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[en] Based upon the fast development of energy efficiency, energy safety and use of renewable and sustainable energy, various energy systems related to residential refrigeration, power generation and storage have been developing. Some of them are in large scale application, while others are still under development. Current status of residential refrigeration, power generation and energy storage technologies have been briefly summarized in this paper. Also, future residential refrigeration, power generation and energy storage technologies are highlighted, and some roadmaps are discussed. -- Highlights: ▸ Current status and future development of residential refrigeration have been briefly summarized and discussed. ▸ Current status and future development of power generation have been briefly summarized and discussed. ▸ Current status and future development of energy storage have been briefly summarized and discussed
[en] Research highlights: → A dynamic mathematical model is built to predict the performance of DCHE system. → Operation time in dehumidification is a crucial parameter to system performance. → Under ARI summer condition, the largest cooling power can reach to 2.6 kW. → Under ARI humid condition, the largest cooling power can reach to 3.4 kW. → System performs better with smaller fin distance and tube diameter. -- Abstract: Desiccant coated heat exchanger (DCHE) system can handle latent and sensible load simultaneously by removing the released adsorption heat in dehumidification process. The system can also be driven by low grade thermal energy such as solar energy. In this paper, a dynamic one-dimensional mathematical model validated by experimental data is established to predict the performance of DCHE system, using conventional silica gel as desiccant material. Cooling performance of DCHE system is calculated under ARI (American Air-conditioning and Refrigeration Institute) summer and humid conditions. Simulated results show that the operation time in dehumidification process is a crucial factor for cooling capacity of DCHE system, which can be enhanced by eliminating the initial period with higher outlet air temperature, the largest cooling power of DCHE system increase from 2.6 kW to 3.5 kW by eliminating first 50 s of operation time under ARI summer condition. The results also prove that the system can provide cooling power to indoor condition with selective operation time when regeneration temperature varies from 50 oC to 80 oC. Besides, the model is adopted to analyze the effects of some structural parameters on system performance under simulated condition. The system performs well in smaller cobber tube external diameter condition, while both transient heat and mass transfer capacity can be enhanced under the condition of smaller distance between the fins.
[en] Research highlights: → Composite adsorbent 'employing lithium chloride in silica gel' and water as working pair. → A new type adsorbent bed is used to accommodate the composite adsorbent. → A dynamic model of the adsorption chiller is built. → The coefficient of performance (COP) and the cooling capacity will be improved. -- Abstract: This paper presents a novel adsorption chiller using composite adsorbent 'employing lithium chloride in silica gel' as adsorbent and water as adsorbate. A new type adsorbent bed is used to accommodate the composite adsorbent. The mass recovery between two adsorbent beds usually results in the adsorbate unbalance. So a novel auto water makeup unite is used to solve the problem. A dynamic model of the adsorption chiller is built based on the adsorption isotherms to predict the performance. The simulation result shows that the coefficient of performance (COP) and the cooling capacity will increase by using this new composite adsorbent. When the temperatures of hot water inlet, cooling water inlet, and chilled water inlet are 363, 303 and 293 K, COP will be 0.43, and the cooling capacity will be 5.295 kW. Also operation strategy is optimized. Different temperatures of hot water inlet, cooling water inlet and chilling water inlet will result in different COP and cooling capacity.
[en] Highlights: → A resorption refrigerator employing MnCl2-NH3 and NH4Cl-NH3 was designed and investigated. → The experiments were operated under different ambient temperatures from 20 to 35 oC. → The refrigerator provided simultaneously two cooling levels: at 0-6 oC and at -16 ∼ -14.5 oC. → With 3 h operation the total cooling capacity was 475 kJ per kg of NH4Cl salt. → The effective cooling production was 25-42% of the total cooling capacity. -- Abstract: A small refrigerator based on resorption technique, employed MnCl2 and NH4Cl as sorbent salts and ammonia as refrigerant, was presented for simultaneously cooling at 0-6 oC and freezing at -16 to -14.5 oC in this work. The cooling capacity of this device was investigated by measuring the mass amount of the ice generated during a certain period of 3 h operation, and the experiments were conducted at different ambient temperature ranging from 20 oC to 35 oC. The total cooling capacity was calculated 475 kJ per kg of NH4Cl salt, and the mean specific cooling power (SCP) was 43 W per kg of NH4Cl salt, the effective cooling production responsible for making ice accounted for 25-42% of the total cooling capacity depending on the different operating conditions studied in this work.
[en] Research highlights: → We compare refrigerant flow ranges under different working modes for a multi-functional heat pump. → We propose control methods of electronic expansion valve specialized for such a system. → Although some loss in the cooling capacity maybe occur in mode 3, average cooling COP can be improved. -- Abstract: Multi-functional domestic heat pump systems (MDHPS) can reduce operating costs, lessen thermal pollution to the environment, and improve equipment utilization rate. Compared with the traditional heat pump system, the MDHPS has a wider range and more dramatic changes in operating conditions. This paper incorporates the refrigerant flow characteristic and performance analysis of an electronic expansion valve (EEV)-controlled MDHPS which operating in four typical modes (sanitary water heating mode, space cooling mode, space cooling combined with condensing heat recovery mode, radiant floor heating mode). The calculating results demonstrate that there are considerable differences in the refrigerant mass flow range when the MDHPS operates in the different modes. Moreover, sudden changes in working conditions due to mode switching easily result in large-scale fluctuations of system parameters. Therefore, to ensure the MDHPS to work more reliably and efficiently, a control scheme of the EEV specialized for the MDHPS is proposed and applied in the presented experimental system. The experimental results indicate that the system is able to perform efficiently and stably under various conditions by this control method. In the sanitary water heating mode, the average heating coefficient of performance (COP) reaches 2.2, 3.2 and 4.1 when the ambient temperature is 5 oC, 20 oC and 35 oC, respectively. In the condensing heat recovery mode, besides yielding free sanitary hot water, the average cooling COP can be improved 9% when the water temperature ranges from 30 oC to 55 oC. In the radiant floor heating mode, the COP is 3.3 at 6 oC ambient temperature.
[en] A novel rotary desiccant cooling cycle is proposed and studied using thermodynamic analysis method. The proposed cycle integrates the technologies of isothermal dehumidification and regenerative evaporative cooling, which are beneficial for irreversibility reduction. Thermodynamic investigation on the basic rotary desiccant cooling cycle shows that the exergy efficiency of the basic cycle is only 8.6%. The processes of desiccant dehumidification and evaporative cooling, which are essentially the basis for rotary desiccant cooling, affect the exergy performance of the cycle greatly and account for about one third of the total exergy destruction. The proposed cycle has potential to improve rotary desiccant cooling technology. It is advantageous in terms of both heat source utilization rate and space cooling capacity. The exergy efficiency of the new cycle is enhanced significantly to 29.1%, which is about three times that of the ventilation cycle, and 60% higher than that of the two-stage rotary desiccant cooling cycle. Furthermore, the regeneration temperature is reduced from 80 °C to about 60 °C. The corresponding specific exergy of the supply air is increased by nearly 30% when compared with the conventional cycles. -- Highlights: ► A novel rotary desiccant cooling cycle is developed using thermodynamic analysis method. ► Isothermal dehumidification and regenerative evaporative cooling have been integrated. ► The cycle is advantageous in terms of both heat source utilization rate and space cooling capacity. ► Cascaded energy utilization is beneficial for cycle performance improvement. ► Upper limits, which will be helpful to practical design and optimization, are obtained.
[en] Research highlights: → We studied a point focus Fresnel solar collector using different cavity receivers. → The collector heat removal factors are derived to find the optimal cavity shape. → Numerical and experimental analysis shows that the conical cavity is optimum. -- Abstract: A high concentration imaging Fresnel solar collector provided with different cavity receivers was developed and its behavior was investigated. Round copper pipes winded into different spring shapes were used as receiver by placing in the cylindrical cavity to absorb concentrated solar energy and transfer it to a heat transfer fluid (HTF). The collector efficiency factor and collector heat removal factor were derived for the cavity receivers to find out heat transfer mechanism and to propose an effective way for evaluating the performance of Fresnel solar collector and determining the optimal cavity structure. The problem of Fresnel solar collector with synthetic heat transfer oil flow was simulated and analyzed to investigate heat loss from different cavity receivers. Solar irradiation as well as convection and heat transfer in the circulating fluid and between the internal surfaces of the cavity and the environment are considered in the model. The temperature distribution over its area as well as the collector thermal efficiency at nominal flow rate was used in order to validate the simulation results. It was found that the simulated temperature distribution during operation and the average collector efficiency are in good agreement with the experimental data. Finally, the optimal shape of solar cavity receiver, as well as its thermal performance, are deeply analyzed and discussed.
[en] Highlights: → Use two kinds of circulation media in the solar collector. → Air heating and pebble bed heat storage are applied with different operating modes. → Design parameters of the system are optimized by simulation program. → It is found that the system can meet 32.8% of the thermal energy demand in heating season. → Annual solar fraction aims to be 53.04%. -- Abstract: The application of solar air collectors for space heating has attracted extensive attention due to its unique advantages. In this study, a solar air heating system was modeled through TRNSYS for a 3319 m2 building area. This air heating system, which has the potential to be applied for space heating in the heating season (from November to March) and hot water supply all year around in North China, uses pebble bed and water storage tank as heat storage. Five different working modes were designed based on different working conditions: (1) heat storage mode, (2) heating by solar collector, (3) heating by storage bed, (4) heating at night and (5) heating by an auxiliary source. These modes can be operated through the on/off control of fan and auxiliary heater, and through the operation of air dampers manually. The design, optimization and modification of this system are described in this paper. The solar fraction of the system was used as the optimization parameter. Design parameters of the system were optimized by using the TRNSYS program, which include the solar collector area, installation angle of solar collector, mass flow rate through the system, volume of pebble bed, heat transfer coefficient of the insulation layer of the pebble bed and water storage tank, height and volume of the water storage tank. The TRNSYS model has been verified by data from the literature. Results showed that the designed solar system can meet 32.8% of the thermal energy demand in the heating season and 84.6% of the energy consumption in non-heating season, with a yearly average solar fraction of 53.04%.
[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] 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)