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Abstract The operation of a solid desiccant evaporative cooling system largely depends on the dehumidification ability of the desiccant wheel and mathematical models are an effective tool to predict the transport behaviour of this wheel. A complete theoretical model would account for both the gas-side resistance, which is due to the convective heat and mass transfer between the air and the desiccant surface, and the solid-side resistance, which is caused by the diffusion of moisture and conduction of heat through the solid desiccant layer. A mathematical model is developed by deriving the partial differential equations of mass and energy balance of a representative channel the desiccant wheel moving through the supply and regeneration air streams in a 360° circular path. The effect of these resistances at different operating conditions on the performance of the wheel is rarely investigated. In this paper, two heat and mass transfer models are presented, the first one incorporating gas-side resistance and the second one includes both solid-side and gas-side resistances. The models are compared with experimental data. It can be concluded that the gas-side resistance is of considerably higher significance compared to the solid-side resistances. [ABSTRACT FROM AUTHOR]

Abstract A liquid desiccant-indirect evaporative cooling (LD-IEC) system has been proposed. The design is able to dehumidify and cool the product air simultaneously in one unit. A computational model has been developed to determine the performance of the heat and mass transfer process. The validation of the model demonstrated good agreement with the experimental data to within 10%. The detailed air treatment process has been theoretically studied. The thermal performance of the LD-IEC has been evaluated. Simulation results showed that the outlet temperature and humidity ratio were influenced by the liquid desiccant film length, intake air temperature, and intake air humidity ratio. For a specific inlet temperature and humidity ratio condition, a desired outlet condition can be obtained by adjusting the length of the liquid desiccant film. [ABSTRACT FROM AUTHOR]

A novel design of rotary desiccant wheel has been tested experimentally in a two channel duct with countercurrent flow arrangement. Silica gel coated radial blades extending from the centre of the wheel were arranged at equally spaced intervals in 32-blade and 20-blade configurations. The design was focused on reducing the pressure drop across the device, as well as the regeneration temperature required for desorption of the desiccant compared to 80-120°C temperature currently required. It was envisioned that the increased air volume between radial blades would reduce the pressure drop and the regeneration temperature would be lowered due to the use of silica gel beads as compared to powder coating. The maximum pressure drop across the device was measured as 10.31Pa, significantly lower than current dehumidification systems. The regeneration air temperatures were set between 25°C and 40°C, increasing at 5°C increments. The experiments showed that reduction of the relative humidity of the airstream by up to 67% was possible within this range, whilst the silica gel continued to desorb water molecules, even at regeneration temperatures as low as 25°C. Further investigation with various parameter variables and designs will be undertaken to optimise the rotary desiccant wheel for low pressure drop and low regeneration air temperature. [ABSTRACT FROM AUTHOR]

By using small, decentralized liquid desiccant dehumidification combined with radiant panels or other low exergy chiller technologies large amounts of energy can be saved. This study builds off previous work characterizing a novel liquid desiccant system using a vapor permeable Pebax® membrane in conjunction with an alkoxylated siloxane liquid desiccant. Previous work addresses the chemical viability of the membrane/desiccant pair to produce dehumidified air by leveraging partial pressure differences as well as the full scale adaptation including pumping and regeneration costs. This study considers the overall heat and mass exchange of such a system, from initial kinetics experimentation through scaling the system up to dehumidify air at building-level flow rates, and develops a 3D printed prototype mass exchanger element for kinetic optimization. The results show further progress in the development of novel mixing stages to maintain good kinetics for water vapor removal from the air stream. [ABSTRACT FROM AUTHOR]

An experimental study of the performance of an air conditioning system, using the concept of humidification-dehumidification is presented and investigated. The technique (AWVP) relies on utilizing the moisture present in atmospheric air and to increase its content to certain extent. The water extracted through this technique is of good standard and can be used for drinking and other purposes. The test setup consists of four loops namely fresh water circuit, air circuit, refrigerant circuit and dirty water circuit. Certain operating parameters like volume flow rate of air, air inlet temperature after heating and relative humidity was varied and its effect on the performance of the system was studied and analyzed. [ABSTRACT FROM AUTHOR]

The main objective is to develop and experimentally investigate a thermoelectric fresh water generator (TFWG) based on the fundamental of Thermoelectric Cooling Effect by condensing the moisture from the ambient moist air. It can be made useful to the people in coastal and humid regions with relative humidity above 60% having scarcity of drinking water. A prototype of the generator consisting of a 0.7 m long cooling channel along with ten thermoelectric modules of dimension 0.04 * 0.04 m2 each placed linearly in an array is fabricated and experimented. An internal heat sink of surface area 0.2m 2 and length 0.65m is placed on the cold side of the modules to enhance heat transfer rate. The observations from the experiments show that with the use of internal heat sink, the quantity of water generated per 10 hours increases by 81% as compared without internal heat sink. Electric current, air mass flow rate and humidity of moist air were varied to understand their impact on the quantity of water generated. Based upon the observed results, the quantity of water generated is directly proportional to all the three parameters in the domain of experimentation. [ABSTRACT FROM AUTHOR]

The productivity of the humidification-dehumidification solar desalination systems (HDHSDS) significantly increases when the temperature of the feed water increases, so, high temperature solar water collectors as parabolic trough or evacuated tube collectors are recommended for these systems. On the other hand, the effect of air temperature on the productivity of the HDHSDS is insignificant. Thus, the utilization of solar air heater is not recommended in these systems. Based on these recommendations, three research points are suggested for future work: 1) using the recovered PV thermal energy for heating the feed water in the HDHSDS. This will provide an annual fresh water productivity more than 833 L/m 2 of PV in addition to 278 kWh of electricity; 2) using phase change material with melting temperature around 90 ˚C as a thermal energy storage medium to provide feed water with high and almost constant temperature during the day and keeps the system in operation 24 h/day; 3) using the thermal energy rejected from the thermal power cycles for water heating in the HDHSDS. [ABSTRACT FROM AUTHOR]

Liquid desiccant dehumidifier is one of the most desirable systems for dehumidification of air when compared to conventional refrigeration system and solid desiccant based dehumidifier. In the present study, a finite difference model is developed to simulate the coupled heat and mass transfer processes occur in a counter flow adiabatic dehumidifier employing lithium chloride (LiCl) as a desiccant solution. Mat-lab R13 is used as a simulation package for solving the aforementioned model. This model has taken into the consideration of thermal effectiveness, effective height and moisture effectiveness as variable parameters for obtaining the correlation of the desired operating parameters. The predicted numerical parameters for absorption process have good agreement with the experimental data reported in the literature. This model is unique and can be extended to any type of liquid desiccant solution by changing the solution properties. The performance analysis of adiabatic counter flow dehumidifier is also carried out by varying the operating parameters and the detailed results are presented in the full manuscript. [ABSTRACT FROM AUTHOR]

This study aims to investigate the hygrothermal environment by estimating the room air conditioner (RAC) heat load in a room with hygroscopic materials. The sensible and latent heat capacity and the water retention quantity in the RAC indoor unit are tested in cooling and dehumidification operation modes. Then, a model is developed to predict their values and investigate room temperature and humidity. The RAC model numerical analysis estimates the heat load by taking into account indoor hygroscopicity. In particular, the water is retained from several hundred grams to approximately 1 kg in the indoor unit. The RAC model is implemented considering the heat exchanger temperature distribution. In the weak cooling dehumidification mode, the room relative humidity is maintained between larger than 5% and 8% of the target value with and without hygroscopicity, respectively. Hygroscopicity does not affect the heat load in the bedroom during night time. [ABSTRACT FROM AUTHOR]

Museum storage buildings should be able to provide a considerable stable indoor environment in terms of temperature and relative humidity (RH). To obtain such stable conditions with the lowest possible energy consumption, passive air conditioning is one-way solution. In this paper, indoor environment facilities of a passive museum storage building in Vejle region in Denmark, are investigated. Results demonstrate that the weather conditions of the previous yearś considerably affect the indoor environment of the storage. What is more, concentrated dehumidification is a sufficient technique to maintain RH within acceptable levels. Therefore, renewable energy such us excess wind energy during the night can be utilized. [ABSTRACT FROM AUTHOR]

Solar-assisted liquid desiccant air-conditioning system (SLDAC) has been considered as a promising application as traditional AC systems have many problems. In this paper, the operation performance of the SLDAC of a typical commercial building in Hong Kong was investigated, for evaluating the energy-saving potential. Combing the numerical model of individual component and inputting the weather data and load profile, the annual energy consumptions of SLDAC and traditional system could be obtained. The simulation results show that the electricity driven LDAC is not suitable for the commercial building due to the high energy demand in the regeneration. But, the solar-assisted system with thermal storage could provide promising energy saving potential. However, with the cooling tower as the only cooling source of the dehumidifier, the dehumidification capacity could not satisfy the requirement and only up to 12.5% of electricity consumption could be saved annually compared to traditional systems. Therefore, to improve the energy-saving potential, extra cooling source should be supplied for the application of SLDAC of buildings in Hong Kong. [ABSTRACT FROM AUTHOR]

Radiant cooling is an alternative air-conditioning that have been implemented successfully in high latitude regions. In tropical region as Thailand, radiant cooling is quite challenge due to its cooling performance being limited by high-moisture ambient air. This paper reports an investigation of radiant cooling in a tropical building. The study comprises full-scale experiments of a radiant cooling system with cool panels installed in a room of a laboratory building. A separate fan coil unit was installed to remove humidity of the ventilation air before suppluying it into the room. A software namely TRNSYS was used to model the systems in order to determine the heat extraction rate of the cool panels. Thermal comfort level in the room was evaluated by predicted mean vote (PMV) index. The results show that the radiant cooling is able to use for air conditioning for human comfort in tropical buildings. However, a sophistical system to control temperature of the chilled water supplied to the cool panels and the fan coil unit for the ventilation air dehumidification is inevitably required. [ABSTRACT FROM AUTHOR]

Abstract: The current work focuses on the Queen''s University Solar Liquid Desiccant Cooling Demonstration project. A solar Liquid Desiccant Air Conditioning system (LDAC) has been installed at a field site in Kingston, Ontario, Canada, and is currently being tested to evaluate the performance of the system when driven by solar energy. The installed system features a low-flow parallel plate liquid desiccant air conditioner, and a 95m2 evacuated tube solar collector array. While summer testing has only recently begun, five test days have shown an overall solar collector efficiency of 56%, solar fraction of 63% and a thermal COP of 0.47. The average total cooling was 12.3kW and average latent cooling was 13.2kW. The solar array was also operated between October 2011 and May 2012 and heat was rejected using a dry cooler. Over the heating season 18,800kWh were collected with an average collection efficiency of 61%. TRNSYS simulations over-predicted the amount of energy collected by 13% (21,264kWh) likely due to failed vacuum tubes, snow cover of collectors, and improper sensor location. [Copyright &y& Elsevier]

Abstract: In this paper, performance of the liquid desiccant dehumidification system in evaporation coolers was investigated by the Second Law of Thermodynamics analysis. This system was designed and manufactured for this purpose. Lithium chloride (LiCl), as liquid desiccant, and a packed bed column were used for dehumidification. The described system includes a part for processed air simulation in various temperatures and humidities. Entropy generation of the liquid desiccant dehumidifier was analyzed based on the second thermodynamic law. The effect of inlet parameters of the dehumidification column on the entropy generation was also investigated. The results showed that the entropy generation was highly dependent to operational conditions and inlet parameters of the desiccant dehumidification column. [Copyright &y& Elsevier]

Abstract: The objective of this research is evaluating and comparing two methods of improving dehumidification in air conditioning systems. The two methods are the hybrid system: (refrigeration cycle – rotary desiccant) and the heat exchanger cycle. The impact of the desiccant performance on the hybrid system performance was studied. The impact of the heat exchanger efficiency on the performance of heat exchanger cycle was studied. Hybrid system, heat exchanger cycle, and conventional refrigeration cycle were compared at different design air flow rates and different air conditions. It was found that the hybrid system and the heat exchanger cycle can achieve lower SHR and dew point temperature than those of the conventional cooling system. On general, the hybrid system can achieve lower SHR and dew point than those of the heat exchanger cycle. Although the heat exchanger cycle can achieve lower SHR and dew point than those of the conventional cooling system, the coefficient of performance and the cooling effect of the heat exchanger cycle are lower than those of the conventional cooling system, because the temperature of the cooling coil of the heat exchanger cycle is lower than that of the conventional cooling system. The coefficient of performance and the cooling effect of the hybrid system are close to those of the conventional cooling system, because the temperature of the cooling coil of the hybrid system is close to that of the conventional cooling system. [Copyright &y& Elsevier]