Calculation of the expansion tank for a closed heating system - Examples
An expansion tank is used to balancing the autonomous heating system.
Its problem is to equalize the volume of coolant heated to high temperatures, and maintain the specified pressure.
The reliability of the execution of functions assigned to this element depends on how correctly its volume is selected.
This parameter is not a constant and depends on the specific conditions. Let us consider how the expansion tank is calculated for the closed heating system.
The principle of the compensating device is simple, there are no complex technical solutions in it. However, the slightest error in the calculation may entail the failure of the heating system as a whole.
The internal space of the tank is divided into two parts of the elastic membrane. The upper cavity is called air - air is injected into it. The purpose of this operation is to create an initial pressure in the container. Water from the system is fed to the lower cavity. As soon as the membrane takes a stable position - it will fall on the surface of the liquid, the system can be considered ready to work.
Principle of operation of a closed expansion tank
The heated coolant is expanding, and its excess enters the tank, shifting the membrane towards the air chamber. As soon as water begins to cool, the air pressure membrane returns to its original position, thereby maintaining the given pressure in the heating system.
Too big expansion tank is not able to create the pressure in the system.Insufficient capacity of the compensating device will not allow to take the entire excess extended water.
In the heating system must be mandatory. Why do you need, read on the site.
The heating circuit of the two-storey house is presented. What is the fundamental difference from the heating system of a two-story house?
Methods of air booming from the heating system are described.
Approximate values \u200b\u200bof water content in heating systems
To determine the volume of the expansion tank, it is necessary to know how much the coolant fits in the heating system. This parameter is equal to the amount of boiler volumes, pipelines and heating devices.
Approximately 1 kW power system accounts for:
- 7 liters - when used in the system of convectors;
- 10.5 liters - if radiators are installed as heating devices.
The presence of warm floors requires the volume of the coolant in the amount of 17 l / kW.
The calculation of the capacity of the heating system is quite complicated, it is possible to perform it for only specialists. A consumer who does not have engineering knowledge can take advantage of the approximate dependence - 1 kW of the boiler power \u003d 15 liters of the coolant volume.
For example, with a boiler power equal to 25 kW, the volume of water in the system will be:
25 x 15 \u003d 375 (liters).
Volume of expansion tank
The choice of the size of the expansion tank depends on the three main parameters:
- the volume of the coolant in the system - than it is more, the greater the size of the tank;
- the temperature of the coolant - the higher the heating, the greater the extensive capacity;
- pressure in the system - the higher its permissible indicator, the less the tank volume should be.
In other words, the volume of the expansion tank is directly dependent on the amount of coolant and its temperature, and in the opposite - from pressure in the heating system.
The coefficient of increasing the volume of water / water-type mixture depending on temperature
As is well known from the laws of physics, all fluids are expanding during heating (as, however, any bodies). This fact must be taken into account when calculating the volume of the expansion tank.
Water increases in volume when heated to 95 0 s per 4%. This statement is quite accurate, so they can be operated in calculations without fears.
If a water-collective mixture is used as a coolant, the picture changes somewhat - depending on the content of ethylene glycol.
Expansion capacity in the heating system
In this case, the coefficient of expansion of the working fluid is determined as follows:
- 4% x 1.1 \u003d 4.4% - with the content of ethylene glycol in the amount of 10% of the total coolant;
- 4% x 1.2 \u003d 4.8% - if the volume of ethylene glycol in the mixture is 20%, and so on.
The above values \u200b\u200bwill vary depending on which temperature is heated by the coolant. For example, at 80 degrees, the water expansion coefficient will be 0.0290. If 10 percent of its volume is replaced by ethylene glycol, the coefficient will be 0.0320. A mixture of glycol in water with water (50%) is characterized by an extension coefficient of 0.0436.
Calculation of the volume of expansion tank for heating
V \u003d (VL X E) / Dwhere
VL is the total capacity of the heating system, which includes the volume of the boiler, all heat accumulators (convectors, radiators, etc.) and pipelines;
- E - the coefficient of expansion of the working fluid (coolant);
- D is the efficiency of the expansion tank (membrane).
The last parameter depends on two values \u200b\u200b- pressure:
- PV - maximum working in the system;
- PS - Charging the membrane tank.
PS should be equal to the static pressure of the heating system and receives 0.5 bar \u003d 5 m.
Heating with natural circulation is applied more and less often due to the obvious disadvantages of this system. It has a number of advantages.
You can watch the circulation of the circulating pump in the heating system.
Example of calculation
As an example, consider the system of heating a cottage of 300 square meters. m. To provide autonomous heating, a 30 kW boiler is installed. In addition, the heat accumulator of 1000 liters is involved. The height of the system is 5 meters.
First calculate the total coolant:
VL \u003d 30 x 15 + 1000 \u003d 1450 (liters)where
- 30 - boiler power, kW;
- 15 - the specific volume of the coolant for 1 kW of the boiler power, liters;
- 1000 - the volume of accumulating capacity.
D \u003d (PV - PS) / (PV + 1)
In our example:
- PV \u003d 2.5 bar;
- PS \u003d 0.5 bar.
Consequently, d \u003d (2.5 - 0.5) / (2.5 + 1) \u003d 0.57
Now you can determine the volume of the tank:
V \u003d 1450 x 0.04 / 0.57 \u003d 101.75 (liter), where
0.04 - The coefficient of the expansion of the coolant (in our case it is water without adding glycol).
Manufacturers produce expansion tanks of a certain size range, so it is not always possible to buy a container, the volume of which is estimated.
In such cases, the result of the calculation must be rounded into the biggest. In our case, the nearest standard value will be 110 liters. It is such a tank that needs to be bought.
The expansion tank of the closed type is optionally installed in the highest point of the system.
The main advantage of membrane compensators is precisely the possibility of placing it in the place most convenient for installation and operation.
Little tanks with a volume of 20-25 liters are usually set to the system with a circulating pump, the power of which is 1.2 kW. Increased capacity up to 20-60 liters will lead to an increase in the pump power to 2.0 kW.
There are compensating devices of 100-200 liters on sale. In addition to their direct destination, they can play the role of a cumulative reservoir for warm water. True, it is possible to use them in such a key only in case of disconnecting the main source of DHW for a short time.
Size of expansion tanks occupy a fairly wide range. Among them are models with dimensions so large that standard doorways do not allow them to make them inside the room. In such a situation, it is better to replace one huge container into several small. The main thing is that their total volume is equal to the calculation.