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• The coupled heat transfer process of rooftop photovoltaic shading units and indoor heat gain are analyzed. • The energy-saving potential of photovoltaic rooftops compared to traditional rooftops is revealed. • The energy-saving performance of photovoltaic and traditional rooftops under different roof reflectivity are summarized. • The impact of the optimal tilt angle on the power generation of the photovoltaic rooftop are discussed. • An energy-saving scheme for applying rooftop photovoltaic systems in hot summer areas is proposed. Rooftop photovoltaic panels can serve as external shading devices on buildings, effectively reducing indoor heat gain caused by sunlight. This paper uses a numerical model to analyze rooftop photovoltaic panels' thermal conduction, convection, and radiation in hot summer areas as shading devices. The researcher builds an experimental platform to verify the model, exploring the potential for energy savings of photovoltaic rooftop units in the Wuhan area. The results show that after installing photovoltaic panels, the delay performance of the roof increases by 0.5 h, the roof heat flux is reduced by 41.7%, the peak temperature of the roof is reduced by 22.9 °C, and the daily heat gain is reduced by 74.84%. Finally, this paper discusses the impact of high-reflectance and low-reflectance roofs on the shading effect. The study finds that low-reflectance roofs are more energy-efficient in the hot summer, as high-reflectance roofs lead to a 10.8% increase in indoor heat gain when the photovoltaic panel is installed. Finally, a quantitative method for evaluating the comprehensive potential for energy savings is proposed, considering the electricity generation gain of photovoltaic panels and the comprehensive energy-saving efficiency of photovoltaic roofs, which generates a total potential for energy savings rate of 61.06%. The model presented in this paper provides theoretical guidance for analyzing the comprehensive energy-saving effects of photovoltaic rooftop systems and reveals the potential for energy savings of rooftop photovoltaic panels as external shading devices. [ABSTRACT FROM AUTHOR]

The glazed roof has better lighting performance and is widely used in modern building design. However, its poorer heat insulation performance can decrease indoor thermal comfort. Therefore, the interlayer of insulating glazed roof is injected with phase change material (PCM) to improve the indoor thermal environment of building and reduce the energy consumption, while obtain sufficient indoor light. Based on enthalpy method, a numerical heat transfer model of double-slope PCM glazed roof was established and verified in this paper. The heat transfer performance of double-slope hollow glazed roof and double-slope PCM glazed roof were compared. Finally, the design of double-slope PCM glazed roof in hot summer and cold winter area was optimized by further studying the roof angle, phase change layer thickness, glazing layer thickness, the melting temperature and phase change latent heat of PCM. The results show that the suitable melting temperature is 26–30 °C under the typical climate of hot summer and cold winter in Wuhan. Increasing the thickness of phase change layer and glazing layer can improve the thermal insulation performance of the roof, but the former effect is more significant. Moreover, a smaller roof angle within a certain range can reduce the amount of solar radiation received by the roof, and a larger latent heat energy of PCM can absorb more solar radiation to improve the heat transfer performance of the roof. [ABSTRACT FROM AUTHOR]

Groundwater heat pump (GWHP) systems are central heating and cooling systems that utilize groundwater heat. With the rapid development of this technology in China, it has become imperative to study the changes in the ground environment, including the flow features, heat transfer characteristics and clogging caused by long-term recharge, during the operation of GWHP systems. In this paper, a mathematical model considering the effect of particle deposition was proposed to describe a GWHP system based on the typical geological and hydrogeological conditions (i.e., a dual-structure strata) in Wuhan, China. During research on a GWHP engineering project in the Baibuting Garden community, four groundwater flow conditions (including no flow, forward flow, reverse flow and cross flow) and two typical flow modes (continuous and flushing modes) were considered. The groundwater temperature and flow rate were measured through measuring wells, and a comparison between theoretical and actual values shows that this model can provide an easy yet effective way to describe GWHP engineering. The seepage and temperature fields both display periodic trends under the continuous flow mode and can be significantly affected by well flushing. The central area is marginally influenced by groundwater flow when compared with the surrounding areas; for instance, the temperature fluctuation at MW3 can reach 8.2 °C, while the fluctuation reaches 2.9 °C at MW1. Particle deposition can affect the parameters of the ground environment; we find considerable correspondence between the concentration of deposited particles and the porosity. Moreover, both the concentration of deposited particles and the porosity change by a large margin after flushing, especially in regions around pumping wells (the concentration of deposited particles can fluctuate by 108 g/L, and the porosity can change by 0.055). [ABSTRACT FROM AUTHOR]