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[en] Highlights: • Preparation and characterization of clay additives based CaCl2 composite desiccant is described. • The exit air humidity ratio relative to inlet air humidity ratio is expressed in terms of percentage reduction in moisture. • Process air relative humidity, air velocity and bed weight influences the dehumidification performance. • Experimental results for percentage reduction in moisture are compared with theoretical mass transfer model. - Abstract: Transported clay suitable for pot making is used as desiccant carrier. Additives like saw dust and horse dung are considered in particle preparation. Particles nearly spherical in shape are prepared manually and are dried under shadow and subsequently the particles are dried at different temperatures. These burnt particles are characterized for pore volume and surface area. The BET test reveals that clay particles subjected to 500 °C possess higher pore volume but clay-horse dung particles exhibit higher surface area. Heat treated particles of clay with additives are impregnated with CaCl2 solution of 50% concentration. The ratio of desiccant water content to surrounding layer water content varies from 14.09 to 75.34 for CaCl2 based composite desiccants. One dimensional PGC mass transfer model for process air through burnt clay – additives - CaCl2 desiccant bed is adopted. The RMSE of measured and predicted results for reduction of moisture content from the process air by composite desiccant beds are in the range of 3.26–13.2%.
[en] Highlights: • The experimental operation of a solar driven hybrid DEC system is presented. • In situ monitoring data are analysed and compared to the system’s expected performance. • Drawbacks affecting the system’s performance are explained. • Fine-tuning of the control and maintenance strategy of the main system components is suggested. - Abstract: The aim of this paper is to report on a two-year operational experience with a solar driven desiccant and evaporative cooling (SDEC) system coupled with a vapour compression heat pump. The main objectives are to analyse the benefits and drawbacks of this innovative hybrid SDEC system, to compare the monitoring results against the expected theoretical ones, and to assess the system’s performance with respect to a reference air handling unit. The comparison focuses on the summer key operation modes using Primary Energy Ratio (PER) as indicator of the entire system performance. The results of the detailed analysis lead to the following conclusions: the specific design of the hybrid SDEC leads to high air quality, simpler control process and low electricity consumption for partial load conditions. The monitoring results show a summer mode PER 20% lower than expected due to underperformance of the desiccant wheel. Nevertheless, this innovative system is still very efficient as its PER is twice as high as the one of the considered reference system. Lastly, suggestions for optimization of the existing system through the fine-tuning of the control strategy of its main components are presented.
[en] Highlights: • An adjacently internally-cooled plate membrane liquid desiccant dehumidifier (AIMLDD) is applied. • The AIMLDD is used for liquid desiccant air dehumidification. • A lumped parameter model is established to study the heat and mass transports in the AIMLDD. • An analytical solution of the performances are obtained and experimentally validated. • The performances of the AIMLDD are about 3.3–9.1% larger than those of the cooling tube type. - Abstract: An adjacently internally-cooled plate membrane liquid desiccant dehumidifier (AIMLDD) is like a four-fluid heat and mass exchanger. The feed air and the solution streams flow in the neighboring channels formed by plate membranes. The water falling film and the sweeping air stream flow in the cooling channel formed by two plastic plates. Absorption heat generated in the solution by absorbing the water vapor transferred from the feed air across the membranes can be taken away by the water. A lumped parameter model is established in a unit cell containing half of a feed air channel, a membrane, a solution channel, and half of a cooling channel, to study the heat and mass transports in the AIMLDD. An analytical solution of the normalized governing equations is obtained. Cooling effectiveness, dehumidification effectiveness, dehumidification rate, energy transfer rate of the feed air, and the ratio of the sensible heat transfer rate of the water to the energy transfer rate are calculated and experimentally validated. The performances of the AIMLDD are compared with those of an internally-cooled plate membrane liquid desiccant dehumidifier with cooling tubes inside the solution channels (IMLDD). The performances of the AIMLDD are about 3.3–9.1% larger than those of the IMLDD.
[en] Highlights: • A hybrid liquid desiccant-heat pump for cooling in humid regions was modeled. • Modeling was performed in energy, exergy, economic and environmental aspects. • By two objective functions and eight system design parameters system was optimized. • Using LD-HP system decreased the electricity consumption for 45.6% with COP 4.83. • With payback period 3.37 years, CO2 production was decreased for 3.12 (45.6%) kg. - Abstract: A hybrid liquid desiccant-heat pump (LD-HP) system for cooling in hot and humid regions is modeled and optimized in this paper. This hybrid LD-HP system contained dehumidifying and cooling sections. The whole system was modeled and analyzed in four energy, exergy, economic and environmental aspects. Then the system was optimized using multi-objective Genetic Algorithm (GA) method. With two objective functions (total annual cost and exergy efficiency) and eight system design parameters the optimum values of design parameters were estimated. Results for our case study showed that the proposed optimized LD-HP system decreased the electricity consumption for 33.2% in comparison with that for an electrical HP system during seven months of operation in a year (18.9% due to using desiccant dehumidifying system and 81.1% due to using a heat exchanger instead of an electrical heater). This amount of lower electricity consumption also provided 1.85/year lower CO2 production (33.2%) in comparison with that for a conventional HP system. The COP of LD-HP system at the optimum point was also about 4.83 (in comparison with 2.74 for the conventional case in which heat pump and electrical heater were used). Finally, added equipment to the traditional HP system (dehumidifier, regenerator, heat exchangers, pumps and fans) had 3.04 years payback period.
[en] Highlights: • The energy potential and desiccant capacity of two HVAC systems was analysed. • Both HVAC systems served air to a spa room for 6 different climate zones. • The energy consumption of the DW-IEC system was lower than that of the DX system. • High energy savings were obtained with the DW-IEC system for hot climate zones. • These energy savings resulted in better SCOP values for the DW-IEC system. - Abstract: Air handling in buildings with high latent loads usually requires a high-energy cost to satisfy the user’s thermal comfort needs. Hybrid systems composed of desiccant wheels, DW, and indirect evaporative coolers, IEC, could be an alternative to direct expansion conventional systems, DX systems. The main objective of this work was to determine the annual energy consumption of a hybrid system with a DW activated at low temperatures and an IEC, DW-IEC system, compared to a DX system to serve air in a small building with high latent loads, such as spas. Several annual energy simulations for 6 climate zones were performed, analysing electric energy consumption, seasonal mean coefficient of performance, SCOP, and energy consumption per unit of dehumidified water, Econs, of each system. The simulations were based on experimentally validated models. The annual energy consumption of the DW-IEC system was lower than that of the DX system for the 6 climate zones, achieving significant energy savings, up to 46.8%. These energy savings resulted in better SCOP values for the DW-IEC system. Therefore, the proposed DW-IEC system has high potential to reduce energy costs, achieving the user’s thermal comfort.
[en] Highlights: • Performance of closed-type heat-source tower (CCHT) is investigated experimentally. • Correlations of heat and mass transfer coefficients for the CCHT are developed. • Mass transfer coefficient of CCHT is larger than that of liquid dehumidifier. • Latent heat ratio of CCHT is 6–31%, while that of liquid dehumidifier is 42–124%. - Abstract: A heat-source tower heat pump (HTHP) is a potential heating source for space heating due to frost-free characteristic. The heat and mass transfer between the antifreeze solution and air at low ambient temperatures is a key issue for performance enhancement. In this study, a test bench for evaluating the cross-flow closed-type heat-source tower (CCHT) is fabricated to investigate its performance under variable working conditions. Based on the experimental results, correlations of heat and mass transfer coefficients are developed, which can be used to predict the performance of the CCHT. As a result, the mass transfer coefficient between the solution and the air of the CCHT is 0.015–0.051 kg m−2 s−1, while that of the liquid desiccant dehumidifier is 0.0037–0.015 kg m−2 s−1. However, the latent heat ratio of the CCHT is 6–31%, while that of the liquid desiccant dehumidifier is 42–124%.
[en] Highlights: • A novel refrigerant subcooling method is experimentally studied for the first time. • Condensation heat is used to drive an integrated cycle to subcool the refrigerant. • COP and exergy efficiency are improved by 18.6% and 27.9% respectively. • Effects of key parameters on the system performance are disclosed. • Economic analysis shows payback period varies from 2.4 to 3.2 years. - Abstract: Refrigerant subcooling could increase the refrigerating capacity and potentially improve the performance of refrigeration systems. In this paper, a novel subcooling method is experimentally studied for the first time in a hybrid vapor compression refrigeration system. In this system, condensation heat (~40 °C) is used to drive an integrated subcooling cycle to subcool the refrigerant leaving the condenser, which significantly increases the system performance. Changes in system performance are measured as functions of the following variables: the mass flow rates of the dehumidification air, ambient air, dehumidification solution, regeneration solution, and spraying water. Comparisons are made between the proposed system and the traditional water-cooled chiller. The proposed system can achieve a larger degree of subcooling (15–20 °C); what’s more, it shows much higher performances than the traditional water-cooled chiller: COP and exergy efficiency of the chiller are improved by 18.6% and 27.9%, respectively. Performance of the integrated subcooling cycle is also evaluated; it has a low COP, with the maximum value of 0.13, due to the low-grade condensation heat; however, it has a pretty high exergy efficiency, with the maximum value of 0.28, which indicates the effective use of the low-grade heat. In addition, an economic analysis of the integrated subcooling cycle is made with a project life cycle of 15 years; the payback period varies from 2.4 to 3.2 years based on different electricity tariffs, and the savings to investment ratio is between 1.3 and 2.1, which indicates that the project is profitable.
[en] Highlights: • A liquid-desiccant dehumidification system is raised for industrial applications. • The low-temperature heat is efficiently used in a cascaded way. • The new system can save 92.29% power comparing to the conventional system. • The ratio of saving power to absorbed heat can reach 7.35% in proposed system. • A driving force analysis and an economic and environmental analysis is given. - Abstract: Cooling dehumidification driven by power is widely used in industrial processes to obtain dry air, but the main drawback is its large power consumption. In these processes, large amounts of low-temperature waste heat are released to the environment directly, so there is a great energy-saving potential to recover low-temperature waste heat and generate dry air. A new two-stage liquid desiccant dehumidification system with the cascade utilization of low-temperature heat is proposed. The waste heat is used in a cascade manner. The higher-temperature heat is used to generate a strong desiccant solution, which will be used in the first-stage dehumidifier. The lower-temperature heat is used to drive a single-effect absorption refrigerator and provide cooling energy to the second-stage dehumidifier. Simulation results showed that the proposed system can reduce electricity consumption by 92.29% compared with the conventional cooling dehumidification system driven by power. The ratio of electricity savings to absorbed heat can reach 7.35%. The advantage of the cascade utilization of the low-temperature heat was further illuminated by studying the driving force in the dehumidifiers, and a preliminary economic and environmental analysis was performed. The increased initial investment can be recovered in only 3.39 years. Approximately 11,028 tons of standard coal are saved per year, and a reduction of 27,488 tons CO2 can also be realized per year. Finally, a parametric sensitivity analysis was conducted to optimize the system performance. This study may provide a new method to perform dehumidification by efficiently using a low-temperature heat source.