Clean Heating Research Articles

Thermal performance of solar-biomass energy heating system coupled with thermal storage floor and radiators in northeast China

Solar-biomass heating system can effectively reduce carbon dioxide (CO2) emissions and achieve clean heating. However, there are some limitations, as ignoring the features of dynamic thermal demand and living habits of Chinese rural households. In the present study, a novel solar-biomass energy heating system is proposed that integrates a variety of heating terminals with a thermal storage floor and radiators. Experimental study and theoretical analysis were carried out to explore the thermal performance of the proposed heating system and investigated its impact on reducing energy consumption and emissions in a typical rural residence. The results demonstrate that during the operation of biomass stove, which corresponds to high heat demands, the surface temperature rising rate of radiators is 100 times than that of thermal storage floor, which allows the increase of indoor air temperature around 20℃. When heat input was stopped during the night, the thermal storage floor can maintain the indoor air temperature at 17℃. The average primary energy efficiency of the novel system is 0.57, which outperforms the traditional heating system. The energy consumption and average carbon dioxide (CO2) emissions are both reduced significantly throughout the heating season. This study has well considered the features of the dynamic thermal environment required by rural households, and the novel system has better adaptability and adjustability for heat demand to provide a potential technical solution for clean heating in rursal China.

Experimental and computational analyses for advanced wastewater treatment by volcanic rocks.

Treating and reusing wastewater is a promising alternative for the water shortage problem. The advanced treatment of such water can provide a good source for plant irrigation and other applications and reduce the demand for the available freshwater resources. This alternate is highly recommended for arid and semi-arid counties. In this research, volcanic rock (VR) is introduced as an advanced and low-cost treatment option for wastewater. The volcanic rock was adopted as an adsorption tool for removing impurities from the secondary treated wastewater effluents. The study relies on experimental work on a lab scale. Many parameters were investigated such as loose and compacted layered samples, and pretreated methods for the rocks including soaking in clean water or heating for different temperatures. Simulation work also was adopted to validate the experimental results. The study results showed a decline in most physiochemical properties of wastewater after adding VR compared with the control sample. A notable removable for the measurements of the biological oxygen demand and chemical oxygen demand (COD) from wastewater in the presence of VR was observed, which may introduce it as a tool for the advanced treatment of wastewater. The numerical results depicted the experimental data and reflected the effectiveness of the VR-based geomaterial filter for the treatment of wastewater. PRACTITIONER POINTS: Prewashing process for volcanic rock (VR) exhibited an improvement in its removal efficiency ranged between 18% to 98% as for TDS and removal of NO3 - , respectively. Heating samples does not improve the removable properties of VR. A notable removable for biological oxygen demand and COD by 96% and 99%, respectively, for some cases from wastewater, may introduce the VR as a tool for advanced treatment of wastewater. The numerical test results are in consistent with the experimental behavior of the VR and reflect the effectiveness of the VR-based geomaterial filter for the treatment of wastewater.

Does energy transition help narrow the urban-rural income gap? Evidence from China

With climate change and inequality concerns being the twofold challenge for societies, vigorously facilitating the pace of energy transition in parallel to promoting social justice is addressed by global societies. Using an empirical analysis of 30 provinces in China, we examine how the pace of multi-dimension energy transition influences urban-rural income gap. It starts from an assessment of China's energy transition performance by constructing a comprehensive index framework. Then we investigate the impacts of the energy transition on the urban-rural income gap by employing panel data of China's 30 provinces from 2008 to 2019. Our results demonstrate a significant upward trend in China's overall energy transition performance. Meanwhile, this paper highlights the positive but heterogenous contributions of the energy transition to narrowing the urban-rural income gap. We also gauge the positive moderating effects of energy transition and various targeted transition policies and environmental factors on the urban-rural income gap in China, such as the clean heating and PV-based poverty alleviation project; but the negative effect of coal phaseout policy cannot be ignored. Our findings in the context of urban-rural income inequality in China provide practical insights and pertinent policy implications to deepen understanding of the global just energy transition.

Is solar heating an appropriate choice in rural areas of northern China? Evidence from numerical simulation and life cycle assessment

Solar heating is generally regarded as a clean and low-carbon heating method, while its high initial investment hinders its promotion in economically underdeveloped areas. With the implementation of the clean heating policy and the proposal of the carbon neutralization target, rural bulk coal heating in northern China is restricted. The Chinese government proposes to widely adopt solar heating to meet the heating demands of rural residents. In this research, the application of solar assisted heat pump systems in Beijing, Tianjin, Hebei and its surrounding areas in China is numerically simulated. A new evaluation method under the same initial investment constraint is proposed to verify its benefits throughout the entire life cycle. The results indicate that although solar thermal heating has the lowest environmental impact and carbon emissions among various heating methods, it is not the best solution to rural clean heating. The reason is that equal investment in other projects can bring much more benefits, such as roof solar photovoltaic. In contrast to the air source heat pump and photovoltaic panel scheme with the same initial investment, solar heating has obvious negative environmental impact, 53.3 % higher economic cost, 35.9 tons more carbon emissions, and 105.9 % higher roof area occupation. The sensitivity analysis of solar fraction, geographical coordinates, and energy price also supports the above findings. The recommendation is proposed to promote air source heat pumps or solar photovoltaic, rather than solar thermal collectors, so as to reduce the cost of rural clean heating and carbon emission reduction.

Study on Energy Flow Characteristics of Solar–Gas Combined Heating System for Settling Tank of Oilfield

Heating furnaces fueled by fossil fuels are commonly utilized in oilfields to provide heat to the settling tank, which heats the layer of crude oil. However, this traditional heating method consumes a significant amount of oil and gas resources, resulting in low energy utilization and environmental pollution. As the water content of the extracted crude oil increases over time, the operating costs of the settling tanks also continue to increase. Therefore, it is crucial to develop and implement clean and efficient heating technologies to facilitate the efficient operation of settling tanks. This paper proposes a solar–gas combined heating technology for settling tanks. A simulation model for the solar–gas combined heating system for the settling tank is constructed, considering the overall perspective of the system. The simulation model analyzes the impact of the control strategy for the oil collection period of the settling tank on the system performance. This analysis covers various aspects including the heat collection of the solar collector, the heat supply of the gas boiler, and the heat storage and release of the phase-change heat storage tank. The results demonstrate that when the oil collection cycle is Scheme E (4:00–8:00), the collector achieves the highest annual cumulative heat collection, the gas boiler provides the lowest annual total heat supply, and the phase-change heat storage tank exhibits the highest heat storage and release efficiency. Over the course of the system’s 15 year service life, the settling tank solar–gas combined heating system saves 727,988.69 MJ of energy annually, resulting in total energy-saving costs of CNY 397,007. The dynamic investment payback period is estimated at 9.14 years, and the system reduces CO2 emissions by 753,069.8 kg.

Comparative study on flexibility enhancement of combined heat and power for wind power accommodation

Flexibility enhancement of coal-fired combined heat and power units is an essential approach for improving the wind power accommodation and a significant low-carbon way to achieve clean urban heating. To consume excess wind power, this paper proposed a novel combined heat and power system integrated with the various flexible technologies. The EBSILON software was applied for modeling the proposed thermal systems and analyzing the thermal performance under different operating conditions. On this basis, the mechanism of their heating compensation and wind power consumption was revealed and the indicator, the heating compensation capacity, was presented considering from both peak shaving and coal-savings perspectives. Compared with the conventional system, the wind power accommodation rate of the novel system had a maximum increment of 31.7% and the standard coal consumption had a maximum reduction of 14.3%. Meanwhile, by adding dynamic payback period and internal rate of return, the techno-economic performances were more reasonable and precise. The results showed that the heating compensation capacities of absorption heat pumps, low-pressure cylinder of turbine removal and thermal energy storage with extracted steam from turbine are 0.29 t/MWh, 0.26 t/MWh, and 0.25 t/MWh, respectively, which are better than that of other technologies. The net annual revenue of thermal energy storage system could reach 3.87 M$, 0.57 and 0.37 M$ higher than that of low-pressure cylinder of turbine removal and absorption heat pumps, respectively. It can be concluded that thermal energy storage can be the best to balance the peak shaving demand and techno-economic performance. In all, the proposed systems provided a promising method for the flexibilization of coal-fired combined heat and power units alongside new renewable systems.

CO2 system integrated with ejector and mechanical subcooling: A comprehensive assessment

To achieve the goal of clean annual space heating and cooling for residential buildings, the concept of annual space heating and cooling transcritical CO2 system combined with ejector and mechanical subcooling is proposed. The problem of large throttling loss and performance degradation when CO2 system is applied for residential space heating and cooling can be solved. A theoretical model of the new proposed system is developed, and then optimized by the method of genetic algorithm. Moreover, taking an ordinary residential building located in 70 cities belonging to different climate zones as the application scenario, the seasonal, annual, environmental, and economic performance of eight heating and cooling solutions are compared and discussed. The results indicate that the COP and exergy efficiency of the new proposed system is significantly improved in contrast to conventional mechanical subcooling system, which increases by 11.48% and 21.64% in heating mode, and 8.99% and 8.69% in cooling mode, respectively. The annual performance coefficient of the new proposed system is 7.21%∼8.21% higher than conventional mechanical subcooling system. Additionally, the life cycle carbon emissions of the new proposed system can be significantly reduced by 12.23%∼89.58% compared with the combined solution of coal-fired boiler and R32. With the advancement of CO2 technology, it is possible to improve the economic performance of CO2 systems and the price of the new proposed system is lower than all solutions when the price of compressor is reduced by 60%. This study can provide a theoretical reference for the development and optimization of CO2 combined heating and cooling system, and provide a feasible solution for residential annual space heating and cooling.

Mechanical and permeability tests under the influence of geomembrane temperature

Aquatic solar energy cross-season heat-storage technology can store and transfer abundant solar energy from the non-heating season to the heating season, which is one of the important technical routes for renewable energy to be used for clean building heating. Anti-seepage components are an important part of the thermal storage of the water body. As a common anti-seepage material for the thermal storage of the water body, a geomembrane is laid on the pool body and the top cover. In this paper, the mechanical and permeability changes of two kinds of geomembranes are analyzed based on the tests under different temperature environments. The results show that GM1 has better thermal stability. The elongation at break of GM1 increases by 33% and GM2 by 189% when the temperature rises by 40 °C. The osmotic coefficient of GM1 is reduced by 45% and GM2 by 58%.

Low-cost solar concentrating collector-receiver system as an effective enabler for clean cooking and heating in urban areas

The present work reports a dual-purpose solar concentrating cooker’s design and thermal performance. The uniqueness of the proposed system is the simultaneous dual-mode operation that enables cooking and heating. The Cooker Opto-Thermal Ratio (COR) as a Thermal Performance Parameter (TPP) allows the solar concentrating cooker’s (SCCs) rating using glycerin as a cooking load (test load). The energy and second law analyses account for the thermal analysis of the water heater. The Levelized cost of cooking a meal (LCCM) comments on the economic analysis of the proposed system. The mean value of COR for the SCC (with simultaneous water heating at different flow rates) is 0.0908 ± 0.0032 and remains approximately the same. The exergy efficiencies of water heating at flow rates of 10, 15, 20, and 30 kg/h are 0.71, 0.81, 0.72, and 0.57 %, respectively.Additionally, the average values of the exergy factor at the specified flow rates are 0.034, 0.029, 0.024, and 0.018, respectively. The LCCM for the proposed system is 0.021 USD/meal. Thus, the proposed solar concentrating cooker combined with a water heater is a unique and low-cost dual-application system that efficiently performs simultaneous cooking and water heating.

System optimization and mode modification of the solar assisted ground source heat pump system for primary schools in northern rural areas of China

With the increasing application of geothermal and solar energy in northern regions of China, it has become one of the main clean heating technologies for rural primary schools. However, the mismatch in equipment capacity has led to poor operating effect and economic efficiency of such systems. This paper puts forward experimental and analysis on a solar assisted ground source heat pump system in a primary school in Beijing's Daxing District. And then, to address the above issues, a TRNSYS model is established and verified to optimize the system strategy and form during 15 years period. What’ more, the main factors affecting solar collector selection are screened by sensitivity analysis. And through the step-by-step regression analysis, the collector selection correction model based on the coefficient Km is obtained. The results show that the temperature difference of the optimized collector control is 10 °C/1°C, and that of the supplementary heat is 20 °C/1°C. The applicable scenarios of the two system forms are different, and the energy efficiency of the system operation is increased by 23% and 23.4% respectively. In addition, the revised model ensures the balance of soil temperature for 15 years of operation under the condition of considering multiple elements, which provides a reference for the matching and selection of equipment for the same type of project in the future.

Techno-economic-environmental analysis of seasonal thermal energy storage with solar heating for residential heating in China

Seasonal thermal energy storage (STES) of solar heat is an option of interest for clean heat transition, as residential heating is often fossil fuel-based. This study 1) proposes an integrated optimization criterion to examine how local context influences the optimal configuration planning, techno-economic-environmental performance, and feasibility of STES application; 2) identifies the position of STES in comparison to other sustainable heating options considering the local context; and 3) provides a comprehensive and transparent showcase highlighting the importance of the local context in determining the feasibility of STES in the clean heating transition. The TRNSYS modeling tool is adopted to analyze the performance, and Pareto optimization is applied to treat the multi-objective optimization. The solar fractions and storage efficiencies of the four case studies range between 58-67% and 57–69%, respectively. STES has significant potential to reduce CO2 emissions (52–72%) compared to conventional heating systems. However, the heating cost of the STES system (5.4–8.7 €-ct/kWh) is more than twice that of the conventional heating system. The CO2 avoidance cost of the four case studies ranges between 114 and 368 €/t. Properly reducing the borehole number in cold climate zones and increasing the solar collector area in warm climate zones help improve the system performance.

Design optimization of medium-deep borehole heat exchanger for building heating under climate change

Geothermal thermal energy with a medium-deep borehole heat exchanger (MDBHE) is a clean solution for building heating. There lacks a proper design of the MDBHE based on long-term performance evaluation, which is essential to promoting the efficient application of geothermal thermal energy for building heating. This study proposes a design optimization of the MDBHE for building heating under climate change. First, the long-term heating energy performance of the MDBHE under climate change is evaluated. Second, the operation cost is evaluated based on the long-term heating energy performance, considering the discount rate and inflation rate. Third, an optimization algorithm is employed to determine the optimal design of the diameter ratio of the inner pipe to the outer pipe, pipe depth, and inlet velocity of the MDBHE. The optimization method minimizes the cost of initial and operational expenditure while satisfying the system safety requirement. Results show that climate change should be considered, which helps to robustly reduce energy consumption and cost by 9.3%–44.4% and 3.9%–21.8% respectively, under different design conditions compared with the typical meteorology. This study contributes to the proper design of the MDBHE as a clean building heating solution.

Implementation gap of China’s environmental policies: logic behind the over-implementation of the coal to gas transition

ABSTRACT China has implemented numerous energy-related policies to tackle environmental and energy challenges, but not all policies have yielded desired outcomes. While policy failure due to insufficient implementation is often highlighted, less attention has been given to the issue of over-implementation. In the last decade, China has experienced a process of power recentralization, which has brought about systemic changes in environmental policy implementation. Over-implementation has emerged as a prevalent phenomenon in environmental governance. The questions thus arise are: why does over-implementation happen? What are the consequences? This study examines the phenomenon of policy over-implementation within China's environmental governance system, using the coal-to-gas clean heating project as a case study. The findings reveal that China's recentralization efforts have addressed long-existing root problems in the environmental governance system. The strong environmental commitment from the central government, coupled with authoritarian pressure and positive incentives, has resulted in local implementers self-reinforcing for better career prospects, leading to over-implementation of policies. However, such authoritarian enforcement may overlook conflicts at the street bureaucratic level and opposition from those affected by the policies, potentially causing social injustice.

Energy, exergy, exergoeconomic, environmental (4E) evaluation and multi-objective optimization of a novel SOFC-ICE-SCO2-HRSG hybrid system for power and heat generation

To achieve sustainable development of the global energy system, it is essential to develop efficient and cost-effective cogeneration systems. This paper introduces a new cogeneration system named SOFC-ICE-SCO2-HRSG, which combines solid oxide fuel cells (SOFC), internal combustion engines (ICE), supercritical carbon dioxide (SCO2) power cycles, and heat recovery steam generators (HRSG) to generate electricity and heating simultaneously. The proposed system offers a promising solution for achieving high efficiency and cost-effective clean power generation and heating. Energy, exergic, exergoceconomic, and environmental analyses were conducted to evaluate the system's performance. The impact of fuel flow, steam carbon ratio, and other parameters on the system's efficiency was also analyzed. The system was optimized using a genetic algorithm, and the optimal operating condition was determined using the TOPSIS method. The results indicate that the proposed system can achieve a total output power and net output power of 345.58 kW and 288.94 kW, respectively, under optimal conditions, with a 1:1 fuel flow ratio between the SOFC and ICE systems. The total unit cost of the product can be as low as 42.98 $/GJ, while the theoretical and actual generation efficiencies can reach 48.00% and 40.13%, respectively. The overall energy efficiency and exergy efficiency were found to be 65.82% and 42.28%, respectively. Additionally, the system can achieve a CO2 emission rate of 0.4712 kg/kW·h, and the social cost for pollutant emissions was estimated to be 3.34 $/GJ. This study provides evidence that the proposed hybrid system has excellent performance in terms of efficiency, cost, and environmental impact. As an advanced energy conversion technology, it holds great potential for practical applications in meeting energy demands while reducing environmental pollution.

Optimization of biomass energy coupled multi-source heat pumps cooperative heating system: A case study

ABSTRACT To achieve the goal of clean heating in northern rural areas, a cooperative heating system, composed of a biomass boiler and a multi-source heat pump was proposed, based on building heat load and resource conditions. This cooperative heating system combined biomass energy, geothermal energy and air energy. A dynamic simulation model is established by using the TRNSYS software. Under the condition of energy balance, an optimization model is proposed based on the minimum annual cost. The proposed model is applied in a demonstration project for the Miaofuan rural community in Linzi Town, Linyi County, Dezhou City in Shandong Province, China. The heat supply ratio of each equipment and the operation mode of the coupled system are optimized. Results show that the coupled system with the optimal configuration can reduce the annual cost by 9.60%, 14.22% and 11.66%, respectively; compared with the geothermal heat pump, air source heat pump and biomass boiler alone. Therefore, the proposed cooperative heating system can be well applied in rural areas.

Optimal rule based double predictive control for the management of thermal energy in a distributed clean heating system

Solar energy coupled with electric heat storage is a kind of promising energy saving technology for distributed building heating. Precise and quick heat load prediction for the demand side of heating system and renewable energy prediction for the supply side are imperative in realizing the flexibility of building clean energy supply systems. A predictive control based on back propagation (BP) artificial neural network is built to predict the demand heat load of an office building and the heat supply quantity of solar collector (SC) system. The heat dissipation of the SC system is considered to improve the prediction accuracy of its heat supply quantity. A double predictive (DP) control is introduced and combined with dynamic adjustment to optimize the operation of renewable energy, phase change heat storage and valley electric heating system. The results indicate that predictive model is of high precision and the variation coefficient of root mean squared errors corresponding to each prediction parameter are all greater than 0.9. Furthermore, the optimization results indicate that the DP control would save, in March, about 59.3% of charge heat quantity of phase change material (PCM) tank and terms of cost (30.4%). Meanwhile, maintaining indoor temperature between 20 °C and 22 °C.

Experimental investigation of an air source heat pump with multigroup heat pipe radiators

As a clean and sustainable electrified heating technology, air source heat pump (ASHP) has been widely used in household in China. However, some problems occurred with the commonly used water loop system, such as low efficiency, complicated structure, more likely to be frozen and burst as well as high electric energy consumption, etc. In this paper, a new air source heat pump with multigroup heat pipe radiators (ASHPMP) was presented. In ASHPMP system, the condenser and heat pipe were coupled together to form a new type of heat radiation terminal, which was named as heat pipe radiators, multiple terminals driven by the compressor provided heat for several rooms. An experimental apparatus of the ASHPMP system was developed and the experiment was carried out in residential buildings also, and R410A was used in the heat pump and R134a was used in heat pipes. The influence of temperature, pressure of heat pump and heat pipe on the heating performance of ASHPMP under frosting/defrosting condition was analysed. The results showed that the new system can operate stably under outdoor temperatures of −12.7 °C to 6.5 °C. As the indoor temperature was set at 20 °C, the heating coefficient of performance (heating COP) could reach up to 3.15 with outdoor temperature −12.7 °C, and it was 6.73 with outdoor temperature 6.5 °C.

Households' participation in energy transition and sustained use of clean energy: Evidence from China's clean heating program

Household energy transition is a critical tool for air pollution mitigation and energy inequality reduction. The effectiveness of the transition largely relies on not only households' decision to participate but also their sustained use of clean energy after participation. However, the sustained use of clean energy has not yet received sufficient attention in policy making and in literature. This study examines China's Household Clean Heating program, which has switched millions of households' heating energy sources from coal to electricity and gas. We focus on both households' adoption and coal substitution behavior in the program. Based on the large-scale household survey conducted in rural areas of Northern China, we find that both high subsidies and compulsory measures effectively increased the household adoption rate; however, the latter did not guarantee sustained use of clean energy. We also find that In-person and repeated dissemination of program information had a better effect on involvement than passive announcements. Moreover, lower-income households were less likely to participate. Our findings suggest effective implementation approaches and supplementary measures to promote household energy transition, with fewer negative consequences for participants, particularly for the participants with lower income.

Effect of Clean Heating on Carbonaceous Aerosols in PM2.5 During the Heating Period in Baoding

In order to study the effects of clean heating measures on the concentration and source of carbonaceous aerosols in PM2.5 in Baoding, we collected PM2.5 samples in Baoding during the winter heating periods of 2014 and 2019. The concentrations of OC and EC in the samples were determined by using a DRI Model 2001A thermo-optical carbon analyzer.The results showed that the average values of ρ(OC) and ρ(EC) in the heating period in 2014 were 60.92 μg·m-3 and 18.15 μg·m-3, and the average values of ρ(OC) and ρ(EC) in the heating period in 2019 were 36.63 μg·m-3 and 6.07 μg·m-3. Compared with those in 2014, the concentrations of OC and EC decreased by 39.87% and 66.56%, respectively, in 2019; the decrease in EC was larger than that in OC, and the meteorological conditions in 2019 were more severe than those in 2014, which was not conducive to the spread of pollutants.The correlation analysis and SOC estimation of OC and EC indicated that the correlation R2 of OC and EC in Baoding in 2014 and 2019 were 0.874 and 0.811, respectively, indicating that OC and EC in Baoding had relatively consistent sources. The average values of ρ(SOC) in 2014 and 2019 were 16.59 μg·m-3 and 11.31 μg·m-3, respectively, and the contribution rates to OC were 27.23% and 30.87%, respectively. This showed that in 2019, compared with that in 2014, the primary pollution decreased, but the secondary pollution increased, and the atmospheric oxidation increased.The analysis of the pollution sources of carbonaceous aerosols revealed that in 2014 and 2019 before and after the implementation of clean heating, the carbonaceous aerosols in the atmosphere were mainly from biomass combustion, coal combustion, and vehicle exhaust emissions. However, the contribution from biomass burning and coal burning decreased in 2019 compared to that in 2014. The decrease in OC and EC concentrations was attributed to the control of coal-fired and biomass-fired sources by clean heating. At the same time, the implementation of clean heating measures reduced the contribution of primary emissions to carbonaceous aerosols in PM2.5 in Baoding City.

Clean and low-carbon heating in the building sector of China: 10-Year development review and policy implications

Space heating in China relies heavily on fossil fuels that cause heavy air pollution and greenhouse gas emissions. The clean heating policy began in 2013 to improve air quality and is now expanding to clean and low-carbon heating (CLCH) for the 2030 carbon dioxide peaking targets. However, few studies have focused on the transformation of China's heating sector over the past decade. The heating areas in China are categorized into urban areas in Northern China, town areas in Northern China, rural areas in Northern China, and regions in Southern China. Six types of CLCH technologies with the highest potential and prospects were reviewed and summarized. In northern urban and town areas, waste heat utilization could help achieve zero-carbon district heating. However, energy-efficient and affordable distributed (household) heating technologies should be promoted in rural and southern areas. In addition, the energy-efficient retrofit of buildings is crucial for reducing heating energy demand and should be given priority. This review provides an overview of CLCH development in China and can be used as a reference for other countries to develop heating strategies.