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• Overlapping heating and cooling demand in the entire European building stock is assessed. • Evaluation is based on hectare-sized units and GIS method. • 8 scenarios representing future climate, renovations, and cooling area are considered. • Less than 0.1% of the current building stock has enough overlapping demand for 5GDHC. • The future potential of 5GDHC considering overlapping demand and density is limited. With warmer climate conditions, the growing need to cool down building environment in Europe calls for efficient solutions to solve the heating and cooling demand altogether. To meet such requirement, the bi-directional fifth generation district heating and cooling (5GDHC) system has been proposed in recent years, while having the capability of integrating the renewable and waste energy sources. The overlapping heating and cooling demand, or referred to as the simultaneous demand, is proved as the key pre-requisite to guide the application of 5GDHC through several case studies. However, how large is this overlapping part in the practical building stock and where are the feasible areas for 5GDHC remain unclear. To close the gap, this study assesses the quantities and geographical distributions of overlapping heating and cooling demand across Europe in EU 27, UK, and EFTA countries. Using GIS-based methods and data sources, the study region is split into 28 million hectare-sized units where the overlapping demand is specifically calculated. Moreover, the possible future changes to the heating and cooling demand alone brought by warmer climate, building renovations, and increased cooling area were investigated. The results from reference condition at year 2016 reveal that less than 0.1% of the building stock has DOC larger than 0.3, which is the threshold for 5GDHC being energy efficient. These potential areas are primarily found in city centres involving cooling demands from commercial and industrial processes. In the future scenarios of year 2050, while a better energy performance of buildings and warmer climate may decrease the heating and increase the cooling demand, the overlapping part is only slightly increased by around 5%. Accordingly, around 2500 ha-sized units from the entire study region are found to meet the DOC limit required by the 5GDHC while having large enough demand density to support district energy systems. The presented works geographically identified the potential areas for 5GDHC and can be extended with regional details to serve as the connection between top-level planning and bottom-level case studies. [ABSTRACT FROM AUTHOR]

• The energy consumption of 38 Chinese district heating systems was investigated and compared. • Method to break down the consumption and evaluate the operational problems was presented. • Field measurements were conducted to evaluate problems leading to high energy consumption. • Overheating was responsible for 23% of total heat consumption. • Resistance, operation flow, and pump efficiency were three major problems in distribution networks. Worldwide, China has the largest district heating (DH) area and is also the fastest growing country. This paper presents field measurement results for operational energy consumption from 38 DHSs to fill in the gaps in understanding of the current operational issues of the district heating system (DHS). The average heat consumption during the heating period was 98.6 kWh/m2 and the monthly average electricity consumption for circulating pumps in the primary and secondary networks was 0.27 kWh/(m2 × month) and 0.29 kWh/(m2 × month), respectively. Thereafter, a systematic method for breaking down the energy consumption and quantitatively evaluating the underlying problems is presented. Based on several detailed measurements conducted in typical heat-exchange substations (HESs), it was found that overheating was the most prominent problem in energy-efficient buildings, constituting 23% of the total heat consumption. Another problem encountered was heat loss through pipes, which constituted approximately 5%–10% of the total heat consumption and was highly dependent on the actual conditions. In distribution networks, problems such as high resistance, high operational flow, and low pump efficiency were also identified and analyzed. Finally, practical energy-efficiency suggestions and future potential targets for the Chinese DHS are discussed from both a design and operational perspective. [ABSTRACT FROM AUTHOR]

In view of the problems that the surface of radiant air conditioning is prone to condensation and the cooling capacity is limited by the dew-point temperature, a model for radiant air conditioning with an infrared-transparent membrane has been developed which installs an infrared-transparent membrane vertically below the radiant cooling plate of a radiant air conditioner to form a closed gas interlayer between them. On the basis of this, the effects of the gas type (vacuum, nitrogen, air, argon, and carbon dioxide) and relative air humidity in the interlayer on the radiative heat transfer, convective heat transfer, and radiative heat-transfer ratio of the radiant cooling plate, and the surface temperature of the infrared-transparent membrane were investigated by CFD (Computational Fluid Dynamics) numerical simulation. When the thickness and gas type of the interlayer were 20 mm and vacuum, respectively, the radiant cooling plate showed the most radiative heat transfer, the least convective heat transfer, the largest radiative heat-transfer ratio, and the highest surface temperature of the membrane, followed by when the gas type was argon. There was no risk of condensation in the air conditioning when the relative air humidity in the interlayer did not exceed 80%. The results of the study provide a theoretical basis for the optimal design of radiant air conditioners. [ABSTRACT FROM AUTHOR]

Adaptive building envelopes with advanced optical materials have received much attention as they can actively regulate solar heat gain. In present work, an adaptive building roof (ABR) combining variable transparency shape-stabilized PCM (VTSS-PCM) was proposed. A numerical model was developed firstly for dealing with time-space effect of radiation properties of VTSS-PCM and validated by experiments. The difference in performance between ABR and the common insulation roof was simulated. Then, a global sensitivity analysis based on the Monte-Carlo method was conducted to determine key parameters among 22 system parameters. Finally, the influences of key parameters on the performance of ABR were studied in detail. The results show that the ABR can reduce the heat gain by 35.25 % compared with the common insulation roof. The thickness of VTSS-PCM, the extinction coefficient of VTSS-PCM in the transparent state, and the albedo of reflective film are three key parameters. The thickness of the VTSS-PCM layer and the extinction coefficient of VTSS-PCM in the transparent state have positive correlations with the heat gain, whereas the albedo of the reflective film has a negative correlation with the heat gain. The time-space effect of radiation properties of VTSS-PCM during the phase change causes the solar absorptance of ABR to be unstable. This research guides the modeling of VTSS-PCM and facilitates the application of ABR. [ABSTRACT FROM AUTHOR]