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A novel hybrid air conditioning system with combination of indirect evaporative cooling and air-cooled thermoelectric cooling technologies (i.e. IEC/air-cooled TEC system) is proposed, in order to make full use of natural cold source and increase the energy efficiency and environmental performance of the air conditioning system. The effects of main operational parameters (such as the electric current I and number n of the TEC modules, inlet temperature, relative humidity and mass flow rate of the primary air, as well as the mass flow rate ratio of the secondary air to the primary air) on the performance of the hybrid system are experimentally investigated. A numerical model is also established and validated by using the experimental results. The performance optimization of the hybrid system is conducted numerically. The results indicate that the primary air temperature can be reduced below the dew point temperature by selecting appropriate operational parameters. Under fixed dew point effectiveness, maximum coefficient of performance (i.e. COP) can be achieved by optimizing I and n of the TEC modules. Moreover, there exists an optimal mass flow rate ratio and an optimal ratio of the IEC channel number to the TEC channel number that maximize the COP of the hybrid system. Additionally, comparative analysis on the performances of hybrid systems with and without spray water in the TEC's primary air channel is also made. It is found that, on the whole, introducing spray water into the TEC's primary air channel could enhance the system's performance. • A novel hybrid IEC/air-cooled TEC system is proposed. • Effects of main operation parameters on the performance are studied experimentally. • A mathematical model of the system is developed and validated experimentally. • The system's performance has been optimized theoretically. • The system's cooling performance increases with the assistance of TEC modules. [ABSTRACT FROM AUTHOR]

• The effects of oscillatory electronic valve settings on PDO characteristics are examined numerically and experimentally. • The PDO amplitude can be reduced significantly by a specific range of valve oscillation amplitude and frequency. • The square function has a better PDO suppression than the sinusoidal and sawtooth functions under the same conditions. • An overly large oscillation amplitude of the valve could increase the amplitude of the mass flow rate and the pressure drop significantly. Pressure drop oscillation (PDO) is one of the most common flow instabilities occurred in microchannel cooling systems, which could result in partial dry-out, heat transfer deterioration, and temperature fluctuation. In this study, the effects of three oscillatory electronic valve settings (square, sinusoidal, and sawtooth) on mass flow rate and PDO characteristics are examined numerically and experimentally. A one-dimensional lumped model is developed for the microchannel cooling system, which indicates that a specific range of valve oscillation amplitude and frequency can reduce PDO amplitude significantly. The PDO amplitude can be reduced by 85 % when the valve amplitude is 30 % and the frequency is 0.1 Hz. A smaller valve oscillation amplitude shows a weaker effect on the suppression of PDO. The square function has a better PDO suppression than the sinusoidal and sawtooth functions under the same pulsating valve amplitude and frequency. Experimental results demonstrate a similar effect of valve setting on PDO, for instance, a valve setting oscillates from 20 % to 80 % and a fixed frequency of 0.05 Hz can reduce pressured drop amplitude from 3 kPa to 0.5 kPa, and reduce the mass flow rate oscillation amplitude from 60 ml / min to 10 ml / min. The overly large oscillation amplitude of the valve setting could increase the oscillation amplitude of the mass flow rate and the overall pressure drop significantly. Thus, both the pressure drop through the microchannel evaporator and the valve should be considered in the selection of the oscillatory valve parameters. Based on the analysis of this study, an active control strategy could be developed to suppress flow oscillation and optimize the overall cooling performance using the oscillatory valve setting. [ABSTRACT FROM AUTHOR]

Abstract: Tailrace tunnel ventilating can be used as a highly efficient and energy saving air conditioning for factory buildings in hydropower station. This paper describes an improved model of heat and moisture transfer for tailrace tunnel ventilating system with the assumption of thermal insulated for the tunnel wall and with the same temperature at any cross section as the wet bulb temperature of that air, and the improved model has been validated against the field test from Yingxiuwan hydropower station and compared with the reference simplified model, the results show that the improved model has a good agreement with the field test data and a better precision than the reference simplified model for the performance prediction of heat and moisture transfer of tailrace tunnel ventilating, especially for the short tunnel system. Moreover, the thermodynamic calculation method of heat and moisture transfer is presented, and the method is intended for use in annual performances prediction or design tools for tailrace tunnel ventilating system in hydropower station. [Copyright &y& Elsevier]

A novel hybrid cooling system combining indirect evaporative cooling and thermoelectric cooling technologies was built and experimentally investigated. The system was mainly comprised of a cross flow regenerative indirect evaporative cooler and a water cooled thermoelectric cooler. The incoming air was firstly pre-cooled in the indirect evaporative cooler, and then further conditioned in the thermoelectric cooler to achieve desirable temperature and humidity. In particular, the thermoelectric cooler could operate under two modes of with or without spray water on the air channel surface. The performance of the proposed system under the above mentioned two operation modes was experimentally investigated and compared in detail under various operation parameters. The experimental results show that the product air temperature decreases more significantly with larger electric current and larger number of thermoelectric modules, smaller relative humidity, larger temperature and smaller velocity of inlet primary air. Under certain conditions, air condensation occurs leading to the increase of the product air temperature and the decrease of moisture content of the product air. Adding spray water in the air channel of the thermoelectric cooler would further decrease the temperature and increase the moisture content of the product air, which is more obvious under smaller electric current and number of thermoelectric modules, smaller relative humidity, smaller temperature and larger velocity of inlet primary air. The coefficient of performance of the system with spray water is smaller but the dew point effectiveness is higher compared to the system without spray water. • A novel hybrid IEC/TEC system under two operation modes is proposed. • The performance of the novel system is experimentally investigated. • Effects of main operation parameters on the system's performance are studied. • The performances of the systems under two different operation modes are compared. [ABSTRACT FROM AUTHOR]

Semi-flexible crystalline silicon photovoltaic (SFPV) modules, leveraging ultra-thin silicon and special encapsulation materials, feature innovative flexibility, lighter weight, and improved stability, making them ideal for rooftops with a load-bearing capacity under 15 kg/m2. This study experimentally evaluated the photovoltaic and thermal performance of a ventilated building-integrated semi-flexible crystalline silicon photovoltaic (V-BI-SFPV) system under warm climates, addressing the research gap in its performance under specific climatic conditions. The results indicate that the ventilated design of the V-BI-SFPV system significantly enhanced the power generation performance of the SFPV module, increasing its daily average photovoltaic efficiency by 7.37 % under grid-connected test conditions. Furthermore, the average and maximum operating temperatures of the SFPV module were reduced by 5.09 °C and 4.21 °C, respectively. The ventilated structure also effectively lowered the base plate temperature under high daytime temperatures, thereby reducing heat transfer into the building and mitigating overheating issues for both the SFPV module and the indoor environment. The findings demonstrate that the V-BI-SFPV system, with its effective enhancement of power generation efficiency and thermal management, offers a viable solution for rooftop photovoltaic applications with low load-bearing capacity. [ABSTRACT FROM AUTHOR]

The traditional monofacial PV-Trombe wall can harness both solar photovoltaic (PV) and thermal energy in buildings, but its performance is hindered by the need for transparent PV glass panels, which reduces PV power generation performance. To address this issue, this paper introduces a novel bifacial PV-Trombe Wall that leverages the rear-side power generation capability of bifacial PV cells. Theoretical analysis of the PV power generation performance of the system highlighted key factors and relationships, indicating that at a coverage rate of 0.5, the increase in its power generation compared to traditional systems reaches a maximum of 17.46 %. Furthermore, an experimental setup was devised and tested to explore the system's PV performance and thermal behavior during the summer season. The experimental results show that the reflective function of reversible louvers had successfully reduced the maximum temperature and rate of temperature rise on the attached wall, effectively alleviating the issue of solar heat absorption in buildings during summer. Besides, the system with reversible louvers improved the overall PV efficiency from 15.40 % to 16.17 %, with a total power generation increase of 5.04 %. Therefore, the system can enhance PV power generation and efficiently decrease the building's cooling energy consumption during the summer. • Mitigates power losses in PV-Trombe wall systems caused by transparency design limitations. • Enhances the seasonal adaptability of the PV-Trombe wall system. • Analyzes the impact of photovoltaic cell coverage on power output. • Assesses the system's photovoltaic performance and thermal behavior under real-world conditions. • Introduces louver gain as a metric to evaluate the effectiveness of the new system. [ABSTRACT FROM AUTHOR]

The novel ventilated building-integrated photovoltaic system with lightweight flexible crystalline silicon modules (VL-BIPV) has a self-weight of only about 6 kg/m2, which helps to address weight-bearing challenges on low-capacity industrial building rooftops. However, the unique thermal dissipation features of the system pose challenges for the analysis of its photovoltaic performance and thermal processes. Therefore, a comparative experimental testing approach was employed, comparing the VL-BIPV system with a conventional rooftop photovoltaic system. Using the efficiency equations of the conventional photovoltaic system as a reference, the functional equations were fitted based on experimental results. Based on typical meteorological year data in Nanjing, annual power generation and PV cell temperature variations were evaluated, along with power generation and carbon reduction benefits over a 25-year lifetime. The results indicate that the VL-BIPV system achieves an annual power generation of 262.22 kWh/m2, a 6.52% increase compared to the conventional system. Additionally, the highest average and maximum cell temperatures in the VL-BIPV system during the year are 58.39 °C and 64.74 °C, respectively, both lower than the conventional system's peak at 68.34 °C. Over a 25-year lifespan, the VL-BIPV system reduces carbon emissions by 20.17 kgCO 2 /W p , exceeding the conventional system's reduction by 1.25 kgCO 2 /W p. [ABSTRACT FROM AUTHOR]

The existing large-scale of industrial buildings with lightweight insulated roofing structures presents a challenge for traditional glass crystalline silicon photovoltaic (PV) systems due to insufficient load-bearing capacity. Meanwhile, traditional PV rooftop applications also face challenges due to limited rooftop resources. To address these issues, this study proposes a ventilated building-integrated lightweight photovoltaic (VL-BIPV) system. The VL-BIPV system incorporates lightweight and flexible crystalline silicon modules, which increase rooftop load by about 6 kg/m2. Additionally, the system features a ventilation channel design to enhance thermal management performance. To evaluate the PV performance and thermal characteristics of the proposed system, an experimental setup was implemented to compare the performances of the VL-BIPV system with a building-attached lightweight photovoltaic (L-BAPV) system that utilizes color steel sheet base plates. The results demonstrate the exceptional performance of VL-BIPV system, with a 100.56% higher ratio of the product of short-circuit current and open-circuit voltage compared to L-BAPV. Moreover, the VL-BIPV system achieved a 1.77% increase in PV efficiency and a 2.35% enhancement in daily electricity generation. In hot weather, the adoption of VL-BIPV reduced the extreme temperature of PV cells by 9.23 °C below 85 °C, surpassing the 6.29 °C reduction achieved by L-BAPV system. Furthermore, the ventilation channel exhibited a gradual temperature increase with slower changes in the flow direction, while the base plate temperature decreased by 13.41 °C, which indicates that VL-BIPV can effectively reduce solar heat gain in the building envelope and improve the indoor thermal environment. The research findings provide important guidance for promoting and applying VL-BIPV technology in large-scale industrial buildings with low rooftop load-bearing capacity, thereby promoting the production and utilization of clean electricity in industrial parks. • The system had a higher product of short-circuit current and open-circuit voltage. • The proposed system achieved a 2.35% increase in daily power generation. • The peak temperature of PV cells was well kept below 85 °C. • Ventilation channel design demonstrated efficient heat dissipation. • The novel system's base plate was 13.41 °C cooler than the normal one on average. [ABSTRACT FROM AUTHOR]

Tree-shaped fin exhibits an excellent performance in balancing the strong and weak heat flow in latent heat exchangers, which renders higher solidification efficiency and more uniform temperature distribution. Based on the enthalpy-porosity method, a transient model of the solidification heat transfer in the heat exchangers with five tree-shaped fins are established and numerically analysed. The solidification behaviours of the phase change material (PCM), including liquid fraction and temperature evolution, in tree-shaped heat exchanger are investigated and compared with corresponding ones. The results indicate that the tree-shaped fin introduces more uniform solidification front and yield a higher solid fraction. Compared with the traditional longitudinal fins, the efficiency of heat exchanger with four-level tree-shaped fins increases by 53%. In terms of solidification efficiency, the tree-shaped fin configuration with four-level is considered as the optimal fin configuration. The initial temperature difference and the thermal conductivity of fins largely determine the solidification trend of the PCM in the heat exchanger. Compared with the width ratio, the heat exchanger with larger length ratio stores more energy during the phase change process. • Tree-shaped fin is introduced to optimize heat transfer performance of heat exchanger. • The solidification behaviour of PCM in the heat exchanger with five fin configurations are analysed. • The efficiency of heat exchanger with tree-shaped fin increases by 53%. • The tree-shaped fins render the solidification front more uniform and yield a higher solid fraction. [ABSTRACT FROM AUTHOR]

• Performance evaluation of bifacial PV systems incorporating dynamic albedo. • Study of the optimal installation angle of bifacial PV systems in the Chinese grid. • Prediction of carbon reduction potential for bifacial PV systems on life cycle. • Comparison between optimal fixed tilt and biannual tilt angle adjustment. Bifacial PV modules, capable of generating electricity from both sides, are highly efficient but vulnerable to environmental factors. This study investigated the photovoltaic performance characteristics and carbon emission reduction potential of bifacial PV systems, considering China's regional power grid independence, environmental diversity, variations in carbon emission factors, and daily fluctuations in albedo. When the installed capacities of bifacial and monofacial PV systems are 253.80 Wp/m2 and 235.00 Wp/m2 respectively, the initial annual electricity generation of the bifacial PV system installed in Beijing is 461.11 kWh/m2, which is only 83.95 % of that in Lhasa, but the corresponding carbon reduction in Beijing exceeds that of Lhasa by 11.13 %, amounting to 407.75 kgCO 2. These indicate significant regional disparities in both the electricity generation capacity and carbon reduction potential of PV systems. Furthermore, compared to fixed installations, adjusting the tilt angles twice a year can increase the annual electricity generation of bifacial PV systems by approximately 2.37 %-3.17 % and monofacial PV systems by approximately 2.23 %-3.83 %. The research findings offer valuable insights regarding the impact of regional climate and grid characteristics on bifacial PV systems, thereby providing a reliable reference for optimizing their design and enhancing performance. [ABSTRACT FROM AUTHOR]

• MPPT strategy achieved higher PV efficiency than PWM strategy. • Solar energy for passive heating in winter was harnessed by both control strategies. • PCM and PV glass presented unique thermal properties in the absorber wall. • Minimal temperature variations observed across the thickness of the PCM plate. Due to the lack of research on the impact of photovoltaic (PV) power tracking methods on the performance of Building-Integrated Photovoltaic-Thermal (BIPV/T) systems, this study comparatively analyzes the photovoltaic-photothermal performance of the PV-PCM-Trombe Wall system operating in Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT) modes during winter passive heating conditions. Additionally, the study investigates the influence of these modes on the thermal characteristics of buildings. The results indicate that the MPPT strategy achieved a PV efficiency of 15.50 %, while the PWM strategy resulted in a significant reduction to 12.72 % (a decrease of 2.78 % compared to MPPT). Importantly, both strategies effectively utilized solar energy for passive space heating without noticeable differences in photothermal performance. Furthermore, the study observed that the upper part of the PCM plate reached higher peak temperatures earlier in the vertical dimension. Experiment A exhibited peak temperatures ranging from 33.57 °C to 34.76 °C, while Experiment B had a wider range of 27.99 °C to 36.10 °C. Minimal temperature variations were observed across the PCM plate in the thickness direction, measuring only 0.60 °C in Experiment A and 0.70 °C in Experiment B. These research findings provide valuable insights into the roles and impacts of different PV power tracking strategies in PV-PCM-Trombe wall systems. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a novel thermoelectric assisted indirect evaporative cooling system is proposed. Specifically, thermoelectric cooling (TEC) modules are sandwiched between channels of a flat plate cross flow indirect evaporative cooler. A mathematical model of the novel system is developed, and influences of main operating and geometrical parameters on the system's performance are analyzed in detail. Analytical results show that with the assistance of the thermoelectric cooling, the proposed system is able to cool primary air to a temperature much lower than inlet air wet bulb temperature, even dew-point temperature, meanwhile keep a relatively high coefficient of performance (COP), by selecting appropriate number and electric current of TEC modules. The dew point effectiveness and COP of the proposed system change monotonously with inlet mass flow rate, temperature and humidity ratio of primary air, respectively. The dew point effectiveness also varies monotonously with the mass flow rate ratio of secondary air to primary air. However, there exists an optimal mass flow rate ratio resulting in a maximum COP. Moreover, under variable number and electric current of TEC modules, there always exist optimal widths of primary air channel and secondary air channel, leading to a maximum COP. Highlights • A novel thermoelectric assisted indirect evaporative cooling system is proposed. • A mathematical model of the novel system is developed. • Effects of main operating and geometrical parameters are studied. • The system's cooling effectiveness increases with the assistance of TEC modules. [ABSTRACT FROM AUTHOR]

• A novel two stage IEC/thermoelectric assisted DEC system is proposed. • Effects of main operation parameters are studied experimentally. • A mathematical model of the novel system is developed and validated. • Operation parameters of TECs and mass flow rate ratios are optimized theoretically. The performance of a novel two-stage indirect/thermoelectric assisted direct evaporative cooling (i.e. IEC/TDEC) system is studied by using experimental and numerical simulation methods. In the IEC/TDEC system, the outdoor air is firstly pre-cooled in the first stage cross-flow regenerative IEC to make full use of the nature cooling source, and then further cools down in the second stage TDEC. An experimental set up is designed and built to investigate the influences of main operation parameters (i.e. operating current and number of TEC modules, inlet temperature, humidity and velocity of primary air, the mass flow rate ratio of regenerative air to primary air in the IEC, and also the mass flow rate of cooling water in the TDEC) on the system performance. It is found that the outlet air temperature and relative humidity could be conditioned to meet the comfort demand by adjusting the influential operating parameters. The dew point efficiency could be higher than unity, and the air moisture content increases or decreases dependent on given working conditions. The numerical model of the IEC/TDEC system is established, and validated by comparing with experimental results. The numerical results agree well with experimental results with relative errors within ±10%. Then, the working parameters of TEC modules and several mass flow rate allocation ratios of air are optimized theoretically by using the numerical model. Analytical results show that in the premise of a certain dew point efficiency, a maximum coefficient of performance can be obtained by adjusting the operating current and number of TEC modules. Moreover, the inlet velocity of primary air and two main mass flow rate allocation ratios of air can be optimized to achieve higher system performance. [ABSTRACT FROM AUTHOR]