Heat accumulator for heating boilers

The lack of an opportunity to use relatively inexpensive natural gas as a source of energy for heating housing causes the owners of houses to look for other acceptable solutions. So, in regions where there are no special problems with harvesting or purchasing firewood, solid fuel boilers come to the rescue. It also happens that the only alternative is electrical energy. In addition, new technologies are being used more and more, allowing solar energy to be sent to heating.

All these approaches are not devoid of significant drawbacks. So, to them it is possible to carry unevenness, expressed frequency of receipt of thermal energy. In the case of an electric boiler, the main negative factor is the high cost of consumed energy. It is obvious that it is essential to raise the efficiency of the heating system, improve efficiency, uniformity of its operation, and simplify operations operations as much as possible. It would help to include in the general scheme a special device that would accumulate unclaimed thermal energy and give it as needed. This is the function of the heat accumulator for heating boilers.

The main purpose of the heat accumulator of the

• The simplest heating system with a solid fuel boilermarked cyclic operation. After loading of firewood and their ignition, the boiler gradually reaches the maximum capacity, actively transferring heat energy to the heating circuits. But as the load burns down, the heat transfer begins to decrease gradually, and the coolant, carried by the radiators, cools down.

. It turns out that during peak heat production it can remain unclaimed, since a tuned, thermostatically controlled heating system will not take excess. But in the period of fuel burn-out and, moreover, the boiler's idle time, the thermal energy will obviously be lacking. As a result, part of the fuel potential is wasted simply, but the owners often have to deal with the loading of firewood.

To some extent, the severity of this problem can be reduced by installing a long-burning boiler, but it is not possible to completely remove it. The mismatch of the peaks of heat production and its consumption can remain quite significant.

• In the case of an electric boiler, the high cost of consumed energy is of primary importance, which makes the owners think about the maximum use of the equipment during the periods of preferential night tariffs and the minimization of consumption during the day.

Benefits of using differential electricity tariffing

With a competent approach to electricity consumption, preferential tariffs can bring quite tangible savings. This is described in detail in a special publication of the portal dedicated to two-rate electricity meters .

An obvious solution arises - to accumulate heat energy at night, in order to achieve a minimum consumption in the daytime.

• The frequency of generation of thermal energy in the case of solar collectors is even more pronounced. Here the dependence not only on the time of the day can be traced( at night, the receipt is generally zero).

. There is no comparison of the heating peaks in a bright sunny day or in cloudy weather. It is clear that you can not directly put your heating system in dependence on the current "whims" of nature, but you also do not want to neglect such a powerful additional source of energy. Obviously, some kind of buffer is required.

These three examples, for all their diversity, combine one common circumstance - the apparent mismatch of the peaks in the production of thermal energy with rational uniform use for heating. To eliminate this imbalance, a special device called a heat accumulator( heat accumulator, buffer capacity) serves.

The principle of its operation is based on the high heat capacity of water. If its considerable volume during the peak heat energy intake is heated to the required level, then for a certain period it is possible to use for this heating needs this accumulated energy potential. For example, if we compare the thermophysical parameters, only one liter of water when cooled down by 1 ° C is capable of heating the air cubic meter by as much as 4 ° C.

The thermal battery is always a volumetric tank with an effective external thermal insulation, connected to the circuit( circuits) of the heat source and the heating circuits. The simplest scheme is better considered with the example:

The simplest design of a heat accumulator( TA) is a vertically located volumetric tank, into which four nozzles are cut from two opposite sides. On the one hand, it is connected to the solid fuel boiler circuit( KTT), and on the other hand to the heating circuit in the house.

After loading and ignition of the boiler, the circulation pump( Nc) of this circuit starts to pump the coolant( water) through the heat exchanger. From the bottom of the TA, cold water enters the boiler, and the hot water comes to the top in the boiler. Because of the significant difference in the density of the cooled and hot water, there will be no active mixing in the tank - in the process of burning the fuel bookmark, the TA will be gradually filled with a hot coolant. As a result, with the correct calculation of the parameters, after the burned fuel has completely burnt out, the tank will be filled with hot water heated to the calculated level. All the potential energy of the fuel( minus, of course, the inevitable losses reflected in the efficiency of the boiler) is converted to thermal energy, which is stored in the TA.Quality thermal insulation allows you to keep the temperature in the tank for hours, and sometimes even - and days.

The second stage - the boiler does not work, but the heating system functions. With the help of its own circulation pump, the heating circuit pumps the coolant through pipes and radiators. The fence is made from above, from the "hot" zone. Intense self-mixing is again not observed - for the reason already mentioned, and hot water enters the supply pipe, the cooled one returns from below, and the tank gradually gives its heating in the direction from the bottom up.

In practice, during the heating of the boiler, the selection of the coolant in the heating system does not usually stop, and the TA will accumulate only the excess energy, which at the current moment remains unclaimed. But if the buffer capacity is correctly calculated, no kilowatts of thermal energy should be wasted, and by the end of the furnace cycle the TA should be "charged" to the maximum extent.

It is clear that the cyclic operation of such a system with an installed electric boiler will be tied to preferential night rates. The control unit timer will turn the power on and off at the set time in the evening and in the morning, and during the day the heating circuits will be powered only( or predominantly) from the heat accumulator.

Design features and basic circuits for connecting various heat accumulators

So, the heat accumulator is always a volumetric tank of vertical cylindrical design, which has a high-efficiency thermal insulation and is equipped with nozzles for connection of heat generation circuits and its consumption. But the internal design can be different. Let's consider the main types of existing models.

Basic types of heat accumulator designs

1 - The simplest type of TA design. It assumes direct connection of both heat sources and consumption contours. Such buffer capacities are used in the following cases:

• If the same coolant is used in the boiler and in all heating circuits.
• If the maximum allowable pressure of the heating medium in the heating circuits does not exceed the analogous indicator of the boiler and the HA itself.

If the requirement can not be met, the heating circuits can be connected via additional external heat exchangers

• . If the temperatures in the supply pipe at the outlet of their boiler do not exceed the permissible temperature in the heating circuits.

However, this requirement can also be bypassed when installed on circuits that require a lower temperature head, mixing units with three-way valves.

2 - The heat accumulator is equipped with an internal heat exchanger located at the bottom of the tank. The heat exchanger is usually a spiral wound from a stainless steel pipe, conventional or corrugated. There can be several such heat exchangers.

This type of TA is used in the following cases:

• If the pressure and flow temperature values ​​of the heat source circuit in the heat source circuit are significantly higher than the allowable values ​​for the consumption contours and for the buffer capacity itself.
• If there is a need to connect several heat sources( according to the bivalent principle).For example, to help the boiler come solar system( solar collector) or geothermal heat pump. In this case, the lower the temperature head of the heat source, the lower the heat exchanger should be located in the TA.
• If a different type of coolant is used in the heat source and consumption circuits.

Unlike the first scheme, such a TA is characterized by active mixing of the coolant in the tank - heating occurs in its lower part, and less dense hot water tends upward.

The magnesium anode is shown in the diagram on the center of the GA.Due to the lower electric potential, it "pulls" ions of heavy salts onto itself, preventing overgrowth by the scum of the inner walls of the tank. Subject to periodic replacement.

3 - The heat accumulator is supplemented with a flow loop of hot water supply. The cold water inlet is from the bottom, the feed to the hot-water point, respectively, from below. Most of the heat exchanger is located in the upper part of the TA.

This scheme is considered optimal for conditions where the consumption of hot water is characterized by sufficient stability and uniformity, without pronounced peak loads. Naturally, the heat exchanger must be made of metal that meets the standards of food water consumption.

Otherwise, the circuit is a descent from the first, with direct connection of heat generation circuits and its consumption.

4 - Inside the heat accumulator there is a tank for creating a reserve of hot water for domestic consumption. As a matter of fact, such scheme reminds the built in boiler of indirect heating.

The use of such a structure is fully justified in cases where the peak of heat production by the boiler does not coincide with the peak of the consumption of hot water. In other words, when the domestic way of life in the house involves a massive, but rather short-lived expenditure of hot water.

All listed schemes can vary in different combinations - the choice of a particular model depends on the complexity of the heating system being created, the number and type of body sources and consumption contours. Please note, most heat accumulators have a plurality of outlet nozzles spaced vertically.

The fact is that in any scheme inside the buffer tank, a temperature gradient is formed in any way or another( the difference in the temperature head in height).It is possible to connect the heating system circuits that require different temperature conditions. This greatly facilitates the final thermostatic control of heat exchangers( radiators or "warm floors"), with minimal unnecessary energy losses and reduced load on the regulating devices.

Typical connection schemes for

heat accumulators Now it is possible to consider the basic schemes of installing heat accumulators in a heating system.

Illustration	Short circuit diagram
	The temperature and pressure conditions are the same in the boiler and in the heating circuits. The heat carrier requirements are the same. A constant temperature is maintained at the outlet of the boiler and in the TA. On heat exchange devices, the adjustment is limited only by the quantitative change of the coolant passing through them.
	Connection to the heat accumulator itself, in principle, repeats the first circuit, but the adjustment of the modes of operation of heat exchangers is carried out on a qualitative principle - with a change in the temperature of the coolant. For this purpose, the thermostatic mixing units are included in the circuit, for example, three-way valves. This scheme allows the most rational use of accumulated heat accumulator potential, that is, its "charge" will last for a longer time.
	This circuit, with circulation of the heat medium in the small circuit of the boiler through the built-in heat exchanger, is used when the pressure in this circuit exceeds the allowable in heating appliances or in the buffer tank itself. The second option - in the boiler and in the heating circuits used different heat carriers.
	The reference conditions are similar to scheme No. 3, but an external heat exchanger is used. Possible reasons for this approach: - the heat exchange areas of the built-in "coil" are not sufficient to maintain the required temperature in the accumulator. - TA has already been purchased without an internal heat exchanger, and modernization of the heating system required this approach.
	Scheme with the organization of hot water supply through the built-in spiral heat exchanger. Designed for uniform consumption of hot water, without peak loads.
	This scheme, using a heat accumulator with a built-in tank, is designed for peak consumption of hot water, but not very positive. After consuming the created stock and, accordingly, filling the container with cold water, heating to the required temperature can take quite a long time.
	A bivalent circuit that allows the use of an additional heat source in the heating system. In this case, the variant with the solar collector connection is simplified. This circuit is connected to the heat exchanger at the bottom of the heat accumulator. Typically, such a system is calculated in such a way that the main source is the solar collector, and the boiler is switched on as needed, for reheating, with insufficient energy from the main one. The solar collector, of course, is not a dogma - in its place can be a second boiler.
	A scheme that can be called multivalent. In this case, the application of three sources of thermal energy. In the role of high-temperature boiler stands, which, again, can only play an auxiliary role in the overall heating scheme. Solar collector - by analogy with the previous scheme. In addition, another low-temperature source is used, which, at the same time, is stable and independent of the weather and time of day - a geothermal heat pump. The lower the temperature head from the connected power source, the lower the connection point to the heat accumulator.

Of course, the diagrams are given in a very simplified form. But in practice the connection of the heat accumulator to complex, branched systems, with various heating circuits, and even receiving heat from sources of different power and temperature, requires highly professional design with engineering heat engineering calculations, using a variety of additional adjusting devices.

One example is shown in the figure:

1 - solid fuel boiler.

2 - electric boiler, which is only switched on as needed and only during the grace period.

3 - special mixing unit in the circuit of a high-temperature boiler.

4 - helio-station, solar collector, which in the clear days can serve as the main source of thermal energy.

5 - heat accumulator, which converge all the circuits of heat generation and its consumption.

6 - high-temperature heating circuit with radiators, with regulating the regimes on a quantitative basis - only with the use of stop valves.

7 - low-temperature heating circuit - "warm floor", which necessarily provides for a qualitative control of the heating water temperature.

8 - a flow-through hot water circuit, equipped with its own mixing unit for high-quality regulation of domestic hot water temperature.

In addition to all of the above, in the heat accumulator can be built-in electric heaters - heating elements. Sometimes it is advantageous to maintain with their help a given temperature, without resorting, for example, once again to the unplanned heating of a solid fuel boiler.

Special additional heaters can be purchased separately - their mounting thread is usually adapted to the connection sockets available on many models of heat accumulators. Naturally, the connection of heating electricity will require the installation of an additional thermostatic unit, which will ensure the inclusion of heaters only when the temperature in the TA falls below the user-set level. Some heaters are already equipped with a built-in thermoregulator of this type.

Video: Recommendations of a specialist for creating a heating system with a solid fuel boiler and a heat accumulator

. What should be considered when choosing a heat accumulator

. It is of course recommended that the heat accumulator is selected at the design stage of the house heating system, guided by the calculated data of specialists. Nevertheless, the circumstances are different, and it is still necessary to know the basic criteria for evaluating such a device.

• The first place will always be the capacity of this buffer capacity. This value is calculated in accordance with the parameters of the system being created, the capacity of the boiler, the required amount of energy for heating, hot water supply. In a word, the capacity should be such as to ensure the accumulation of all excess heat at the moment, not allowing its loss. Some rules for calculating capacity will be described below.
• Of course, the size of the product and its weight depend directly on the capacity. These parameters are also decisive - not always and not everywhere it is possible to place in a dedicated room a heat accumulator of the required volume, so the question should be thought out in advance. It happens that large tanks( over 500 liters) do not pass into standard doorways( 800 mm).When assessing the mass of TA, it should be taken into account together in the entire volume of the water of the fully filled instrument.
• The next parameter is the maximum allowable pressure in the heating system that is being created or already functioning. A similar indicator of TA should be, in any case, not lower. This will depend on the thickness of the walls, the type of fabrication material, and even the shape of the container. Thus, in buffer tanks designed for a pressure of over 4 atmospheres( bar), the upper and lower covers usually have a spherical( toroidal) configuration.

• Material of the container. Tanks from carbon steel, with anti-corrosion coating are cheaper. Stainless steel tanks, of course, are more expensive, but also the warranty period of their operation is also much higher.
• Presence of additional built-in heat exchangers for heating circuits or hot water supply. Their purpose has already been mentioned above - the models are selected depending on the total complexity of the heating system.
• Availability of additional options - the possibility of embedding TEN, installation of instrumentation, safety devices - safety valves, air vent, etc.
• The thickness and quality of the outer thermal insulation of the hull TA is necessarily assessed, so that you do not have to deal with this issue yourself. The better the tank is isolated, the more natural it will be to store the "thermal charge" in it for longer.

Features of installation of thermal accumulators

Installation of a thermal battery implies compliance with certain rules:

• All connected circuits must be connected with threaded couplings or flanges. Welded joints are not allowed.
• The connecting pipes must not exert any static load on the TA sleeves.
• It is recommended to install shut-off valves on all pipes connected to the TA.
• All visual inputs and outputs are equipped with visual temperature control( thermometers).
• At the lowest point of the TA or on the pipe in the immediate vicinity of it there should be a drain valve.
• All the pipes of the entrance to the heat accumulator are equipped with filters for mechanical water purification - mud pumps.
• In many models, there is a nozzle for connecting the automatic air vent. If there is no such, then the air vent must be installed on the uppermost outlet pipe.
• In the immediate vicinity of the heat accumulator is provided the installation of a pressure gauge and a safety valve.
• It is strictly forbidden to make any independent changes in the design of the heat accumulator, not specified by the manufacturer.
• The installation of the TA should be carried out only in a heated room, which excludes the possibility of freezing of liquid.
• A water filled tank can have a very large mass. A platform of his kind must be capable of withstanding such a high load. Often, for these purposes, you have to pour a special foundation.
• No matter how the heat accumulator is installed, a free access to the inspection hatch should be ensured.

Performing the simplest calculations of the parameters of the

heat accumulator As mentioned above, a comprehensive calculation of a heating system with several circuits for generating and consuming thermal energy is a task only feasible for specialists, since many many factors have to be taken into account. But certain calculations can be done on their own.

For example, a solid fuel boiler is installed in the house. Known is its power, produced at full fuel loading. The combustion time of the complete burning of firewood was determined experimentally. It is planned to purchase a heat accumulator, and it is necessary to determine how much it will take to ensure that it is safe to use all the heat produced by the boiler.

We take as a basis the known formula:

W = m × s × Δt

W is the amount of heat necessary to heat the mass of the liquid( m ) with a known heat capacity( with ) by a certain number of degrees( Δt ).

From here it is easy to calculate the mass:

m = W /( s × Δt)

It does not hurt to take into account the boiler efficiency( k ), since energy losses are somehow inevitable.

W = k × m × s × Δt, or

m = W /( k × s × Δt)

Now let's look at each of the values:

• m - the required mass of water, from which, knowing the density, it will be easy to determine the volume. It will not be a big mistake to calculate 1000 kg = 1 m³ .
• W is an excessive amount of heat generated during the heating period of the boiler.

It can be defined as the difference in the energy values ​​generated during the combustion of the fuel bookmark and spent at the same time on heating the house.

The maximum capacity of the boiler is usually known - this is a passport value calculated for optimal solid fuel water. It shows the amount of thermal energy produced by the boiler per unit time, for example, 20 kW.

Any host always knows quite well how long it takes to burn the fuel book. Let's say it will be 2.5 hours.

Next, you need to know how much energy at this time can be spent on heating the house. In a word, the need for a particular building in thermal energy is necessary to ensure comfortable living conditions.

Such a calculation, if the value of the required power is unknown, can be made independently - for this there is a convenient algorithm given in the special publication of our portal.

How to conduct a heat calculation for your own home?

The information on the amount of heat necessary for heating a house is quite often in demand - when choosing equipment, arranging radiators, when conducting insulation work. With the calculation algorithm, including a convenient calculator, the reader can get acquainted by opening a link on the publication dedicated to requirements for the installation of gas boilers .

For example, 8.5 kW of energy per hour is required for heating the house. This means that for 2.5 hours of combustion of the fuel bookmark, the following will be received:

20 × 2.5 = 50 kW

During the same period, the following will be spent:

8.5 × 2.5 = 21.5 kW

Excess heat to be storedin the heat accumulator:

W = 50 - 21.5 = 28.5 kW

• k - Boiler plant efficiency. Usually indicated in the product certificate in percent( for example, 80%) or decimal fraction( 0,8).
• with is the heat capacity of water. This is a tabular value that is equal to 4.19 kJ / kg × ° C or 1.164 W × h / kg × ° C or 1.16 kW / m³ × ° C.
• Δt is the temperature difference for which water needs to be heated. It can be determined for your system by experiment, by measuring the values ​​on the feed pipe and the return flow when the system is operating at maximum power.

Assume that this value is equal to

Δt = 85 - 60 = 35 ° C

So, all the values ​​are known, and we only need to substitute them in the formula:

m = 28500 /( 0.8 × 1.164 × 35) = 874.45kg.

Thus, in order to fully conserve all the heat produced by the boiler, when it is operating at full power it will take 875 kg of water, that is, a capacity of about 0.875 m³.

The same approach can be applied also in case the volume of the heat accumulator connected to the electric boiler is calculated. The only difference is that the timing of the firebox is not taken into account, but the time interval of the preferential tariff, for example, from 23.00 to 6.00 = 7 hours. To "unify" this value, it can be called, for example, "the period of boiler activity".

To simplify the task for the reader, below is a special calculator that will allow you to quickly calculate the recommended amount of thermal battery for the existing( planned to install) boiler.

Calculator for calculating the required amount of heat accumulator

The value obtained is rounded upwardsand becomes a reference point for the selection of the optimal model of the heat accumulator. They are in special stores are presented in different volumetric versions.

Advantages and disadvantages of including the heat accumulator

in the heating system So, summing up the results of the publication, we will briefly formulate the "pluses" and "cons" of using heat accumulators.

The has the following advantages for the :

• Energy savings are achieved, especially in the application to solid fuels - the heat generated is used to the maximum. The efficiency of the boiler and the whole heating system is increasing.
• Boilers and other elements of the heating system receive reliable protection against overheating.
• Minimizes the need for intervention in the system, reduces the number of solid fuel loads.
• The whole system works more smoothly and is easy to control and precise adjustments. Stable installed heating is provided in all rooms of the house.
• It is possible to connect alternative energy sources. With a competent approach, this gives serious financial savings. For example, in the daytime the main load falls on the helio-station, at night, while the preferential tariff operates, the "relay" intercepts the heat pump, and a short gas boiler compensates for the possible shortage.
• Installing a thermal battery at the same time can solve the problem of hot water supply of their homes.

There are not so many drawbacks to the , but they should also be mentioned:

• The installation will make some sense if the capacity of the boiler or other sources of heat is at least twice the calculated values ​​of the heat energy required for heating the housing.
• The system with a heat accumulator always has a very high inertia, that is, a lot of time can pass from the moment of starting up to the output in the design mode of operation. There is no sense in using it in heating systems where there is a need for rapid heating of premises, for example, in country houses, which are visited only by owners from time to time in the winter.
• The equipment is usually very cumbersome, which creates a lot of problems in its transportation, unloading, skidding and installation. As a prerequisite is the installation of TA in the immediate vicinity of the boiler, the boiler room will require a very large area.
• Thermal batteries belong to the category of expensive purchases - their price is quite comparable, and often even exceeds the cost of boilers. True, there is a high probability that costs will quickly pay off by saving on energy resources.

However, the last of the listed shortcomings advances folk craftsmen to design and install their own models of heat accumulators.

Is it difficult to manufacture a heat accumulator on its own?

Probably, the Russian amateur master - everything on the shoulder! For example - the technological recommendations for for the independent manufacture of the thermal battery are listed in the special publication of our portal.

Video: the advantages of a heating system with integrated heat accumulator