Prospects for Heat Pump Heating Technology under the Goal of "Carbon Neutrality"
Prospects for Heat Pump Heating Technology under the Goal of "Carbon Neutrality"
Heating and cooling energy consumption accounts for about 50% of the global terminal energy consumption, which is a very important terminal energy demand and a key area to focus on in achieving the "carbon neutrality" goal.
A heat pump is a device that uses energy to do work, elevating heat from lower temperatures to higher temperature levels and releasing it to meet the requirements of heat usage. Heat pump technology can be widely applied in fields such as building heating, domestic hot water, industrial drying, and greenhouse aquaculture. It is one of the most valuable energy-saving and carbon reduction technologies in the world in the 21st century, and the industrial development prospects are very broad. In recent years, driven by China's clean heating policy, heat pump heating technology has rapidly developed in rural areas of northern China. With the continuous improvement of people's living standards, the market potential for winter heating in the vast Yangtze River Basin is rapidly releasing. As the preferred technology for decentralized household heating, heat pump heating has also developed rapidly. As a technological measure for effectively utilizing renewable energy, heat pumps will be a necessary technology for low-carbon transformation in China's heating industry. In addition to the alternative role of heat pumps in clean heating, their application scope can also be further expanded in fields such as domestic hot water and industrial drying. Technological progress is expected to drive China's heat pump industry to achieve a breakthrough of 100 billion yuan in scale, playing an important role in achieving China's goal of "carbon peaking and carbon neutrality".
1、 Heat pump heating is the most practical technology to improve the level of heating electrification
The global heat pump market is continuously growing and will be the fastest-growing heating technology in the future, as well as a key technology supporting energy conservation and carbon reduction in various countries. Currently, heat pumps meet nearly 5% of the global heating demand. In 2019, nearly 20 million households worldwide purchased heat pumps, while in 2010, only 14 million households purchased heat pumps. In Europe, the sales of heat pumps have increased by 25% in just two years, with air source heat pumps having higher sales. In countries such as Germany, the heat pump heating area in newly built buildings has continued to exceed the gas heating area. According to the International Energy Agency's prediction, under the scenario of achieving "net zero" emissions globally by 2050, the share of heat pumps in heating demand will reach 20% and 55% respectively by 2030 and 2050, and the number of installed heat pumps will reach 600 million and 1.8 billion, respectively. At present, China's heat pump industry ranks first in the world in terms of development scale and application area, especially in the air source heat pump market, which has exceeded half of the global application scale and has transformed from a follower to a leader.
In global heat consumption, the industrial sector accounts for about 50%, the construction sector accounts for about 46%, and the agricultural sector accounts for about 4%. The heat consumption in China is mainly concentrated in the two major markets of industrial and civil heating. At present, the industrial sector is the main heat consumption sector in China, with heat demand accounting for approximately 70% of the national heat demand. In industrial production processes in industries such as chemical, papermaking, pharmaceuticals, textiles, and non-ferrous metal smelting, a large amount of heat is required. Except for some large industrial enterprises that use their own thermal power plants for heating, most industrial enterprises use boilers for heating. The daily heat consumption of residents in the construction sector is another aspect of heat demand, mainly used for room heating and domestic hot water, among which room heating is the main area of heat consumption.
At present, there are approximately 15.2 billion square meters of urban buildings in northern China that require winter heating. With the further development of urbanization and the continuous improvement of residents' requirements for building environment, the winter heating area of urban buildings in northern China is expected to reach 20 billion square meters in the future. In addition, there are still 7 billion square meters of rural buildings in the northern region that also have heating needs. At present, the average winter energy consumption of heating buildings in northern cities and towns in China is 0.3 GJ/m2, which requires 4.5 billion gigajoules of heat per year to meet heating needs. In northern urban areas, heating needs are mainly met through centralized heating facilities such as cogeneration and large regional boiler rooms. Areas not yet covered by centralized heating are supplemented by decentralized heating such as coal-fired small boilers, natural gas, electricity, and renewable energy. In recent years, through clean heating actions, a pattern of clean heating sources in the northern region has basically formed, with ultra-low emission coal-fired cogeneration as the main source and natural gas heating as the auxiliary, supplemented by other heat sources. Among them, cogeneration accounts for about 50%, coal-fired and gas boilers of various sizes account for about 40%, and only 10% extract heat from various low-grade heat sources such as air, sewage, groundwater, and underground soil through different electric driven heat pumps to meet heating needs. In 2019, the heating energy consumption of urban buildings in northern China reached 213 million tons of standard coal, accounting for 20% of the total building energy consumption in the country; The carbon dioxide emissions from heating buildings in northern cities and towns are 550 million tons, accounting for 26% of the total carbon dioxide emissions related to fossil energy consumption in the operation of buildings nationwide.
Except for northern heating, the vast areas with hot summer and cold winter are not within the traditional centralized heating range in China. However, the daily minimum temperature in this area is below 5 ℃ for over two months, and the problem of "cold winter" has not been fundamentally solved for a long time. The demand for heating from residents in the region is increasing, and the potential of the winter heating market is rapidly being released. The heating energy consumption in the region increased from less than 2 million tons of standard coal in 2001 to around 33.8 million tons in 2019, with an average annual growth rate of about 17%. During the 13th Five Year Plan period, the average annual growth rate further increased to 20%. As of the end of 2019, the urban residential construction area in hot summer and cold winter regions was about 7 billion square meters, and the rural construction area was about 9 billion square meters. In the future, the residential building area and heating energy consumption intensity in the region will further increase, leading to a significant increase in heating energy consumption.
From the perspective of domestic hot water, cities and towns in China have basically reached a widespread state. Except for a few cases where solar energy is used to prepare domestic hot water, gas water heaters and electric driven domestic hot water each account for approximately half. At present, the preparation of domestic hot water nationwide results in annual carbon dioxide emissions of about 80 million tons, nearly 1% of the total carbon emissions in the country. With the improvement of living standards, the demand for domestic hot water by residents will continue to grow, and heat pump production of domestic hot water will be the main way to replace gas water heaters.
Under the goal of "carbon peaking and carbon neutrality", it is necessary to promote the low-carbon use of building energy at a faster pace and with greater efforts. Improving the level of electrification is a key path to promote green and low-carbon development in the construction field. Compared with fossil fuel heating schemes, the carbon dioxide emissions generated by heat pump heating are significantly reduced, making it more energy-efficient and environmentally friendly. The electric conversion efficiency of heat pumps can reach over 300% throughout the year, while the thermal efficiency of boilers will not exceed 100%. For households with decentralized heating, it is more suitable to use heat pump heating technology. Moreover, with the continuous improvement of building energy efficiency standards, future ultra-low energy consumption buildings and near zero energy consumption buildings will be widely promoted, greatly reducing the heating load of such buildings. Traditional centralized heating network heating is no longer needed, and only a small amount of heat supply using heat pump heating technology can meet winter heating needs. The large-scale application of heat pump technology in the heating field can significantly improve the level of heating electrification and accelerate the clean and low-carbon development of heating systems.
2、 There are various forms of heat pump systems that can only achieve true energy-saving effects by adapting to local conditions
There are various forms of heat pump systems, which can be divided into underground water source heat pump, surface water source heat pump, soil source heat pump, sewage source heat pump, medium to deep ground source heat pump, air source heat pump, etc. according to different heat sources. There are two main driving methods for heat pumps: electric motor drive and thermal drive. Currently, various scales of heat pump heating mainly rely on electric drive. Whether heat pump heating is energy-saving depends on actual engineering conditions, geographical and meteorological conditions, as well as the level of design, installation, and operation management. It is necessary to use heat pumps in appropriate situations and conditions according to local conditions in order to achieve true energy-saving effects.
（1） Ground source heat pump
Ground source heat pump is an efficient and energy-saving system that utilizes shallow geothermal energy (including energy from groundwater, soil, or surface water) to provide both heating and cooling. The groundwater temperature is basically constant throughout the year, with lower temperatures than outdoor air in summer and higher temperatures than outdoor air in winter. It also has a large heat capacity and high system efficiency. The surface water source heat pump system utilizes low-temperature and low-level thermal energy resources from surface water sources on the Earth, such as rivers, lakes, or pools. It can be divided into open and closed systems based on whether the heat transfer medium is connected to the atmosphere. The ground source heat pump system is a system where a large number of plastic pipes for heat exchange are buried underground, and the circulating water exchanges heat with the underground soil through these pipes to extract heat from the underground soil as a low-temperature heat source for the heat pump. Due to the relatively constant soil temperature, the operation of the ground source heat pump unit is relatively stable and reliable, and there is no frost problem in the evaporator in winter. The thermal efficiency (COP) of a ground source heat pump system is generally 3.5-5, which is relatively high. Compared to air source and water source heat pumps, ground source heat pumps have the widest range of adaptability and are basically not limited by geographical conditions. As long as there is sufficient underground space, they can be used. At present, the heating area of ground source heat pumps in northern China has exceeded 150 million square meters, and they have also been applied on a certain scale in areas such as Jiangsu, Hubei, and Shanghai. The annual recoverable resources of shallow geothermal energy in major cities in China are equivalent to 700 million tons of standard coal, which can meet the heating (cooling) needs of 32 billion square meters of buildings. The Huang Huai Hai Plain and the Middle and Lower Yangtze Valley Plain Plain are more suitable for the development and utilization of shallow geothermal energy.
（2） Sewage source heat pump
The sewage source heat pump system uses the heat from domestic sewage as the low-temperature heat source of the heat pump, and is suitable for urban areas with abundant sewage source resources. The temperature of domestic sewage discharged from civil buildings can generally reach around 20 ℃ in winter, which is higher than the temperature of groundwater and is a good heat source. When there are large sewage pipes around the building, it is possible to use raw sewage (even untreated and directly discharged sewage) as a low-temperature heat source to achieve good energy consumption performance of the heat pump system. The use of sewage source heat pump systems requires scientific coordination and reasonable layout of sewage source heat pump devices in planning, and technical attention should be paid to the issues of pollution, corrosion, and blockage of heat exchangers.
（3） Medium to deep ground heat pump
The medium to deep geothermal heat pump system consists of a sealed geothermal energy intake hole, a heat source side water system, a heat pump unit, and a user side water system. Compared with conventional ground source heat pump systems, the main difference lies in the use of casing structures for mid to deep geothermal energy heat exchange devices, which extract geothermal energy from rocks 2000 to 3000 meters underground at temperatures of 70 ℃ to 100 ℃ as a low-temperature heat source. The outlet water temperature of geothermal energy heat exchange devices can be stable above 30 ℃ in winter. The heating technology of medium to deep ground heat source heat pumps requires 100% recharge of underground water, mainly suitable for areas with good geothermal resource conditions, cold winter with heating needs, or hot summer with cooling needs; When used for heating residential buildings, there is no need to supplement heat to the underground in summer. There are various ways to use the indoor end, among which floor radiation heating is better. The application technology of mid to deep geothermal energy heating has been basically mature, and the heating area of mid to deep geothermal energy in northern China has exceeded 100 million square meters, mainly distributed in Hebei, Tianjin, Henan, Shandong and other places. Medium to deep geothermal energy heating has high safety, low unit operating cost, low carbon, environmental protection, cleanliness, and comfort. However, the construction investment is large, the site selection is affected by regional conditions, and it is difficult to recharge, which affects the sustainable development and utilization of geothermal resources. In areas with hot summer and cold winter, large-scale development of deep geothermal energy heating is not encouraged. However, under the premise of good geothermal resource conditions, high heating demand, and strong economic capacity, deep geothermal energy heating projects can be developed.
（4） Air source heat pump
An air source heat pump extracts heat from outdoor air, which is driven by a fan to flow through a heat harvesting device (evaporator of the heat pump) installed outdoors to obtain heat from the outdoor air. Then, it is produced by an indoor heat exchanger (condenser of the heat pump) to produce hot water or air, which is provided to users for room heating. Air source heat pumps can be divided into air/air heat pumps and air/water heat pumps according to the different thermal media. Air/air heat pump, the heat released from its condenser is used to generate hot air for room heating. An air/water heat pump, in which the heat released from the condenser is used to produce hot water, which is then supplied to the room for heating through terminals such as fan coils. There are various methods for indoor end heating using air source heat pumps, including floor radiation heating, direct hot air heating, and so on. The air source heat pump can be used in both residential and public buildings, and can be used separately or collectively. For ultra-low energy consumption buildings, centralized heating is not required, and the use of small air source heat pumps for heating can meet the heating needs. The energy consumption of air source heat pump heating is only one-third of that of direct electric heating, which is the same principle as traditional split air conditioning but has different performance. Traditional split air conditioners mainly meet the performance requirements of summer cooling conditions while also taking into account the winter heating function. They cannot operate efficiently when the outdoor environment temperature is low, while air source heat pumps mainly meet the performance requirements of winter heating conditions, with better environmental temperature adaptability and system efficiency.
Air source heat pump hot air fan is a new technology that has rapidly developed in China in recent years driven by market demand, and is in an international leading position. Through new compressor technology, frequency conversion technology, and new system forms, it can expand the application range of air source heat pump hot air fans to outdoor low-temperature environments of -30 ℃. Compared with general cold and warm air conditioning products, the heating capacity in low-temperature environments is increased by 50% to 100%, energy efficiency is improved by about 20%, and indoor temperature can be rapidly increased. Currently, the market has reached one million units. The air source heat pump hot air fan does not require the installation of radiators, floor heating, and other heating terminals, avoiding potential risks of leakage and leakage in hot water heat pump heating projects. Multiple indoor heat pump hot air fans can be independently controlled and operated, and the probability of failure is low, making it easy to use and maintain. At present, the market price of air source heat pump hot air fans is about 4500 yuan per unit, and two air source heat pump hot air fans can meet the heating needs of 100 square meters of buildings.
Air source heat pump water heater is another type of air source heat pump heating equipment that can currently operate normally at an ambient temperature of -20 ℃, providing hot water for heating from 30 ℃ to 50 ℃. It forms a heating system with floor radiation coils or radiators to provide stable room temperature and good comfort for residents; When the water supply temperature is not particularly high, the COP of the air source heat pump hot air fan is basically equivalent. The air source heat pump water heater is suitable for the "all time, all space" heating mode, and has good heating comfort. However, due to the difficulty of starting and stopping at any time and regulating the heating of some rooms, the heating room is heated throughout the winter, and the actual energy consumption may be more than twice that of the air source heat pump fan.
3、 The market demand for heat pump heating has broad prospects and huge potential for energy conservation and carbon reduction
The decentralized heating market in China is mainly distributed in buildings that cannot be covered by centralized heating systems in northern cities and towns, including rural houses in the north, ultra-low energy buildings, and residential buildings in the Yangtze River Basin that require heating. Air source heat pumps are generally suitable for residential and public buildings in hot summer and cold winter, cold, and severe cold areas.
In northern rural areas, if efficient air source heat pumps are chosen to replace inefficient bulk coal stoves or direct electric heating, it will bring huge market potential. There are about 50 million farmers in the Yellow River Basin alone, with a market demand for 100 million to 150 million air source heat pumps. After large-scale promotion of air source heat pump equipment, wireless communication and regional joint control technology for a single device can also be adopted. By controlling a certain number of heat pump equipment to start and stop in different time zones, active and effective peak shaving and valley filling can be achieved for the local power grid, which is more conducive to the safe, stable, and efficient operation of the regional power system.
Based on the practical case data of low-temperature air source heat pump equipment in clean heating of Beijing rural residential areas during the "coal to electricity" transformation, air source heat pumps are used to replace bulk coal furnace heating systems. Depending on the insulation status of the building, the electricity consumption per unit area during the heating season is only 20 kWh