Clean Heating Research Articles

Suitable promotion scope of different clean heating technology paths in northern China

The Chinese government has implemented a clean heating policy to alleviate the severe air pollution and high energy consumption associated with winter heating in northern China. However, the promotion of clean heating technology paths (CHTPs) is limited by the problems of rising energy prices and insufficient supply capacity. To quantitatively study the promotion scope of each CHTP, this paper adopts the K-means clustering method in machine learning to analyze the clean heating methods suitable for the characteristics of each region in northern China based on 37 pilot cities. The results show that the 10 CHTPs based on coal, electricity and natural gas as energy, the most widely applied is Air-source heat pump technology, accounting for 86.7 % in cities. The least number of cities suitable for application are water-source heat pumps and sewage-source heat pumps due to economic constraints, with a proportion of 44 %. The 3 kinds of CHTPs applying solar, biomass and geothermal energy, accounted for more than 60 %, among them, ground-source heat pumps are recommended to promote the smallest scope, concentrated in Hebei, Henan, Shandong, and Heilongjiang provinces. This study is of great significance in guiding the selection of CHTPs on a large spatial scale.

Seasonal thermal energy storage employing solar heat: A case study of Heilongjiang, China, exploring the transition to clean heating and renewable power integration

Seasonal thermal energy storage (STES) offers an attractive option for decarbonizing heating in the built environment to promote renewable energy and reduce CO2 emissions. A literature review revealed knowledge gaps in evaluating the technical feasibility of replacing district heating (DH) with STES in densely populated areas and its impact on costs, fossil fuel consumption, CO2 emission reduction, and renewable power integration. The effects of large-scale STES applications on the power and DH sectors in a regional energy system were quantified by applying the 2030 and 2050 power structure scenarios. The results indicated that STES reduces fossil fuel consumption and CO2 emissions at an affordable cost. It facilitates the integration of wind and solar power into power grids. With 100 % replacement of DH by STES, fossil fuel consumption and CO2 emissions can be reduced by approximately 40 % and 45 % in 2030 and 2050, respectively, with an annual cost increase of 20 %. The CO2 avoidance costs were predicted to be approximately 60 €/t in 2030 and well below 50 €/t in 2050. STES will reduce renewable power curtailment by 10 % in 2030 and 18 % in 2050. This study investigated STES from an energy-system perspective, supporting the formulation of clean heating transition policies.

Cleaner heating policies contribute significantly to health benefits and cost-savings: A case study in Beijing, China

Cleaner heating policies aim to reduce air pollution and may bring about health benefits to individuals. Based on a fixed-effect model focusing on Beijing, this study found that after the onset of air pollution, daily clinic visits, hospitalization days, and hospitalization expenses increased several days after the occurrence of air pollution. These hospitalization changes were observed in males and females and three different age groups. A difference-in-differences (DID) model was constructed to identify the influences of cleaner heating policies on health consequences. The study revealed that the policy positively affects health outcomes, with an average decrease of 3.28 thousand clinic visits for all diseases. The total hospitalization days and expenses tend to decrease by 0.22 thousand days and 0.34 million CNY (Chinese Yuan), respectively. Furthermore, implementing the policy significantly reduced the number of daily clinic visits for respiratory diseases, asthma, stroke, diabetes, and chronic obstructive pulmonary diseases (COPDs).

Optimization of solar-air source heat pump hybrid heating system

Abstract In order to construct a versatile, complementary, low-carbon, clean, and efficient heating system, this study explores the potential of a solar-air source heat pump (SAHP) hybrid heating system. A simulation model is established in TRNSYS, and the particle swarm algorithm (PSO) and genetic algorithm (GA) from GENOPT and MATLAB are employed. With the aim of minimizing the annual cost, optimization is conducted on the key parameters and operational strategies of the system. Comparative analysis between the two algorithms reveals that PSO slightly outperforms in cost reduction, while GA exhibits a slight advantage in enhancing system performance. Significantly improved energy savings are achieved by appropriately reducing the rated heating capacity of the air source heat pump and increasing the volume of the water tank.

Carbon Nanotube Films with Fewer Impurities and Higher Conductivity from Aqueously Mono-Dispersed Solution via Two-Step Filtration for Electric Heating.

With the intensification of global climate problems, electric heating has recently attracted much attention as a clean and low-carbon heating method. Carbon nanotubes (CNTs) are an ideal medium for electric heating applications due to their excellent mechanical, electrical, and thermal properties. The preparation of electrothermal films based on an aqueous CNT dispersion as a raw material is environmentally friendly. However, in the traditional one-step filtration method, the residual excess dispersant and the small aspect ratio of the CNTs in the preparation process limit the performance of electrothermal CNT films. In this paper, we report a two-step filtration method that removes the free dispersant and small CNTs in the first filtration step and obtains denser CNT films by controlling the pores of the filter membrane in the second filtration step. The results suggest that, compared to the CNT1 film obtained from one-step filtration, the CNT1-0.22 film, obtained from two-step filtration using 1 and 0.22 μm membranes, has a smoother and flatter surface, and the surface resistance is 80.0 Ω sq-1, which is 29.4% lower. The convective radiation conversion efficiency of the CNT1-0.22 film is 3.36 mW/°C, which is 36.1% lower. We anticipate that such CNT films could be widely applied in building thermal insulation and underfloor heating.

Analysis of geothermal heat recovery from abandoned coal mine water for clean heating and cooling: A case from Shandong, China

Exploiting heat from abandoned mine water using heat pumps is attracting increasing attention worldwide. China has a large number of abandoned coal mines, but there are few applications of geothermal heat recovery from mine water. Here, we report a new case from Shandong, North China. Based on actual geological and underground space structures, numerical analysis is performed to study the flow and heat transfer in the complex connection network among roadways. For given temperature differences on the source side, the underground heat transfer is greatly influenced by flow rates in roadways. Under the acceptable performances and long-term stability of heat pumps, the maximum heat transfer capacity of roadways reaches 697.3 kW at the flow rate of 100 m3/h, with the power per unit length of 151.3 W/m, indicating a promising heat recovery potential. When switching between the extraction and injection well, both fluid directions and the distribution of flow rates in roadways change obviously, thereby affecting the underground heat transfer. Besides dominant flow paths, there exist weak flow paths, which can be identified by numerical analysis, and necessary blocking can be applied to optimize the flow and heat transfer. Excessively long horizontal straight roadways for heat exchange should be avoided.

Clean energy pipeline energy storage system and its economy

The economic problem of a clean energy heating system under a peak and valley electricity pricing system is investigated, and a pipe network energy storage system is correspondingly proposed to solve this problem. The system makes use of large-capacity primary network pipe network water storage to store heat during the valley electricity hours when the electricity price is lower, and releases the stored heat to supply heat during the peak electricity hours when the electricity price is higher, with a view to reducing the operating time of the heating system during the peak electricity hours when the electricity price is higher. The principle of the system and the efficient regulation scheme are given, and a mathematical model of primary pipe network energy storage and release is established, and the reliability of the model is verified with a heating project in Qingdao as an example, and the results show that the maximum temperature deviation of the return temperature of the primary pipe network obtained by the calculation of the energy storage and release model is 0.23 °C, and the maximum temperature hysteresis error is in 15 %, which meets the requirements of engineering practice. Based on the energy storage model, the simulation of the actual heating economy of the project using the pipe network energy storage system was carried out, and the results showed that compared with the original scheme based on the maximum heat load adjustment of the proportion of heating units and boilers, the electricity consumption of the project using the pipe network heat storage scheme was increased by 18.8 % in the whole heating season, the total operating costs were reduced by 14.5 %, with an annual saving of 800,600 yuan in operating costs, and the payback period for the investment was relatively short, at 2.1 years, which is of good economy.

Numerical study on the interface characteristics of gas–liquid falling film flow considering the interface forces

As an energy quality improvement device, an air source heat pump plays an important role in clean heating applications. When operating in a cold and wet environment in winter, the outdoor evaporator will have the problem of frost, which affects the operation efficiency. To solve the frosting problem, the development of frost-free evaporators has attracted more and more attention. The fluctuation characteristics of the gas–liquid interface are the key factors affecting the intensity of gas–liquid heat transfer on the air side of this kind of heat exchanger. Therefore, a mathematical model is established to describe the falling film flow on the surface of the flat finned tube heat exchanger in a closed-type heat source tower. The model takes into account the interfacial tension and interphase friction force between the air flow and the liquid film. On this basis, the fluctuation intensity of the central channel interface during falling film flow with different inlet parameters is studied. It is found that there is a critical value of 1.5 m/s (i.e., Reg = 1643.0) in the air flow rate under the study conditions. When the air flow rate is higher than this velocity, the interface near the gas–liquid outlet fluctuates more frequently and the stability is poor. The distributions of interfacial velocity and pressure are also studied, and the relationship between them and interface fluctuation is analyzed. This paper aims to provide theoretical support for enhanced heat and mass transfer on the air side of finned tube heat exchangers in the closed-type heat source tower.

Clean heating and clean air: Evidence from the coal-to-gas program in China

Environmental degradation, especially air pollution, has been a prevalent problem in China in recent decades. Rather than focus on traditional regulatory policies aimed at enterprises engaged in production activities, this paper studies the effects of the clean heating policy targeting residents in China. Taking the coal-to-gas program as a quasi-natural experiment and using a city-level dataset of daily air quality, we study the effects of the clean heating policy implemented in Beijing and its surrounding areas on air quality with the difference-in-differences method. The results show that the clean heating policy significantly reduced air pollution in coal-to-gas cities, bringing improved economic welfare, with stronger effects in Beijing's neighboring cities. We find no evidence suggesting a decreasing policy effect over time. In addition, we find that increasing subsidies can further enhance the policy's effectiveness. We also test the spatial spillover effects of this policy and calculate its geographical boundary. Changing the energy structure in conjunction with regulating residential emissions is crucial to improving air quality.

Experimental and theoretical investigation on a novel solar-assisted absorption-resorption heat pump (ARHP) system towards clean heating

Among thermally-activated heat pumps, absorption-resorption heat pump (ARHP) is dominant by the ability of combining with low-temperature heat for efficient space heating. In this work, an ARHP experimental prototype is developed based on the previous thermodynamic cycle and tested to obtain the operation details such as coefficient of performance (COP), supply water temperature, heating capacity and so on. The experimental and the previous theoretical results are compared and mutually verified. The exact performance of the solar-assisted ARHP heating system is then investigated and compared with that of the conventional vapor compression heat pump (VCHP) in terms of primary energy ratio (PER) and primary energy saving ratio (PESR). The experimental results show that the COP increases greatly from 1.125 to 1.353 when the heat source temperature increases from 90 °C to 150 °C at the ambient temperature and return water temperature of 0 °C and 30 °C, respectively. Under given conditions, the measured heating capacity reaches a maximum value of 18.5 kW, 9.0 % lower than the rated value. The theoretical results reveal that solar fraction above 30 % can make PER of the solar-assisted ARHP heating system comprehensively greater than that of the reference VCHP system. Optimal solar contribution to space heating can be achieved based on the proposed ARHP if solar heat is dividedly utilized in its temperature zones of 10–35 °C, 35–83 °C and above 83 °C.

The uneven distribution of health benefits and economic costs from clean heating in rural Northern China

The uneven distribution of health benefits and economic costs from clean heating in rural Northern China

Evaluation of Urban Quality Improvement Based on the MABAC Method and VIKOR Method: A Case Study of Shandong Province, China

In the current stage of urbanization in China, urban construction has gradually shifted from incremental construction dominated by real estate to stock transformation based on improving urban quality. The evaluation of urban renewal projects is crucial for decision-making and resource allocation. However, there is no consensus on the evaluation indicators and methods. This study evaluates the current status of urban quality using the MABAC method based on numerical indicators. It evaluates the improvement of urban quality using the VIKOR method based on public satisfaction indicators. It is found that the comprehensive weights and subjective weights of the five first-level indicators in the evaluation index system of urban quality improvement in Shandong Province, namely blue–green space improvement, air cleanliness improvement, road traffic improvement, life service improvement, and governance capacity improvement, are quite different. The weight distribution of these indicators needs to be adjusted and optimized, especially for improving living services, as well as secondary indicators such as black and odorous water treatment, urban clean heating, the number of public vehicles per 10,000 people in the city, the 15 min living circle, the renovation of old residential areas, and the construction of urban intelligent management platforms. Based on the comprehensive evaluation results, an attempt is made to propose a more scientific evaluation index system, providing valuable references for urban renewal management.

Research on the optimization of the clean heating system for regional residential buildings based on the multi-objective optimization strategy

For the residential building district heating (RBDH) system, choosing the appropriate combination of heat sources according to local conditions is the key to improving economic efficiency. In this study, three climatic regions in China were selected, namely, a hot summer and cold winter region, cold region, and severe cold region. Among them, Nanjing, Tianjin, and Shenyang were selected as typical representative cities in the hot summer and cold winter region, cold region, and severe cold region, respectively. Taking the levelized cost of heat (LCOH) as the economic evaluation index and considering the carbon emission cost of the system operation, the energy consumption and the CO2 emissions were analyzed. TRNSYS software was used to simulate and analyze the system performance. The multi-objective optimization based on a genetic algorithm was proposed to optimize system parameters. From an economic point of view, the SA system was suitable for the hot summer and cold winter region, the SAS system was suitable for the cold region, and the SE system was suitable for the severe cold region. The operation control strategy based on quality adjustment can reduce heating energy consumption and maintain indoor temperatures at approximately 20°C. The proportion of clean energy heating in the optimized heating system decreased after the multi-objective optimization strategy. However, the initial investment and maintenance costs of the system were reduced, which reduced the LOCH of the system. Therefore, the multi-objective optimization strategy can effectively reduce the heating costs.

Differentiating Periodic Drivers of Air Quality Changes: A Two‐Step Decomposition Approach Integrating Machine Learning and Wavelet Analysis

AbstractAir quality time series exhibit significant periodic patterns, which are linked to a diverse array of emission sources and atmospheric processes. To discern and distinguish these periodic drivers, we have devised a two‐step decomposition approach that integrates a machine learning‐based model for weather normalization with Morlet wavelet analysis. This approach was applied to a 7‐year data set encompassing six regulated air pollutants across eight Chinese cities. Our analysis revealed distinct periodicities in weather‐normalized concentrations of primary air pollutants: a dominant annual cycle with periodicity around 365 days, which accounts for over 50% of the variance on average and is primarily driven by recurrent winter heating activities; daily cycles characterized by regular diurnal patterns attributable to combustion sources such as traffic; and periodicities exceeding 512 days that associated with long‐term regulatory policies targeting SO2. Particularly notable was the significant drop in the strength of the annual cycle in northern cities following the implementation of China's clean heating policies in 2017/2018, affirming the success of these initiatives. Additionally, diurnal dispersion and photochemistry, large‐scale atmospheric circulation, and synoptical weather patterns are likely responsible for the observed daily cycle (accounting for over 40% of the variance), annual periodicities, and intra‐monthly variations in the meteorologically driven concentrations, respectively. The varying power of these periodic drivers across time and locations implies the heterogeneity of emission rates and region‐specific climates. This work highlights the efficacy of this decomposition approach in air quality research, warranting attention for its potential value for enhancing our understanding of air pollution dynamics.

Comprehensive evaluation on performance and local impact in energy, environment, and economy of different rural clean heating modes: A case study in Northeastern China

To improve the atmospheric environment, the clean heating projects such as “coal-to-electricity” and “coal-to-gas” have been implemented in China, while leading to significantly increase in heating costs for rural residents and the supply pressure of fossil fuels in some rural areas. As the local renewable energy, biomass briquette can be used for rural heating. However, the local resource feasibility for the biomass heating has not been paid enough attention to, besides, the performance and potential local impacts of different heating modes has not been comprehensively estimated. Based on multiple attribute decision-making, this paper proposes an evaluation system by integrating the performance comparison and local impact in energy, environment, and economy, especially including an assessment on local biomass resource feasibility. The clean heating modes of biomass, electricity, and gas are evaluated along with the current coal heating mode in Harbin and Qiqihar as case studies. Results show that in the case regions, the biomass mode has sufficient resources and achieves significant comprehensive benefits, with the relative proximity nearly twice that of the coal mode. All the three clean heating modes can achieve environmental benefits. Due to the best economic feasibility, the biomass mode is suitable for the current rural economic level, with the cost intensity of 0.01 yuan/MJ, and the ratio of heating cost to disposable income less than 1%. The electric mode hardly produces comprehensive benefits because of the high cost. The gas mode is the least recommended due to significant energy demand and great economic burden.

Does energy poverty influence decarbonisation through electrification of the heating Sector?

Cleaner end-uses of energy, including electrified heating, represent a cornerstone of a decarbonised energy transition. On the other hand, many governments have adopted measures to mitigate energy poverty and facilitate access to modern energy services, including heating. Both objectives may be interrelated, since energy poor people are less likely to use cleaner (and costlier) heating fuels. This paper analyses the impact of energy poverty on the decision to use different heating sources and identifies whether the events of COVID and the Ukraine war have affected this decision. Thus, a multinomial probit model is estimated using information from a large database of Spanish households in 2019, 2021 and 2022. The results show that being energy poor increases the probability to use carbon-intensive energy sources for heating compared to electricity, and that COVID and the war in Ukraine have affected this relationship. The increase in energy poverty over those years has negatively affected the decarbonisation goal with respect to heating choices. The influence of those events on the probability to use electric heating depends on some household and dwelling features. Therefore, mitigating energy poverty increases the welfare of energy poor people while supporting the choice of cleaner heating.

Rural household energy transition in China: Trends and challenges

Against the backdrop of both environmental and health issues caused by inefficient combustion of solid fuels in households, the transition to clean energy is a critical development imperative. This study uses publicly available administrative data spanning nearly 30 years at the provincial level to characterize the “business as usual” (BAU) energy transition in China's rural household sector in order to inform interventions needed to achieve clean energy goals. We first describe the temporal trends and spatial characteristics of energy transitions over the past three decades. We then use a simple two-way fixed effects model to estimate the role that household income growth plays in this transition process. Finally, we predict the timeline for the BAU rural energy transition with an autoregressive integrated moving average (ARIMA) model. Our results show that China's rural household sector has gradually undergone a consistent but geographically uneven transition over the past three decades. Compared with warmer provinces without indoor heating, where a 1000 RMB increase in per capita income is associated with a 5–10% increase in the share of clean energy, in provinces with heating needs the predicted effect is less than 2%. ARIMA model projections suggest that without policy interventions, for most provinces in northern China the share of clean energy would remain less than 40% by the year 2050. The “clean heating program” implemented in the North China Plain in 2015 has therefore advanced the energy transition by 10 years in just the 3 years between 2015 and 2018. Together, these results show the potential for interventions in helping spur energy transitions.

Energy systems capacity planning under high renewable penetration considering concentrating solar power

With the rapid development of renewable generation and the promotion of “Clean Heating”, the uncertainty of renewables as well as rising energy demand has posed significant problems to the energy system’s economical and flexible operation. As a renewable energy generation technology, concentrating solar power (CSP) with thermal energy storage (TES) offers a promising approach by providing operational flexibility and thermal energy supply to the energy system. We propose a long-term high-resolution planning model considering the operational characteristics of CSP and improved flexibility constraints of energy systems under high renewable penetration to meet the electricity and heat demand simultaneously in this paper. By applying the proposed model to a typical “Clean Heating” area in China, it demonstrates that the optimal deployment by integrating CSP can reduce the peak-valley depth of coal units, minimize the renewable curtailment and carbon emissions by 37.64 % and 19.05 % respectively with more than 5.98 % cost reduction at 85 % renewable penetration compared with the base scenario, which provides an economic and stable zero-carbon pathway for multi-energy systems.

Heterogeneous variations in wintertime PM2.5 sources, compositions and exposure risks at urban/suburban rural/remote rural areas in the post COVID-19/Clean-Heating period

Inevitably, both unblocking of the COVID-19 (UNCOV) and uncertainty in the clean heating policy (2017–2021) in winter 2022 imposed complex impacts on PM2.5 variations. Together, the urban-rural and rural-rural disparities in these impacts remain unclear. To address this gap, we conducted a synchronous observation at urban (UA)/suburban rural (SRA)/remote rural (RRA) areas to probe PM2.5 evolutions in the post COVID-19/clean-heating (PCOV/PCH) period for further site-specific policy implications. Similar meteorological conditions among sites benefited examining the effects of emission variations. On average, PM2.5 presented a decline order as RRA > UA > SRA. Invoking the positive matrix factorization (PMF) results, specially, the primary emissions (PE) rebounded again after experiencing a continuous decline since the stringent emission-control polices initiated in 2013. PE contributions were up to 80.2 %–83.0 % for three points. SRA benefited most from coal-to-gas and coal combustion (CC) has become its minimum contributor (10.8 %). Concurrently, subsidy reduction and natural-gas (NG) shortage compelled biomass burning (BB) to be the largest origin (21.9 %) marked by the highest K+, Cl− and OC/EC. Regarding RRA, CC (26.5 %) and BB (19.6 %) have been the first and second largest origins despite that the coal-to-electricity policy, indicating the slowdown of policy enforcement. The highest SO42−, As, Sb, Tl, OC, EC and the lowest NO3−/SO42− further verified the dominant CC. Production recovery made industrial emissions (IE) become the largest source (26.8 %) at UA. The metal associated health risks peaked at RRA due to large impacts of CC, though the most of metals related to small-scale industries peaked at UA. This is the first work to highlight that more targeted site-specific strategies in prevention/control of dominant primary sources should be formulated in the PCOV/CH period.

Analysis of coupling characteristics of clean heating systems based on complementary solar, geothermal, and wind energy

In order to overcome the limitations of traditional clean energy utilization methods, this paper proposed an innovative technical solution for a combined heating system that cleverly integrated solar, wind, and geothermal energy to achieve complementarity and synergized among them, thereby ensuring stable and efficient energy utilization. First, a comprehensive mathematical model was developed for the entire heating system, encompassing solar thermal subsystem, geothermal subsystem, wind power generation subsystem, and a second-stage reheating subsystem. Subsequently, Ebsilon simulation software was utilized to cleverly couple these subsystems together, with corresponding boundary conditions set to ensure the overall efficiency and stability of the system. Based on meteorological data and geothermal resource parameters from a typical heating season in Zhengzhou, Henan Province, China, this paper thoroughly analyzed the variations in key performance indicators such as the photothermal conversion efficiency of solar thermal subsystem and the heating capacity of geothermal subsystem. This provided valuable insight for optimizing the design of heating system. The results indicated that during the daylight hours of the heating season, both the photothermal conversion efficiency and the heat supply from the solar thermal subsystem exhibited an increasing trend as solar radiation increased. Among them, the photothermal conversion efficiency peaked at 76.013%, while the maximum heat supply output reached 40.311 kW. When solar direct radiation was relatively weak, the system primarily relied on the heat release process of the thermal storage tank to maintain heating, with a minimum heat supply of 27.268 kW. During nighttime hours of the heating season, the geothermal subsystem dominated the heating process, with a maximum heat supply of 125.556 kW. Additionally, for every 5 °C increased in geothermal water temperature, the heat supply from the geothermal subsystem increased by an average of 6.553 kW, demonstrating excellent heating response performance. Therefore, the integrated clean heating system that combines solar, geothermal, and wind energy not only significantly improves the utilization efficiency of clean energy but also enhances the heating stability of the integrated clean energy coupling system to a certain extent. The clean heating technical solution proposed in the paper had a theoretical total heating capacity of 19 680 kW during the heating season. When converted, this equates to a substitution of 6.9 tons of standard coal, resulting in a reduction of carbon dioxide emissions by 17.94 tons. This demonstrates the considerable cleanliness and environmental benefits of the proposed heating system. This study provides a valuable reference for the engineering application of renewable energy in the field of clean heating.