The efficiency of its further work and its service life depend on how correctly tying the solid fuel boiler is made. In operation, wood and coal heat generators differ from units for other types of fuel, therefore they require a special approach.
It is proposed to consider in detail how, after installing the heating wiring, to connect a solid fuel boiler, including with your own hands. You can find a description of the various schemes for connecting a TT boiler to a heating system in this material.
What is the difference between solid fuel boilers
In addition to burning various types of solid fuels, heat generators have a number of differences from other heat sources. These features should be taken for granted and always taken into account when tying a solid fuel boiler with a water heating system. What are they:
- High inertia. At the moment, there is no way to abruptly extinguish a burnt solid fuel in a combustion chamber.
- Condensation forms in the firebox during warm-up. The peculiarity is manifested due to the receipt of a coolant with a low temperature (below 50 ° C) in the boiler tank.
Note. The inertia phenomenon is absent only in one type of solid fuel aggregates - pellet boilers. They have a burner where the wood pellets are dosed, after the cessation of supply, the flame dies away almost immediately.
Inertia creates the risk of overheating of the heater’s water jacket, as a result of which the coolant in it boils. Steam forms, which creates high pressure, tearing the unit body and part of the supply pipe. As a result, there is a lot of water in the furnace room, a lot of steam and a solid fuel boiler unsuitable for further operation.
A similar situation can occur when the piping of the heat generator is incorrect. After all, in fact, the normal mode of operation of wood boilers is the maximum, it was at this time that the unit reached its passport efficiency. When the thermostat reacts to the temperature reaching 85 ° C and covers the air damper, combustion and smoldering in the furnace still continue. The water temperature rises another 2-4 ° C, or even more, before its growth stops.
In order to avoid overpressure and subsequent accident, an important element is always involved in the piping of the solid fuel boiler - the safety group, more about it will be discussed below.
Another unpleasant feature of the unit working on wood is the appearance of condensate on the inner walls of the firebox due to the passage of an unheated coolant through the water jacket. This condensate is not God's dew at all, because it is an aggressive liquid, from which the steel walls of the combustion chamber quickly corrode. Then, mixed with ash, the condensate turns into a sticky substance, tearing it off the surface is not so easy. The problem is solved by installing a mixing unit in the piping of a solid fuel boiler.
It is too early for owners of heat generators with cast-iron heat exchangers that are not afraid of corrosion to breathe with relief. They can expect another misfortune - the possibility of destruction of cast iron from temperature shock. Imagine that in a private house, electricity was turned off for 20-30 minutes and the circulation pump, which was driving water through a solid fuel boiler, stopped. During this time, the water in the radiators has time to cool, and in the heat exchanger - to heat up (due to the same inertia).
Electricity appears, the pump turns on and sends the cooled coolant from the closed heating system to the preheated boiler.From a sharp temperature difference, the heat exchanger experiences a temperature shock, the cast-iron section gives a crack, water runs to the floor. It is very difficult to repair, it is not always possible to replace a section. So, even in this situation, the mixing unit will prevent the accident, which will be discussed later.
Emergencies and their consequences are not described in order to frighten the users of solid fuel boilers or to encourage them to buy unnecessary elements of piping schemes. The description is based on practical experience that must always be considered. With the correct connection of the thermal unit, the probability of such consequences is extremely low, almost the same as that of heat generators using other types of fuel.
How to connect a solid fuel boiler
The canonical solid fuel boiler connection scheme contains two main elements, allowing it to function reliably in the heating system of a private house. This is a safety group and a mixing unit based on a three-way valve with a thermal head and a temperature sensor, shown in the figure:
Note. An expansion tank is not conventionally shown here - it should be connected to the return line of the heating system in front of the pump (in the direction of the water flow).
The task of the security group, installed directly at the outlet of the supply pipe of the solid fuel boiler, is to automatically relieve the pressure in the network when it rises above the set value (usually 3 Bar). The safety valve is engaged in this, and in addition to it, the element is equipped with an automatic air vent and pressure gauge. The first releases air that appears in the coolant, the second serves to control pressure.
Attention! On the pipeline section between the safety group and the boiler, installation of any stop valves is not allowed. If you have installed a ball valve to cut off and repair group parts, remove the handle from the stem.
How the circuit works
The mixing unit, which protects the heat generator from condensate and temperature changes, works according to this algorithm, starting from kindling:
- Firewood only flares up, the pump is on, the valve on the heating side is closed. The coolant circulates in a small circle through the bypass.
- When the temperature in the return pipe rises to 50–55 ° С, where the overhead type sensor is mounted, the thermal head, at his command, begins to press the stem of the three-way valve.
- The valve slowly opens and cold water gradually enters the boiler, mixing with hot from the bypass.
- As all radiators warm up, the overall temperature rises and then the valve closes the bypass completely, passing the entire coolant through the heat exchanger of the unit.
An important nuance. Paired with a 3-way valve, a special head is installed with a sensor and a capillary, designed to control the water temperature in a certain range (for example, 40 ... 70 or 50 ... 80 degrees). A conventional radiator thermal head will not work.
This strapping scheme is the simplest and most reliable, its installation can be safely done with your own hands and thus ensure the safe operation of a solid fuel boiler. Regarding this, there are a couple of recommendations, especially when tying a wood heater in a private house with polypropylene or other polymer pipes:
- Make a section of the pipe from the boiler to the safety group of metal, and then lay plastic.
- Thick-walled polypropylene conducts heat poorly, which is why the overhead sensor will openly lie, and the three-way valve will lag. For the correct operation of the unit, the section between the pump and the heat generator, where the copper flask stands, must also be metal.
Another point is the installation site of the circulation pump. It is best for him to stand where he is depicted in the diagram - on the return line in front of the wood-burning boiler.In general, you can set the pump on the feed, but remember what was mentioned above: in case of an emergency, steam may appear in the supply pipe.
The pump is unable to pump gases, therefore, when the chamber is filled with steam, the impeller will stop, the circulation of the coolant will stop. This will accelerate the possible explosion of the boiler, because it will not be cooled by the water flowing from the return pipe.
The way to reduce the cost of strapping
The condensate protection circuit can be reduced by installing a three-way mixing valve of a simplified design that does not require the connection of an overhead temperature sensor and a thermal head. A thermostatic element is already mounted in it, tuned to a fixed temperature of the mixture 55 or 60 ° C, as shown in the figure:
Note. Such valves, which maintain a fixed temperature of mixed water at the outlet and are intended for installation in the primary circuit of a solid fuel boiler, are produced by many well-known brands - Herz Armaturen, Danfoss, Regulus and others.
The installation of such an element unambiguously allows you to save on tying the TT boiler. But at the same time, the possibility of changing the temperature of the coolant with the help of a thermal head is lost, and its deviation at the outlet can reach 1–2 ° С. In most cases, these shortcomings are not significant.
Buffer capacity strapping option
The presence of a buffer tank is highly desirable for the operation of the boiler on solid fuels and that is why. In order for the unit to function efficiently and produce heat with the efficiency stated in the passport (from 75 to 85% for different types), it must operate at maximum speed. When an air damper is used to slow down combustion, there is a lack of oxygen in the furnace and the efficiency of burning wood is reduced. At the same time, emissions of carbon monoxide (CO) increase into the atmosphere.
For reference. It is because of emissions in most European countries that solid fuel boilers without a buffer tank are prohibited.
On the other hand, with maximum combustion, the coolant temperature in modern heat generators reaches 85 ° C, and one bookmark of firewood lasts only an hour for 4. This does not suit many owners of private houses. The solution to the problem is to put a buffer tank and include it in the strapping of the TT boiler in such a way that it serves as a storage tank. Schematically, it looks like this:
When the furnace burns with might and main, the buffer tank accumulates heat (in technical language it is loaded), and after attenuation it gives it to the heating system. To control the temperature of the coolant supplied to the radiators, on the other side of the storage tank, a three-way mixing valve and a second pump are also installed. Now it’s not at all necessary to run to the boiler every 4 hours, because after the firebox decays, heating the house for some time will provide buffer capacity. How long - depends on its volume and heating temperature.
Reference. Based on practical experience, the capacity of the heat accumulator can be determined as follows: for a private house of 200 m², you will need a tank with a volume of at least 1 m³.
There are a couple of important nuances. For the strapping scheme to work safely, you need a solid fuel boiler, whose power is enough for simultaneous heating and loading of the buffer tank. This means that a power of 2 times higher than the calculated one is required. Another point is the selection of pump performance so that the flow rate in the boiler circuit slightly exceeds the amount of flowing water in the heating circuit.
An interesting option for docking a TT boiler with a home-made buffer tank (aka indirect heating boiler) without a pump was demonstrated by our expert in the video:
Joint connection of two boilers
To increase the comfort of heating a private house, many owners install two or more heat sources operating on different energy sources. At the moment, the most relevant combinations of boilers for:
- natural gas and wood;
- solid fuel and electricity.
Accordingly, a gas and solid fuel boiler must be connected in such a way that the second automatically replaces the first after burning another portion of firewood. The same requirements are put forward for tying an electric boiler with wood. This is quite simple to do when a buffer capacity is involved in the strapping scheme, since it simultaneously plays the role of a hydroarrow, as shown in the figure.
Tip. Information on calculating the volume of the buffer tank can be found in a separate publication.
As you can see, due to the presence of an intermediate storage tank, 2 different boilers can serve several heating distribution circuits at once - batteries and underfloor heating, and in addition load an indirect heating boiler. But not everybody puts a heat accumulator with a TT boiler, since this is an expensive pleasure. For this case, there is a simple circuit, and you can mount it yourself:
Note. The scheme is valid for both electric and gas heat generators working together with solid fuel.
Primary and secondary ring binding
There is another way to jointly bundle a solid fuel boiler with an electric one to provide a large number of consumers. This is the method of primary and secondary circulation rings, which provides for the hydraulic separation of flows, but without the use of a hydraulic arrow. Also, for reliable operation of the system, a minimum of electronics is required, and the controller is not needed at all, despite the apparent complexity of the circuit:
The trick is that all consumers and boilers are connected to one primary circulation ring, both by the supply pipe and the return one. Due to the small distance between the connections (up to 300 mm), the pressure drop is minimal compared to the pump head of the main circuit. Due to this, the movement of water in the primary ring does not depend on the operation of the pumps of the secondary rings. Only the coolant temperature changes.
Theoretically, any number of heat sources and secondary rings can be included in the main circuit. The main thing is to choose the diameters of pipes and the performance of pumping units correctly. The actual capacity of the main ring pump should exceed the flow rate in the “gluttonous” secondary circuit itself.
Conclusion
As you can see, it is not so simple to make a solid fuel boiler piping correctly. The question should be taken responsibly and before completing installation and connection work, additionally consult with a specialist whose qualifications are beyond doubt. For example, with someone who gives an explanation in the videos presented.