The cold amount and heat produced by the cold source or heat source are transported to the indoor cooling or heating equipment through the energy transfer medium, and the indoor cooling load or heat load is assumed.
The energy transfer media commonly used in air conditioners are:
（1）制冷剂（如R22、R134a、R410a等）；
(2) Water - the transfer of cold amount is called chilled water, also known as cold water; The one that transfers heat is called hot water;
(3) Steam – only used to transfer heat.
Cooling the building from a cold source:
Heat source for cooling the building:
The power for the circulating flow of chilled water and hot water comes from the water pump. The water pump converts the mechanical energy of the prime mover into the mechanical energy of the water flow.
A water pump dragged by an electric motor consumes electrical energy. In the air conditioning system, the energy consumption of the water pump (called the energy consumption of transportation) accounts for a non-negligible share.
The power for the circulating flow of chilled water and hot water comes from the water pump. The water pump converts the mechanical energy of the prime mover into the mechanical energy of the water flow.
A water pump dragged by an electric motor consumes electrical energy. In the air conditioning system, the energy consumption of the water pump (called the energy consumption of transportation) accounts for a non-negligible share.
Hot and cold water pumps account for 19.5% of the total energy consumption of air conditioners.
The energy consumption of hot and cold water pumps and cooling water pumps accounts for 28% of the total energy consumption of air conditioners.
GB50189-2015 Energy Efficiency Design Standard for Public Buildings stipulates:
4.3.6 The layout of the air conditioning water system and the selection of pipe diameter should reduce the relative difference of pressure loss between the parallel loops. When the relative difference in pressure loss between parallel loops under the design conditions exceeds 15%, hydraulic balancing measures should be taken.
4.3.7 The circulating water pump of the secondary air conditioning water system heated or cooled by heat exchanger should be adjusted at variable speed.
4.3.8 Except for the similarity of the design flow, pipe network resistance characteristics and working characteristics of the water pump of the air-conditioning chilled water system and the air-conditioning hot water system, the cold water and hot water circulating pumps shall be provided separately for the air-conditioning water system of the two controls.
4.3.9 When selecting the circulating water pump of the air conditioning cold (hot) water system, the cold (heat) ratio of power consumption and transmission of the air conditioning cold (hot) water system [EC (H) R-A] shall be calculated, and shall be marked in the design description of the construction drawing. The calculation of the cold (heat) ratio of electricity consumption and cold (heat) of the air conditioning (hot) water system shall comply with the following provisions:
1. The ratio of electricity consumption and cold (heat) to cold (heat) of the air conditioning system should be calculated as follows:
Where: EC (H)R-A - the ratio of power consumption to cold (heat) of the circulating water pump of the air conditioning cold (hot) water system;
G—the design flow rate of each running pump (m3/h);
H—每台运行水泵对应的设计扬程(mH2O)；
ηb - the efficiency of the design working point corresponding to each running pump;
Q—design cold (heat) load (kW);
△ T - the specified calculation of the temperature difference of water supply and return (°C), according to Table 4.3.9-1 selection;
A—the calculation coefficient related to the flow rate of the pump, selected according to Table 4.3.9-2;
B—The calculation coefficient related to the water resistance of the computer room and the user, selected according to Table 4.3.9-3;
α - Calculation factors related to ∑L, selected according to Table 4.3.9-4 or Table 4.3.9-5;
∑L - the total conveying length (m) from the outlet of the heating and cooling plant room to the farthest user supply and return pipe of the system.
Table 4.3.9-1 △T value (°C)
Table 4.3.9-2 A-values
Table 4.3.9-3 B values
Table 4.3.9-4 α values of four-pipe cold and hot water piping systems
Table 4.3.9-5 α values of the two-pipe hot water piping system
2. The calculation parameters of the cold (heat) ratio of electricity consumption and cold (heat) of the cold (hot) water system of air conditioning shall comply with the following provisions:
1) The temperature difference between hot water supply and return of air source heat pump, lithium bromide unit, water source heat pump and other units should be determined according to the actual parameters of the unit; For units that directly provide high-temperature cold water, the temperature difference between the supply and return of cold water should be determined according to the actual parameters of the unit.
2) When multiple pumps are running in parallel, the A value should be selected according to the larger flow rate.
3) The B value of the two-pipe cold water pipeline should be selected according to the B value of the four-pipe single-cold pipe; For multi-stage pump chilling system, the B value can be increased by 5 for each additional pump; For multi-stage pump hot water system, the B value can be increased by 4 for each additional pump.
4) The calculation formula of the two-control chilled water system should be the same as that α four-control chilled water system.
5) When the farthest user is the fan coil unit, the ∑L should be determined by subtracting 100m from the total length of the water supply and return pipe from the outlet of the machine room to the farthest end of the fan coil unit.
Types of Air Conditioning Water Systems:
1. Two-control and four-control systems
2. Constant flow and variable flow system
Air conditioning handling units need to adjust the cooling capacity or heat to adapt to changes in room load.
Adjustment method: Mass adjustment - change the temperature and quantity of water - change the flow rate of water through an air/water heat exchanger (called a coil).
Water Flow Regulation Methods – Two-way Valve Adjustment and Three-Way Valve Adjustment (Bypass Adjustment)
Schematic diagram of constant flow and variable flow water system:
Single-stage and two-stage pump systems:
Pumps in air conditioning water systems:
The pressure (head) provided by the pump is to overcome the frictional resistance (also known as the resistance along the way or the resistance along the length) and the resistance (called local resistance) through various components (such as elbows, valves, tees, equipment, etc.) when water flows through the pipe.
The pressure provided by the pump in a closed water system should be equal to the total pressure loss of the water circulating in the loop for one week.
Pressure of the water pump = total loop resistance through branch (1).
Frictional resistance of the pipeline (in Pa):
Local resistance (in Pa):
where λ is the coefficient of frictional resistance;
ζ—local drag coefficient;
l、d—分别为管长和管径，m；
ρ—流体密度，kg/m3；
υ—flow velocity, m/s.
设管内流量为V（m3/s），则：
For the same piping system there are:
where, △P—total resistance of the pipeline, Pa; S—pipeline characteristic coefficient.
The water pump commonly used in the air conditioning water system is the centrifugal water pump.
Centrifugal pumps are divided into single-stage pumps and multi-stage pumps. Single-stage pumps are further divided into single-suction centrifugal pumps and double-suction centrifugal pumps, horizontal and vertical (also known as pipeline pumps).
Main performance parameters of water pump:
1）流量：单位m3/s，l/s；习惯上用m3/h。
2) Head:
Head - the energy obtained by the unit volume of water conveyed by the pump, J/m3, that is, Pa, is expressed by the pressure P. It is customary to express the head of the pump with the height of the water column H, and the unit is written as mH20, and the conversion relationship with the SI system is
1mH20=9.8×103Pa=9.8kPa ≈10kPa
例1，20mH20=20×9.8×103=19.6×103Pa=19.6kPa。
例2，100kPa=100/9.8=10.2mH20≈10mH20。
Power & Efficiency:
Effective power (in W) – the amount of energy that water receives in the pump:
The unit of pump power is usually kW, therefore:
Note: Traffic
The unit is m3/s.
Shaft power
(in kW)—The power of the input pump.
In the formula, the η is called the pump efficiency, which is generally between 0.5~0.8.
The power of the motor used in the water pump needs to consider the safety margin. The actual power consumed by the pump should also take into account the efficiency of the motor.
Speed: When the speed is changed from n1 → n2, the changes of flow, head and power are as follows:
Working Pressure:
Operating pressure – the maximum pressure that the pump may withstand. There are two types of identification:
(1) Stipulate a certain value ≤ suction pressure.
(2) The working pressure ≤ a certain value. For example, the working pressure ≤ 1.6MPa, that is, the suction pressure + head ≤ 1.6MPa.
Performance curve of water pump:
Performance curve of a single unit:
There are three performance curves:
（1）
, commonly used performance curves
（2）
（3）
The pump is most efficient at the design operating point, and the greater the deviation from it, the lower the efficiency.
Two pumps with the same performance in parallel working performance:
Fig.9. Performance curves of two pumps with the same performance in parallel
Parallel working performance of two pumps with different performance:
Fig.10. Performance curves of two pumps with different performances in parallel
The change in the performance curve when the speed changes
Fig.11. Changes in the performance curve when the speed of the pump is changed
图中A1→A2，B1 →B2，C1 →C2按3.2.4中关系式变换。 例如：原转速n1=1450rpm，变频转速n2=1305rpm，固有：
Rule:
Water System Condition Adjustment:
Pipeline valve adjustment:
When the valve in the pipeline is closed, the characteristic curve of the pipeline is changed from 1→2 to the operating point O→O'
Fig. 12 also shows the consequences of selecting too large a pump head.
Let the design flow rate be
The selected pump head HO', the actual operating point is O, and the actual flow rate is
To be in traffic
Running, the working point is at O', (HO'—HO") for the excess head, which is the excess power consumed.
Ideally: press O" to select the pump.
Frequency conversion regulation:
Adjustment of the number of pumps: Take 2 pumps in parallel as an example:
One variable speed pump and one variable frequency pump regulation:
The flow rate is between VA and VC, and the two pumps work; When the traffic ≤ VC, one inverter works.
Identification of pipeline characteristics and forms:
where H1 is the static head of the system, mH20.
H1？ The physical significance is unknown!
Open Water System:
Selection of water pump in air conditioning water system:
The pump is selected according to the flow rate and head. The flow rate is determined based on the flow rate of the equipment (chiller, direct combustion engine, flue gas engine).
Pump head = resistance of water circulating in the pipeline for one week in a single-stage pumping system, i.e., water pump→ chiller→ water separator→ air handling unit→ water collector → pump.
Two-stage pumping system:
Head of primary pump = (a→ resistance of primary pump →LC→b).
Head of the secondary pump = (b→ resistance of the secondary pump → air handling unit →a).
Constant pressure of the water system:
The constant pressure of the water system ensures the stable operation of the system under the determined pressure and prevents vacuum and overpressure.
There are many kinds of constant pressure equipment, and its main function is to keep the pressure constant at a certain point in the system; Accommodating or replenishing excess or deficient water as water temperature changes.
1. Constant pressure of expansion tank
Expansion tank on the tube:
Expansion pipe - connected to the constant pressure point, this pipe shall not be installed on the valve circulation pipe - when the expansion tank is not in the heating area, to prevent the water from freezing, and the expansion tank is connected to the return pipe at the same time, 1.5~3m apart.
Signal pipe - used to check whether there is water in the water tank, connected to the water basin of the computer room.
Overflow pipe - used for overflow when there is too much water in the expansion tank, and connect to the drain.
Drain pipe – used to drain water during tank maintenance.
Expansion tube connection position analysis:
Design: the elevation of the center of the pump is ±0.0, and the elevation of point D is 20m; Pump head 25mH20; Chiller resistance 10mH20; The water level elevation of the expansion tank is 25m;
When the expansion tube is connected at point A:
Ha=25 mH20（定压点）；
Hb=25+25=50 mH20（冷水机组承压约0.5MPa）；
Hc=50-10=40 mH20；
Hd=25-20+△hda＞0；
He=40-20-△hce＞Hd＞0。
When the expansion tube is connected at point B:
Hb=25 mH20（定压点）；
Ha=25-25=0 mH20；
Hc=25-10=15 mH20；
He=15-20-△hce＜0；
Hd=0-20+△had一般说是负压。
When the expansion tube is connected at point C:
Hc=25 mH20（定压点）；
Hb=25+10=35mH20；
Ha=35-25=10 mH20；
He=25-20-△hce，当△hce＞5 mH20，He＜0；
From the above analysis, it can be seen that the constant pressure point is suitable on the suction pipe of the water pump.
The elevation of point D is 90m, and the elevation of the water surface of the expansion tank is 95m. When the constant pressure point is still at point A, then:
Ha=95 mH20;
Hb=95+25=120 mH20。
If the pressure capacity of the unit is 1MPa, the pressure capacity of the unit < the working pressure in the system. What to do?
Solution 1: Replace the unit with high pressure capacity.
Solution 2: Move the pump to point C, and the constant pressure point remains unchanged, at this time:
Ha=95 mH20;
Hd=95-90+△hda＞0。
2. Constant pressure of the air pressure tank
The pressure tank operates between the lowest pressure P1 and the highest pressure P2, and the constant pressure point a basically fluctuates between P1~P2.
P1 is determined by the highest point of the system
P2=P1+（0.03~0.05）MPa
When the system is short of water, the tank fills the system with water, the water level in the tank drops, and the pressure is P↓.
P=P1, the make-up pump is activated to replenish water to the tank.
P=P2, the water supply pump stops, the water level in the air supply tank drops, the suction valve is opened, the air is replenished, and after multiple gas replenishment, the gas volume is ↑, and the water volume is ↓.
When the water level drops to the water level limited by the automatic exhaust valve, it automatically exhausts and the water level returns to normal.
When the temperature increases, the water volume increases, P↑. When P=P2+(0.01~0.02)MPa, open the solenoid valve and drain the water.
When P=P2-(0.01~0.02)MPa, close the solenoid valve.
When P=P2+ (0.02+0.04)MPa, the safety valve is opened and the water is discharged.
Selection of expansion tank and air pressure tank:
Selected according to the volume, volume = volume change caused by temperature change of water in the system.
The expansion tank is selected and made according to the national standard atlas.
The pneumatic tank is available and can be selected according to the sample.
Room water system of flue gas machine:
The connection mode of the flue gas machine in the air conditioning water system:
This kind of parallel connection requires different types of units to have the same water supply temperature and temperature difference under the design working conditions.
Refrigeration condition: The general supply/return temperature of the chiller is 7/12°C, which is consistent with the flue gas machine, and can be directly connected in parallel.
When the supply/return temperature of the chiller is 7/13°C, the temperature difference of the flue gas machine should be adjusted.
Heating condition: conventional design, water supply temperature 60°C, temperature difference 8~10°C;
The supply/return temperature of the flue gas machine is different for different models. Yazaki flue gas 55/48°C; Yuanda flue gas machine 65/55°C; Sanyo flue gas machine 60/56°C; Sanyo flue gas water heater 60/57.2°C.
When the temperature of the supply and return water of the equipment producing hot water is inconsistent, it needs to be adjusted to be consistent.
Configuration of flue gas pump
Number of flue gas pumps:
Some flue gas engines have the same cold water flow rate as the hot water flow rate under rated working conditions, such as Yazaki and Sanyo equipment. Some are not equal, such as Yuanda.
When the flue gas machine is connected in parallel with other refrigeration and heating equipment in a system, the flue gas machine should generally be equipped with a cold water pump and a hot water pump respectively, or a variable frequency pump for both winter and summer, for the following reasons:
1) The temperature of cold and hot water supply and return of different types of units is adjusted to be consistent, resulting in changes in flow rate.
2) The load of the building is different in winter and summer, and the temperature of cold and hot water is also different, resulting in the flow rate and system resistance of the air conditioning water system in winter and summer.
GB50736-2012 Code for Design of Heating, Ventilation and Air Conditioning in Civil Buildings requires:
8.5.4 The selection of centralized air-conditioning chilling system shall comply with the following provisions:
1 Except for minor works to install a chiller, a constant flow primary pump system should not be used;
2. For small and medium-sized projects where the temperature difference between cold water temperature and supply and return water is consistent and the pressure loss of pipelines in each region is not much different, it is advisable to use a variable flow one-stage pump system; When the power of a single pump is large, after technical and economic comparison, under the premise of ensuring the adaptability of the equipment, the control scheme and the reliable operation management, the variable flow mode of the chiller can be adopted;
3. For large-scale projects with a large radius of action and high design water resistance, it is advisable to adopt a variable flow secondary pump system. When the design water temperature of each loop is consistent and the design water flow resistance is close, the secondary pump should be set up centrally; When the design water flow resistance of each loop is quite different or the water temperature or temperature difference requirements of each system are different, it is advisable to set up secondary pumps according to regions or systems;
4. For large-scale air-conditioning chilled water systems such as centralized cooling equipment and scattered users, multi-stage pump systems can be used when the conveying distance of the secondary pump is far away and the resistance of each user's pipeline is large, or the water temperature (temperature difference) requirements are different.
8.5.5 The circulating water pump of the secondary air conditioning water system heated or cooled by heat exchanger should be adjusted at variable speed. For cooling (heating) load and large-scale projects, when the pipeline resistance in each region is large or the secondary water system needs to be managed separately, heat exchangers and secondary circulation pumps can be set up separately according to regions.
8.5.10 The design of secondary and multistage pump systems shall comply with the following requirements:
1. A balance pipe should be set up at the boundary between the cold source side and the load side between the water supply and return main pipes, and the balance pipe should be set up in the cold source machine room, and the pipe diameter should not be less than the total water supply and return pipe diameter;
2. When the secondary pump system is used and the secondary pump is set up separately by region, the plane layout of the service area, the pressure distribution of the system and other factors should be considered to reasonably determine the setting position of the secondary pump;
3. Variable speed pumps should be used for pumps at all levels on the load side of secondary pumps.
8.5.11 Except for the situation that the flow rate of the air-conditioning hot water and the air-conditioning cold water system are consistent with the resistance characteristics of the pipe network and the working characteristics of the water pump, the cold water and hot water circulation pumps shall be provided separately for the two controlled air-conditioning water systems.
8.5.12 When selecting the circulating water pump of the air conditioning hot and cold water system, the power consumption and cold (heat) ratio of the circulating water pump EC (H) R shall be calculated, and shall be marked in the design description of the construction drawing. The ratio of cold (heat) to power consumption should meet the requirements of the following formula:
8.5.13 The number of air conditioning water circulating pumps shall comply with the following requirements:
1. The number and flow rate of the first-stage pump operated by the water pump with a constant flow rate should correspond to the number and flow rate of the chiller, and should be connected with the pipeline of the chiller one-to-one;
2. There should be no less than 2 pumps at all levels in each zone of variable flow operation. When all pumps of the same level adopt variable speed adjustment, the number of units should not be too much;
3. The number of air conditioning hot water pumps should not be less than 2 units; In severe cold and cold areas, when there are no more than 3 hot water pumps, one of them should be set as a standby pump.
8.5.14 When arranging and selecting the pipe diameter of the air conditioning water system, the relative difference of pressure loss between the parallel loops should be reduced. When the relative difference in pressure loss between parallel loops exceeds 15% during the design condition, hydraulic balancing measures should be taken.
8.5.15 The design water replenishment (hourly flow) of the air-conditioning chilled water system can be calculated at 1% of the water capacity of the system.
8.5.16 The water replenishment point of the air-conditioning water system should be set at the suction inlet of the circulating water pump. When the high expansion tank is used to stabilize the pressure, the water should be directly replenished to the system through the expansion tank; When other constant pressure methods are used, if the water replenishment pressure is lower than the pressure at the water replenishment point, a water replenishment pump should be set. The selection and setting of the air conditioning water supply pump shall comply with the following provisions:
1. The head of the water replenishment pump should ensure that the water replenishment pressure is 30kPa~50kPa higher than the working pressure of the water replenishment point;
2. Two make-up pumps should be set up, and the total hourly flow of the make-up pump should be 5%~10% of the water capacity of the system;
3. When only one make-up pump is installed, a standby pump should be set up for hot water for air conditioning and hot water for cold and cold areas.
8.5.17 When a make-up pump is installed, the air-conditioning water system shall be equipped with a make-up regulating tank; The adjustment volume of the water tank should be determined according to the water supply capacity of the water source, the intermittent operation time of the softening equipment and the operation of the water replenishment pump.
Flow rate and head of flue gas pump
Flow rate:
When the water pump and flue gas machine are configured one-to-one, the flow rate of the water pump = the flow rate of the flue gas machine;
When the water pump and flue gas machine are configured in two-to-one, the water pump flow rate = flue gas machine flow rate/2;
Head:
The pump head depends on the resistance of the system, which is divided into two parts:
Load-side resistance (∑△H)l—resistance from the separator→ air handler → water collector;
Resistance on the side of the cold and heat source (∑△H)s—the resistance from the water collector → the water pump → the cooling and heating equipment → the water separator
单级泵系统循环水泵的扬程：H= (∑△H)S+(∑△H)l
The head of the primary pump in the two-stage pump system: H1 = (∑△H)S
双级泵系统中二次泵的扬程：H2= (∑△H)S
Air conditioning water systems are usually designed according to refrigeration conditions. At the time of estimation, it can be converted to the resistance during heating operation based on the resistance during cooling operation.
Conversion of cold and hot water resistance on the side of the cold and heat source (flue gas).
Set the cold water flow rate under the rated working condition of the flue gas machine
, resistance △HC; Hot water flow
, resistance △Hh1 (all of the above are sample data).
The actual operating cold water flow rate is also set
, the resistance of the pipeline in the machine room except for the flue gas machine is △Hp.c, and the flow rate of hot water
During refrigeration operation, the resistance of the cold source side:
During heating operation, the resistance of the pipeline:
Resistance of flue gas machine during heating operation:
Resistance on the heat source side during heating operation:
Load side hot and cold water resistance conversion:
The total flow rate of the load side (including flue gas and other refrigeration equipment) during refrigeration operation shall be
； The resistance of the air handling unit △Hu, the resistance of the pipeline (△Hl.p) c, then the resistance of the load side is
During heating operation, the resistance on the load side:
The head of the flue gas chiller pump in the single-stage pump system is:
The head of the hot water pump is:
The design manual recommends: when selecting the pump, it is advisable to increase the margin of 5%~10% for the calculated flow rate and head.
The flue gas machine is divided into several configurations of hot and cold water pumps:
A flue gas machine with other heating equipment in the system:
Two flue gas engines of the same specification
In the first scheme, each flue gas machine is equipped with a water pump according to Figure 22.
Option 2 is shown in Figure 23.
Air Conditioning Water System Control Requirements:
Differential pressure bypass control for single-stage pump system:
Does the differential pressure controller (PD) set the differential pressure value?
制冷工况应为(∑△H)l.c，制热工况应为(∑△H)l.h。
What are the consequences if the same differential pressure control is used in cooling and heating operations?
例：设冷水泵扬程27mH2O；冷源侧阻力(∑△H)s.c=14mH2O；负荷侧阻力(∑△H)l.c=13mH2O；热水泵扬程为20mH2O；热源侧阻力(∑△H)s.h=10.5mH2O；负荷侧阻力(∑△H)l.h=9.5mH2O。
If the differential pressure setting value is 13mH2O throughout the year, the head of the hot water pump for the heat source side is 20-13=7mH2O<(∑△H)s.h=10.5mH2O during heating operation; Causing the flow rate of the heating unit to be less than the set value.
Control of the number of units in operation:
There are many combinations of different types of units in the system, and the following only discusses the control scheme of the system of electric chiller and flue gas machine combination.
Control principle: Preferential use of flue gas machine
When the cooling load drops, the differential pressure bypass valve is opened or opened, the cold water (such as 7°C) returns to the water collector, the return water temperature drops, and the water supply temperature drops after passing through the unit.
The temperature sensor T signal → DOC → unloaded from the electric chiller, and the water supply temperature was restored to 7°C. The flue gas machine is not regulated, and the water supply temperature is below 7°C.
One of the control schemes for increasing and decreasing the machine: control according to the current value of the chiller motor
When the current value of the two electric chillers is 45% of the current value of the full load, one chiller is turned off.
When the load of one chiller drops to the minimum allowable load and the load drops again, the unit is shut down when the water supply temperature reaches a set value below 7°C.
When only one flue gas turbine is left in operation, the cooling capacity of the flue gas turbine is adjusted according to the water supply temperature to adapt to the load.
When the load increases and the water supply temperature rises to a set value of 7°C or more, one additional electric chiller is opened.
When the load continues to increase, the current value of the chiller = 110% of the current value of the full load, open 1 additional chiller.
Control scheme 2: increase or decrease the machine according to the cold water load of the system
When the load is reduced to 110% of the cooling capacity of 1 chiller, 1 chiller is shut down;
When the load increases and reaches 110% of the chiller's cooling capacity, one additional chiller is opened.
Cooling water system:
The cooling water system is shown in Figure 26:
The number of cooling towers, the number of cooling water pumps and the number of refrigeration units correspond to one by one.
The same type of cooling tower is connected in parallel on the waterway, and a balance pipeline needs to be set up to make the water level of each tower consistent.
Electric valves are interlocked on chillers, cooling water pumps, cooling towers and cooling tower inlet pipes.
Flue gas engines and direct combustion engines have certain requirements for cooling water temperature, which shall not be lower than the allowable value. Generally, it is 22~24°C.
If the cooling water temperature in the area is likely to fall below the minimum allowable temperature, measures shall be taken to prevent the water temperature from falling below the specified value. The control scheme is shown in Figure 27.
The head of the cooling water pump = pipeline resistance + LC resistance + cooling tower pre-flow water spray pressure + h
Recommended flow rate and velocity of the pipeline:
When designing the pipeline system, the pipe diameter is usually selected first according to the flow rate; In the design manual, the friction resistance R per unit length and the local resistance coefficient ζ are found, and finally the resistance of the pipeline system is calculated.
How to choose the pipe diameter? Usually the control R is within a certain range. Table 1 shows the recommended flow rates for the various pipe diameters and the corresponding flow rates and R.
Table 1 Recommended flow rate, flow rate and friction resistance per unit length of steel pipes
This article comes from the Internet, compiled and edited by HVAC South Press.