Buffer tank for heating: connecting to a solid fuel boiler with your own hands, piping

You can get seriously burned if accidentally touched.

Connection diagram for the presence of three heat generators.

The priority and main criterion for choosing a modern and well-thought-out heat accumulator will be the boiler itself, if its working time of heat supply and power are somehow limited: To generate heat only a single one-time load of any fuel and its further disassembly by the installed full heating system for the whole day. We will carry out the necessary work according to your order - see Buffer tank

Closed type with natural circulation. Also a fairly simple piping scheme with a small number of heat consumers. The boiler is installed half a meter below the level of the radiators. In this regard, wood and coal heat generators differ from all others and require a special approach to the issue. They are quite common among professional craftsmen, but you can learn this on your own, since there is nothing complicated or supernatural in these schemes.

In addition to solid fuel boilers, using a heat accumulator is beneficial for gas and electric heating devices: Using gas boilers, savings are achieved due to the variable use of the heat accumulator and the boiler itself.

The second stage - the fuel fill is completely burned out, there is no influx of thermal energy.

However, this version imposes limitations: finding free space in the house for installing a large heat accumulator, as well as the technical capabilities of the heating boiler itself. How to approach the choice of buffer capacity? Solid fuel and gas boilers in combination with a buffer tank!

Operating principle of the device

Each heating device has its own special principle of operation.
Some boilers are characterized by a uniform operating mode (gas and electric heating equipment), others, on the contrary, are characterized by an unstable process. The heating intensity depends on the method of fuel supply and the presence of devices that control the combustion process. With appliances running on natural gas or electricity, everything is simple and clear. To regulate the heating temperature of the coolant, it is enough to reduce or even stop the gas supply and turn off the power supply. Constant power supply ensures uninterrupted operation of boiler equipment. Both day and night, the boiler operates in automatic mode, independently regulating the heating temperature of the coolant. Solid fuel boilers are units with high inertia. The fuel placed in the firebox burns constantly, and it is physically impossible to quickly stop this process. The thermal energy obtained during the combustion process should not be wasted. Excess heat is accumulated along with the coolant in a special container, which acts as a thermal energy accumulator.

The situation is similar with a decrease in the intensity of boiler operation. When the fuel mass is burned, the boiler sharply loses its performance, and the boiler water in the heating circuit begins to rapidly cool down. Without the next portion of fuel, there is a threat of a decrease in temperature in heated rooms. Of course there is a way out. A new supply of firewood or coal will solve the problem. Another question is how often you can carry out such a procedure, especially if the firebox is empty at night.

A solid fuel boiler connected to a buffer tank is a complex that can solve the problem of heating residential premises for you. Installing a buffer tank frees you from frequent and hard work of loading the combustion chamber of the heating device with another amount of firewood.

You can understand the principle of operation of a buffer tank using the example of a car battery. While the engine is turned on in the car, the electric current generator runs in parallel. The electricity generated by the generator is stored in the battery. When the main engines stop, the battery supplies the necessary energy back to the vehicle systems.

The buffer capacity works similarly. There is heat, the heat accumulator accumulates it, as soon as the heating installation stops producing heat, hot water from the storage tank is used to heat all heating systems.

Pros and cons of using

Each heat source intended for heating rooms has its own characteristics that must be taken into account during the design and installation of the heat source.

Installing a buffer tank in a heating system has undeniable advantages:

energy resources are saved by almost fifty percent,
the container allows the boiler to operate at full capacity. This extends the life of the heat source, because condensate forms in minimal quantities. In addition, the fuel burns in full, the amount of harmful emissions into the atmosphere is reduced, the boiler needs cleaning less often,
the volume of coolant contained in the buffer tank protects the heating system from overheating,
The operation of the heat storage tank is best demonstrated in the off-season, when the heating boiler is used periodically.

Buffer tank for heating saves resources

Now let's look at the negative aspects that are inherent in the buffer capacity:

you will have to incur additional costs for the purchase of a buffer tank and other components necessary for piping. But practice has already proven that all expenses will pay off within two to three years,
the heating system becomes more complicated, additional space will be required to install the equipment,
a heating system with a buffer tank will “accelerate” within two to four hours.

Application of additional boilers

You can include a rather unusual element in the wiring diagram of a solid fuel boiler - an electric boiler. It cannot be called a harness, it is rather a simple duplicating addition. Such schemes are used when there is no space for placing a heat accumulator. The electric boiler works in tandem with a wood-burning unit, automatically turning on when a drop in temperature in the circuit is detected. Advantages of the scheme:

Maintaining a stable heating temperature;
There is no need to spend money on a tank - the simplest electric boiler costs only a few thousand rubles;
Possibility of heating in the temporary absence of firewood;
A restful night's sleep, since you don't have to jump out of your warm bed to throw the next batch of firewood into the insatiable firebox.

There are also disadvantages:

In addition, using a backup electric boiler is extremely ineffective if your area experiences frequent power outages.

A backup electric boiler consumes a lot of electricity, which increases the cost of operating the heating system - this is not the most profitable scheme;
To power a powerful boiler you will need a separate line and good electrical wiring;
Particularly powerful models of electric boilers require connection to a three-phase network.

Therefore, investing in the purchase of a heat storage tank will be more profitable.

The nuances of connecting to the heating system

When a buffer tank is purchased for an existing circuit, before connecting it to the general heating system, it is recommended to think through the question of how you will bring it into the boiler room. You will probably have to remove the door leaf or even widen the opening. If the area for a tank filled with water is not strong enough, you will have to build an additional foundation.

Be sure to familiarize yourself with the connection options for the buffer tank you have chosen, the installation of heating elements, measuring devices, and instruments to ensure safe operation. Here it is necessary to remember that welded connections are prohibited - only threads or flanges.

The efficiency of your buffer device will depend on the thickness of the thermal insulation layer and the material from which it is made.

A safety valve and pressure gauge must be installed next to the tank.

A shut-off valve and a device for visual monitoring of the temperature regime are installed on each used pipe of the system. If such items are not included in the package, they must be purchased separately.

Some models have air vents that operate automatically. Otherwise, they are purchased in addition and installed in a special socket on the top of the tank or the pipe located there.

It is not recommended to independently improve buffer systems, so as not to create problems for safe living.

Solid fuel boilers and their connections

Some requirements for installing TT boilers

Solid fuel boiler Viadrus U22C-5

The correct operation of the heating system depends, first of all, on the system itself, since it is possible to correctly connect a solid fuel boiler (with or without a water circuit) only if the installation of pipes and radiators is done professionally. After all, in fact, a water heating device of this type has only an input and an output, into which the rest of the circuit fits.
In order for a solid fuel boiler to work with maximum efficiency and have the longest uninterrupted service life, the operating instructions suggest a minimum outlet temperature of 55⁰C, and an inlet (return) temperature of 45⁰C. Otherwise, condensation on the cold walls of the unit will reduce its temporary performance, destroying the metal. This can be avoided by using different schemes for connecting the boiler to the heating system.

Pyrolysis boiler

The installation of the unit is no less important, because the boiler must stand strictly vertically, on a rigid foundation, and this implies a cement screed of at least 5 cm thick with a bedding (half-layer) of the same thickness. The open type expansion tank must be located above the entire heating system and for this purpose it is most often placed in the attic.
The boiler's chimney must be equipped with a stainless steel valve, and a condensate collection tank must be installed in its lower part. To be able to clean the channel from soot, small, easily accessible hatches can be made along its length. In the unheated part of the room through which the soot removal pipe passes, you should insulate it yourself to extend its service life.

Connection diagrams for TT boilers

TT boiler connection

There are many schemes for connecting a solid fuel boiler, and all of them in one case or another are the most acceptable, and sometimes even irreplaceable. But, nevertheless, it is not at all necessary to memorize all the drawings in order to achieve the most optimal result - it is enough to know well the principle of operation of solid fuel units, their advantages and disadvantages.

The simplest and most popular connection diagram for a pyrolysis boiler

To calculate the ideal heating scheme, you need to combine the operation of a solid fuel unit with a thermal energy storage tank as best as possible. The fact is that the operating temperature of a water heating device constantly fluctuates around 60⁰C-90⁰C and it is almost impossible to keep it constant. After all, a boiler that runs on wood or coal is an inert device, unlike similar gas, electric and even diesel installations (you can see the connection diagram for a solid fuel boiler in this material).

Connecting a solid fuel boiler without forced circulation

It is not always possible to install a water pump for forced circulation of coolant and the reasons for this may be the most trivial. One of them is frequent voltage drops in the network, which are difficult to equalize with a stabilizer, or even the complete absence of power lines near the house. Of course, the price of such a system will be lower due to the lack of additional equipment, but its installation will require special care to maintain slopes.

Another diagram for connecting a TT boiler to a heating system

Between the boiler and the tank in the heating system, it would be useful to have safety lines on the inlet and outlet pipes, as close as possible to the water heater

Also, the connection of the boiler to the expansion tank should take place in the shortest possible way, in which taps or safety valves cannot be cut in. Pay attention to the distance h in the diagram, which determines the rise of the expansion tank above the top point of the heating system. If for some reason it is impossible to lift the tank, so that the circulation pump should be cut into a straight pipe

Otherwise, you will open up the possibility of air being sucked into the upper radiators.

The principle of inserting a circulation pump

The circulation pump is installed on the return pipe near the heating boiler. This is done so that in the event of a power failure, the system continues to function without coercion. This unit is mounted along a bypass route and, if necessary, it can be disconnected from the network and the bypass can be closed with taps.

To summarize: What are the advantages and disadvantages of using buffer tanks?

The obvious “advantages” of autonomous solid fuel heating systems with a heat accumulator include the following:

The energy potential of solid fuel is used to the maximum extent possible. Accordingly, the efficiency of boiler equipment increases sharply.
The operation of the system will require much less human intervention - from reducing the number of boiler loadings with fuel to expanding the ability to automate the control of operating modes of various heating circuits.
The solid fuel boiler itself receives reliable protection against overheating.
The operation of the system becomes smoother and more predictable, providing a differentiated approach to heating different rooms.
There are ample opportunities to modernize the system, including the launch of additional sources of thermal energy, without dismantling the old ones.
In most cases, the problem of hot water supply at home is also solved.

The disadvantages are very peculiar, and you also need to have an idea about them:

A heating system equipped with a buffer tank is characterized by very high inertia. This means that from the moment of initial ignition of the boiler until reaching the nominal operating mode it will take quite a lot of time. This is unlikely to be justified in a country house, which in winter the owners visit only on weekends - in such situations, rapid heating is required.
Heat accumulators are bulky and heavy (especially when filled with water) structures. They require enough space and a well-prepared, reliable foundation. Moreover, it is close to the heating boiler. This is not possible in every boiler room. Plus, there are difficulties with delivery and unloading, and often also with bringing the container into the room (it may not fit through the door). All this should be taken into account in advance.
The disadvantages include the very high price of such devices, which sometimes even exceeds the cost of the boiler. This “minus”, however, brightens up the expected saving effect from more rational use of fuel.
The heat accumulator will fully reveal its positive qualities only if the rated power of the solid fuel boiler (or the total power of other heat sources) is at least twice as high as the calculated value required for effective heating of the house. Otherwise, purchasing a buffer capacity seems unprofitable.

How to calculate the required thermal power for heating a house?
Such thermal engineering calculations must be carried out both when purchasing a boiler and when planning the installation of heating radiators. You can carry out the calculations yourself - if you use the algorithm described in detail in the publication of our portal dedicated to the calculation of heating by room area . There you will also find a convenient calculator.

Why is it needed?

A buffer tank, also called a heat accumulator, is used in a heating system to accumulate and preserve heat. In appearance, this device resembles a cylindrical tank, has insulated walls, which allows you to maintain the temperature of the coolant for a long time. Heat-resistant foam rubber is used as thermal insulation.

According to experts, the heat accumulator is considered one of the main devices in the heating system. With its help, heat is distributed throughout all rooms of a country house or any other building. The main task of a buffer tank is considered to be the accumulation of heat, which can come from different devices, be it an electric or solid fuel boiler.

Heat accumulator device

The main element of the container is considered to be a heat-accumulating substance responsible for the preservation and further distribution of heat. The products in question can work:

Steamed;
Using liquid;
With additional heating devices.

They can also be:

Thermochemical;
Solid state.

Most heating systems, including underfloor heating, use antifreeze, although it is best to use water for heating. Each of the buffer tanks has outlets for entering the boiler and heating pipes. A special valve is installed at the top of the container, protecting the device from excess pressure. Its main purpose is to remove accumulated air.

A drain valve is installed at the bottom of the tank to drain liquid if necessary. The tank has sockets for attaching sensors that indicate the pressure and temperature of the liquid.

The operation of the device in question is based on increasing the capacity of the coolant (water or antifreeze liquid - antifreeze). After fixing the tank, additional volume for liquid appears, as a result of which the inertia of the structure increases.

Note! When the buffer tank is heated by any heating device, a coolant of a certain temperature accumulates in the container. Heat distribution throughout the building occurs as the liquid cools, and thermal energy can be transferred even during the cessation of combustion processes in heating devices

Let's consider the principle of operation of a heat accumulator using the example of a solid fuel boiler. In this case, a pump is installed between these two devices, which serves to distribute heat evenly in all rooms of the building. Cold water moves from the bottom of the tank to the boiler, where it is heated.

After heating, the coolant enters the upper storage part of the tank. When the pump, which is fixed in the return pipeline, operates, cold water from the system enters in small portions into the lower part of the tank, displacing hot liquid, which is sent to the heating system.

After the boiler is turned off, there is a continuous supply of heat. Note that this process continues until the cold coolant completely displaces the hot water from the tank. The duration of operation of the buffer tank after stopping the heating device (boiler) will depend on factors such as the volume of the tank, the air temperature outside the house, and the number of heating sources.

The principle of operation of the buffer tank

The main advantages of a buffer tank are:

Uniform heat supply throughout the system. Most boilers heat the room unevenly, and this is due to the intensity of combustion or possible extinguishing of pallets, gas, or firewood. Using a buffer tank will avoid this phenomenon. During intense combustion, excess heat accumulates in the tank, which will be supplied to the system after the boiler dies out;
Independence from the operating schedule of heating devices. The fact is that you need to constantly add firewood or other types of fuel to solid fuel boilers; doing this at night is inconvenient. Using a buffer tank will allow you to supply coolant at night using accumulated resources. In this case, the interval between firing the boiler increases. When using electric heating devices and having two tariff meters, you can program the boiler to operate at night;
Protection against possible overheating;
Fuel savings (up to 30% compared to a standard heating system).

Where to put the circulation pump

In most schemes for piping a heat accumulator with a circulation pump, it is located in the return pipeline in front of the boiler. In the return - because the temperature is lower here, but you can also put it in the supply. Modern pumps are designed to pump coolant up to 110°C, so they do well there. Second point: when installed on the supply side, the pump will not create additional pressure on the heat exchanger, which will extend its service life.

In any case, when installing a circulation pump in the supply or return, there is no possibility of natural circulation. That is, if there is a power outage, the circulation will stop and the boiler will inevitably boil. To avoid this, install a four-way valve through which overheated water is discharged into the sewer system and recharged with cold water from the cold water supply system. This way, emergency cooling of the heat exchanger is organized and boiling of the coolant is prevented.

One way to avoid overheating of the coolant in a heating boiler

Please note that this scheme can only be implemented on steel or copper heat exchangers. With cast iron - you can't. If exposed to cold water, they may burst.

There is another way. It is more gentle on the heat exchanger (also suitable for cast iron) and requires less materials. You can make a connection between the boiler and the heat accumulator for heating so as to maintain natural circulation. In this case, when the power supply is turned off, the boiler will not boil - it will continue to heat the water in the container.

To maintain the natural circulation of the coolant, the pump is installed in a separate, specially created circuit. For the circuit to work, a large-section reed check valve is installed in the circuit.

This way natural circulation is maintained even in the absence of power supply

When the circulation pump is not working, it passes the coolant flow from the heat exchanger. When the circulation pump is operating, its pressure props up the valve and the coolant flows through the pump. There is a pipe running to the pump that is at least an inch in diameter. Only in this case can natural circulation be maintained.

About the specifics of the buffer tank in practice

Let's look at the diagram

Water heated by the boiler is supplied to the buffer tank using a circular pump 1. The same amount of water (but already cooled) is accordingly returned to the boiler. From the upper section of the buffer tank, pump 2 supplies hot water to the radiators. And the corresponding amount of cooled water is returned to the lower part of the buffer tank. Pump 1 operates while the boiler is burning. And the operation of pump 2 is regulated using a room thermostat: depending on the temperature in the room, it can turn the pump off or on.

Let's take a closer look at the mechanism for accumulating unclaimed power in a buffer tank. The boiler heats the water, in other words the thermal power, is transferred to the buffer tank. For example, let's take the figure of 15 kW from the situation described above. This power is transferred to the radiators using pump 2 (heat loss is compensated). Let's imagine that the performance level of both pumps is the same. In this case, the volume of thermal power,

which will enter the buffer tank will be equal to the volume that will enter the radiators (that is, designated 15 kW). But let us remember that it is early autumn in the yard, the temperature is 0°C, and the heat loss of the house is 8 kW. We transport too much heated water to radiators. What will happen? The temperature in the house will begin to increase, reach a comfortable temperature (indicated on the thermostat - for example, 20°C) and pump 2 will turn off. After a while, the radiators cool down, and the temperature in the room decreases. When the temperature in the house drops below that indicated on the thermostat, pump 2 will turn on and begin heating the radiators again. That is, as we have already noted, pump 1 operates constantly, and pump 2 alternates. Based on the fact that the performance is the same, but they work for different amounts of time, a larger volume of hot water enters the buffer tank than decreases. This means that the temperature in it will increase, and this is how heat accumulates.

Next, let's look at how the buffer tank releases accumulated heat. So, the boiler has worked and pump 1 is turned off - no more heat flows into the buffer tank. But pump 2 still functions as before: it pumps out hot water from the buffer tank and returns cold water. As a result, the temperature in the buffer tank decreases.

Functional diagram of the installation with a gas boiler, fireplace and solar collectors.

By using a tank-in-tank thermal buffer, the entire system can not only be significantly simpler, but also have a number of very important advantages. So:

1. the number of circulation pumps is lower, which increases reliability and reduces operating costs of the system (a pump for loading hot water cylinders, a fireplace or a solid fuel boiler works with only one pump);

2. control over the entire system is much less problematic. The system needs to tell the gas boiler that it should not be turned on because the fireplace is already running, which requires installing a thermostatic switch, for example on the heat exchanger. The system is regulated automatically - if the water in the tank is heated by solar panels or a fireplace, the boiler does not turn on, since its own automatic control system reports that this is not necessary;

3. High temperature heating circuit (radiators) and low temperature circuit (floor heating) can be connected at different buffer tank heights, which improves the efficiency of the heating system;

4. The system is assembled in stages, without problems, for example, the first installation of one boiler and buffer, and then, depending on investment opportunities, the connection of other heat sources to the tank without any modifications to the existing system.

Dozens of others can be invented, for example, a system with a tank-in-tank buffer (with the already mentioned disadvantage that the availability of hot water depends on the state of the buffer) can be replaced by a system with a separate tank loaded from a boiler or buffer. It is also possible - if boilers or other heat sources allow - to leave the buffer and use a “normal” tank with a large number of connecting pipelines.

Popular models

It's time to understand the most popular models of heat accumulators for heating systems. We will consider products from domestic and foreign manufacturers.

Heat accumulator for heating boilers made in Russia Prometheus

The manufacturer of Prometheus heat accumulators is Novosibirsk. It produces models with volumes of 230, 300, 500, 750 and 1000 liters. The equipment warranty is 5 years. The heat accumulators are equipped with four outlets for connection to heating and heat sources. A layer of thermal insulation made of mineral wool is responsible for preserving the accumulated energy. The working pressure is 2 atm, the maximum is 6 atm. When purchasing equipment, take into account its dimensions - for example, the diameter of a 1000-liter model is 900 mm, which is why its body may not fit into standard doorways 80 cm wide.

The price of the presented heat accumulator for heating systems varies in the range from 65 to 70 thousand rubles.

SPSX-2G 1000

Another capacious heat accumulator for 1000 liters of water. It is equipped with one or two smooth-tube heat exchangers, but lacks thermal insulation, which must be taken into account when installing it - it will have to be purchased separately. The diameter of the case is 790 mm, but if thermal insulation is added to it, the diameter increases to 990 mm. The maximum temperature in the heating system is +110 degrees, in the DHW circuit – up to +95 degrees.

Buderus Logalux P 500-1000/5

These heat accumulators are available in modifications with six or ten connections. Temperature sensor terminals are also provided on board. The tank capacity is 960 liters, operating pressure is up to 3 bar. The thickness of the thermal insulation layer is 80 mm. The use of liquids other than water as a coolant is not allowed - this applies to both circuits, and not just the heating circuit. If necessary, it is possible to connect several heat accumulators in series into a single cascade.

Connection diagram

Connection diagram
In the simplest case, the heat accumulator is connected in series between the boiler and the heating circuit. A circulation pump is installed between the heat exchanger and the boiler so that hot water enters the top of the heat exchanger, pushing cold water from the bottom into the boiler. A circulation pump is installed between the heat exchanger and the heating circuit to draw hot water from the upper part and transport it to the radiators.

However, this significantly increases the overall heat capacity of the system, and when starting the heating initially, you will have to wait until the entire volume of the heat exchanger is heated before the heat reaches the radiators.

Another option for switching on is parallel to the heating boiler. This option works well in combination with a gravity heating system. The upper outlet of the heat accumulator is connected to the highest point of the distribution box, and at the lower point - to the boiler.

The disadvantages are the same as in the first case; the entire volume of coolant in the system and in the heater is heated, which significantly increases the time to start heating.

The only advantages are ease of connection and a minimum of elements used.

Switching circuit with mixing

It is best to use a switching circuit with mixing or hydraulic isolation . Three-way valves with a thermostat are used. The heat accumulator is installed as a separate element of the system, parallel to the heating circuit.

The main part of the automation is installed on the supply pipeline: three-way valve, thermostats, safety group, etc. By default, the three-way valve directs the coolant from the boiler to the radiators until the room temperature reaches the required level.

Connection diagram with mixing

As soon as there is no need for active heating, the valve transfers part of the coolant from the boiler to the heat accumulator, discharging excess heat.

When the maximum water temperature in the heater and the target temperature in the radiators are reached, the overheating sensor installed in the boiler is triggered and it turns off. While heating is required or the heat accumulator is not warmed up, the boiler continues to operate.

If for some reason the boiler stops producing rated power or switches off completely when the temperature on the supply line drops, water from the heat accumulator is mixed into the heating circuit, replenishing the heat loss of the system.

You can use several three-way valves on the supply and return lines and a group of thermostats. As an option, ready-made assemblies for connecting heat accumulators are available for sale - an automatic mixing unit, for example LADDOMAT.

Calculation of the volume of the boiler buffer tank

The most optimal solution to this task would be to entrust its implementation to heating engineers. Calculating the volume of a heat accumulator for the entire heating system of a private house requires taking into account various factors known only to them. Despite this, you can make preliminary calculations yourself. To do this, in addition to general knowledge of physics and mathematics, you will need a calculator and a blank sheet of paper.

We find the following data

boiler power, kW;
time of active fuel combustion;
thermal power of heating the house, kW;
boiler efficiency;
temperatures in the supply and return pipes.

Let's look at an example of a preliminary calculation. Heated area - 200 m2, active burning time of the boiler - 8 hours, coolant temperature during heating - 90° C, in the return circuit - 40° C. The estimated thermal power of the heated rooms is 10 kW. With such initial data, the thermal device will receive 80 kW (10×8) of energy.

We calculate the buffer capacity of a solid fuel boiler based on the heat capacity of water

m=Q/1.163×∆t

where: m – mass of water in the container (kg); Q – amount of heat (W); ∆t – difference in temperature of water in the supply and return pipes (°C); 1.163 – specific heat capacity of water (W/kg °C) .

Substituting the numbers into the formula, we get 1375 kg of water or 1.4 m3 (80000/1.163×50). Thus, for the heating system of a house with an area of 200 m2, it is necessary to install a heating unit with a capacity of 1.4 m3. Knowing this figure, you can safely go to the store and see which heat accumulator is acceptable.

Dimensions, price, equipment, manufacturer are already easily determined. By comparing known factors, it is not difficult to make a preliminary choice of a heat accumulator for your home. This calculation is relevant when the house is built and the heating system is already installed. The result of the calculation will show whether it is necessary to disassemble the doorways due to the dimensions of the TA. Having assessed the possibility of installing it in a permanent place, the final calculation of the heat accumulator for the solid fuel boiler installed in the system is made.

Having collected data on the heating system, we perform calculations using the formula

W = m×c×∆t (1)

where: W is the amount of heat required to heat the coolant; m is the mass of water; c is the heat capacity; ∆t is the water heating temperature;

In addition, you will need the value k - boiler efficiency.

From formula (1) we find the mass:m = W/(c×∆t) (2)

Since the efficiency of the boiler is known, we refine formula (1) and obtain W = m×c×∆t×k (3) from where we find the updated mass of water m = W/(c×∆t×k) (4)

Let's look at how to calculate a heat accumulator for a home. The heating system is equipped with a 20 kW boiler (indicated in the passport data). The fuel fill burns out in 2.5 hours. To heat a house you need 8.5 kW/1 hour of energy. This means that during the burning time of one bookmark, 20 × 2.5 = 50 kW will be obtained

8.5 × 2.5 = 21.5 kW will be spent on space heating

The excess heat produced 50 – 21.5 = 28.5 kW is stored in the heat exchanger.

The temperature at which the coolant is heated is 35° C. (The difference in temperature in the supply and return pipes. Determined by measurements during operation of the heating system). Substituting the required values into formula (4) we obtain 28500/(0.8×1.163×35) = 874.5 kg

This figure means that to preserve the heat generated by the boiler, you need to have 875 kg of coolant. To do this, you will need a buffer tank for the entire system with a volume of 0.875 m3. Such simplified calculations make it easy to select a heat accumulator for heating boilers.

Design, principle of operation and piping diagram of a heat accumulator for heating boilers

Currently, owners of private houses are actively switching to solid fuel boilers, which are a good alternative to gas and electric ones.

The fuel for them is coal, firewood, pellets. Due to the availability of fuel, the design features of solid fuel boilers and the ease of their installation, it is possible to achieve high-quality operation of the heating system. But despite a number of advantages, these devices also have one obvious drawback - in order not to be left without heat and maintain the required temperature in the room, they often have to be heated twice a day. To eliminate such inconveniences, another element is built into the heating system - a heat accumulator for a solid fuel boiler.

Heat accumulator for heating boiler

Functions, advantages and disadvantages of using a heat accumulator

The heat accumulator serves to store heat. Thanks to it, a heating system with a solid fuel boiler becomes more profitable, practical and productive.

Connectable systems to the buffer tank

The heat accumulator performs a number of functions:

Accumulation of heat from the boiler and its subsequent consumption as required by the heating system. This became possible thanks to the use of a three-way valve or special automation.
Protecting the heating system from overheating.
Maximum efficiency in boiler operation.
The ability to link various heat sources in one circuit.

The volume of the storage tank can range from one hundred to several thousand liters. The larger the buffer tank for the boiler in volume, the larger its dimensions.

A heating system using a heat accumulator has the following advantages:

boiler protection from overheating;
work with maximum energy savings and increase the efficiency of the entire heating system;
simplicity and ease of use of the boiler, the ability to load it at any time;
ensuring stable temperature throughout the entire area of the room;
the ability to provide hot water supply to homes without using additional water heating devices.

Disadvantages of thermal energy batteries:

heavy weight and large size;
it must be installed next to the heating boiler, so the house must have a separate room of the appropriate size;
high price.

Design and principle of operation

The heat accumulator is a buffer tank, which is made in the shape of a cylinder from stainless or black steel.

Heat accumulator device

As a rule, there are two cycles in the operation of a solid fuel boiler with a heat accumulator:

In the first cycle, two fuel loads are made, then they are burned at maximum power. During this process, all excess heat accumulates in the battery rather than being expelled into the chimney.
There is no need to heat the boiler, since the optimal temperature is maintained by heat transfer from the tank.

Depending on the design, the following types of buffer tanks are distinguished:

empty (no heat exchanger);
with the presence of one or two heat exchangers;
with built-in boilers of smaller diameter, which are used to ensure autonomous operation of the hot water supply system.

The steel body of the tank has several threaded holes through which the heat accumulator is connected to the boiler.

Calculation of buffer capacity

The main criterion that must be followed when choosing a heat accumulator for a solid fuel boiler is its capacity or volume. To calculate the buffer capacity, you need to know the following factors:

heating boiler power;
expected duration of heating without a heat source;
thermal load on the heating system.

Calculation example

Initial data:

house with an area of 200 m²;
Boiler downtime is 8 hours;
Presumably the water in the tank will heat up to 90 °C, and during heating operation it will cool down to 40 °C.

In order to heat a house of such area in winter with 20 kW of heat, on average its consumption will be about 10 kW/h. Thus, the battery must accumulate 10 kW/h x 8 hours = 80 kW of energy.

Next, the volume of the heat accumulator is calculated using the formula for the heat capacity of water.

m = Q / 1.163 x Δt, where:

Q – estimated amount of thermal energy required for accumulation, W;
Δt – the difference between the temperature of the coolant in the tank, which was at the beginning and the one that turned out in the final result, is equal to 90 – 40 = 50 °C;
163 W/kg °C or 4.187 kJ/kg °C – specific heat capacity of water.

Formula for the heat capacity of water

Connecting the heat accumulator to the heating system and solid fuel boiler

In order to connect the buffer tank to the heating system, you can use the diagram.

Buffer tank connection diagram

Stages of connecting to the heating system:

It is necessary to transit the heat accumulator through the entire tank with a return pipeline, at the ends of which there should be an inlet and an outlet measuring one and a half inches.
At the first stage, the tank and boiler return are connected, a circulation pump is placed between them, which drives water from the barrel to the tap, tank and boiler.
A shut-off valve and a circulation pump are mounted on the reverse side.
The supply pipeline is connected according to the same principle as the previous one, however, in this case there is no installation of heat pumps.

This scheme is suitable for connecting a buffer tank to a heating system operating on the basis of only one boiler. As the number of boilers increases, the connection diagram for the heat accumulator will become more complicated.

Option for piping a solid fuel boiler and a heat accumulator

Stages of piping with a solid fuel boiler:

On the one hand - to the boiler: the supply pipeline is led to the upper pipe, the return pipe, respectively, to the lower one. In this case, in the boiler piping, it is necessary to make a jumper with a mixing unit, which will not allow cold water to enter the heat exchanger.
On the other hand, it is necessary to lead to the heating circuit, which is also equipped with a mixing unit and a jumper. Water will be taken into the circuit from above, and returned from below. One circulation pump must be installed in each circuit. The pump that is installed between the heat exchanger and the boiler will drive the coolant through the heat generator, thereby carrying out the process of charging the storage tank. The second pump, installed on the side of the heating circuit, is designed to drive coolant through the radiators.

How to make it yourself

The easiest way to make a heat accumulator for heating with your own hands involves having a ready-made steel barrel.

Barrel for heat accumulator

If the required container is not available, then it must be welded from steel sheets, the thickness of which should be 2 mm. If the heat accumulator is connected as a hydraulic separator, then two fittings must be inserted from below and two from above; the length of these devices must be identical to the thickness of the insulation. Tees with thermometers must be connected to the lower pipes. Next, the barrel needs to be wrapped with foil, and then with insulation. As insulation, it is important to use a material that, when in contact with hot surfaces, does not emit toxic fumes. The last stage: the container, previously lined with a heat insulator, is covered from the outside with a casing made of thin sheet steel or tin.

If the heat accumulator is used in parallel to heat hot water, then it is necessary to make another coil. The material is a copper pipe with a diameter of 20 mm.

Another method that ordinary people prefer is to make a heat accumulator from a Eurocube with a capacity of 1000 liters. It is recommended to use Eurocubes, the high quality of which is confirmed by an international quality certificate.

Before you start making a thermal accumulator from a Eurocube, you should remember that the temperature of the liquid that will be in such a tank should not exceed 72°C, therefore standard Eurocubes are not suitable for heating systems with high temperatures.

In order to independently build a heat accumulator from a Eurocube, you need the following materials:

Eurocube made from food materials;
heating element 3000 W, 3 pieces;
foot with gaskets G2″ to G1″1/4, 5 pieces;
coupling D32 - G1 1/4″, 2 pieces;
adapter adapter G1″1/4, 2 pieces;
lock nut G1″1/4, 5 pieces;
bend G1″1/4 30 cm, 2 pieces;
plumbing flax or special paste;
sealant;
cardan key.

Heat accumulator made of Eurocube 1000 l

Assembly is carried out in the following way:

Using a drill in the container body, you need to make an insert for the heating elements, then insert the fittings into the holes using gaskets and silicone glue-sealant, secure the fittings from the inside with locknuts and install the heating elements.
Then it is necessary to ensure the supply of water to the heat exchanger, this is done using a standard drain neck through adapters.
The next stage: the “return” is cut into the upper part of the Eurocube and connected, after which you need to mark the place for the cut-in and installation of the heat exchanger, as well as cut in the fittings and screw the fittings into them.
On the inside of the ejectors, you need to screw the couplings to connect the corrugation, then secure it and distribute it evenly throughout the volume of the heat accumulator for heating.
When connecting a heat accumulator, you need to install an EPS sheet at the installation site of the device, the thickness of which should be 10 cm, and also lay a 15 cm thick PSB along the rear wall.

The heat accumulator is insulated using a 10-centimeter sheet of polystyrene foam. It needs to be glued to the body of the Eurocube.

In addition to solid fuel boilers, using a heat accumulator is beneficial for gas and electric heating devices:

Using gas boilers, savings are achieved due to the variable use of the heat accumulator and the boiler itself. In this case, gas is consumed in smaller quantities, since the gas burner is turned on much less often.
For electric boilers, it is enough to turn on the heat accumulator at full power only at night, since electricity tariffs are much lower at this time. During the daytime, when the boiler is turned off, heating is carried out using the heat that has accumulated during the night.

The heat accumulator has no moving mechanical elements and its operation is static. This means that this device is reliable and long-lasting in use.

Tags: do-it-yourself heat accumulator heating element

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Application of buffer tank

The wiring diagram for a solid fuel boiler with a battery tank is not widely used. It is quite cumbersome, but allows for more correct heating operation. Its advantages:

Stabilization of temperature in the system due to the increased volume of water in the circuit;
Possibility of reducing the number of approaches for adding fuel to the boiler furnace due to the accumulation of excess heat in the storage tank;
Possibility of accumulating clearly unnecessary excess thermal energy when using too powerful a boiler or excessive stacking of firewood.

The heat accumulator circuit has one drawback - it is necessary to allocate space for the device itself. The volume of the container used reaches several hundred liters, so you will need free space to place the tank.

There are many schemes for connecting buffer tanks. The simplest of them involve the use of the same coolant in the boiler and in the heating system. A more efficient scheme is using a three-way valve with a thermostat, which ensures a more uniform and economical consumption of thermal energy from the buffer tank.

Schemes with two circuits are also used. In this case, heat accumulators of heating systems are equipped with heat exchangers connected to solid fuel boilers. Heat exchangers heat the water in the tank, which is the coolant of the heating circuit. This option is distinguished by its efficiency and more uniform heating.

This scheme with a buffer tank is gentle for solid fuel boilers that are not designed for high heating pressure. And in this case, the coolants will be separated, the pressure in the tank and in the radiators will not in any way affect the pressure in the boiler itself and the heat exchanger.

Using a single-circuit solid fuel boiler often forces you to look for schemes for organizing hot water supply. For these purposes, you can adapt a storage or instantaneous water heater. It is also possible to use a more advanced heat storage tank with a built-in DHW circuit coil. This piping scheme will be an optimal and profitable solution, as it will solve the problem with hot water supply.

Types and structure of heat accumulators

Containers are distinguished by the material used as thermal storage:

solid state;
steam;
as well as thermochemical;
liquid;
with additional heating.

At the top of the tank there are a pair of fittings (pipes) designed to combine with the boiler and the entire system, as well as a safety valve for releasing excess air if the pressure in the depths increases. There is a tap at the bottom through which you can drain the water. Also, the manufacturer sometimes places flanges here for mounting a pressure and temperature sensor.

Attention! The tank operates due to the difference in water pressure created by the pump. The built-in heat accumulator significantly increases the inertia of the entire heating system.

Options for designs and their connection diagrams

Buffer tanks for heating systems can be rectangular or flat. But this measure is forced, determined by the installation conditions in a particular boiler room. Plain water or antifreeze can be used as a heat carrier.

To improve the efficiency of the container, it is recommended to insulate it with a layer of four to ten centimeters. In addition, the buffer tank for the heating boiler can be equipped with:

built-in electric heating elements (heating elements);
copper or steel coils made of stainless material or ferrous metal. Their main purpose is to prepare hot water supply, connect additional heat sources, solar systems, “warm floors”;
tanks for preparing hot water with a capacity of one hundred to two hundred liters.

Now let's look at the most common options for connecting a buffer tank to a heating system.

The main purpose of the mixing unit is to prevent cold water from returning to the heat generator. A three-way valve, adjusted to a temperature of at least forty-five degrees, directs the coolant in a small circle until it heats up to the set parameter. After this, cold liquid begins to flow through the valve in a dosed manner. To clean the system of scale, it is recommended to install a dirt filter upstream of the valve. It must be remembered that the vertical installation scheme is a mistaken action.

Most manufacturers strongly advise the use of heat accumulators (buffer tanks). This is due to certain reasons:

after closing the damper, wood with a minimal amount of oxygen smolders in the chamber, which increases the amount of carbon monoxide and increases the level of environmental pollution. For this reason, the boiler must operate at average or maximum levels, concentrating excess heat in the container;
as soon as the wood burns out, the thermal energy accumulated in the buffer zone will be enough to heat all the rooms for some time. The duration of this heating option depends on the size of the tank.

A connection option alternative to the previous method is to connect a solid fuel boiler with a buffer tank. The method of connecting the buffer tank to the heating system differs in that the tank does not accumulate heat, but separates the boiler from the pipe circuit of the heating system, of which there may be several, with different temperature conditions of the coolants.

Often, solid fuel boilers are installed as an additional element in houses that already have electrical installations. In order for joint work to proceed correctly, it is necessary to perform the correct piping, which provides for the units to secure each other. For example, coal burns out in a boiler. At this moment, the electric or gas boiler is automatically activated.

Intermediate link or heart of the heating system

It is also possible - this is a solution for the most modern owners - to connect a heat pump to it, which will comfortably and cheaply heat the building at least during the transition period. And this is what we have come to: the buffer does not have to be an intermediate link between the boiler and the heating system, it can be the heart of the latter.

In most houses commissioned nowadays, the heating system includes: a gas (or oil) boiler, a solid fuel boiler or a fireplace with a water jacket (the first is usually used to save on heating costs, the second is also for pleasure), increasingly installed ( especially if during the heating season the water needs to be heated with expensive oil or liquefied gas) solar collectors or, more recently, air source heat pumps to produce hot water. The coexistence of a radiator and underfloor heating is also standard.

Typically, the hydraulic circuit implemented is quite complex, since the connection of a boiler or fireplace (usually operating in an open system) requires the use of a heat exchanger, and the efficient operation of all hydraulic circuits is guaranteed only with the help of a hydraulic coupling. In fact, some elements are often omitted. For example, coal boilers are connected to a closed system without the use of a heat exchanger, which poses a risk to the safety of users (unless the boiler has a separate protection - a cooling coil).

How to choose the right heat accumulator for your heating system

Before installing the heating system, the type of main heat source is determined. The volume of the heat accumulator also depends on the power of the solid fuel boiler and the volume of tasks that the device will solve during operation. The size and capacity of the storage device is also determined by your household needs. When choosing a buffer tank, the priority when choosing a buffer tank is the model of the heating unit, which has a power limit and a limited time resource.

In other words:

when working in tandem with a solid fuel boiler, the buffer tank must ensure the accumulation of thermal energy during a one-time loading of fuel, sufficient to distribute hot coolant throughout the system until the subsequent loading of the combustion chamber.

Here it is appropriate to say a few words about the calculated data that influences the choice of the optimal volume of buffer capacity. Using calculations, it is possible to determine the real storage capacity of a specific volume of coolant, which affects the heat capacity.

To complete the picture, we count. When installing a heat accumulator with a volume of 1000 liters. (1000 kg), to heat water to a temperature of 50 0 C, the amount of thermal energy stored in the tank will be 1000 x 50 = 50,000 kcal or 58 thousand kW/h.

When hot water is consumed from the buffer tank and the water temperature decreases by 50 degrees, the amount of heat will correspondingly decrease by the same amount. Each connection diagram has its own method for calculating the capacity of a heat accumulator, however, there are the following general requirements that must be taken into account:

the storage tank must be capable of accumulating the maximum amount of excess thermal energy during the combustion of fuel with a single load;
the higher the peak thermal energy consumption in the heating circuit and the longer the maximum heat consumption, the larger the volume required for the buffer tank;
if the boiler burns at a high intensity in short periods of time, it will be necessary to install an additional heat exchanger, either separately or integrated into the buffer tank;
the drive must have a nominal pressure inside that is greater than at the point at which the device is connected to the system;
in hot water storage tanks with two or more built-in heat exchangers, the system with lower operating pressure is connected to the lower heat exchange devices, and with high operating pressure, on the contrary, to the heat exchangers located at the top;
installation of a heat accumulator requires the installation of an expansion tank and a safety, thermo-mixing valve in the system.

Diagram of a buffer tank-heat accumulator of a heating system, consisting of several tanks

Some craftsmen make themselves or outsource the production of buffer tanks from sections of large-diameter steel pipes - 300-800 mm. After installation in place, the tanks are insulated.

Such tanks are often much cheaper than ready-made buffer tanks that are sold on the construction market. The lack of corrosion protection in such homemade tanks is partially compensated by the increased thickness of the metal wall.

To protect against electrochemical corrosion, it is recommended to ground the tank and place a magnesium anode from an industrial water heater inside the tank.

A buffer tank of the required volume can be obtained by connecting two or more smaller tanks with pipes.

The upper and lower parts of the tanks are connected to each other by pipes with a diameter of at least one and a half inches .

It turns out to be a battery of tanks connected to each other like sections of a heating battery.

The battery from the tanks is connected to the boiler and heating circuits in a diagonal pattern. This connection ensures the same water temperature distribution in all buffer tanks.

The last tank in the battery (tank No. 2 in the diagram) can serve as a hydraulic separator between the radiator heating system and heated floors.

Final stage

The last steps before starting operation will be:

Cleaning, priming and painting the inside of the tank. It should be primed and painted several times.
Afterwards, pre-prepared coils (heat exchangers) are connected.
The tightness and reliability of the structure is checked. This is done using pressurized water.
The outside of the tank is painted.
Thermal insulation material is installed. The outer casing made of galvanized steel sheet is mounted on pre-prepared fastenings.

If it is possible to entrust this matter to professionals or buy a factory buffer tank, it is better to do so.
Since its independent production requires extensive experience in welding and skills in thermal and hydraulic engineering. In addition, this will require a lot of resources, effort and time. Date: September 25, 2022

Criterias of choice

When deciding to install a container, you will have to take into account certain nuances:

The heat volume of the container depends on the capacity. The amount of coolant must be such that energy is not wasted, and all excess heat is concentrated in the tank,
the permissible pressure limit is specified. It must be no less than similar indicators for any heating circuit,
Based on the values of the indicators given above, the dimensions and weight of the container are determined. Do not forget that there will be water in the tank, the mass of which will also have to be taken into account,
The choice of model is carried out taking into account the connection diagram and the tasks to be solved. For this reason, tanks with the required number of heat exchangers can be installed,
Of no small importance is the material from which the tank is made. Stainless steel will last a long time, but it will also cost you significantly more money.

When choosing a buffer tank for heating, pay attention to the material of manufacture

Parameter calculation methods

Experienced specialists choosing a buffer tank for installing a heating system use one of the well-known methods when calculating the tank.

Statistical

This option involves determining the required volume of the container, taking into account the amount of fuel loaded. The basis is the principle of balance between the indicators of generated and used energy.

To ensure that thermal energy is not taken away by the heating system, the container must absorb the entire amount of energy produced by the boiler at maximum furnace load. To make this calculation, you will have to multiply the rated power of the boiler by the time it takes for the fuel to burn out completely.

Dynamic

To carry out calculations using this method, it is necessary to know the amount of energy spent on heating the building and the current temperature regime at that moment. The maximum time for boiler operation in this case is determined by the user, measured in days.

The buffer tank will protect your heating boiler from water hammer; heating of the coolant in the system will occur more evenly. The storage tank will take an important place in your space heating system.