3. Present Situation of Urban Heating in China

According to the data in the China Urban–Rural Construction Statistical Yearbook, the centralized heating area in China had grown rapidly in the last decade from 2011 to 2020, with an average annual growth rate of 8.7%, and the urban centralized heating area in northern China was about 12.21 billion m² in 2020, of which the centralized heating area in cities accounted for 80.9% and that in small towns accounted for 19.1%. Recent years have seen the rapid development of centralized heating in small towns in China with the advancement of new urbanization, and the situations in small towns should be taken into full account during the study of centralized heating (Fig. 3.2).

A stacked column chart plots percentage values versus 15 Chinese provinces. The stacks indicate values for cities, counties, and towns in fluctuating trends, with the highest share of cities in stacks for all provinces.

The centralized heating area given in the China Urban–Rural Construction Statistical Yearbook only counted the heating area covered by the for-profit centralized heating systems. However, in addition to this part, there are lots of buildings supplied with heat by not-for-profit centralized heating systems. For example, higher education institutions, troops, office compounds, and some large enterprises have their own independent heating management teams to operate their centralized heating systems, but the building floor area for which this centralized heating systems supply heat is not counted by relevant departments for a variety of reasons. Table 3.2 lists the centralized heating areas given in the China Urban–Rural Construction Statistical Yearbook (the Yearbook) for some typical cities and the current values of the centralized heating areas given in the local special plan on heating to make a comparison. Taking Beijing for example, the centralized heating area given in the Yearbook (2020 edition) is 659.35 million m², but the current value of the centralized heating area by the end of 2020 given in Beijing’s 14th Five-Year Plan on Heating Development is about 895.21 million m² (approximately 1.36 times the former). That is to say, about 236 million m² of area are not counted, which are mainly composed of those not-for-profit centralized heating systems.

According to the estimate by Building Energy Research Center (BERC), Tsinghua University, the NUH area had reached 15.63 billion m² by the end of 2020. The not-for-profit centralized heating area was considered on the basis of the centralized heating area given in the China Urban–Rural Construction Statistical Yearbook. After correction, the centralized heating area in northern urban areas in 2020 was about 13.78 billion m² and the centralized heating rate was 88.2%.

In 2020, China District Heating Association (CDHA) counted various data from 90 heating enterprises across the country. In combination with the area of heating by non-coal-fired and non-gas-fired heat sources in 2020 as counted below, the relative relationship between coal and gas proportions in the participating enterprises is utilized to calculate the total heating area of coal-fired and gas-fired heat sources in northern China, and the checked heat source structure for NUH in 2020 is shown in the right diagram in Fig. 3.3 compared to the 2016 heat source structure (left diagram in Fig. 3.3), the proportion of coal-fired CHP rises by 6%, the proportion of coal-fired boiler rooms drops by 13%, and the proportion of gas-fired heating does not change much. However, the proportion of heating by ground-source heat pumps, biomass, and other renewable energy shows an increase of about 6%. Considering the development of heating by the residual heat from nuclear power in recent years and the heating potential of industrial residual heat and renewable energy in northern China, the proportion of heating by traditional fossil energy will further decrease in the future.

Two pie charts comprise the following information. 1. Coal-fired C H P, 45.5%. Gas-fired C H P, 2.6%. Coal boiler, 31.9%. Gas boiler, 11.2%. Domestic gas boiler, 3.5%. Others, 5.3%. 2. Coal-fired C H P, 55.6%. Gas-fired C H P, 5.9%. Coal boiler, 18.5%. Gas boiler, 17.9%. Industrial waste heat 1%. Oil and electric boiler, 0.1%. Heat pump and others 1.1%.

In the NUH region in China, there is still a considerable proportion of old residential buildings with poor indoor comfort, high energy consumption, and prominent heating contradictions. In 2007, China officially launched the heating measurement and energy-saving retrofit of existing residential buildings in the NUH region. During the 13th Five-Year Plan period, the energy-saving standard for new urban residential buildings in severe cold and cold areas in China reached 75%, approximately 10 million m² of buildings with ultra-low and near-zero energy consumption were constructed, and 514 million m² of existing residential buildings and 185 million m² of public and commercial (P&C) buildings completed the energy-saving retrofit. By the end of 2020, the newly built building stock of China’s urban green buildings made up 77% of the total newly built building stock of that year, and the cumulative built floor area of green buildings exceeded 6.6 billion m². The cumulative built floor area of energy-efficient buildings exceeded 23.8 billion m², accounting for more than 63% of the total floor area of urban civil buildings. The new prefabricated buildings commenced across the country accounted for 20.5% of the total newly built building stock of that year.

Figure 3.4 reflects the completion of the energy-saving retrofit of existing buildings during the 13th Five-Year Plan period in the NUH region.

A column chart plots the area of energy-saving retrofit of existing residential buildings versus years. The estimated data are as follows. (2016, 9000), (2017, 3800), (2018, 3200), (2019, 6200), and (2020, 11900).

By the end of 2020, the NUH region had completed the energy-saving retrofit of 339 million m² of existing residential buildings in total during the 13th Five-Year Plan period. Figure 3.5 illustrates the completion of the energy-saving retrofit of existing buildings during the 13th Five-Year Plan period in northern provinces, autonomous regions, and municipalities.

A column chart of the area of energy-saving retrofit of existing residential buildings versus 12 northern provinces plots the following estimated data. (Shandong, 8100), (Shanxi, 4200), (Heilongjiang, 3200), (Jilin, 2400), (Shannxi, 2000), (Hebei, 1800), (Inner Mongolia, 1700), (Gansu, 1300), (Tianjin, 1000), and more.

As shown in Fig. 3.6, the proportions of urban building floor areas classified by the energy efficiency grade in the NUH region in China in the present situation can be estimated based on the data from the survey of the heating situations of heating companies in provinces conducted by CDHA and BERC, Tsinghua University and in combination with the public information released by the Ministry of Housing and Urban–Rural Development.

A pie chart comprises the following information. First step or below, 19.3%. Second step, 20.5%. Third step, 55.2%. Fourth step, 4.9%.

Since 2017, Tsinghua University and CDHA have jointly performed statistical work on the operation of the heating industry, and the total network coverage area of statistical samples is 3.37 billion m², taking up about 27.6% of the total centralized heating area given in China Urban–Rural Construction Statistical Yearbook; after the deduction of the suspended area, the actual heating area is 2.68 billion m².

Figure 3.7 indicates the heat consumption per unit area of the participating enterprises in the 2019–2020 heating season, and the ordinate represents the cumulative frequency distribution of statistical data. According to the statistical results, the heat consumption per unit area of the participating heating enterprises on the heat source side is distributed in the 0.10–0.80 GJ/m² range, the median is 0.376 GJ/m², and 80% of the survey results are in the 0.27–0.50 GJ/m² range. The survey results of northern provinces are gathered in Table 3.3 Heating area after deduction of suspended area, average heat consumption, and average heating degree days of buildings surveyed in northern provinces, in which, the average heat consumption and the average heating degree days (HDDs) are obtained based on the weighted heating areas of relevant cities. It can be seen that the average heat consumption per unit area of all northern cities surveyed is about 0.377 GJ/m², and the corresponding number of heating degree days is 2,879.

A line graph of cumulative frequency distribution versus heat consumption per unit area plots a curve in increasing trend at the following estimated values. (0.10, 0%), (0.30, 17%), (0.50, 90%), and (0.70, 97%).

Since the release of the Clean Winter Heating Plan in Northern China by ten ministries and commissions in 2017, the relevant places have accelerated the adjustment of the energy structure and actively promoted the centralized heating system for energy saving and consumption reduction. Figure 3.8 and the data measured at the heat source outlets are taken. In the 2019–2020 heating season, heating time was extended generally in the northern provinces, autonomous regions, and municipalities due to the COVID-19 pandemic, therefore the overall heat consumption levels of some provinces went up a little. However, compared with the 2017–2018 heating season, the energy consumption for heating in Beijing, Shanxi, Inner Mongolia, Shandong, Henan, and Gansu decreased somewhat, reflecting a huge success achieved through energy-saving and consumption reduction measures in recent years.

A grouped column chart plots the heat consumption by buildings and additional heating days versus 11 provinces. The columns indicate values for 2017 to 2018 heating period and, 2019 to 2020 heating period in different trends. The plots for 2019 to 2020 additional heating days indicate fluctuating trends with a maximum value of 23 for Hebei.

Moreover, the energy efficiency grade of buildings also has a significant impact on the heat consumption for system heating. Let’s take Tianjin for example. Figure 3.9 illustrates the heat consumption per unit area at heating stations of residential buildings under different energy-saving standards in Tianjin in the 2019–2020 heating season. It can be seen that the average heat consumption per unit area decreases steadily with the increase of the energy efficiency grade of buildings.

An area chart plots heat consumption per unit area at heating stations versus energy saving standards. The graph has 4 sections on the x-axis labeled not reformed, and first, second, and third steps, all indicating decreasing trends for heat consumption. A horizontal line each indicates an average value for all sections.

Also, it can be observed that the actual heat consumption varies greatly with heating stations under the same climatic conditions and the same energy efficiency grade of buildings. At present, there is still massive overheating in the heating system, and greater potential for energy saving may be realized through enhanced regulation.

In conclusion, in the 2019–2020 heating season, the overall heat consumption level in the NUH region in China was about 0.377 GJ/m²; in the meantime, overheating and uneven temperatures between buildings still exist in the heating system. For one thing, the energy-saving retrofit of existing old buildings should be promoted continuously, and the energy-saving standard should be followed strictly in new buildings; for another, the regulation of the heating system should be enhanced to put an end to overheating and reduce heat loss. These two aspects should be combined to achieve the objectives of energy saving and consumption reduction.

It should be noted that the heat consumption of a centralized heating system is not only related to the thermal insulation performance of the building but also subject to significant influence by the occupancy level of the building. Due to the heat transfer between two adjoining rooms, the suspension of heating will lead to a substantial increase in the energy consumption for heating of adjacent rooms. For the time being, the suspension of heating by consumers in northern China is prevalent.

As revealed by Fig. 3.10, the requests for suspension of heating were mainly made in the central cold area. Because of the great difference in the heat demands of consumers in this area, some consumers demanded the suspension of heating. The suspension of heating for consumers of the centralized heating system would lead to an increase in the actual heat consumption of buildings. As illustrated in Fig. 3.11, the heat consumption increases by about 0.1 GJ/m² for each 10% decrease in occupancy.

A stacked column chart plots the percentage versus 14 provinces. The stacks indicate values for suspension area and actual heating area in decreasing and increasing trends, respectively, with the highest share of actual heating areas in all provinces.

Two dot plots titled Residential districts with and without heat measurements plot heat consumption versus residential occupancy rate. The plots indicate decreasing trends along regression lines, with a sharp decline in the second graph. The plots are concentrated between 22% to 95% and 62% to 100% in the 2 graphs.

Hence, the heat transfer between adjacent rooms caused by low occupancy will lead to an obvious increase in the energy consumption of the system and have serious consequences on the fairness in heating between consumers. Currently, some cities do not charge consumers that suspend heating, but the suspension of heating causes other consumers to bear more heat fees, which is in severe breach of the principle of fairness in meter-based tariffs. For this reason, charging the consumers that suspend heating certain “suspension fees” not only reflects the fair settlement for all consumers in a building but also serves as an incentive means to promote energy saving in the heating system (Table 3.4).

In 2020, Wen Zheng, Yichi Zhang, et al. from Tsinghua University calculated the current heating loads in 1,047 northern districts and county units by taking prefecture-level cities, districts, and counties as the units (Zheng W et al. 2020). Multiple factors including population development, urbanization rate, building floor area index, and energy-saving retrofit progress were taken into full account, and such data as permanent resident population, per capita floor area, and the heat consumption index for buildings were calculated reasonably to evaluate the current heating load levels in northern China. The calculation process is shown in Figs. 3.12, 3.13 and Tables 3.5, 3.6.

A schematic diagram reads as follows. Urban building heat load curve branched into heat consumption of urban buildings and ambient temperature during heating season. The former further branches into urban architecture areas and comprehensive indexes of urban buildings heat consumption, each with further subdivisions.

A graph of space heat consumption plots kilowatt hour per meter square occupied living area versus countries. The columns plot values for the year 2015, and the dot plots plot values for the year 2000, in increasing trends. The maximum values are plotted for Belgium at 170 and 240 kilowatt hours per meter square in 2015 and 2000, respectively.

The heat demand under the future “dual carbon” goals may be estimated based on the current heating load level through the comprehensive consideration of the energy-saving retrofit of existing buildings in China. There are three different energy-saving retrofit modes, i.e. fast, medium-speed, and slow retrofit modes, for buildings. In the slow retrofit mode, 30% of urban buildings will remain non-energy-efficient in 2035, and 25% will remain non-energy-efficient in 2050; in the medium-speed retrofit mode, 15% of urban buildings will remain non-energy-efficient in 2035, and all of the current non-energy-efficient buildings will complete retrofits in 2050; in the fast retrofit mode, all of the current non-energy-efficient buildings will complete retrofits by 2035. The following Tables 3.7 and 3.8 show the heat consumption and heating demands of northern buildings in 2035 and 2050 under three different retrofit modes.

In terms of the energy consumption per unit area of heating, the heat consumption per unit area of building heating in 2050 is expected to reach 0.21 GJ/m² in the fast retrofit mode, and the corresponding peak heating load is expected to be 28.13 W/m². Considering the total 15% loss of the primary and secondary networks and overheating, the heat consumption per unit area on the heat source side and the peak load will be 0.25 GJ/m² and 33.09 W/m² respectively, and energy can be saved by 34.5% compared with the current level.

With reference to the situation in foreign countries from 2000 to 2015, the average heat consumption per unit area for heating in 28 EU countries is expected to drop to 0.305 GJ/m² by 2050, which is still higher than the foregoing expected value of energy consumption (0.25 GJ/m²). Thus, it can be inferred that this value (0.25 GJ/m²) is very close to the ultimate level of energy saving and consumption reduction that the current system can achieve.

According to the China Urban–Rural Construction Statistical Yearbook, the centralized heating pipelines in China totaled around 507,300 km in length by 2020, and all of them are hot water pipelines. Figure 3.14 illustrates the changes in the lengths of centralized heating pipelines in China over the years. Figure 3.15 shows the lengths of centralized heating pipelines in various regions of China in 2020. The length of primary pipe networks was 140,900 km and that of secondary pipe networks was 366,400 km, with a proportion of 28 and 72% respectively.

A stacked column chart plots the length of pipelines versus years. The stacks indicate values for steam and water in fluctuating decreasing, and increasing trends, with a higher share for water in all years.

A stacked column chart plots the length of pipelines versus provinces. The stacks indicate values for primary and secondary networks in different trends, with a higher share for secondary network in most provinces.

The aging of pipe networks is shown in Fig. 3.16. The proportion of old primary pipe networks with a service life of more than 15 years is 19.4%, while that of old secondary pipe networks is 32.2%.

A horizontal bar graph plots the pipe network conditions versus length of pipelines. The data are as follows. Primary network, (more than 30 years, 0.03), (15 to 30 years, 0.57), (less than 15 years, 2.50). Secondary network, (more than 15 years, 2.93), (less than 15 years, 6.17).

The renovation of old pipe networks in the primary and secondary pipe networks counted by the included enterprises from different provinces is shown in Figs. 3.17 and 3.18 respectively. The average proportion of the length of annually renovated pipe networks in the total length of the primary pipe networks is about 2%, indicating a slow renovation speed.

A stacked column chart plots the percentage value versus provinces. The stacks indicate values for the primary proportion of the old pipe network, excluding reconstruction and the proportion of annual reconstruction length to the primary pipe network. The share for the former is higher in most provinces.

A stacked column chart plots the percentage value versus provinces. The stacks indicate values for the secondary proportion of the old pipe network, excluding reconstruction and the proportion of annual reconstruction length to the secondary pipe network. The share for the former is higher in all provinces.

Indirect connection is adopted for most of the centralized heating systems in China. The water supply parameters on the primary side depend on the demands for heat transfer in pipe networks. With the promotion of low-temperature heating technology, more and more heating systems are developing towards low heating parameters. According to statistics, the average return water temperature in the primary network in the heating season was 44.3 and 46.8 °C respectively for severe cold and cold areas in 2020, representing a substantial decrease compared with the statistical data in 2016.

Table 3.9 lists the supply and return water temperatures in primary and secondary networks of centralized heating systems for typical cities and ranks the same based on the latitudes of the cities. In most cities, the average temperature of supply water in the primary network in the heating season is 80–90 °C, and the temperature of return water is 40–50 °C. The average temperature of supply water in the secondary network in the heating season is about 45 °C, and the temperature of return water is mostly 30–40 °C. The temperature level trends downward compared to the temperatures in previous designs (120/70 and 90 °C/50 °C). The temperature of return water is lower in places with higher latitudes.

In Datong and Taiyuan in Shanxi and Chifeng in Inner Mongolia etc., absorption heat exchange equipment were installed at some terminal heating stations to averagely reduce the return water temperature in the primary network in the heating season to 24 °C, and the overall return water temperature reaches 35–38 °C, thus the temperature difference between the supply and return water in the primary network can be increased effectively to improve the transmission capacity of pipelines and facilitate the recovery of residual heat from exhaust steam from power plants.

Because the collected data about the electricity consumption in primary networks are few and varied, Fig. 3.19 only presents the data on electricity consumption in secondary networks of enterprises counted by CDHA. Given the influence of climatic conditions and the heating duration, the data of enterprises in cold areas and severely cold areas are separated for comparison. From Fig. 3.19, it can be seen that the electricity consumption per square meter in the secondary network in the heating season varies greatly from place to place. The average value of enterprises in cold areas is 1.28 kWh/m². The average value of electricity consumption per square meter in the heating season in severe cold areas is 1.44 kWh/m², slightly higher than that in cold areas. Compared with 2018, electricity consumption has a significant decrease of about 25%.

A line graph of the percentage of accumulating enterprises versus electricity consumption per square meter in the secondary networks in the heating season counted by C D H A plots 2 curves for cold and extreme cold areas in increasing trends. The average and maximum values of the 2 curves are 1.28 and 2.77, and 1.44 and 3.40 kilowatt hour per meter square, respectively.

However, the difference in electricity consumption from transmission and distribution is significant between heating enterprises. The reasons for the difference are generally as follows: 1. Unreasonable pressure loss at heating stations; 2. Unreasonable selection of water pump models for heating stations and low pump efficiency. 3. Heavy operation flow rate in the secondary network. If the electricity consumption in transmission and distribution in the secondary pipe network in northern China can reach about 1 kWh/m² through the future energy-saving retrofit, about 7.8 TWh of electricity may be saved annually, indicating a marked energy-saving effect.

Figures 3.20 and 3.21 illustrates the water loss per unit area in primary and secondary networks of enterprises counted as above respectively (unit: kg/(m²·month)). Due to the different levels of pipeline installation and maintenance, as well as operation management, water consumption varies greatly from enterprise to enterprise. Because of the different scales of heating and pipe networks, the district boiler rooms, and CHP heat sources are counted separately in the statistics of water make-up volume in the primary network.

A line graph of the percentage of enterprises versus water loss per unit area plots 2 curves for C H P and district boiler heating in increasing trends. The average and maximum values of the 2 curves are 4.65 and 28.66, and 2.78 and 21.39 kilogram per m square dot month, respectively.

A line graph of the percentage of accumulating enterprises versus water make-up volume per unit area plots a curve for water make-up volume in district heating hubs in an increasing trend. The average and maximum value of the curves is 8.30 and 46 kilogram per m square dot month.

It can be seen from the statistical results that the average values of water make-up volume per unit area in the primary networks of district boiler rooms and CHP are 2.78 kg/(m²·month) and 4.65 kg/(m²·month) respectively. The average value of water make-up volume per unit area of heating stations is 8.3 kg/(m²·month). Hence, the water consumption per unit area of the secondary network is almost twice that of the primary network. The difference in water consumption is considerable between enterprises. This not only leads to a serious waste of water resources and heat but also brings in hard water and dissolved oxygen during frequent water replenishment, exacerbating the fouling and rust corrosion of pipelines and heat-exchange equipment and jeopardizing the quality of heating. Therefore, renovating old pipe networks and solving the water loss problem should be the priorities in the modernization management of the heating industry).

According to the statistical data in the China Electric Power Yearbook, China’s installed capacity for heating (namely the installed capacity of CHP) maintained a growth rate of 40 million kW/year, and the installed capacity for non-heating purposes only increased by <20 million kW during the 13th Five-Year Plan period. As of 3.22020, China’s CHP unit capacity was 560 million kW, accounting for 45% of the total installed capacity of thermal power in the country (the scope of statistics covered units with a capacity of more than 6,000 kW, including some thermal power units mainly serving the heating for industrial production) (Fig. 3.22).

A Pareto chart plots the installed capacity and percentage versus years. The stacked column indicates values for plants larger than 6 megawatts without and with heating in increasing trends. The curve for the rate of plants with heating also indicates an increasing trend.

The installed capacity of thermal power in all provinces of China in 2020 is shown in Fig. 3.23. The proportion of installed capacity for heating in the southern regions was <30%. The proportion of installed capacity for heating in the northern regions was generally above 50%. Thus it can be seen that the development of CHP varied greatly among provinces and the heating capacity should be further explored.

A graph plot installed capacity and percentage versus provinces. The stacked columns indicate values for plants larger than 6 megawatts without and with heating in different trends. The plots for the rate of plants with heating indicates an increasing trend.

The flexibility retrofit of thermal power is the key to the achieve a high proportion of renewable energy in the power system. For the CHP units, in addition to the conventional technologies on the boiler side, the heat-power decoupling technologies may be adopted on the steam turbine side to achieve deep peak shaving. Such technologies include cutting off the heat supply to the low-pressure cylinder, using most of the exhaust steam from the medium-pressure cylinder to supply heat, installing a regenerative electric boiler on the heat source side, installing a heat storage tank as a supplement to the extraction steam for heating when the power grid is under low load, and absorption heat pumps.

In June and July 2016, the National Energy Administration (NEA) successively issued notices about two batches of pilot projects for thermal power flexibility retrofit, and a total of 22 projects, including the Dandong Power Plant and the Changchun Thermal Power Plant, became the first and second batches of pilot projects for thermal power flexibility retrofit. Among them, 15 projects were located in Liaoning, Jilin, and Heilongjiang, with a cumulative installed capacity of 11.97 million kW. By the end of 2019, nearly 50 power grids in northeast China completed the flexibility retrofits, and the peak shaving capacity increased by more than 8.5 million kW; among them, 14 power grids used regenerative electric boilers.

Looking nationally, by the end of 2021, approximately 900 million kW of China’s coal-fired generating units completed energy-saving and carbon-reduction retrofits, over 100 million kW completed flexibility retrofits, 1.03 billion KW completed ultra-low-emission retrofits, and the average coal consumption for power supply of thermal power plants dropped to 302.58 gce/kWh.

On November 25, 2022, NEA released the Basic Rules for the Electricity Spot Markets (Draft for Comments) and the Measures for the Supervision of the Electricity Spot Markets (Draft for Comments). With the further development of the ancillary service market for peak shaving and the perfection of the electricity spot markets, the enthusiasm for flexibility retrofits and deep peak-shaving of power plants will see further increase, which will be more favorable to the further exploitation of the residual heat from thermal power plants and promote the development of the power system with a high proportion of renewable energy.

Survey on two large domestic manufacturers of heat exchangers for heating with residual heat shows that they had completed and operated 86 industrial residual heat recovery projects since 2013, including an increase of about 44 million m² during the 13th Five-Year Plan period. The geographical distribution of the counted projects and the newly built projects over the years are illustrated in Figs. 3.24 and 3.25 respectively.

A graph plots heating capacity and number of projects versus provinces. The columns indicate heating capacity, and the plots indicate the number of projects at the following estimated maximum and minimum values. Heating capacity (Tangshan, 720) and (Linfen, 0). Number of projects (Tangshen, 650) and (Linfen, 1.8).

A Pareto chart plots the number of projects and heating capacity versus years. The stacks plot values for foundry, steel, and others, with the highest share of steel in all years. The curve for copper smelting indicates an increasing trend, with the highlighted maximum value of 2119.2 megawatts in 2021.

In the counted projects, the completed industrial residual heat projects involved 53 industrial enterprises, and 97% of the projects were located in northern China; the average heating capacity of a single project was about 25 MW. More than 90% of the projects were supplied with heat by steelworks, 88% of them were supplied with residual heat from slag washing water, and most of them had low-pressure steam as the supplementary heat source. Only <10 projects used residual flue gas heat, residual heat from ring cooling, and other low-grade residual heat for heating.

The floor area of heating with the industrial residual heat of the two manufacturers accounted for about half of the total in northern China. Thus, it could be calculated that the floor area of heating with industrial residual heat in China had been nearly 200 million m² by 2021, which is close to the 100 million m² of new areas as planned by the ten ministries and commissions in 2017. Compared with the increase in the floor area of heating with such heat sources as heat pumps and biomass, heating with industrial residual heat still needs vigorous promotion and strong support from policy measures related to environmental control, investment, and construction.

According to the 2021 Report on Natural Gas Development in China published by NEA, in 2020, China’s natural gas production was 192.5 billion m³ and its natural gas consumption was 328 billion m³, including 37–38% of urban gas consumption. The natural gas consumption for urban centralized heating was 15.59 billion cubic meters.

During the 13th Five-Year Plan period, there was an accumulated increase of 19 million consumers “switching from coal to gas”, and the floor area of heating with natural gas reached 3.06 billion m², increasing by 1.1 billion m² compared to that of 2016 and accounting for 31% of the total increased floor area of clean heating. Centralized heating with gas-fired boilers, heating with wall-hung gas boilers, CHP, and other types of gas-fired decentralized heating accounted for 47, 44, 8, and 1% of the total floor area of natural gas heating respectively.

In terms of the natural gas consumption for heating, the natural gas consumption in northern China in 2022 was 167.33 billion m³, approximately 50% of China’s total natural gas consumption, based on the relevant data disclosed by government departments and the unofficial statistics given by relevant research institutions. If only the natural gas consumption of gas-fired boiler rooms and wall-hung gas boilers was counted, the total gas consumption for centralized heating in northern China was about 30.2 billion m³, making up over 18% of the total gas consumption in northern China. The natural gas consumption for heating in northern regions is listed in Table 3.10.

From the perspective of the type of natural gas heat source, the percentage of gas-fired thermal power plants used for heating in China is not high, and natural gas-fired boiler rooms are most commonly used for heating. The Beijing–Tianjin–Hebei region is the main region adopting natural gas for heating, and there are very few centralized heating systems using natural gas as energy in northeast China. In northwest China, natural gas is widely used for heating in Xinjiang, Gansu, and Shaanxi. Given China’s “more coal and less gas” energy endowment, natural gas is more suitable for peak shaving in centralized heating. In Beijing, policies have been put in place to ban new natural gas heating projects.

Figure 3.26 is the structural diagram of the direct utilization of geothermal energy in China. From this diagram, we can see that shallow geothermal energy for heating and cooling and medium and deep geothermal energy for heating are predominant and that ultra-deep geothermal energy is rarely used.

A pie chart comprises the following information. Shallow geothermal heating and cooling, 56%. Medium and deep geothermal heating and power generation, 22%. Hot spring bath, 14%. Industrial and agricultural energy supply, 5%. Others, 3%.

By the end of 2020, China had used geothermal energy for heating and cooling for about 1.39 billion m² of area, including shallow geothermal energy for heating and cooling for 0.81 billion m², and medium and deep geothermal energy for heating for 0.58 billion m². It is visible that geothermal energy has been used for heating in China on a large scale and with rapid growth. In terms of cost and efficiency, the construction cost per unit area of heating in medium and deep geothermal energy heating projects is 90–160 RMB yuan/m² and the operation cost is 5–10 RMB yuan/m².

With the advancement of urbanization and the increase in population, China’s wastewater treatment volume and rate have been rising significantly. In 2020, the total wastewater treatment volume of cities above the county level in China reached 65.59 billion m³, and the total wastewater treatment rate was 97.2% (Fig. 3.27).

A Pareto chart plots sewage discharge and sewage treatment rate versus years. The stacks indicate values for annual sewage treatment capacity in increasing trends and annual untreated sewage capacity in decreasing trends. The curve for the total sewage treatment rate indicates an increasing trend.

Additionally, relevant statistics indicate that some cities have applied the heat energy of the wastewater source to urban centralized heating. By the end of 2021, the area of heating with reclaimed water-source (wastewater source) heat pumps in Beijing had reached 1.29 million m², and the area of heating with wastewater source heat pumps in Xi’an had reached 2.72 million m². In 2018, Harbin used wastewater at around 14 °C as a heat source and replaced coal-fired boilers with wastewater source heat pumps to supply heat to over 6,600 residential households for an area of 660,000 m², producing good operation results.

Municipal domestic waste and its treatment are not negligible in urban development. As urbanization continues and the population increases, China has seen an obvious increase in the volume and rate of harmless treatment to municipal waste. In 2020, China’s total volume of municipal waste subject to harmless treatment reached 301 million tons, increasing by 19% compared to that in 2016, and its harmless treatment capacity reached 1.32 million tons per day. The percentage of incineration rose from 31% in 2016 to 54%. According to statistics, 504 waste-to-energy incineration projects had been put into operation in China by the end of 2019. From the changes in the installed capacity of waste-to-energy incineration over the years in China, as demonstrated in Fig. 3.28, we can know that the installed capacity of waste-to-energy incineration maintains to grow every year (Fig. 3.29).

A pie chart comprises the following information. Sanitary landfill, 42%. Waste incineration, 54%. Others, 4%.

A grouped column chart plots the installed capacity versus years. The column plot values for total installed capacity and yearly installed capacity in increasing trends at the following values. 2015, 468 and 44. 2016, 549 and 82. 2017, 725 and 176. 2018, 916 and 191. 2019, 1202 and 286, respectively.

According to industrial statistics, the annual output of main biomass resources in China is about 3.494 billion tons, and its exploitable potential for energy utilization is 460 million tons of standard coal. As of 2020, China had about 829 million tons of theoretical resources of straws, about 694 million tons of collectible resources, and 88.215 million tons of straws utilized as a fuel; China’s total excrement of livestock reached 1.868 billion tons (excluding wastewater from cleaning), and total excrement utilized to produce marsh gas reached 211 million tons; The total available forest residues in China was 350 million tons, and 9.604 million tons of them were utilized as a source of energy; The cleared and transported domestic waste amounted to 310 million tons, including 143 million tons of waste incinerated; The annual output of waste oils and fats was about 10.551 million tons, and about 527,600 tons of them were utilized as a source of energy; The dry weight of the annual output of wastewater sludge was 14.47 million tons, and about 1.147 million tons of them were utilized as a source of energy.

China’s straw resources are mainly distributed in northeast China, Henan, Sichuan, and other granary provinces, and the top five in total straw resources are Heilongjiang, Henan, Jilin, Sichuan, and Hunan, making up 59.9% of the national total; Livestock excrement is concentrated in the key breeding areas, and the top five are Shandong, Henan, Sichuan, Hebei, and Jiangsu, accounting for 37.7% of the national total; Forest residues are concentrated in southern mountain areas, and the top five are Guangxi, Yunnan, Fujian, Guangdong, and Hunan, making up 39.9% of the national total; Domestic waste is concentrated in central and eastern densely-populated areas, and the top five are Guangdong, Shandong, Jiangsu, Zhejiang, and Henan, taking up 36.5% of the national total; Wastewater sludge is concentrated in regions with a higher level of urbanization, and the top five are Beijing, Guangdong, Zhejiang, Jiangsu and Shandong, accounting for 44.3% of the national total.

As of 2021, China’s installed capacity of power generation with biomass energy (including agricultural and forestry biomass, domestic waste incineration, and biogas) reached 37.98 million kW, the generating capacity reached 163.7 TWh, the annual output of briquettes fuels was 22 million tons, the annual output of fuel ethanol was 2.9 million tons, and the area of clean heating with biomass was about 310 million m², increasing by around 10 million m² compared to that in 2020.

Electric heating technologies fall into two categories, i.e. direct electric heating and heat pump. In 2020, China’s total installed capacity of power generation with non-fossil energy reached 980 million kW, making up 44.7% of the total installed capacity; The generating capacity of non-fossil energy reached 260 million kWH, accounting for more than 1/3 of the total electricity consumption of the whole society. As the proportion of clean electricity increased, the heating area of such electric heating methods as electric heat storage boilers, air-source heat pumps, water-source heat pumps, and ground-source heat pumps also grew rapidly.

Among them, electric heat storage boilers were mainly applied in two aspects: One was the flexibility retrofit of thermal power plants, which worked together with the ancillary market for power peak shaving to realize the deep peak shaving of power plants while guaranteeing the heat supply. The other was the utilization of wind power, solar PV power, and other renewable power for district heating.

In terms of region, the heating area of air source, ground source, and other forms of heat pumps also increased greatly. By the end of 2019, the total installed capacity of renewable energy generation in Zhangjiakou reached 15 million kW, accounting for more than 70% of the total installed capacity in the region. The heating area of wind power exceeded 8 million m². According to the data from the Beijing Municipal Commission of Development and Reform, as of the end of 2021, the heating area of renewable energy in Beijing was over 100 million m², in which the heating areas of air source heat pumps, ground source heat pumps and wastewater source heat pumps were 65, 35 and 1.29 million m² respectively, and carbon emissions were reduced by 1.75 million tons per year.

In terms of the total amount, with the promotion of the “switching from coal to electricity” policy in the northern region and the increasing heating demand in non-centralized heating areas in northern and southern regions, the heating area of air source heat pumps in residential buildings grew rapidly during the 13th Five-Year Plan period. As estimated by the China Academy of Building Research, the heating area of air source heat pumps in northern China was about 725 million m² in 2021, which was a relatively large scale.

The Yangtze River Basin traverses western, central, and eastern China, connects southern and northern China, and passes through 9 provinces (Yunnan, Guizhou, Sichuan, Hunan, Hubei, Jiangxi, Jiangsu, Zhejiang, and Anhui) and 2 municipalities (Chongqing and Shanghai), where the population, gross regional product, civil building floor area account for 42, 45 and 48% of the national total respectively (Zhang and Su). From the point of view of climate zone, the vast majority of areas in the Yangtze River Basin are in the HSCW zone. The outdoor meteorological conditions in winter are mostly cold and wet, the average temperature of the coldest month in most areas is 0–5 °C, and the temperature in non-heated rooms is only 2–5 °C higher than the outdoor temperature. Therefore, to meet the demands of people for thermal comfort in their work and living environments, buildings in this zone need to be provided with corresponding heating facilities.

Since the 12th Five-year Plan period, the state has continued to increase the support for the study of heating in the HSCW zone. Jiang Yi, an Academician of the Chinese Academy of Engineering, suggests that all categories of building operation energy consumption should be allocated as the quantitative goals and upper limits for the energy-saving work based on the total energy capacity and environmental capacity available to China in the future and the demands for energy in all respects of social and economic development. In terms of the measured data on energy consumption, if the centralized heating mode is adopted in the Yangtze River Basin, the annual power consumption of large heat pumps will be about 40 kW · h/m² and the energy consumption of CHP will be about 15 kgce/m², also equivalent to 45 kW · h of electricity; if the CHP for heating and the decentralized air-conditioning are adopted, the annual energy use intensity will also amount to 40 kW · h/m². In contrast, if the decentralized air source heat pumps that enable the realization of the “part time and part space” manner are used, the electricity consumption is likely to be controlled within 30 kW · h/m².

In 2016, “Building Heating and Air Conditioning Solutions and Corresponding Systems in the Yangtze River Basin” was listed as a project in the National Key Research and Development Program, “The annual electricity consumption of heating, ventilation and air conditioning (HVAC) in residential buildings in the HSCW zone should be controlled within 20 kW · h/m²” was set as the quantitative goal, and the limit on the energy use intensity of HVAC in residential buildings in this zone was further identified. The heating method for the middle and lower reaches of the Yangtze River should be determined in combination with the local natural resource endowment and view of both energy efficiency and economy.

From the perspective of energy consumption, the drawbacks of the large-scale centralized heating system, including high energy consumption from transportation, large heat loss, and going against the energy-saving behaviors, have shown up fully in the operation of the NUH system. The indoor and outdoor temperature difference in winter is small in the Yangtze River Basin, so the use of the “full time, full space” centralized heating method adopted in northern China would lead to a huge waste of energy and environmental pollution. Besides, due to the short cold period, the utilization rate of heating equipment will be very low, causing immense waste. From the perspective of resource endowment, natural gas, and electricity are the major energy types. Residents generally have the habit of opening windows for ventilation every day, the use of the centralized heating method will lead to a lot of heat loss.

Consequently, for urban heating in the Yangtze River Basin, it is not suitable to adopt the northern method of large-scale municipal centralized heating; instead, the “part time and part space” heating strategy should be adopted to utilize the method of heating driven by clean energy and dominated by decentralized heating. The use of decentralized heat sources and terminals for household or room heating is characterized by a small construction scale, short period, and low investment, and their operation can be started and stopped depending on the specific demands of consumers. They are flexible, convenient, and more suitable for areas that have natural gas and electricity as the main heat sources, a low heating demand, a short heating duration, as well as a demand for flexible regulation and control.

However, considering such factors as the difficulty in securing natural gas resources, the large peak-valley difference in seasonal demands, and the high cost, the decentralized heating method dominated by air source heat pumps should be advocated among consumers when promoting the decentralized heating system in the Yangtze River Basin. Urban distributed district heating may be developed for residential compounds where residual heat or renewable energy resources are abundant in the surrounding areas and residents have a high willingness to pay. For rural families in southern China, air-source heat pumps should remain the dominant method of decentralized heating. With the large-scale promotion of rooftop PV in the future, direct electric heat with storage may be used for heating. For rural areas with rich biomass resources in southern China, biomass boilers should be promoted according to local conditions to meet the heating, cooking, and DHW demands simultaneously.

In 2013, Tsinghua University surveyed the use of heating appliances in 761 households in the Yangtze River Basin, among which 85% had split air conditioners, 80% had local heating appliances, and <1% used the centralized heating of the residential compound. Over the past two decades, the urban heating market in the Yangtze River Basin has developed from a small scale to a large scale and from a slow speed to a rapid speed. By the end of 2019, the floor area of urban residential buildings alone was around 7 billion m² in the HSCW zone, including about 8 million households using wall-hung gas boilers for heating, 4.9 million households using various radiators for heating, and approximately 8.2 million households using appliances including small heaters and electric heaters. The floor area of centralized heating was about 80–100 million m², and the main technologies utilized were industrial residual heat, CHP, and water-source heat pumps.

Take Heating Company D in Wuhan as an example. Its centralized heating system uses the extraction steam from a thermal power plant as the heat source, which is far from the concentrated areas of heat consumers, and the consumers are small in number and scattered. The temperature of supply water in the initial heating station and the secondary network may be adjusted depending on the outdoor temperature (Figs. 3.30 and 3.31).

A line graph plots the supply water temperature versus the lowest temperature in days. The curve indicates an increasing trend at the following estimated values. (8 to 9, 80), (2 to 3, 85), (negative 4 to negative 3, 88), and negative 6 to negative 5, 90).

A multi-line graph of supply water temperature versus outdoor temperature plots 4 curves in decreasing trends. From top to bottom, they are radiator with indoor heat exchanger, floor heating with indoor heat exchanger, fan coil unit no indoor heat exchanger, and floor heating no indoor heat exchanger.

Based on the practical household tests, it is found that the room temperature of households in residential compounds is about 21 °C in general, higher than the room temperature standard of 18 °C. The typical room temperatures in the heating season are shown in Fig. 3.32. It can be seen that the room temperature is above 20 °C for most of the time in the heating season, and the highest room temperature can reach nearly 25 °C.

A graph plots room temperature versus date. The curve plots a fluctuating trend at the following estimated values. (26 December, 22), (9 January, 21), (16 January, 20.5), (30 January, 23), (20 February, 20).

In the 2013–2014 heating season, Company D supplied heat to 5,646 households, and the total number of households in the residential compounds supplied with heat was 12,957, so the heating rate was 43.6%. In the 2013–2014 heating season, Company D supplied heat to all consumers from December 1 to March 1 and supplied heat to some consumers after March 1 and before December 1. The converted heat consumption per unit area was 0.345 GJ/m², the average heating index was 33.84 W/m², and the electricity consumption per unit area in the initial heating station was 0.93 kWh/m².

The actual heating methods of the vast majority of consumers at present are closer to the “full time, full space” mode. If households can be guided to properly control the frequency of opening windows while ensuring indoor air quality, considerable energy-saving effects will be achieved.

The heat consumption data of two residential compounds supplied with heat by Heating Company D are compared with those of Residential Compound A in Wuhan which uses water-source heat pumps for heating. All residents in Compound A use fan coils for heating, which can be started and stopped by consumers depending on demand, and the corresponding heating fees are charged based on the heat consumed. The test was conducted from January 27 to February 26, 2013.

The comparison of heat consumption of the three residential compounds is given in Table 3.11.

As can be observed from the comparison data, the heat consumption of the two compounds under test is much higher than that of Compound A. The reasons for this may be as follows:

Take the 2013–2014 heating season as an example. An economic analysis of heating is made for Heating Company D. The percentage of heat cost alone is up to 50.1%. Given factors including equipment overhaul, materials, labor, and rental, it is difficult to make a profit. According to the company, it is actually operating at a loss at present (Table 3.12).

As can be found through the comparison of the heat consumption per unit area among three compounds adopting different heating methods, the heat consumption of the compound adopting the “full time, full space” heating mode is more than 3–4 times that of the compound adopting the “part time and part space” heating mode. Hence, effective approaches to the reduction of energy consumption in the Yangtze River Basin will be as follows: guiding the heating behaviors of households; encouraging them to switch off the heating measures when there is no one in the room; and reducing the frequency of opening windows while ensuring the indoor environment. With reference to the average heat consumption of Company D in the 2013–2014 heating season, ideally, the energy consumption per unit area of decentralized heating is only 0.06 GJ/m².

According to the statistics of the Ministry of Housing and Urban–Rural Development, the floor area of buildings with potential heating demand in the 9 provinces and 2 municipalities in the Yangtze River Economic Belt was approximately 27.7 billion m² in 2015. In consideration of the further increase in the floor area of civil buildings in the future, the floor area of buildings with potential heating demand in the Yangtze River Basin is expected to reach 35 billion m² by 2050. If this region can be guided effectively through policies to adopt the “part time and part space” decentralized heating mode for buildings, properly reduce the target room temperature, and shorten the heating duration, the total energy consumption of heating in the Yangtze River Basin will not exceed 2.1 billion GJ in 2050 through the calculation based on the 0.06 GJ/m² of energy consumption per unit area.