Water system, water temperature, water quality and water supply stability of water source heat pump system is an important factor in the operation of the effect. The application of water source heat pump, the principle of the water system requirements are: adequate water, moderate water temperature, water quality, water supply stability. Specifically, the water source of water should be sufficient enough to meet the user heating load or cooling load needs. If the water is not enough, the unit's heating capacity and cooling capacity will be reduced, failing to meet user's requirements. Water temperature should be moderate, suitable for unit operating conditions. For example, Tsinghua Tongfang GHP type water source central air-conditioning system in the heating operation conditions, the water source temperature should be 12-22 â„ƒ; cooling operating conditions, the water source temperature should be 18-30 â„ƒ. The water quality of the water source should be suitable for the materials of the system unit, pipeline and valve without causing serious corrosion damage. Water source system to ensure high water supply, water supply function with long-term reliability, to ensure water source heat pump central air conditioning system long-term and stable operation.
First, water In principle, any water, water temperature to meet the needs of the user heating load or refrigeration load, the water quality of the unit equipment does not produce corrosion damage to any water source can be used as water source heat pump system, either renewable water source , Can also be a natural source of water.
1. Recycled water source refers to the water discharged from man-made but treated urban domestic sewage, industrial waste water, mine waste water, oilfield waste water and thermal power plant cooling water, etc. Users who make use of recycled water source conditionally can turn waste into profits and reduce initial investment , Save water resources. But for most users, the water of choice in nature is available.
2. Water in Nature Water in nature is found in the atmosphere, the Earth's surface and crustal rocks, called atmospheric, surface and groundwater, respectively. Surface water and groundwater on land come from precipitation in the atmosphere. Surface water accounts for about 96.5% of the total natural water reserves. The coastal city of the conditional use of seawater, foreign application of seawater as an example of heat pump water. Some coastal cities in China have used sea water for industrial cooling water sources for many years. In recent years, there is a useful sea water for heat pump water research, but the practical application of seawater source heat pump technology still needs time. Surface water on land, that is, rivers, rivers, lakes and reservoirs has a lower degree of salinity than seawater and groundwater, but there are more organic matters such as sediment and other solid particulates, colloidal suspensions and algae, sand content and turbidity High, subject to necessary treatment before heat pump water. Groundwater refers to the body of water that is buried and transported in aquifers below the earth's surface. Groundwater is widely distributed, water quality is better than surface water, water temperature with surface water than climate change is small, is the water source central air conditioning can use more ideal source of water.
3. The choice of water quantity and water quantity The water quantity is the key factor that affects the working effect of the 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 amount of water source and water should meet the load requirements. If other conditions are available, but the water slightly less than the gap can take some remedial measures to make up. If the water gap is large, can not meet the load requirements, it should consider other options. For a specific project, we should proceed from the actual situation to determine whether there is available water source. Different projects of the site environment and hydrogeological conditions vary widely available sources of water should be selected according to local conditions suitable for water. When there are different water sources to choose from, they should be technically and economically analyzed and compared to determine the optimum.
Second, water quality Water in nature in endless cycle of movement, and constantly with the atmosphere, soil and rock and other environmental media contact, interaction, it has a complex chemical composition, chemical and physical properties. Application of water source heat pump, in addition to water should be concerned about the amount of water, but also should be concerned about the water temperature, chemical composition, turbidity, hardness, salinity and corrosion and other factors. However, there is no relevant regulation on the water quality of the water source heat pump at present. The data presented in this paper refer to the relevant provisions of the cooling water quality standards and some groundwater recharge quality.
1. Temperature Surface water temperature varies with season, latitude and elevation. North of the Yangtze River and the plateau, winter surface water freezing, can not be used for heating. Summer water temperature is generally below 30 â„ƒ, can be used for refrigeration and air conditioning. Groundwater temperature varies with the physical and geographical environment, geological conditions and depth of circulation. Near the surface of the variable temperature zone, variable temperature zone for a certain depth of constant temperature, the groundwater temperature is not affected by solar radiation. Different latitudes have different depths of temperature, water temperature range 10-22 â„ƒ. With the temperature decreasing, the groundwater temperature increases with the increase of depth, and the increase depends on the geothermal warming rate in different regions and different lithologies. The average geothermal warming rate of the crust is 2.5 â„ƒ / 100m, which is greater than this value for geothermal anomalies. Geothermal anomalous area rich in groundwater can form geothermal field. According to 1997 statistics, more than 3,200 geothermal spots have been discovered in the country, 130 geothermal fields have been exploited and utilized, and 345 million cubic meters of geothermal water have been mined annually. At present, many geothermal users discharge high temperatures (about 40 â„ƒ). Application of water source heat pump can be discarded in the 30 â„ƒ temperature difference be reused, greatly improving geothermal energy utilization.
2. Sand content and turbidity Some water contains sediment, organic matter and colloidal suspended solids, the water becomes turbid. The high sand content of water can cause wear to the unit and the valve. Sand with high turbidity and water used for groundwater recharge can cause aquifer plugging. Water source for heat pump system, sand content should be <1/20000, turbidity <20 mg / liter. If the water source heat pump system is equipped with a plate heat exchanger, the particle size of solid particles in the source water should be <0.5 mm.
3. The chemical composition of water and its chemical nature Water dissolved in different ions, molecules, compounds and gases, making the water has a chemical nature of pH, hardness, salinity and corrosive, have a certain impact on the unit material. PH pH value of water is less than 7, acidic, whereas it is alkaline. Water source heat pump water source pH value should be 6.5-8.5. Hardness The total amount of Ca2 + and Mg2 + in water is called total hardness. Hard, easy to scale. Water source heat pump water CaO content should be <200 mg / L. The total amount of various ions, molecules and compounds contained in the volume of water per unit of salinity is called the total salinity. The salinity of the water source water used in the water source heat pump system should be <3 g / L. Corrosive water Cl-, free CO2 are all corrosive, the presence of dissolved oxygen to increase the corrosion of the metal pipe corrosion. Application of water source heat pump system, the corrosive, high hardness of the water source should be installed in the system anti-corrosion stainless steel heat exchanger or plate heat exchanger.
Third, water structures from water sources to water source heat pump room water supply, water structures to be built. According to different water sources, water intake structures can be divided into two categories: surface water intake structures and groundwater intake structures.
1. Surface water intake structures by structure Surface water intake structures can be divided into two kinds of activities and fixed. Active surface water intake structures floating pontoon and active cable car. More commonly used is the fixed surface water intake structures, which are more types, but generally include water intakes, aqueducts (or horizontal headers) and water collection wells. Surface water intake structures are greatly affected by water flow, velocity and water level, Construction is more complex, to choose the construction plan for the specific circumstances.
2. Groundwater abstraction structures Groundwater abstraction structures include tube wells, large wells, combination wells, radial wells and seepage channels. Table 1 lists the types and application ranges of groundwater intake structures . In practical projects, different forms should be selected according to the depth of groundwater, the thickness of aquifer, the amount of water discharged, and the technical and economic conditions.
3. Tube well water intake structures in the most common type of tube wells, generally by the borehole, borehole pipe, drainage pipe, sinking pipe composition. The well bore is drilled by a drilling machine. The well wall pipe is installed at a non-aquifer to support the hole wall of the well bore so as to prevent collapse. The well pipe and the porthole are sealed with impervious materials such as clay or cement to prevent the seepage of the ground water. Water pipes installed in the aquifer, in addition to the role of the shaft wall outside its main role is to filter water and sand; the bottom of the tube for the sinking pipe, used to sediment sediment in water to extend tube life.
Fourth, water system design and construction should pay attention to the problem
1. Feasibility Study of Water Supply Source When using water source heat pump system, you should investigate the water supply conditions of the project site, consult the local water management department or ask the professional team to conduct the necessary hydrogeological survey or hydrogeophysical survey to see if there is any Suitable for water source heat pump to use water through the feasibility study to determine the use of surface water or groundwater supply water program.
2. Design and construction of surface water source When surface water is selected, the design water intake shall take into account the guarantee factor of water temperature and water demand, the relationship between the elevation of the water intake structure and the flood season water level. Construction should also consider the water supply pipes and drainage pipe layout.
3. Pipe Well Engineering Design and Construction To choose groundwater source and pipe well water intake program, the larger projects should be based on the required amount of water and groundwater recharge needs, combined with the site environment and hydrogeological conditions, according to a certain pumping ratio to determine pumping Wells and wells number of wells, rational distribution of well spacing and well spacing. Well depth should be greater than the depth of the variable temperature, in order to ensure winter water temperature> 10 â„ƒ. In order to prevent plugging of recharging wells and ensure the long-term stable water supply of water source system, the pumping wells and recharging wells should be switched to each other. Therefore, the depth and well structure of each well should be similar. Wells in the filter pipe and filter should have a certain intensity, can withstand the pressure pumping pumping reciprocating flow.
Tube well construction quality must attach great importance to the quality of tube wells. Should find a team of professionals construction, good every aspect of the process, built high-quality wells, in order to get a larger amount of water and quality water. A quality well can be used for more than 20 years. Well into the poor quality, not only affect the life of the well, but also affect the water and recharge effect, the final impact of the normal operation of water source heat pump and heating or cooling effect. Party A should participate in the final phase of the pumping test work, identify credible and accurate pumping test results data. After completion of the tube well, Party A, the construction unit and the administrative department or the Supervisory Commission to the scene, according to the contract the amount of water, water temperature and water quality for project quality inspection. Groundwater structure and the scope of the water intake structure Form Size Depth (m) Scope Water (m3 / d)
Groundwater type groundwater depth aquifer thickness hydrogeological characteristics
Tube well diameter 50-1000mm150-600mm Well depth 20-1000m, commonly used within 300m Diving, confined water, fissure water, cave water within 200m, commonly used within 70m Greater than 5m or with aquifers Suitable for any sand, pebbles, gravel Strata and structural fractures, karst fracture zone single well 500-6000m3 / d, up to 2-3 million m3 / d
Large well diameter 2-10m, commonly used 4-8m depth of well within 20m, commonly used 6-15m diving, pressure water is generally within 10m 5-15m sand, pebbles, gravel, the permeability coefficient of 20m / d Above single-well water discharge 500-1 million m3 / d, the maximum of 2-3 million m3 / d
Radiation well set water well diameter 4-6m, radiation tube diameter 50-300mm, commonly used 75-150mm well depth of 3-12m diving, confined water depth of 12m, radiant tube from the precipitation layer should be greater than 1m generally greater than 2m good supply Coarse sand, gravel layer, but can not contain gravel single well 5000-50000 m3 / d, a maximum of 31000 m3 / d
Drainage channel diameter of 450-1500mm, commonly used for the 600-1000mm depth of 10m, commonly used 4-6m diving, riverbed infiltration water generally buried within 8m generally 4-6m good supply of coarse sand, gravel, pebble layer is generally 10-30m3 / dm, a maximum of 50--100m3 / dm
Fifth, water treatment and water-saving technology
1.Water treatment technology If the water quality of the water source is not suitable for the use of water source heat pump units, you can take appropriate technical measures to carry out water quality treatment to meet the unit requirements. Water treatment systems commonly used in water systems are the following:
Desander and sedimentation tank When the water content in the sand is high, the water source piping system can be equipped with a cyclone desander to reduce the amount of sand in the water, to avoid unit and valve suffered wear and blockage. Domestic swirl desander covers an area smaller, with different specifications, according to the standard flow rate matching desander models and the number of units. If the project site area larger, but also the construction of sedimentation tank sand removal. Sedimentation costs less than desander, but covers an area of â€‹â€‹?? large.
Water purification filter some of the water, turbidity greater, when used for recharge pipe easily lead to clogged aqueducts and aquifers, affecting the stability and service life of the water supply system. For turbid water, you can install a water purifier to filter.
Electronic water treatment instrument in the water central air conditioning system operation process, the condenser in the circulating water temperature is high, especially in winter heating conditions, the water temperature is often above 50 â„ƒ, calcium and magnesium ions in the water prone to scaling , Affect the heat transfer effect. Usually in the condenser circulating water pipe installation of electronic water treatment instrument to prevent pipe scaling. Some of the plate heat exchanger water salinity higher metal corrosive strong, such as direct access to the unit will be due to corrosion to reduce unit life. If you reduce the degree of salinity by water treatment, costly. The heat exchanger is usually used to install the middle of the heat exchanger, the water source and unit isolated, so that the unit completely avoid the water source may have a corrosive effect. When the salinity of water source water is less than 350mg / L, the water source system can not add heat exchanger, using direct supply connection. When the source water salinity 350-500mg / L, you can install stainless steel plate heat exchanger. When the water salinity> 500mg / L, corrosion-resistant titanium plate heat exchangers should be installed. Volume-type heat exchanger can also be installed, the cost is less than the plate heat exchanger, but covers an area of â€‹â€‹?? large.
De-iron equipment water central air-conditioning system can also be used to supply domestic hot water. But sometimes the source of iron in the water more, although no effect on the heating, bathing on human health will not cause damage, but iron soluble in water prone to precipitation of iron hydroxide in sanitary ware, the formation of visual sensory obstacles Brown stains. When the amount of iron in the water is> 0.3 mg / L, the iron removal treatment equipment should be installed in the water system.
2. Water-saving power-saving technology Water source heat pump air conditioning system costs and well pump running costs are often the largest operating system engineering costs, in order to rational and effective use of water, reduce water waste and electricity savings in the system design should be considered Water saving and energy saving technologies.
In order to save the amount of water used in the water source, the water mixing device can be installed in the system. The volumetric water mixing device is usually used, and the jet water mixing device can also be used. The former large volume of low cost, the latter small size with high cost.
In order to save the source water and electricity, the inverter can be installed with a variable frequency drive to control the water source pump to achieve the effect of reducing water consumption and power consumption.
VI, artificial recharge of groundwater (commonly known as recharge)
1. Artificial recharge and its purpose The so-called groundwater artificial recharge (ie, recharge), that is, will be after the water source heat pump unit to exchange heat discharged into the underground aquifer to go. In this way, groundwater can be supplemented, the water level can be adjusted, and the balance of reserves can be maintained; energy storage can be recharged to provide hot and cold sources, such as winter irrigation and summer irrigation; summer irrigation can maintain the head pressure of the aquifer and prevent land subsidence. Therefore, in order to protect the groundwater resources and ensure the long-term reliable operation of the water source heat pump system, the water source heat pump system project should generally take the recharge measures.
2. Water Quality of Recycled Water At present, there is no national standard for the quality of recharged water. The standards set by various regions and departments vary. The principle that should be noticed is that the quality of the recharged water is better than or equal to that of the original groundwater and will not cause regional groundwater pollution after the recharge. In fact, after the source water passes through the heat pump unit, only heat is exchanged, water quality hardly changes, and recharge does not cause groundwater pollution.
3. Type of irrigation According to the actual situation of the project site, ground infiltration supplies can be used to induce supply and recharge. Injectable recharging is generally carried out using tube wells, often using no pressure (gravity flow), negative pressure (vacuum) and pressure (positive pressure) recharge and other methods. Pressureless recirculation is suitable for aquifer permeability, the wells have a return water level and static water level difference. Vacuum negative pressure is suitable for deep buried water table (hydrostatic depth below 10 meters), aquifer permeability is good. Pressurized recharging is suitable for formation with high groundwater level and poor water permeability. For pumping dual wells, in order to prevent interference between wells, should control the well spacing.
4. Recharge The amount of recharging is related to hydrogeological conditions, well-forming technology and recharge method. Among them, the hydrogeological conditions are the main factors affecting the recharging amount. In general, large amount of well water injection volume is also large. In the bedrock fissure aquifer and karst aquifer recharge, in a recharge year, the return of irrigation and the unit of the amount of change is not large; in the gravel aquifer, the unit is generally the amount of water per unit of water 80% or more. In grit aquifers, the amount of recharge is 50-70% of the water produced. Fine sand aquifer, the unit of the amount of water is 30-50% of the unit of water. Irrigation ratio is to determine the number of pumping well the main basis.
5 back to prevent and deal with the management of pipe blockage is mainly used to Yang Yang method, the so-called recovery that is open pumping wells in the pumping drainage plug. The number of recharge wells per recharge well and the duration of recharge are mainly determined by the size and permeability of the aquifer particles. In the karst fissure aquifer for tube well recharge, the long-term does not rebound, recharge ability can still be maintained; loose coarse granular aquifer for tube well recharge, back to Yang time of about 1-2 times a week; in, fine-grained aquifer In the tube well recharge, back interval should be shortened, should be 1-2 times a day. In the process of recharging, we can get a good recharging effect by grasping the appropriate times and times of reheating. If we are afraid of recovering more time, we can not even rewind or rebound. As a result, pipe wells and aquifers are blocked, but not worth the candle. Reviving the duration of muddy water out to see the water so far. For fine-grained aquifers, reintroduction is particularly important. Experiments show that: between several times of recharging and continuous recharging without reinjection compared to the former to restore the water level to ensure the normal operation of recharging wells.
Seven, the application of water source heat pump restrictions
Water source heat pump central air conditioning system is an efficient, energy saving, environmentally friendly products, but not under any conditions can be applied. The constraints are the power and water. At present, China's electricity supply is adequate and easily solved. The water is its main constraint, not suitable for reliable water, you can not use water source heat pump. For example, some projects have large scale, large cooling or heating load, and many water sources are required. Although there is a certain area of â€‹â€‹the project site, drilling can also be performed. However, due to insufficient water resources, it is difficult to fully meet the project load requirements. Although some projects have groundwater beneath the site, due to the fact that the project is located in the bustling urban area, the site area is small and there is no place for pumping well water. The site environmental conditions limit the application of water source heat pump system.
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