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. 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. the analysis and compare on the climate and geographical features between Sweden and China, it is concluded that the perspective of application in China is wide. Keywords: seawater heat pump, Sweden, district cooling 1 background In the 21st century, energy and the 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. Projections indicate that, after 2025, the total amount of carbon dioxide emissions is likely to surpass the United States, ranking first in the world [1]. 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] . Faced with this grim form, structure and energy scholars from multiple angles to explore the Earth's environment for how to reduce the environmental burden of air conditioning design, pointed to accelerate renewable energy technology in the above air conditioning applications is a very worth exploring road [3 -4] . The ocean is a huge reservoir of renewable energy. Some of the solar radiation entering the ocean is converted into the kinetic energy of the ocean currents, and more of it is stored in seawater as heat energy. The heat capacity of seawater is relatively large, 3996 kJ / (m 3 · ℃), while the air is only 1.28 kJ / (m 3 · ℃). 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 sea ​​water heat pump An energy-saving device that utilizes high energy to flow heat from a low-level heat source to a high-level heat source, a low-level heat source (such as air, soil, water, solar energy, industrial waste heat, etc.) that can not be directly used can be converted into an available 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 Seawater heat pump is the 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 seawater heat pump system advantages Figure2 The advantages with seawater HP cooling / heating system The whole seawater heat pump system mainly includes: seawater take-off discharge 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. Figure 3 A typical seawater heat pump system Figure3 A common used SWHP system 3 Sweden Stockholm seawater heat pump system introduction International studies on the use of seawater for heating and cooling have been carried out for several decades, but so far only a handful of seawater heat pump systems have been built that are actually operating [7] . Among the more notable projects are the Purdy "s Wharf project in Halifax, Canada, the Nova-Scotia Power project in Nova Scotia and the Toronto Lake Water Cooling Project, as well as several projects in Hawaii, New York, and Florida in the United States [7] .Northern Europe leads the way in seawater heat pumps, and Sweden and Norway have reached the scale of application, with more than 180 large heat pumps now operating throughout northern Europe, of which Sweden has a total installed capacity of about 1,000 megawatts District heating, large-scale heat pump units for district heating and industrial areas using seawater, lake water, sewage, process waste water, groundwater and waste fumes from heat sources; a total construction volume of about 500 MW has been applied to urban and / Industrial production of regional cooling, freezer, freezer, chiller and heat pump cooling water. [8] The following is an overview of the Swedish capital of Stockholm. 3.1 Stockholm Stockholm, the capital of Sweden, 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. [9] In Stockholm, about 60% of users use district heating systems. A huge energy supply system uses a variety of energy forms. Table 1. Table 1 Energy used in the district heating system in Stockholm Table1 Energy Sources used in Stockholm's district heating system 50% of the district heating uses a heat pump system that provides the base load for district heating and the other 50% is peak-load-adjusted by oil-fired boilers, electric boilers and a few coal-fired boilers, respectively. The district heating network has been throughout the city, connecting more than 20 million square meters of construction, heating temperature is about 80 ℃, indoor temperature maintained at above 20 ℃, to meet the market demand for heating. The heating network is geographically divided into three main pipe networks: The Central Network, the North-Western Network and the Southern Network. The total pipeline length of 765Km. Table 2 shows the pipelines for heat production and heating in different heat pump stations in the Stockholm area in 1994.
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Key words: Seawater heat pump Swedish district cooling
Application of Seawater Heat Pump Systems in Stockholm and its Perspective in China
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Application of seawater heat pump system in Stockholm and its prospect in China (1)
Energy form
Use percentage
fossil fuel
35%
Biofuels
26%
Wastewater and sea water
26%
Heat pump electricity
13%
Energy form
Use percentage
fossil fuel
35%
Biofuels
26%
Wastewater and sea water
26%
Heat pump electricity
13%
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