What are the requirements of water source heat pump for water source system

Author : sherry

Update time : 2020-10-31 13:52:49

The water quantity, water temperature, water quality and water supply stability of water source system are important factors affecting the operation effect of water source heat pump system. When applying water source heat pump, the principle requirements of water source system are: sufficient water quantity, moderate water temperature, suitable water quality and stable water supply. Specifically, the water quantity of the water source should be sufficient to meet the needs of heating or cooling load of users. If the water is insufficient, the heating and cooling capacity of the unit will be reduced, which can not meet the requirements of users. The water temperature of the water source should be moderate and suitable for the operating conditions of the unit. For example, in the heating operation condition, the water temperature of the GHP water source central air conditioning system of Tsinghua Tongfang should be 12-22 ℃ and 18-30 ℃ respectively. The water quality of the water source should be suitable for the material of system units, pipes and valves, so as not to cause serious corrosion damage. The water supply guarantee rate of water source system should be high, and the water supply function has long-term reliability, which can ensure the long-term and stable operation of water source heat pump central air-conditioning system.

Water source

In principle, any water source whose water quantity and water temperature can meet the needs of heating load or refrigeration load of users, and the water quality does not cause corrosion damage to the unit equipment, can be used as the water source for the water source heat pump system, which can be either renewable water source or natural water source.
1. Reclaimed water source
It refers to the urban domestic sewage, industrial wastewater, mine wastewater, oilfield wastewater, cooling water of thermal power plant and other water sources discharged after artificial utilization. Users who have the conditions to use renewable water sources can turn waste into profit, which can reduce initial investment and save water resources. But for most users, the alternative is natural water.
2.Water source in nature
Water in nature is distributed in the atmosphere, the earth's surface and the rocks in the earth's crust, which are called atmospheric water, surface water and groundwater respectively. Both surface water and groundwater on land come from atmospheric precipitation.
The seawater in surface water accounts for 96.5% of the total natural water reserves. Sea water can be used in coastal cities, and there are some examples of seawater as heat pump water source in foreign countries. Some coastal cities in China have used seawater as industrial cooling water source for many years. In recent years, seawater has been used as the source of heat pump in China, but the practical application of seawater source heat pump technology still needs time. The surface water on land, that is, the water from rivers, lakes and reservoirs, is less mineralized than that of seawater and groundwater. However, it contains more solid particles such as sediment, colloidal suspended solids, algae and other organic matters, with high sand content and turbidity. Therefore, it can be used as heat pump water source only after necessary treatment.
Groundwater refers to the water body buried and transported in the aquifer below the surface. Groundwater is widely distributed, the water quality is better than surface water, the water temperature changes with climate is smaller than surface water, it is an ideal water source for central air conditioning.
3. Selection of water quantity and water source
Water quantity is the key factor affecting the working effect of water source heat pump system. The amount of water required for a project is determined by the load of the project and the performance of the unit. The selected water quantity should meet the load requirements. If other conditions are available, but the water is slightly insufficient, some auxiliary measures can be taken to solve the gap. If the water gap is too large to meet the load requirements, other schemes should be considered. For a specific project, it is necessary to judge whether there is available water source from the actual situation. The site environment and hydrogeological conditions of different projects are very different, and the available water sources are different, so the suitable water sources should be selected according to local conditions. When there are different water sources to choose from, it should be determined by technical and economic analysis and comparison.

Water quality

Water in nature is in the endless cycle movement, constantly contact with the atmosphere, soil, rock and other environmental media, so that it has complex chemical composition, chemical properties and physical properties. In the application of water source heat pump, we should not only pay attention to the water quantity, but also the temperature, chemical composition, turbidity, hardness, salinity and corrosivity of water. However, there are no relevant regulations on the water quality of water source heat pump at present. The data in this paper refer to the cooling water quality standard and some relevant provisions of groundwater recharge quality.

1.Temperature

The surface water temperature varies with season, latitude and elevation. In the north of the Yangtze River and the plateau area, the surface water freezes in winter and cannot be used for heating. In summer, the water temperature is generally lower than 30 ℃, which can be used for refrigeration and air conditioning.
The groundwater temperature varies with the natural geographical environment, geological conditions and circulation depth. Near the surface of the ground is a variable temperature zone, and a certain depth below the variable temperature zone is a constant temperature zone. The depth of the constant temperature zone is different in different latitudes, and the water temperature range is 10-22 ℃. When the constant temperature zone is downward, the groundwater temperature increases with the increase of depth, and the increase depends on the geothermal warming rate of different regions and lithology. The average geothermal warming rate of the crust is 2.5 ℃ / 100M, which is higher than this value is geothermal anomaly. Geothermal fields can be formed in geothermal anomaly areas rich in groundwater. According to the statistics of 1997, more than 3200 geothermal spots have been discovered in China, 130 geothermal fields have been developed and utilized, and 345 million m3 geothermal water has been exploited annually. At present, the temperature of waste water discharged by many geothermal users is relatively high (about 40 ℃). The application of water source heat pump can reuse the temperature difference of 30 ℃ in waste water and greatly improve the utilization rate of geothermal energy.
2.Sand content and turbidity
Some water sources contain sediment, organic matter and colloidal suspended solids, which make the water turbid. The high sand content of water source will cause abrasion to the unit and pipe valve. Water with high sand content and turbidity will cause aquifer blockage when it is used for groundwater recharge. The sand content of water source used in water source heat pump system should be less than 1 / 200000 and turbidity less than 20 mg / L. If a plate heat exchanger is installed in the water source heat pump system, the particle size of solid particles in the source water should be less than 0.5 mm.
3. Chemical composition and chemical properties of water
Different ions, molecules, compounds and gases are dissolved in the natural water, which makes the water have the chemical properties of pH, hardness, salinity and corrosivity, which has a certain impact on the material of the unit.
When the pH value of pH value is less than 7, it is acidic, otherwise it is alkaline. The pH value of water source of water source heat pump should be 6.5-8.5.
The total amount of Ca2 + and Mg2 + in hardness water is called total hardness. High hardness, easy to scale. The content of Cao in source water of water source heat pump should be less than 200mg / L.
The total amount of various ions, molecules and compounds contained in unit volume of water is called total salinity. The salinity of source water used in water source heat pump system should be less than 3G / L.
Cl - and free CO2 in corrosive water are corrosive, and dissolved oxygen increases the corrosion damage of metal pipes. In the application of water source heat pump system, stainless steel heat exchanger or titanium plate heat exchanger should be installed in the water source with high corrosion and hardness.
.Intake structure
To supply water from the water source to the water source heat pump room, it is necessary to build water intake structures. According to different water sources, water intake structures can be divided into surface water intake structures and groundwater intake structures.
1.Surface water intake structureAccording to the structure form, the surface water intake structure can be divided into movable type and fixed type. Movable surface water intake structures include floating ship type and movable cable car type. The fixed surface water intake structure is more commonly used, which has many types, but generally includes water intake, water diversion pipe (or horizontal water collecting pipe) and water collecting well. The surface water intake structure is greatly affected by the water source flow, velocity and water level, and the construction is complex. Therefore, the construction scheme should be selected according to the specific situation.
2. Underground water intake structure
Groundwater intake structures include tube well, large mouth well, combination well, radiation well and seepage channel. Table 1 lists the types and application scope of groundwater intake structures. In practical engineering, different forms should be selected according to different groundwater depth, aquifer thickness, water yield and technical and economic conditions.
3. Tube well
The most common type of underground water intake structure is tube well, which is generally composed of well hole, well wall pipe, filter pipe and sand settling pipe. The borehole is drilled with a drilling rig, and the wall pipe is installed at the non aquifer to support the borehole wall and prevent collapse. The well pipe and the orifice are sealed with impermeable materials such as clay or cement to prevent the infiltration of surface sewage. The filter pipe is installed in the aquifer, and its main function is to filter water and prevent sand; The bottom of the well tube is a sand settling tube, which is used to deposit sediment in water and prolong the service life of the tube well.

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