To create a comfortable temperature in the house, various heating schemes are used. Providing forced circulation of the coolant is effective, but not always possible. If there may be power outages or lack of electricity in a country house (summer residence), another scheme would be the best option. A self-designed and self-installed closed-type gravitational heating system will perform its functions without installing a pump and other electrical equipment.
Features of the gravitational heating system
The principle of operation is based on the property of water to expand with increasing temperature. The creation of a pressure difference in a closed loop of pipes is the basis for fluid circulation. Thanks to this effect, the gravitational closed heating system received another name - gravity.
Structurally, it should consist of the following elements:
- Boiler... A device designed to transfer the energy of burning fuel (wood, coal, gas, etc.) to a heat carrier (water, antifreeze). In a closed gravity heating system, this is done using a heat exchanger located as close as possible to the combustion chamber in the boiler;
- Pipelines... Necessary for the transportation of heated liquid from the heat exchanger to heating devices;
- Radiators... They are the main source of heat in the room. Their large area ensures maximum heat exchange between heated water and air in the room;
- Control and safety devices... These include an expansion vessel, a gravity valve for heating, valves and throttles.
During the heating of the water in the heat exchanger, it expands, which creates excess pressure. In turn, the cold heat carrier from the return pipe has a higher density and begins to displace the liquid with a high temperature. As a result, circulation occurs.
One of the main elements of the system is the booster manifold - a vertical branch pipe connected to the boiler. If a do-it-yourself gravitational heating system is made, he needs to pay special attention - starting from the material for making the pipes, and ending with their diameter.
The larger the volume of the boost manifold, the higher the speed of the coolant. To do this, you need to calculate its optimal section and height.
The gravitational heating system of a two-story house should be designed in such a way that the coolant can be distributed as evenly as possible over several circuits.
Detailed system description
In the process of heating water, some of it will inevitably evaporate in the form of steam. For timely removal, an expansion tank is installed at the very top of the system. It performs 2 functions - excess steam is removed through the upper hole and the loss of liquid volume is automatically compensated. This scheme is called open.
However, it has one significant drawback - the relatively rapid evaporation of water. Therefore, for large branched systems, they prefer to make a closed-type gravitational heating system with their own hands. The main differences between its scheme are as follows.
- Instead of an open expansion tank, an automatic air vent is installed at the highest point of the pipeline. A closed-type gravitational heating system, in the process of heating the coolant, produces a large amount of oxygen from water, which, in addition to excess pressure, is a source of rusting of metal elements. For the timely removal of steam with a high oxygen content, an automatic air vent is installed;
- To compensate for the pressure of the already cooled coolant, a membrane expansion tank of a closed type is mounted in front of the inlet header of the boiler. If the gravitational pressure in the heating system exceeds the permissible norm, then the elastic membrane compensates for this by increasing the total volume.
Otherwise, when designing and installing a gravitational heating system only with your own hands, you can adhere to the usual rules and recommendations.
Gravitational heating schemes for a one-story and two-story house
If it is planned that gravitational heating under pressure will be installed in a one-story house, you can use the one-pipe scheme "Leningrad".
A feature of this scheme is one pipe to which several heating devices are connected in parallel. However, this leads to an uneven distribution of heat - the further the radiator is from the boiler, the lower the temperature of the water entering it. To solve this problem, you can upgrade the closed-type gravitational heating system:
- Installation of valves. With its help, you can reduce the volume of the coolant for heating devices located closer to the boiler. Thus, the heat output of energy in the first sections of the system will decrease;
- Increase the number of radiator sections with distance from the boiler;
- Install pipes of a larger diameter at the point where the branch pipes are connected to the heating devices. This will reduce the gravitational pressure of the heating system in this area, which will reduce the speed of water circulation in the radiator.
Such a scheme is acceptable for a small length of the highway. However, it is not recommended to install it for a two-story house. In this case, a two-pipe branched gravitational heating system will be required, the calculation for which is performed on separate sections.
Its peculiarity lies in the fact that separate circuits lead to the central pipe located in the upper part of the line. Heating devices are connected to each of them. It is important that they are the same length. Otherwise, all the liquid will rush into the area of least resistance - into a short circuit.
To prevent the movement of the coolant to the outlet of the boiler, a gravity check valve for heating is installed. This is an indispensable element for the gravitational heating system of a two-story house.
Calculation of the gravitational heating system
Before proceeding with the installation of pipes and heating devices, it is necessary to calculate the parameters of the entire system. For this, hydraulic characteristics are calculated, which will subsequently affect the selection of the optimal pipeline diameter. Before calculating a gravitational heating system, you need to know the basic parameters. They will be required to calculate the actual value of the circulating head (Рц):
- Distance from the center of the boiler to the center of the heater (h). The larger it is, the better the fluid circulation will be. Therefore, when installing a gravitational heating system with your own hands, it is recommended to mount the boiler at the lowest point of the house - the basement;
- Circulation pressure of the heated (Pr) and cooled (Po) coolant.
Regardless of whether the gravitational heating system is calculated for two-story or one-story houses, the value of the latter parameters directly depends on the difference in water temperature. This data can be taken from tabular data.
For example, with a value of h-4 m and a temperature difference of 20 ° (80/60), gravitational heating will have a pressure of 4 * 112 = 448 Pa. For further calculations, it is recommended to use specialized software systems that take into account all the parameters of a closed-type gravitational heating system.
Often the diameter of the pipe connected to the outlet of the boiler must be DN 40 or DN 50. This will ensure minimal losses arising from the friction of water against the pipe walls.
Another feature is the difference in coolant temperatures. The larger it is, the higher the circulating pressure. Therefore, in addition to the uniform distribution of heat over the heating devices, during the design of the gravitational heating system, you yourself need to ensure the minimum temperature of the liquid before entering the boiler heat exchanger.
Selection of components and material of manufacture
After the advent of polymer pipes, the gravitational heating system made of polypropylene (PP) became very popular. This material is easy to process; a minimum of equipment is required to connect individual sections.
However, not every type of these pipes is intended for installation as a heating element. Consider the main selection criteria:
- The presence of a reinforcing layer... The gravitational polypropylene heating system can be affected by high temperatures - up to 95 ° C. To preserve the original shape of the pipe, a stiffener is required, which is a layer of foil or fiberglass;
- Wall thickness... In a gravitational heating system with a closed expansion vessel, high pressure can build up. To avoid damage to the pipeline, polypropylene pipes must be PN20 or higher. The thickness of their walls depends on the diameter.
This pipe can be used to equip a booster manifold. However, to achieve the temperature difference, it is recommended to make the return line from steel. In addition to lowering the temperature of the coolant before entering the boiler, this material helps to reduce the hydraulic resistance.
Installation recommendations
Having completed the calculation for a gravitational heating system made of polypropylene or steel pipes, you can proceed with its installation. To achieve optimal efficiency, experts recommend making small but important changes to the standard scheme:
- Slope of highways... The optimal gravitational pressure for the heating system can be achieved by the slope of the pipes after the air vent and on the return line after the last heating device;
- Installation of a circulation pump on the bypass... It will help to reduce the inertia of the system. The time for heating the coolant can be very long, so the pump can increase the speed of its movement along the line until the desired temperature regime is reached;
- Minimum turning points in the pipeline... They create unnecessary hydraulic resistance, which affects the decrease in the speed of water movement;
- Installation of protective elements... By installing a check valve for gravity heating, it is possible to avoid water circulation in the wrong direction. This is especially necessary for a system with top routing and multiple circuits.
The main components of a properly made gravity heating under pressure are professionally calculated preliminary calculations, selection of the right materials and adherence to installation technology. This will make it possible to create an effective system for maintaining a comfortable temperature in the house.
Tips for arranging and using a gravity valve for heating when installing a warm floor, additional elements, can be seen in the video:
