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This paper dealt with a series of numerical investigations on a new porous cooling channel applied to PV/T systems in order to improve the insufficient heat transfer in the conventional channel. The proposed porous cooling channel based on field synergy theory had a higher overall heat transfer coefficient, which enhanced the total efficiency of the PV/T system. The numerical model was validated with experimental data. The results showed that holes distributed non-uniformly near the outlet of the cooling water led to a better cooling effect, and a hole diameter of 0.005 m led to an optimal performance. The total efficiency of the PV module with the new cooling channel was 4.17% higher than the conventional one at a solar irradiance of 1000 W/m2 and an inlet mass flow rate of 0.006 kg/s. In addition, as the solar irradiance increased from 300 to 1200 W/m2, the total efficiency of the new PV/T system dropped by 5.07%, which included reductions in both the electrical and thermal efficiency. The total efficiency was improved by 18.04% as the inlet mass flow rate of cooling water increased from 0.002 to 0.02 kg/s.

The performance of a solar lighting and heating system (SLHS) based on the spectral splitting effect of nanofluids is presented in this paper. SLHS through nanofluids would split the sunlight spectrum into different wavelength, and then introduce the visible light into the offices for lighting and absorb infrared energy to generate hot water. The Energy Plus software was used to analyze the energy consumption of typical office building located in the city of Harbin in China coupled with SLHS. Based on the simulation results two lighting zones were identified in the offices and the optimal lighting control strategy was developed for a full year. The performance models of SLHS with different light-receiving areas of 10 m2 and 40 m2 were simulated and validated using the existing experimental data. The overall energy-saving of the offices over a full year were analyzed using the validated model. Results demonstrated that for SLHS with the area of 40 m2, the rate of the energy saving in the offices due to lighting and hot water systems were 58.9%, and 19.3%, respectively. The system also had the additional benefit of reducing the cooling load of the air conditioning system during summer period together with improving the quality of the indoor environment resulting in better health and productivity of the occupants.

Hourly global solar radiation data is an important factor for solar energy utilization. Due to the lack of solar radiation observation stations in many areas, some hourly solar radiation models are proposed to predict hourly solar radiation. However, the existing models perform poorly in heavy fog-haze areas because the weakening effect of fog-haze on solar radiation is not considered. Thus, in this paper, hourly global solar radiation prediction models are developed considering air quality index (AQI) using XGBoost algorithm. The results show a general improvement in the accuracy of models with AQI as an additional input (Model B1-B6) compared to models that do not consider AQI (Model A1-A6). Compared to Model A, Model B have an increase in R value from 0.927 to 0.948, a decrease in RMSE value from 0.300 to 0.282 and a decrease in MAPE value from 0.159 to 0.145. In addition, for hourly solar radiation prediction, the six most important inputs are the day of the year, air temperature difference, surface temperature difference, hour, AQI, and total cloud cover.

Variable air volume air-conditioning system (VAV system) has multiple control loops that interfered with each other, which has serious impacts on its actual operation effect. To solve this problem, the index of global hydraulic stability, which takes the physical quantity of the pipe network pressure and the air flow rate as reference, is proposed based on Graph theory, and a pipe network model for the hydraulic calculation is built. Then, the simulation study based on the actual operation data is carried out in MATLAB. The distribution of the pressure and the air flow in the pipe network is obtained, and the action interferences among adjacent terminal boxes are analyzed based on global hydraulic stability under damper position regulation strategy (DP strategy) and fan frequency regulation strategy (FF strategy). Results indicate that the FF strategy can decrease the total change distance of the damper position compared with the DP strategy, and then the fluctuation of the pressure and the air flow can be reduced. The contribution of this study is to provide an evaluation index of global hydraulic stability, which can also be used in other air-conditioning systems with multiple terminals and multiple control loops.

With the development of social economy, heating in the south of China has been concerned widely. As one of the energy sources of decentralized heating, natural gas (NG) has been used more and more popularly. This paper aimed to study the impact of residential building heating on NG consumption, and took Wuhan city, the representative city needing heating in winter of the south of China due to its location and climate, as an example. Firstly, a typical residential building model was established through DeST software. The heating load was simulated, and the corresponding NG consumption index was calculated. Secondly, appropriate methods were used to forecast the basic data of Wuhan city in 2020, including households and per capita gross national product (GDP), etc. Thirdly, the NG consumption of residential buildings with and without heating were predicted. Finally, the impact of residential building heating on NG consumption was analyzed. The results showed that the average annual household heating consumption of residential building in Wuhan city in 2020 was 2100 kWh/ household, and the NG consumption using for residential building heating was 295 Nm3/household. In addition, the NG consumption of residential building generated by space heating with 100% heating rate was 2.82 times the NG consumption generated by the stove and water heater, showing that residential building heating had a large impact on NG consumption. This study can contribute to choosing appropriate heating method in the southern cities of China, and further planning the gas pipe network in these cities.

Solar lighting technologies can lead sunlight into indoor actively, which has been proved that has great potential to reduce electric lighting consumption and create a healthy visual environment. In this paper, a mathematics model was developed to explore performance characteristics and economic applicability of solar lighting/heating system that combine ordinary solar lighting system with nanofluids to spectroscopically utilize sunlight. The results show that the luminous efficiency of output visible light can reach at 242 lm/W, which is 1.62–2.42 times higher than that of current LED light. Moreover, it can be found that the energy-saving capacity of this system is remarkable when used in most areas of China. As for Harbin, its annual total solar radiation ranges 4190 MJ/m2 to 5020 MJ/m2, the system's annual output energy (per square meter of collection area) is 188.15 kW•h for daylighting and 248.2 kW•h for domestic hot water. Besides, the integrated using of infrared radiation can improve the economy of solar lighting technologies by calculating the comprehensive price of unit output energy.

This paper introduces a kind of open cycle absorption heat wet flue gas heat recovery system, which use CaCl2 as the working medium. The system will use the wet heat recovery method and combined with an efficient heat pump system for flue gas as a heat source generator. Through direct contact with the solution in the absorber, the flue gas is going to carry out gas, liquid heat transfer between heat exchanger, realization of sensible heat and latent heat step by step.As the key part of the system, absorber is established by one-dimensional steady-state heat transfer and mass transfer model. This paper uses the finite difference method to model the discrete numerical methods, and analyzes the characteristics of heat and mass transfer in the absorber. We obtain the concentration curves of the three kinds of working medium's temperature and flow along the height direction. We also analyze the influence of CaCl2 solution parameters changes on the absorption process, parsing the reason of the temperature change by analyzing the three working medium's energy flow trend. We found that the temperature change of flue gas is non-monotonic, which decreases gradually in the range of absorption tower height 0–0.9 m, and then increases gradually. The reason for this change is that sensible heat exchange and latent heat exchange exist between flue gas and solution. Although such a change has an impact on the efficiency of the system, it prevents the ''white smoke'' from condensing in the air, which effectively protects the environment. Compared with conventional LiBr absorption heat pump, the system constructed in this paper has certain advantages in latent heat recovery, flue gas heat energy utilization, energy conservation and emission reduction and economy.