Water source heat pump related water problems

Tsinghua Tongfang artificial environmental equipment company this year to the market launch of energy-saving, environmentally friendly new products-GHP-type water source central air conditioning system. Other domestic manufacturers also have similar products available, such as "energy-saving air-conditioning", "warm air temperature and temperature", "temperature air-conditioning", "geothermal heat pump" and so on. Although the name varies, but basically the same heat pump products. Heat pumps make good use of low-temperature heat stored in air, water and soil. Water source heat pump system is one of the best ways to use energy in the 21st century. Suitable and reliable water source is the prerequisite for effective application of water source heat pump. When promoting the use of water source heat pump technology, attention should be paid to solve the related water source problem.

The term "heat pump" is derived from the word "water pump." In a natural environment, water flows downwards and heat travels to lower temperatures. Pumps pump water from low to high altitude use. The heat pump can heat energy at low temperature "pumping" (exchange transfer) to high temperature to provide access. In our country "HVAC terminology standard (GB50155-92)", the interpretation of "heat pump" is "to achieve evaporator and condenser function conversion refrigerator"; in the "New International Dictionary of Refrigeration ) ", The interpretation of" heat pump "is" a refrigeration system that heats the heat released by the condenser. " Can be seen that the heat pump is essentially the same with the refrigerator, but different operating conditions. Its working principle is driven by the electric compressor, so that the working fluid (such as R22) repeated cyclic physical phase transition process, respectively, in the evaporator gasification heat absorption in the condenser liquefied heat, the heat is constantly being exchanged Pass, and through the valve switch to make the unit to achieve heating (or cooling) function. In this process, the heat pump compressor requires a certain amount of high-energy drive, the evaporator absorbs low heat, but the heat pump heat is available high heat, in quantity is the high heat and energy consumed Absorb the sum of low heat. The ratio of heat pump output power to input power is called the coefficient of heat pump performance, that is, the COP value (Coefficient of Performance). There are a variety of heat pumps, water as a heat source and heating medium heat pump called water source heat pump. Water source heat pump coefficient of performance (ie COP value) is higher than the air source heat pump, the system performance and stability.

Water source heat pump project is a systematic project, generally by the water source system, water source heat pump room system and the end of the cooling system consists of three parts. Among them, the water system includes water, water intake structures, water pipe network and water treatment equipment.

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 ℃; cooling operating conditions, the water source temperature should be 18-30 ℃. 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.

In principle, any water source whose water quantity and water temperature can meet the heating load or refrigeration load of users and whose water quality does not cause any corrosive damage to the equipment of the unit can be used as the water source for the water source heat pump system, either as a regenerative water source or Is a natural source of water.

3.1 Recycled water

Refers to the manual discharge of used but treated urban sewage, industrial waste water, mine waste water, oilfield wastewater and thermal power plant cooling water and other water sources, the conditional use of renewable water sources users, turning waste into profits, can reduce the initial investment and save water resources . But for most users, the water of choice in nature is available.

3.2 Nature in the water

Water in nature is distributed 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.

3.3 The choice of water and water

The amount of water is the key factor that affects the work efficiency 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 amount of water 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.

Water in nature is in an endless cycle of movement, constantly with the atmosphere, soil and rock and other environmental media contact, interact with each other to make it with 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.

4.1 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 ℃, 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 ℃. 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 ℃ / 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 ℃). Application of water source heat pump can be discarded in the 30 ℃ temperature difference be reused, greatly improving geothermal energy utilization.

4.2 sand content and turbidity

Some sources contain sediment, organic matter, and colloidal suspensions that make the water 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.

4.3 The chemical composition of water and its chemical properties

Natural water is dissolved in different ions, molecules, compounds and gases, making water has a pH, hardness, salinity and corrosion and other chemical properties of the unit material has a certain impact.

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.

From the water source to the 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.

5.1 Surface water intake structures

According to the structure of surface water intake structures can be divided into two 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.

5.2 groundwater water structures

Groundwater intake structures include tube wells, large wells, combination wells, radial wells and seepage channels. Table 1 lists the types of groundwater intake structures and the applicable scope [1]. 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.

5.3 tube well

The most common type of groundwater withdrawal structures are tube wells, which generally consist of wellbores, borehole tubes, drainage pipes, and grit tubes. 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.

6.1 Water Supply Feasibility Study

When it is planned to adopt water source heat pump system, it is necessary to investigate the water supply conditions of the project site, consult the local water management department or ask the professional team to carry out the necessary hydrogeological survey or hydrogeophysical survey to find out whether there is a suitable water source for water source heat pump to pass Feasibility study to determine the water supply scheme using surface or groundwater.

6.2 Surface Water Engineering Design and Construction

When surface water is selected, the design water intake shall take into account the factors 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.

6.3 Pipe Well Engineering Design and Construction

When choosing the scheme of groundwater and tube well water intake, for the large-scale project, the number of wells for pumping and recharging should be determined according to the required ratio of irrigation water and groundwater recharge and the site environment and hydrogeological conditions , Reasonable layout of wells and well spacing. Well depth should be greater than the depth of the variable temperature, in order to ensure winter water temperature> 10 ℃. 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.

6.4 tube construction quality

We 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.

7.1 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 ​​?? 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 ℃, 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 ​​?? 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.

7.2 water saving technology

Water source heat pump air-conditioning systems and water pump running costs are often the biggest expense of operating system engineering costs, in order to rational and effective use of water sources to reduce water wastage and electricity savings in the system design should consider the use of water-saving and energy-saving technology measures .

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.

8.1 artificial recharge and its purpose

The so-called artificial recharge of groundwater (that is, recharge), that is, will be water source heat pump unit to exchange heat discharged after the water 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.

8.2 Recharge water quality

At present, there is no national standard for the quality of recharged water and the standards set by various regions and departments are different. 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.

8.3 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.

8.4 Recharge volume

The amount of recharge is related to hydrogeological conditions, well-forming technology and recharge method, among which the hydrogeological conditions are the main factors that affect the amount of recharge. 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.

8.5 back up

In order to prevent and deal with tube blockage, the main method is to use pull-back method. The so-called pull-back method is to block the blockage in pumping and drainage in the recharging well. 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.

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 ​​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.

10.1 Project Overview

In order to control air pollution in Beijing, Beijing Institute of Geological Prospecting undertook the completion of the project of heating and geothermal water source heat pump heating demonstration project. The schematic diagram of the project is shown in Figure 1. There are 6 office buildings and family buildings in winter with a building area of ​​about 30,000 square meters. The brick-concrete structure and the original HVAC are designed to be heated by coal-fired boilers. Back to system, cast iron four columns 813 radiator. The heat source of the demonstration project is a geothermal well with a water temperature of 68 ℃ and a water volume of 125m3 / h. The 45m shallow Quaternary wells of both eyes have a water temperature of 16 ℃ and a single well discharge volume of 50 m3 / h with well spacing of 100m.

Figure 1 Geothermal heat pump heating project plan

Figure 2 Schematic Diagram of Geothermal and Water Source Heat Pump Heating Process

The project due to geothermal drilling construction cycle limit, heating test carried out in two phases. Project flow diagram shown in Figure 2. The first phase of the project from December 5, 1999 to March 8, 2000 to 16 ℃ groundwater as a heat source, the use of water source heat pump on the fifth floor of a comprehensive office building heating test. The floor area of ​​4078m2, building height 18m, Panax wall, single-pane glass. Heating before the operation of 14-year-old heating pipe for chemical cleaning, replacement of some rust radiator. In order to compare the effect of heating and cooling in summer, a fan coil was installed in the first and second floor office buildings. Groundwater discharged from No. 1 well at 16 ℃ is sent to the heat pump unit for heat absorption, and then injected into the ground from No. 2 well to protect the underground water source. Heat pump output of 52 ℃ hot water on the office building heating.

The second phase since March 8, 2000 (geothermal wells completed) to April 5, conducted a geothermal water source heat pump heating operation test. Geothermal wells 68 ℃ geothermal water on 25,000 m2 building "once" heating, part of the hot water through the board change to 13 ℃ after the temperature as a waste water discharge, board side of the cold water circulation heat pump heat conversion after the output 52 Hot water on the office building for heating. The summer of 2000, the use of 1,2 pumping, well irrigation and water source heat pump units on the building for refrigeration and air conditioning.

10.2 The main technical parameters

Heat pump host: Tsinghua Tongfang artificial environment equipment company GHP type water source central air conditioning system, a Taiwan, the nominal heating capacity of 360kW, cooling capacity of 275 kW, installed power of 64 kW, heating conditions, the condenser out of the backwater temperature 52 ℃ / 42 ℃, the evaporator back to the cooling water temperature 7 ℃ / 12 ℃, heating / cooling conditions switch by the water pipeline valve switch. Plate heat exchanger: BR0.24 Ⅶ type 1, 12 m2, 300 kW, 40-13 / 10-15 ℃, stainless steel. Cold water submersible pump: QJ50-50 / 6 type 2, flow 50m3 / h, lift 50m, power 7.5kW. South House Heating Circulation Pump: ISG 80-160, Taiwan, flow 50 m3 / h, lift 32 m, power 7.5 kW. Cold water circulation pump: DFB80-32B type 2, flow 42 m3 / h, head 24m, power 5.5kW.

10.3 operating results

Winter heating, water source heat pump running for 126 consecutive days, stable performance, with the return water temperature (52/42 ℃) control press start and stop, the average hourly consumption of 40 degrees, cold water well water consumption 18 m3 / h, outdoor temperature - 10 ℃, the majority of room temperature 18 ℃, a few rooms at the end of the heating system 15-16 ℃, the installation of a wind-tray room temperature up to 20-25 ℃. Summer cooling, water source heat pump continuous operation of 120 days to chilled water backwater temperature (12 ℃) control press start and stop, the outdoor temperature of 33-40 ℃, the indoor temperature of 22-26 ℃.