Repair and design

Natural circulation heating system

An individual heating device is a responsible task. It is not easy to choose the method of its device, given the many options that exist.

Individual heating scheme.

Autonomous heating is not only an option for a private house, many modern apartments are also often equipped with autonomous heating equipment.

Central heating often does not heat the room enough. In any case, the device for autonomous heating of a room is most often carried out due to a gravity-fed system in which the coolant moves naturally.

Heating systems with natural circulation are the simplest, therefore the most common, they are installed in houses and apartments with independent heating. In addition, natural circulation systems are highly durable. Their device does not require the installation of additional circulation pumps. Water in the heating pipe moves under the influence of gravitational forces.
Basic principles of work

Scheme of the heating system with natural circulation.

The main disadvantage of a natural circulation heating system is its small radius of action. Effective heating is only provided that the radius does not exceed 30 m horizontally. The thing is that the circulation pressure in the system is small. In addition, there is a high risk that the water in the expansion tank will freeze if it is installed in an unheated room.

Schemes of all heating systems with natural circulation are based on a single principle. The following equipment is included in the system:

  • heating element - boiler;
  • pipeline (supply and return);
  • heating devices (radiators);
  • expansion tank.

The water cycle begins with the boiler, in which the coolant is heated and enters the radiators through the supply pipe and risers. In the radiators, the coolant gives off its heat, cools down and through the return pipe goes back to the boiler. After that, it heats up again, and the circulation cycle repeats.

The main condition for the proper organization of the work of such heating is to place the pipeline at a slight slope, which is done in the direction of the movement of water. Through a horizontal pipeline, water moves by gravity. In addition, the location of the pipeline at a slope contributes to the fact that air bubbles are discharged into the expansion tank. This is due to the different density of water and gas. Due to the difference in densities, the gas tends to rise upward and through a pipeline located at an angle, enters the expansion tank and is vented to the atmosphere.

The principle of operation of the heating system with natural circulation.

Thanks to the expansion tank, a constant pressure is created in the system. In addition, its purpose is to take the increasing volume of water, which is formed due to its heating. When the coolant cools and its volume decreases. From the expansion tank it enters the return pipe.

A natural circulation heating system provides movement of water under the action of natural forces. When heated, the water displaces the cold, and due to this, warm water rises along the supply riser. Under the influence of gravity, the coolant overcomes the resistance arising due to friction between it and the inner walls of the pipeline. Installation of pipes of wide diameter can reduce resistance.

The efficiency of heating with natural circulation depends on the circulation pressure. The circulation pressure is determined by such characteristics:

  1. The difference between the marks of the center of the heating element and the lower radiator. The larger this value, the better the circulation pressure of the coolant.
  2. Density of hot and density of chilled water.

Heating with natural circulation is arranged in such a way that the water in the boiler and radiators is not evenly distributed: hot water above, cold water below. Chilled water has a high density, that is, the mass of the same volumes of cold and hot water is not the same - cold is heavier.

Possible schemes of heating systems
Schemes of gravity heating systems differ in the way the coolant is supplied. This feature distinguishes heating with natural circulation of the upper and lower water supplies, which is most often used as a coolant. Natural circulation heating circuits are shown in Figures 1 and 2, respectively.

Top Feed Scheme

Top heating circuit.

At the upper supply of the coolant, after it is heated in the boiler, it is supplied through the pipeline to the upper part of the system. Typically, in this case, install a feed pipe with a larger diameter than the wiring pipe. This creates a greater resistance of the heat exchanger.

After the heated coolant is distributed along the supply pipe, it moves into vertical risers, and already through them it enters the radiators. For efficient heating, it is advisable to use a diagonal connection of radiators. When the coolant cools down, it returns to the boiler and repeats the cycle.

Horizontal piping is installed with a slope. The minimum slope is 10 mm per 1 linear meter. With an upper supply of coolant, an expansion tank is installed above other heating equipment.

The boiler must be positioned at the upper flow of the coolant at the lower point of the system. To implement this condition, it is convenient to place the boiler in the basement, if this is not possible, it is necessary to equip the so-called boiler room, which will be equipped in such a way that the boiler is located below the rest of the heating equipment.

Bottom feed circuit

Scheme with lower heating.

With a lower supply of coolant, the peculiarity is that the distribution pipes are located under the radiators. Water is circulated in the same way, and the expansion tank must also be located above all other heating equipment. To achieve this arrangement of the expansion tank, it can be placed under the ceiling. This can be done in any room of a house or apartment, if you equip a separate boiler room, it is more convenient to place an expansion tank there.

Which method of heating your room you choose is up to you. Carefully read the principles of operation of each of the described options, correlate them with the opportunities that exist in your house or apartment and make your choice.

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