Efficient operation of the water heating system is possible only with the correct choice of the heat carrier. Before creating a heat supply project, it is necessary to determine in advance its type, find out the main technical and operational characteristics. There are certain parameters inherent in the heating medium of the heating system: temperature, volume of thermal expansion, viscosity.
Functions of the coolant in the heating system
How to choose the right heat transfer fluid for heating? To do this, you should decide on its purpose for heat supply systems. Calculation of its characteristics is included in the design. Therefore, it is necessary to know the functional features of water or antifreeze in heating.
The main task that a safe coolant for heating systems must perform is the transfer of thermal energy from the boiler to batteries and radiators.
In autonomous heating, this process is carried out using a heating element, which raises the temperature of the coolant to the required level. Then, the thermal expansion and the operation of the circulation pump create the proper speed of hot water to transport it to the radiators of the system.
Before calculating the volume of the coolant in the heating system, it is recommended that you familiarize yourself with its secondary functions:
- Partial protection of steel elements against corrosion... This will only happen with a minimum oxygen content in the water and no foaming. It has been observed that rusting occurs much faster in unfilled heating;
- Cooler for circulation pump... The most common pump model has a so-called "wet rotor". Even if the maximum temperature of the coolant in the heating system is reached, it will still reduce the heating level of the pump power unit.
These functions are influenced by the parameters of the heating medium of the heating system. Therefore, when choosing, you should carefully study the characteristics of water or antifreeze. Otherwise, the actual parameters of heat supply will not coincide with the calculated ones, which will lead to the creation of an emergency.
Even if simple water is poured into the heating system, it cannot be used for hot water supply at home. During operation, the content and parameters of the coolant of the heating system change
Types of heat carrier for heating
Water and some types of antifreeze can be used as the circulating fluid. This does not affect the amount of coolant in the heating system, but does affect heat transfer, speed and safety requirements of the system.
To identify the most acceptable option, it is necessary to compare heat carriers for heating systems. Most often, plain water is used. This is due to its affordable cost, good heat capacity and density. When the boiler stops working, it can accumulate the received heat for some time to transfer it to the surface of the batteries. In this case, the volume of the coolant in the heating system will remain the same.
However, despite its positive properties, water has a number of disadvantages:
- Freezes... When exposed to negative temperatures, crystallization and an increase in volume occur. This is what causes damage to pipes and radiators. Therefore, the optimal temperature of the coolant in the heating system must be maintained;
- Impurity content... This applies to ordinary water. Often this is what causes the appearance of scale on the batteries, radiators and the heat exchanger of the boiler. Experts recommend using distilled liquids, in which the percentage of alkalis, salts and metals is minimal;
- With a high oxygen content, it provokes the rusting process... This is more typical for open heating systems. But even in closed heat supply circuits, over time, the% oxygen content in the water can increase.
At the same time, water can be used as a heat carrier for aluminum radiators. If the composition of the liquid and the minimum amount of oxygen are observed, destructive processes will not occur in it.
If the operating conditions of the heating system imply the possibility of exposure to negative temperatures, a different type of circulating fluid should be used. How to choose a coolant for heating systems in this case, and what criteria should be followed?
One of the defining parameters is the freezing point. For antifreeze, it can be from -20 ° C to -60 ° C. This allows you to operate the heat supply even in subzero temperatures without the occurrence of breakdowns.
However, antifreezes have a higher density than water - the optimal speed of the coolant in the heating system in this case can be achieved only with the installation of a powerful circulation pump.
Depending on the composition and components, there are the following types of antifreezes:
- Ethylene glycol... Low cost but extremely toxic. Not recommended for autonomous heating of a private house;
- Propylene glycol... Completely safe for human health. Has a worse coefficient of thermal conductivity than ethylene glycol based fluid. Differs in high cost;
- Glycerin based antifreezes... It is he who is most often chosen as a heat transfer fluid for heating. The price is much lower than that of propylene-glycol formulations, it is not toxic, it has a good indicator of heat capacity.
You need to know that calculating the amount of coolant in the heating system for antifreeze will be more difficult. This is due to their foaming when the maximum temperature is reached. To minimize this phenomenon, manufacturers add special inhibitors and additives to the fluid.
Before purchasing a safe coolant for heating systems, you should read the recommendations from the manufacturers of the boiler and radiators. Not all types of antifreeze liquid can be used for aluminum radiators and gas boilers.
The main characteristics of the heat carrier for heating
It is possible to determine in advance the flow rate of the coolant in the heating system only after analyzing its technical and operational parameters. They will affect the characteristics of the entire heat supply, as well as affect the operation of other elements.
Since the properties of antifreezes depend on their composition and the content of additional impurities, technical parameters for distilled water will be considered. For heat supply, it is the distillate that should be used - completely purified water. When comparing heat transfer fluids for heating systems, it can be determined that the flowing fluid contains a large number of third-party components. They negatively affect the operation of the system. After use during the season, a layer of scale will form on the inner surfaces of pipes and radiators.
To determine the maximum temperature of the coolant in the heating system, one should pay attention not only to its properties, but also to the limitations in the operation of pipes and radiators. They should not suffer from increased heat exposure.
Consider the most significant characteristics of water as a coolant for aluminum heating radiators:
- Heat capacity - 4.2 kJ / kg * C;
- Bulk density... At an average temperature of + 4 ° C, it is 1000 kg / m³. However, during heating, the specific gravity begins to decrease. Upon reaching + 90 ° С it will be equal to 965 kg / m³;
- Boiling temperature... In an open heating system, water boils at a temperature of + 100 ° C. However, if you increase the pressure in the heat supply to 2.75 atm. - the maximum temperature of the heat carrier in the heat supply system can be + 130 ° С.
An important parameter in the operation of heat supply is the optimal speed of the coolant in the heating system. It directly depends on the diameter of the pipelines. The minimum value should be 0.2-0.3 m / s. The maximum speed is not limited by anything. It is important that the system maintains the optimal temperature of the heating medium in the heating along the entire circuit and there are no extraneous noises.
However, professionals prefer to be guided by the holes of the old SNiP of 1962. It indicates the maximum values of the optimal speed of the coolant in the heat supply system.
Pipe diameter, mm | Maximum water speed, m / s |
25 | 0,8 |
32 | 1 |
40 and more | 1,5 |
Exceeding these values will affect the flow rate of the heating medium in the heating system. This can lead to an increase in hydraulic resistance and "false" operation of the drain safety valve. It should be remembered that all parameters of the heat carrier of the heat supply system must be pre-calculated. The same applies to the optimal temperature of the coolant in the heat supply system. If a low-temperature network is being designed, you can leave this parameter empty. For classic schemes, the maximum heating value of the circulating fluid directly depends on the pressure and restrictions on pipes and radiators.
For the correct choice of a coolant for heating systems, a temperature schedule for the operation of the system is preliminarily drawn up. The maximum and minimum values of water heating should not be lower than 0 ° С and above + 100 ° С
Calculation of the volume of the coolant in heating
Before filling the system with a coolant, it is necessary to correctly calculate its volume. It directly depends on the heat supply scheme, the number of components and their overall characteristics. They affect the amount of coolant in the heating system.
First, the parameters of the supply line are analyzed. The material of its manufacture is of great importance. To calculate the volume of the coolant in the heating system, you need to know the inner diameter of the pipe. According to modern standards in the article number of steel pipelines, the internal cross-sectional size is given, and for plastic ones, the external one is adopted. Therefore, in the latter case, two wall thicknesses must be subtracted.
In order to independently calculate the volume of the coolant in the heating system, you do not need to do calculations. It is enough to use the data from the table below. With its help, you can calculate the amount of coolant in the heat supply system.
Diameter, mm | Coolant volume (l) in 1 lm pipes, depending on the material of manufacture | ||
Steel | Polypropylene | Reinforced plastic | |
15 | 0,177 | 0,098 | 0,113 |
20 | 0,314 | 0,137 | 0,201 |
25 | 0,491 | 0,216 | 0,314 |
32 | 0,804 | 0,353 | 0,531 |
40 | 1,257 | 0,556 | 0,865 |
Having this information, it is enough to determine the length of pipes of a certain diameter according to the heat supply scheme and multiply the resulting value by a volume of 1 mp. In this way, the volume of the coolant in the heat supply system is calculated, but only in the pipes.
But in addition to the supply lines, the heating circuit contains radiators and batteries.They also affect the volume of the heat carrier in the heating system. Each manufacturer indicates the exact capacity of the heater. Therefore, the best calculation option would be to study the battery passport and determine the amount of heat carrier fluid required for heat supply.
If this is not possible for a number of reasons, you can use approximate figures. It should be noted that with a large number of batteries, the calculation error will increase. Therefore, for an accurate calculation of the amount of coolant in the heat supply system, it is recommended to find out the passport characteristics of the battery. This can be done on the manufacturer's website in the technical information section.
The table shows the average volume of the heating medium for one section in aluminum, bimetallic and cast iron radiators.
Radiator type | Center-to-center distance, mm | ||
300 | 350 | 500 | |
| Aluminum | — | 0,36 | 0,44 |
| Bimetallic | — | 0,16 | 0,2 |
| Cast iron | 1,1 | — | 1,45 |
These figures must be multiplied by the total number of sections in the heating system. Then, the already calculated volume of water in the pipes should be added to the obtained data and the total amount of coolant in the heating system can be determined.
However, it should be remembered that when comparing heat carriers for heat supply systems, it was noted that over time, the volume may decrease for objective reasons. Therefore, to maintain the performance of the system, coolant should be periodically added to it.
For an accurate calculation of the volume of calculation of water in the heating system, it is necessary to take into account the capacious boiler heat exchanger. For solid fuel models, this figure can be several tens of liters. For gas, it is slightly lower.
Methods for filling the heating system with coolant
Having decided on the type of coolant and calculating its volume in heating, it remains to solve its one problem - how to add water to the system. This is an important point in the design of heat supply, since when a critical water level is reached, the boiler heat exchanger and radiators can fail.
For an open heating system, water can be added through an expansion tank located at the highest point in the system.
To do this, it is necessary to lay the supply line and connect it to the tank structure. When the volume of the coolant decreases, it is enough to turn on the supply of a new portion of water to replenish the system.
Filling a closed system is carried out according to a different scheme. It must have a make-up unit. This component is located on the return pipe, in front of the expansion vessel and circulation pump. The make-up unit package includes the following components:
- Shut-off valves installed on the connected branch pipe;
- Check valve, which prevents the change in the direction of the flow of the coolant;
- Mesh filter.
To automate the operation of the unit, you can install a servo mechanism on the crane. It connects to a pressure transducer. When the pressure indicator decreases, the servo mechanism opens the valve and thereby adds a coolant to the system.
The video tells about the parameters for choosing a coolant for the heating system:
