The introduction of modern technologies has led to the gradual replacement of gravity heating systems. New types of space heating are more efficient and require lower costs during the cold period. Then why are gravity systems still being installed in modern private homes? The answer to this question is simple: they have great reliability based on an understanding of the laws of physics, as well as energy independence from sources of electric current.
On what principle does the gravity heating system work
Gravity heating is also called a natural circulation system. It has been used to heat houses since the middle of the last century. At first, ordinary people did not trust this method, but seeing its safety and practicality, they gradually began to replace brick stoves with water heating.
Then with the advent of solid fuel boilersthe need for bulky ovens disappeared altogether. The gravitational heating system works on a simple principle. The water in the boiler heats up, and its specific gravity becomes less cold. As a result of this, it rises along the vertical riser to the highest point of the system. After that, the cooling water begins its downward movement, and the more it cools, the greater the speed of its movement. A flow is created in the pipe directed to the lowest point. This point is the return pipe installed in the boiler.
As it moves from top to bottom, water passes through radiators, leaving some of its heat in the room. The circulation pump does not participate in the process of movement of the coolant, making this system independent. Therefore, she is not afraid of a power outage.
The calculation of the gravity heating system is done taking into account the heat loss of the house. The required power of the heating devices is calculated, and on this basis the boiler is selected. It should have a power reserve of one and a half times.
Scheme Description
In order for such heating to work, the ratios of pipes, their diameters and angles of inclination must be correctly selected. In addition, some types of radiators are not used in this system.
Let's consider what elements the whole structure consists of:
- Solid fuel boiler. The entry of water into it should be at the lowest point of the system. Theoretically, the boiler can also be electric or gas, but in practice for such systems they are notapply.
- Vertical riser. Its bottom is connected to the boiler supply, and the top branches out. One part is connected to the supply pipeline, and the second is connected to the expansion tank.
- Expansion tank. Excess water is poured into it, which is formed during expansion from heating.
- Supply pipeline. In order for the gravity water heating system to work efficiently, the pipeline must have a downward slope. Its value is 1-3%. That is, for 1 meter of pipe, the difference should be 1-3 centimeters. In addition, the pipeline should decrease in diameter as it moves away from the boiler. For this, pipes of different sections are used.
- Heating appliances. Either large-diameter pipes or cast-iron radiators M 140 are installed as them. Modern bimetallic and aluminum radiators are not recommended. They have a small flow area. And since the pressure in the gravitational heating system is small, it is more difficult to push the coolant through such heating devices. The flow rate will decrease.
- Return pipeline. Just like the supply pipe, it has a slope that allows water to flow freely towards the boiler.
- Cranes for draining and taking water. The drain cock is installed at the lowest point, directly next to the boiler. The tap for water intake is done where it is convenient. Most often, this is a location close to the pipeline that connects to the system.
System Benefits
The most basic advantage of the gravitational heating system is its complete autonomy. Because of the simplicityits elements do not require electricity. Its other advantage is reliability, because the simpler the system, the less maintenance it requires. It should be noted that the lower pressure in the gravity heating system is less dangerous.
Flaws
Proponents of closed systems cite a lot of disadvantages of gravity heating. Many of them look far-fetched, but let's list them anyway:
- Ugly appearance. Large-diameter supply pipes run under the ceiling, disrupting the aesthetics of the room.
- Difficulty in installation. Here we are talking about the fact that the supply and discharge pipes change their diameter in steps depending on the number of heating devices. In addition, the gravity heating system of a private house is made of steel pipes, which are more difficult to install.
- Low efficiency. It is believed that indoor heating is more economical, but there are well-designed natural circulation systems that work just as well.
- Limited heating area. The gravity system works well on areas up to 200 square meters. meters.
- Limited number of storeys. Such heating is not installed in houses above two floors.
In addition to the above, gravitational heating has a maximum of 2 circuits, while modern houses often have several circuits.
Differences in the operation of a solid fuel boiler
The heart of any heating system is the boiler. Although it is possible to installsame models, work with different type of heating will be different. For normal operation of the boiler, the temperature of the water jacket must be at least 55 °C. If the temperature is lower, then in this case the boiler inside will be covered with tar and soot, as a result of which its efficiency will decrease. It will need to be constantly cleaned.
To prevent this from happening, a three-way valve is installed in a closed system at the outlet of the boiler, which drives the coolant in a small circle, bypassing the heaters, until the boiler heats up. If the temperature starts to exceed 55 °C, then in this case the valve opens, and water is mixed into a large circle.
A three-way valve is not required for a gravity heating system. The fact is that here the circulation does not occur due to the pump, but due to the heating of the water, and until it heats up to a high temperature, the movement does not begin. The boiler furnace in this case remains constantly clean. A three-way valve is not required, which reduces the cost and simplification of the system and adds to its advantages.
Heating safety
As mentioned above, the pressure in a closed system is greater than in a gravitational one. Therefore, they take a different approach to security. In closed heating, the expansion of the coolant is compensated in the expansion tank with a membrane.
It is fully sealed and adjustable. After exceeding the maximum allowable pressure in the system, the excess coolant, overcoming the resistance of the membrane, goes into the tank.
Gravity heating is called open because of a leaky expansion tank. You can install a membrane-type tank and make a closed gravity heating system, but its efficiency will be much lower, because the hydraulic resistance will increase.
The volume of the expansion tank depends on the amount of water. For calculation, its volume is taken and multiplied by the expansion coefficient, which depends on temperature. Add 30% to the result.
Coefficient is selected according to the maximum temperature that water reaches.
Air congestion and how to deal with them
For normal operation of heating, it is necessary that the system is completely filled with coolant. The presence of air is strictly prohibited. It can create a blockage that prevents the passage of water. In this case, the temperature of the water jacket of the boiler will be very different from the temperature of the heaters. To remove air, air valves, Mayevsky taps are mounted. They are installed at the top of the heating devices, as well as on the upper sections of the system.
However, if gravity heating has the correct inlet and outlet pipe slopes, no valves are required. The air in the inclined pipeline will freely rise to the top of the system, and there, as you know, there is an open expansion tank. It also adds an advantage to open heating by reducing unnecessary items.
Is it possible to mount a system of polypropylenepipes
People who make heating on their own often think about whether it is possible to make a gravity heating system from polypropylene. After all, plastic pipes are easier to mount. There are no expensive welding jobs and steel pipes, and polypropylene can withstand high temperatures. You can answer that such heating will work. At least for a while. Then the efficiency will start to decrease. What is the reason? The point is the slopes of the supply and discharge pipes, which ensure the gravity flow of water.
Polypropylene has greater linear expansion than steel pipe. After repeated cycles of heating with hot water, plastic pipes will begin to sag, breaking the required slope. As a result of this, the flow rate, if not stopped, will decrease significantly, and you will have to think about installing a circulation pump.
Difficulties in installing a gravity system in a two-story house
The gravity heating system of a two-story house can also work efficiently. But its installation is much more difficult than for a one-story one. This is due to the fact that attic-type roofs are not always made. If the second floor is an attic, then the question arises: where to put the expansion tank, because it should be at the very top?
The second problem that you will have to face is that the windows of the first and second floors are not always on the same axis, therefore, the upper batteries cannot be connected to the lower ones by laying pipes in the shortest way. This means that you will have to make additional turns and bends that will increase the hydraulicresistance in the system.
The third problem is the curvature of the roof, which may make it difficult to maintain proper slopes.
Tips for installing gravity heating in a two-story house
Most of these problems can be solved at the design stage of the house. There is also a little secret of how to increase the efficiency of heating a two-story house. It is necessary to connect the outlet pipes of radiators installed on the second floor directly to the return of the first floor, and not to make a return on the second.
Another trick is to make the supply and return pipelines from pipes of large diameters. Not less than 50 mm.
Do I need a pump in a gravity heating system?
Sometimes there is an option when the heating was installed incorrectly, and the difference between the temperature of the boiler jacket and the return is very large. The hot coolant, not having sufficient pressure in the pipes, cools down before reaching the last heating devices. Rebuilding everything is hard work. How to solve the problem with minimal cost? Installing a circulation pump in a gravity heating system can help. For these purposes, a bypass is made, into which a low-power pump is built.
High power is not required, because with an open system, additional pressure is created in the riser leaving the boiler. A bypass is needed in order to leave the possibility of working without electricity. It is installed on the return before the boiler.
How to raise moreefficiency
It would seem that the system with natural circulation has already been brought to perfection, and it is impossible to think of anything to increase efficiency, but it is not. You can significantly increase the convenience of its use by increasing the time between boiler fires. To do this, you need to install a boiler of greater power than is required for heating, and remove excess heat to a heat accumulator.
This method works even without using a circulation pump. After all, the hot coolant can also rise up the riser from the heat accumulator, at a time when the firewood burnt out in the boiler.
