Hydraulic calculation of the heating system taking into account pipelines. Physical parameters and speeds of coolant movement

In order for the water heating system to function correctly, it is necessary to ensure the required coolant speed in the system. If the speed is low, heating the room will be very slow and distant radiators will be much colder than nearby ones. On the contrary, if the coolant speed is too high, then the coolant itself will not have time to heat up in the boiler, and the temperature of the entire heating system will be lower. The noise level will also increase. As we can see, the speed of the coolant in the heating system is a very important parameter. Let's take a closer look - what should be the most optimal speed.

Heating systems where natural circulation occurs, as a rule, have relatively low speed coolant. The pressure drop in the pipes is achieved correct location boiler, expansion tank and the pipes themselves - direct and return. Only correct calculation before installation allows you to achieve correct, uniform movement of the coolant. But still the inertia of heating systems with natural circulation liquid is very large. The result is slow heating of rooms, low efficiency. The main advantage of such a system is maximum independence from electricity; there are no electric pumps.

Most often, homes use a heating system with forced circulation of coolant. The main element of such a system is circulation pump. It is this that accelerates the movement of the coolant; the speed of the liquid in the heating system depends on its characteristics.

What affects the coolant speed in the heating system:

Heating system diagram,
- type of coolant,
- power, performance of the circulation pump,
- what materials are the pipes made of and their diameter,
- absence air jams and blockages in pipes and radiators.

For a private home, the most optimal coolant speed will be in the range of 0.5 - 1.5 m/s.
For administrative buildings - no more than 2 m/s.
For production premises– no more than 3 m/s.
The upper limit of coolant velocity is selected mainly due to the noise level in the pipes.

Many circulation pumps have a liquid flow rate regulator, so it is possible to choose the most optimal one for your system. You also need to choose the pump itself correctly. There is no need to take it with a large power reserve, as there will be greater electricity consumption. With a large heating system, a large number of circuits, number of floors, and so on, it is better to install several pumps of lower capacity. For example, install the pump separately on a warm floor, on the second floor.

Water speed in the heating system
Water speed in the heating system In order for the water heating system to function correctly, it is necessary to ensure the required speed of the coolant in the system. If the speed is low,

The speed of water movement in the pipes of the heating system.

Thượng Tá Quân Đội Nhân Dân Việt Nam

Oh, and they're making a fool of your brother!
What do you want? Should you find out “military secrets” (how to actually do it), or pass the coursework? If only a course student - then according to the manual, which the teacher wrote and does not know anything else and does not want to know. And if you do how to, won’t accept it yet.

1. Yes minimum speed of water movement. This is 0.2-0.3 m/s, based on the condition of air removal.

2. Yes maximum speed, which is limited so that the pipes do not make noise. Theoretically, this should be checked by calculation, and some programs do this. Practically knowledgeable people they use the instructions of the old SNiP from 1962, where there was a table limit speeds From there it spread across all reference books. This is 1.5 m/s for a diameter of 40 or more, 1 m/s for a diameter of 32, 0.8 m/s for a diameter of 25. For smaller diameters there were other restrictions, but then they didn’t care about them.

The permissible speed is now in clause 6.4.6 (up to 3 m/s) and in Appendix Z of SNiP 41-01-2003, only “associate professors with candidates” tried to ensure that poor students could not figure it out. There it is tied to the noise level, and to kms and other crap.

But acceptable is absolutely Not optimal. SNiP does not mention optimal at all.

3. But still there is optimal speed. Not some 0.8-1.5, but the real one. Or rather, not the speed itself, but the optimal diameter of the pipe (the speed itself is not important), taking into account all factors, including metal consumption, complexity of installation, configuration and hydraulic stability.

Here are the secret formulas:

0.037*G^0.49 - for prefabricated highways
0.036*G^0.53 - for heating risers
0.034*G^0.49 - for mm mains of the branch, until the load is reduced to 1/3
0.022*G^0.49 - for the end sections of a branch with a load of 1/3 of the entire branch

Here, everywhere G is the flow rate in t/h, and the internal diameter is obtained in meters, which must be rounded to the nearest larger standard.

Well and correct the boys don’t set any speeds at all, they just do it at residential buildings all risers of constant diameter and all lines of constant diameter. But it’s too early for you to know what exactly the diameters are.

The speed of water movement in the pipes of the heating system
The speed of water movement in the pipes of the heating system. Heating

Hydraulic calculation of heating system pipelines

As can be seen from the title of the topic, the calculation involves parameters related to hydraulics, such as coolant flow rate, coolant flow rate, hydraulic resistance of pipelines and fittings. Moreover, there is a complete relationship between these parameters.

For example, when the coolant speed increases, the hydraulic resistance of the pipeline increases. When the flow of coolant through a pipeline of a certain diameter increases, the speed of the coolant increases and the hydraulic resistance naturally increases, while changing the diameter upward, the speed and hydraulic resistance decrease. By analyzing these relationships, hydraulic calculation turns into a kind of parameter analysis to ensure reliable and efficient operation of the system and reduce material costs.

The heating system consists of four main components: pipelines, heating devices, heat generator, regulating and shut-off valves. All elements of the system have their own hydraulic resistance characteristics and must be taken into account when calculating. However, as mentioned above, the hydraulic characteristics are not constant. Manufacturers heating equipment and materials usually provide data on the hydraulic characteristics (specific pressure loss) for the materials or equipment they produce.

Nomogram for hydraulic calculation polypropylene pipes wires manufactured by FIRAT (Firat)

The specific pressure loss (pressure loss) of the pipeline is indicated for 1 m.p. pipes.

After analyzing the nomogram, you will more clearly see the previously indicated relationships between the parameters.

So we have determined the essence of the hydraulic calculation.

Now let's go through each of the parameters separately.

Coolant flow

Coolant flow, for a broader understanding, the amount of coolant, directly depends on the thermal load that the coolant must move from the heat generator to the heating device.

Specifically for hydraulic calculations, it is necessary to determine the coolant flow rate in a given design area. What is a settlement area? The design section of the pipeline is taken to be a section of constant diameter with a constant coolant flow rate. For example, if a branch includes ten radiators (conditionally each device with a power of 1 kW) and total consumption The coolant is designed to transfer thermal energy equal to 10 kW by the coolant. Then the first section will be the section from the heat generator to the first radiator in the branch (provided that the diameter is constant throughout the section) with a coolant flow rate for transfer of 10 kW. The second section will be located between the first and second radiators with a flow rate for transferring thermal energy of 9 kW and so on until the last radiator. The hydraulic resistance of both the supply and return pipelines is calculated.

The coolant flow rate (kg/hour) for the area is calculated using the formula:

Q uch - thermal load plot W. For example, for the above example, the thermal load of the first section is 10 kW or 1000 W.

с = 4.2 kJ/(kg °С) - specific heat capacity of water

t g — design temperature hot coolant in the heating system, °C

t o - design temperature of the cooled coolant in the heating system, °C.

Coolant flow rate.

The minimum coolant velocity threshold is recommended to be within the range of 0.2 - 0.25 m/s. At lower speeds, the process of releasing excess air contained in the coolant begins, which can lead to the formation of air jams and, as a result, complete or partial failure of the heating system. The upper threshold of coolant velocity lies in the range of 0.6 - 1.5 m/s. Compliance with the upper speed threshold allows you to avoid the occurrence of hydraulic noise in pipelines. In practice, the optimal speed range was determined to be 0.3 - 0.7 m/s.

A more accurate range of recommended coolant speed depends on the material of the pipelines used in the heating system, or more precisely on the roughness coefficient of the inner surface of the pipelines. For example for steel pipes wires It is better to adhere to a coolant speed of 0.25 to 0.5 m/s for copper and polymer (polypropylene, polyethylene, metal-plastic pipelines) from 0.25 to 0.7 m/s, or use the manufacturer’s recommendations if available.

Coolant flow rate
Coolant flow rate. Hydraulic calculation of heating system pipelines As can be seen from the title of the topic, the calculation involves parameters related to hydraulics such as flow

Speed - movement - coolant

The speeds of movement of coolants in technological devices usually provide a turbulent flow regime, in which, as is known, there is an intense exchange of momentum, energy and mass between adjacent sections of the flow due to chaotic turbulent pulsations. In physical essence, turbulent heat transfer is convective transfer.

Coolant movement velocities in pipelines of heating systems with natural circulation are usually 0 05 - 0 2 m / s, and with artificial circulation - 0 2 - 1 0 m / s.

The speed of movement of the coolant affects the drying speed of the brick. From the above studies it follows that the acceleration of drying bricks with an increase in the speed of movement of the coolant is more noticeable when this speed is more than 0 5 m / sec. During the first drying period, a significant increase in the speed of movement of the coolant is detrimental to the quality of the brick if the coolant is not wet enough.

The speed of movement of the coolant in the tubes of heat exchangers must be in all operating modes at least 0-35 m/s with water coolant and at least 0-25 m/s with non-freezing coolant.

The speed of movement of the coolant in heating systems is determined hydraulic calculation and economic considerations.

The speed of coolant movement, determined by the cross-section of the channels of the heat exchanger, fluctuates within very wide limits and cannot be accepted or established without a large error until the issue of the type and size of the heat exchanger is decided.

The coolant velocity w greatly influences heat transfer. The higher the speed, the more intense the heat exchange.

The speed of movement of the coolant in the drying channel should not exceed 5 - 6 m/min to avoid the formation of a bumpy surface of the working layer and an overly stressed structure. In practice, the coolant speed is chosen within the range of 2 - 5 m / min.

The speed of coolant movement in water heating systems is allowed up to 1 - 15 m/s in residential and public buildings and up to 3 m/s in production areas.

Increasing the speed of coolant movement is beneficial only up to a certain limit. If this speed is higher than optimal, the gases will not have time to give up their entire heat to the material and will exit the drum with high temperature.

An increase in the speed of movement of the coolant can also be achieved in elemental (battery) heat exchangers, which are a battery of several heat exchangers connected in series with each other.

With an increase in the speed of movement of coolants, Re w / / v, heat transfer coefficient a and density increase heat flow q aAt. However, along with the speed, the hydraulic resistance and power consumption for pumps pumping coolant through heat exchanger. Exists optimal value speed, determined by comparing the increase in heat exchange intensity and more intensive growth hydraulic resistance with increasing speed.

To increase the speed of coolant movement in the interpipe space, longitudinal and transverse partitions are installed.

Great Encyclopedia Oil and Gas
Great Encyclopedia of Oil and Gas Speed - movement - coolant The speed of movement of coolants in technological devices usually ensures a turbulent regime of flow movement, with

Individual hydraulic heating systems

In order to correctly carry out a hydraulic calculation of a heating system, it is necessary to take into account some operational parameters of the system itself. This includes the coolant speed, its flow rate, hydraulic resistance of shut-off valves and pipelines, inertia, and so on.

It may seem that these parameters are in no way related to each other. But this is a mistake. The connection between them is direct, so you need to rely on them when analyzing.

Let's give an example of this relationship. If you increase the speed of the coolant, the resistance of the pipeline will immediately increase. If you increase the flow rate, the speed of hot water in the system increases, and, accordingly, the resistance. If you increase the diameter of the pipes, the speed of movement of the coolant decreases, which means the resistance of the pipeline decreases.

The heating system includes 4 main components:

Boiler.
Pipes.
Heating devices.
Shut-off and control valves.

Each of these components has its own resistance parameters. Leading manufacturers must indicate them because hydraulic characteristics may vary. They largely depend on the shape, design and even on the material from which the components are made heating system. And these characteristics are the most important when conducting hydraulic heating analysis.

What are hydraulic characteristics? These are specific pressure losses. That is, in every type of heating element, be it a pipe, valve, boiler or radiator, there is always resistance from the structure of the device or from the walls. Therefore, passing through them, the coolant loses its pressure, and, accordingly, speed.

Coolant flow

To show how hydraulic heating calculations are performed, let’s take as an example a simple heating scheme, which includes a heating boiler and heating radiators with kilowatt heat consumption. And there are 10 such radiators in the system.

Here it is important to correctly divide the entire scheme into sections, and at the same time strictly adhere to one rule - the diameter of the pipes in each section should not change.

So, the first section is the pipeline from the boiler to the first heating device. The second section is the pipeline between the first and second radiators. And so on.

How does heat transfer occur, and how does the temperature of the coolant decrease? Getting into the first radiator, the coolant gives off part of the heat, which is reduced by 1 kilowatt. It is in the first section that hydraulic calculations are made at 10 kilowatts. But in the second section it’s already below 9. And so on with a decrease.

Please note that this analysis is performed separately for the flow and return circuits.

There is a formula by which you can calculate the coolant flow:

G = (3.6 x Qch) / (c x (tr-to))

Qch is the calculated thermal load of the area. In our example, for the first section it is 10 kW, for the second 9.

c is the specific heat capacity of water, the indicator is constant and equal to 4.2 kJ/kg x C;

tr is the temperature of the coolant at the entrance to the site;

to is the temperature of the coolant at the exit from the site.

Coolant speed

Schematic calculation

There is a minimum speed of hot water inside the heating system at which the heating itself operates at optimal mode. This is 0.2-0.25 m/s. If it decreases, then air begins to be released from the water, which leads to the formation of air jams. Consequences - the heating will not work and the boiler will boil.

This is the lower threshold, and as for the upper level, it should not exceed 1.5 m/s. Exceeding it threatens the appearance of noise inside the pipeline. The most acceptable indicator is 0.3-0.7 m/s.

If you need to accurately calculate the speed of water movement, you will have to take into account the parameters of the material from which the pipes are made. Especially in this case, the roughness of the internal surfaces of the pipes is taken into account. For example, through steel pipes hot water moves at a speed of 0.25-0.5 m/s, on copper 0.25-0.7 m/s, on plastic 0.3-0.7 m/s.

Selecting the main outline

Hydraulic arrow separates boiler and heating circuits

Here it is necessary to consider separately two schemes - one-pipe and two-pipe. In the first case, the calculation must be carried out through the most loaded riser, where it is installed a large number of heating devices and shut-off valves.

In the second case, the busiest circuit is selected. It is on this basis that the calculation must be made. All other circuits will have much lower hydraulic resistance.

In the event that horizontal pipe decoupling is considered, the busiest ring of the lower floor is selected. Load refers to thermal load.

Conclusion

Heating in the house

So, let's summarize. As you can see, in order to make a hydraulic analysis of the heating system of a house, a lot needs to be taken into account. The example was deliberately simple, since it is very difficult to understand, say, a two-pipe heating system for a house with three or more floors. To carry out such an analysis, you will have to contact a specialized bureau, where professionals will sort everything out “to the bones.”

It will be necessary to take into account not only the above indicators. This will have to include pressure loss, temperature reduction, circulation pump power, system operating mode, and so on. There are many indicators, but they are all present in GOSTs, and a specialist will quickly figure out what’s what.

The only thing that needs to be provided for the calculation is the power of the heating boiler, the diameter of the pipes, the presence and quantity of shut-off valves and the power of the pump.

Hydraulic calculation of heating system pipelines

The heating system consists of four main components: pipelines, heating devices, heat generator, control and shut-off valves. All elements of the system have their own hydraulic resistance characteristics and must be taken into account when calculating. However, as mentioned above, the hydraulic characteristics are not constant. Manufacturers of heating equipment and materials usually provide data on hydraulic characteristics (specific pressure loss) for the materials or equipment they produce.

For example:

Nomogram for hydraulic calculation of polypropylene pipelines produced by FIRAT (Firat)

The specific pressure loss (pressure loss) of the pipeline is indicated for 1 m.p. pipes.

After analyzing the nomogram, you will more clearly see the previously indicated relationships between the parameters.

So we have determined the essence of the hydraulic calculation.

Now let's go through each of the parameters separately.

Coolant flow

Coolant flow, for a broader understanding, the amount of coolant, directly depends on the thermal load that the coolant must move from the heat generator to the heating device.

Specifically for hydraulic calculations, it is necessary to determine the coolant flow rate in a given design area. What is a settlement area? The design section of the pipeline is taken to be a section of constant diameter with a constant coolant flow rate. For example, if a branch includes ten radiators (conditionally, each device has a power of 1 kW) and the total coolant flow rate is designed to transfer thermal energy equal to 10 kW by the coolant. Then the first section will be the section from the heat generator to the first radiator in the branch (provided that the diameter is constant throughout the section) with a coolant flow rate for transfer of 10 kW. The second section will be located between the first and second radiators with a flow rate for transferring thermal energy of 9 kW and so on until the last radiator. The hydraulic resistance of both the supply and return pipelines is calculated.

The coolant flow rate (kg/hour) for the area is calculated using the formula:

G uch = (3.6 * Q uch) / (s * (t g - t o)) kg/h

Q uch - thermal load of the area W. For example, for the above example, the thermal load of the first section is 10 kW or 1000 W.

с = 4.2 kJ/(kg °С) - specific heat capacity of water

t g - design temperature of the hot coolant in the heating system, °C

t o - design temperature of the cooled coolant in the heating system, °C.

Coolant flow rate.

The minimum threshold for coolant velocity is recommended to be within the range of 0.2 - 0.25 m/s. At lower speeds, the process of releasing excess air contained in the coolant begins, which can lead to the formation of air jams and, as a result, complete or partial failure of the heating system. The upper threshold of coolant velocity lies in the range of 0.6 - 1.5 m/s. Compliance with the upper speed threshold allows you to avoid the occurrence of hydraulic noise in pipelines. In practice, the optimal speed range was determined to be 0.3 - 0.7 m/s.

A more accurate range of recommended coolant speed depends on the material of the pipelines used in the heating system, or more precisely on the roughness coefficient of the inner surface of the pipelines. For example, for steel pipelines it is better to adhere to a coolant speed of 0.25 to 0.5 m/s; for copper and polymer (polypropylene, polyethylene, metal-plastic pipelines) from 0.25 to 0.7 m/s, or use the manufacturer’s recommendations, if available.

The calculation will be considered on systems with forced ventilation. In such systems, the movement of the coolant is ensured by a constantly running circulation pump. When choosing the diameter of the pipes, it is taken into account that their main task is to ensure the delivery of the required amount of heat to the heating devices.

Data: how to calculate the diameter of a heating pipe

To calculate the diameter of the pipeline, you will need the following data: this is the total heat loss of the home, the length of the pipeline, and the calculation of the power of the radiators in each room, as well as the wiring method. The outlet can be one-pipe, two-pipe, have forced or natural ventilation.

Also pay attention to the markings on copper and polypropylene pipes of outer diameter. The internal one can be calculated by subtracting the wall thickness. For metal-plastic and steel pipes, the internal size is indicated when marking.

Unfortunately, it is impossible to accurately calculate the pipe cross-section. One way or another, you will have to choose from a couple of options. This point is worth clarifying: a certain amount of heat needs to be delivered to the radiators, while achieving uniform heating of the batteries. If we are talking about systems with forced ventilation, then this is done using pipes, a pump and the coolant itself. All that is needed is to drive the required amount of coolant over a certain period of time.

It turns out that you can choose pipes of a smaller diameter and supply the coolant at a higher speed. You can also make a choice in favor of pipes of a larger cross-section, but reduce the intensity of the coolant supply. The first option is preferable.

Selecting water speed in the heating system

High water speed and smaller diameter pipes are the most common choice. If you increase the diameter of the pipe, the speed of movement will decrease. But the latter option is not so common; reducing movement is not very beneficial.

Why high speed and a smaller pipe diameter is more profitable:

Smaller diameter products cost less;
It is easier to work with smaller diameter pipes at home;
If the gasket is open, they do not attract attention so much, and if the installation goes into the walls or floor, then smaller grooves will be required;
A small diameter provides less coolant in the pipe, and this, in turn, reduces the inertia of the system, which saves fuel.

Special tables have been developed to determine the size of pipes for a home. Such a table takes into account the required amount of heat, as well as the speed of movement of the coolant, as well as the temperature indicators of the system. It turns out to carry out the selection of pipes the required section, the required table is found, and the diameter is selected from it. Today there may be a suitable online program that replaces the table.

Heating system wiring diagram and heating pipe diameter

The heating wiring diagram is always taken into account. It can be two-pipe vertical, two-pipe horizontal and single-pipe. A two-pipe system involves both upper and lower placement of lines. But the single-pipe system takes into account the economical use of the length of the lines, and is suitable for heating with natural circulation. Then the two-pipe system will require the mandatory inclusion of a pump in the circuit.

There are three types of horizontal wiring:

Dead end;
Beam or collector;
With parallel movement of water.

By the way, in the diagram of a single-pipe system there may also be a so-called bypass pipe. It will become an additional line for fluid circulation if one or more radiators are turned off. Usually, shut-off valves are installed on every radiator, which allow you to shut off the water supply if necessary.

What could be the consequences: narrowing the diameter of the heating pipe

Narrowing the pipe diameter is extremely undesirable. When wiring around the house, it is recommended to use the same standard size - there is no need to increase or decrease it. The only possible exception would be a large length of the circulation circuit. But even in this case you need to be careful.

But why does the size become smaller when replacing a steel pipe with a plastic one? Everything is simple here: with the same internal diameter, the outer diameter of the plastic pipes themselves is larger. This means that the holes in the walls and ceilings will have to be expanded, and seriously - from 25 to 32 mm. But for this you will need a special tool. Therefore, it is easier to pass thinner pipes into these holes.

But in this same situation, it turns out that the residents who made such a replacement of pipes automatically “stole” approximately 40% of the heat and water passing through the pipes from their neighbors in this riser. Therefore, it is worth understanding that the thickness of pipes that are arbitrarily replaced in a heating system is not a matter of private decision; this cannot be done. If steel pipes are replaced with plastic ones, no matter how you look at it, you will have to widen the holes in the ceilings.

There is such an option in this situation. When replacing risers, you can pass new pieces of steel pipes of the same diameter into the old holes; their length will be 50-60 cm (this depends on such a parameter as the thickness of the ceiling). And then they are connected by couplings to plastic pipes. This option is quite acceptable.

Correct calculation of pipe diameter for heating (video)

If you are incompetent in calculating the diameter of pipes, return lines, diagrams and choosing a coolant, it is better to call specialists and ask them to comment on their work.

Magazine “Heat Supply News” No. 1, 2005, www.ntsn.ru

Ph.D. O.D. Samarin, Associate Professor, Moscow State University of Civil Engineering

Currently existing proposals regarding the optimal speed of water movement in pipelines of heating supply systems (up to 3 m/s) and permissible specific pressure losses R (up to 80 Pa/m) are based mainly on technical and economic calculations. They take into account that with increasing speed, pipeline cross-sections decrease and the volume of thermal insulation decreases, i.e. capital investments in network construction are reduced, but at the same time operating costs for pumping water increase due to an increase in hydraulic resistance, and vice versa. Then the optimal speed corresponds to the minimum reduced costs for the estimated depreciation period of the system.

However, in a market economy, it is imperative to take into account the discounting of operating costs E (rub./year) and capital costs K (rub.). In this case, the formula for calculating total discounted costs (CDC), when using borrowed funds, takes on the following form:

IN in this case- discount factors for capital and operating costs, calculated depending on the estimated depreciation period T (years), and the discount rate p. The latter takes into account the level of inflation and investment risks, i.e., ultimately, the degree of instability of the economy and the nature of changes in current tariffs, and is usually determined by the method of expert assessments. To a first approximation, the value of p corresponds to the annual interest rate for a bank loan. In practice, it can be taken in the amount of the refinancing rate of the Central Bank of the Russian Federation. Starting from January 15, 2004, it is equal to 14% per annum.

Moreover, it is not known in advance that the minimum SDZ, taking into account discounting, will correspond to the same level of water velocity and specific losses that are recommended in the literature. Therefore, it is advisable to carry out new calculations using the current price range for pipelines, thermal insulation and electricity. In this case, if we assume that the pipelines operate under quadratic resistance conditions and calculate the specific pressure loss using the formulas given in the literature, the following formula can be obtained for the optimal speed of water movement:

Here Kti is the coefficient of increase in the cost of pipelines due to the presence of thermal insulation. When using domestic materials such as mineral wool mats, Kti = 1.3 can be taken. Parameter C D is the specific cost of one meter of pipeline (RUB/m 2) divided by the internal diameter D (m). Since price lists usually indicate the price in rubles per ton of metal C m, recalculation must be made using the obvious relationship, where is the thickness of the pipeline wall (mm), = 7.8 t/m 3 is the density of the pipeline material. The value of C el corresponds to the electricity tariff. According to Mosenergo OJSC for the first half of 2004 for utility consumers C el = 1.1723 rub./kWh.

Formula (2) is obtained from the condition d(SDZ)/dv=0. The determination of operating costs was carried out taking into account the fact that the equivalent roughness of the pipeline walls is 0.5 mm, and the efficiency network pumps is about 0.8. The water density p w was considered equal to 920 kg/m 3 for the characteristic temperature range in the heating network. In addition, it was assumed that circulation in the network occurs year-round, which is quite justified based on the needs of hot water supply.

Analysis of formula (1) shows that for long depreciation periods T (10 years and above), characteristic of heating networks, the ratio of discount factors is almost equal to its maximum minimum value p/100. In this case, expression (2) gives the lowest economically feasible water velocity, corresponding to the condition when the annual interest on the loan taken for construction is equal to the annual profit from reducing operating costs, i.e. with an infinite payback period. At a finite time, the optimal speed will be higher. But in any case, this speed will exceed that calculated without discounting, since then, as is easy to see, and in modern conditions it still turns out to be 1/T< р/100.

The values of the optimal water speed and the corresponding appropriate specific pressure losses, calculated from expression (2) at the average level of C D and the limiting ratio , are shown in Fig. 1. It should be borne in mind that formula (2) includes the value D, which is unknown in advance, so it is first advisable to set the average speed value (about 1.5 m/s), determine the diameter based on the given water flow G (kg/h), and then calculate the actual speed and optimal speed according to (2) and check whether v f is greater than v opt. Otherwise, the diameter should be reduced and the calculation repeated. You can also obtain the relationship directly between G and D. For the average level C D it is shown in Fig. 2.

Thus, the economically optimal water speed in heating networks, calculated for the conditions of a modern market economy, in principle does not exceed the limits recommended in the literature. However, this speed depends less on the diameter than if the conditions for permissible specific losses are met, and for small and medium diameters, increased R values up to 300 - 400 Pa/m are appropriate. Therefore, it is preferable to further reduce capital investments (in

in this case - to reduce the cross-sections and increase the speed), and to a greater extent, the higher the discount rate. Therefore, in a number of cases, in practice, the desire to reduce one-time costs when installing engineering systems receives theoretical justification.

Literature

1. A.A. Ionin et al. Heat supply. Textbook for universities. - M.: Stroyizdat, 1982, 336 p.

2. V.G. Gagarin. A criterion for cost recovery for increasing the thermal protection of building envelopes in various countries. Sat. report conf. NIISF, 2001, p. 43 - 63.