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[en] Ongoing research and development works suggest that good system configurations have significant potential for improving the performance and reducing the cost and size of rotary desiccant dehumidification and air conditioning system. In this paper, a novel desiccant cooling system using regenerative evaporative cooling and a one-rotor two-stage desiccant cooling system are analyzed and compared under Air-conditioning and Refrigeration Institute (ARI) summer, ARI humid and Shanghai summer conditions. The objective of this paper is to compare the thermodynamic performance of the two systems and obtain useful data for practical application. It is found that compared with the conventional desiccant cooling system, the novel desiccant cooling system with regenerative evaporative cooling can handle air to a much lower temperature while maintaining good thermal performance. Under ARI summer, ARI humid and Shanghai summer conditions, the minimum attainable supply air temperatures are reduced from 13.5 °C to 7.9 °C, from 14.2 °C to 9.2 °C and from 18.0 °C to 13.0 °C respectively. It is suggested that the novel desiccant cooling system with regenerative evaporative cooling is beneficial to breaking the obstacle of limited temperature reduction encountered by conventional desiccant cooling system, especially in the case of extreme high humid conditions. - Highlights: ► Desiccant cooling system with regenerative evaporative cooling (REDC) has been studied. ► Comparison between REDC and conventional desiccant cooling system (DCS) has been performed. ► REDC is superior to conventional DCS in thermal utilization, air conditioning and energy saving. ► REDC has significant potential for breaking the obstacle of limited temperature reduction.
[en] Air conditioning system based on liquid desiccant has been recognized as an efficient independent air humidity control HVAC system. To improve thermal coefficient of performance, a novel two-stage liquid desiccant dehumidification system assisted by calcium chloride (CaCl2) solution is developed through exergy analysis based on the second thermodynamic law. Compared with the basic liquid desiccant dehumidification system, the proposed system is improved by two ways, i.e. increasing the concentration variance and the pre-dehumidification of CaCl2. The exergy loss in the desiccant-desiccant heat recovery process can be significantly reduced by increasing desiccant concentration variance between strong desiccant solution after regeneration and weak desiccant solution after dehumidification. Meanwhile, the pre-dehumidification of CaCl2 solution can reduce the irreversibility in the regeneration/dehumidification process. Compared to the basic system, the thermal coefficient performance and exergy efficiency of the proposed system are increased from 0.24 to 0.73 and from 6.8% to 23.0%, respectively, under the given conditions. Useful energy storage capacity of CaCl2 solution and LiCl solution at concentration of 40% reach 237.8 and 395.1 MJ/m3, respectively. The effects of desiccant regeneration temperature, air mass flux, desiccant mass flux, etc., on the performance of the proposed system are also analyzed.
[en] A concentrating solar collector based on linear Fresnel lens is investigated experimentally in this paper. This solar collector is expected to acquire a higher thermal efficiency at a relatively high temperature level than the commonly used flat-plate or evacuated tube solar collectors. Experimental results show that the thermal efficiency is about 50% when the conversion temperature (water) is 90 deg. C. The test shows that the indication of lost energy is 0.578 W/m2 K, which is much smaller than that of commonly used evacuated tube solar collector without concentrating. In order to make analysis, a mathematical model for evacuated tube absorber heated by linear Fresnel lens has been built. The validation shows that the model agrees with the experimental data well. The analysis indicates that Fresnel lens collector with evacuated tube absorber has good efficiency (50%) in clear day even when the conversion temperature approaches 200 deg. C. The influence of ambient conditions and the percent of different types of energy loss, etc., are also analyzed.
[en] Highlights: ► A solar desiccant cooling/heating system is simulation studied. ► The mean deviation is about 10.5% for temperature and 9.6% for humidity ratio. ► The 51.7% of humidity load and 76% of the total cooling can be handled. ► About 49.0% of heating load can be handled by solar energy. ► An optimization of solar air collector has been investigated. - Abstract: To increase the fraction of solar energy might be used in supplying energy for the operation of a building, a solar desiccant cooling and heating system was modeled in Simulink. First, base case performance models were programmed according to the configuration of the installed solar desiccant system and verified by the experimental data. Then, the year-round performance about the system was simulated. Last, design parameters of solar air collectors were optimized that include collector area, air leakage and thermal insulation. Comparison between numerical and experimental results shows good agreement. During the simulation, the humidity load for 63 days (51.7%) can be totally handled by the two-stage desiccant cooling unit. For seasonal total heating load, about 49.0% can be handled by solar energy. Based on optimized results, the thermal energy subsystem functioned to its expected performance in solar energy collection and thermal storage
[en] Experimental comparison between two honeycombed desiccant wheels, namely, a conventional one treated with silica gel and a new one fabricated with a new kind of composite desiccant material, was made in this paper. It is found that the newly developed composite desiccant wheel performs better than the conventional one and can remove more moisture from air by approximately 50%. Also encouraging is that the new desiccant wheel can be driven by a lower regeneration temperature for acquiring the same amount of moisture removal. The reason is that the composite desiccant materials, which are constructed with LiCl and silica gel solutions in an optimal way, behave better than silica gel in moisture adsorption, according to the findings from the scanning electron microscope (SEM) pictures as well as the equilibrium adsorption test results. Some parameters, such as inlet air humidity, regeneration temperature, air mass flow rate, etc., which may affect the performance of the desiccant wheels, are also analyzed and discussed. It is further identified that the new composite desiccant wheel has potential for dehumidification applications in many fields
[en] Multi-source systems for the fulfilment of electric, thermal and cooling demand of a building can be based on different technologies (e.g. solar photovoltaic, solar heating, cogeneration, heat pump, absorption chiller) which use renewable, partially renewable and fossil energy sources. Therefore, one of the main issues of these kinds of multi-source systems is to find the appropriate size of each technology. Moreover, building energy demands depend on the climate in which the building is located and on the characteristics of the building envelope, which also influence the optimal sizing. This paper presents an analysis of the effect of different climatic scenarios on the multi-source energy plant sizing. For this purpose a model has been developed and has been implemented in the Matlab® environment. The model takes into consideration the load profiles for electricity, heating and cooling for a whole year. The performance of the energy systems are modelled through a systemic approach. The optimal sizing of the different technologies composing the multi-source energy plant is investigated by using a genetic algorithm, with the goal of minimizing the primary energy consumption only, since the cost of technologies and, in particular, the actual tariff and incentive scenarios depend on the specific country. Moreover economic considerations may lead to inadequate solutions in terms of primary energy consumption. As a case study, the Sino-Italian Green Energy Laboratory of the Shanghai Jiao Tong University has been hypothetically located in five cities in different climatic zones. The load profiles are calculated by means of a TRNSYS® model. Results show that the optimal load allocation and component sizing are strictly related to climatic data (e.g. external air temperature and solar radiation)
[en] A linear Fresnel reflector (LFR) solar collector with modified V-shaped cavity receiver was investigated both experimentally and theoretically in this paper. Simplified ray tracing technique was employed to optimize the optical design of the LFR system. The Monte Carlo ray tracing method was used to predict the optical performance of the proposed LFR system. A 2D mathematical model was developed to investigate the effect of receiver surface temperature on the overall heat transfer coefficient which reflects the thermal performance of the modified linear cavity receiver. CFD simulation was carried out for the modified cavity receiver treated at various surface temperatures within a range of 90–150 °C, by taking into account the conductive, convective and radiative heat losses. Experimental results show that the overall heat loss coefficient varied from 6.25 to 7.52 W/m2 K for the tested surface temperature range, with an average deviation of about 12% when compared with simulation results. Also, at higher surface temperatures, heat loss through radiative mode was predominant and the system stagnation was found to be about 260 °C with optimal operating temperature of about 121 °C. The thermal efficiency decreased from 45% to 37% as the average surface temperature increased from 90 °C to 150 °C. -- Highlights: ► An LFR solar collector was investigated both experimentally and theoretically. ► Simplified ray tracing technique was used to optimize the optical design. ► The MCRT method was used to predict the optical performance of the LFR system. ► Thermal performance of the LFR system was evaluated by CFD method and experiments. ► The LFR system is a promising technology in generating mid-temperature heat
[en] Highlights: → Energy supply concepts for zero energy residential building in Shanghai and Madrid are simulated and discussed. → Besides energy balance, indoor comfortable comparisons are presented to show optimal design strategies for HVAC. → Primary energy payback time and the CO2 equivalent saving are used to evaluate the performance of energy systems. -- Abstract: Energy supply concepts for zero energy residential building (ZERB) in Shanghai (humid) and Madrid (dry) are discussed in this paper. Simulation is employed as the main research method. Two typical housing models are designed according to the real occupancy condition, the life schedule, the thermostats settings, etc., for the two cities. An energy analysis considering the annual balance of input from the grid and output from renewable power systems is made. Indoor comfortable comparisons between the two models are presented to show optimal design strategies for HVAC under different weather conditions. Also performed is the analysis on the primary energy payback time and the CO2 equivalent saving in order to evaluate the performance of novel energy systems to verify the feasibility.
[en] Hybrid desiccant-assisted preconditioner and split cooling coil system, which combines the merits of moisture removal by desiccant and cooling coil for sensible heat removal, is a potential alternative to conventional vapor compression cooling systems. In this paper, experiments on a hybrid desiccant air-conditioning system, which is actually an integration of a rotary solid desiccant dehumidification and a vapor compression air-conditioning unit, had been carried out. It is found that, compared with the conventional VC (vapor compression) system, the hybrid desiccant cooling system economizes 37.5% electricity powers when the process air temperature and relative humidity are maintained at 30 oC, and 55% respectively. The reason why the hybrid desiccant cooling system features better performance relative to the VC system lies in the improvement brought about in the performance of the evaporator in VC unit due to desiccant dehumidification. A thermodynamic model of the hybrid desiccant system with R-22 as the refrigerant has been developed and the impact of operating parameters on the sensible heat ratio of the evaporator and the electric power saving rate has been analyzed. It is found that a majority of evaporators can operate in the dry condition even if the regeneration temperature is lower (i.e. 80 oC)
[en] A solar adsorption ice maker with activated carbon-methanol adsorption pair was developed for a practical application. Its main features include utilization of a water cooled condenser and removing all valves in the refrigerant circuit except the one that is necessary for refrigerant charging. Year round performance tests of the solar ice maker were performed in Kunming, Yunnan Province, China. Test results show that the COP (coefficient of performance) of the solar ice maker is about 0.083-0.127, and its daily ice production varies within the range of 3.2-6.5 kg/m2 under the climatic conditions of daily solar radiation on the surface of the adsorbent bed being about 15-23 MJ/m2 and the daily average ambient temperature being within 7.7-21.1 deg. C. The suitable daily solar radiation under which the solar ice maker can run effectively in Kunming is above 16 MJ/m2