Buffer tank and indirect boiler

Distinguishing features of the indirect heating boiler

Boiler is a large barrel, the main function of which is storage. It comes in different volumes and shapes, but its purpose does not change. Without a boiler can be a problem when using, for example, two showers or a shower and a kitchen faucet at once.

If a 24-28 kW domestic 2-circuit boiler produces only 12-13 l/min flow, and a single shower requires 15-17 l/min, then turning on any additional faucet will cause a shortage of water supply. The boiler simply does not have enough working capacity to provide hot water to several points.

All storage boilers can be divided into 2 large categories:

  • direct heating, which creates a supply of hot water with the help of a heating element. for example, an electric heating element;
  • Indirect heating, which heats the water with the already hot water.

There are other types of boilers. for example, conventional storage water heaters. But only bulk storage units can indirectly receive energy and heat water.

BCH, unlike the energy-dependent equipment operating on electric, gas or solid fuel, uses the heat generated by the boiler. To put it simply, no additional energy is needed for its operation.

The accumulator is easy to fit into the DHW system, while causing no problems during operation.

Users see many advantages in the use of BKN:

  • The unit does not require electrical power and benefits economically;
  • hot water is always “at the ready”, no need to skip the cold water and wait for it to heat up
  • Multiple water-dispensing points can work freely;
  • Stable, not dropping in the process of consumption of water temperature.

Disadvantages also exist: the high cost of the unit and additional space in the boiler room.

By all characteristics BKN is suitable to be used in combination with a gas boiler. over, it is one of the best solutions for equipping a hot water treatment system for a private house with a large number of residents.

But boilers are different, so let’s consider both acceptable options, and those where there may be problems.

What is different about the indirect heating boiler

Accumulator can be used not only for heating, but also as a boiler indirect heating (they call a boiler without built-in heating element, which can not heat water independently) for hot water (DHW). In the second case, the accumulator must be provided with additional capacity for DHW and built-in heat exchanger.

Heat accumulator, working only for heating purposes, can do without the built-in heat exchanger. But it is better to buy a model with it. Then the unit will operate more reliably over a longer period of time. Most manufacturers install a spiral-shaped heat exchanger consisting of several coils of smooth or corrugated tube made of stainless steel.

How to choose a buffer tank for solid fuel boiler

The greatest disadvantage of solid fuel boilers is their cyclicality: at maximum loading and burning, a peak (often excessive) heat output is achieved, which constantly decreases to 0 (complete attenuation) and is resumed by a new stack of fuel. This cycling does not allow for a stable, quickly and accurately regulated heating system.

To smooth out the uneven heat output of the TH boilers a buffer tank (also known as a heat accumulator), which accumulates excess heat during peak operation of the boiler unit. There are however many nuances in choosing and calculating the required volume of the thermal accumulator.

Why do you need an expansion vessel for BCH?

Simply put it is necessary to protect the hot water supply equipment from hydraulic shocks. Such a need arises if the need for DHW is satisfied by indirect heating boiler, connected to the solid fuel boiler.

Control the intensity of combustion and heat output of solid fuel boiler. When heated, the water expands and creates excessive pressure in the system, which leads to water hammer.

Membrane tank levels out differences in pressure and protects water taps, pipes and the boiler itself from damage. It does this as follows:

  • The design of the tank consists of a vessel, divided inside by a membrane into two sections. The first sealed part has gas or air pumped into it, creating pressure. The second section is connected to the water supply system.
  • When water is heated, it increases in volume, which leads to a load in the DHW system. The fluid acts on the diaphragm, pushing it out. The higher the pressure in the system, the more water is pumped into the expansion tank.
  • After cooling and reducing the volume of the coolant, the membrane, which is pressed by the pumped gas, squeezes the water out of the expansion tank.

Inside the indirect heating boiler is a heating element connected to the heating system. At overheating of the coolant the DHW temperature rises, the load on the pipes and important structural elements increases, which leads to damage of expensive plumbing equipment.

The principle of operation of the expansion tank with the safety group BKN is to prevent high pressure in the DHW system and the occurrence of water hammer. There are check and drain valves to help in case of emergency.

The connection of a safety and expansion tank is a prerequisite for the long-term performance of the STB and for free customer service. Equipment manufacturers often refuse warranty repair if the boiler harness is not installed safety equipment.

What do you need a boiler, where and how is it used?

Main destination BKN providing needs of a private country house in hot water supply. The water heater can be installed in an apartment that has independent heating. In an apartment house it is more difficult to do due to the limited usable space. Select a heater for DHW with a capacity of 60-100 liters.

Boiler indirect heating is needed for hot water supply from the heating system in which heating water was not originally built. BKN is effective in the following cases:

On the Internet you can find recommendations for connecting BCH to the underfloor heating system. The purpose of this solution is often to reduce the temperature of the heating medium. STB acts as a buffer tank to regulate the temperature. In fact, in the underfloor heating system does not need a boiler. To balance the heating, install a sub-meter and the comb.

In order to select the correct BKN it is necessary to take into account several important parameters that affect the further operation and economic component of the use. In the calculations, consider the capacity of the boiler, the actual demand for DHW.

Regulatory documents on which the main principle of the calculations is based: SNiP 2.04.01-85 “Internal Water Supply and Sewerage of Buildings” and the designer’s handbook Part. 2.

Selection of the boiler begins by determining the flow of hot water. Correctly selected boiler must meet the following requirements:

  • Sufficient quantity of hot water supplied to several points of use at the same time. It is generally accepted that the maximum costs are achieved when the bath is filled.
  • To heat DHW to the required temperature for comfortable showering, dishwashing.
  • Short waiting time between opening the faucet and hot water coming in.

The average family uses HTW at least 12 times a day. Average consumption by the number of people in the family and the calculation of the volume of the indirect heating boiler, using the following tables:

Number of family members Water heater tank capacity (l)
Kitchen sink Hand wash Shower Wash and shower Sink, shower, bathtub
1 10 2 30 50 100
2 15 4 55 80 120
3 20 6 80 100 150
4 30 8 110 120 200
5 35 10 120 150 250
6 35 10 120 160 310
7 50 12 150 200 340
8 55 12 160 220 340
Water point Approximate water consumption (l) Typical temperature Water consumption at t = 60°C (l)
Kitchen sink 10 to 20 50°C 8 to 16
Bath 150 to 180 40°C 90 to 108
Shower 30 to 50 37°C 16 to 27
Sink 10 to 15 37°C 5 to 8
Hand wash 2 to 5 37°C 1 to 3

For further calculations you can use the formula for calculating the volume of the tank:

Water heater volume = P. water x (t°. t1): (t2. t1)

  • Р. the water. the planned consumption of DHW;
  • t°. temperature of the heated water supplied to the user;
  • t1. temperature of HTW in the pipeline, (when calculating the flow rate of cold water is usually taken the value of 10 °;)
  • t2. temperature of the water heated by the water heater.

The specified calculation formula is used to determine the constant capacity of the water heater. Let’s try to perform calculations for a family of 5 persons, assuming that the HTW will be used for showering and washing dishes:

  • Water consumption. for a 10-minute shower, one person consumes about 80 liters. or 400 l of water, or. per family. For washing the dishes, including three meals a day, about 45 liters. Accordingly, the daily consumption will be 445 l.
  • The comfortable temperature for washing will be on average 35°C (t°). To avoid scalding DHW is set to a temperature not exceeding 65 ° (t2). The cold water for the sub-balance is equal to 10 ° C (t1).
  • Carry out the calculation according to the formula: 445 x (35. 10): (65. 10) = 200 liters. In the calculations, the maximum values were used, giving a certain power reserve.

Based on the calculations for a family of 5 people will be sufficient to install BCH with a maximum capacity of 200 liters, which is possible if the boiler, to which the water heater is connected will have a capacity of at least 33 kW.

In determining the volume of the future boiler, you need to consider the boiler capacity. Practice shows that often this criterion is ignored when choosing a water heater, despite the fact that it directly affects the performance of BCH. Selection of indirect heating boiler according to the capacity of the boiler is carried out according to the table:

Water heater capacity: Boiler capacity:
80 liters not less than 16 kW
100 liters not less than 16 kW
120 liters not less than 23 kW
140 liters not less than 23 kW
200 liters not less than 33 kW

There is a direct correlation between the boiler capacity and the boiler output. Of course you can connect a larger capacity STB to the boiler, but it will not deliver the required volume of water. By installing a water heater with excessive capacity, the consumer will be faced with a longer heating time, which will lead to overspending of the energy carrier and an increase in costs.

STB volume selection begins with a thermo-technical calculation of the boiler capacity. Usually the given values are enough for the average user to choose a boiler for DHW. Construction companies additionally take into account a few more technical parameters and perform:

  • Calculation of heat exchanger area.
  • Take into account thermal conductivity and heat capacity of water when calculating the boiler. this value is necessary to clarify the peak and constant load on the water heater. The basic values are calculated from the table:
t, °C 0,1 10 15 20 25 30 35 40 45 50
Cp, J/(kg/°C) 4217 4191 4187 4183 4179 4174 4174 4174 4177 4181
t, °C 55 60 65 70 75 80 85 90 95 100
Cp, J/(kg-grad) 4182 4182 4185 4187 4191 4195 4202 4208 4214 4220
Specific heat capacity of water at 0.1100°C

In the case of a combined heater model (with built-in heating element), the following additional electricity consumption is to be taken into account. In order to transfer the heat to 1 kg of water (the volume used is not the volume, but the mass) and to raise the temperature by 1°C 4,187 kJ of energy or 0,001 kW is needed.

By performing a simple calculation, we understand that to heat 1 liter of water from 10 to 60 ° C will need 0.05 kWh. Further calculation of electricity for the combined BKN is carried out depending on what the actual consumption of DHW exists. For a large family a 10 kW boiler with a volume of 200 liters is usually sufficient.

Independent calculation of the boiler capacity requires an understanding of physical laws and the basics of mathematical calculations. To facilitate yourself, it is better to use special online calculators, located on the website or seek help from the brigade, which will connect the water heater.

Choosing a boiler of indirect heating

Before buying and connecting a buffer tank-accumulator (as it is also called BKN), you should understand the design features of the most popular types. The fact that there are many types of equipment, including combined models, which operate from heating systems and alternative energy sources simultaneously.

We will consider traditional boilers with coils, which use hot water as a heater.

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Design features and operating principle

What does indirect heating mean? Devices with direct heating function by connecting to electricity or a gas burner, BKN has another source of heat. Water is heated at the expense of the connection to the DHW, i.e. it turns out that the source is the coolant. hot water (or its substitute).

If you consider the new models of well-known brands, you will notice that gas boilers and boilers KN often have the same design. They are installed side by side or one under the other. so you can save on space.

The main element that performs the heating function is a steel or brass heat exchanger (coil) with a large surface area, which is located inside a metal, coated with a protective layer of enamel tank. To prevent the water from cooling too quickly, the outside of the body is surrounded by a layer of thermal insulation, and some models. and the shell.

An important detail, which now equip most of the heating devices, is a magnesium anode. The rod, fixed at the top of the device, protects the metal parts from corrosion, as a result, the water heater serves much longer.

Safety valve and built-in thermostat act as a barrier against high pressure. If the tank is not equipped with a safety group, it is installed separately, with the arrangement of piping.

Often, the water circulating in the heating system does not exceed 65-70 ° C. Many doubt its effectiveness when it acts as a heat source for heating in a BCH. In fact, the specified temperature is sufficient, because the speed and magnitude of heat transfer depends largely on the area of (quite large) contact between the coil and the water.

How the heating process works? Cold water intended for heating, comes through a separate hole and fills the entire tank. From the boiler to the heat exchanger also receives water, but already heated. The hot walls of the coil transmits heat to the cold water, which in the output already has a temperature suitable for showering or washing dishes.

Advantages of controlled equipment

Control capability is a characteristic that affects the assembly of the whole water heating system. There are two types of BCH: simple (cheaper) and with built-in control function.

Distinctive feature of the controlled models is the additional equipment with a temperature sensor and the ability to supply/stop the water to the heat exchanger. Such equipment operates in automatic mode.

After that you can start the boiler. the water begins to heat.

The process of connecting and strapping indirect heating boiler is one of the ways (description. below).

How the control can affect the temperature of the water? Virtually none. The maximum value that can reach the output temperature does not exceed the parameters of the coolant in the DHW system. Most likely it will be lower by 1-2 ° C.

If more intense heating is needed (this can happen if the boiler usually operates in a low-temperature mode), it is better to choose a model with a built-in heating element.

It is advisable to buy such equipment along with solid fuel boilers (water remains hot even after the boiler cools down).

Varieties of devices with additional functions

Tanks with a simple design. this is only part of the range presented in the market of water heating equipment. There are many models of boilers, the functions of which are very useful for integration into the DHW system.

For example, one of the purposes of more expensive models. heat accumulation. If there may be power outages or the daily consumer rates are too high, the accumulation mode will be very useful. The design features of such models. reinforced insulation and increased tank volume (300 liters and more).

Another option that implements the fastest supply of hot water to the hot water outlets, the boiler with recirculation. Unlike the usual design, this one is equipped with three nipples of communication with the hot water system. Two of them supply hot water, one. cold water. Water supply is carried out with the help of a pump.

When using a model with recirculation, you can equip an additional useful circuit, for example, for the installation of a towel dryer.

Water in such a tank is heated faster than in units with a heat exchanger, but the cost is higher.

The size of the tank and its importance

Cylindrical and cubic tanks differ in size. Their volume is specified in liters: there are small models at 80-100 liters, but there are and bulky, holding up to 1400-1500 liters. The size is chosen based on the family’s need for hot water.

Dimensions are important when installing. For wall installation suitable only light models. up to 200 liters, all others have a floor version. Both horizontal and vertical wall-mounted units come with special mountings, while the floor-mounted ones are equipped with legs or a small stand.

Rectangular units take a little less space than the cylindrical ones, due to the tight adjacency to the pipes.

What are the boilers of indirect heating?

The most common and affordable is the classic boiler. Most often it is made in the form of a cylinder, less often in the form of a cube and rectangle. The main feature of this device is the complete absence of an additional power source, in addition to the heat accumulator. Cold water comes from the bottom, moving upwards, it gradually heats up. When a person opens the hot water faucet, it is pressurized and flows through the pipes and out through the faucet. Such a system of water heating is bad in that it takes a long time to heat up with large volumes.

How else do indirect heating boilers differ?

DHW differ not only in the number of circuits, but also in volume. When choosing a model, it is extremely important to look at this distinction. Since if you choose a small tank. you will not have enough water, and if it is too big, then there is nothing wrong with it, you just pay extra money for the volume. We can offer you DHW volume:

Accordingly, the more family members live in the house, and the more you consume water, the more volume in terms of liters you need a boiler. If we talk about the average figures, for one person will be enough for 65 liters, for 2-3 people. 100 liters, and so on. For example, to take a shower, a man usually spends about 40-60 liters, and to wash dishes or cook food. 10-20 liters.

Electric water heater or indirect water heater: what to choose??

Summer is coming, and with it the scheduled turn off of hot water. This inconvenience is a tribute to the harsh climate in which the central heating and water supply system must be serviced annually. But fortunately, today’s citizen or owner of a private home can solve the problem of lack of hot water by installing a special device: a boiler of indirect heating or an electric water heater.

In this article we will consider the device, types and scope of these devices, and at the same time highlight their advantages and disadvantages. If you read the article to the end, you can make the right choice of water heater, based on your living conditions.

What are electric water heaters

About what an electric water heater is. knows all or almost all. It is a device that can be used to heat water, using a tubular electric heater, which converts electrical energy into thermal energy. Electric water heaters are of two types: storage (boilers) or flow-through.

  • Accumulation heater or boiler is a sealed tank, inside which there is a heating element. With the help of an automatic control system, it heats the water to the desired temperature and maintains it at a predetermined level;
  • Flow-through heater is much smaller in size and contains a very powerful heating element with a high-speed compact heat exchanger, passing through which the cold water is heated almost instantly.

Boilers allow you to get hot water by opening a faucet, but its consumption is limited by the volume of the tank. If you run out of water in the tank, you have to wait from 1 to 3 hours until it heats up again. Flow-through water heater does not limit the volume of consumption, but consumes a lot of energy. Because of the high power of the heating element, it requires sufficient power network. In addition, when you turn on a flow heater requires a fairly long wait for hot water, because the heating element requires time to heat up.

What is an indirect water heater

Externally, indirect water heater can easily be confused with the storage water heater, it is also a cylindrical tank of sheet steel. On the inner walls are applied corrosion protection, such as polymer coating, enamel or fiberglass. Outside the tank is insulated with polyurethane foam.

The principle of operation of indirect heating boiler is quite simple he has inside instead of the TEN is a spiral, which is constantly circulating heated coolant. This coolant comes from the heating system or directly from the heat accumulator. boiler. The tank can be divided into several compartments, each of which is equipped with a spiral with an intermediate coolant and is responsible for a separate heating circuit.

Indirect water heaters are classified by the shape of the tank (rectangular, cylindrical), the method of installation (floor, wall, vertical, horizontal), and the number of loops.

What to choose for water heating

When the general principle of operation of indirect water heaters and electric water heaters is understood, you can proceed to the choice of device. And the first thing that will influence the choice is the type of heating system.

In apartment buildings with central heating BKN installing makes no sense, for them perfectly suit storage water heaters. The need of residents of the city apartment in hot water is not so great, and the tank is usually enough for all household needs.

For a private home with a gas or solid fuel boiler boiler is perfect indirect heater. It will heat water in parallel with the heating system, and maintain its temperature automatically. But what if it happens in the summer, when the house is not heated?

The first generation of BKNs really only worked during the heating season. But modern models can switch to summer mode and work independently they are combined devices, and contain in addition to the spiral with an intermediate coolant also TEN. Therefore, for private homes with a gas or solid fuel boiler BKN is a great option.

Let us note its advantages:

  • Significant energy savings. Indirect heating boiler uses the intermediate heat transfer fluid directly from the heating system, not consuming electricity to heat the heating element;
  • The possibility of replacing the two-circuit heating system with a set of BKN single-circuit boiler. Considering the difference in the cost of the equipment, this is a big savings;
  • If there are several hot water outlets, WCHS provides them all without sudden temperature jumps and changes in the work of the boiler.

The disadvantages of BKN can include the cost of its installation, the large volume and the inertia of the device. To assess the feasibility of its use, it is necessary to remember that BKN is suitable for:

  • Gas or solid fuel boilers. When connected to an electric boiler, the effect of its cost-effectiveness is reduced to zero;
  • Facilities with high water consumption. Indirect heating boiler is ideal when hot water consumption exceeds 1.5 liters./min, this corresponds to the permanent residence of a family of 4 or more people.

As for electric water heaters, they have their own list of advantages and disadvantages. Their advantages include complete autonomy, as a result they can be used in apartment buildings with central heating. On the plus side is the affordable price of devices, everyone can find a heater to their s, depending on the type, capacity and power of the unit.

Disadvantage common to all electric water heaters: high power consumption. And flow-through heaters, it is especially great: it takes a large amount of energy to heat the heating element, but then, when it warms up, the expense is reduced.

The disadvantages of storage-type heaters include the limited water supply capacity of the tank. The disadvantages of flow-through heaters long time waiting for hot water from the faucet at first turn on. In addition, the flow heater requires a properly made and very powerful electrical network, an ordinary apartment wiring it will not withstand.

  • If you live in a private home with a gas or solid fuel boiler, buy BCN. You will have to spend money on installation, but in the future it will save you a lot of money;
  • If you live in a city apartment with central heating, or in a private home with an electric boiler, you’re better off opting for an electric water heater. Flow heaters are put only where it is not possible to set storage, because the cost of laying a powerful power grid can nullify the economic sense of acquiring a heater.
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Want to choose an electric water heater or a boiler of indirect heating ?

Central heating system plan ( solid fuel boiler buffer tank water heater ) with room thermostat 1

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