• Energy Research

District Heating (DH) is considered as an efficient, environmentally friendly and cost-effective method for providing heat to buildings, and is playing an important role in the mitigation of climate change. Nowadays, Swedish DH companies are facing multiple challenges, and in urgent need for new price models to increase transparency and keep the competitiveness. In this paper, a survey is carried out to understand the structure of the present price models. Then, two restructured price models are proposed and compared with the price model most commonly used. To increase the transparency, price models should be based on users’ measured consumption profile; while to reduce the peak load, adoption of a pricing strategy based on a load demand component is an effective way. Consequently, users with flat consumption profiles will reduce cost, whereas users with steep consumption profiles will have a cost increase, both when charging the load demand cost based on the maximum daily or hourly peak load.

Abstract Transcritical CO2 refrigeration cycle integrated with mechanical subcooling (MS) cycle operating with zeotropic mixture is proposed in this study, based on the concept of Lorenz cycle. An energetic model is developed and analyses are conducted in detail. A maximum overall coefficient of performance (COP) is achieved at the optimum discharge pressure and optimum subcooling degree. The maximum overall COP, optimum subcooling degree and discharge pressure are closely related to the temperature glide of the mixtures. The energy efficiency of the transcritical CO2 refrigeration cycle can be efficiently improved, and the high pressure can be reduced when mixtures with proper temperature glide are used as MS cycle refrigerant. Compared with pure R32, the overall COP is enhanced by 4.91%, and the discharge pressure decreases by 0.11 MPa at evaporation temperature of −5 °C and ambient temperature of 35 °C when R32/R1234ze(Z) (55/45) is employed as MS refrigerant. The mixtures with proper temperature glide are recommended. The thermal performance of the overall cycle can be enhanced more significantly for hot and warm climate regions, or relative low evaporation temperature applications, though a high subcooling degree is required to meet the optimum operation condition.

Abstract Viscosity and thermal conductivity are key transport properties in the design of plate-fin multi-stream heat exchanger in CO 2 cryogenic processes. It is necessary to evaluate the reliabilities of viscosity and thermal conductivity models. In addition, the differences in design of multi-stream heat exchanger by using different property models need to be studied as well. In this paper, viscosity models and thermal conductivity models of CO 2 mixtures with non-condensable gas impurities were evaluated separately by comparison with existing experimental data. Recommendations were given on model selections and their impact on the design of plate-fin multi-stream heat exchanger were analyzed. The results show that for viscosity, the uncertainty range of Wilke's model is the smallest with a maximum absolute deviation of 6.1%. This model is therefore recommended to be used. For thermal conductivity, GERG model, with a maximum absolute deviation of 8.7% is preferred. The choice of thermal conductivity model has a noticeable impact on the plate-fin multi-stream heat exchanger design, and the maximum deviation by using different thermal conductivity models is 7.5%.

Photovoltaic water pumping technology is considered as a sustainable and economical solution to provide water for irrigation, which can halt grassland degradation and promote farmland conservation ...

Great attention has been paid to develop non-fossil fuel energy sources to reduce carbon emissions and create a sustainable energy system for the future. Storing the intermittent energy is one of t ...

AbstractNatural gas (NG) is expected to be used broadly in China to replace coal in district heating sector in order to reduce air pollution due to coal burning. However, it is difficult for natural gas to penetrate district heating market due to its relatively high cost. In the present study, a market simulation method is proposed to find the marginal conditions and policy to promote natural gas utilization for district heating. In the proposed method, technology improvement, pricing mechanism, carbon tax and user's pricing response are considered. The prerequisite of the market simulation is that the heating expenses of end-users won’t increase and the benefit of heat producers won’t decrease when using NG to replace coal. Based on the obtained analysis results, gas pricing revolution, heating pricing revolution and carbon tax mechanism are discussed in order to promote the gas-fired heating through market mechanism.

This study developed a conceptual model based on the industrial metabolism approach and the generic model can be used to analyze the energy flows for the iron and steel (Is) industry. based on the ...

Abstract The development of heat metering has promoted the development of statistic models for the prediction of heat demand, due to the large amount of available data, or big data. Weather data have been commonly used as input in such statistic models. In order to understand the impacts of direct solar radiance and wind speed on the model performance comprehensively, a model based on Elman neural networks (ENN) was adopted, of which the results can help heat producers to optimize their production and thus mitigate costs. Compared with the measured heat demand, the introduction of wind speed and direct solar radiation has opposite impacts on the performance of ENN and the inclusion of wind speed can improve the prediction accuracy of ENN. However, ENN cannot benefit from the introduction of both wind speed and direct solar radiation simultaneously.