How to calculate the heat accumulator for a solid fuel boiler and perform its piping

An effective and efficient way to heat your home is with a solid fuel boiler and heat accumulator installed together. It keeps your house comfortable even when the boiler isn’t actively burning fuel in addition to providing warmth. To get the most out of this system, though, meticulous planning and installation are necessary, particularly with regard to determining the heat accumulator’s size and piping system configuration.

Making sure your heating system operates as efficiently as possible requires that you calculate the size of the heat accumulator. The excess heat generated by the boiler is stored in a heat accumulator, sometimes referred to as a thermal store, so you can use it later. The size of your home, the amount of insulation inside, and the kind of solid fuel boiler you have are some of the variables that affect the accumulator’s size. You can be sure that your home is always warm and that there is a steady supply of hot water with a properly designed heat accumulator.

For heat to be distributed efficiently throughout your house, proper plumbing is necessary. After the solid fuel boiler and heat accumulator are connected, the hot water is distributed to the radiators or underfloor heating system via the piping system. Heat is dispersed evenly via a well-designed plumbing system, preventing cold spots and guaranteeing optimal comfort. Furthermore, appropriate piping increases the heating system’s efficiency, which ultimately reduces your fuel expenses.

Although installing a heat accumulator and setting up the plumbing system may seem difficult, you can accomplish them on your own with the correct assistance. This post will walk you through the process of figuring out how big your solid fuel boiler’s heat accumulator should be and assist you in setting up the plumbing system for maximum efficiency. You can save money on heating expenses and have a warm and cozy home with the appropriate strategy.

What is a buffer tank

The heat accumulator intended for the heating system is actually a standard metal tank with a calculated capacity that is wrapped in a layer of thermal insulation. The most basic factory-made models simply have sleeves to install thermometers and spigots to connect coolant. The priciest models come with coil heat exchangers, while the more expensive buffer tanks already have thermometers integrated in. The figure illustrates the device of a heat accumulator of this type.

As you can see, the buffer tank’s design is not very complicated, so various artisans have modified it to be made by hand; this is covered in a different topic.

The coils’ dual functions are to connect solar collectors, an alternate source of heat energy, and to heat water for domestic hot water heaters. It’s evident that this function is only needed when the local climate is suitable for habitation. Generally speaking, the heating boiler’s buffer tank is made to address these issues:

1. Creation of conditions for operation of the TT-boiler with maximum efficiency and minimum emissions into the atmosphere.
2. Comfortable operation of the heat generator, when it is not necessary to throw wood into the furnace every 4-6 hours, including night time.
3. Heating and supply of drinking water to 1-2 consumers (optional).

In the accompanying documentation, the majority of manufacturers of solid fuel heating equipment state that connecting a heat accumulator to the TT-boiler is highly desirable. The rationale is that the unit operates at near maximum efficiency, which is the highest efficiency possible in the mode of operation. Additionally, a buffer tank filled with water will be required because the extra heat that is produced needs to be stored somewhere before it is fed into the heating system.

We make every effort to "choke" the thermal unit—that is, to reduce the amount of combustion air available—in the absence of a thermal accumulator. This not only releases harmful carbon monoxide into the atmosphere, but it also lowers its efficiency by as much as 40% (much like a stove). This is the reason that burning coal and wood in heating boilers without a buffer tank is prohibited in several European countries.

Everything is evident with fewer trips to the furnace room: if the volume of the heat tank is calculated correctly, the heat it has accumulated over an extended period of time will be used to heat the house. Furthermore, the likelihood of a solid fuel boiler overheating and causing water in the unit’s jacket to boil when used in tandem with a heat accumulator is nearly eliminated.

You can interact not only with wood heat generators but also with electric boilers and thermal accumulators. This makes sense considering that the tariff counts the amount of electricity used at night, which is two to three times less than usual. The electrical installation will be able to completely "charge" the heat accumulator during the time that this tariff is in effect, providing the energy needed to heat the house during the day.

To ensure that the heat output of the electric boiler is adequate to heat the house and fill the tank at the night tariff, the results of the previous calculation of the boiler’s capacity will need to be doubled in this instance.

Calculation of the buffer tank

The primary factor used to choose a buffer tank for a solid fuel boiler is its volume, which is computed. Its worth is determined by things like:

• Heat load on the heating system of a private house;
• capacity of the heating boiler;
• expected duration of operation without the help of a heat source.

All of the aforementioned points must be understood before determining the heat accumulator’s capacity, beginning with the average heat capacity used by the system during the winter. The maximum capacity shouldn’t be used for calculations as this will increase the tank’s size and, consequently, raise the price of the product. Paying an outrageous amount for a big heat accumulator that will be used irrationally is preferable to being inconvenienced a few days a year and loading the furnace more frequently. Furthermore, it will occupy too much room.

Professional judgment. A buffer tank with a capacity of 1 t of heat transfer fluid, or a volume of 1 m³, is adequate to supply heat energy to a 200 m² house. The middle zone of the Russian Federation is where the statement is true; however, the layout will differ in more southern or northern regions.

When the heat source has a small capacity reserve, the heat accumulator in a heating system cannot operate normally. Since the heat generator needs to heat the house and load the tank at the same time, it will never be able to "charge" the battery to its full capacity in this scenario. It is important to keep in mind that choosing a solid fuel boiler for pipework with a heat accumulator implies having two reserves for heat output.

The calculation algorithm is suggested to be studied using the example of a 200 m² house with an 8 h boiler outage. During the heating process, it is anticipated that the water in the tank will reach a temperature of 90 °C and then cool to 40 °C. In the coldest months, 20 kW of heat will be required to heat such an area, with an average consumption of roughly 10 kW/h. Thus, the battery should store 80 kW of energy (10 kWh x 8 h). Using the water’s heat capacity formula, the volume of the heat accumulator for a solid fuel boiler can be further calculated:

Where: m = Q / 1.163 x Δt

• Q is the calculated amount of heat energy to be accumulated, W;
• m – mass of water in the tank, kg;
• Δt – the difference between the initial and final temperature of the coolant in the tank, is equal to 90 – 40 = 50 ° C;
• 163 W/kg °C or 4.187 kJ/kg °C – specific heat capacity of water.

The mass of water in the heat accumulator for the example will be as follows:

80000 divided by 1.163 times 50 is 1375 kg, or 1.4 м³.

As you can see, computations have led to a buffer tank that is bigger than what the expert suggests. The explanation is straightforward: erroneous starting data were used in the computation. In actuality, the average heat consumption for 200 m² will be less than 10 kWh, especially if the house is well-insulated. Thus, the conclusion: more precise initial data on heat consumption are required in order to accurately determine the size of the heat accumulator for a solid fuel boiler.

As a point of reference. There is an additional calculation method that states that there are 25 liters of heat accumulator volume for every kW of heat output produced by the boiler.

Selection of the heat accumulator

The remaining capacity selection criteria mostly relate to options and are not as significant. A built-in coil is one of them; it heats water for domestic use. can be helpful if there are no other options for heating, but this approach is most definitely inappropriate for significant DHW network expenses. Moreover, a portion of the heat accumulator’s "charge" will be removed by the heat exchanger, cutting down on how long it takes for autonomous heating to operate.

A helpful option is a TEN that is integrated into the upper portion of the tank and has the ability to keep the coolant’s temperature at a specific level. Electric heating ensures that in the event of an accident, the system won’t defrost and that the house will remain warm for a while even after the battery has "discharged" and the boiler hasn’t been started.

In southern regions only, where solar activity permits loading the heat accumulator, is the second coil for connecting the solar system useful. Additionally, you ought to consider the tank’s working pressure when making your choice. Remember that the majority of solid fuel boilers are made to withstand jacket pressure of up to 3 bar, so the buffer tank should be able to withstand that amount without issue.

Selecting and installing a heat accumulator is essential for effectively heating your home with a solid fuel boiler. In order to keep your home at a constant temperature, a heat accumulator retains extra heat produced by the boiler and releases it when needed. Consider variables like your home’s size, insulation levels, and heating needs when determining the size of heat accumulator you need. For best results, the heat accumulator’s plumbing must be done correctly. You may optimize the performance of your solid fuel boiler, keep your house warm and cozy, and save energy expenses by making sure your heat accumulator is installed and sized correctly.

Connection schemes

There are numerous ways to connect a heating system and a heat accumulator to a solid fuel boiler. However, they are all descended from the fundamental plan depicted below. It makes it simple to comprehend how these devices function in pairs with its assistance, after which you can install everything by hand.

The purpose of the mixing unit in the conventional boiler circuit of the solid fuel heat source is to stop the boiler from receiving cold, cool coolant. Subsequently, the buffer tank is connected to the supply and return pipelines from the top and bottom, respectively. Similarly, the heat accumulator is connected to the heating system, which is also outfitted with a mixing unit. Its goal is to keep the system’s water temperature at the appropriate level by adding hot coolant as needed.

Important point. The boiler circuit’s circulation pump’s actual capacity needs to be marginally greater than the heating network’s pump unit’s capacity. The accumulator’s flows (represented by the white arrows in the diagram) will flow in the correct direction if this condition is satisfied.

For the following reason, the boiler pump will not be as powerful as the mains pump. From the solid fuel boiler to the heat accumulator, there is more than three to five meters of pipe resistance in the network of pipelines and radiators. To overcome this resistance, the unit requires more strength and intelligence. Hence, if both units are configured properly, a weaker boiler pump can deliver a higher flow rate. There are two ways to answer the query:

1. When using 3-speed pumps, you can adjust their performance by switching speeds.
2. Place a balancing valve at the inlet of the return flow from the system to the buffer tank and use it to adjust the flow.

Layer-by-layer loading of the heat accumulator and simultaneous heating of heating appliances are made possible by horizontal flows inside the tank that slightly favor the side of the solid fuel boiler. So the question is, how can we verify this? The solution is as follows: thermometers must be installed on both return to tank inlets (per the scheme) and adjustments must be made by adjusting the balancing valve or altering the pump speeds. Important requirement: the heating network’s three-way valve needs to be manually opened all the way.

It is vital to regulate the heat accumulator so that the temperature at its inlet (T1) is lower than that at its outlet (T2). This indicates that the battery is "charged" by some of the hot water. By watching the video, you can gain additional knowledge about each of the expert’s points:

Alternative scheme

One of the members of a well-known forum suggests connecting the buffer tank and solid fuel boiler together. Its unique feature is that, despite requiring larger steel pipe diameters to compensate, the scheme’s operability is maintained in the event of a power outage. The heat accumulator’s connection to a closed heating system is depicted in the figure below; however, as the author notes, it is preferable to leave it open during installation.

The essence is as follows, to put it briefly: the radiators are heated simultaneously and the thermoaccumulator, which you made yourself, is "charged" thanks to the T-shaped inlet from the top of the tank. When the unit’s interior temperature reaches 60 ° C, an overhead sensor on the supply line activates the boiler circuit pump. The room thermostat that the network pump is connected to controls network circulation.

Note: The suggested pipe scheme is tested based on the author’s personal experience. The author describes every aspect of how to install and use it on the forum.

For a solid fuel boiler, installing a heat accumulator can greatly increase the heating system’s performance and efficiency. Through the process of accumulating surplus heat produced by the boiler, the accumulator guarantees a more stable and dependable heat distribution throughout your house. For best results, though, you must measure the heat accumulator and pipe it into your heating system correctly.

The size of your home, your heating requirements, and the heat output of your boiler are all important considerations when determining the size of the heat accumulator. To choose the ideal accumulator size for your unique needs, it is imperative that you speak with an expert. Accumulators that are either too large or too small can result in inefficiencies and higher energy expenses.

Ensuring that heat is distributed effectively throughout your house also requires proper piping of the heat accumulator. In order to minimize heat loss and ensure uniform distribution throughout your home, the piping system should be designed. To guarantee that the piping is completed correctly and that your heating system performs at its peak, professional installation is advised.

You can have a more dependable, economical, and efficient heating solution for your house by purchasing a heat accumulator and making sure it is piped into your heating system correctly. This will not only make your living area more comfortable over time, but it will also result in lower long-term heating costs.

Video on the topic

HEAT ACCUMULATOR (volume calculation), convenient heating

Scheme of solid fuel boiler piping and heat accumulator tank

Strapping of solid fuel boiler with heat accumulator

Strapping of solid fuel boiler with heat accumulator