The introduction of modern technology has led to the gradual displacement of gravity heating systems. New types of space heating are more efficient and require lower costs in the cold season. Then why are gravity systems still 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 non-volatility from electric current sources.
What principle does gravity heating system work on?
Gravity heating is also called the natural circulation system. It began to be used to heat homes from the middle of the last century. At first, the simple population 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 boilers, the need for bulky furnaces disappeared altogether. Gravity heating system works on a simple principle. The water in the boiler is heated, and its specific gravity becomes less cold. As a result of this, it rises along the vertical riser to the top of the system. After this, the cooling water begins to move downward, and the stronger it cools, the greater the speed of its movement. A stream is created in the pipe directed towards the lowest point. This point is the return pipe mounted in the boiler.
As it moves from top to bottom, water passes through heating radiators, leaving part of its heat in the room. In the process of moving the coolant, a circulation pump is not involved, making this system independent. Therefore, she is not afraid of a power outage.
The calculation of the gravitational heating system is made taking into account the heat loss of the house. The required power of heating devices is calculated, and on this basis the boiler is selected. It should have a power reserve of one and a half times.
Circuit description
In order for such heating to work, the ratios of the pipes, their diameters and tilt angles must be correctly selected. In addition, some types of radiators are not used in this system.
Consider what elements the whole structure consists of:
- Solid fuel boiler. The entry of water into it should be at the lowest point in the system. Theoretically, the boiler can also be electric or gas, but in practice they are not used for such systems.
- Vertical riser. Its bottom is connected to the boiler feed, and the top forks. One part is connected to the supply pipe, and the second is connected to the expansion tank.
- Expansion tank. Excess water is poured into it, which is formed during expansion from heating.
- The giving pipeline. In order for the gravitational water heating system to work efficiently, the pipeline must have a lower 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 its 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 pipe. Just like the feed pipe, it has a slope that allows water to flow freely towards the boiler.
- Taps for draining and withdrawing water. The drain valve is installed at the lowest point, directly next to the boiler. A tap for water intake is made where convenient. Most often, this is a place close to the pipeline that connects to the system.
Advantages of the system
The most basic advantage of the gravitational heating system is its complete autonomy. Due to its simplicity, all its elements do not require electricity. Its other plus is reliability, because the simpler the system, the less it requires maintenance. It should be noted that the lower pressure in the gravitational heating system is less dangerous.
disadvantages
Proponents of closed systems give a lot of disadvantages of gravitational heating. Many of them look far-fetched, but still we list them:
- Ugly appearance. Large diameter feed pipes pass under the ceiling, violating the aesthetics of the room.
- Difficulty in installation. Here we are talking about the fact that the supply and outlet pipes stepwise change their diameter depending on the number of heating devices. In addition, the gravitational heating system of a private house is made of steel pipes, and they are more difficult to install.
- Low efficiency. Indoor heating is thought to be more economical, but well-designed natural circulation systems are found to work just as well.
- Limited heating area. Gravity system works well in 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, the gravitational heat supply has a maximum of 2 circuits, while in modern homes often make several circuits.
Differences in the operation of a solid fuel boiler
The heart of any heating system is the boiler. Despite the fact that you can install the same model, the work with different types 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, in a closed system, a three-way valve is installed at the outlet of the boiler, which drives the coolant in a small circle, bypassing heating devices, until the boiler heats up. If the temperature begins to exceed 55 ° C, then in this case the valve opens and water begins to mix in a large circle.
A three-way valve is not required for a gravity heating system. The fact is that here the circulation is not due to the pump, but due to the heating of the water, and until it is heated 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 simplifies the system and adds advantages 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 completely sealed and adjustable. After exceeding the maximum permissible pressure in the system, 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 gravitational 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. To the result, add 30%.
The coefficient is selected according to the maximum temperature that water reaches.
Air congestion and how to deal with them
For normal heating operation, it is necessary that the system is completely filled with coolant. The presence of air is strictly not allowed. He can create a cork that impedes the passage of water. In this case, the temperature of the boiler’s water jacket will be very different from the temperature of the heating devices. To remove air mounted air valves, Maevsky cranes. They are installed at the top of the radiators, as well as in the upper sections of the system.
However, if gravity heating has the correct slopes of the supply and outlet pipes, then no valves are required. The air in the inclined pipeline will freely rise to the upper point of the system, and there, as you know, there is an open expansion tank. It also adds the advantage of open heating, reducing the number of unnecessary elements.
Is it possible to mount a system of polypropylene pipes
People who make their own heating often think about whether it is possible to make a gravitational heating system out of 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, efficiency will begin to decline. What is the reason? The point is the slopes of the supply and discharge pipes, which provide gravity of the water.
Polypropylene has a greater linear expansion than a steel pipe. After repeated cycles of heating with hot water, the plastic pipes will begin to sag, violating the necessary slope. As a result of this, if the flow rate does not stop, it will significantly decrease, and you will have to think about installing a circulation pump.
The difficulties of 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 complicated than for a one-story building. This is due to the fact that roofs of the attic type 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 the pipes in the shortest way. This means that you will have to make additional turns and bends that will increase the hydraulic resistance in the system.
The third problem is the curvature of the roof, because of which it may be difficult to maintain the correct 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 on how to increase the heating efficiency of a two-story house. It is necessary to connect the exhaust pipes of radiators installed on the second floor directly to the return of the first floor, and not to do the return on the second.
Another trick is to make the supply and return pipelines from pipes of large diameters. Not less than 50 mm.
Is a pump needed in a gravity heating system?
Sometimes the option arises when the heating was improperly installed, and the difference between the temperature of the boiler jacket and the return is very large. The hot heat carrier, not having sufficient pressure in the pipes, cools down before reaching the latest heating appliances. Remaking everything is a laborious job. How to solve the issue with minimal cost? Installing a circulation pump in a gravity heating system can help. For these purposes, a bypass is manufactured in which a low-power pump is built.
Large power is not required, since with an open system an additional pressure is created in the riser exiting the boiler. Bypass is needed in order to leave the possibility of working without electricity. It is installed on the return line in front of the boiler.
How to increase efficiency
It would seem that a system with natural circulation has already been perfected, and it’s impossible to come up with anything to increase efficiency, but this is not so. It is possible to significantly increase the convenience of its use by increasing the time between the furnaces of the boiler. To do this, you need to install a boiler of greater power than is required for heating, and remove excess heat into the heat accumulator.
This method works even without using a circulation pump. After all, the hot heat carrier can also rise along the riser from the heat accumulator, while the laying of firewood burned out in the boiler.