How to choose a buffer tank for solid fuel boiler

A solid fuel boiler’s buffer tank selection is an important choice for both heating and insulation of your house. A thermal store, sometimes referred to as a buffer tank, is essential to maximizing the effectiveness and performance of your heating system. It serves as a reservoir, holding onto extra heat produced by the boiler and releasing it when necessary to keep the temperature in your house constant.

A number of factors must be taken into account when choosing a buffer tank to make sure it fulfills your unique needs and optimizes the efficiency of your heating system. The size of the buffer tank is one important consideration; it should be selected in accordance with the size of your house and your heating requirements. An excessively large buffer tank could result in needless energy waste, while a buffer tank that is too small might find it difficult to meet the demand for heat.

The buffer tank’s material is another crucial factor to take into account. Copper and stainless steel are popular choices, and each has pros and cons of its own. Because they are strong and resistant to corrosion, stainless steel tanks are a well-liked option for long-term dependability. Conversely, copper tanks have a reputation for having superior heat transfer qualities, which enable faster heating and more effective operation.

It’s also critical to take the buffer tank’s insulation into account. In order to ensure that the heat that has been stored is usable when needed, proper insulation helps reduce heat loss. Seek for buffer tanks that have foam insulation or double walls, two features that reduce thermal bridging, along with other high-quality insulation materials.

Additionally, consider the features and functionalities that various buffer tank models offer. The efficiency and convenience of your heating system can be improved by adding extra parts to some tanks, such as immersion heaters, mixing valves, or integrated control systems. When comparing these features, take into account your unique requirements and preferences in order to select the buffer tank that best meets your needs.

In conclusion, one of the most important steps in maximizing the effectiveness and performance of your heating system is choosing the appropriate buffer tank for your solid fuel boiler. Size, material, insulation, and feature considerations, among others, can help you make sure your buffer tank efficiently satisfies your heating requirements while optimizing energy efficiency and comfort in your house.

What is a buffer tank for solid fuel boiler?

A buffer tank, also known as a heat accumulator, is a tank with a specific capacity that is filled with coolant. Its function is to store excess heat capacity and then distribute it more sensibly for hot water supply or house heating (HWS).

What it is needed for and how effective it is

The buffer tank is typically utilized in conjunction with solid fuel boilers, which also apply to long-burning boilers due to their inherent cyclicality. Following ignition, the fuel’s heat output in the combustion chamber rises quickly and reaches its peak values. After that, the production of heat energy diminishes and eventually stops when a fresh batch of fuel is not laid.

The only exceptions are hopper boiler units with automatic feeding, where combustion occurs with the same heat output because of consistent, regular fuel feeding.

Because of this cycling, there’s a chance that there won’t be enough heat energy to keep the house at a comfortable temperature during the cooling or fading period. The house is also much hotter than is comfortable during the peak heat output period, and some of the excess heat from the combustion chamber just goes up the chimney, which is not the most economical or efficient use of fuel.

The buffer tank’s effectiveness is best demonstrated by a tangible example. When cooled by 1°C, one m 3 of water, or 1000 liters, produces 1–1.16 kW of heat. As an example, let’s consider a typical 100 m 2 home with traditional 2-brick masonry, where the heat loss is roughly 10 kW. A 750-liter thermal accumulator can provide approximately 30 kW of heat to the heating system after being heated to 80°C by multiple deposits and cooled down to 40°C. This means an additional three hours of battery heat for the house mentioned above.

When heating at night, using a buffer tank in addition to an electric boiler makes sense because the cost of electricity is lower. Nevertheless, such a plan is rarely justified because a tank that holds two or even three thousand liters is needed to accumulate heat over night for daytime heating.

Device and operating principle

Heat accumulators are hermetic, typically vertical cylindrical tanks that are also thermally insulated on occasion. It serves as a bridge between the heating appliances and the boiler. Two pairs of pipe connections are included with standard models: the first pair connects to the boiler’s supply and return (small circuit); the second pair connects to the house’s heating circuit’s supply and return. There is no crossover between the heating circuit and the small circuit.

When used in conjunction with a solid fuel boiler, the heat accumulator operates on a straightforward principle:

1. After the boiler is fired up, the circulation pump constantly pumps the coolant in the small circuit (between the boiler heat exchanger and the tank). The boiler supply is connected to the upper pipe of the heat accumulator and the return to the lower pipe. This allows the entire buffer tank to be filled smoothly with heated water, without a pronounced vertical movement of warm water.
2. On the other hand, the supply to the radiators is connected to the buffer tank from above and the return from below. The heat carrier can circulate both without a pump (if the heating system is designed for natural circulation) and forcibly. Again, such a connection scheme minimizes vertical mixing, so the buffer tank gives the accumulated heat to the batteries gradually and more evenly.

Heat loss can be reduced in solid fuel boilers by carefully choosing the buffer tank’s volume and other features. This will improve the furnace’s comfort level as well as its fuel efficiency. A well-insulated thermal storage unit can hold its stored heat for at least 30 to 40 hours.

Furthermore, all of the assigned heat is accumulated because of the adequate volume, which is significantly larger than in the heating system (based on boiler efficiency). With just one to three hours of heating—even at maximum attenuation—you have access to a fully "charged" heat accumulator.

Types of constructions

Any of the buffer tank types mentioned above can have more pairs of spigots, enabling you to connect the water floor heating in addition to differentiating the heating system’s parameters by zone.

Reviews of domestic heat accumulators for boilers: advantages and disadvantages

How to choose a buffer tank

Calculation of the minimum required volume

The vessel’s volume is the most crucial parameter that needs to be established right away. To maximize efficiency, it should be as large as possible, but only to the extent that the boiler power is sufficient to "charge" it.

The following formula is used to determine the buffer tank volume for a solid fuel boiler:

M is equal to Q / (k*c*Δt).

• where, m – The mass of the coolant, after calculating it is not difficult to convert it into liters (1 kg of water ~ 1 dm 3 );
• Q – the amount of heat needed is calculated as: boiler output * period of boiler activity – heat losses of the house * period of boiler activity;
• k – Boiler efficiency;
• c – specific heat capacity of the heat transfer medium (for water this is a known value – 4.19 kJ/kg*°C = 1.16 kW/m 3 *°C);
• Δt – temperature difference in the boiler supply and return pipes, the values are taken at steady-state operation of the system.

For instance, the approximate heat loss per hour for a typical house with two bricks of masonry and an area of 100 m 2 is 10 kW. As a result, 10 kW of heat (Q) are needed to keep the balance. The house is heated by a 14 kW boiler that has an 88% efficiency rate; the boiler burns wood for 3 hours during this time. 85°C is the temperature in the supply pipe and 50°C is the temperature in the return pipe.

The necessary amount of heat must first be determined.

14*3–10*3 = 12 kW is Q.

Consequently, m = 12 / 0,88*1,16*(85-50) = 0,336 tons, or 3,36 cubic meters. This is the buffer tank’s minimum required capacity. With this capacity, the heat accumulator will continue to accumulate and distribute 12 kW of heat after burning the tab for three hours. This means that the house in the example will have warm batteries for longer than an hour on a single charge.

As a result, in actuality, the result may vary by 10% to 15% depending on the fuel quality, the heat carrier’s purity, and the initial data’s accuracy.

Calculator for calculating the minimum required capacity of the heat accumulator

Number of heat exchangers

The number and presence of heat exchangers should be considered second after choosing the volume. The decision is based on preferences, CO requirements, and tank connection scheme. A basic heating system only needs an empty model without any heat exchangers.

The small boiler circuit can only operate with forced circulation, so if natural circulation is intended for the heating circuit, an additional heat exchanger is needed. Compared to a heating circuit with natural circulation, there is more pressure in this situation. Connections for underfloor heating or DHW will also need additional heat exchangers.

Maximum permissible pressure

The maximum allowable working pressure should not be lower than in any of the heating circuits, so keep that in mind when selecting a buffer tank with an extra heat exchanger. Most models without heat exchangers are made with tanks that can withstand internal pressures of up to 6 bar, which is more than sufficient for a typical CO.

Material of the inner tank

Currently, there are two ways to have the inner tank manufactured:

• mild carbon steel – coated with waterproof anticorrosive coating, has a lower production cost, is used in inexpensive models;
• stainless steel – more expensive, but more reliable and durable.

In the tanks, some manufacturers additionally add extra wall protection. One of the most popular is a magnesium anode rod located in the middle of the tank, which shields the heat exchangers and tank walls from the accumulation of solid salts. These components do, however, require routine cleaning.

Other selection criteria

Once the primary technical requirements have been established, you can focus on other aspects that improve effectiveness and user comfort:

• the possibility of connecting TEN for additional heating from the power grid, as well as additional control and measuring devices, which are mounted threaded or socketed (but in no case welded) connection;
• the presence of a layer of thermal insulation – in more expensive models of thermal accumulators between the inner tank and the outer shell there is a layer of insulating material, contributing to even longer heat retention (up to 4-5 days);
• weight and dimensions – all of the above parameters affect the weight and dimensions of the buffer tank, so it is worth determining in advance how it will be brought into the boiler room.

Best known manufacturers and models: characteristics and prices

Sunsystem PS 200

A standard, low-cost heat accumulator that fits a small, private home up to 100–120 m 2 well is ideal for a solid fuel boiler. It is a traditional tank in terms of technology, devoid of heat exchangers. 200 liters of capacity and a maximum pressure of 3 bar are permitted. A 50 mm layer of polyurethane thermal insulation and the ability to connect the heating element are features of the low-cost model.

Hajdu AQ PT 500 C

One of the best buffer tank models available at this price point, featuring an integrated heat exchanger. Capacity: 500 liters; allowable pressure: 3 bar. A great choice for a home between 150 and 300 square meters with a sizable solid fuel boiler reserve. The line includes models with varying volumes.

The models (optionally) come with a layer of polyurethane thermal insulation and an artificial leather cover, starting at 500 liters. It is feasible to install a heating element. The model is renowned for its durability, dependability, and overwhelmingly positive owner feedback. Hungary is the manufacturing nation.

S-TANK AT PRESTIGE 300

Another low-cost buffer tank with a 300-liter capacity. It is a storage tank by design with a maximum allowable operating pressure of 6 bar and no additional heat exchangers. Internal walls are composed of carbon steel, just like in earlier instances. The primary distinction is a crucial layer of fire and heat insulation composed of polyester material that complies with NOFIRE technology, offering superior fire and heat resistance while also being environmentally friendly. Belarus is the manufacturing nation.

ACV (ACV) LCA 750 1 CO TP

Expensive, high-performing 750-liter buffer tank for district heating and water with an extra tubular heat exchanger for DHW, intended for boilers with a big reserve capacity.

Protective enamel covers the inner walls, and a superior 100 mm layer of thermal insulation is present. To stop a layer of solid salts from building up inside the tank, a magnesium anode is installed (three spare anodes are included). It is feasible to install extra control and measurement equipment in addition to a heating element. Belgium is the manufacturing nation.

Prices: summary table

Choosing the right buffer tank for your solid fuel boiler is crucial for optimizing heating efficiency and ensuring consistent warmth in your home. A buffer tank acts as a storage reservoir for heated water, smoothing out fluctuations in demand and allowing your boiler to operate more efficiently. When selecting a buffer tank, consider factors such as size, material, insulation, and additional features like temperature sensors and connections for renewable energy sources. The tank should be adequately sized to accommodate your heating system"s capacity and provide sufficient thermal mass to stabilize temperature fluctuations. Opting for a well-insulated tank helps minimize heat loss and maximize energy savings. Additionally, look for durable materials that resist corrosion and can withstand the demands of continuous heating cycles. By carefully assessing your requirements and selecting the right buffer tank, you can enhance the performance and longevity of your solid fuel boiler system while keeping your home comfortably warm.

Strapping and connection diagrams

Simplified visual scheme (click to enlarge)	Description
	Standard scheme of connection of "empty" buffer tanks to the solid fuel boiler. It is used when the heating system (in both circuits: before and after the tank) has a single coolant and a single permissible working pressure.
	The scheme is similar to the previous one, but assuming the installation of a thermostatic three-way valve. With this arrangement, the temperature of the heating devices can be regulated, which allows even more economical use of the heat accumulated in the tank.
	Scheme of connection of heat accumulators with additional heat exchanger. As already mentioned, it is used when a different coolant or higher working pressure is supposed to be used in the small circuit.
	Scheme of hot water supply organization (if the tank has a corresponding heat exchanger).
	A scheme involving the use of 2 independent sources of heat energy. In the example it is an electric boiler. The sources are connected in the order of decreasing heat head (from top to bottom). In the example, the main source – solid fuel boiler – comes first, and the auxiliary electric boiler comes below it.

A tubular electric heater (TEN), for instance, can be used as an additional heat source in place of an electric boiler. The majority of contemporary models already include flange or socket mounting for installation. TEN can partially replace the electric boiler or avoid heating the solid fuel boiler entirely by installing in the appropriate spigot.

It is important to understand that these are simplified, not complete connection schemes. To ensure the control, metering and safety of the system, a safety group is installed on the boiler feeder . Besides, it is important to take care of the operation of the CO in case of power failure, i.e. in the event of a power failure.к. the energy produced by the thermocouple of non-volatile boilers is insufficient to power the circulation pump. Lack of coolant circulation and heat accumulation in the heat exchanger of the boiler with a high probability will lead to the rupture of the circuit and emergency emptying of the system, it is not excluded boiler burnout.

As a result, caution must be used to guarantee system functionality at least until the tab is entirely burned out for safety reasons. This is accomplished by using a generator, the power of which is chosen based on the boiler’s specifications and the amount of time it takes for one fuel tab to burn.

Selecting the appropriate buffer tank for your solid fuel boiler is essential for effective home insulation and heating. You can make sure you get the best performance and energy savings by taking into account elements like size, material, insulation, and extra features.

First and foremost, consider your property’s size and heating needs. More hot water will be stored in a larger buffer tank, giving your heating system a constant supply and lowering the frequency of boiler fires. Finding the right balance is crucial, though, as an overly large tank may result in heat loss and wasted energy.

Second, think about the buffer tank’s material. While mild steel tanks are less expensive, they might need more care to keep from rusting. In contrast, stainless steel tanks are robust and resistant to corrosion. The thickness of the tank walls should also be considered, as thicker walls offer superior insulation and lower heat loss.

Another important thing to think about when selecting a buffer tank is insulation. Select high-quality insulated tanks to reduce heat loss and increase energy economy. Because of its exceptional thermal qualities, foam insulation is frequently used to keep water hotter for longer.

Finally, look into extra features that can improve your buffer tank’s functionality and convenience. Temperature sensors, mixing valves, control panels, and other features enable more precise control over the heating system, resulting in maximum comfort and energy savings.

To sum up, choosing the appropriate buffer tank for your solid fuel boiler requires taking into account a number of variables, including size, composition, insulation, and extra features. You can increase the effectiveness of your heating system, lower energy costs, and improve the comfort level in your house by making wise decisions.

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