Capacity for expanding the coolant is a necessary element of the heating system. In the design process, the question arises: how to calculate the expansion tank for heating, determine its volume and dimensions? The parameters will depend on several factors, which will be studied in detail in the article.
What is the expansion tank for
The fluid circulating in the heating system expands significantly when heated. For different coolants, this coefficient will be different. For example, water as a coolant is much more efficient. It has a lower thermal expansion coefficient and higher heat dissipation than ethylene glycol antifreeze. Also, the increase in volume depends on the operating temperature.
To compensate for the increase in the liquid level in the system, an expansion tank is built in, the calculation of which will depend on:
- Amounts of fluid in the system.
- Heating structures. There are two varieties: closed and open type. For each of them, the volume calculation is done differently.
- Peak fluid temperature in the system. If the calculation is based on the operating temperature, then the size of the tank will be lower, but emergency situations should be taken into account when the coolant is close to the transition to a vapor state, which significantly increases its volume.
- A type of liquid. Several different substances are used: water, antifreeze, water with the addition of alcohol, oil. For each of these coolants, the calculation of the volume of the expansion tank will be different.
Open tanks
Currently, three types of expansion tanks are used. The most antediluvian is used in the gravitational heating system. It is an open tank. It is installed at the highest point and serves not only to collect excess fluid, but also helps to remove air from the system.
Such heating works only on water, because the rest of the coolants are quite toxic. Their use in an open system will result in vapor poisoning. The main disadvantage of an open system is the freezing of water at low temperatures. Such a house cannot be left for several days without heating in winter. If this happens, then the water expanded during freezing will burst the heating pipes.
Calculation of open-type expansion tanks is based on the coefficient of expansion of water, in which this value depends on temperature: the higher it is, themore value. To calculate the volume of fluid displaced during heating, you need to multiply the coefficient corresponding to the operating temperature by the amount of coolant in the heating system. This will give the required volume of the expansion tank.
For example, if there is a network with a volume of 400 liters of water, operating at a temperature of 75 degrees, then the expansion volume will be: 4000.0258=10.32 liters.
For an open system, it makes no sense to oversize the tank, since such a design provides for a bypass that is connected to the sewer. Excess water flows into it if the temperature exceeds the nominal value.
Sealed expansion tanks
The next variety are closed-type expansion tanks. They are used both in gravity systems and in heating with forced circulation. The main difference between closed tanks is their complete tightness. This was done to prevent contact of water with atmospheric air, which contains a large amount of oxygen, which adversely affects the condition of the pipes. Excess pressure here is discharged into the atmosphere with the help of safety valves.
The calculation of this type of expansion tank is the same as the previous one. However, here you need to add the volume of air that will be compressed when the water is forced into the tank. Unlike liquids, gases have a significant ability to compress. Therefore, the volume for air in the tank can be kept small - about 30% of the volume for water.
How a membrane-type expansion tank works
The main variety of modern heating systems is forced heating with a membrane-type expansion tank. It differs from the usual sealed container by the presence of a rubber layer that separates the liquid part from the air.
When the system is completely filled, the liquid in the tank reaches the top level of the diaphragm. During heating, the coolant begins to expand and, overcoming the resistance of the membrane and air, rises to the upper level of the tank until the pressure of compressed air and the pressure of the coolant are equal. If the antifreeze pressure significantly exceeds the allowable values, the safety valve of the safety system will work.
When calculating the expansion tank for closed type heating, the expansion coefficient is corrected for the use of antifreeze. It increases its volume by about 15% more water.
Calculation of a closed membrane-type expansion tank
When determining the size of a membrane type tank, you can follow a simple path. Knowing that the coefficient of expansion of water at a temperature of 80 degrees is 0.029, as well as the volume of the system, a primitive calculation can be made.
Let's say there are 100 liters in the system. Multiplying the amount of liquid by a coefficient, we get the expansion volume 2, 9. For a simplified calculation, this value must be doubled. In addition, remember that the expansion of antifreeze is approximately 15% more than water, and add this value. Happenedabout 7 l.
For a more accurate calculation of the expansion tank, use the formula:
V=(Ve + Vv)(Pe + 1) / (Pe - Po), where
V- the required volume of the membrane tank for the heating system.
Ve - the volume of coolant obtained when the system is heated. This is the total of all heaters, pipes, boiler.
Vv - the volume of the water seal in the tank. In other words, the amount of liquid that is always present in the reservoir as a result of hydrostatic pressure. Approximately 20% in small tanks and about 5% in large ones. But not more than 3 years.
Po - constant pressure. Depends on the height of the liquid column in the system.
Pe - the maximum pressure that occurs when the safety valve is activated.
Conclusion
Calculating an expansion tank is a simple process available to anyone familiar with simple arithmetic. It is only necessary to take into account the design of the heating system, its volume and type of coolant.
