical, total COP, air temperature and relative humidity at the dehumidifier outlet with the inlet air conditions have been generated using the linear regression method. It is found that the ILDAC system COP rises with the increasing inlet air temperature and relative humidity. By comparing the energy consumption of the residential building without and with the ILDAC system in three different locations, the building energy consumption is reduced by 77.6%, 74.8% and 78.8% in Barcelona, Rome and Methoni, and the corresponding carbon reduction rate is 88.8%, 84.3% and 76.9%. The ILDAC system could achieve higher COP of 6.41, 8.14 and 7.52 in Barcelona, Rome and Methoni, which are significantly higher than those of the complete LDD and AWHP systems. The discounted payback period varies between 7 and 9 years, with the annual return on investment ranging from 8.40% to 11.90%. Moreover, it is appropriate to invest in the ILDAC system in Spain, Italy and Greece when the inflation rates fall between -6.80% and 12.20%, -6.90% and 12.20%, and -5.40% and 8.70%, respectively

A heat pipe internally-cooled membrane-based liquid desiccant dehumidification system

In recent years, membrane-based liquid desiccant dehumidification has emerged as an efficient approach for air humidity control in building air conditioning process, in which the internally-cooled liquid desiccant dehumidifier is regarded as an energy-efficient device with high dehumidification effectiveness and cooling performance. This research project aims at investigating the dehumidification and cooling performance of a heat pipe internally-cooled liquid membrane-based desiccant dehumidification (HP-ICMLDD) system and its application in multi-family terraced houses under subtropical and humid Mediterranean climate conditions. The project also develops an integrated liquid desiccant air-conditioning (ILDAC) system by combining the HP-ICMLDD system with an air-water heat pump (AWHP), photovoltaics-thermal (PVT), and hot water storage. An innovative HP-ICMLDD system is established by integrating the heat pipe internal cooling method with the dehumidification system, where experimental investigation is conducted. Moreover, the energy simulation of the building with the ILDAC system has been conducted via the IES VE and EnergyPro software using the reference buildings (RBs) in Spain, Italy and Greece. The research output indicates that the dehumidification performance is influenced by the heat pipe's internal cooling effect, which is significantly improved by reducing the cold water temperature and increasing the cold water flow rate. The optimal operating conditions for the complete LDD system have been determined. For the dehumidifier in the HP-ICMLDD system, the optimal inlet cold water temperature, mass flow rate, solution temperature and solution concentration are 18 ℃, 0.017 kg/s, 18℃, 32%, respectively; For the regenerator in the system, the optimal solution temperature is 55 ℃. The correlations of thermal, electrical, total COP, air temperature and relative humidity at the dehumidifier outlet with the inlet air conditions have been generated using the linear regression method. It is found that the ILDAC system COP rises with the increasing inlet air temperature and relative humidity. By comparing the energy consumption of the residential building without and with the ILDAC system in three different locations, the building energy consumption is reduced by 77.6%, 74.8% and 78.8% in Barcelona, Rome and Methoni, and the corresponding carbon reduction rate is 88.8%, 84.3% and 76.9%. The ILDAC system could achieve higher COP of 6.41, 8.14 and 7.52 in Barcelona, Rome and Methoni, which are significantly higher than those of the complete LDD and AWHP systems. The discounted payback period varies between 7 and 9 years, with the annual return on investment ranging from 8.40% to 11.90%. Moreover, it is appropriate to invest in the ILDAC system in Spain, Italy and Greece when the inflation rates fall between -6.80% and 12.20%, -6.90% and 12.20%, and -5.40% and 8.70%, respectively

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

To investigate the technical feasibility of a novel cooling system for commercial greenhouses, knowledge of the state of the art in greenhouse cooling is required. An extensive literature review was carried out that highlighted the physical processes of greenhouse cooling and showed the limitations of the conventional technology. The proposed cooling system utilises liquid desiccant technology; hence knowledge of liquid desiccant cooling is also a prerequisite before designing such a system. Extensive literature reviews on solar liquid desiccant regenerators and desiccators, which are essential parts of liquid desiccant cooling systems, were carried out to identify their advantages and disadvantages. In response to the findings, a regenerator and a desiccator were designed and constructed in lab. An important factor of liquid desiccant cooling is the choice of liquid desiccant itself. The hygroscopicity of the liquid desiccant affects the performance of the system. Bitterns, which are magnesium-rich brines derived from seawater, are proposed as an alternative liquid desiccant for cooling greenhouses. A thorough experimental and theoretical study was carried out in order to determine the properties of concentrated bitterns. It was concluded that their properties resemble pure magnesium chloride solutions. Therefore, magnesium chloride solution was used in laboratory experiments to assess the performance of the regenerator and the desiccator. To predict the whole system performance, the physical processes of heat and mass transfer were modelled using gPROMS® advanced process modelling software. The model was validated against the experimental results. Consequently it was used to model a commercials-scale greenhouse in several hot coastal areas in the tropics and sub-tropics. These case studies show that the system, when compared to evaporative cooling, achieves 3oC-5.6oC temperature drop inside the greenhouse in hot and humid places (RH>70%) and 2oC-4oC temperature drop in hot and dry places (50%<RH< 65%)

Building integrated solar thermal collectors for heating & cooling applications

International Energy Agency Solar Heating & Cooling (IEA SHC) programme states the fact that space/water heating and cooling demand account for over 75% of the energy consumed in single and multi-family homes. Solar energy technology can meet up to 100% of this demand depending on the size of the system, storage capacity, the heat load and the region’s climate. Solar thermal collectors are particular type of heat extracting devices that convert solar radiation into thermal energy through a transport medium or flowing fluid. Although hybrid PV/T or thermal-alone systems offer some advantages to improve the solar heat utilisation, there are a few technical challenges found in these systems in practice that prevented wide-scale applications. These technical drawbacks include being expensive to make and install, inability of switching already-built photovoltaic (PV) systems into PV/T systems, architectural design etc. The aims of this project, therefore, were to investigate roof integrated solar thermal roof collectors that properly blend into surrounding thus avoiding ‘add on’ appearance and having a dual function (heat absorption and roofing). Another objective was to address the inherent technical pitfalls and practical limitations of conventional solar thermal collectors by bringing unique, inexpensive, maintenance free and easily adaptable solutions. Thus, in this innovative research, unique and simple building integrated solar thermal roof collectors have been developed for heating & cooling applications. The roof systems which mainly based on low cost and structurally unique polyethylene heat exchanger are relatively cost effective, competitive and developed by primarily exploiting components and techniques widely available on the market. The following objectives have been independently achieved via evaluating three aspects of investigations as following: • Investigation on the performance of poly heat exchanger underneath PV units • Investigation on the performance of a Building Integrated PV/T Roof ‘Invisible’ Collector combined with a liquid desiccant enhanced indirect evaporative cooling system • Investigation on the build-up and performance test of a novel ‘Sandwich’ solar thermal roof for heat pump operation These works have been assessed by means of computer simulation, laboratory and field experimental work and have been demonstrated adequately. The key findings from the study confirm the potential of the examined technology, and elucidate the specific conclusions for the practice of such systems. The analysis showed that water temperature within the poly heat exchanger loop underneath PV units could reach up to 36°C and the system would achieve up to 20.25% overall thermal efficiency. Techno-economic analysis was carried out by applying the Life Cycle Cost (LCC) method. Evaluations showed that the estimated annual energy savings of the overall system was 10.3 MWh/year and the cost of power generation was found to be £0.0622 per kWh. The heat exchanger loop was coupled with a liquid desiccant enhanced indirect evaporative cooling unit and experimental results indicated that the proposed system could supply about 3 kW of heating and 5.2 kW of cooling power. Lastly, the results from test of a novel solar thermal collector for heat pump operation presented that the difference in water temperature could reach up to 18°C while maximum thermal efficiency found to be 26%. Coefficient Performance of the heat pump (COPHP) and overall system (COPSYS) averages were attained as COPHP=3.01 and COPSYS=2.29, respectively. An economic analysis pointed a minimum payback period of about 3 years for the system

Water Ice Films in Cryogenic Vacuum Chambers

The space simulation chambers at Arnold Engineering Development Complex (AEDC) allow for the testing and calibration of seeker sensors in cryogenic, high vacuum environments. During operation of these chambers, contaminant films can form on the components in the chamber and disrupt operation. Although these contaminant films can be composed of many molecular species, depending on the species outgassed by warm chamber components and any leaks or virtual leaks (pockets of gas trapped within a vacuum chamber) that may be present, water vapor is most common, and it will be the focus of this dissertation. In this dissertation, some properties of the water molecule and low pressure ice are reviewed with a focus on the optical properties. The method of angular coefficients is utilized to calculate flux distributions for general three dimensional situations and the program written is applied to a model of the AEDC 10V space simulation chamber. The optical effects of varying amounts of contamination on a generic germanium window and gold mirror, along with the effects on two components specific to the space chambers, is determined. Also, an experiment to measure the thickness and other properties of contaminant films is discussed, and initial results are given for the first two tests of the experimental setup