A two-pipe heating system is more complex than a single-pipe one, and the amount of materials needed for installation is much larger. Nevertheless, it is the 2-pipe heating system that is more popular. As the name implies, it uses two circuits. One serves to deliver the hot coolant to the radiators, and the second takes the cooled coolant back. Such a device is applicable for any type of structures, as long as their layout allows the installation of this structure.
The demand for a double-circuit heating system is due to the presence a number of significant benefits. First of all, it is preferable to single-circuit, since in the latter the coolant loses a significant part of the heat even before it enters the radiators. In addition, the double-circuit design is more versatile and is suitable for houses of different heights.
The disadvantage of a two-pipe system its high price is considered. However, many people mistakenly believe that the presence of 2 circuits involves the use of twice the number of pipes, and the cost of such a system is twice as much as a single-pipe system. The fact is that for a single-pipe design it is necessary to take pipes of large diameter. This ensures the normal circulation of the coolant in the pipeline, and hence the efficient operation of such a design. The advantage of a two-pipe is that for its installation, pipes of a smaller diameter are taken, which are much cheaper. Accordingly, additional elements (drives, valves, etc.) are also used with a smaller diameter, which also somewhat reduces the cost of the design.
The budget for installing a two-pipe system will not be much larger than for a single-pipe system. On the other hand, the efficiency of the former will be noticeably higher, which will be a good compensation.
Application example
One of the places where two-pipe heating will be very useful is garage. This is a working room, so there is no need for constant heating. In addition, a do-it-yourself two-pipe heating system is a very real undertaking. Installing such a system in a garage is not necessary, but it will be absolutely not superfluous, since it is very difficult to work here in winter: the engine does not start, the oil freezes, and it’s just uncomfortable to work with your hands. The two-pipe heating system provides quite acceptable conditions for being indoors.
Varieties of two-pipe systems for heating
There are several criteria by which such heating structures can be classified.
open and closed
Closed systems suggest the use of an expansion tank with a membrane. They can work at high pressure. Instead of ordinary water in closed systems, ethylene glycol-based heat transfer fluids can be used, which do not freeze at low temperatures (up to 40 °C below zero). Motorists know such liquids under the name "antifreeze".
1. Heating boiler; 2. Security group; 3. Overpressure relief valve; 4. Radiator; 5. Return pipe; 6. Expansion tank; 7. Valve; 8. Drain valve; 9. Circulation pump; 10. Pressure gauge; 11. Make-up valve. However, we must remember that for heating devices there are special compositions of coolants, as well as special additives and additives. The use of conventional substances can lead to the breakdown of expensive heating boilers. Such cases can be regarded as non-warranty, because the repair will require significant costs.
open system it is characteristic that the expansion tank must be installed strictly at the highest point of the device. It must be provided with a pipe for air and a drain pipe through which excess water is drained from the system. Also through it you can take warm water for household needs. However, this use of the tank requires automatic feeding of the structure and excludes the possibility of using additives and additives.
1. Heating boiler; 2. Circulation pump; 3. Heating appliances; 4. Differential valve; 5. Gate valves; 6. Expansion tank. And yet, a closed-type two-pipe heating system is considered safer, so modern boilers are most often designed for it.
Horizontal and vertical
These types differ in the location of the main pipeline. It serves to connect all structural elements. Both horizontal and vertical systems have their own advantages and disadvantages. However, both of them demonstrate good heat transfer and hydraulic stability.
Two-pipe horizontal heating design found in one-story buildings, and vertical- in high-rise buildings. It is more complex and therefore more expensive. Here, vertical risers are used, to which heating elements are connected on each floor. The advantage of vertical systems is that they usually do not have air locks, since the air exits through the pipes up to the expansion tank. 
Systems with forced and natural circulation
Such types differ in that, firstly, there is an electric pump that causes the coolant to move, and secondly, the circulation occurs on its own, obeying physical laws. The disadvantage of designs with a pump is that they depend on the availability of electricity. For small rooms, there is no particular point in forced systems, except that the house will heat up faster. With large areas, such structures will be justified.
In order to choose the right type of circulation, it is necessary to consider which piping type used: top or bottom.
Top wiring system involves laying the main pipeline under the ceiling of the building. This provides a high pressure of the coolant, so that it passes well through the radiators, which means that the use of a pump will be redundant. Such devices look more aesthetic, pipes at the top can be hidden with decorative elements. However, a membrane tank must be installed in this system, which entails additional costs. It is also possible to install an open tank, but it must be at the highest point of the system, that is, in the attic. In this case, the tank must be insulated. 
Bottom wiring involves the installation of the pipeline just below the windowsill. In this case, you can install an open expansion tank anywhere in the room slightly above the pipes and radiators. But without a pump in such a design is indispensable. In addition, difficulties arise if the pipe must pass by the doorway. Then it is necessary to let it run along the perimeter of the door or make 2 separate wings in the contour of the structure. 
Dead end and passing
In a dead end system the coolant hot and cooled go in different directions. In a passing system constructed according to the Tichelman scheme (loop), both flows go in the same direction. The difference between these types is the ease of balancing. If the associated one, when using radiators with an equal number of sections, is already balanced in itself, then in a dead end, a thermostatic valve or a needle valve must be installed on each radiator.
If, in the Tichelman scheme, radiators with an unequal number of sections are used, the installation of valves or valves is also required here. But even in this case, such a design is balanced easier. This is especially noticeable in extended heating systems. 
Selection of pipes by diameter
The choice of pipe section must be made based on the volume of coolant that must pass per unit of time. It, in turn, depends on the heat output required to heat the room.
In our calculations, we will proceed from the fact that the amount of heat loss is known and there is a numerical value of the heat required for heating.
Calculations begin with the final, that is, the farthest radiator of the system. To calculate the coolant flow rate for a room, you need the formula:
G=3600×Q/(c×Δt), where:
- G - water consumption for space heating (kg / h);
- Q is the thermal power required for heating (kW);
- c is the heat capacity of water (4.187 kJ/kg×°C);
- Δt is the temperature difference between the hot and cooled coolant, assumed to be 20 °C.
For example, it is known that the heat output for space heating is 3 kW. Then the water consumption will be:
3600×3/(4.187×20)=129 kg/h, i.e. about 0.127 cu. m of water per hour.
In order for water heating to be balanced as accurately as possible, it is necessary to determine the cross section of the pipes. For this we use the formula:
S=GV/(3600×v), where:
- S is the cross-sectional area of the pipe (m2);
- GV is the volume flow of water (m3/h);
- v is the speed of water movement, is in the range of 0.3−0.7 m/s.
If the system uses natural circulation, then the speed of movement will be minimal - 0.3 m / s. But in this example, let's take the average value - 0.5 m / s. According to the indicated formula, we calculate the cross-sectional area, and based on it, the inner diameter of the pipe. It will be 0.1 m. We select a polypropylene pipe of the nearest larger diameter. This product has an inner diameter of 15mm.
Then we move on to the next room, calculate the coolant flow rate for it, sum it up with the flow rate for the calculated room and determine the pipe diameter. And so to the boiler.
System installation
When installing the structure, certain rules should be followed:
- any two-pipe system includes 2 circuits: the upper one serves to supply hot coolant to the radiators, the lower one - to drain the cooled one;
- the pipeline should have a slight slope towards the final radiator;
- the pipes of both circuits must be parallel;
- the central riser must be insulated to prevent heat loss when the coolant is supplied;
- in reversible two-pipe systems, it is necessary to provide several taps with which it is possible to drain water from the device. This may be needed during repair work;
- when designing a pipeline, it is necessary to provide for the smallest possible number of angles;
- the expansion tank must be installed at the highest point in the system;
- diameters of pipes, taps, spurs, connections must match;
- when installing a pipeline from heavy steel pipes, special fasteners must be installed to support them. The maximum distance between them is 1.2 m.
How to make the correct connection of heating radiators, which will ensure the most comfortable conditions in the apartment? When installing two-pipe heating systems, it is necessary to adhere to the following sequence:
- The central riser of the heating system is diverted from the heating boiler.
- At the highest point, the central riser ends with an expansion tank.
- From it, pipes are bred throughout the building, which bring the hot coolant to the radiators.
- To remove the cooled coolant from the heating radiators with a two-pipe design, a parallel supply pipeline is laid. It must be connected to the bottom of the boiler.
- For systems with forced circulation of the coolant, an electric pump must be provided. It can be installed at any convenient location. Most often it is mounted near the boiler, near the entry or exit point.
Connecting a heating radiator is not such a complicated process, if you approach this issue scrupulously.
The heating system is divided into two types: one-pipe and two-pipe. Obviously, it is most advantageous to install a more efficient one that will not only cope with its functions, but will also serve you for more than one year. In order not to remain "out of the blue" and not make a mistake with the choice of the heating system.
You need to properly understand which of the heating systems is best for you and why.
Thus, you will know which system is better from a technical point of view and how to choose it, taking into account your budget.
High water pressure ensures a natural cycle, and antifreeze makes the system more economical.
Disadvantages of a single pipe system - a very complex thermal and hydraulic calculation of the network, since, having made a mistake in the calculations of devices, it is very difficult to eliminate it.
Also, this is a very high hydrodynamic resistance and an involuntary number of heating devices on one line.
The flow of the coolant goes immediately to everything and is not subject to separate adjustment.
In addition, very high heat losses.
In order to be able to regulate the operation of individual devices connected to one riser, bypasses (closing sections) are connected to the network - this is a jumper in the form of a piece of pipe connected by a direct and return radiator pipes, with taps and valves.
To be able to control the temperature of each individually, the bypass allows you to connect automatic thermostats to the radiator.
In addition, it also makes it possible, in the event of a breakdown, to replace or repair individual devices without turning off the entire heating system.
Single-pipe heating is divided into vertical and horizontal:
- vertical - this is the connection of all batteries in series from top to bottom.
- horizontal - this is a serial connection of all heating devices on all floors.
Due to the accumulation of air in batteries and pipes, so-called traffic jams occur, which is a disadvantage of both systems.
Installation of a one-pipe system
Connection is made according to the scheme, using valves for airing radiators, which block the valves and plugs.
Crimping system - after which the coolant is poured into the battery and the system adjustment is directly adjusted.
Two-pipe heating system
The advantage of a two-pipe heating system - this is the installation of automatic thermostats, which gives you the full ability to adjust the temperature in individual rooms.
This also includes the independence of the operation of the circuit devices, which is provided by a special collector system.
The difference between a two-pipe and a single-pipe system is that in the first one you can connect additional batteries after connecting the main ones, as well as the possibility of extending in vertical and horizontal directions.
Unlike a single-pipe, here you can also easily correct permissible errors.
The disadvantages of this system are minimal if you have enough material resources and have the opportunity to call the master.
Installation of a heating system with lower horizontal piping
This system allows you to locate the open tank in a convenient warm place. Also, it is possible to combine expansion and supply tanks allow you to use hot water directly from the heating system itself.
In systems with forced circulation, to reduce pipe consumption, the discharge and supply risers are located at the level of the first.
There are several ways to heat a room with water. There is a two-pipe, one-pipe layout and two types of pipes: lower and upper. Consider a design with two pipes and wiring at the bottom.
Characteristic
The most common is precisely the two-pipe organization of heating, despite some advantages of single-pipe structures. No matter how complicated such a main line with two pipes (separately for supplying water and returning it) is, most people prefer it.
Such systems are in high-rise and apartment buildings.
Device
The elements of dual-main heating with a lower pipe insert are as follows:
- boiler and pump;
- air vent, thermostatic and safety valves, valves;
- batteries and expansion tank;
- filters, control devices, temperature and pressure sensors;
- bypasses can be used, but not required.
Advantages and disadvantages
The considered two-pipe connection scheme, when used, reveals many advantages. Firstly, the uniformity of heat distribution throughout the line and the individual supply of coolant to the radiators.
Therefore, it is possible to regulate the heating devices separately: turn on / off (you only need to close the riser), change the pressure.
You can set different temperatures in different rooms.
Secondly, such systems do not require shutting down or draining the entire coolant in the event of a breakdown of one heater. Thirdly, the system can be installed after the construction of the lower floor and not wait until the whole house is ready. In addition, the pipeline has a smaller diameter than in a single pipe system.
There are also some disadvantages:
- more materials are required than for a single-pipe line;
- low pressure in the supply riser makes it necessary to bleed air frequently by connecting additional valves.
Comparison with other types
In the lower tie-in, the supply line is laid from below, next to the return line, therefore the coolant is directed from the bottom up along the supply risers. Both types of wiring can be designed with one or more circuits, dead-end and associated water flow in the supply pipe and return.
Natural circulation systems with a bottom connection are used very rarely, since they require a large number of risers, and the point of such a tie-in of pipes is to minimize their number. With this in mind, such designs most often have forced circulation.
Roof and floors - meaning
In the upper connection, the supply line is above the level of the radiator. It is mounted in the attic, in the ceiling. The heated water comes up, then - through the supply risers it evenly spreads over the batteries. Radiators must be above the return. To exclude air accumulation, a compensating tank is mounted at the topmost point (in the attic). Therefore, it is not suitable for houses with a flat roof without an attic.
The wiring from the bottom has two pipes - supply and discharge - radiators must be above them. It is very convenient for removing air congestion with Mayevsky cranes. The supply line is located in the basement, in the basement, under the floor. The supply pipeline must be higher than the return. The additional slope of the line towards the boiler minimizes air pockets.
Both wirings are most effective in a vertical configuration, when the batteries are mounted on different floors or levels.
Principle of operation
The main characteristic of a two-pipe system is the presence of an individual water supply line to each radiator. In this scheme, each of the batteries is equipped with two separate pipes: water inlet and outlet. The coolant flows to the batteries from the bottom up. The cooled water returns through the return risers to the return line, and through it to the boiler.
In a multi-storey building, it is appropriate to install a two-pipe structure with a vertical arrangement of the main line and a lower wiring. In this case, the temperature difference between the coolant in the supply pipe and the return pipe creates a strong pressure that increases as the floor rises. Pressure helps water move through the pipeline.
In the considered lower pipe connection, the boiler must be in a recess, since the radiators and heaters must be higher to ensure uniform delivery of water to them.
The air that accumulates is removed by Mayevsky taps or drains, they are mounted on all heating appliances. Automatic vents are also used, which are fixed on risers or special air vent lines.
Kinds
A two-pipe heating system can be of the following types:
- horizontal and vertical;
- direct-flow - the coolant flows in one direction through both pipes;
- dead end - hot and cooled water moves in different directions;
- with forced or natural circulation: the first requires a pump, the second requires a pipe slope towards the boiler.
The horizontal scheme can be with dead ends, with the associated movement of water, with a collector. It is suitable for one-story buildings with a considerable length, when it is advisable to connect the batteries to a horizontally located main pipe. Such a system is also convenient for buildings without piers, in panel-frame houses, where it is convenient to place risers in a stairwell or corridor.
According to experts, the vertical scheme with forced water flow has become the most effective. It needs a pump, which is located on the return line in front of the boiler. An expansion tank is also mounted on it. Due to the pump, the pipes can be smaller than in the design with natural movement: water with its help is guaranteed to move along the entire line.
All heaters are connected to a vertical riser. This is the best option for multi-storey buildings. Each floor is connected to the riser pipe separately. The advantage is that there are no air pockets.
Installation
Conventionally, several stages of work can be distinguished. First, the type of heating is determined. If gas is supplied to the house, then the most ideal option would be to install two boilers: one is gas, the second is a spare, solid fuel or electricity.
Stages
Briefly, the installation consists of the following items:
- the supply pipe is brought up from the boiler and connected to the compensatory tank;
- a pipe of the upper line is taken out of the tank, which goes to all radiators;
- a bypass (if provided) and a pump are installed;
- a return line is drawn parallel to the supply line, it is also connected to radiators and cut into the boiler.
For a two-pipe system, the boiler is installed first, for which a mini-boiler room is created. In most cases, this is a basement (ideally, a separate room). The main requirement is good ventilation. The boiler must have free access and be located at some distance from the walls.
The floor and walls around it are lined with refractory material, and the chimney is led out into the street. If necessary, a circulation pump, a manifold for distribution, regulating, measuring instruments are installed near the boiler.
They are installed last. They are located under the windows and are fixed with brackets. The recommended height from the floor is 10-12 cm, from the walls - 2-5 cm, from the window sills - 10 cm. The inlet and outlet of the battery is fixed by locking and regulating devices.
It is advisable to install temperature sensors - with their help, you can monitor the temperature and regulate them.
If the heating boiler is gas, then it is necessary to have the appropriate documentation and the presence of a representative of the gas industry at the first start.
The expansion tank is located at or above the peak point of the line. If there is an autonomous water supply, then it can be integrated with a supply tank. The slope of the supply and return pipes should be no more than 10 cm per 20 linear meters or more.
If the pipeline is at the front door, it is appropriate to divide it into two knees. Then the wiring is created from the place of the highest point of the system. The lower line of a two-pipe design should be symmetrical and parallel to the upper one.
All technological units must be equipped with taps, and it is desirable to insulate the supply pipe. The distribution tank is also desirable to be placed in an insulated room. In this case, there should be no right angles, sharp fractures, which will subsequently create resistance and air congestion. Finally, we must not forget about the pipe supports - they must be made of steel and crash every 1.2 meters.
In apartments and private houses, an integral part of comfort is the provision of heat. Mostly use water heating. Water heating comes with a single-pipe and two-pipe circuit. In the first case, the water, passing through a closed circuit, cools down greatly. Each subsequent radiator receives a colder liquid. The two-pipe system eliminates this disadvantage.
A two-pipe heating system is effective for a private house. These designs have become more popular. The complexity of installation and a slightly higher consumption of materials pay off with clear advantages.
Advantages of two-pipe heating:
- Each radiator receives an equally heated coolant, increasing the air temperature in the room.
- Possibility to regulate the heat of each battery by setting a thermostat.
- If one of the systems breaks down, repairs can be carried out without stopping the heating. To do this, it is necessary to install locking elements.
- For installation, you can use pipes of small diameter, significantly saving money.
- Installation in a room of any size.
A distinctive feature of the system is the connection to each radiator 2 pipes. Through the first, heat enters the battery, the second removes the cooled liquid from the device. This design allows you to effectively heat the room.
Layout of pipes of a two-pipe heating system
The two-pipe wiring diagram is of 2 types - vertical and horizontal. In the first case, the heating elements are located vertically along one riser, which is typical for apartment buildings. In most cases, the coolant is fed upwards, the outlet descends by gravity.
In the horizontal version, the batteries are arranged in one line. Such wiring is inherent in single-story buildings.
The two-pipe design can be open and. Any heating includes an expansion tank as part of the elements. When heated, the pressure in the pipes increases, and the compensation system allows you to maintain the required operating level. The device is located at the highest point, usually in the attics of houses. With open wiring, the liquid in the tank comes into contact with air. Part of it evaporates, so such a system requires constant monitoring. In the closed type, the design is equipped with a membrane, and does not require constant attention.
Circuit advantage:
- A more aesthetic appearance of the room, the pipes are hidden under the radiators and are not conspicuous;
- For passage to the radiators, one opening is required;
- Reduced heat loss.
All heating systems can be made with natural and forced circulation. The choice of design is influenced by the top or bottom water supply. For the bottom supply, it is necessary to install forced water circulation. Pipes from the boiler to the radiators are laid at floor level, just below the batteries. Around the entire perimeter of the room, 2 pipes are passed: distribution and return. They are connected to each radiator using fittings and tees. Such a system can be constructed from metal-plastic or polypropylene pipes independently, without resorting to the services of specialists.
Option with top wiring in a two-pipe heating system of a private house
In private houses, you can install both lower and upper distribution. For upper wiring, the use of natural water circulation is preferable. Distribution with hot coolant is pulled from the boiler to the ceiling, then laid along the perimeter of the building.
Design description:
- Branches are vertically lowered from the upper pipe to the radiators;
- The reverse stroke is laid at the level of the floor;
- Connect both pipes to radiators;
- For physical circulation, the slope of the pipe should be 3-5ᵒ, while the expansion tank is installed at the highest point of the circuit.
The heating system of natural circulation starts to work when the water is heated. The coolant becomes lighter and rushes up, reaching the highest point of the circuit, then descends through the pipes into the radiators, cools down and becomes heavier, goes back to the boiler.
The lower the room temperature, the faster the circulation of water in the batteries.
The maximum effect from the top distribution can be obtained in a 2-storey building. Natural circulation will be stimulated by the difference in the height of the batteries on the 2nd floor and the installation of a boiler in the basement. The disadvantage of the upper scheme is the external aesthetic appearance, in addition, part of the heat goes up. You can compensate for the disadvantage by combining one-pipe and two-pipe heating. For example, make a single-pipe warm floor on the 2nd floor, on the 1st conduct a two-pipe wiring.
Accurate calculation of a two-pipe heating system
Before starting work, it is necessary to draw up a heating scheme, decide on the material, and make a hydraulic calculation. It is necessary to calculate the pressure drop in the back section or to calculate the diameter of the pipe.
The calculation is carried out taking into account the following factors:
- The inner surface of the pipes and its roughness;
- Section diameter;
- Number of pipe bends;
- Pressure drop between supply and return;
- The number of radiators and their cross section;
- Locking elements.
When carrying out the calculation, formulas and an axonometric table are used. You can use a special software program. The most loaded ring or contour is taken as the main object. As a result of calculations, the optimal speed of movement should be from 0.3 to 0.7 m/s.
At a higher speed, the heating will make noise, at a lower speed, there will be a strong temperature variation.
After the calculations, they acquire pipes of effective diameter, the required number of radiators, a boiler, fittings, squeegees, an expansion tank, a circulation pump, if such a need exists.
Do-it-yourself steps for installing two-pipe heating
Installation of the heating system begins with the installation of the boiler. The heat generator on gas and electricity is located in any room. For liquid and solid fuel boilers, a separate niche is required. When installing radiators, it is necessary to take into account the pipeline slope of 1-2% in relation to the entire length of the pipe.
Work plan:
- Boiler installation.
- From the heat generator, the main pipe with hot water is discharged, which runs through all the radiators.
- Parallel to the first, a second line with a reverse course is carried out.
- With a forced heating option, a circular pump is inserted.
- Install radiators. Batteries are hung on special brackets. All radiators must be at the same level. For ease of use, they are equipped with shut-off valves at the entry and exit points. Batteries are connected in several ways: side, diagonal, bottom connection. The most effective side and diagonal design.
- The heating system is completed by installing pipes of related units, installing an expansion tank and additional elements.
The main line should not contain straight and sharp corners, as resistance will increase. Taps and valves must match the dimensions of the pipes. With a design with top wiring, the expansion tank is placed in an insulated attic. After completion of all installation work, it is time to connect the system.
To do this, close all the taps, and be sure to slowly fill the supply circuit.
Next, the valve of the first battery is opened, and with the help the air is bled until an even jet exits. The element is closed and the radiator outlet cock is opened. These manipulations must be carried out with each radiator. All found defects are eliminated.
Do-it-yourself two-pipe heating of a private house (video)
Do-it-yourself installation of a two-pipe system will take more time, ultimately provide efficient and practical heating, and save on installation work. It is important to choose the right option for the house, and make a competent calculation of the system parameters. Skillful hands and following the instructions will transform the house, making it cozy and warm.
Examples of heating wiring in a private house (photo)
The water heating system can be one-pipe and two-pipe. Two-pipe is called so because two pipes are needed for operation - one from the boiler is supplied with hot coolant to the radiators, the other is cooled down from the heating elements and fed back into the boiler. Boilers of any type on any fuel can work with such a system. Both forced and natural circulation can be implemented. Two-pipe systems are installed in both one-story and two- or multi-story buildings.
Advantages and disadvantages
The main disadvantage of this method of organizing heating follows from the method of organizing the circulation of the coolant: a double number of pipes compared to the main competitor - a single-pipe system. Despite this situation, the cost of purchasing materials is slightly higher, and all due to the fact that with a 2-pipe system smaller diameters of both pipes and, accordingly, fittings are used, and they cost much less. So as a result, the cost of materials is higher, but not significantly. What is really more is the work, and accordingly it takes twice as much time.
This disadvantage is compensated by the fact that a thermostatic head can be installed on each radiator, with the help of which the system is easily balanced in automatic mode, which cannot be done in a single-pipe system. On such a device, you set the desired temperature of the coolant and it is constantly maintained with a small error (the exact value of the error depends on the brand). In a one-pipe system, it is possible to realize the ability to regulate the temperature of each radiator separately, but this requires a bypass with a needle or three-way valve, which complicates and increases the cost of the system, negating the savings in money for the purchase of materials and installation time.
Another disadvantage of a two-tube is the impossibility of repairing radiators without stopping the system. This is inconvenient and this property can be circumvented by placing ball valves near each heater on the supply and return. By blocking them, you can remove and repair the radiator or heated towel rail. The system will continue to function indefinitely.
But such an organization of heating has an important advantage: unlike a single pipe, in a system with two lines, water of the same temperature flows to each heating element - immediately from the boiler. Although it tends to take the path of least resistance and will not spread beyond the first radiator, installing thermostatic heads or flow control valves solves the problem.
There is another advantage - lower pressure losses and easier implementation of gravity heating or the use of smaller pumps for systems with forced circulation.
Classification of 2 pipe systems
Heating systems of any type are divided into open and closed. In the closed ones, a membrane-type expansion tank is installed, which makes it possible for the system to function at elevated pressure. Such a system makes it possible to use not only water as a coolant, but also ethylene glycol-based compounds, which have a lower freezing point (up to -40 ° C) and are also called antifreezes. For the normal operation of equipment in heating systems, special compounds designed for these purposes should be used, and not for general purposes, and even more so, not for automobiles. The same applies to the additives and additives used: only specialized ones. It is especially tough to adhere to this rule when using expensive modern boilers with automatic control - repairs in case of malfunctions will not be guaranteed, even if the breakdown is not directly related to the coolant.
In an open system, an open-type expansion tank is built in at the top point. A pipe is usually connected to it to remove air from the system, and a pipeline is also organized to drain excess water in the system. Sometimes warm water can be taken from the expansion tank for household needs, but in this case it is necessary to make the system recharge automatically, and also not to use additives and additives.
Vertical and horizontal two-pipe system
There are two types of organization of a two-pipe system - vertical and horizontal. Vertical is used most often in multi-storey buildings. It requires more pipes, but the possibility of connecting radiators on each floor is easily realized. The main advantage of such a system is the automatic air outlet (it tends to rise and exits there either through the expansion tank or through the drain valve).
The horizontal two-pipe system is used more often in one-story or, at most, two-story houses. To bleed air from the system, Mayevsky cranes are installed on the radiators.
Two-pipe horizontal heating scheme for a two-story private house (click on the picture to enlarge)
Top and bottom wiring
According to the method of distributing the supply, a system with an upper and lower supply is distinguished. With the upper wiring, the pipe goes under the ceiling, and from it the supply pipes go down to the radiators. The return line runs along the floor. This method is good in that you can easily make a system with natural circulation - the difference in height creates a flow of sufficient force to ensure a good circulation rate, you just need to observe the slope with a sufficient angle. But such a system is becoming less and less popular due to aesthetic considerations. Although, if at the top under a suspended or stretch ceiling, then only pipes to the appliances will remain in sight, and they, in fact, can be monolithic into the wall. Upper and lower wiring are also used in vertical two-pipe systems. The difference is shown in the figure.
With lower wiring, the supply pipe goes lower, but higher than the return. The supply tube can be placed in the basement or semi-basement (the return line is even lower), between the rough and finish floor, etc. The coolant can be supplied / removed to the radiators by passing the pipes through the holes in the floor. With this arrangement, the connection is the most hidden and aesthetic. But here you need to select the location of the boiler: it does not matter in its position relative to the radiators - the pump will “push through”, but in systems with natural circulation, the radiators must be above the level of the boiler, for which the boiler is buried.
The two-pipe heating system of a two-story private house is illustrated in the video. It has two wings, the temperature in each of which is regulated by valves, the lower type of wiring. System with forced circulation, because the boiler hangs on the wall.
Dead-end and associated two-pipe systems
A dead-end system is such a system in which the movement of the coolant supply and return flow is multidirectional. There is a system with passing traffic. It is also called the Tichelman loop / scheme. The latter option is easier to balance and configure, especially with long networks. If radiators with the same number of sections are installed in a system with a passing movement of the coolant, it is automatically balanced, while with a dead-end circuit, a thermostatic valve or a needle valve will be required on each radiator.
Even if radiators of different numbers of sections and valves / valves are installed with the Tichelman scheme, it is still necessary to install, then the chance to balance such a scheme is much higher than a dead-end one, especially if it is quite long.
To balance a two-pipe system with multidirectional movement of the coolant, the valve on the first radiator must be screwed very tightly. And a situation may arise in which it will need to be closed so much that the coolant will not flow there. It turns out that then you need to choose: the first battery in the network will not heat, or the last one, because in this case it will not be possible to equalize the heat transfer.
Heating systems for two wings
And yet, a system with a dead-end scheme is more often used. And all because the return line is longer and it is more difficult to assemble it. If your heating circuit is not very large, it is quite possible to adjust the heat transfer on each radiator and with a dead-end connection. If the circuit turns out to be large, but you don’t want to make a Tichelman loop, you can divide one large heating circuit into two smaller wings. There is a condition - for this there must be a technical possibility of such a network construction. In this case, after separation, valves must be installed in each circuit, which will regulate the intensity of the coolant flow in each of the circuits. Without such valves, it is either very difficult or impossible to balance the system.
Different types of coolant circulation are demonstrated in the video, it also provides useful tips on installation and selection of equipment for heating systems.
Connecting heating radiators with a two-pipe system
In a two-pipe system, any of the ways to connect radiators is implemented: diagonal (cross), one-sided and bottom. The best option is a diagonal connection. In this case, the heat transfer from the heater can be in the region of 95-98% of the rated heat output of the device.
Despite the different values of heat loss for each type of connection, they are all used, just in different situations. The bottom connection, although the most unproductive, is more common if the pipes are laid under the floor. In this case, it is the easiest to implement. It is possible to connect radiators with hidden laying according to other schemes, but then either large sections of pipes remain in sight, or they will need to be hidden in the wall.
Lateral connection is practiced, if necessary, with the number of sections not exceeding 15. In this case, there is almost no heat loss, but if the number of radiator sections is more than 15, a diagonal connection is already required, otherwise circulation and heat transfer will be insufficient.
Results
Although more materials are used to organize two-pipe circuits, they are becoming more popular due to the more reliable circuit. In addition, such a system is easier to compensate.