Heat accumulator for boiler

Features of installing heat accumulators

All installation work is carried out according to a previously approved project in accordance with the recommendations of the heating equipment manufacturer.

In this case, it is necessary to take into account the features of the installation work:

The surface of the storage tank must be insulated from heat loss without fail.
Thermometers should be installed on pipelines through which water circulates (outlet and inlet).
Accumulator containers with a volume of more than 500 liters in most cases do not pass through the doorway. In such cases, collapsible structures should be used or several smaller batteries should be installed.
At the lowest point of the tank, the installation of a drainage channel will not interfere. It will come in handy when you have to completely drain the water.
On pipelines through which water enters the tank, it is advisable to install mesh filters. They will prevent large inclusions from getting inside (dross from welding, minerals that have entered the system, etc.).
If a valve is not provided in the upper part of the tank to remove air, then it should be installed at the top of the outlet pipe.
It is necessary to mount a pressure gauge and a safety valve on the line next to the battery.

If you are the owner of a solid fuel boiler and have not yet purchased a heat accumulator, think about it. You will not only extend the life of your heating equipment, but also significantly save on fuel.

Functionality of heat accumulators

The principle of operation of the equipment is that during the operation of the boiler, part of the heat is used to heat the coolant from an additional tank. The connected tank has good thermal insulation and perfectly retains the heat received. After the boiler is turned off, the water in the heating system cools down, and the control devices turn on the pump that supplies hot water from the storage tank.

These cycles continue as long as the temperature of the water in the additional tank remains high enough. The total duration of the system operation without switching on the boiler depends on the volume of the additional tank. In practice, it allows heating rooms from a few hours to 2 days.

The heat accumulator performs the following functions:

Accumulates the heat coming from the boiler of the system and releases it over time to heat the rooms in the room.
Prevents the possibility of boiler overheating by removing excess heat from the exchanger.
Allows you to easily combine different heating devices (electric, gas, solid fuel) into a common system.
Helps to improve the operation of heating equipment, reducing fuel consumption and improving efficiency.
In systems with solid fuel boilers, it allows you to exclude constant monitoring of the state of heating equipment. By heating the coolant in an additional tank, homeowners can forget about the need to constantly load fuel into the boiler.
It is a source of hot water for domestic needs.

Heating system diagram

How profitable a heating system with a heat accumulator can be seen in this example.

Assume that a boiler with a capacity of 10 kW is installed in the heating system. Firewood needs to be loaded every 3 hours. This does not fit into the plans of homeowners. To lengthen the breaks between loads, it is necessary to use a larger boiler. But in this case, boiling of the coolant is possible, since the system will not have time to take away all the generated heat.

Connecting a heat accumulator with a capacity of about 200 liters easily solves the problem. The equipment allows you to accumulate 110 kW of energy, subject to full and frequent boiler loads. Subsequently, the accumulated heat will maintain a comfortable room temperature for about 10 hours.It is not necessary to load the boiler with fuel all this time.

What is a heat accumulator buffer capacity and its purpose.

The purpose of the heat accumulator (TA) will be easier to describe with several examples-tasks.

Task one. The heating system is based on a solid fuel boiler. It is not possible to constantly monitor the temperature of the coolant at the supply and throw firewood in time, as a result of which the supply temperature either exceeds what we need, or drops below the norm. How to ensure that the required coolant temperature is maintained?

Task two. The house is heated by an electric boiler. Electricity is two-tariff. How to reduce energy costs by reducing energy consumption during the day and increasing at night?

Task three. There is a heating system in which heat is generated by heat generators operating on various types of fuel and energy - for example. gas, electricity, solar energy (solar collectors), earth energy (heat pump). How to ensure their efficient operation without loss of generated heat when there is no need for it, while providing the house with heat during peak energy consumption?

Without really going into the theory of heat engineering, for all problems, a solution suggests itself in the form of installing a buffer tank in the system, which would serve as a reservoir for the coolant and in which its temperature would be maintained at a given level. It is this buffer capacity that is the heat accumulator. To solve these problems, the heat accumulator is usually included in the "break" of the system with the formation of the boiler and heating circuits. The conditional scheme for including a heat accumulator in the heating system is shown in the figure below.

Rice. Schematic diagram of the inclusion of a buffer tank (heat accumulator)

For various ways to include a buffer tank in the heating system, see the article “Heat accumulator connection diagrams”.

Currently, heat accumulators are most often used in heating systems with solid fuel boilers. In these systems, the use of a heat accumulator makes it possible to load fuel less often, to ensure comfortable heat supply, regardless of fluctuations in the temperature of the coolant at the outlet of the boiler. Buffer tanks are often installed with electric boilers to save money due to a reduced night tariff and in combined systems with the simultaneous use of solid fuel and electric boilers. A heat accumulator (TA) can be useful in systems with gas boilers, especially when the minimum heat output of the boiler exceeds the heat load of the object. Due to the longer periods of "loading" of the TA (heating of the coolant), it is possible to avoid the "clocking" of the boiler.

In addition to being used as a buffer tank, TA performs the function of a hydraulic separator. Especially this property of a heat accumulator is in demand in systems with heat generators operating on different types of energy (including alternative). As a rule, these heat sources operate on special heat carriers that do not allow mixing with other types, require a unique temperature and hydraulic regime, often incompatible with the regimes of the heating circuit (radiator, underfloor heating). For example, the temperature range of a heat pump is usually

5°C, and in the heat distribution circuit the temperature range can be much larger (10-20°C). To separate the circuits, the heat accumulator can be equipped with additional built-in heat exchangers.

How to calculate the volume of a heat accumulator

If desired, it is easy to find methods for calculating the volume of a heat accumulator on the Internet, but none of them suited me.

Some "specialists" recommend multiplying the maximum power of the existing boiler in kilowatts by some coefficient, and this coefficient on different sites differs by a factor of two or more - from 25 to 50. In my opinion, it's complete nonsense.Simply because the result obtained has nothing to do with your particular house, nor with your wishes, how often you want to heat the boiler.

The normal technique takes into account all factors: the climate in your area, and the thermal insulation of the house, and your ideas about comfort. In a good way, this calculation will also need to be carried out many times for different temperature conditions, and choose the maximum volume of the heat accumulator. And, by the way, the power of the boiler in the correct methodology is obtained as a result of calculations, and not according to the principle "what it was, it was put like that." But all this is quite complicated, and is more suitable for boiler rooms, and not for private households.

I did it much easier. I did the calculation of the heat accumulator for a solid fuel boiler as follows.

It is necessary to estimate the amount of heat that the house needs per day. This is the most difficult and responsible part of the work. Again, you can delve into the calculations (in textbooks for construction universities you can find all the necessary methods). But, if possible, it is easier and more reliable to carry out a direct measurement - simply by heating the house in cold weather and measuring the amount of fuel used. My house is relatively small - a little less than 100 square meters. m, and quite warm. Therefore, it turned out that at a temperature outside of about 0 degrees, to maintain a comfortable temperature, it takes a substantial margin of 50 kWh, for - 10 degrees - 100 kWh, for - 20 degrees - 150 kWh.
Choosing a boiler is very simple. The most common boilers have a power of about 25 kW and with one maximum load they give this power of about 3 hours. Therefore, one kindling gives about 75 kWh of heat. For zero temperature, therefore, even one full load will be too much for me. And for -20 degrees, it will be enough to heat 2 times a day. This option suits me just fine.
Now the actual volume of the heat accumulator. The heat capacity of water is 4.2 kJ per liter per degree. the maximum temperature in the heat accumulator is 95 degrees, the comfortable temperature of the water in the heating system is 55 degrees. That is 40 degrees difference. In other words, 1 liter of water in a heat storage tank can store 168 kJ of heat, or 46 Wh. And 1000 liters, respectively - 46 kWh. It follows that in order to save heat from one full load of the boiler, I need a 1500 liter heat accumulator. It's all stock. In fact, a little less is required, but after studying the prices of buffer tanks, I decided to neglect this.

This calculation means that in severe frosts I have to heat the boiler twice a day, and in very severe frosts three times. Moreover, this should be done evenly throughout the day: in the morning and in the evening or in the morning, at the beginning of the evening and before bedtime. And when there are no big frosts, I heat the boiler only once - at any time of the day.

Of course, if you put a heat accumulator even larger in volume, you can make your life even more comfortable. But here we already have to deal with the fact that a large barrel needs a lot of space.

Advantages and disadvantages

A heating system with a heat accumulator, in which a solid fuel installation serves as a heat source, has a lot of advantages:

Increased comfort in the house, because after the combustion of fuel, the heating system continues to heat the house with hot water from the tank. No need to get up in the middle of the night and load a portion of firewood into the firebox.
The presence of a container protects the water jacket of the boiler from boiling and destruction. If the electricity is suddenly cut off or the thermostatic heads installed on the radiators cut off the coolant due to reaching the desired temperature, the heat source will heat the water in the tank. During this time, the power supply may be restored or the diesel generator will be started.
The supply of cold water from the return pipeline to the red-hot cast-iron heat exchanger is excluded after the sudden activation of the circulation pump.
Heat accumulators can be used as hydraulic separators in the heating system (hydraulic arrows). This makes the operation of all circuit branches independent, which provides additional savings in thermal energy.

The higher installation cost of the entire system and the requirements for equipment placement are the only disadvantages of using storage tanks. However, these investments and inconveniences will be followed by minimal operating costs in the long run.

Calculation of the capacity of the heat accumulator

The method by which the calculation is made may be different depending on the application scheme. Here is an example calculation scheme:

Determining the maximum fuel load. For example, the firebox holds 20 kg of firewood. 1 kg of firewood is capable of generating 3.5 kWh of energy. Thus, when burning one bookmark of firewood, the boiler will give off 20 3.5 = 70 kWh of heat. The time for which a full bookmark burns out can be determined empirically or calculated. If the boiler power is, for example, 25 kW 70:25=2.8 h.
The temperature of the coolant in the heating system. If the system is already installed, it is enough to measure the temperature at the inlet and outlet and determine the heat loss.
Determination of the desired download frequency. For example, loading in the morning and in the evening is possible, but it is not possible to service the boiler during the day and at night.

Calculation of the heat accumulator

If for an hour the heat loss of a room, for example, is 6.7 kW, then for a day it will be 160 kW. In this example, this is a little more than two bookmarks of fuel. As defined above, one load of firewood burns for about 3 hours, releasing 70 kWh of thermal energy.

The need for heating the house is 6.7 3 = 20.1 kWh, the stock of the storage tank will be 70-20.1 = 49.9, that is, approximately 50 kWh. This energy is enough for a period of 50:6.7 - this is about 7 hours. This means that two full zaklakhs and one incomplete one are required per day.

Based on these calculations, having considered several options, we stop at this: at 23:00, an incomplete load is made, at 6:00 and 18:00 - full. If you draw a graph of the charge level of the heat accumulator, you can see that the maximum charge falls on 60 kWh at 9 am.

Since 1 kWh=3600 kJ, the reserve should be 60 3600=216000 kJ of thermal energy. Temperature margin (difference between the maximum water index and the required supply index) 95-57=38°C. The heat capacity of water is 4.187 kJ. Thus, 216000 / (4.187 38) \u003d 1350 kg. In this case, the required volume of the heat accumulator will be 1.35 m3.

The considered example gives a general idea of how the capacity of the storage tank is calculated. In each individual case, it is necessary to take into account the features of the heating system and the conditions of its operation.

Features of installing a heat accumulator

Before installing the equipment, a detailed design must be drawn up. It is necessary to take into account all the requirements of manufacturers of heating equipment. When installing a storage tank, the following rules must be observed:

The surface of the container must have reliable thermal insulation.
Thermometers should be installed at the inlet and outlet to monitor the water temperature.
Volumetric tanks most often do not fit into the doorway. If it is not possible to bring in the tank before the end of construction, you will have to use a collapsible option or several smaller tanks.
It is desirable to have a coarse filter on the inlet pipe.
A safety valve and pressure gauge must be installed next to the tank. The tank itself should also have a vent valve.
It must be possible to drain the water from the tank.

The use of a heat accumulator in a system with a solid fuel boiler increases the efficiency of the heat generator and its service life, and also allows for more economical fuel consumption. The possibility of a rarer filling of fuel makes the use of the heating boiler more convenient for the consumer. The calculation of the required capacity of the storage tank must take into account the type of boiler, the features of the heating system and the conditions of its operation.

Despite the simplicity of the device, and the obvious benefits of using heat accumulators, this type of equipment is not yet very common. In this article we will try to talk about what a heat accumulator is and the benefits that its use in heating systems brings.

The use of heat accumulators

There are several methods for calculating the volume of a tank. Practical experience shows that, on average, 25 liters of water are additionally needed for each kilowatt of heating equipment. The efficiency of solid fuel boilers, which includes a heating system with a heat accumulator, increases to 84%. Due to the leveling of combustion peaks, up to 30% of energy resources are saved.

When using tanks for supplying domestic hot water, there are no interruptions during peak hours. At night, when the needs are reduced to zero, the coolant in the tank accumulates heat and in the morning again provides all the needs in full.

Reliable thermal insulation of the device with foamed polyurethane (polyurethane foam) allows you to save the temperature. Additionally, it is possible to install heating elements, which helps to quickly “catch up” with the desired temperature in case of emergency.

Sectional heat accumulator

Heat storage is recommended in cases of:

high demand for hot water. In a cottage where more than 5 people live, and two bathrooms are installed, this is a real way to improve living conditions;
when using solid fuel boilers. Accumulators smooth the operation of heating equipment during the hour of greatest load, take away excess heat, preventing boiling, and also increase the time between laying solid fuel;
when using electric energy at separate tariffs for day and night;
in cases where solar or wind batteries are installed to store electrical energy;
when used in the heat supply system of circulation pumps.

This system is perfect for rooms heated by radiators or underfloor heating. Its advantages are that it is able to accumulate energy received from different sources. The combined energy supply system allows you to choose the most optimal option for obtaining heat in a given period of time.

1 Initial data for design

Microdistrict
built up with nine twos, threes, and
four section nine-storey
buildings. The section plan is shown in
figure 3.1. Each apartment has:
sink with mixer, washbasin with
faucet, bath with faucet and shower.
The height of the typical floor of the building is accepted
3 meters. Number of people in the apartment
determined based on the norm of the total area
for one person f= 17 m2.
Total number of inhabitants in one section
buildings will be 147 people, in the microdistrict

3822 people.

General
useful area of residential buildings of the microdistrict
is 64650 m2.
Estimated outdoor temperature
for the design of heating systems
Heat accumulator for boiler .
Temperature of network water for a point
high temperature fracture
supply line graphics
,
in the return pipeline
.
Estimated temperature of network water in
supply pipeline
,
in the return pipeline
.
Cold tap temperature
water at the inlet to the water heater
Heat accumulator for boiler .
Hot water outlet temperature
water heater
.
Guaranteed urban pressure
water supply at the input to the central heating station
.

Design features of the heat accumulator

The device is a cylindrical container made of stainless steel or black steel. The dimensions of the container depend on its volume, which varies from several hundred to tens of thousands of liters. Due to the large volumes, such a device is difficult to place in an existing boiler room, so it is often necessary to complete it.There are models both with factory thermal insulation and containers without it.

When installing a heat accumulator, it must be taken into account that the thickness of the insulation is 10 cm. After it, a leather casing is put on top of the tank. Inside the tank there is a coolant, which, when the fuel is burned in the boiler, heats up quickly and retains heat for a long time due to the insulation layer. After the boiler stops working, the accumulator gives off its heat to the room, heating it. For this reason, it will not be necessary to fire up the boiler as often as before.

According to their device, the capacities of the heat accumulator are:

with an internal boiler. This design was created to provide housing with hot water from an autonomous source;
with one or two heat exchangers;
empty (without coolant).

Threaded holes are provided for connecting the drive to the boiler and the heating system of the house.

background

It so happened that some time ago I bought a private house at some “remote from civilization”. The remoteness from civilization is determined mainly by the fact that there is no gas there in principle. And the permitted power of the electrical connection does not provide a technical opportunity to heat the house with electricity. The only real source of heat in winter is the use of solid fuel. In other words, the house was equipped with a stove, which the former owner heated with wood and coal.

If someone has experience using the stove, then he does not need to be explained that this activity requires constant monitoring. Even in not too cold weather, it is impossible to lay firewood in the stove once and “forget” about it. If you put too much firewood, the house will become hot. And after the fuel burns out, the house will still quickly cool down. Willy-nilly, to maintain a comfortable temperature, you need to constantly add a little firewood. And in severe frosts, the stove cannot be left unattended even for 3-4 hours. If you don’t want to wake up in the morning in a cold room, be kind at least once a night to go to the stove ...

Of course, I had no desire to work as a stoker. And so I immediately began to think about a more convenient way of heating. Of course, if it was impossible to use gas or electricity, only a modern solid fuel heating system, consisting of a solid fuel boiler, a heat accumulator and the simplest automation for turning the recirculation pump on and off, could become this way.

Why is a modern boiler better than a conventional stove? It takes up much less space, you can put more fuel into it, it provides better combustion of this fuel at maximum load, and theoretically, with its help, you can leave most of the heat in the house, and not release it into the chimney. But unlike a stove, a solid fuel boiler is practically impossible to use without a heat accumulator. I am writing about this in such detail because I know many people who have tried to heat the house with such boilers, connecting them directly to the heating pipes. Nothing good happened to them.

What is a heat accumulator or, as it is also called, a buffer tank? In the simplest case, this is just a large barrel of water, the walls of which have good thermal insulation. The boiler heats the water in this barrel in two or three hours of its operation. And then this hot water circulates through the heating system until it cools down. As it cools down, the boiler needs to be fired up again. The simplest heat accumulator can be easily made by any welder. But I, after some deliberation, abandoned this idea and bought a ready-made one. Since I live in Ukraine, I turned to the Teplobak company and never regretted it: here accumulating tanks are made professionally and very high quality.

Depending on the volume of the heat accumulator, the power of the boiler and how much heat the house needs, the boiler does not have to be heated constantly, but once or twice a day, or even once every two or three days.

Calculation of the volume of the buffer tank of the boiler

The most optimal solution to this task will 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, preliminary calculations can be done independently. For 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;
fuel active burning time;
thermal power of heating the house, kW;
boiler efficiency;
temperature in the supply and return pipes.

Consider an example of a preliminary calculation. Heated area - 200 m 2. Boiler active burning time - 8 hours, coolant temperature during heating - 90 ° C, in the return circuit - 40 ° C. Estimated thermal power of heated rooms - 10 kW. With such initial data, the thermal device will receive 80 kW (10 × 8) of energy.

We make a calculation of the buffer capacity of a solid fuel boiler according to the heat capacity of water :

where: m is the mass of water in the tank (kg); Q is the amount of heat (W); ∆t is the difference in water temperature in the supply and return pipe (°С); 1.163 is the specific heat capacity of water (W / kg ° С) .

Calculation of the buffer capacity of a solid fuel boiler

Substituting the numbers in the formula, we get 1375 kg of water or 1.4 m 3 (80000 / 1.163 × 50). Thus, for a house heating system with an area of 200 m 2, it is necessary to install a TA with a capacity of 1.4 m 3. 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. Comparing the known factors, it is not difficult to make a preliminary choice of a heat accumulator for a home. Such a calculation is relevant in the case when the house is built, the heating system has already been 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 a solid fuel boiler installed in the system is made.

Having collected data on the heating system, we perform calculations according to the formula :

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 of k - the efficiency of the boiler.

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 which we find the corrected mass of water m = W/(c×∆t×k) ( 4 )

Let's consider how to calculate a heat accumulator for a house. A 20 kW boiler is installed in the heating system (indicated in the passport data). The fuel bookmark burns out in 2.5 hours. Heating a house requires 8.5 kW/1 hour of energy. This means that during the burnout of one tab, 20 × 2.5 \u003d 50 kW will be received

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

Excess generated heat50 - 21.5 = 28.5 kW is stored in the HE.

The temperature at which the coolant is heated is 35 ° C. (The temperature difference in the supply and return pipes. It is determined by measurement during the operation of the heating system). Substituting the desired values in formula (4) we get 28500 / (0.8 × 1.163 × 35) = 874.5 kg

This figure means that in order to save the heat generated by the boiler, it is necessary to have 875 kg of coolant. To do this, you need a buffer tank for the entire system with a volume of 0.875 m 3. Such lightweight calculations make it easy to choose a heat accumulator for heating boilers.

Advice. For a more accurate calculation of the volume of the buffer capacity, it is better to contact specialists.

Choosing a heat accumulator

TA is chosen when designing a heating system. Thermal engineers will help you choose the right heat accumulator. But, if it is impossible to use their services, you will have to choose on your own. It is not difficult to do this.

Heat accumulator for solid fuel boiler

The main criteria for the selection of this device are considered to be the following :

pressure in the heating system;
the volume of the buffer tank;
external dimensions and weight;
equipment with additional heat exchangers;
the possibility of installing additional devices.

Water pressure (pressure) in the heating system is the main indicator. The higher it is, the warmer it is in the heated room.

Given this parameter, when choosing a heat accumulator for solid fuel boilers, attention is paid to the maximum pressure that it can withstand. The heat accumulator for solid fuel boiler shown in the photo is made of stainless steel, can withstand high water pressure

The volume of the buffer tank. The ability to accumulate heat for the heating system during operation depends on it. The larger it is, the more heat will accumulate in the container. Here you need to take into account that it is pointless to raise the limit to infinity. But if the water is less than the norm, the device simply will not perform the function of heat accumulation assigned to it. Therefore, for the correct choice of a heat accumulator, it will be necessary to calculate its buffer capacity. A little later, it will be shown how it is performed.

External dimensions and weight. These are also important indicators when choosing a TA. Especially in an already built house. When the calculation of the heat accumulator for heating is made, delivery to the installation site is carried out, there may be a problem with the installation itself. In terms of overall dimensions, it may simply not fit into a standard doorway. In addition, large-capacity TAs (from 500 liters) are installed on a separate foundation. A massive device filled with water will become even heavier. These nuances must be taken into account. But it's easy to find a way out. In this case, two heat accumulators for solid fuel boilers are purchased with a total volume of buffer tanks equal to the calculated one for the entire heating system.

Equipment with additional heat exchangers. In the absence of a hot water system in the house, its own water heating circuit in the boiler, it is better to immediately purchase a TA with additional heat exchangers. For those living in the southern regions, it will be useful to connect a solar collector to the TA, which will become an additional free source of heat in the house. A simple calculation of the heating system will show how many additional heat exchangers it is desirable to have in a heat accumulator.

Possibility to install additional devices. This implies the installation of heating elements (tubular electric heaters), instrumentation (instrumentation), safety valves and other devices that ensure uninterrupted and safe operation of the buffer tank in the device. For example, in case of emergency attenuation of the boiler, the temperature in the heating system will be maintained by heating elements. Depending on the volume of space heating, they may not create a comfortable temperature, but they will definitely prevent defrosting of the system.

The presence of instrumentation will allow timely attention to possible problems that have arisen in the heating system

Important

When choosing a heat accumulator for heating, pay attention to its thermal insulation. It depends on the conservation of the received heat.