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Abstract: In this paper, taking the current situation of energy and environment in China as a background, this paper introduces the application of seawater heat pump based district heating and cooling system in Stockholm, Sweden, which is very important in energy saving and environmental protection. By comparing the situation in our country and Sweden, we point out the development prospects of using regional seawater and heat pump system in our country. Keywords: Seawater heat pump, Swedish district cooling Application of Seawater Heat Pump Systems in Stockholm and its Perspective in China School of Civil and Hydraulic Engineering, Dalian University of Technology Jiang Shuang Li Zhen Duanmu Lin Abstract: District cooling / heating with seawater heat pump systems , an untapped resource in China, has a great benefits on energy conservation and environment protection. This paper mainly introduces the district cooling / heating systems based on seawater heat pump in Stockholm, Sweden. Through the analysis and compare on the climate and geographical features between Sweden and China, it is concluded that the perspective of the application of China is wide. Background: In the 21st century, energy and environment are two major problems facing mankind. The global warming caused by the energy crisis and the greenhouse effect has aroused widespread concern. In China, coal-based energy production and consumption increased rapidly. From 1990-2001, China's carbon dioxide emissions increased by 823 million tons, accounting for 27% of the world's increase over the same period. Coal is a fuel with a very high pollution index and is the main cause of air quality degradation. The health damage caused by urban residents in 1995 in this respect accounted for 5% of GDP, presumably by 2020 at 13%. According to the estimation by the International Energy Agency, the total amount of carbon dioxide emissions from burning fossil fuels in China was about 840 million tons of carbon in 2001, accounting for about 13% of the total global carbon dioxide emissions from fossil fuels. It has become the second largest in the world after the United States Emissions countries. Forecast shows that by 2025, China's total carbon dioxide emissions are likely to exceed the United States, ranking first in the world. In 2002, the national building energy consumption accounted for about 27.8% of the national energy consumption, while in the building energy consumption, air conditioning electricity accounted for about 30% -40% each summer due to the large increase in air conditioning power consumption Power supply tension, the contradiction between supply and demand is very prominent [2]. Facing this severe form, domestic scholars have discussed how to reduce the environmental load in air conditioning design from the aspects of energy structure and geo-environment, and pointed out that accelerating the application of renewable energy to air-conditioning technology is a worthwhile exploration. -4]. The ocean is a vast reservoir of renewable energy. Some of the solar radiation entering the oceans is converted to the kinetic energy of the ocean current, more in the form of heat stored in seawater, and the heat capacity of seawater is relatively large, at 3996 kJ / (m3 · ℃), while the air is only 1.28 kJ / (m3 · ℃). With the development of heat pump technology, it is technically possible to use sea water as a source of heat and cold instead of a traditional boiler room and freezer for district heating and cooling. It is one of the practical technologies for utilizing renewable energy. In most parts of the Yellow Sea and the Bohai Sea in China, the sea temperature in winter is generally above + 2 ℃ and the freezing temperature is usually around -2 ℃. Using this condition, heat pump technology can convert the low heat energy of seawater to high heat potential by using a small amount of electric energy Do district heating, you can replace some or all of the boiler room. Summer, the sea water temperature is generally about 20-30 ℃, is a very good cooling water. It is the most energy-efficient air-conditioning system to get seawater below 15 ℃ in suitable sea area and depth in the appropriate season, which can be directly used as chilled water to air-condition the building. Seawater heat pumps have eliminated the need to use seawater as a cooling source and can save significant amounts of freshwater resources, which is of great significance to China, where there is a shortage of fresh water. 2 Seawater heat pump Heat pump is a high-level energy-saving device which can transfer heat from a low-level heat source to a high-level heat source. Low-level heat sources (such as air, soil, water, solar energy, industrial waste heat, etc.) Can use the high heat, so as to achieve the purpose of saving some high energy (such as coal, gas, oil, electricity, etc.) [5]. As an efficient energy-saving device, heat pump has a wide range of applications and prospects. The system energy composition shown in Figure 1. Figure 1 Heat pump system energy composition Figure 1 The energy construction of the heat pump system Sea water heat pump is a seawater heat pump system. In summer, using seawater as cooling water, the cooling system no longer needs the cooling tower, which will greatly increase the COP of the unit. It is estimated that the cooling coefficient of the unit can be increased by 2% -3% every time the cooling water temperature is reduced by 1 ℃ [6] . In winter, the seawater passes through the evaporator and through the operation of the heat pump, the heat in the seawater is extracted and supplied to the building for use. The tremendous heat in the oceans and seas is of great importance to today's energy-saving and environmental issues. The use of marine resources, combined with heat pumps, for district heating / cooling, has a distinct advantage, as shown in Figure 2. Figure 2 The advantages of seawater heat pump system Figure 2 The advantages of seawater HP cooling / heating system The entire seawater heat pump system includes: seawater take-off system, heat pump, heat exchanger and pipe network. Figure 3 is a typical seawater heat pump system. Due to the direct use of seawater as a source of heat and heat, seawater heat pump systems can partially or even completely replace freezers and boilers in conventional air conditioning and heating systems. A typical seawater heat pump system Figure 3 A common used SWHP system 3 Stockholm, Sweden Introduction to the seawater heat pump system International studies of seawater heating and cooling have been carried out for several decades, but so far only a few The actual operation of the seawater heat pump system has been completed [7]. More notable projects include the Purdy's Wharf project in Halifax, Canada, the Nova-Scotia Power project in Nova Scotia, Toronto's water and cooling project utilizing the Lake Ontario, and several projects in the Hawaii, New York and Florida regions of the United States [7 ]. Scandinavia has taken a leading position in the application of seawater heat pumps, with Sweden and Norway having reached the point of large-scale applications, and now has more than 180 large heat pumps operating throughout northern Europe. Among them, Sweden has a total construction volume of about 1000 MW since 1985, and is applied to large-scale heat pump units in district heating and industrial areas. The heat sources include seawater, lake water, sewage, process wastewater, groundwater and waste fume. To date, the total construction volume is about 500 MW for district cooling for urban and industrial production, and the cooling sources use free cooling, chillers and heat pumps for cooling water [8]. Here's a briefing on the application of the Swedish capital Stockholm. 3.1 Stockholm Stockholm is the capital city of Sweden. It is located on 14 islands and is one of the most beautiful cities in the world. Since the 1960s, Stockholm has been using regional heat pumps for district heating. Its clean sea, fresh air and clear blue sky benefit from the strict protection of the environment. In Stockholm, about 60% of users use district heating systems. A huge variety of energy supply systems are used