No matter how engineers and builders predicted in the eighties, the heating system with natural circulation is alive and well in the twenty-first century, and even warms our homes. Pumping equipment significantly increases the cost of the boiler and creates dependence on the electrical network, so many people refuse it. The gravity system is the cheapest and simplest in design. It, of course, has its drawbacks, the main one of which is the limitation on the building area. Due to its low inertia, it is suitable for houses up to one hundred square meters.
How does the principle of natural circulation work?
The coolant, most often ordinary water, moves along circuits from the boiler to the radiators and back due to changes in its thermodynamic characteristics. When, when heated, the density of the liquid decreases and the volume increases, it is squeezed out by the cold flow going back and rises through the pipes. As the coolant is distributed by gravity along the horizontal branches, the temperature drops and it returns to the boiler. This completes the cycle.
Diagram of a heating system with natural circulation: 1 - solid fuel boiler, 2 - main riser, 3 - distribution lines, 4 - expansion tank, 5 - water tank for replenishing the expander, 6 - pipe that drains excess coolant volume into the sewer (tank), 7 – heat exchangers, 8 – ball valves, 9 – boiler, 10 – return, 11 – return riser
If water heating with natural circulation was chosen for the house, then all horizontal sections of pipes are laid with a slope running in the direction of fluid movement. This allows you to effectively deal with "" batteries. Air is lighter than water, so it rushes up through the pipes, enters the expansion tank, and then, accordingly, into the atmosphere.
The tank accepts water, the volume of which increases with increasing temperature, and creates constant pressure.
What does circulation pressure depend on?
The creation of the required circulation pressure must be calculated when designing a heating system. It depends on how different the levels of the middle of the boiler and the lowest radiator are. The greater the height difference, the better the fluid moves through the system. It is also affected by the difference in densities of hot and cooled water.
The circulation pressure in the heating system primarily depends on the difference in height between the boiler and the lower radiator. The greater this difference (h), the greater the pressure
Heating with natural circulation is characterized by a cyclical change in temperature in the heat exchangers and in the boiler, which occurs along the central axis of the devices. Hot water is at the top, cold water is at the bottom. Under the influence of gravity, the cooled coolant moves down through the pipes.
The circulation pressure directly depends on the installation height of the batteries. Its increase is also facilitated by the angle of inclination of the supply line, directed towards the radiators, and the slope of the return line facing the boiler. This allows the coolant to more easily overcome the local resistance of the pipes.
When installing a heating system with natural circulation in a private house, the boiler is installed at the lowest point so that all radiators are higher.
In a cottage, when installing a heating system with natural circulation, the boiler is installed at the lowest point. All heat exchangers (radiators) must be located above
For apartment buildings, heating schemes with natural circulation are used very rarely, since when installed in an apartment, the boiler is lowered into a “pit” - directly onto the floor slab. The floor around it is cut out, and the recess itself and the perimeter around it must be protected with fireproof materials.
Schemes of such heating systems
The design of the heating system, regardless of the method of circulation of the coolant, depends on several factors:
- method of connecting radiators to supply risers. Here there are one-pipe and two-pipe systems;
- places where the hot water supply line is laid. You need to choose between lower and upper wiring;
- main line laying schemes: dead-end system or associated movement of coolant in main lines;
- arrangement of risers, which can be either horizontal or vertical.
Single-pipe system: how to regulate the temperature?
It has only one wiring option - top. There is no return riser, so the coolant cooled in the batteries returns to the supply line. Fluid movement is ensured by the difference in fluid temperatures in the lower and upper radiators.
To ensure the same temperature conditions in rooms on different floors, the surface of heating devices on the first floor should be slightly larger than on the second and subsequent ones. A mixture of hot and cooled water in the upper heat exchangers enters the lower radiators.
In a one-pipe system, there can be two options for movement: in the first, one part goes to the radiator, the other goes further along the riser to the lower devices.
With parallel single-pipe distribution, heat exchangers on the upper floors receive hot water, and the lowest ones receive cooled water. Therefore, the area of the latter must be increased in order to equalize the heating of all rooms
In the second case, the entire volume of water passes through each heat exchanger, starting from the top ones. The main feature of this layout is that the radiators on the first and basement floors receive only chilled water.
With a flow-through version of a single-pipe installation, it is impossible to turn off or limit the flow of coolant into a separate radiator. Blocking one of them would lead to a stop in circulation in the entire system
And if in the first case the temperature in the rooms can be controlled using taps, then in the second they cannot be used, as this will lead to a decrease in the supply of liquid to all subsequent heat exchangers. In addition, completely shutting off the tap would mean stopping the circulation of water in the system.
When installing a single-pipe system, it is better to focus on the wiring, which makes it possible to regulate the water supply to each radiator. This will allow you to regulate the temperature in individual rooms and, naturally, makes the heating system more flexible, and therefore more efficient.
Since single-pipe wiring can only be at the top, its installation is possible only in buildings with an attic space. This is where the supply pipeline should be located. The main disadvantage is that heating can only be started throughout the entire building at once. The system, of course, also has advantages. The main ones are simple installation and lower cost. From an aesthetic point of view, the fewer pipes, the easier it is to hide them.
How should a two-pipe system be arranged?
This version of the heating scheme assumes the presence of a supply and exhaust line. Hot coolant circulates in the upper part of the system, and cooled coolant circulates in the lower part.
A two-pipe heating system is more flexible in terms of temperature control in individual rooms. However, it requires more materials than a single-pipe
A pipe extends from the boiler and is connected to the expansion tank. From the tank there is a pipe for the hot line of the circuit, which is then connected to the wiring. Depending on the size of the container and the volume of water in the system, an overflow pipe may extend from the tank. It drains excess water into the sewer.
The pipes leaving the bottom of the heat exchangers are combined into a return line. Through it, the cooled coolant again enters the boiler. The return must pass through the same rooms as the supply pipeline.
Horizontal or vertical riser in the wiring?
A heating system with a vertical riser involves connecting radiators to it from different floors. Its advantage: lower risk of “airing” the system, disadvantage – higher cost.
When heat exchangers from one floor are connected to a supply pipe, this is a system with a horizontal riser. This option will cost homeowners less, but will have to solve the problem of air locks. As a rule, it is enough to install air vents.
Pros and cons of arranging heating of this type
As for the advantages of a heating system with natural circulation of water, there are several:
- no difficulties during installation, start-up and operation;
- thermal stability of the system. Based on the gravitational circulation of the coolant, it ensures maximum heat transfer and maintains the indoor microclimate at a given level;
- efficiency (with proper insulation of the building);
- quiet work. No pump – no noise and vibration;
- independence from power outages. Naturally, in the case when the installed boiler can operate without electricity;
- long service life. With timely maintenance without major repairs, the system can operate for 35 years or more.
The main disadvantage of a gravity heating system is the limitations on the building area and radius of action. It is installed in houses whose area usually does not exceed 100 square meters. Due to the low circulation pressure, the radius of the system is limited to thirty meters horizontally. A mandatory requirement is the presence of an attic space in the building in which the expansion tank will be installed.
A significant drawback is the slow heating of the entire house. With a system with natural circulation, it is necessary to insulate pipes running in unheated rooms, as there is a risk of water freezing.
Typically, few materials are used for such wiring, but when the local resistance of the pipeline needs to be reduced, costs increase due to the need to use larger diameter pipes.
The construction of an autonomous gravity-type heating network is chosen if it is impractical, and sometimes impossible, to install a circulation pump or connect to a centralized power supply.
Such a system is cheaper to install and is completely independent of electricity. However, its performance largely depends on the accuracy of the design.
In order for a heating system with natural circulation to function smoothly, it is necessary to calculate its parameters, correctly install the components and reasonably select the water circuit design. We will help in resolving these issues.
We described the main principles of operation of the gravity system, provided advice on choosing a pipeline, and outlined the rules for assembling the circuit and placing working units. We paid special attention to the design and operation features of one- and two-pipe heating schemes.
The process of water movement in the heating circuit without the use of a circulation pump occurs due to natural physical laws.
Understanding the nature of these processes will allow you to competently handle standard and non-standard cases.
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With water heating with natural circulation, the speed depends on the following factors:
- pressure difference between fragments of the contour at its lower point;
- hydrodynamic resistance heating system.
Methods for ensuring maximum pressure difference were discussed above. The hydrodynamic resistance of a real system cannot be accurately calculated due to the complex mathematical model and the large number of input data, the accuracy of which is difficult to guarantee.
However, there are general rules that, if followed, will reduce the resistance of the heating circuit.
The main reasons for the decrease in the speed of water movement are the resistance of the pipe walls and the presence of narrowings due to the presence of fittings or shut-off valves. At low flow rates, there is virtually no wall resistance.
The exception is long and thin pipes, typical for heating with. As a rule, separate circuits with forced circulation are allocated for it.
When choosing types of pipes for a natural circulation circuit, you will have to take into account the presence of technical restrictions when installing the system. Therefore, it is undesirable to use them with natural water circulation because they are connected with fittings with a significantly smaller internal diameter.
Rules for the selection and installation of pipes
The slope of the return line is usually made in the direction of movement of the chilled water. Then the lowest point of the circuit will coincide with the entrance of the return pipe to the heat generator.
The most common combination of supply and return pipe slope directions for removing air pockets from a natural circulation water circuit
Open water natural heating systems are used mainly in private homes, where it is possible to install a heating boiler and an expansion tank. If it is not possible to connect a gas boiler, you can use waste or solid fuel boilers.
Why do owners of small cottages choose a heating system with natural circulation? The gravity heating system is considered the least expensive of all available. It does not involve the installation of a circulation device, since the water moves through the pipes naturally.
To install a heating system, you need a boiler, a pipeline, high-quality batteries and an expansion tank. The peculiarity of the gravity system is that the water heated in the boiler rises and spreads throughout the system, pushing cold water back into the boiler for heating.
The main condition when installing the system is that the pipes through which hot water flows must be placed at a slight slope.
The slope of the pipes is necessary in order to facilitate the movement of cold water from the radiators into the heating boiler. The higher the radiators are along the vertical axis, and, accordingly, the lower the boiler, the faster the coolant will move through the system.
In a gravity heating system made of polypropylene, it is advisable to install a reservoir - an expansion tank, which will create additional pressure and speed up the movement of water through the pipes. The coolant circulation will be continuous while the heating unit is operating.
Natural circulation of water in the heating system: pros and cons
In a gravity heating system, the coolant moves through the pipes by gravity, without the participation of a pump. Water moves through pipes that are placed at a slight angle. The water cycle in the system will be better if the pipes are of a larger diameter. Plastic pipes are considered standard, although they may rupture if the boiler overheats. Metal pipes retain heat well and will last longer, although their installation entails financial costs.
The system must remain open; air must be available for proper functioning.
If there is a large volume of water in the tank, gravity heating will be inert. After the boiler is turned off, the coolant will be able to move through the system for a long time, heating the radiators. Thus, the room temperature will decrease slowly. This system does not depend on electricity.
Gravity heating has disadvantages:
- There is no way to regulate the temperature;
- If one battery breaks down, the entire heating system fails;
- It is not possible to connect a heated floor to the system;
- Low efficiency.
Judging by the complexity of installation and subsequent maintenance, it is believed that a heating system with natural circulation is quite understandable for the owner to install it with his own hands.
What is good about a single-pipe heating system with natural circulation?
Single-pipe water heating is considered the easiest to install and maintain. This heating system involves placing heating pipes at a maximum height under the ceiling, and return pipes are located below and lead back to the boiler.
In a single-pipe system, it is allowed to install the boiler and heating devices on the same level.
A closed one-pipe system is equipped with an expansion tank, which helps get rid of air in the system and regulates the change in the volume of coolant in the pipes.
Basic installation principles:
- The angle of inclination of pipelines is no more than 7 degrees;
- Metal-plastic pipes leading to the battery must have a diameter of 20 mm;
- The volume of the expansion tank is 30 l, while a quarter of the tank should remain unfilled;
- An air valve is installed on each radiator, thanks to which it is possible;
- Installing thermal heads on a radiator will help regulate the temperature in each individual room.
With a single-pipe gravity heating system, the main thing is that the water level in the tank does not fall below the pipe leaving it, otherwise the supply of hot coolant to the system will stop. To replenish the volume of water in the tank, it is recommended to install a hose with a tap through which you can replenish the amount of coolant in the system.
It is worth noting that this system is not suitable for a two-story house - in this case it is needed.
Modern equipment makes it possible to install autonomous heating in an apartment building. This is discussed in our material: .
Two-pipe heating scheme for a private house with natural circulation
A two-pipe gravity heating system is an order of magnitude more complex and more expensive than a single-pipe one. This heating design involves installing two lines - one circulates hot water, the second returns the cooled coolant to the boiler. Before installing the system, you need to calculate the materials.
Installation steps:
- There is a pipe going up from the boiler, which connects to the expansion tank. The tank can be placed under the ceiling or in the attic.
- At the bottom, a pipe for the hot coolant circuit is connected to the tank, which leads to distribution throughout the house. On the other side, a pipe leading to the sewer is connected to the tank to remove excess coolant.
- Distribution pipes are connected throughout the house and connected to radiators.
- From the bottom of the radiator there is a return pipe through which the cooled coolant will be returned to the heating boiler. The return line is located parallel to the hot water pipes.
When installing a two-pipe heating system with free circulation, it should be taken into account that the attic space in which the expansion tank is located is strongly recommended to be insulated. In this way, prevent cooling or partial freezing of the heating system.
Proper planning of the placement of the boiler and expansion tank is the key to the efficient operation of the entire heating system. In this case, the heating boiler should be located as low as possible, ideally in the basement, specially equipped for the unit.
Types of heating systems with natural circulation (video)
Proper installation of a gravity heating system makes it possible to use it for up to 40 years. Such a system is the best solution for a country house that cannot be connected to a central heating main.
The option of using a heating system with natural circulation of a one-story house (gravity or gravity system) is still popular, despite the achieved level of technical progress. This is explained simply: natural fluid circulation (LC) systems operate autonomously and do not need to be connected to power sources.
Therefore, it is difficult to overestimate the importance of such a heating system with natural circulation for a one-story country house located on a site where there is no possibility of connecting electricity to install circulation pumps. Or in places where there are frequent power outages.
On the operating principle of gravity circulation systems
The operation of the gravitational system is based on the principle of expansion of a liquid when heated, familiar from school times. That is, as a result of heating, the weight and density of water decrease, and when cooled, they return to their previous values.
The process of natural circulation in the heating system is as follows: when a boiler heats a certain volume of liquid, the liquid expands and, due to a decrease in density, rises to the top point of the gravity heating system, displaced by denser cold layers. Making a circle around the heating system, the liquid gradually cools down and returns to the heating source itself. This cycle is then repeated.
That is, the basic principle of heating by circulating warm water is based on the use of the difference in the levels of hydrostatic pressure of cold and hot liquid columns. When hot water is displaced by cold water flowing towards the heat exchanger, the heated water rises through the pipe. The magnitude of the circulation pressure is directly dependent on the location of the middle of the boiler and the lowest radiator in the house. As the height difference increases, the speed of fluid movement through the pipes increases. This is how the scheme with natural circulation of liquid works.
Conventionally, the heating circuit of a building can be divided into separate fragments: “hot” with liquid flowing upward and “cold” – with water flowing downward. The role of boundaries between fragments will be played by the lower and upper points of the heating circuit.
When modeling gravity systems, it is important to ensure a maximum difference between the pressure levels of liquid columns in the “cold” and “hot” circuits.
As a rule, the system is designed in such a way as to ensure maximum coincidence of the upper extreme points of the acceleration manifold (the main riser extending from the heat exchanger) and the rest of the circuit. At the level of the top point, the outlet to the expansion tank or air vent valve is also installed (when using a membrane tank). This helps make the “hot” part of the overall contour as short as possible. Thanks to this measure, water circulation in the heating system in this section will be carried out with minimal heat loss.
An acceptable speed of liquid movement along the circuit is possible if there is a temperature difference between the outgoing (from the boiler) and incoming circuits - no less than 25 0 C degrees. Moreover, as the length of the pipeline increases, the temperature difference should increase.
About the types and diagrams of these systems
There are two ways to install the circuits of a gravity heating system. We are talking about one-pipe and two-pipe circuits. In the first case, water is removed and supplied from the radiator through the same pipe, in the second, two different pipes are responsible for the removal and entry of liquid. Open and closed circulation systems are also used.
Single-pipe
It is distinguished by its ease of installation and low (almost floor level) placement of the pipeline. A one-pipe heating system is represented by a riser with an accelerating pipe extending from its top point and directed as far down as possible, which ends with a supply circuit. The connection of the system (water inlet and outlet) to the batteries is carried out from below using a pair of pipes having a smaller diameter (if we are talking about a two-inch pipeline, it is advisable to use ¾-inch bends). Next, the coolant from the batteries moves towards the boiler.
The disadvantage of such a scheme with natural coolant circulation is its low efficiency: when cooling, the liquid enters the same pipeline through which warm water moves to the next battery. Thus, the heat loss of each subsequent radiator is noticeably different, which causes uneven heating of the house. To solve this problem, it is necessary to increase the number of sections of each subsequent battery.
Closed
One of the most popular in Europe. It differs favorably from conventional gravity heating schemes by the presence of an expansion tank. This process can be divided into stages:
- Due to the increase in temperature, the heated coolant is displaced by cold layers and leaves the heating circuit;
- The heated liquid ends up in a closed expansion membrane tank (in a container divided in half using a separating membrane, with one half filled with water, and the second containing gas - most often nitrogen);
- Heating the water leads to an increase in pressure, as a result of which the gas in the second half of the tank is compressed, cooling the coolant leads to the opposite process - the gas, expanding, pushes the liquid out of the tank.
Its disadvantage, if it is necessary to heat large areas, may be the need to install a sufficiently large tank.
Open system
It differs from the previous diagram in the design of the expansion tank. In this case, it is made independently and installed in the attic or right under the ceiling. Typically an open system is used to heat small spaces.
The downside is the frequent “swallowing” of air and its entry into the batteries, which negatively affects the operation of the entire system, and also leads to premature wear of the batteries and metal pipes due to increased corrosion processes. To combat battery airing, Mayevsky cranes are recommended.
Two-pipe
Provides more efficient use of heat due to strict separation of cold and warm circuits and provides the ability to connect a significant number of batteries.
From a supply pipe located near the ceiling and extending from the manifold, several pipes (with a top connection) are lowered (one to each radiator). A return pipe runs along the floor, in which the cooled coolant coming from the batteries is collected (lower diagonal connection). As a result, cooled and hot liquids do not mix, which ensures uniform heating of all rooms in the house.
Radial
It is a hybrid that combines the operating principles of a two-pipe heating circuit and a warm water floor. The supply and return circuits depart from the distribution manifold. In this case, the return line is laid under the floor. Direct connection to radiators is used with a minimum of turns.
About the advantages and disadvantages of a gravity heating system
When listing the advantages of heating systems with natural coolant circulation, it is worth mentioning:
- ease of installation, startup and maintenance;
- independence from access to power sources;
- good thermal output;
- efficiency (subject to good thermal insulation of the walls and window openings of the building);
- silent operation, since there is no need to use a pump, which often creates a sound background unfavorable for rest and work;
- durability (minimum service life - from 30-35 years, subject to installation from new high-quality pipes).
Speaking about the disadvantages of this type of heat supply for private houses, one cannot fail to say something about:
- limited range of the system (no more than 30 meters);
- low productivity when installed in buildings with an area of more than 100 m2;
- the need for attics to install systems with an expansion tank;
- the significant amount of time required to warm up all rooms in the building;
- the need for insulation of pipes laid in unheated rooms;
- increasing costs for the purchase of pipes of significant diameter, used to reduce resistance during the passage of water.
On calculating the parameters of a heating system with natural circulation for a one-story house
Due to the absence of additional mechanisms in the gravity heating systems of a one-story building that provide consistently high pressure, any possible violation during the installation of the pipeline can result in problems with the heat supply. Such violations include:
- neglecting the need to maintain inclination angles;
- incorrect choice of pipes;
- excess turns when installing the system.
The level of slope when installing a heating pipeline in a private house is regulated by the provisions of SNiPs. In accordance with them, for each linear meter a slope of 1 cm is required. This ensures normal movement of the coolant through the pipeline. If this standard is violated, the system may become air-filled and the overall level of its efficiency may decrease.
About calculating pressure and heating power
Based on the provisions of SNiP, each kW of thermal power is intended to heat an area of 10 square meters of the house. When calculating power levels for regions with hot or cold climates, special coefficients should be used. In the first case it will be from 0.7 to 0.9, in the second – from 1.5 to 2.
However, a calculation method that neglects the height of ceilings is not always ideal. Therefore, there is another option - based on the volume of the room. In this case, the calculations are based on the thermal power indicators (40 watts) for each cubic meter. In this case, the presence of windows increases the resulting number by 100 watts (for each window), and doors - by 200 watts (for each). In this case, for one-story private houses a coefficient of 1.5 is applied.
Actually, the standard amount of power included in the design of private one-story buildings requires a heating power of at least 50 watts per 1 sq.m.
Calculation of pipe diameter in a system with natural circulation
The diameter of pipes in gravity systems is calculated based on:
- building needs for thermal energy (+20%);
- determining the required type of pipe material (for example, the diameter of a steel pipe must be at least 0.5 cm);
- SNiP data regarding the ratio of power and internal diameter of the pipe.
It is worth considering that when choosing pipes with an unreasonably large cross-section, heating costs may increase while heat transfer decreases. Calculating the diameter of pipes for systems with self-circulation involves following another simple rule, which involves narrowing the diameter of the pipe by a size after each branch.
How to make your own heating of a private house with natural circulation
A high-quality heating system for a private house with natural circulation can be installed independently, without the involvement of specialists. To do this, you must perform the necessary calculations and strictly follow the detailed instructions of special manuals that describe step by step the entire process of installing water heating systems with natural circulation in a private home.
For private country houses and cottages, a heating system with natural coolant circulation is often installed. This decision has its positive and negative sides. The scheme is performed in four different ways.
A system with gravity circulation is sensitive to errors made during heating installation.
The principle of operation of a natural circulation system
The heating scheme for a private house with natural circulation is popular due to the following advantages:- Easy installation and maintenance.
- No need to install additional equipment.
- Energy independence – no additional energy costs are required during operation. When the power goes out, the heating system continues to operate.
At the same time, there is practically no pressure in the heating system. In thermotechnical formulas, a ratio of 1 atm is accepted for every 10 m of water column pressure. Calculation of the heating system of a 2-story building will show that hydrostatic pressure does not exceed 1 atm, in one-story buildings 0.5-0.7 atm.
Since the liquid increases in volume when heated, an expansion tank is required for natural circulation. The water passing through the boiler water circuit heats up, which leads to an increase in volume. The expansion tank should be located on the coolant supply, at the very top of the heating system. The purpose of the buffer tank is to compensate for the increase in liquid volume.
A self-circulating heating system can be used in private homes, making the following connections possible:
- Connection to heated floors– requires installing a circulation pump only on a water circuit laid in the floor. The rest of the system will continue to operate with natural circulation. After a power outage, the room will continue to be heated using the installed radiators.
- Working with an indirect water heating boiler– connection to a system with natural circulation is possible, without the need to connect pumping equipment. To do this, the boiler is installed at the top point of the system, just below the air expansion tank of a closed or open type. If this is not possible, then the pump is installed directly on the storage tank, additionally installing a check valve to avoid recirculation of the coolant.
In systems with gravitational circulation, the coolant moves by gravity. Thanks to natural expansion, the heated liquid rises up the acceleration section, and then “flows” down an incline through pipes connected to the radiators back to the boiler.
Types of heating systems with gravity circulation
Despite the simple design of a water heating system with self-circulation of coolant, there are at least four popular installation schemes. The choice of wiring type depends on the characteristics of the building itself and the expected performance.To determine which scheme will work, in each individual case it is necessary to perform a hydraulic calculation of the system, take into account the characteristics of the heating unit, calculate the diameter of the pipe, etc. You may need professional help when performing the calculations.
Closed system with gravity circulation
In EU countries, closed systems are the most popular among other solutions. In the Russian Federation, the scheme has not yet received widespread use. The operating principles of a closed-type water heating system with pumpless circulation are as follows:- When heated, the coolant expands and water is displaced from the heating circuit.
- Under pressure, the liquid enters the expansion tank. The design of the container consists of a cavity divided by a membrane into two parts. One half of the tank is filled with gas (most models use nitrogen). The second part remains empty for filling with coolant.
- When the liquid is heated, pressure is created sufficient to push through the membrane and compress the nitrogen. After cooling, the reverse process occurs and the gas squeezes water out of the tank.
Otherwise, closed-type systems work like other heating schemes with natural circulation. The disadvantages include the dependence on the volume of the expansion tank. For rooms with a large heated area, you will need to install a spacious container, which is not always advisable.
Open system with gravity circulation
The open type heating system differs from the previous type only in the design of the expansion tank. This scheme was most often used in old buildings. The advantage of an open system is the ability to independently manufacture containers from scrap materials. The tank usually has modest dimensions and is installed on the roof or under the ceiling of the living room.The main disadvantage of open structures is the entry of air into pipes and heating radiators, which leads to increased corrosion and rapid failure of heating elements. Airing of the system is also a frequent “guest” in open-type circuits. Therefore, radiators are installed at an angle; Mayevsky valves must be provided to bleed air.
Single-pipe self-circulating system
A single-pipe horizontal system with natural circulation has low thermal efficiency and is therefore used extremely rarely. The essence of the circuit is that the supply pipe is connected in series to the radiators. The heated coolant enters the upper branch pipe of the battery and is discharged through the lower outlet. After this, the heat flows to the next heating unit and so on until the last point. The return flow returns from the outermost battery to the boiler.
This solution has several advantages:
- There is no pair pipeline under the ceiling and above the floor level.
- Saves money on system installation.
Two-pipe self-circulating system
A two-pipe heating system in a private house with natural circulation has the following design features:
As a result, a two-pipe radiator-type system provides the following advantages:
- Even heat distribution.
- No need to add radiator sections for better heating.
- Easier to adjust the system.
- The diameter of the water circuit is at least one size smaller than in single-pipe circuits.
- Lack of strict rules for installing a two-pipe system. Small deviations regarding slopes are allowed.
The main advantage of a two-pipe heating system with bottom and top wiring is the simplicity and at the same time efficiency of the design, which allows you to eliminate errors made in calculations or during installation work.
How to properly make water heating with natural circulation
All gravity systems have a common drawback - the lack of pressure in the system. Any violations during installation work, a large number of turns, non-compliance with slopes, immediately affect the performance of the water circuit.To make proper heating without a pump, take into account the following:
- Minimum slope angle.
- Type and diameter of pipes used for the water circuit.
- Features of supply and type of coolant.
What pipe slope is needed for gravity circulation
The design standards for an in-house heating system with gravity circulation are specified in detail in building codes. The requirements take into account that the movement of liquid inside the water circuit will be hampered by hydraulic resistance, obstacles in the form of corners and turns, etc.The slope of heating pipes is regulated by SNiP. According to the standards specified in the document, a slope of 10 mm is required for each linear meter. Compliance with this condition guarantees unhindered movement of fluid in the water circuit.
Violation of the slope when laying pipes leads to airing of the system, insufficient heating of radiators remote from the boiler, and, as a result, a decrease in thermal efficiency.
The pipe slope standards for natural coolant circulation are specified in (formerly SNiP 41-01-2003) “Laying heating pipelines”.
What pipes are used for installation
The choice of pipes for the manufacture of the heating circuit is important. Each material has its own thermal characteristics, hydraulic resistance, etc. When performing installation work yourself, additionally take into account the complexity of installation.The most commonly used building materials are:
- Steel pipes - the advantages of the material include: affordable cost, resistance to high pressure, thermal conductivity and strength. The disadvantage of steel is its complex installation, which is impossible without the use of welding equipment.
- Metal-plastic pipes– have a smooth inner surface that prevents the circuit from clogging, light weight and linear expansion, no corrosion. The popularity of metal-plastic pipes is somewhat limited by their short service life (15 years) and the high cost of the material.
- Polypropylene pipes– are widely used due to ease of installation, high tightness and strength, long service life and resistance to freezing. Polypropylene pipes are installed using a soldering iron. Service life of at least 25 years.
- Copper pipes are not widely used due to their high cost. Copper has maximum heat transfer. Withstands heating up to + 500°C, service life over 100 years. The appearance of the pipe deserves special praise. Under the influence of temperature, the surface of copper becomes covered with a patina, which only improves the external characteristics of the material.
What diameter should the pipes be for circulation without a pump?
Correct calculation of pipe diameters for water heating with natural circulation is carried out in several stages:- The room's need for thermal energy is calculated. About 20% is added to the result obtained.
- SNiP indicates the ratio of thermal power to the internal cross-section of the pipe. We calculate the cross-section of the pipeline using the given formulas. To avoid performing complex calculations, you should use an online calculator.
- The diameter of the pipes of the natural circulation system must be selected according to thermal engineering calculations. An excessively wide pipeline leads to reduced heat transfer and increased heating costs. The width of the section is affected by the type of material used. So, steel pipes should not be narrower than 50 mm. in diameter.
If the diameter calculations were carried out correctly and the slopes of the pipelines were observed when designing and performing installation work on a heating system with gravity circulation, operational problems are extremely rare and mainly occur due to improper operation.
Which bottling is better - bottom or top?
The natural circulation of water in the heating system of a one-story house largely depends on the chosen scheme for supplying coolant directly to the radiators. It is customary to classify all types of connection or filling into two categories:
Errors in choosing the type of filling lead to the need to modify the water circuit by installing circulation equipment.
Which coolant is better for self-circulation systems
The optimal coolant for a heating system with natural fluid movement is water. The fact is that antifreeze has a higher density and less heat transfer. To heat glycol compounds to the required state, it takes more time to burn fuel, while the heat transfer remains at the water level.There are two arguments for using antifreeze liquid:
- High fluidity of the material, improving circulation.
- Ability to maintain fluidity when reaching -10°C, -15°C.
Which heating is better to choose - natural or forced?
The design features of the system with natural gravitational circulation, ease of installation and the ability to carry out work independently have made this scheme quite popular among domestic consumers.But the self-circulating design loses compared to a circuit connected to pumping equipment in the following aspects:
- Start of operation - the heating system with natural circulation begins to operate at a coolant temperature of about 50°C. This is necessary for the water to expand in volume. When connected to a pump, the liquid moves through the water circuit immediately after switching on.
- A decrease in the power of heating devices during natural circulation of the coolant as the distance from the boiler increases. Even with a properly assembled circuit, the temperature difference is about 5°C.
- Influence of air - the main reason for the lack of circulation is the airing of part of the water circuit. Air in the heating system can form due to non-compliance with slopes, the use of an open expansion tank and other reasons. To pressurize the system, you have to turn on the boiler at maximum power, which leads to significant costs.
- Heating a two-story house with natural coolant circulation is difficult due to existing obstacles to the movement of fluid.
- Regarding heating regulation, self-circulating systems are also inferior to circuits connected to pumps. Modern circulation equipment is connected to room thermostats, which ensures accurate heat transfer and heating of the room temperature with an error of up to 1°C. The installation of thermostats is also allowed in circuits with self-circulation, but the setting error will be 3-5°C.
The main advantage of self-circulation schemes is their energy independence, but after making simple calculations, we can come to the conclusion that the savings on electricity do not justify the heat loss during the independent movement of the coolant. Forced circulation circuits have greater heat transfer and efficiency.
