Application example analysis of surface water sour

2022-07-24
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Application case analysis of surface water source heat pump system (Part 1)

1 surface water source heat pump system

a research and development base is located in Tongzhou District, Beijing, with a construction land of 580 mu, and about 150 mu of cooling area is achieved by injecting water from waste pits and ponds. The building scale is 95000 square meters, mainly used for supporting facilities such as scientific research, development, storage, office space and experimental residence. The approximate distribution ratio is: research and development - building area of 100000 square meters, experimental residence -30000 square meters, public construction -7400 square meters and municipal -2200 square meters. According to the actual situation of the base and the opinions of relevant departments of the Institute, considering the environmental protection requirements, it is proposed to use the surface water source heat pump system for heating and cooling

2 feasibility of using water source heat pump and selection of water source heat pump system. Because of its environmental protection and energy saving, it has been vigorously promoted and applied at home and abroad recently

surface water is prone to pollution, with high content of sediment, algae and other impurities. The water surface is in direct contact with the air. The water body has high oxygen content and strong corrosivity. If surface water is directly supplied to each heat pump unit for heat exchange, it is easy to reduce the service life of the heat pump unit, scale the heat exchanger and reduce the performance. In serious cases, it will also lead to pipeline blockage. Therefore, it is not suitable to directly supply surface water to each heat pump unit for heat exchange. For example, the relevant lithium battery materials also show a synchronous and high-speed growth trend. As a result, the surface water and the circulating water in the building are separated by heat exchangers, and the heat exchangers operate in the way of small temperature difference heat exchange. In this way, the expensive water source heat pump unit can be protected by cheap heat exchangers. If there is the possibility of heat recovery between buildings, this system can also automatically recover heat between buildings. However, due to the heat exchange temperature difference, Cause the problem that the energy of surface water can not be fully utilized. When the surface water flow or temperature cannot meet the use requirements, some auxiliary equipment can be used, such as boilers in winter and cooling towers in summer as peak shaving equipment, which can also help the system meet the use requirements

according to the meteorological and hydrological conditions in Beijing, the average surface temperature in Beijing in summer is generally 25~27 ℃. Considering the 5 ℃ temperature difference of the heat exchanger, the average inlet water temperature of the heat pump unit in summer will not be higher than 32 ℃. If the temperature difference between the inlet and outlet of the cooling water side of the heat pump in summer is 5 ℃, the outlet water temperature of the heat pump unit will be less than 37 ℃. According to the technical requirements of the heat pump unit, At this time, the temperature difference between the supply and return water of the cooling water can ensure the normal operation of the refrigeration of the heat pump unit in summer

in winter, the average surface temperature in Beijing is generally about 4 ℃. Considering the 2 ℃ temperature difference of the heat exchanger, the inlet water temperature of the heat pump unit in winter will not be higher than 2 ℃. Considering the 5 ℃ temperature difference of the inlet and outlet of the chilled water side of the heat pump in winter, the outlet water temperature of the heat pump unit will not be lower than -3 ℃, so antifreeze must be added to the circulating water. At this time, the C.O.P. value of the heat pump unit under the heating condition is about 2~3 (the C.O.P. value of the units produced by different manufacturers is slightly different), and the higher the C.O.P. value, the higher the heating capacity of the heat pump unit. When the liquid crystal display shows that the surface water temperature is too low (below 4 ℃) in real time, or the surface water is insufficient, it is necessary to consider using other auxiliary heat sources such as boilers to heat the chilled water circulating water of the heat pump unit, To ensure that the heat pump unit operates under high heating capacity. The use of auxiliary heat sources, such as the chilled water circulating water of boiler heating heat pump units, has no advantage in energy saving compared with conventional heating forms such as direct heating with boilers. However, the use of auxiliary heat sources is only used under extreme conditions such as low surface water temperature or insufficient surface water volume. Generally speaking, the number of days this happens is very few, or even does not happen, Considering the whole heating season, it is energy-saving to use water source heat pump units for heating compared with the above conventional heating methods, which will be further analyzed below

in terms of the form of system end devices, the water source heat pump system is divided into centralized large-scale water source heat pump units + fan coil units and decentralized water air source heat pump units. The final output of the water water source heat pump unit is cold and hot water. This type of unit is relatively large. Generally, the whole project is equipped with a water source heat pump room, and the generated cold and hot water is transmitted to each single building by pump. According to the needs, a water water source heat pump room can also be set in each single building to transmit the circulating water after heat exchange with geothermal water to each single building, The water-water source heat pump unit of each single building produces cold and hot water, which is then transmitted to each air conditioning area in the building through the water pump, and the energy in the cold and hot water is transmitted to each room through the fan coil unit and the air handling unit. The water air source heat pump unit is a direct evaporation unit, which is relatively small. It is generally divided into many small systems according to the use function and use requirements of each area. The circulating water is transferred to the units in each single building through the water pump after heat exchange in the central water pump room. The return air in the air conditioning area is sent out after heating/cooling by the unit, and the energy does not need secondary transmission, Therefore, other heat and moisture treatment units such as fan coil units are no longer required. The two systems have their own characteristics. The water water source heat pump system is a more centralized air conditioning mode, which has been produced in China. Due to the concentration of units, the initial investment of the water source heat pump unit is small, but the heat pump unit needs to set up a special machine room in the building; The water air water source heat pump system is relatively scattered. At present, the mature products are mainly foreign brands. The initial investment of the unit is slightly high, but the indoor circulating water pipe does not need insulation. As the units are scattered to the end, the required machine room area is also small. In terms of the comprehensive cost of the system, the water air source heat pump unit is more expensive, but the fan coil, air conditioning box, thermal insulation cost and the cost of the machine room required by the water water source heat pump system increase. Although the comprehensive investment of the water air source heat pump unit is more expensive, the difference between the two is not large. In terms of operation, since the energy regulation of water-water source heat pump unit can only be carried out in limited stages, and four tubes must be used to supply cooling and heating at the same time, it is more suitable for occasions with uniform work and rest time and consistent load; The water air source heat pump unit is equipped with a temperature controller, which can be adjusted and operated independently according to the use requirements. It can also realize the simultaneous heating and cooling function of four tubes in the case of two tubes. Therefore, it is more suitable for commercial and public buildings with diversified work and rest hours and use requirements

according to the characteristics of the above water source heat pump system and the specific conditions of the project, we believe that the form of centralized large-scale water source heat pump unit + fan coil unit should be adopted. The reasons are as follows:

1.1 the equipment used in this form of water source heat pump system has mature products in China, which is easier to be guaranteed in terms of price and after-sales service

1.2 as the end water air source heat pump unit is equipped with compressor, it is unfavorable in noise control. Considering the high environmental noise requirements of scientific research office, it is more advantageous to use fan coil unit with only fan but no compressor as the end equipment

1.3 as Beijing is located in the north, the calculated temperature of air conditioning in winter is as low as -12 ℃. As the water air unit has requirements on the inlet air temperature (generally not lower than 5 ℃, otherwise the low temperature protection will be started), the treatment of fresh air in winter must be preheated by electric heating, and the free geothermal resources cannot be effectively utilized when the surface water is sufficient

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