• Energy Research

Abstract A sorption air cooler experimental setup including a reactor and fin tube condenser/evaporator was built. The reactor was developed with inner copper fins and dual layers of curing copper meshes. Composite material made by impregnating LiCl into the mesopores of Wakkanai Siliceous Shale (WSS) micropowders was packed between the intervals of two fins. Heat transfer was enhanced by the attached fins, and the dual layers of curing meshes installed between each interval of two fins were designed to improve the sorbate mass transfer. On the other hand, the fin-tube evaporator/condenser with fins outside is valuable for improving the convective heat transfer between the functional water inside the evaporator/condenser and the flowing outside heat transfer medium, air. The sorption capacity of the composite material increased dramatically after being impregnated with LiCl. Among the four tested samples, WSS + 40 wt% LiCl exhibits the best performance. A regeneration temperature of 80 °C appears to be optimal for obtaining both a high COP and high specific cooling power. A lower condensation temperature can increase the cooling power. The sorption and desorption times of 60 min yield a reasonable compromise between cooling COP and mass specific cooling powers. The developed sorption air cooler system using WSS + 40 wt% LiCl can store heat at temperatures below 100 °C and produce cooling energy with a cooling coefficient of performance (COP) of approximately 0.3.

Abstract Today, a significant amount of low-temperature ( An open sorption thermal energy storage system was proposed, and the experimental setup was constructed. A low regeneration temperature (80–100 °C) of the storage medium was achieved with this open system. In the case of the 22.4 wt% CaCl2 supported with the honeycomb filter (926.2 g; 2 L), air was heated to a temperature greater than 40 °C for a duration of 432 min by supplying air at 25 °C at a flow rate of 3.0 m3/h when the regeneration temperature was 80 °C. The volumetric heat storage density obtained was 272 MJ/m3, and the coefficient of the heat extraction performance during the heat release process was 65%.

Abstract Heat storage performance of an open thermochemical heat storage (TCHS) system using composite salt hydrates of Wakkanai siliceous shale (WSS) - 9.6 wt.% LiCl was investigated numerically. A two-dimensional model considering the combined heat and mass transfer was developed. The calculation results were validated by the experimental results obtained in our previous study. The inlet air temperature, inlet air relative humidity, humid air flow rate, the ratio of the thickness of air channel and the thickness of composite solid wall, and length of the TCHS unit were evaluated to evaluate the heat storage performance. When the ratio of the thickness of air channel and the thickness of composite solid wall is 5 and the length of the heat storage unit is 0.1 m, the volumetric heat storage density of the open TCHS system can reach 510 MJ/m3.

Abstract A building-integrated photovoltaic-thermal (BIPVT) system integrates building envelope and photovoltaic-thermal collectors to produce electricity and heat. In this paper, the electrical and thermal performance of roof-based BIPVT systems developed in the recent two decades and their effects on heating and cooling load of the building are reviewed. According to the use of thermal energy from the photovoltaic (PV) panels, the roof-based BIPVT are classified into three classes: cooling of PV, air heating, and water heating. Each class is further divided into several types according to the designs of the integrated PV roofs. Compared with BIPV systems, the total efficiency of most BIPVT systems is significantly improved. However, the decrease in electricity output and adverse impact on the indoor environment is also found for some designs of BIPVT systems in some climates. The advantages and disadvantages of various designs are discussed. Issues to be further studied in the future are also provided in this review.

Abstract In this study we developed a composite mesoporous honeycomb element based on Wakkanai siliceous shale (WSS) and lithium chloride (LiCl), to act as a thermal energy storage medium that can directly contact the functional air in an open sorption thermal energy storage system. The mesopores of the WSS were filled with LiCl to improve its sorption capability as a new sorption thermal energy storage material. The honeycomb thermal energy storage element impregnated with 9.6 wt% LiCl was installed in the developed open sorption thermal energy storage experimental setup. The experimental results showed that this impregnated honeycomb element could be regenerated at a lower regeneration temperature, even at 60 °C, and also exhibited high volumetric heat storage density. Furthermore, at a certain regeneration temperature, the element impregnated with 9.6 wt% LiCl supplied air with a relatively constant high outlet air temperature compared to the element filled with 22.4 wt% CaCl 2 under the same inlet air conditions in the sorption process, and the proposed element was less affected by the humid air flow rate. The sorption rate was observed to significantly affect the outlet air temperature during the sorption process. We confirmed that the developed composite material filled with LiCl exhibited good stability, boosting the possibility of its long-term use.

Abstract Accumulation of moisture in the building envelopes may corrode the building structures or deteriorate the indoor environment. In this paper, a hybrid method for moisture transport analysis for solar structures was developed. This hybrid method first adopts state space method to calculate the joint surface temperature between the solar collector and building structure, and then simulate the moisture transport of the building structure by Delphin. The hybrid method was validated by experiments. The moisture transport of an integrated structure of solar collector with a wall, i.e. solar wall, in Shanghai under dry and wet conditions were studied and compared with an ordinary wall by the hybrid method. The results indicated that the solar wall had lower moisture content than ordinary walls in dry conditions. However, if there was wet layer of 10 mm in the wall, the solar wall took much more days to turn dry than the ordinary wall. Therefore, the sealing and waterproof measures should be carefully taken when integrating solar collectors with buildings to prevent water from entering into the solar wall.

In this paper, a new type of unit dew-point evaporative cooler with fibrous membrane was designed and constructed. The effects of three air state parameters (temperature, humidity, air velocity) on the outlet air temperature, wet-bulb efficiency and dew-point efficiency were studied, as well as the regional adaptability in four typical cities in China. The porous fibrous membrane can be used to improve the moisture permeability and diffusion characteristics of the wet channel. It was found that the wicking height rate of the porous fibrous membrane was 0.203 cm/min, the diffusivity rate was 0.118 cm2/s, which was better than the performance of Kraft Paper. The usage of this novel device in Urumqi and Lanzhou, as regions with lower relative humidity, showed better regional adaptability than in Beijing and Shanghai with higher relative humidity. When the inlet air velocity was 1 m/s, the temperature decreased from 33.4 °C to 24.2 °C and 31.3 °C–24.5 °C respectively in the former area, while, decreased from 33.6 °C to 28.1 °C and 34.6 °C–29.5 °C respectively in the latter area. With the inlet air velocity increasing from 1 m/s to 3 m/s, the outlet air temperature would rise, and the wet-bulb efficiency and dew-point efficiency would decrease, but the cooling capacity would increase.

The composite material made by impregnating 40 wt. % lithium chloride (LiCl) into the mesopores of a kind of natural porous rock (Wakkanai Siliceous Shale: WSS) micropowders (short for “WSS + 40 wt. % LiCl”) had been developed previously, and can be regenerated below 100 °C with a cooling coefficient of performance (COP) of approximately 0.3 when adopted as a sorbent in a sorption cooler. In this study, experiments have been carried out on an intermittent solid sorption chiller with the WSS + 40 wt. % LiCl coating over two aluminum corrugated heat exchangers. Based on the experimental condition (regeneration temperature of 80 °C, condensation temperature of 30 °C in the desorption process; sorption temperature of 30 °C and evaporation temperature of 12 °C in the sorption process), the water sorption amount changes from 20 wt. % to 70 wt. % in one sorption cooling cycle. Moreover, a specific cooling power (SCP) of 86 W/kg, a volumetric specific cooling power (VSCP) of 42 W/dm3, and a specific sorption power of 170 W/kg can be achieved with a total sorption and desorption time of 20 min. The obtained cooling COP is approximately 0.16.

Abstract Evaporative cooling has been widely used due to its environment-friendly characteristic of cooling air by water evaporation. Nowadays, there are two common forms of evaporative cooling: indirect evaporative cooling (IEC) and dew point evaporative cooling (DPEC). While, the heat-moisture migration in the wet surface composed of porous materials is an important factor that affecting the heat and mass transfer of IEC. Therefore, the application of porous materials in IEC has been reviewed in this paper. Firstly, a comprehensive classification of the porous materials used in the IEC was introduced, which could be divided into porous ceramics and fibers. Porous ceramics had the function of storing water, and the fiber in the form of composite membranes was the current research hotspot. Then, by referring theoretical analysis and experimental research, the structural parameters (Porosity, Specific surface, Tortuosity) and characteristic parameters (Wicking height, Diffusivity, Evaporation rate) of porous materials were introduced in detail, which could be used as important indicators for selecting suitable porous materials. Since the heat and mass transfer process brought by the unique porous structure was quite complicated, the heat and mass transfer model of porous materials in IEC could be simplified. Based on the spray water flow, the theoretical research of the IEC mathematical model can be summarized into three situations. Among them, moderate water spray had the best cooling capacity for IEC, and could predict the temperature change of the water film surface well. Finally, four future research directions based on the characteristics of porous materials were also proposed in this paper. The aim of this paper is to provide a reference for the field of IEC.