The concept of a gravity coolant device can be compared in some sense with natural ventilation, in which free circulation of air flows is realized. In the case of the aquatic environment, movement occurs along the contours without energy and power support from third-party devices and resources. This gives the advantages of a gravity heating system, but also causes a number of disadvantages. One of them is the complexity of its technical implementation.
How the system works
Spontaneity is ensured by the law of physics, according to which hot streams of air and water rise naturally. Unlike systems with forced circulation, there is no need to turn on pumping equipment or steam generators that push the working medium under pressure along thecontours. In the conditions of a private house, a gravity-flow heating system is beneficial just by the minimal connection of indirect communication and energy nodes. But this does not mean at all that the user will have to deal only with pipes. A boiler located at the lowest point of the complex will be responsible for heating the water. From it, through pipes, the flows will be directed to the heaters-consumers of the coolant (convectors, radiators, batteries). Further, the already cooling water passes into the section of the expansion tank and, as it accumulates, overflows into the drain channel - either to the boiler or to the sewer.
One-pipe and two-pipe systems
Schemes for heating circuits can be different. In the simplest one-pipe system, there is no coolant return riser with water intake. Vertical systems of this type are technically easier to implement, which saves on physical effort and finances. But there are also serious drawbacks in single-pipe gravity heating systems, which are expressed in the following nuances:
- The lack of the ability to adjust the temperature for each heater separately, as they are connected in series.
- Mandatory placement of expansion tank for vertical filling.
- Higher pressure requirements for water circulation. For this reason, single-pipe systems are more often performed according to the principles of forced movement of the coolant with the connection of pumps.
In a two-pipe system, heat is distributed evenly. One circuit directs hot streams to conditional radiators,and the second serves the return branch, through which cold water returns to the receiving equipment. Due to the balance of the coolant in the pipeline, the two-circuit scheme is more easily amenable to natural regulation with the effect of gravity without the support of additional circulation equipment.
Open and closed systems
The difference between these systems lies in the performance of the expansion tank - the top point of the entire complex. In open tanks, water accumulates until the float mechanism operates. The liquid fills the tank to a certain level, after which the float activates the release of the air mixture and filling through the connected riser. In a closed gravity heating system, a membrane tank is used, in which two sections are provided - with air (gas mixture) and water in the lower part. At minimum pressure, the container is empty, but as it fills with liquid, the membrane begins to compress the upper section, thus opening the air valve and equalizing the pressure.
Boiler selection
Using the concept of gravity heating in itself means that neither gas nor electricity is provided in the house. Otherwise, it would be more rational to organize forced circulation with heat supply of sufficient power from the main energy source. Therefore, the only option for a boiler for a gravity-flow heating system will be a solid fuel unit - for example, a wood-burning one. The combination of natural circulation and a traditional stove also gives reasonstalk about the low power of the complex. The system will be initially inefficient, but its efficiency can be increased due to the pyrolysis effect, which distinguishes modern modifications of solid fuel boiler plants with a capacity of 20 to 40 kW with two combustion chambers. In the additional compartment, the gases generated during the first combustion of the fuel are burned. By the way, minimizing combustion products at the outlet will also reduce the requirements for chimney.
Choice of pipe material
As with plumbing, pipes made of plastic and metal can be used for a natural circulation heating system. Restrictions on the use of certain materials depend on individual factors and conditions. For example, an open heating system provides for a greater effect of airing the circuits with oxygen and carbon dioxide, which is undesirable for steel. Conversely, solid metal will justify itself in closed branches of large-format networks operating with high loads. When servicing poor quality water, it is better to use copper pipes. For a gravity-flow heating system, the use of this metal is advantageous due to its resistance to high temperatures and mineral inclusions in the coolant.
In principle, both copper and plastic have the advantage of being lightweight materials that allow precise installation of complex pipeline communication lines, which is very important in the implementation of gravity systems. However, plastic is still not the best option for the heating system as such - all the moreoperating under high pressure of the order of 0.6 MPa. There are heat-resistant polypropylene pipes designed specifically for heating and can withstand about 120 ° C, but sealing problems are more common in butts and transitions, which are not as reliable as metal contour welds.
Optimal pipe diameter
Unlike systems with forced circulation, in this case the thickness of the contours will be greater. The diameter of the pipe of a gravity-flow heating system is 50 mm, but there may be adjustments in different areas. For example, in order to maintain the thermal efficiency of the complex, plumbers recommend narrowing the contours. The amount of adjustment depends on the length of the solid line from the seam to the other transition point.
Mounting Tools and Consumables
The main tool will be needed for laying, fastening and connecting pipes. Cutting and welding are performed with pipe cutters, gas cutters, inverter devices and solder. Both for plastic and for copper with steel, your welding tool of the appropriate power is selected. The same applies to consumables. For example, copper structures are connected by soldering using clamping and crimping fittings. To connect a copper gravity heating system with circuits made of other materials, only detachable adapters and fittings are used. This metal does not adhere well to other materials. But in other cases, light solder up to 450 ° C can be obtainedacetylene or propane-butane torches, as well as electric soldering irons. In addition, for high-quality connections, it will be useful to use Teflon tapes, fittings, tees, dielectric gaskets, etc.
Installation technique
Before work, a communication scheme and an action plan should be drawn up. Further, typical installation is carried out in the following order:
- Assembly of individual nodes, transition sections and large lines without attachment to the base of the site.
- Installation of equipment - expansion tank and boiler. The tank can be mounted in the attic - the main thing is to keep the possibility of a free supply of communications. The boiler may require a small heat-resistant screed. Additional fastening is not required, since this type of floor equipment is practically motionless on a flat surface.
- The bearing fittings are installed along the contours of the gasket - supports, clamps, suspensions and other fixation units.
- Prepared pipe contours, transition parts, elbows and corners are mounted. How to make a gravity heating system so that it is as reliable and protected from external influences as possible? For fastening, it is recommended to use the so-called floating clamps, which provide not hard, but soft fixation. They are firmly attached to the prepared carrier equipment, but the clamping mechanisms give the pipe some freedom of movement - a springy effect, due to which the risk of damage is eliminatedpipes under external dynamic load.
- Communications and equipment are being tied up - branch pipes, fittings and instrumentation are connected if necessary.
Pipe slope
A feature of the device of gravity systems is the need to maintain the angle in the position of horizontal contours. It is necessary to provide the effect of natural gravitational circulation required for the movement of water. As noted in the technical regulations of SNiP, the slope of the gravity heating system should be 10 mm per 1 m. If this nuance is not foreseen, the lines will fill with air, and the heating of the circuits will be uneven.
Which coolant to use?
The optimum working medium for natural circulation systems is water. The rejection of antifreeze, which is often used in liquid heating, is associated with its high density and low heat transfer. Taking into account the modest performance of a gravity-flow heating system and the mandatory requirement for the gravitational displacement of the coolant, antifreeze is eliminated. But this does not mean that alternative antifreeze compositions can be abandoned in principle. Suitable mixtures must have high fluidity (not lower than water) and the ability to not lose physical properties at extremely high and low temperatures.
Pluses of a gravity flow system
Among the strengths of natural circulation heating systems are the following:
- Energy independence. Absenceno external source of energy is an obstacle to the use of gravity heating, so in many remote regions this option remains the only option.
- Reliability and durability. Absence of vibrations, which in conventional systems create circulation pumps. This allows the use of copper pipelines, as well as the organization of gravity heating systems made of polypropylene, but subject to their resistance to high temperatures.
- Easy maintenance. The absence of complex regulatory units with automation makes the system more accessible for diagnostics and repairs at home.
Cons of gravity flow system
Of course, the lack of support for the movement of the coolant from the circulation pump or other power equipment with resources led to a number of shortcomings of such systems:
- Functional limitations in terms of adjustment. This mainly concerns the possibility of flexible adjustment of the temperature regimes of heaters, but the operation of solid fuel boilers in itself excludes any automation in control.
- Due to its modest performance, a gravity heating system can only be used in small houses with low heating requirements. Added to this is the instability of circulation.
- Delays in the movement of the coolant in winter can lead to freezing of the liquid. For this reason, the search for antifreeze water additives is justified.
Conclusion
Pipes with natural circulation of the working medium in the age of progressive mechanics and programmable boilers with boilers seem obsolete and inefficient. In many ways, this is true, but in the context of growing energy consumption, a gravity heating system for a private house does not look completely out of place. Firstly, if country conditions do not allow the use of gas and electric boilers, then this decision will be more than justified. Secondly, several expense items are removed at once, due to the cost of energy with fuel and maintenance of complex equipment.
