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[en] Highlights: •Thermodynamic principles are applied to systematically compare three technologies. •Merits and limits of standalone versus integrated designs are identified. •Effect of climate conditions on performance and technology selection is evaluated. •Integrated desiccant/membrane technologies outperform current state-of-the-art VCS. -- Abstract: 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.
[en] Regenerator is major component of liquid desiccant regeneration system. The influence of operating parameters; air flow rate, solution flow rate and concentration of desiccant is investigated experimentally on the performance parameters; outlet specific humidity, evaporation rate, air outlet temperature, mass transfer coefficient and effectiveness of the regenerator. Air and desiccant solution flow in counter direction with celdek pads as packing material. It is concluded that evaporation rate increases with increasing solution temperature, air flow rate and solution flow rate whereas same decreases with increasing concentration of desiccant. The effectiveness of regenerator is increased by 99 % with increase in air flow rate. A comparison of present finding with those available in the literature is presented in the last. Simulation results have revealed good agreement between the present experimental results.
[en] Concerning reevaluation research of the Hiroshima atomic bomb neutron, there was the necessity of measuring amount of moisture in the exposure rock. The moisture analysis technique which is ever known in the geochemistry field is examined in detail and the water-content characteristic experiments were carried. It was deduced that there were other two kinds of component of the conventional water content as a result. (author)
[en] The effect of water molecules on the electrostatic collection of 218Po ions onto the surface of silicon detectors (neutralization) is evaluated through the comparison with a scintillation cell (ZnS), not affected by air humidity. A radon monitor (RAD7, Durridge Company) was connected to a stainless steel radon chamber, equipped with the scintillation cell. Radon gas, extracted from an acidified RaCl2 source, was injected into the chamber and the amount of water molecules in the system was alternatively lowered or increased (from 0.00075 to 0.014 g of water in RAD7) by connecting the chamber to a desiccant or to a bubbling water bottle. The relative efficiency of the silicon detector with respect to the scintillation cell decreases with the growth of water molecules inside RAD7. This dependence, with a fixed i) electrostatic chamber geometry and ii) nominal high voltage, diverges during the humidification or the drying phase because it is in turn influenced by the length of interaction of polonium atoms with water molecules, which impacts on the size of 218Po clusters and thus on the neutralization process. For water contents higher that 0.01 g in RAD7, this effect is greatly enhanced. Temperature in the investigated range (18.5–35.6 °C) does not affect the efficiency of electrostatic collection-based silicon detectors. Based on these experiments, admitting a certain error on the efficiency (from 1.8 to 7.5%, depending on the water content), proper corrections were developed to adjust soil radon readings, when a desiccant is removed. This operation is necessary if recent Non-Aqueous Phase Liquids (NAPLs) leakage has occurred in the subsoil to avoid the sorption and possible later release of radon by Drierite, with related partition between the solid and liquid phases (water and NAPL). - Highlights: • Desiccant needs to be removed when measuring soil radon in NAPL polluted soils. • H2O interference on electrostatic collection has been studied. • Efficiency corrections vs water content in RAD7s have been experimentally obtained. • Delayed efficiency recovery has been evidenced when using RAD7 without desiccant. • Corrections are specific for single RAD7 instruments.
[en] Highlights: • The study objective is to reduce the energy consumption of desiccant AC system. • Heat and mass losses are recovered in the proposed system using a condenser. • The conventional and the proposed systems are compared in terms of COP. • The proposed system performance is better than the conventional system. • The proposed system produces freshwater in addition to space cooling. - Abstract: Liquid desiccant air conditioning systems are cost-effective, environmentally friendly and energy efficient techniques, especially in coastal areas. In the conventional liquid desiccant air conditioning system, the scavenging air is expelled into the atmosphere carrying a considerable amount of energy and water vapor. Thus, there is plenty of room to improve the system performance by recovering these losses. The proposed system consists of a conventional liquid desiccant air conditioning system plus a condenser. The aim of this study is to reduce the energy consumption by recovering the heat from the scavenging air using the condenser while also producing freshwater in addition to space cooling. Lithium chloride (LiCl) is used as the liquid desiccant for this study. The mathematical formulation for simultaneous heat and mass transfer between the condenser and the regenerator was developed to establish a comparison between the performance of the conventional and modified systems. Using the generated model, it is found that the modified system performance is 11.25% better than the conventional system and that it produces 86.4 kg of freshwater per hour as a by-product under the given conditions.
[en] A cross-flow heat exchanger type adsorber was investigated for a desiccant humidity control system. The aim of the adsorber was to improve dehumidification performance by forcibly cooling an adsorbent with flowing air. Aluminophosphate (AlPO) zeolite was coated on the heat exchanger, because it was expected to regenerate sufficiently even with a low-temperature heat source of around 333 K. Fundamental dehumidification behavior with the adsorber was experimentally investigated at various inlet absolute humidities, regeneration temperatures, and air flow velocities. Dehumidified water in an equilibrium state was kept even at a regeneration temperature of 333 K, indicating that the adsorber coated with AlPO zeolite could be driven using low-temperature heat at 333 K. The dehumidification rate was found to increase as the cooling and the process air velocities increased. However, the increase in the dehumidification rate decreased when the cooling air flowed at a velocity of 2 m/s or more. Heat removed by the cooling air increased as the cooling air velocity increased and the process air velocity decreased. It was also found that dehumidified air could be supplied for a longer period at a sufficiently low absolute humidity suitable for practical use as the cooling air velocity increased.
[en] Highlights: • The performance of a solar hybrid air conditioner integrated with HDH desalination system is numerically investigated. • For increase the regeneration air from 70 to 130 m3/h, the distillate water productivity increases from 2.988 to 4.78 L/h. • For increase the regeneration air from 70 to 130 m3/h, COPoverall daily decreases from 4.66 to 3.386. • For increases the regeneration air temperature from 75 to 95 °C, the distillate water increases from 3.1752 to 5.011 L/h. • For increases the regeneration air temperature from 75 to 95 °C, COPoverall daily decreases from 4.392 to 3.636. - Abstract: In this study, the performances of a solar energy assisted hybrid desiccant air conditioning system integrated with humidification–dehumidification (HDH) desalination system are numerically investigated. The aim of this study is to benefit from the temperature rise of the regeneration air outside of the desiccant conditioning system as well as the water vapor content in this regeneration air by feeding it to the humidification-dehumidification water desalination unit to produce distillate water. The distillate water productivity, human thermal comfort issues, and energy saving represent the main objective of the present numerical study. The simulated results developed for subsystems are validated with the published experimental results. The effects of regeneration air temperature and flow rate on supply cooled air temperature, distillate water productivity, the cooling coefficient of performance and overall daily coefficient of performance of the proposed system are investigated. The results show that (i) the distillate water productivity increases from 3.175 to 5.011 L/h and overall daily coefficient of performance decreases from 4.392 to 3.636 with increasing the regeneration air temperature from 75 to 95 as (ii) the increase in the regeneration air flow rate from 70 to 130 m3/h, increases the distillate water productivity from 2.988 to 4.78 L/h and decrease the overall daily coefficient of performance from 4.66 to 3.386. The study demonstrates that the proposed system represents the best options in hot and humid regions.
[en] Graphical abstract: Cycle performance of a small scale heat pump type air conditioner coupled with a liquid desiccant/humidification cycle has been theoretically and experimentally evaluated by the present study. The liquid desiccant and humidification cycle is driven by the exhaust heat of the compressor. LDAC not only greatly improves the indoor air quality by controlling the humidity and temperature independently, but also decrease the electrical energy consumption of the traditional air conditioner. Parametric analysis on cycle performance of the present cycle based on both theoretical and experimental methods are carried out. - Highlights: • Hybrid cycle consists of refrigeration cycle and liquid desiccant cycle is proposed. • Liquid desiccant cycle is driven by the compressor exhaust heat. • Theoretical and experimental studies on cycle performance are provided. • Energy consumption decreases about 22.64% compared with the conventional one. - Abstract: In recent years, liquid desiccant air-conditioning system (LDAC) has shown a great potential alternative to the conventional vapor compression systems. LDAC not only greatly improves the indoor air quality by controlling the humidity and temperature independently, but also deceases the electrical energy consumption of the conventional air conditioner. In this work, the liquid desiccant and humidification cycle is driven by the exhaust heat of the compressor. Cycle performance of a small-scale heat pump type air conditioner coupled with a liquid desiccant/humidification cycle has been theoretically and experimentally evaluated by the present study. Parametric analysis on cycle performance of the present cycle is carried out through both theoretical and experimental methods, and lithium chloride aqueous solution is used as the working fluid of the solution cycle. The thermodynamic analysis results show that while the evaporating temperature of the present cycle increases to 15 °C, the energy consumption decreases by about 22.64% when compared with conventional air conditioner. Theoretical results also indicate that the coefficient of performance (COP) of the novel system has a potential improvement of about 35.3%. Based on the theoretical results, experimental analyses of this novel cycle under summer and winter working conditions are carried out. In addition, comparison of the humidification and dehumidification ability as well as COP of the present novel system and the traditional one are carried out. Researching results of the present study provide important reference for investigator of this field.