Owners of private houses who use solid fuel stoves to heat up are well aware of the problem of cooling their homes after they completely burn through laying firewood or coal. This happens at night or in the absence of the owners, when there is no one to plant new logs in the furnace. The issue is resolved in several ways:
- use a combined wood heating boiler - electricity;
- install 2 separate heat sources - solid fuel and electric;
- Do not get involved in electricity and put the boiler on long burning wood.
We suggest that you consider the listed options in detail in order to choose the most comfortable way of heating a country house.
The use of combined boilers
Heat generators operating on various energy carriers did not appear yesterday. Since the days of the USSR, “dual-fuel” gas-firewood boilers have been known, in which they had to remove a burner device to switch to wood. In modern heating units, solid fuel is combined not only with gas, but also with electricity, which is more important for users. A homeowner who decides to buy a wood and electric heating boiler resolves several issues in one fell swoop:
- It applies for heating two energy carriers at once, alternative to natural gas.
- It excludes cooling of the rooms of a private house when the contents of the firebox are completely burned out, and a new portion of coal or firewood is not loaded.
- It increases the convenience of operating water heating, since you no longer need to get up in the middle of the night and run to the boiler room.
The new generation combined heat generators are designed in such a way that the electric heating turns on automatically when the water in the boiler tank starts to cool. The reverse transition to wood burning without the intervention of the owner of the house is impossible.
The principle of operation of an electric wood boiler
The design of this type of heater is similar to that of a traditional solid fuel boiler, consisting of the following main elements:
- a combustion chamber (firebox), where logs and coal are loaded;
- from the outside, it is washed by a coolant enclosed inside a water jacket;
- a heat exchanger of a fire tube or water tube type, where the combustion products give off most of the heat to the water before being released to the outside through a chimney;
- the grate stands at the bottom of the firebox, and under it is an ash chamber;
- the firebox and ash pan in front are equipped with doors;
- To change the intensity of combustion in the heat generator, use a mechanical draft regulator or a fan - air blower (if manual control of the air damper is not provided).
Household combined heating boilers are distinguished by the design of a water jacket, which provides a place for installing a block of tubular electric heaters - heating elements. The heating part of the element is immersed in the coolant, and the contacts are brought out and connected by a cable to the control panel.
The algorithm of operation of a solid fuel heater equipped with electric heaters looks like this:
- The kindling and heating of the boiler is carried out as usual. While the wood is burning, the temperature of the coolant is maintained by a mechanical temperature controller or a fan together with the sensor, and the heating elements are inactive.
- After burning the contents of the firebox, the water in the system begins to cool, which registers the temperature sensor. When the coolant is cooled to a certain point, at the signal of the sensor, the heater (one or more) will turn on. From this moment, the boiler switches to electricity.
- After loading another portion of solid fuel, the heat carrier is heated from the side of the combustion chamber, and the electrical part is automatically turned off until the next cooling.
The transition from one mode to another allows you to provide continuous water heating, which is what the inhabitants of a private house need for comfort.
Pros and cons of universal heat generators
By installing a combined boiler for heating a private house firewood - electricity, you get these bonuses:
- Thanks to the built-in heating elements, water heating will continue to function after the attenuation of the main firebox. This will keep the house warm, and during your absence will prevent the pipes and heating radiators from defrosting.
- Comfort. Support for heating the system with electricity will save you from night trips to the boiler room for laying logs.
- If electricity metering is carried out according to a multi-tariff scheme, then in addition to convenience, you will receive savings from the operation of heating elements at night.
Electric heaters of the combined boiler are designed only to maintain the temperature of the water in the system; they cannot fully replace the burning of solid fuel. The reason is the insufficient power of the block of heating elements installed by manufacturers on TT-boilers.
Example: in all Kupper units of the famous Russian brand Teplodar with a capacity of 9 ... 20 kW there are identical electric heaters with a heat transfer of 6 kW.
This feature of combined heat generators can be safely attributed to the disadvantages. The exception is low-power heaters (the same 9-kW Cooper with 6 kW heating elements) purchased for small-sized dwellings (up to 100 m²). In this case, the heat transfer from electricity is comparable to burning wood, therefore, in moderately cold weather (about -5 ° C in the yard), heaters are able to completely heat a modest-sized house.
Another important point. Like a conventional solid fuel heater, a combined wood-electricity boiler should be connected to water heating via a three-way valve, as shown in the diagram below. A small circulation circuit serves to protect the firebox from the harmful effects of condensate during kindling.
If the power of the heating elements is sufficient to heat the coolant to a temperature of +55 ° C and above, then condensation never forms in the combustion chamber of the combined boiler during kindling, and the unit with a three-way mixing valve becomes as if irrelevant. In reality, a small circulation loop is still needed, at least in case of a power outage or breakdown of one of the heating elements.
Heating a private house with wood and electricity from one boiler has other negative sides:
- The block of heaters takes away the useful volume of the firebox at the expense of the burning time from one load.
- The operation of the unit depends on the stability of the power supply.
- The prices of combined products are higher than classic solid fuel boilers.
- The efficiency during operation of electric heaters is reduced by 2-5% due to the air flow passing through the cooled furnace. The reason is the constant draft in the chimney, forcing the air from the premises to go through the fuel path into the chimney and cool the water jacket of the heater.
In order to fully replace natural gas with electricity and wood, it is better to look at another option for heating a building - put 2 separate heat sources, correctly tie them and connect them to the heating system.
Connection of boilers for wood and electricity
Without a doubt, the purchase, installation and strapping of two separate units will cost you more than one combined heat generator. But, implementing this option, you get full heating with two energy carriers, which effectively operates in automatic mode.
Reference.In non-gasified private houses of the Russian Federation, the joint operation of a solid fuel and electric boiler is used quite often, since this is the most convenient way to heat a house with wood. The combination of gas and firewood is no less common, and the third place is occupied by the so-called multi-fuel boilers, which we will discuss in a separate article.
In our pair of heat sources, a wood (coal) boiler is the main one, and the electric one is the auxiliary unit. As the latter, you can use any of the three varieties of electric boilers on the market:
- traditional heating element with integrated circulation pump and control unit;
- electrode with an external control panel;
- induction with a separate remote control.
We will not analyze the advantages and disadvantages of each type of electric boiler, this is the topic of another article. Here we show on the diagrams how to connect boilers for wood and electricity, so that the second hedges the first in automatic mode. Let's start with the joint strapping of the wood and heating elements of the heating unit:
Reference. The presented scheme can be used for joint connection with a gas wall-mounted boiler, which is put in place of the heating element.
The system operation algorithm looks like this:
- The TT boiler is inactive and its circulation pump is turned off. Heating appliances receive heat from an electric boiler that focuses on a room thermostat, where you set the desired temperature. So that the coolant does not move in a circle through a parallel ring, 2 check valves are involved in the circuit.
- You have melted a solid fuel unit. For some time it will begin to gain temperature, and water will circulate in a small circle, guided by a three-way valve with a thermal head. The pump will turn on at the command of the overhead thermostat installed on the supply pipe.
- When the coolant in the small ring heats up to 55 ° C, the temperature sensor of the thermal head, located on the return line, will work. The three-way valve opens and the heat goes into the heating system.
- The electric boiler will turn off the heating according to the signal of the room thermostat and switch to standby mode.
- After burning solid fuel, the water in the system, and after it the air in the rooms, will begin to cool. The overhead thermostat of the TT boiler “sees” that the coolant has cooled and will stop the pump.
- When the temperature in the house drops to the value you set, the room thermostat again activates the electric boiler.
Important! Since the internal circulation pump of the wall-mounted heat generator cannot be turned off, a more powerful unit must be selected for a solid fuel heat source. As a rule, a pump with a pressure of 0.6 Bar is enough (in an electric boiler it usually costs 0.5 Bar). The second moment: put all overhead sensors and thermostats on metal pipes, they will lie on metal-plastic or polypropylene.
Induction and electrode heat generators are not equipped with their own filter and circulation pump, so you will have to buy and install the latter separately. This is all the difference in the connection diagram of the heaters of this type, only the pump unit must be connected to the network through the control cabinet so that the room thermostat disconnects it together with the electric boiler, as shown in the diagram:
If the heating system of a private house consists of several circuits (radiators on different floors, underfloor heating and an indirect heating boiler), then for joint work, a wood and electric boiler is connected using the primary and secondary rings method. The principle of operation of this type of strapping is described here.
Using TT boilers for long burning
Not every homeowner has the technical ability to connect powerful electrical equipment, which include combined and purely electric boilers. The reason is the limitation of the limit of allocated power to a private house.The size of the limit depends on the capacity of local electricity networks, which the owner of a suburban cottage cannot increase.
In the absence of natural gas on the site or at the high cost of connecting to the highway, there is only one real way out - to buy a boiler using wood and long burning coal or to make it yourself. The duration of work from 1 load in a conventional TT boiler is 3-6 hours, which makes the owner work near him as a stoker. A comfortable interval between fuel bookmarks is at least 8 hours, and not every heater provides so much.
The trouble is that any seedy manufacturer calls their products boilers of long burning in order to sell to an ignorant user. You can find out the correct unit among other heat generators by the following signs:
- at the same power, the boiler with a large power reserve is equipped with a firebox of increased volume (from 100 l) and differs in size;
- the passport indicates a burning time of 8 hours (on wood);
- for convenience, the unit is equipped with an additional loading door.
Detailed information on heat generators of this type and recommendations for their choice are published in a separate topic.
Conclusion
As conclusions, we will offer some simple tips for organizing comfortable heating of a private house using solid fuel and electricity:
- A combined boiler for wood and electricity is one of the best options for a cottage or residential house of a small area. In a cottage on 2-4 floors, heating elements can only protect the system from defrosting.
- In a country house over 100 m², it is appropriate to use 2 separate heat sources with the correct binding.
- When electricity is intermittently supplied or the power limit does not exceed 5 kW, you should not contact electricity at all. Find the opportunity to purchase a continuous combustion heat generator, although at a price it will cost more than usual.
- Do not discard the possibility of arranging air heating on wood from the stove, if it has already been bought or built. For safety at night, put electric convectors or fan heaters equipped with thermostats.