Air conditioning water system
Overview of air conditioning water systems
Due to the limitation of space in modern high-rise buildings and the convenience of user adjustment and use, a large number of air-water air-conditioning systems are used, and the indoor cooling and heating load is borne by chilled water and hot water. In the refrigeration system for air conditioning, the water pipe system includes the chilled water system and the cooling water system.
Energy efficiency ratio of refrigeration units:
(kW/kW)
System Energy Efficiency Ratio:
(KW/KW)
Seasonal energy efficiency ratio of the system:
(KWh/KWh)
Chilled water system
The chilled water system of air conditioning is composed of: water pump, pipeline, constant pressure equipment, valve, heat exchanger, dirt remover and other main components.
The main form of chilled water system
Chilled water systems are circulating water systems, and chilled water systems can be divided into open systems and closed systems from the layout of pipes and equipment.
1. Open and closed system
(1) Open system
The system has a large amount of water and stable operating conditions, but it is easy to be polluted, and the pump head is high.
In recent years, due to the shortage of energy and the development of air-conditioning technology, many projects at home and abroad have adopted the air-conditioning method of cold storage pool, and the corresponding water system needs to adopt an open system.
(2) Closed system
The closed water system has less contact with the outside air, the possibility of pipe corrosion is small, and the energy consumption of the pump is small. The closed system must use a shell-and-tube evaporator, and the user should use surface heat exchange equipment (surface cooler or air conditioning box), and an expansion tank should be added to accommodate the volume expansion of the water in the water system when the temperature changes. In engineering design, the chilled water system mostly adopts a closed water system.
There is a big difference between the pump head of the open and closed systems:
In a closed-circuit system, the head of the pump is: the sum of the pressure loss of each component in the closed-loop waterway such as pipes, refrigeration units, heat exchangers, valves, etc.
In an open system, the pump not only bears the pressure loss of the pipes and other components, but also overcomes the height difference that lifts the water from the open tank to the highest point of the pipeline.
Things to keep in mind when designing:
For the open system, pay attention to the problem of the vacuum height of the water pump, and prevent the vaporization of the water pump at the inlet, and ensure that the water pressure at the inlet of the pump is greater than the vaporization pressure of the water.
For the closed system, a constant pressure water tank is set at the suction inlet of the water pump to ensure that the minimum operating pressure of any point of the water system is more than 5kPa, so as to prevent negative pressure at any point in the system, otherwise it is possible to suck air into the water system (evacuate) or cause some soft connections to shrink inward.
The function and installation position of the expansion tank
Its functions are: (1) to counteract the expansion and contraction of water volume when the temperature changes in the system;
(2) replenish the water loss in the system;
(3) Stabilize the pressure in the system, especially at the suction inlet of the water pump.
Installation location: try to connect to the suction inlet of the water pump, do not install any valves on the connecting pipe, the water level of the expansion tank should be higher than the maximum water level of the system more than 1m, and pay attention to its anti-freezing in winter. At present, the expansion tank is gradually being replaced by a constant pressure tank located in the pump room.
Principle of determining the capacity of the water storage tank of the open system:
(1) Store all the water capacity of the system and attach a certain safety factor;
(2) Calculated according to 5%~10% of the hourly circulating water volume of the system.
In the actual design, the greater of the above two values should be taken.
2. Direct connection system and indirect connection system
According to the different connection methods between the user's water system and the refrigeration unit, the chilled water system can be divided into direct connection system and interconnected system.
3. Different-path system and same-path system
Chilled water systems can be divided into heterogeneous systems and same-pass systems.
4. Two-control, three-control and four-control systems
5. Primary pump and secondary pump system
The primary pump system is simple in composition, easy to control, convenient in operation and management, and generally uses this kind of system.
Secondary pump system: The primary loop is responsible for the preparation of chilled water ------- the operation of constant flow, and the secondary loop is responsible for the transmission and distribution of chilled water ------- variable flow operation.
The biggest advantage of the secondary pump system is that it can supply the chilled water required on the user side in separate circuits, which is suitable for large systems.
6. Variable water volume and water determination system
Typical chilled water system analysis
1. One pump water quantity system
2. Primary pump variable water system
3. Secondary pump variable water system
Cooling water system
The inlet temperature of cooling water should generally not be higher than 32 °C, and the cooling water mainly refers to the cooling water of condenser and compressor.
(1) Direct flow cooling water system
The simplest cooling water system is the direct flow water supply system, that is, the cooling return water after heating is directly eliminated and not recycled. This kind of system is only suitable for areas with particularly sufficient water sources, such as near rivers, rivers, lakes, seas and other places, and urban tap water is not suitable for use.
(2) Circulating cooling water system
1. Natural ventilation cooling circulation system
2. Mechanical ventilation and cooling circulation system
| | Advantages: reasonable flow distribution, little interaction between each unit, high operational reliability. |
| Disadvantages: The piping pipeline layout is the most complex, the number of pipelines is large, the space is large, and the equipment cannot be used for backup. | |
| | Advantages: The water supply and return are in the form of centralized main pipes, the number of pipelines is small, the space occupied is small, the equipment can be backed by each other, and the energy consumption of the cooling tower fan when the refrigeration unit is partially loaded can be reduced by the number of cooling fans or speed control, so it is the most widely used. |
| In both main-pipe and hybrid systems, because cooling towers can be backed by each other, water systems are prone to "overflow", "bypass" and "pump-out" if the water system is not properly designed and controlled. |
When the above phenomenon occurs in the cooling water system:
An electric valve is installed on the inlet pipe of the cooling tower, but not on the return pipe;
When the outlet motor valve is closed and the water inlet motor valve is opened;
When the water distribution of the cooling tower is unbalanced;
When multiple cooling towers of different sizes are set up in parallel and the water level of the water collection tray is different, the problem of "overflow" is prone to occur.
At present, most of the cooling water systems use circulating cooling water systems, which are mechanically circulated by cooling towers. The final temperature of the cooling water in the cooling tower can generally reach a temperature of about 5°C (about 32°C) above the local wet-bulb temperature.
The cooling water system is composed of a condenser, a cooling tower, a water pump, etc., the cooling tower is based on the cooling water flow of the condenser, the low-noise type is selected, the installation location is far away from the residential area, close to the refrigerator, and is generally installed on the surface of the refrigerator house, and the outlet pipe is one size larger than the inlet pipe, because the outlet pipe is returned to the pump by gravity. The parallel use of multiple cooling towers of the same model should consider pressure equalization connection and automatic (manual) water replenishment, and each unit is a backup for each other.
3. Determination of the head of the cooling water pump
Hydraulic calculations of cooling water systems
(mH2O)
hf, hd - the total resistance along the cooling water pipeline system and the local resistance (mH2O);
hm-冷凝器阻力(mH2O)(一般为5~10mH2O);
hs – the lifting height of the water in the cooling tower (the difference in height from the cooling tower basin to the nozzle) (mH2O);
ho——冷却塔喷嘴喷雾压力(mH2O),3-6mH2O。
Design of the refrigeration plant room
Design steps
Six steps:
1. Determine the total cooling load of the refrigeration machine room
The total cooling load of the refrigeration plant room shall include the actual cooling capacity required by the user and the cooling loss of the refrigeration system itself and the cooling system.
2. Determine the type of refrigeration unit
According to the user's requirements, cooling load and its annual changes, local energy supply, etc., compare the one-time investment and annual operating cost of the refrigeration machine room, and determine the type of refrigeration unit, including refrigeration mode, refrigerant type, condenser cooling mode, etc. Secondly, the selection of cold and heat source equipment must be determined after comparison according to the principles of technological advancement, economy and safety and reliability.
From the point of view of providing the same cooling capacity and consuming primary energy, electrically driven chillers consume less energy than absorption chillers. However, for the local power supply is tight, or there is a ready-made heat source, especially when there is waste heat and waste heat can be used, the absorption refrigerator should be preferred.
Considering the energy consumption, single unit capacity and regulation, when choosing an electric drive chiller, when the nominal cooling capacity of a single unit is greater than 1758KW, it is advisable to choose a centrifugal chiller, when the cooling capacity is 1054~1758KW, it is advisable to choose a screw type or centrifugal type, when the cooling capacity is 116~1054KW, it is advisable to choose a screw type, and when the cooling capacity is less than 116KW, it is advisable to choose a scroll type.
3. Determine the design conditions of the refrigeration unit
Condensing temperature (tk)
Air as cooling medium: tk = t air inlet + (10-16) °C
Water as the cooling medium: tk = t outlet water + (2-4) °C
Evaporation temperature (t0)
Chilled water and salt water are used as refrigerants: t0 = t refrigerant - (2-3) °C
Air as refrigerant: t0 = t air supply - (6-8) °C
4. Determine the capacity and number of refrigeration units
When designing the refrigeration machine room, the change law of the annual air-conditioning load of the building and the regulation characteristics of the partial load of the refrigerator should be considered, and the model, single unit capacity, number of units and annual operation mode should be reasonably selected, so as to improve the operation efficiency of the refrigeration system at partial load, so as to reduce the annual operating cost.
Generally, 2-3 refrigeration units of the same type are selected, and the number should not be too many. Except for special requirements, there is no need to set up a standby refrigeration unit.
5. Design the water system
Determine the form of chilled water and cooling water system, select the specifications and number of chilled water pumps, cooling water pumps and cooling towers, and calculate the piping system design.
6. Arrange the refrigeration machine room
Refrigeration plant room
According to the system process, equipment type characteristics, operation and maintenance and other comprehensive factors.
(1) The width of the main passage, the operating aisle and the protrusion of the compressor and the switchboard should be ≥ 1.5m.
(2) The width of the non-main passage and operation walkway ≥ 0.8m.
(3) The protruding part of the compressor is ≥ 1m.
(4) The compressor and equipment are ≥ 1.2m away from the wall.
(5) The space for cleaning and replacing the tubes should be considered for horizontal shell-and-tube condensers and horizontal shell-and-tube evaporators.
(6) The net height of the compressor room or equipment room is generally not less than 3.5-4.5m, and the lifting height of the equipment should be considered when the equipment is installed.
(7) When the horizontal shell-and-tube evaporator is used, a closed chilled water system should be used.
(8) The vertical condenser is located outside the machine room.
(9) All kinds of instruments and controllers should be installed in a position that is easy to observe and adjust. For marine refrigeration units, issues such as vibration and moisture protection of these instruments should also be considered.
Insulation of refrigeration units and pipes
The determination of the thickness of the insulation layer of pipes and equipment should consider the economic rationality.
Minimum insulation thickness: The temperature of the outer surface should be about 2 °C higher than the average dew point temperature of the outdoor air in the hottest month to ensure that there is no condensation on the outer surface of the insulation layer.
Estimate the size of the computer room
The following is for reference only:
The location of the refrigeration machine room (including electric refrigeration and direct combustion absorption machine room) and the air conditioning machine room needs to be studied together with the equipment professional to determine its area and floor height when making a plan. Please refer to Table 1.3.2-1 and Table 1.3.2-2.
Table 1.3.2-1 of the approximate floor height of the air-conditioning room
| Gross floor area of buildings (m2) | Ceiling height of main air-conditioning machine room (m) (including refrigeration machine room and boiler room) | Backwater tanks, pump rooms, electrical rooms (including substation rooms, generators) | Gross floor area of buildings (m2) | Ceiling height of the main air-conditioning machine room (including refrigeration machine room and boiler room) | Backwater tanks, pump rooms, electrical rooms (including substation rooms, generators) |
| 1000 | 4.0 | 4.0 | 15000 | 5.5 | 6.0 |
| 2000 | 4.5 | 4.5 | 20000 | 6.0 | 6.0 |
| 3000 | 4.5 | 4.5 | 25000 | 6.0 | 6.0 |
| 4000 | 5.0 | 5.0 | 30000 | 6.5 | 6.5 |
Table 1.3.2-2 of the approximate area occupied by the air-conditioning room on the equipment floor
| Total Building Area (m2) | Air-conditioning plant room area (m2) (general approximate value) | Area of air-conditioning room by different air-conditioning methods (m2) | |
| Single air duct mode of each layer unit (fixed air volume, variable air volume) (general approximate value) | Single-duct method plus fan coil unit method (general approximate value) | ||
| 1000 | 70（7.0%） | 75（7.5%） | |
| 3000 | 200（6.6%） | 190（6.3%） | 120（4.0%） |
| 5000 | 290（5.8%） | 310（6.2%） | 200（4.0%） |
| 10000 | 450（4.5%） | 550（5.5%） | 350（3.5%） |
| 15000 | 600（4.0%） | 750（5.0%） | 550（3.7%） |
| 20000 | 770（3.8%） | 960（4.8%） | 730（3.6%） |
| 25000 | 920（3.7%） | 1200（4.8%） | 850（3.4%） |
| 30000 | 1090（3.6%） | 1400（4.7%） | 1000（3.0%） |
The area of the refrigeration machine room accounts for about 0.5%~1% of the total construction area of public buildings;
The area of heat exchange station accounts for about 0.3%~0.5% of the total construction area of public buildings;
The boiler room area accounts for about 1% of the total construction area of public buildings;
The area of air-conditioning room accounts for about 4%~6% of the total construction area of public buildings;
In terms of layered area: 500m2 is about 30m2 of air-conditioning room;
(The construction area of each floor) 1000m2 is about 35~45m2 of the air-conditioning machine room;
2000m2约要空调机房45~55m2；
3000m2约要空调机房65~75m2。
2) The requirements for the building of the refrigeration machine room, the direct combustion machine room and the air conditioning machine room:
(1) Refrigeration machine room:
a. When there is a basement, it is generally located in the basement, when there is no basement, it is located on the first floor, and some are located on the top floor, but rarely.
b. It is better to set the geometric center of the plane in the basement, which can save the investment of the pipe network and the energy consumption of the pump, because the pipe is short, the system resistance is small, so the head of the pump is low and the energy consumption is less.
c. Be close to the substation and the pumping station.
d. Consider the way out of the pipe network.
e. There should be holes for machines to move in and out.
f. Height requirements for refrigeration plant room (net height):
a) Electric refrigeration machine room: large h=4.5m, small h=3.5m.
b) Direct combustion engine room: large h=5m, small h=4m.
(2) Direct combustion engine room:
Special requirements for direct combustion engine room:
Because gas has fire and smoke prevention requirements, according to the requirements of gas specifications and fire protection specifications, the location of the machine room should meet the following requirements:
a. There are windows and doors that are directly open to the outside.
b. Ventilation.
c. There is a smoke vent surface in the basement.
(3) Air-conditioned machine room:
a. The floor load of the air-conditioning room is 700~800kg/m2.
For example, A.800m2 multi-function hall, 2×30000m3/h, computer room area 50m2.
b. The office building needs about 50 m2 of computer room area for every 1000 m2, accounting for 5%. The air-conditioning machine room should be placed in each fireproof zone, and the machine room of this fireproof zone should not be placed in another fireproof zone.
c. The air-conditioning room should be separated from the main room by at least one room on the plane, in order to avoid the incurable congenital deficiencies caused by noise and vibration.
d. The door of the air-conditioning room shall be a Class A fireproof and soundproof door.
e. Pipeline wells (air duct wells, air duct wells, and cable wells): It is important to note that gas pipelines are not allowed to be located in tube wells. When it must be set, a separate tube well must be set up, and the tube well ventilation must be done. Pipeline wells account for about 1%~2% of the total construction area. The air duct well is divided into anti-smoke and smoke exhaust tube wells, and there must be 1~2m2 anti-smoke and exhaust tube wells near each smoke-proof stairwell.
Refrigeration plant room design (example)
The refrigeration machine room is the cold (heat) source center of the entire central air-conditioning system, and at the same time it is the control and adjustment center of the entire central air-conditioning system. The central machine room is generally composed of chillers, chilled water pumps, cooling water pumps, water replenishment devices, water collection tanks, water distribution tanks, control panels, heat exchangers and other devices.
1 Selection of the location of the refrigeration plant room
The refrigeration machine room is usually close to the air-conditioning machine room, and the freon refrigeration equipment can be set up in the air-conditioning machine room, and the small-scale refrigeration machine room is generally attached to other buildings, and the larger refrigeration machine room (especially the ammonia refrigeration machine room) should be built separately. The refrigeration machine room should be located close to the air conditioning load center, and the basement of the building should generally be fully utilized. For super high-rise buildings, it can also be located on the equipment level or roof. When it is not suitable to be located in the basement due to the limited conditions, it can also be located in the podium or set up independently from the main building.
The building has a special refrigeration room, so the units are arranged in a special machine room.
2. The refrigeration method is determined
(1) When the primary energy such as electricity is sufficient, the vapor compression refrigeration unit driven by electricity should be selected (the energy consumption is lower than that of the absorption refrigeration unit);
(2) Considering from the aspects of energy consumption, single unit capacity and regulation, for relatively large load (such as about 2000kW), lithium bromide absorption chiller should be used; when choosing a vapor compression chiller for air conditioning, centrifugal type should be selected when the refrigeration capacity of a single unit is greater than 1758kW under nominal working conditions; screw type or centrifugal type should be selected when the refrigeration capacity is 1054~1758kW; screw type should be selected when the refrigeration capacity is 700~1054kW; and the refrigeration capacity should be 116~When 700kW, screw type or reciprocating type should be selected, and the refrigeration capacity is less than 116kW piston type or scroll type.
The construction site of this project has sufficient power supply and there is no special occasion for waste heat and waste heat utilization, so the use of steam absorption refrigeration unit is not considered, and the cooling capacity is 510kW, so the screw refrigeration unit is selected.
3 Selection of chillers
The chiller is the heart of the whole air conditioning system, providing cold water for the whole system and related to the daily operation of the whole air conditioning system. Therefore, the selection of chillers for air conditioning system is a very important process.
Generally, the following factors should be considered when choosing a chiller.
The performance and specifications of the unit are suitable for the use requirements. Such as cooling temperature, single-machine cooling capacity, equipment pressure capacity, etc.
The supply of energy and energy consumption is convenient and economical. For example, the possibility of power supply, heat pump or oil and gas supply, the possibility of comprehensive utilization of electricity, heat and cold, and economy.
The impact on the surrounding environment should be small. For example, the influence range of noise and vibration, the toxicity of the refrigerant used, the degree of harm to the surrounding environment for safety, and the ODP value and GWP value should be small.
Reliable operation, convenient operation and enclosure, as well as a comprehensive analysis and comparison of one-time investment and regular operating costs, have high economic benefits and good social benefits for enterprises.
Therefore, what kind of refrigerator to choose should be comprehensively analyzed and compared according to the specific situation and conditions of the project.
3.1 The installed capacity of the chiller
The chilled water system in this design is an indirect system with a total cooling load of 505.585kW, and the cooling load is attached to it to 1.2. The load of the chiller is:
Q=1.2×505.585=606.7kW
3.2 Number of chillers
Refrigeration units are generally suitable for 2~4 units, 2 units for small and medium-sized scales, 3 units for larger units, and 4 units for extra-large units. The possibility of mutual standby and rotational use should be considered between the units. Different types of units with different capacities can be used in the same station to save energy consumption. At least one unit with a high degree of automation, good regulation performance and can ensure efficient operation under partial load should be selected among the units running in parallel.
Considering the comprehensive consideration of this design, two chillers are selected, each with a cooling capacity of not less than 304kW.
3.3 Types of chillers
There are two cooling methods of chillers: air-cooled cooling and water-cooled cooling. Air-cooled chillers are suitable for small and medium-sized air-conditioning and refrigeration systems in areas with low dry-bulb temperature or large temperature difference between day and night and lack of water sources. Therefore, the design adopts a water-cooled chiller.
Screw chiller also has simple structure, compact, light weight, few wearing parts, high reliability, long maintenance cycle; can still be compressed by a single machine under low evaporation temperature or high compression ratio working conditions; using spool valve device, the refrigeration capacity can be infinitely adjusted in the range of 10~100%, and can be started under no-load conditions; it is not sensitive to wet stroke, when steam or a small amount of liquid enters the machine, there is no danger of liquid hammer; the exhaust temperature is low, mainly controlled by oil temperature, and vibration isolation measures are usually not required for basic requirements.
Referring to the sample of Carrier screw chiller, the unit model of this design selection is 30HXY110, and its performance parameters are as follows:
Table 1 Technical parameters of 30HXY110 unit
| Cooling capacity(kW) | Chilled water flow rate (m3/h) | Chilled water pressure drop (kPa) | Cooling water flow rate (m3/h) | Cooling water (kPa) | Refrigerants |
| 330 | 57 | 50 | 68 | 40 | HCF-134a |
4 Selection of cooling towers
Cooling tower is a kind of thermal equipment widely used in refrigeration system, and its function is to dissipate the heat of high-temperature cooling water into the atmosphere through heat and mass exchange, so as to reduce the temperature of cooling water. One unit corresponds to one cooling tower, and the selection should be based on its thermal performance and the surrounding environment's requirements for noise, water drifting, etc. There are two types of cooling towers commonly used: FRP and reinforced concrete. FRP cooling tower has the advantages of high cooling efficiency, small footprint, light weight, energy saving, etc., and is widely used at present.
The cooling water of small and medium-sized refrigerants is generally between 65~500m3/h, which is a medium amount of water in the cooling tower series, and the heat exchange rate of counter-flow cooling towers is higher than that of cross-flow types, so counter-flow cooling towers are mostly used.
Therefore, the design adopts a counter-flow FRP cooling tower, and the cooling tower is placed on the roof.
The safety factor of 1.1~1.2 should be considered for cooling water.
冷却水量:G=1.1×68=74.8 m3/h
According to the selected chiller, the cooling water volume of the cooling tower is not less than 74.8m3/h. According to this, with reference to the electronic sample of Lianyungang Green Company, the model CDBNL3-80 countercurrent FRP cooling tower is selected for this design. Its technical parameters are as follows:
Table 2 Technical parameters of CDBNL3-80 counterflow FRP cooling tower
| Amount of cooling water (m3/h) | Air flow(m3/h) | Inlet pressure (104Pa) | Motor power(kW) | Diameter (m) |
| 80 | 43400 | 3.03 | 2.2 | 2.5 |
5 Selection of water pumps
5.1 Selection of chilled water pumps
The selection of the pump should be selected according to the flow rate and head of the pump, and the flow rate of the primary chiller pump should be the chilled water volume of the corresponding chiller, and the additional 5%~10% of the rich amount. The number of pumps should correspond to the number of chillers. The head of the closed-cycle primary pump is the sum of the resistance of the pipeline, the pipe fittings, the evaporator of the chiller and the surface cooler of the terminal equipment, and the amount of 5%~10% should be added.
There are two chillers in this design, so three chilled water pumps are selected, and one is used for two purposes. If the chilled water volume of a single chiller is 57 m3/h, then the flow rate per pump is
Q=1.05×57=59.85 m3/h
The loss of the most unfavorable loop in this design is 65.6kPa, the loss of the chiller evaporator is 50kPa, and the loss of the machine room is 40 kPa
H=1,1×(65,6+50+40) =155,6 kPa
That is, the head of the pump is 15.56m water column, referring to the electronic sample of xx pump industry Co., Ltd., the model of the pump selected in this design is BYG80-125, two are used, one is standby, and its technical parameters are as follows:
Table 3 Technical parameters of BYG80-125 pump
| Flow rate (m3/h) | Head(m) | Efficiency (%) | Motor power(kW) | Rotation speed(r/min) | Necessary NPSH (m) |
| 65 | 17 | 70 | 5.5 | 2900 | 3.5 |
5.2 Selection of cooling water pump
The number of cooling water pumps should correspond to the chiller one by one, and the flow rate should be determined according to the technical data of the chiller, and the amount of 5%~10% should be added. The head of the cooling water pump is composed of the resistance of the cooling water system (the sum of the resistance of pipes, pipe fittings and condenser), the water level of the water tray of the cooling tower (the lowest water level of the water tank when the cooling water tank is set) and the height difference between the cooling tower and the water distributor, and the pressure required by the cooling tower and water distributor, and the additional 5%~10% of the rich amount.
In this design, three cooling water pumps are selected, with two uses and one standby. The cooling water flow rate of a single chiller is 68 m3/h, taking into account the 10% surplus, then the flow rate per pump is
Q=1.1×68=74.8 m3/h
The resistance of the cooling water system is 40 kPa, the resistance of the condenser is 42 kPa, the inlet pressure of the cooling tower is 31.5 kPa, the height difference between the water tray of the cooling tower and the water distributor is 3.5m, and the head of the cooling pump is considered to be an additional 10%.
H=1,1×(40+42+35,1+35)=152,1kPa
That is, 15.21m water column, with reference to the electronic sample of XX Pump Industry Co., Ltd., the model of the cooling water pump selected in this design is BYG80-125 (I.)A, and its technical parameters are as follows:
Table 4 Technical parameters of BYG80-125(I.)A pump
| Flow rate (m3/h) | Head(m) | Efficiency (%) | Motor power(kW) | Rotation speed(r/min) | Necessary NPSH (m) |
| 88 | 16 | 74 | 7.5 | 2900 | 4.0 |
6. Selection of water replenishment and constant pressure device
The hourly leakage of the system is 1% of the water capacity of the system, the water supply of the system is 2% of the water capacity of the system, the system water capacity of the all-air chilled water system is 0.40~0.55L/m2, and the system water capacity of the air-water system is 0.7~1.3.
If the all-air system takes 0.5, the water capacity is
L=0.5×1485=742.5 L
If the air-water system takes 1, then the water capacity is
L=1×8715=8715 L
The system replenishes water for as follows:
Q=9457.5×2%=189.15 l/h, i.e. 0.19 m3/h
The water replenishment point should be located in the suction section of the circulating water pump, the flow rate of the water replenishment pump is 2.5~5 times of the water replenishment, and the head of the water replenishment pump should be 30~50KPa higher than the pressure of the water replenishment point when the system is stationary. If you take 4 times the amount of water to be replenished, the flow rate of the water pump is
Q=4×0.19=0.76 m3/h
The head is
H=22.5+4=26.5 m
For a closed expansion tank, the total volume is:
In the formula, Vt - adjust the amount of water, take the water volume of the water pump for 3min
β - the coefficient is generally 0.65~0.85,
取β=0.7，则V=0.76/20/(1-0.7)=0.127 m3
Referring to the sample of XX Equipment Co., Ltd., the model of the floor-mounted expansion tank is GSP0.8×1-40×2×3, and its relevant parameters are as follows:
Table 5 Parameters of GSP0.8×1-40×2×3 floor-mounted expansion tank
| Pump flow rate (m3/h) | Pump head(m) | Adjustment volume (m3) | Water supply pipe diameter |
| 6.2 | 35 | 0.4 | DN89 |
7 Selection of water treatment equipment
7.1 Water softeners and softener tanks
The water supply of the air conditioner should be softened, and a softened water tank should be set up to store the water volume of the water supply pump for 0.5~1.0h.
According to the water replenishment, referring to the sample of XX Equipment Company, the SN-0.5A-BLL-T automatic water softener is selected for this design, and the soft water flow rate is 0.5m3/h.
If the softened water tank stores the water of the water replenishment pump for 1.0h, its volume is Q=0.76m3, and the water tank with a volume of 1m3 is selected.
7.2 Water Treatments
According to the flow rate of chilled water and the flow rate of cooling water, with reference to the sample of Nanjing XX HVAC Equipment Company, the model YTD-150F automatic electronic processor is selected.
8 Heat exchange equipment selection
8.1 Heat exchanger selection
Considering the winter heating, the heat exchanger is used to supply heat to the user. Under the condition of air conditioning, the heat medium is used as the water temperature of 60/50°C. The heating index is calculated according to q=60W/m2, and the heat load is 612kw.
Flow calculation: Q=Gc(t1-t2)
where G is the flow rate of the water being heated through the heat exchanger, kg/s;
c——Specific heat of water by mass, 4.2kJ/kg·°C;
t1, t2 – the temperature of the heated water flowing out of and into the heat exchanger, °C.
According to equation (7-2), G = 612× 3.6/4.2/10 = 52.46m3/h, and the heat source is 0.6mpa superheated steam provided by the waste heat of the power plant. Two TS18 plate heat exchangers produced by xx were selected, each with a maximum flow rate of 27m3/h.
8.2 Hot Water Pump Selection
The selection principle of hot water pump is the same as that of chilling water pump, the flow rate Q = 1.05×27 = 28.35m3/h, and the head is 16m water column. The model of the selected pump is BYG65-125, two are in use, one is standby, and its technical parameters are as follows
Table 6 Technical parameters of BYG65-125 pump
| Flow rate (m3/h) | Head(m) | Efficiency (%) | Motor power(kW) | Rotation speed(r/min) | Necessary NPSH (m) |
| 32.5 | 17 | 65 | 3.0 | 2900 | 3.1 |
9 Decontamination Collector and Water Filter
Filters should be installed on the orifice plates, pumps, and inlet pipes of heat exchangers in the water system to prevent impurities from entering, contaminating or clogging these equipment. This design only installs filters for chilled water pumps and cooling water pumps, and adopts commonly used Y-type filters, in which the filter has the characteristics of small dimensions, easy installation and cleaning, and the size of the filter matches the pipe diameter of the corresponding water pump inlet.
The national standard decontamination device can also be used, and the Y-type filter should also be installed before the pressure reducing and stabilization valve, and the model of the decontamination device and water filter is selected according to the diameter of the connecting pipe, and the diameter of the connecting pipe should be the same as the diameter of the main pipe.