Solution. Calculation of pump motor power

In order for the water supply system to work uninterruptedly, the main thing is to choose the right pump.

Pumps are used to supply water from a well or well or to recirculate it. In order for the system to work efficiently and uninterruptedly, and also in order not to overpay for a model with excessive characteristics, they need to be selected. Let's consider how to calculate a pump for water supply and select the parameters of these units.

How to find out the pump flow rate

The calculation formula looks like this: Q=0.86R/TF-TR
Q – pump flow rate in m.cub./h;

R – thermal power in kW;

TF – coolant temperature in degrees Celsius at the system inlet,

Layout of the heating circulation pump in the system

Three options for calculating thermal power

Difficulties may arise in determining the thermal power index (R), so it is better to focus on generally accepted standards.

Option 1. In European countries it is customary to take into account the following indicators:

• 100 W/sq.m. – for small private houses;
• 70 W/sq.m. – for high-rise buildings;
• 30-50 W/sq.m. – for industrial and well-insulated residential premises.

Option 2. European standards are well suited for regions with mild climates. However, in the northern regions, where there are severe frosts, it is better to focus on the standards of SNiP 2.04.07-86 “Heating networks”, which take into account external temperatures down to -30 degrees Celsius:

• 173-177 W/sq.m. – for small buildings whose number of storeys does not exceed two;
• 97-101 W/sq.m. – for houses of 3-4 floors.

Option 3. Below is a table from which you can independently determine the required thermal power, taking into account the purpose, degree of wear and thermal insulation of the building.

Table: how to determine the required thermal power

Formula and tables for calculating hydraulic resistance

Viscous friction occurs in pipes, shut-off valves and any other components of the heating system, which leads to specific energy losses. This property of systems is called hydraulic resistance. A distinction is made between friction along the length (in pipes) and local hydraulic losses associated with the presence of valves, turns, areas where the diameter of pipes changes, etc. The hydraulic resistance indicator is denoted by the Latin letter “H” and measured in Pa (pascals).

Calculation formula: H=1.3*(R1L1+R2L2+Z1+Z2+….+ZN)/10000

R1, R2 indicate pressure loss (1 – supply, 2 – return) in Pa/m;

L1, L2 – pipeline length (1 – supply, 2 – return) in m;

Z1, Z2, ZN – hydraulic resistance of system components in Pa.

To facilitate calculations of pressure loss (R), you can use a special table that takes into account possible pipe diameters and provides additional information.

Table for determining pressure loss

Averaged data for system elements

The hydraulic resistance of each element of the heating system is given in the technical documentation. Ideally, you should use the specifications specified by the manufacturers. In the absence of product passports, you can rely on approximate data:

• boilers – 1-5 kPa;
• radiators – 0.5 kPa;
• valves – 5-10 kPa;
• mixers – 2-4 kPa;
• heat meters – 15-20 kPa;
• check valves – 5-10 kPa;
• control valves – 10-20 kPa.

Information about the hydraulic resistance of pipes made of various materials can be calculated from the table below.

Pipe pressure loss table

Water pipes

In addition to the calculation method in the usual way, we will also give several examples of working with online calculators.

First, let's look at cold water supply systems, that is, regular plumbing, then we'll touch on hot water supply (abbreviated as DHW). Moreover, we will not talk about the choice of powerful pumps that are installed at water supply network stations - our article is about the water supply of small houses and cottages.

If the house is connected to a central water supply, then in most cases the necessary pressure is created at water supply stations or water towers. Therefore, pumps in this case are usually not needed. The exception is high-rise buildings, where normal pressure from the water supply does not allow water to be supplied to the uppermost floors - booster pumps are installed there.

Interesting fact. Columns of water 10 meters high create a pressure of one atmosphere (0.1 MPa), so the difference in pressure on the first and third floors is approximately this amount. If we take for example the tallest building in the world, the Burj Khalifa, with a height of 828 meters, then in order for the water to even reach the top floor, a pressure of about 84 tons of atmospheres is needed. Naturally, no pipes can withstand it, so the pumps are installed in stages across several floors.

To supply water to such buildings, the pressure created in the water supply is not enough; booster pumps are required

With an autonomous water supply system, you cannot do without pumps. As a rule, either conventional (surface) or submersible (deep) pumps are used. With very rare exceptions, their drive is electric.

The choice depends on the specific situation or the wishes of the customer. Let's look at how they differ and the most important characteristics that we will need when carrying out the calculation.

Conventional pumps

Conventional (surface) pump for water supply

Centrifugal pumps are almost exclusively used to supply water. In them, the liquid is captured by the blades in the center of the rotating impeller and is thrown due to centrifugal force to its perimeter, where the pressure pipe is located. In the center where water is taken, a vacuum is naturally created.

Attention. When starting such a motor without water (dry running), without encountering fluid resistance, the wheel, especially on powerful large pumps, can spin very quickly and break off the shaft or be damaged in other ways. Therefore, this situation is prevented by proper startup, installation of check valves at the inlet (they prevent water from draining from the housing) and the use of special automation.

Typically, two types of pumps are used - with an oil seal on the drive shaft and more modern ones with a floating rotor.

• In the first, the impeller drive shaft passes through the housing (scroll) in which the impeller rotates. This place is sealed with oil seals or mechanical seals. The shaft can rest on its own bearings, which are located in the console and connected to the electric motor through a coupling.
• Another option for such a pump is a monoblock. In it, the impeller is mounted directly on the impeller. The first type is more reliable and easier to maintain and repair. The second one is more compact.
• Pumps with a floating rotor do not have seals at the shaft passage. In it, as the name implies, the rotor of the electric motor is located in a housing volumetrically connected to the volute. The stator electromagnets create torque through the wall, the water cools the rotor and lubricates its bearings.

Such pumps are compact and reliable. The downside is the difficulty of repair - you can’t simply replace the motor; you need to completely disassemble the pump.

In addition, standard electric motors cannot be used in such a unit. However, they rarely fail and do not require maintenance throughout their entire service life (many manufacturers guarantee this).

Pump characteristics

Now let's move on to the most important thing.

The type of conventional pump selected for your off-grid water supply system affects the following:

• cost of installation of an autonomous water supply system;
• costs of its operation;
• frequency of maintenance;
• complexity and cost of installation;
• dimensions of the pump installation site.

Otherwise, when calculating, you need to focus on more important characteristics:

1. Suction depth : It determines the mark below the pump from which it can draw water. It is usually determined in meters.
2. Head : It is expressed in terms of the outlet pressure of the pump.
3. Performance : how many cubic meters the pump can pump per hour.

You also need to pay attention to such figures as energy consumption (power); with equal characteristics, it is advisable to give preference to more economical models. However, the price for them is usually higher, so it is advisable to calculate how long it will take for a more expensive model to pay for itself (however, this is an economic calculation).

If the service life is less than the payback period of an expensive pump, then, most likely, you should not overpay, but buy a pump that is more power-hungry.

Deep well pumps

Deep well pumps

They differ from ordinary ones in that they are immersed in water, that is, in the casing of a well, a well, or even an ordinary body of water. By design, they differ from conventional pumps in such features.

1. Most often, they have not one impeller, but several, up to a dozen, located one behind the other. The suction of one is connected to the output of the next (labyrinth system).
2. If conventional pumps most often have a horizontal shaft arrangement, then deep-well ones are always vertical. This is due to their location in well casing pipes of limited diameter, which are also vertical (installation in a well or reservoir is a special case to which designers pay little attention).
3. Electric motors are also of a special design. They do not have casing fins, as they are cooled by water.

Attention. You cannot run a deep-well pump not submerged; it is not designed for such a mode and can immediately burn out.

Also, the motors of these units have more elongated dimensions along the axis with a smaller diameter. This is also related to installation in wells.

In addition to centrifugal pumps, vibration and submersible pumps are also used for small water supply systems. This, for example, is the well-known “Rucheek” (pictured below). According to the principle of operation, it is similar to ancient piston pumps (including bicycle ones), although the piston stroke is shorter, the oscillation frequency is higher (that’s why it is called vibrational), and an electromagnet is used for the drive.

Despite the slightly worse characteristics compared to centrifugal deep-well pumps, everything that is said in our article about them fully applies to the “Rucheyok” and its analogues.

Brook type pump

Characteristics of deep-well pumps

The definitions of the characteristics of deep-well pumps are exactly the same as for conventional ones. The only difference is that the suction is not regulated for them, since the vacuum at the inlet is not important, the unit is already surrounded by water.

But many deep-well pumps have an order of magnitude greater pressure than conventional ones. When installed in a deep well, they must immediately overcome the pressure in a long riser pipe, and then create the required pressure in the water supply.

They are also considered to be somewhat more economical due to water cooling. But this advantage is minimal over pumps with a floating rotor. They also use a similar principle, although the stator does not have contact with the liquid on all sides. Completely washing the pump with water gives minimal savings of a fraction of a percent.

Which pump to choose: deep or surface (regular)

Quite a difficult question - let’s compare their advantages and disadvantages.

Conventional pumps

Pros:

• They are easier to mount on a surface.
• Inspection, maintenance and repair are also easier.
• Typically, conventional pumps are cheaper.

Minuses:

• A place or room for installation is required.
• Protection against dry running is required.
• In terms of suction depth, they are inferior to the pressure of deep-well pumps, so they cannot be used to draw water from deep wells.

Deep well pumps

Pros:

• Can work in deep wells.
• They do not require arrangement of installation sites. Water from the riser pipe can be directly supplied to the water supply system.
• If the pump is immersed below the minimum water level in a well, well or reservoir, it is protected from “dry running”.

Minuses:

To remove deep-well pumps, it is often necessary to use lifting mechanisms

• When installed in wells deeper than 10 meters, removing the pump along with the water-lifting pipe for inspection and repair with your own hands is often impossible; lifting mechanisms must be used.
• If for some reason the pump was torn off from the pipe and insurance (unless, of course, you forgot about the latter), it is quite difficult to get it out.

Interesting fact. The author of this article had to remove the accidentally missed pump using a special trap. After it was “saved,” five more units, mostly almost completely destroyed by corrosion, were pulled out of the well, which were lost by previous operators over the more than thirty-year history of the engineering structure.

• The power cable supplying the unit must be protected from exposure to ambient water. Often its breakdown, which occurs from damage to the insulation, leads to the need to remove the pump, and this, as we said above, is difficult.

Therefore, we will give one piece of advice: if you do not have a very deep well, or even more so, it is just a well and there is space for installation on the surface, you should still give preference to conventional pumps. They are cheaper and easier to operate.

Often, as an advantage of conventional pumps over deep pumps, they also consider the fact that the deep pump is protected from contamination only by a mesh filter on the casing, while the regular one can be additionally protected by multi-stage filters on the suction.

This is a false fact:

1. Any water purification installation works stably only with sufficient pressure, that is, it must be installed after the pump.
2. Pumps for water supply (no matter deep or ordinary) are designed for the presence of impurities in the source water, and they do not significantly reduce their service life. Of course, if you do not pump a mixture of sand and water directly, the latter effectively retains the mesh filter.

Now, having dealt with the choice of pump by type, let’s move on directly to choosing it by characteristics.

A little about pressure units

Pump specifications for measuring pressure can use more than just Pascals

Everyone knows the usual atmospheric pascals well from school, but less well-known units may also be present in the pump characteristics.

1. A meter is a meter of a column of water. As mentioned above, it is equal to one tenth of the atmosphere.
2. A bar is a non-systemic unit (but approved for use in our country) approximately equal to one atmosphere.

Attention. You may also come across such an incomprehensible term as “excessive pressure”. Don’t pay attention, almost all instruments and calculations for water supply use the term “pressure” to mean this.

The absolute pressure will be one atmosphere higher, that is, the pressure that already exists on the surface of the earth, where water supply systems operate. Even in a glass, water is under an absolute pressure of one atmosphere.

Selection (calculation) of a pump for water supply according to characteristics

Let’s make a reservation right away: we do not calculate water supply pumps using hydraulics, that is, we do not take into account the resistance to water flow in pipes and on shut-off elements. For small water supply systems of a private home, it is scanty, and the calculations are complex.

Note. Some pumps have parts that are made of materials that, according to sanitary and hygienic standards, are unacceptable for use in water supply networks. Therefore, you need to choose models that are approved for these purposes.

To select a pump we need to take several steps, the instructions will be as follows.

Choosing performance

Pump performance depends on water flow per unit time

The first thing you need to focus on is water consumption per person per day, it is 400-500 liters. If you have a storage tank of sufficient capacity (like a water tower), you can follow these steps.

1. We multiply the average consumption by the number of people living in the house (for example, an average family of four), plus one person for possible guests (if you have them): 500x5 = 2500 liters.
2. Divide by the number of hours per day: 2500:24 = 104 l/h, this is the average hourly consumption.
3. Since it is desirable that the pump does not work constantly in order to avoid overheating and failure, we additionally divide it by the time of its operation. It is usually recommended that the operating time should not exceed 80%, that is, we divide by 80:100 = 0.8, we calculate: 104:08 = 130 l/h. We take this characteristic for the pump as well.

But, as a rule, storage tanks are not used in water supply systems of small houses. The most common scheme is a combination of a pump and a small-sized tank (hydraulic accumulator), as well as automation systems. Usually they buy an already assembled block of these devices from sellers, and in everyday life (which is not entirely true) they call them pumping stations.

In this case, calculating by daily consumption is not entirely correct. The pump does not operate constantly, feeding a large storage tank (it does not need to be used as a hydraulic accumulator from a small container), but only during water consumption.

So, for example, if mom decides to wash the dishes, dad decides to wash his hands after repairing the car, one child takes a shower, and the other uses the toilet, and the washing machine is working, then the water consumption may be much more than the daily average. Therefore, the calculation of the water supply pumping station and similar systems should be carried out based on these peak analyzes.

To do this, we count all the available water fixtures in the house. Then we take their hourly expenses. To do this, you can use the table in Appendix 2 to SNiP 2.04.01-85. It is given below.

Water consumption and other characteristics of plumbing fixtures

Next, we make a list of all plumbing fixtures and their hourly costs. Moreover, we take not only cold water, but the total flow rate, because hot water is heated cold water, which is taken from the same water supply system.

Advice. In order not to count manually, it is easier to use Excel, as in the table below.

As a result, we obtained the maximum water flow rate in the water supply of your home - 2493 liters per hour. This figure is even a little overestimated, since it is unlikely that all devices will be turned on at the same time; it can be reduced by a factor of 0.9-0.8. We get: 2493x0.8=1994 l/h. True, if the house is small and there is only one kitchen and bathroom, this is not worth doing.

Based on our resulting peak water flow per hour, we will select the pump performance in the future.

Selecting the pressure

Tall cottages require more pressure

Here the choice depends on whether it is a deep-well pump or a regular one.

• For a conventional pump, everything is as simple as possible: according to standards, the pressure in the water supply should be in the range of 0.05-0.5 MPa, that is, from half to five atmospheres. As practice shows, for normal operation of washing machines, dishwashers and other household appliances, it is desirable that the pressure is not less than 1 atmosphere, i.e. 0.1 MPa, so we will choose a pump with exactly this pressure.

If you have a cottage with more than three floors (which is rare), then you need to make sure that there is normal pressure at the top. With a standard ceiling height of about 3 meters, there will be no pressure on the fourth floor, so we add 0.1 MPa.

That is, in most cases, when selecting a pump for water supply, a pressure of 1-1.5 atmospheres (0.1-0.15 MPa) is sufficient.

• When choosing an option with a unit installed in a well, calculating the water supply pump for pressure becomes more complicated, but not much - you just need to take into account its immersion mark. That is, if water is taken from a depth of 15 meters, to the pressure calculated, as in the previous case, we add 1.5 atmospheres (15:10 = 1.5) or 0.15 MPa (15:100 = 0.15 ). We consider: 0.15 + 0.1 = 0.25 MPa, and we will be guided by this figure when choosing a specific pump model.

Suction depth (suction)

The deeper the well, the greater the pump suction should be.

The easiest parameter to select. For deep-well pumps it is not needed and is not described in the characteristics at all, since water is taken from the level at which the pump is located.

In the case of a conventional surface pump, it is necessary that this characteristic be slightly greater than the difference between the elevations of the intake and the location of the pump. The reserve is needed for unforeseen situations, for example, during a drought the level will drop and the intake will have to be lowered.

It is easy to select, for example, the pump is located at ground level, and water is drawn from a depth of 10 meters. This means that the suction must be more than 10 meters.

It is not worth giving a multiple supply; if the intake is located at a depth of 1 meter, then you should not take a pump with a suction depth of 15, 3-5 is enough. This is due to the fact that the greater this characteristic, the more complex and expensive the pump.

Direct selection

When all the parameters are known, you can select a pump or station from price lists and directories. You don’t even have to select a model yourself. Almost all sellers' websites have filters into which we enter the necessary characteristics, then a list of the most suitable models is displayed on the screen.

For example, to make a selection on a website, you only need to take a few steps. We need a surface pump with a capacity of 1.5 liters per minute with a lift height (suction) of 5 meters and a pressure of 1.5 atmospheres (15 meters). Let's do the following.

• On the tab at the top, click on the “surface pump” tab.

Pump type selection

• Then you can enter the necessary parameters in the filter on the right of the page. Additionally, you can select the price range, brand, power, drive type (electric motor, internal combustion engine), etc. If the calculation of the water supply station was carried out, then you can find it.

Entering pump parameters

• After this, we press enter, and our page displays units that meet the specified characteristics.

Pumps selected according to specified parameters

• Additionally, you can select the order in which the pumps will be displayed on the page. That is, options are possible for increasing or decreasing price, popularity, or immediately newer or older models and vice versa. To do this, click on the buttons at the top of the page.

Selecting the order in which models are displayed on the page (sorting)

Why do you need a circulation pump?

It is no secret that most consumers of heating services living on the upper floors of high-rise buildings are familiar with the problem of cold radiators. Its cause is the lack of necessary pressure. Because if there is no circulation pump, the coolant moves slowly through the pipeline and, as a result, cools down on the lower floors

That is why it is important to correctly calculate the circulation pump for heating systems

Owners of private households often face a similar situation - in the most remote part of the heating structure, the radiators are much colder than at the starting point. Experts consider the optimal solution in this case to be the installation of a circulation pump, as it looks like in the photo. The fact is that in small houses, heating systems with natural circulation of coolants are quite effective, but even here it would not hurt to think about purchasing a pump, since if you properly configure the operation of this device, heating costs will be reduced.

What is a circulation pump? This is a device consisting of a motor with a rotor immersed in a coolant. The principle of its operation is as follows: by rotating, the rotor forces a liquid heated to a certain temperature to move through the heating system at a given speed, resulting in the creation of the required pressure.

Pumps can operate in different modes. If you set the circulation pump in the heating system to maximum operation, a house that has cooled down in the absence of the owners can be warmed up very quickly. Then consumers, having restored the settings, receive the required amount of heat at minimal cost. Circulating devices come with a “dry” or “wet” rotor. In the first version, it is partially immersed in the liquid, and in the second - completely. They differ from each other in that pumps equipped with a “wet” rotor make less noise during operation.

Nominal head

Pressure is the difference between the specific energies of water at the outlet of the unit and at the entrance to it.

The pressure happens:

• Volume;
• Mass;
• Weight.

Before buying a pump, you should ask the seller everything about the warranty
. Weight matters in conditions of a certain and constant gravitational field. It increases as the acceleration due to gravity decreases, and when weightlessness is present, it is equal to infinity. Therefore, the weight pressure, which is actively used today, is inconvenient for the characteristics of pumps for aircraft and space objects.

Full power will be used to start. It is supplied externally as the drive energy of an electric motor or with the flow of water, which is supplied to the jet apparatus under a special pressure.

Types of power of the device for the well

When releasing devices, the manufacturer uses the following designations for power types:

1. P1 (kW). Input electrical power is that which the electric motor takes from the electrical network.
2. P2 (kW). On the shaft of the electric motor - the one that it gives to the shaft. The input electric power of pump P1 is equal to the shaft power of electric motor P2 divided by the efficiency of the electric motor.
3. P3 (kW). The input indicator of the hydraulic pump is equal to the value P2 when the coupling that connects the shaft of the device and the shaft of the electric motor does not consume electricity.
4. P4 (kW). The useful power of submersible hydraulic pumping equipment is that which comes out during operation in the form of water flow and pressure.

Without relevant experience, it is not recommended to install the pump yourself.
You can calculate the indicator online; there is a special calculator.

Adjusting circulation pump speeds

Most circulation pump models have a function for adjusting the speed of the device. As a rule, these are three-speed devices that allow you to control the amount of heat that is sent to heat the room. In the event of a sharp cold snap, the operating speed of the device is increased, and when it warms up, it is reduced, despite the fact that the temperature in the rooms remains comfortable for staying in the house.

To change the speed, there is a special lever located on the pump body. Models of circulation devices with an automatic control system for this parameter depending on the temperature outside the building are in great demand.

Selection of a circulation pump for a heating system criteria

When choosing a circulation pump for the heating system of a private home, they almost always give preference to models with a wet rotor, specially designed for operation in any household lines of varying lengths and supply volumes.

These devices have the following advantages compared to other types:

• low noise level,
• small overall dimensions,
• manual and automatic adjustment of the number of shaft revolutions per minute,
• pressure and volume indicators,
• suitable for all heating systems of individual houses.

Pump selection by number of speeds

To increase operating efficiency and save energy resources, it is better to take models with stepwise (from 2 to 4 speeds) or automatic control of the electric motor speed.

If automation is used to control the frequency, then energy savings compared to standard models reach 50%, which is about 8% of the electricity consumption of the entire house.

Rice. 8 The difference between a fake (right) and an original (left)

What else to pay attention to

When purchasing popular Grundfos and Wilo models, there is a high probability of counterfeiting, so you should know some of the differences between the originals and their Chinese counterparts. For example, German Wilo can be distinguished from a Chinese counterfeit by the following characteristics:

• The original sample is slightly larger in size and has a serial number stamped on its top cover.
• A raised arrow in the direction of fluid movement in the original was placed on the inlet pipe.
• The de-airing valve on the fake is yellow in brass color (the same color in the Grundfos analogues)
• The Chinese analogue has a bright shiny sticker on the reverse side indicating energy saving classes.

Rice. 9 Criteria for selecting a circulation pump for heating

How to choose and buy a circulation pump

Circulation pumps face somewhat specific tasks, different from water pumps, well pumps, drainage pumps, etc. If the latter are designed to move liquid with a specific outlet point, then circulation and recirculation pumps simply “drive” the liquid in a circle.

I would like to approach the selection in a somewhat non-trivial way and offer several options. So to speak, from simple to complex - start with the manufacturers’ recommendations and lastly describe how to calculate a circulation pump for heating using formulas.

Select a circulation pump

This simple way to select a circulation pump for heating was recommended by one of the WILO pump sales managers.

It is assumed that the heat loss of the room per 1 sq. m. will be 100 W. Formula for calculating consumption:

Total heat loss of the house (kW) x 0.044 = circulation pump flow rate (m3/hour)

For example, if the area of ​​a private house is 800 sq. m. the required flow rate will be:

(800 x 100) / 1000 = 80 kW - heat loss at home

80 x 0.044 = 3.52 cubic meters per hour - the required flow rate of the circulation pump at a room temperature of 20 degrees. WITH.

From the WILO range, the TOP-RL 25/7.5, STAR-RS 25/7, STAR-RS 25/8 pumps are suitable for such requirements.

Regarding the pressure. If the system is designed in accordance with modern requirements (plastic pipes, closed heating system) and there are no non-standard solutions, such as high floors or long heating pipelines, then the pressure of the above pumps should be sufficient.

Again, this selection of a circulation pump is approximate, although in most cases it will satisfy the required parameters.

Select a circulation pump using the formulas.

If you want to understand the required parameters and select it using formulas before buying a circulation pump, then the following information will be useful.

determine the required pump pressure

H=(R x L xk) / 100, where

H—required pump head, m

L is the length of the pipeline between the most distant points “there” and “back”. In other words, this is the length of the largest “ring” from the circulation pump in the heating system. (m)

An example of calculating a circulation pump using formulas

There is a three-story house measuring 12m x 15m. Floor height is 3 m. The house is heated by radiators (∆ T=20°C) with thermostatic heads. Let's make the calculation:

required thermal power

N (from pl.) = 0.1 (kW/sq.m.) x 12 (m) x 15 (m) x 3 floors = 54 kW

calculate the flow rate of the circulation pump

Q = (0.86 x 54) / 20 = 2.33 m3/hour

calculate the pump pressure

The manufacturer of plastic pipes, TECE, recommends using pipes with a diameter at which the fluid flow speed will be 0.55-0.75 m/s, the resistivity of the pipe wall will be 100-250 Pa/m. In our case, a pipe with a diameter of 40mm (11/4″) can be used for the heating system. At a flow rate of 2.319 m3/hour, the coolant flow rate will be 0.75 m/s, the resistivity of one meter of pipe wall will be 181 Pa/m (0.02 mWG).

WILO YONOS PICO 25/1-8

GRUNDFOS UPS 25-70

Almost all manufacturers, including such “giants” as WILO and GRUNDFOS, post special programs for selecting a circulation pump on their websites. For the above-mentioned companies these are WILO SELECT and GRUNDFOS WebCam.

The programs are very convenient, they are quite easy to use

Particular attention should be paid to the correct entry of values, which often causes difficulties for untrained users

Buy a circulation pump

When purchasing a circulation pump, special attention should be paid to the selling company. There are currently a lot of counterfeit products on the Ukrainian market.

How can we explain that the retail price of a circulation pump on the market can be 3-4 times less than that of a representative of the manufacturer?

According to analysts, the circulation pump in the household sector is the leader in energy consumption. In recent years, companies have been offering very interesting new products - energy-saving circulation pumps with automatic power control. From the household series, WILO has YONOS PICO, GRUNDFOS has ALFA2. Such pumps consume several orders of magnitude less electricity and significantly save owners’ financial expenses.

Thermal expansion of liquids

The thermal expansion of a liquid is quantified by the coefficient of thermal expansion (3/, 1'0 relative change with temperature / ia gs： The coefficient of thermal expansion of water increases with increasing pressure and temperature. For most other dripping liquids, it decreases with increasing pressure.

In table Table 1. 7 shows the values ​​of 3/ water at various pressures and temperatures [14], in table. 1.8—values ​​of some liquids at a temperature of 20° C and a pressure of 0.1 MPa (1 at) [2, 104, 121]. Table 1. 7 Pressure р, МГТа 1–10 10-20 Temperature (, °С 40–-0 | 60–70 00-100 Liquid Alcohol Water Glycerin.

Oil: olive turnip Oil Mercury 0.00! 10 0, 00015 0, 00050 0, 00072 0, 00090 0, 00060 0, 00018 When changing temperature and pressure within small limits, you can take , and then the volume of liquid when the temperature changes by an amount (11 = 1–10 is calculated by the formula in this case Re N Here v and V0 are volumes; p and p0 are densities, respectively, at temperatures.

Checking the selected electric motor a. Checking the rudder shift duration

For the selected pump, look at the graphs of the dependence of the mechanical and volumetric efficiency on the pressure created by the pump (see Fig. 3).

4.1. We find the moments arising on the electric motor shaft at different steering angles:

,

where: M

α – torque on the electric motor shaft (Nm);

Q

mouth – set pump capacity;

P

α – oil pressure created by the pump (Pa);

P

tr – pressure loss due to oil friction in the pipeline (3.4÷4.0)·105 Pa;

n

n – pump speed (rpm);

η

r – hydraulic efficiency associated with fluid friction in the working cavities of the pump (for rotary pumps ≈ 1);

η

mech - mechanical efficiency, taking into account friction losses (in oil seals, bearings and other rubbing parts of pumps (see graph in Fig. 3).

We enter the calculation data in Table 4.

4.2. We find the rotation speed of the electric motor for the obtained torque values ​​(based on the constructed mechanical characteristics of the selected electric motor - see paragraph 3.6). We enter the calculation data in Table 5.

Table 5

4.3. We find the actual pump performance at the obtained electric motor speeds

,

where: Q

α – actual pump performance (m3/sec);

Q

mouth – installed pump capacity (m3/sec);

n

– actual speed of rotation of the pump rotor (rpm);

n

n – nominal speed of rotation of the pump rotor;

η

v – volumetric efficiency, taking into account the reverse bypass of the pumped liquid (see graph 4.)

We enter the calculation data in table 5. We build a graph Q

α
= f ( α )
– see fig.
4 .
Rice. 4. Graph Q

α
= f ( α )
4.4. We divide the resulting graph into 4 zones and determine the operating time of the electric drive in each of them. We summarize the calculation in Table 6.

Table 6

4.4.1. Find the distance covered by the rolling pins within the zone

,

where: H i

– distance covered by rolling pins within the zone (m);

R o

– distance between the axes of the stock and rolling pins (m).

4.4.2. Finding the volume of oil pumped within the zone

,

where: V i

– volume of pumped oil within the zone (m3);

m

cyl – number of pairs of cylinders;

D

– plunger (rolling pin) diameter, m.

4.4.3. Find the duration of the rudder shift within the zone

,

where: t i

– average duration of rudder shift within the zone (sec);

Q

av
i
– average productivity within the zone (m3/sec) – taken from the graph in clause 4.4. or calculate from table 5).

4.4.4. We determine the operating time of the electric drive when shifting the steering wheel from side to side

t

lane
= t 1 + t 2 + t 3 + t 4 + t o
,

where: t

per – time of shifting the rudder from side to side (sec);

t 1 ÷ t 4

– duration of transfer in each zone (sec);

t o

– time to prepare the system for action (sec).

4.5. We compare t shift with T (time of shifting the rudder from side to side at the request of RRR), sec.

t

lane
≤ T
(30 sec)

Basic hydraulic formulas

Feeding performance of pumping equipment

This is one of the main factors to consider when choosing a device. Supply – the amount of coolant pumped per unit of time (m3/hour). The higher the flow, the greater the volume of liquid that the pump can pump. This indicator reflects the volume of coolant that transfers heat from the boiler to the radiators. If the supply is low, the radiators will not heat well. If the performance is excessive, home heating costs will increase significantly.

The power of circulation pumping equipment for a heating system can be calculated using the following formula: Qpu=Qn/1.163xDt [m3/h]

In this case, Qpu is the supply of the unit at the design point (measured in m3/hour), Qn is the amount of heat consumed in the area that is heated (kW), Dt is the temperature difference recorded on the forward and return pipelines (for standard systems this is 10- 20°C), 1.163 – indicator of the specific heat capacity of water (if another coolant is used, the formula must be adjusted).

Compressibility of liquids

Compressibility is a property of a liquid that changes its volume under pressure. The compressibility of a liquid is characterized by the volumetric compressibility coefficient, which is the relative change in the volume of the liquid v0. Au 1 L.S. is represented by cm2 / kgf. If the pressure increment cp = p-p0 and the volume change is assumed (1 .2 (1 .3

In equations (1.2) and (1.3) v and v0 are the volume, and p and p0 are the density at pressures p and p0, respectively. Lyudmila Firmal

The mutual volumetric compressibility coefficient is called the volumetric modulus of elasticity of the fluid. Units Same as pressure: kgf/m2, in the MKGSS system, N/m2, in the SI system or in Pascals (pa), kgf/cm2 is also often used. The liquid of a hedgehog has the value of temperature and pressure p.

There is an adiabatic modulus of elasticity and an isothermal modulus of elasticity, the 1st one being slightly larger than the 2nd one, and apparently representing a transient process of fluid compression, such as during a water hammer in a pipe inside a table. 1. 4 value of isothermal modulus of elasticity Table 1.4 Pressure p, MPa (1 MPa = 104 Pa).

If pressure and temperature vary within a small limit, then the value h> k can be considered a constant value. The table shows the average values ​​of the isothermal modulus of elasticity of some liquids.

Temperature Pressure MPa

Table 1.6

Isotherm modulus of elasticity MPa kgf/cm3

How to determine the required pressure of the circulation pump

The head of centrifugal pumps is most often expressed in meters. The pressure value allows you to determine what hydraulic resistance it can overcome. In a closed heating system, the pressure does not depend on its height, but is determined by hydraulic resistance. To determine the required pressure, it is necessary to perform a hydraulic calculation of the system. In private homes, when using standard pipelines, as a rule, a pump that develops a pressure of up to 6 meters is sufficient.

You should not be afraid that the selected pump is capable of developing greater pressure than you need, since the developed pressure is determined by the resistance of the system, and not by the number indicated in the passport. If the maximum pressure of the pump is not enough to pump liquid through the entire system, there will be no circulation of liquid, so you should choose a pump with a headroom reserve

.