Correctly performed hydraulic calculations at the design stage will help ensure the smooth operation of the heating system. They will allow you to find out the exact costs for each of the elements of the chain, and ideally help to minimize the costs of pipe repairs, their operation and energy costs. In this case, the heating circuit must operate stably and silently.
Why do you need a hydraulic calculation?
The hydraulic calculation provides solutions to the following important problems:- Calculate the head loss in certain areas of the heating circuit.
- Determine the optimal diameter of pipes used for laying heating based on the recommended speed of movement of the coolant.
- Calculate the heat loss and the value of the minimum pressure in the system.
- Correctly perform the linking of parallel hydraulic branches and the devices installed in them. It will be carried out using control valves.
Algorithm for calculations
To carry out a complete hydraulic calculation of the system, you first need to go through several stages:- Establish a heat balance for each specific room.
- Select and install heating devices around the entire perimeter of the building or only in that part of it where the heated rooms are located.
- Work out the final axonometric diagram indicating the lengths of the thermal design sections and the loads on the heating main.
- Establish a closed loop of the system, which will be the final link of successively located sections of the pipeline. In a two-pipe system, they go from the heat source to the most distant heating device, and in a single-pipe system - to the instrument branch-riser.
- Make final decisions on the place of installation of all heat sources, pipelines, shut-off and control valves.
- pressure losses in certain sections of the heating network;
- pipe diameter and throughput;
- pressure loss in the general system;
- optimal flow rate of the coolant.
Hydraulic calculation of the pipe
The efficiency of the heating system largely depends on the correctness of the selected pipe diameter, while you can focus on the indicators below.For reinforced-plastic pipes:
- D16 mm - power limits vary from 2.8 to 4.5 kW;
- D20 mm - values can be from 5 to 8 kW;
- D26 mm - from 8 to 13 kW;
- D32 mm - 13-18 kW.
- D20 mm - the power value is from 4 to 7 kW;
- D25 mm - from 6 to 11 kW;
- D32 mm - from 10 to 18 kW;
- D40 mm - limits vary from 16 to 28 kW.
The numbering of the calculated pipeline sections starts from the heat source. The nodal points located in the places of the pipeline are indicated by capital letters, but on the collection pipelines they are indicated with a dash. On distribution instrument lines, such nodes are designated with Arabic numerals. The lengths of the calculated pipelines are determined according to the heating plans made to scale. They are accurate to within 0.1 meter.
Calculation of the coolant flow
The involved volume of the coolant, which is available in radiators and pipes, should provide a normal temperature inside the house, regardless of what the weather will be outside its walls.It is calculated by the formula:
M = Q / Cp x P delta t, where
- Q is the total power of the heating system, kW;
- Cp - an indicator of the specific heat capacity of water, it is usually taken equal to 4.19 kJ / (kg "multiplied by" degrees Celsius);
- P delta t is the temperature difference at the inlet and outlet of the system, for the calculation of which the "return" and the supply of the boiler are taken.
To get an accurate value, all radiators to which the coolant is supplied should be calculated in terms of power. Calculations are carried out for pipes in front of each battery.
Hydraulic calculation of the speed of the coolant
An important indicator, which is also calculated in all sections of the pipe until it is connected to the radiator. The speed of fluid movement is calculated by the formula:V = m / p x f, where
- m is the loss of the coolant at a certain section of the pipe, kg / s;
- p is the density of water, kg / cu. m (it is taken as 1000 kg / cubic meter);
- f is the cross-sectional area of the pipe, sq. m.
f = Pi x r2, where
- r2 is the inner diameter of the pipe divided by 2;
- Pi is a mathematical constant equal to 3.14.
Calculation of local resistances
They are located at the joints of pipes with fittings, valves or heating equipment. The head loss in this case is calculated by the formula:delta p m. s. = Summa Y x V / 2 x p, where
- delta p m. s. - loss of pressure on local resistances, Pa;
- Summa Y - the sum of the coefficients of all local resistances on the site (for each individual fitting, the manufacturer indicates its own coefficient);
- V is the speed of passage of the coolant through the pipes, m / s;
- p is the density of the liquid circulating in the heating system, kg / cu. m.
Calculation of the pressure loss in the circuit
The calculations take into account both the "return" and the flow. The formula looks like this:delta P p = R x L, where
- delta P p - pressure flow rate in the system, Pa;
- R is the specific friction consumption in the inner part of the pipe, Pa / m (its value is indicated by the manufacturer);
- L is the length of the calculated section of the pipeline, m.
The values of the speed of the coolant should be in the range from 0.25 to 1.5 m / s. If this indicator is higher, noise will be heard in the pipes, and if it falls below the minimum value, then the risk of airing the system will increase.
Hydraulic calculations in Excel
There are several professional and amateur programs that, after entering the formulas, help to calculate all the necessary parameters. The most popular is Excel. There is no decoding of formulas in it, so you need to study them in advance, so that then you can only substitute the necessary values.To perform calculations in Excel, you need to prepare a sequence of actions in advance and select the necessary formulas.
An approximate filling of the table fields of this program is as follows:
- A table is executed with the names of the indicators, their value and the unit of expression.
- Data are entered for the calculation, some of which are taken from reference books, others are set based on experience or equipment characteristics.
- Formulas and calculation algorithms are introduced.
Below is a video showing how to carry out a hydraulic calculation of a heating network for each specific parameter in the ZuluNetTools program, followed by distilling the results into Excel tables:
Features of performing calculations in a one- and two-pipe system
If in a two-pipe system there is a passing movement of the coolant, then for calculations, a ring with a more loaded riser is selected, which is tied through the lower radiator, and in a one-pipe system, a ring with the most heavily loaded riser is selected.If a dead-end movement of hot water is used, then for a two-pipe scheme, the ring of the lower battery is taken, mounted in the farthest riser. In the horizontal layout view, the busiest branch of the basement floor is used.
Video: The first independent hydraulic calculation
In the next video, you are invited to find out what the principle of such calculations is, as well as how you can carry them out using a special program Valtec, Excel or ordinary mathematical calculations:It is better to spend time once on the hydraulic calculations of the heating system than to find yourself in unforeseen circumstances in the winter without it. Repair work and cold in the house will cost much more, even if the calculations are ordered from a private owner.
The correct choice of all elements of the water heating system, their installation, largely determines the efficiency of its operation, the terms of trouble-free and economical operation. How economical and efficient heating will be in the house will be shown by the initial investment at the stage of installation and installation of the system. Let us consider in more detail how the hydraulic calculation of the heating system is carried out in order to determine the optimal power of the heating system.
Heating system efficiency "by eye"
To a large extent, the amount of such costs depends on:
- required pipe diameters
- fittings and corresponding heating devices
- adapters
- control and shut-off valves
The desire to minimize such costs should not go to the detriment of quality, but the principle of reasonable sufficiency, a certain optimum, must be adhered to.
Most modern individual heating systems use electric pumps to ensure forced circulation of the coolant, which is often used as antifreeze antifreeze compositions. The hydraulic resistance of such heating systems for their different types of heat carriers will be different.
Taking into account the constantly growing cost of energy carriers (all types of fuel, electricity) and consumables (heat carriers, spare parts, etc.), one should strive from the very beginning to put in the system the principle of minimizing the cost of operating the system... Again, based on their optimal ratio for solving the problem of creating a comfortable temperature regime in heated rooms.
Of course, the ratio of the power of all elements of the heating system must ensure optimal coolant supply mode to heating devices in a volume sufficient to fulfill the main task of the entire system - heating and maintaining a given temperature regime inside the room, regardless of changes in outside temperatures. The elements of the heating system include:
- boiler
- pump
- pipe diameter
- control and shut-off valves
- thermal devices
In addition, it is very good if the project initially includes a certain "elasticity" that allows transition to a different type of coolant(replacing water with antifreeze). In addition, the heating system, with changing operating modes, should in no way bring discomfort to the internal microclimate of the premises.
Hydraulic calculation and tasks to be solved
In the process of performing the hydraulic calculation of the heating system, a fairly wide range of issues is being resolved to ensure the fulfillment of the above and a number of additional requirements. In particular, the diameter of pipes in all sectors is found according to the recommended parameters, including the definition:
- travel speed coolant;
- optimal heat transfer on all sections and devices of the system, taking into account the provision of its economic feasibility.
In the process of movement of the coolant, its inevitable pipe wall friction, there are speed losses, especially noticeable in sections containing bends, knees, etc. The tasks of the hydraulic calculation include determining the loss of the speed of the medium, or rather, the pressure on sections of the system, similar to those indicated, for general accounting and inclusion of the required expansion joints in the project. In parallel with the determination of the pressure loss, it is necessary to know the required volume, called the flow rate, of the heat carrier in the entire projected hot water heating system.
Taking into account the ramification of modern heating systems and the design requirements for the implementation of the most common wiring schemes, for example, the approximate equality of the lengths of the branches in the collector circuit, the calculation of hydraulics makes it possible to take into account such features. This will provide more high-quality auto-balancing and linking of branches connected in parallel or according to another scheme. Such capabilities are often required during operation with the use of locking and regulating elements, if it is necessary to disconnect or overlap individual branches and directions, if it becomes necessary to operate the system in non-standard modes.
Preparing the execution of the calculation
A high-quality and detailed calculation should be preceded by a number of preparatory measures for the implementation of the estimated schedules... This part can be called the collection of information for the calculation. Being the most difficult part in the design of a water heating system, the calculation of hydraulics allows you to accurately design all of its work. The prepared data must necessarily contain the definition of the required heat balance of the premises that will be heated by the projected heating system.
In the project, the calculation is carried out taking into account the type of selected heating devices, with certain heat exchange surfaces and their placement in heated rooms, these can be batteries of radiator sections or heat exchangers of other types. The points of their placement are indicated on the floor plans of the house or apartment.
The accepted scheme for configuring the hot water heating system should be drawn up graphically. This diagram indicates the location of the heat generator (boiler), shows mounting points for heating devices, laying of the main inlet and outlet pipelines, passage of branches of heating devices. The diagram shows in detail the location of the elements of the control and shut-off valves. This includes all types of installed taps and valves, transition valves, regulators, thermostats. In general, everything that is commonly called control and shut-off valves.
After determining the required system configuration on the plan, it must draw in axonometric projection for all floors... In this diagram, each heating device is assigned a number, the maximum heat output is indicated. An important element, also indicated for a heating device in the diagram, is the estimated length of the pipeline section for connecting it.
Designations and order of execution
The plans must necessarily indicate, determined in advance, circulation ring, called the main one. It necessarily represents a closed loop, including all sections of the system pipeline with the highest flow rate of the coolant. For two-pipe systems, these sections go from the boiler (heat source) to the most distant heating device and back to the boiler. For one-pipe systems, a section of a branch is taken - a riser and a return part.
The unit of calculation is section of pipeline, having a constant diameter and current (consumption) of the carrier of thermal energy. Its value is determined based on the thermal balance of the room. A certain order of designation of such segments has been adopted, starting from the boiler (heat source, thermal energy generator), they are numbered. If there are branches from the supply line of the pipeline, their designation is performed in capital letters in alphabetical order. The same letter with a stroke is denoted collection point of each branch on the return main pipeline.
In the designation of the beginning of a branch of heating devices, the number of the floor (horizontal systems) or the branch - riser (vertical) is indicated. The same number, but with a prime, is placed at the point of their connection to the return line for collecting coolant flows. Paired, these designations make up the number of each branch calculated area. Numbering is carried out clockwise from the upper left corner of the plan. According to the plan, the length of each branch is also determined, the error is no more than 0.1 m.
On the floor plan of the heating system, for each of its sections, the heat load is considered equal to the heat flux transmitted by the coolant, it is taken rounded to 10 W. After determining for each heating device in the branch, the total heat load on the main supply pipe is determined. As above, here the values obtained are rounded up to 10 W. After calculations, each section should have a double designation with an indication in the numerator heat load values, and in the denominator - the length of the plot in meters.
The required amount (flow rate) of the heat carrier in each section is easily determined by dividing the amount of heat in the section (corrected by a coefficient that takes into account the specific heat capacity of the water) by the temperature difference between the heated and cooled heat carrier in this section. Obviously, the total value for all calculated sections will give the required amount of coolant as a whole for the system.
Without going into details, it should be said that further calculations make it possible to determine the pipe diameters of each of the sections of the heating system, the pressure loss on them, to hydraulically balance all the circulation rings in complex water heating systems.
Consequences of calculation errors and how to correct them
It is obvious that hydraulic calculation is a rather complex and crucial stage in the development of heating. To facilitate such calculations, we have developed whole mathematical apparatus, there are numerous versions of computer programs designed to automate the process of its execution.
Despite this, no one is immune from mistakes. Among the most common is the choice of the power of heating devices without carrying out the calculation indicated above. In this case, in addition to the higher cost of the radiator batteries themselves (if the power is more than required), the system will be costly, consuming an increased amount of fuel and requiring more significant for its maintenance. Simply put, it will be hot in the rooms, the vents are constantly open and you will have to pay extra for heating the street. In case of understated heating power will lead to the operation of the boiler at increased power and will also require high financial costs. It is quite difficult to fix such a mistake, it may be necessary to completely redo all the heating.
If the installation of radiator batteries is incorrect, the efficiency of the entire heating complex also decreases. Such errors include violation of battery installation rules... Errors of this group can halve the heat transfer of the highest quality heating devices. As in the first case, the desire to increase the temperature in the room will lead to additional energy consumption. To correct installation errors, it is often sufficient to reinstall and reconnect the radiator batteries.
The next group of errors refers to the error in determining the required power of the heat source and heating devices. If the power of the boiler is obviously higher than the power of heating devices, it will work ineffectively, consuming more fuel. On the face double cost overrun: at the time of purchase of such a boiler and during operation. To fix the situation, such a boiler, radiators or pump, or even all the pipes of the system, will have to be changed.
When calculating the required boiler output, an error may be made in determining the heat loss of the building. As a result, the capacity of the thermal energy generator will be overestimated. The result will be an overconsumption of fuel. To fix the error, you have to replace the boiler.
An erroneous calculation of the balancing of the system, violation of the requirements of the approximate equality of branches, etc. can lead to the need to install a more powerful pump, which allows the carrier to be delivered to distant heating devices in a heated state. However, in this case it is possible the appearance of "soundtrack" in the form of a hum, whistle etc. If such mistakes are made in the system of a warm water floor, then the result of installing a powerful pump can be a "singing floor".
In case of errors in determining the required amount of coolant or transferring the gravitational system to forced circulation, its volume may be too large, and distant heating appliances will not work... As before, attempts to solve the problem by increasing the intensity of heating will lead to excessive consumption of gas and wear of the boiler. The issue can be resolved by using a new pump and a hydraulic arrow, that is, the heating point will still have to be redone.
After all, we can unequivocally say that hydraulic calculation heating systems will guarantee to minimize costs at all stages of design, installation, installation and long-term operation of a highly efficient hot water heating system.
An example of a hydraulic calculation (video)
The fastest and easiest way to make a hydraulic calculation for a heating system is with an online calculator. Without a specialized education, you shouldn't even try to perform a calculation in an Excel spreadsheet. Buying a special program for a lot of money, of course, is also pointless. The advice is this: if you want to avoid problems, then immediately contact a good specialist, of which there are actually not so many, so be careful.
What is hydraulic calculation
Hydraulic calculation is done only for large heating circuits.
The principle of operation of a water heating system is that a coolant circulates through pipes and batteries. This is a liquid (water or) that is heated in a boiler and then driven along the entire circuit by a circulation pump or due to the force of gravity.
The coolant encounters hydraulic resistance during circulation. In addition, the fluid stops slightly due to friction against the pipe walls. The hydraulic calculation of heating systems is carried out in order to calculate the optimal value of the resistance of the circuit, at which the speed of the coolant will be within the normal range (2-3 m / s for a sealed circuit). At the conclusion of the calculations, we find out the following key parameters:
- for the contour;
- circulating pump power;
- the number of revolutions for adjustment on each radiator.
Regardless of where the hydraulic calculation of the heating system was performed, on an online calculator or in Excel, its usefulness can hardly be overestimated. Since with one shot we kill two birds with one stone: the circuit works like a clock and there is no cost overrun, because we will know for sure the optimal parameters of the system elements.
The hydraulic calculation needs to be done only for large heating systems that heat houses with an area of 200 sq. This is not necessary for small contours.
Experts make a hydraulic calculation of the heating system in an Excel table. This is a very complex process that is not within the power of all people with specialized education, not to mention amateurs. You need to understand heat engineering, hydraulics, know the basics of installation and much more. You can get this knowledge only in a higher educational institution. There are specialized programs for the hydraulic calculation of the heating system. But again, only people with specialized education can work with them.
Why do you need an axonometric diagram
An axonometric diagram is a three-dimensional drawing of a heating system. It is simply unrealistic to make a hydraulic calculation of heating without it. The drawing indicates:
- piping;
- places for reducing the diameter of pipes;
- placement of heat exchangers and other equipment;
- places of installation of pipeline fittings;
- battery volume.
Their thermal power depends on the size of the batteries, which should be enough to heat each room. To choose radiators, you need to know the heat loss. The larger they are, the more powerful heat exchangers are needed. Axonometry is performed with respect to scale.
Hydraulic calculation methods
As we have already said, the hydraulic calculation can be done on an online calculator, using a special program, or in an Excel spreadsheet. The first option is suitable even for those who do not understand anything about heating technology and hydraulics. Naturally, this method can only obtain approximate values, which cannot be used in large and complex projects.
An example of an axonometric diagram.
The software is very expensive and it makes no sense to buy it at once, but you can make a table in Excel without investment. You can perform the calculation using different formulas:
- theoretical hydraulics;
- SNIPa 2.04.02-84.
But the calculation method may also differ: specific pressure loss or resistance characteristics. The latter cannot be used for gravitational systems with natural circulation of the coolant. When installing small two-pipe heating circuits with forced circulation, it is enough to adhere to a few simple rules. The main lines are made of polypropylene pipes with an outer diameter of 25 mm. Radiator outlets are made of 20 mm pipes. And we wrote about how to choose a pump.
An example of a hydraulic calculation in Excel
Immediately, we note that the simplest hydraulic calculation of the heating system will be described below. An example of a calculation was made using the formulas of theoretical hydraulics for a straight pipeline in a horizontal plane 100 m long. A pipe with an outer diameter of 108 mm and a wall thickness of 4 mm is used.
Hydraulic calculation in Excel.
For calculations, we need the following initial data:
- water consumption;
- flow and return temperature;
- nominal pipe passage;
- contour length;
- roughness of the pipe;
- overall coefficient of resistance.
Using the example of the hydraulic calculation of the heating system, we need to determine three main criteria - friction pressure loss (PDTr), pressure loss at local resistances (PDMS) and pressure loss in the pipeline (PDTp). All values must be in Pascals (Pa). The formulas below will be calculated in kg / cm. sq. To convert kg / cm. sq. in Pascals, multiply by 9.18 and by 10 thousand.
To calculate the PDTr, we need to multiply the characteristic of the hydraulic resistance by the delta of the coolant temperatures. To calculate the PDMS, you need to multiply the average water density by PDTr, the coefficient of hydraulic friction and by 1 thousand. Then we divide the resulting value by 2, then by 9.18 and by 10 thousand. The pressure loss in the pipeline is calculated by summing PDTr and PDTp.
Outcomes
To make a hydraulic calculation of the heating system, use a program, an online calculator or an Excel spreadsheet. Using an example, we have shown that it is impossible for a person without a specialized education to make correct calculations. Therefore, the best option is to order it from a specialist. If the house is small, then the calculation is not needed.
Saving heat in a home largely depends on the correct calculation of hydraulics, its correct installation, and also use. All elements of the heating system (boiler, heat pipes and radiators that give off heat) must be interconnected so that the initial parameters of the system are preserved, regardless of what time of year it is outside the window and what the loads are.
What does the calculation of hydraulics mean and why is it needed
To make a hydraulic calculation of heating means to correctly select the parameters of certain sections of the network, taking into account the pressure, so that a certain flow of the coolant is carried out along them.
This calculation makes it possible to determine:
- Pressure losses in various sections of the network;
- Pipeline throughput;
- Optimal fluid consumption;
- Indicators required for hydraulic balancing.
Combining all the data obtained, you can select heating pumps.
The main purpose of calculating hydraulics is to ensure that the calculated costs of the heat source correspond to the actual ones.
The amount of heat source entering the radiators must be such that a heating balance is obtained inside the building, taking into account the outdoor temperature and the temperature set by the user for each room separately.
If the heating is autonomous, you can use the following calculation methods:
- Using the characteristics of resistance and conductivity;
- By specific costs;
- By comparing the dynamic pressure;
- For different lengths reduced to one indicator.
Calculation of hydraulics is one of the most important stages in the development of heating systems with a liquid heat carrier.
Before proceeding with its implementation, you must:
- Determine the balance of heat in the required rooms;
- Select the type of heating devices and place them on the building drawings;
- Solve issues on the configuration of the heating system, as well as on the types of pipes and fittings used;
- Draw a diagram of the heating system, where the numbers, loads and lengths of the required sections will be visible;
- Determine the main circulation ring along which the coolant moves.
Typically, for buildings with a small number of floors, a two-pipe heating system is used, and for buildings with a large number of storeys, a single-pipe heating system.
Automated hydraulic calculation of the heating system Excel
To make it more convenient to do hydraulic calculations, you can use various computer programs that allow you to perform accurate calculations. Excel is considered one of the most popular programs.
By the way, if you do not know the basics of hydraulics, then it will be difficult for you to do this, even in computer programs. This is due to the fact that in some of them there is no decoding of formulas and calculations of resistance in especially complex chains.
The nuances of some programs:
- OvertopCO and DanfossCO can calculate natural circulation systems;
- HERZ C.O. 3.5 - works by the method of calculating the specific pressure loss;
- Potok - perfectly copes with calculations for changing temperature drops along the risers.
When entering temperature data, it is imperative to clarify whether the calculation is in Celsius or in Kelvin.
As for working in Excel, it is very convenient to use spreadsheets. You just need to know the sequence of actions and the exact calculation formulas. First, the desired cell is selected into which data is entered. Further calculation is carried out by automatic application of formulas.
- Difference between hot and cold heat source for a two-pipe system or liquid flow rate for a one-pipe system;
- The speed of movement of the heat source and its flow;
- The density of the liquid and the parameters of the studied areas (their length in meters and the number of devices located there).
To calculate the size of pipes inside each section, it is just convenient to use Excel tables.
How to calculate the hydraulic resistance of the heating system
To decide what material to take pipes from, you need to find out the resistance of the hydraulics in all sections of the heating system and compare it.
Resistance can occur in the pipe itself due to its turns, contractions or expansions, as well as in the joints between ball valves, tees or balancing devices.
The calculated section is usually considered to be a pipe with a constant flow rate equal to the planned heat balance of the room.
To calculate the losses, the following data are taken, taking into account the resistance of the reinforcement:
- The diameter and length of the pipe in the desired section;
- Parameters of control valves from the manufacturer;
- The speed at which the coolant moves;
- The roughness of the pipeline and the thickness of its walls;
- Data from the handbook: friction loss and its coefficient, fluid density.
If you need to independently calculate the specific friction loss, you need to know the outer diameter of the pipe, the thickness of its wall and the speed with which the fluid is supplied.
To find the hydraulic resistance in one area, you can use the Darcy-Weisbach formula:
Hydraulics of the heating system and its coordination
The balancing of pressure drops in the heating system is carried out using shut-off and control valves.
Hydraulic linkage is calculated based on:
- Dynamic resistance parameters of pipes;
- Rebar technical properties;
- The total consumption of the heat source;
- The number of available resistances in the calculated area.
It should be borne in mind here that the flow capacity, pressure drops and attachments are determined separately for the valves. It is these characteristics that are used to calculate the coefficients of the heat source entering each riser, and then into the radiators.
The lack of hydraulic balancing in the heating system can lead to the fact that in some rooms it will be very difficult to achieve the desired temperature.
The resistance of the hydraulics in the main circulation ring is equal to the sum of the losses of the local systems, the primary circuit, the heat exchanger and the heat generator.
Hydraulic calculation of the heating system (video)
Performing a hydraulic calculation, you make the heating system more perfect, by correctly selecting its parameters so that in any weather, at any load, the consumption of the heat source does not exceed the specified norms.
What is a hydraulic calculation of a heating system? What quantities need to be calculated? Finally, the main thing: how to calculate them without having the exact values of the hydraulic resistance of all sections, heating devices and elements of shut-off valves? Let's figure it out.
What are we counting on
For any heating system, the most important parameter is its thermal power.
It is defined:
- Coolant temperature.
- Thermal power of heating devices.
Note: in the documentation, the last parameter is indicated for a fixed delta of temperatures between the temperature of the coolant and the air in a heated room at 70 C.
Reducing the temperature delta by half will lead to a twofold decrease in thermal power.
For now, we will leave the methods for calculating the thermal power behind the scenes: there are enough thematic materials devoted to them.
However, in order to ensure the transfer of heat from the line or boiler to heating devices, two more parameters are important:
- Internal section of the pipeline, tied to its diameter.
- The flow rate in this pipeline.
In an autonomous heating system with forced circulation, it is important to know a couple more values:
- Hydraulic resistance of the circuit. Calculation of the hydraulic resistance of the heating system will allow you to determine the requirements for the pressure generated by the circulation pump.
- The flow rate of the coolant through the circuit, which is determined by the capacity at the corresponding head.
Problems
As they say in Odessa, "they are."
In order to calculate the total hydraulic resistance of the circuit, you need to take into account:
- Resistance of straight pipe sections... It is determined by their material, inner diameter, flow rate and the degree of wall roughness.
- Resistance of every turn and transition of diameter.
- Resistance of each element of shut-off valves.
- Resistance of all heating devices.
- Boiler heat exchanger resistance.
Putting together all the necessary data will clearly become a problem, even in the simplest scheme.
What to do?
Formulas
Fortunately, for an autonomous heating system, the hydraulic calculation of heating can be performed with acceptable accuracy and without delving into the jungle.
Flow rate
On the lower side, it is limited by the growth of the temperature difference between the supply and return, and at the same time an increased likelihood of airing. The fast flow will force the air out of the bridges to the automatic air vent; a slow one will not cope with this task.
On the other hand, too fast a flow will inevitably generate hydraulic noise. Valve elements and filling bends will become a source of annoying hum.
For heating, the range of acceptable flow velocity is taken from 0.6 to 1.5 m / s; in this case, the calculation of other parameters is usually performed for a value of 1 m / s.
Diameter
With a known thermal power, it is easiest to select it from the table.
| Internal pipe diameter, mm | Heat flux, W at Dt = 20С | ||
| Speed 0.6 m / s | Speed 0.8 m / s | Speed 1 m / s | |
| 8 | 2453 | 3270 | 4088 |
| 10 | 3832 | 5109 | 6387 |
| 12 | 5518 | 7358 | 9197 |
| 15 | 8622 | 11496 | 14370 |
| 20 | 15328 | 20438 | 25547 |
| 25 | 23950 | 31934 | 39917 |
| 32 | 39240 | 52320 | 65401 |
| 40 | 61313 | 81751 | 102188 |
| 50 | 95802 | 127735 | 168669 |
Pressure
In a simplified version, it is calculated by the formula H = (R * I * Z) / 10000.
In it:
- H is the required head value in meters.
- I - head loss in the pipe, Pa / m. For a straight pipe section of the design diameter, it takes on a value in the range of 100-150.
- Z is an additional compensation factor, which depends on the presence of additional equipment in the circuit.
In the photo - a mixing unit for heating.
If the system contains several elements from the list, the corresponding coefficients are multiplied. So, for a system with ball valves and a thermostat that regulates the throughput of the filling, Z = 1.3 * 1.7 = 2.21.
Performance
Instructions for calculating with your own hands the pump performance is also not difficult.
Performance is calculated using the formula G = Q / (1.163 * Dt), in which:
- G - productivity in m3 / hour.
- Q is the thermal power of the circuit in kilowatts.
- Dt is the temperature difference between the supply and return pipelines.
Example
Let's give an example of a hydraulic calculation of a heating system for the following conditions:
- The delta of temperatures between the supply and return pipelines is equal to the standard 20 degrees.
- The thermal power of the boiler is 16 kW.
- The total length of the one-pipe Leningrad bottle is 50 meters. The heating devices are connected in parallel with the filling. Thermostats for breaking the filling and secondary circuits with mixers are absent.
So let's get started.
The minimum internal diameter according to the table above is 20 millimeters at a flow velocity of 0.8 m / s or more.
Useful: modern circulating pumps often have step or, more conveniently, smooth performance control.
In the latter case, the price of the device is slightly higher.
The optimal head for our case will be (50 * 150 + 1.3) / 10000 = 0.975 m. Actually, in most cases the parameter does not need to be calculated. The difference in the heating system of an apartment building, which provides circulation in it, is only 2 meters; this is the minimum head value for the vast majority of glandless pumps.
The capacity is calculated as G = 16 / (1.163 * 20) = 0.69 m3 / h.
Conclusion
We hope that the given calculation methods will help the reader calculate the parameters of his own heating system without getting into the jungle of complex formulas and reference data. As always, the attached video will offer additional information. Good luck!
