Expansion tank of the heating system: design, calculation and selection of the best option
A correctly selected and correctly installed expansion tank of the heating system will prevent its failure and will maintain the pressure at the required level.It is needed as a reserve for water expanding when heated. Depending on the type of system, the built-in expander can be open or closed.
We will tell you how to select a reserve capacity depending on the heating scheme being created. The article we presented describes the design features and specifics of installing expanders. Recommendations are given that, if followed, will ensure ideal operation of any type of heating circuit.
The content of the article:
Open type expansion tanks
A design feature of open type expanders is the contact of the coolant with the atmosphere. The circulation in systems with an expander of this type is convection. When heated, the volume of liquid increases, its excess is absorbed by the reservoir of the container.
When the temperature drops, the liquid returns by gravity, under the influence of gravity.
Due to zero pressure in the tank, the device does not require a strong metal structure, therefore:
- any metal is used in the manufacture of the case;
- a ready-made container made of heat-resistant plastic can be used;
- The shape of the tank is not important.
In country houses, such equipment can be assembled from available materials. As a container, you can use a plastic canister or barrel equipped with an inlet pipe and an outlet for overflow.
Externally, it is an ordinary metal tank, the upper plane of which is equipped with a hole for servicing and adding liquid. The leak-proof lid provides protection against clogging. Fastening units are provided at the bottom or on the side plane.
Open heating systems are used in low-rise buildings, where the volume of coolant and the length of heating communications are relatively small.
Installation requirements are simple:
- the expander is placed at maximum height, on the supply line;
- the supply is connected to the tank through a pipe;
- To drain excess liquid, an overflow is inserted above the calculated level.
To ensure circulation by gravity, it is recommended to use pipes of increased cross-section for installation.
Usually they try to install the tank in a heated room, equipped with an insulated attic, and if this is not possible, then the tank will need to be insulated. The presence of insulation will prevent freezing of the liquid and loss of system functionality.
Closed expansion tanks
The design specificity of closed modifications of the tank is complete tightness, which allows you to maintain the pressure necessary for circulation at any point in the system.
The reservoir inside is divided by a membrane into air and liquid parts. Each of the compartments is completely sealed - the nitrogen-containing mixture from the air compartment will never mix with the coolant filling the liquid compartment.
Principle of operation closed expansion tank consists in the fact that the heated liquid from the system is pushed into the liquid part of the tank and begins to put pressure on its side on the sealed membrane. The partition is deformed and acts on the air part, compressing it.
As a result, the volume of the air chamber of the tank decreases, and the gas in it is compressed. This situation contributes to an increase in pressure in the system. As soon as the pressure normalizes, the coolant is pushed back out of the liquid compartment.
If the pressure rapidly increases, then, when the critical volume of liquid in the tank is reached, the safety valve is activated. As a result, excess coolant will be removed from the tank.
Depending on the shape, all closed expanders for installation in the heating system are divided into the following types:
- Ball-shaped - a type of membrane structure with an elastic partition.When fluid enters, it stretches and absorbs all the excess volume. The tank itself looks like a spherical capsule.
- Oval - another type of membrane hydraulic compensators. The expander cylinder is traditionally divided by a flexible membrane into gas and liquid chambers, but the body configuration has a somewhat elongated vertical shape.
Externally, oval dilators are a cylindrical balloon, painted red. On the one hand, there is a nipple for creating pressure in the gas chamber, on the other, there is a pipe through which the connection to the system is made.
Fastening units are welded onto the body, which provide hinged installation of the equipment and are able to withstand its operating weight. The spherical modification of the tank differs from the oval one only in shape.
In closed systems, gravity circulation will not be able to provide the required level of pressure. Therefore, the design includes circulation pump.
The expander itself can be installed at any point in the system, but when performing installation work it is advisable to take into account the following recommendations:
- the best place for installation is the return line, to the pump insertion point;
- It is better to supply coolant from above, which will reduce air penetration and maintain functionality if the membrane is damaged;
- the lack of main volume can be compensated by installing an additional expander with a smaller capacity.
When installing, it is not forbidden to take into account the interior of the room, if necessary. For level control heating system pressure The expander must be equipped with a pressure gauge.
The possibility of placement close to the boiler eliminates the question of the need to insulate the tank. The equipment is located in a warm room, which ensures ease of use.
Which design is better?
Systems, depending on the design and material of the expansion tank, differ in the list of pros and cons. But, according to experts and experienced users, the advantages in functionality are on the side of closed options.
Pros and cons of an open tank
A self-flowing system requires larger diameter pipes, which in turn directly increases costs. Development budget open heating system with a leaky dilator increases slightly, although it remains relatively small.
The main advantages of this option are simplicity, plus the low cost of components and installation work. Another positive feature is that there is no need to control the pressure level.
However, there are much more disadvantages:
- the use of anti-freeze is dangerous due to toxic fumes;
- installation possibilities are limited only by the top point of the system;
- constant contact with the atmosphere increases the risk of air locks and corrosion;
- slow warm-up;
- temperature changes accompanying convection circulation accelerate equipment wear;
- used in heating low-rise buildings, maximum two floors;
- large heat losses and energy consumption for heating.
Another disadvantage of an open system is losses from evaporation and overflows. Therefore, when installing the tank, care should be taken to ensure that the filler hole is accessible.
Pros and cons of a closed tank
If open expanders win in terms of prices and ease of installation work, then functionality is the strong point of a closed tank, which is also called an expansion tank.They are used in the construction closed heating systemsthat do not have direct contact with the atmosphere.
Expanzomats have the following advantages:
- complete tightness allows the use of antifreeze;
- The location of the expander does not affect the performance of the system;
- insulation of the internal space of the tank minimizes the likelihood of air locks and corrosion;
- after startup, the system warms up faster and is more sensitive to temperature control;
- smaller difference between the operating conditions of the supply and return lines, which as a result increases the service life;
- does not require the installation of large diameter pipes, which allows saving on construction;
- does not require constant attention to the level and condition of the liquid;
- possibility of use in systems designed for several floors;
- small heat losses, reducing costs during equipment operation.
When choosing expanders of this type, you may encounter sealed cylinders with a non-separable design. If the diaphragm malfunctions, the cylinder will have to be replaced with a new one.
Among the disadvantages, it is important to note the complexity of the design, special requirements for materials, which increase the cost of the equipment. To this we can add the need to constantly monitor pressure and restore it if necessary.
Rules for calculating tank capacity
Any type of dilator will be effective only if the volume is chosen correctly. To do this, take into account the ability of the liquid to expand during the heating period.Water in heating rings expands by at least 3% of the total volume of the water system, antifreeze - by almost 5%.
Liquids belong to the category of incompressible media, so the tank must provide them with a sufficient reserve for thermal expansion with some margin. Provided that the circuit is completely filled with coolant, even thermal expansion in the calculated volumes can lead to the discharge of liquid through safety valve and spilling coolant on the floor.
Therefore, so that exceeding the volume of expanding coolant does not lead to accidents, closed tanks for small circuits in private houses are purchased so that their volume is equal to 10% of the total volume of coolant circulating through the system. This rule is valid for systems with a capacity of up to 150 l.
If more than 150 liters of coolant moves along the heating ring, then the capacity of a closed tank is calculated by multiplying the total volume of liquid by its expansion coefficient at specific operating temperatures in the system.
To the obtained value you need to add the size of the water seal, i.e. the volume of coolant formed in the tank as a result of standard static fluid pressure. For large heating rings, this figure is usually equal to 0.5% of the total coolant volume; for small ones, with a capacity of up to 150 liters, it is taken to be 20%.
The resulting amount is multiplied by a correction factor determined from the values of preliminary and final pressure in the heating system. The preliminary estimate is that there is 1 bar per 10 m of contour height. The final pressure is formed as a result of the operation of the system.
Calculation of the volume of a closed tank for large complex heating structures looks like this:
The capacity of the open type is not strictly regulated by regulations, but there is a rule: the volume of the open tank to the overflow pipe should be 3.5 - 4% of the total volume of coolant in the heating circuit.
This estimate is sufficient for a small country house, but a building for permanent residence will require a more accurate calculation. First of all, you will need to find out the total volume of the heating system.
Options for calculating the total heating capacity
This indicator can be determined with varying degrees of accuracy in three main ways. Firstly, based on the boiler’s passport data. Thus, about 15 liters of liquid are needed per unit of boiler equipment power. To obtain the necessary data, you will need to multiply 15 by the boiler power indicated in the data sheet.
Secondly, you can find out the volume using a water meter when filling the system. As you fill, the amount of liquid used is taken into account. This is a more accurate and troublesome option.
The third method involves calculating the total volume of all elements of the heating system. This is the most accurate option. The capacity of the heat exchanger of the boiler, radiators, convectors, and measuring instruments can be determined from the passport characteristics.To calculate the pipe capacity, data from the table is used.
The table shows the volume of pipes per meter of length, made from the most popular and modern materials. The internal diameter is indicated in inches from 0.5 to 1.5 units.
Another method that claims to be highly accurate is calculation using the formula:
Vtotal = π x D2 x L/4,
Where:
- π is equal to 3.14;
- D - indicates the parameters of the internal diameter of the pipes;
- L - indicates the length of the system pipeline.
After receiving the necessary data, they are summed up and the total volume of the system is obtained, which is used in further calculations.
Steps and formulas for the full cycle of calculations for designing and organizing heating for a private home are given here. We recommend that you read the useful information.
Selecting an expansion tank according to the table
If you have the necessary data, the optimal expander option can be selected using the table of volumes and design pressure.
The total volume of the system is calculated according to the specified method; the pressure parameters are relevant only for closed modifications and are indicated in the equipment data sheet.
This option does not require special calculations other than calculating the total volume of the system. Using the table greatly simplifies and speeds up the selection of an expander with the required tank capacity.
Using calculation formulas
If the table data is not enough, it is possible to calculate the required capacity indicator yourself.
To do this, use the following formula:
Vb = Vc x k/D,
Where:
- Vb - indicates the desired expander capacity;
- Vc – total system capacity;
- k is the expansion coefficient of the liquid when heated;
- D – expander efficiency coefficient.
Of the data necessary for the calculation, the coefficients k and D remain unknown. The first is a tabular value, and the second is calculated using a separate formula.
A temperature expansion table also exists and is used. It allows you to determine the coefficient for systems with water or antifreeze. The value is not linear; it changes when heated, depending on the presence and concentration of glycol in the liquid.
For water, the concentration of ethylene glycol is taken as “0”; for antifreeze, the concentration is determined according to the data declared by the manufacturer. The heating temperature is considered operational for a specific system.
To independently calculate the efficiency coefficient of the expansion tank, use the formula:
(Qm – Qb) : (Qm + 1),
Where:
- Qm is the maximum pressure of the system according to the safety valve’s nominal response threshold;
- Qb is the preliminary pressure in the air chamber of the expander according to the data sheet.
If the latter parameter is unknown, it is measured during inflation or by bleeding through the nipple of the cylinder.
Other calculation methods
In addition to independent calculations using formulas and tables, there are alternative methods. An accessible calculation option is the help of an online calculator.
Another option to obtain the necessary data is to contact professional designers.This is the most reliable way, but the accuracy of the information obtained will be quite expensive.
Will familiarize you with the rules for installing and connecting closed and open type expanders next articlededicated to these issues.
How to choose the right expansion tank?
It is recommended to decide on the type of heating system at the planning stage. The choice of tank is usually postponed until after the box has been erected, when the system is installed and its volume is known.
When selecting the optimal expansion tank option, it is recommended:
- focus on the volume of the closed expansion tank, which exceeds the value of the thermal expansion of the coolant;
- when purchasing, you should pay attention to the connection, the shape of the container and the location of the connectors for fasteners - this will avoid surprises during the installation process;
- It is important to pay attention to the instructions on the case, which contain useful installation information and technical parameters.
When purchasing, it is better to focus on a trusted manufacturer, even if its cylinders will cost more. This will be the key to the longevity of the heating system, provided that it is used correctly and regularly maintained.
Before connection, the preliminary pressure in the gas compartment of the membrane tank is adjusted to a value equal to the static pressure of the coolant column in the heating circuit. The adjustment is made using a regular car pump and is controlled by a pressure gauge.
Do not confuse expanders for heating systems and hydraulic accumulators for cold water supply lines. They differ in appearance and design features.The former are painted red and are usually not dismountable, the latter are blue and equipped with a removable flange for repairing the membrane.
Conclusions and useful video on the topic
The video will help you determine the parameters of a closed modification expander and understand the differences between heating cylinders and boiler systems:
The principle of operation and features of choosing a container in the video clip:
The heating system of a private house can be made according to an open or closed circuit, which requires the installation of an expander of the appropriate design. The key factor in its performance is the volume, which you can calculate yourself or entrust this matter to professional designers.
Properly selected equipment will help maintain the required volume of liquid in an open system, and in sealed heating it will maintain the level of operating pressure.
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